bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasticity of developing cerebellar cells in vitro studied with antibodies against the NG2 antigen
Authors: Levine JM , Stallcup WB
Published: March 2018

The NG2 antigen, a chondroitin-sulfate proteoglycan, is a cell surface marker for a class of smooth protoplasmic astrocytes found throughout the brain and at high frequency in the cerebellar molecular layer (Levine and Card, 1987). To study the development of the cerebellar astrocytes at the level of the single cell, we have analyzed the distribution of the NG2 antigen by indirect immunofluorescence in dissociated cell cultures prepared from postnatal cerebella and compared that distribution to the distribution of several other cell surface and intracellular antigens that identify specific cell types in cultures of nervous tissue. When cerebellar cells from 5 d rat pups were grown in a medium containing 10% fetal calf serum, the NG2-labeled cells, which constituted 0.1-1.0% of the total glial cells present, contained glial fibrillary acidic protein (GFAP)-immunoreactive filaments and bound monoclonal antibody A2B5, a surface marker for neurons and some astrocytes. Approximately 30% of the NG2-labeled cells were also labeled with tetanus toxin, an additional surface marker for neurons and immature astrocytes. Less than 2% of the cells were labeled with antibodies against galactocerebroside or with monoclonal antibody O1, both of which are surface markers for oligodendrocytes. About half the NG2-labeled cells exhibited high-affinity uptake of 3H-GABA, and this uptake was partially inhibited by both beta-alanine and DABA. Thus, the NG2 antigen is a cell surface marker for a subpopulation of the type II or fibrous astrocytes present in the cultures. When the cerebellar cells were grown in a chemically defined, serum-free medium, the NG2-labeled cells had a stellate morphology and between 50-60% of the cells bound tetanus toxin. Although almost all the cells bound antibody A2B5, less than 5% of the cells expressed either of the oligodendrocyte surface markers or GFAP immunoreactivity. As was the case with cells grown in serum-containing medium, 60% of the NG2- labeled cells had high-affinity uptake of 3H-GABA. However, this uptake was inhibited by DABA but not by beta-alanine. This phenotype may be the in vitro analog of the NG2-labeled, filament-lacking, smooth protoplasmic astrocytes identified in the intact adult cerebellum. The expression of these 2 phenotypes could be reversed by switching the tissue culture medium within 5 d of plating the cells. These results demonstrate that the in vitro environment can influence the phenotypic properties expressed by developing cerebellar astrocytes and suggest that smooth protoplasmic astrocytes may be developmentally related to glial cells of the O-2A lineage.
Bipotential glial precursor cells of the optic nerve express the NG2 proteoglycan
Authors: Stallcup WB , Beasley L
Published: March 2018

We have studied the expression of the NG2 chondroitin sulfate proteoglycan on bipotential glial precursor cells in cultures of postnatal rat optic nerve. Purified populations of these precursor cells were prepared by panning dissociated optic nerve cells on dishes coated with monoclonal A2B5 antibody. Using immunofluorescence double staining, we found that NG2 was present on almost 95% of the purified A2B5+ precursor cells. The NG2 core protein from optic nerve cells was identified by immune precipitation and PAGE and was found to be identical to the 300,000 Da NG2 core protein from a clonal rat cell line B49. Over a culture period of 5 d in medium containing 10% fetal calf serum, more than 80% of the NG2+ precursor cells acquired the glial fibrillary acidic protein (GFAP), an astrocyte-specific marker. Under these conditions, fewer than 10% of the NG2+ cells expressed galactocerebroside (GC), an oligodendrocyte-specific marker. These GFAP+GC- type II astrocytes continued to express the NG2 antigen for up to 10 d in culture. During a 5 d culture period in hormonally supplemented, serum-free medium, fewer than 15% of the NG2+ cells expressed GFAP, while up to 40% expressed GC. The NG2 antigen continued to be expressed for only a short period of time by these GFAP-GC+ oligodendrocytes, so that mature oligodendrocytes in the cultures became NG2-. These results support our previous suggestion that the NG2 antigen is found on a class of neural cells that can differentiate along more than one pathway.
N-methyl-D-aspartate receptor-induced, inherent oscillatory activity in neurons active during fictive locomotion in the lamprey
Authors: Wallen P , Grillner S
Published: March 2018

Bath application of N-methyl-aspartate induces fictive locomotor activity in the isolated spinal cord preparation of the lamprey, as well as TTX-resistant membrane potential oscillations in many individual neurons. This inherent oscillatory activity is shown to depend on a specific activation of N-methyl-D-aspartate (NMDA) receptors. This activation initiates voltage-dependent, magnesium- requiring membrane potential bistability, presumably due to a development of a region of negative slope conductance in the current- voltage relation of the neuron. When sodium ions were removed from the bathing solution, oscillations disappeared, and the membrane potential was maintained at a hyperpolarized level, suggesting that the depolarizing current during the oscillatory cycle is mainly carried by sodium ions. Replacing Ca2+ with Ba2+ also leads to a cessation of oscillatory activity, with the membrane potential remaining at the more depolarized level. This indicates an involvement of a Ca2+-dependent K+ current during the repolarization phase. These findings, together with the voltage dependence, can account for the main characteristics of the NMDA receptor-induced, TTX-resistant membrane potential oscillations. This oscillatory behavior has been demonstrated in motoneurons and in several interneurons including CC interneurons but has not been found in edge cells, dorsal cells, or lateral interneurons. The possibility that inherent oscillatory membrane properties may contribute to the activity pattern during fictive locomotion was investigated in experiments with intracellular current injection in the absence of TTX. The stimulation effects obtained required the presence of magnesium ions and were analogous to the stimulation effects seen during oscillations after TTX blockade. Together with similarities in, for instance, frequency and amplitude between the locomotor oscillatory activity and the TTX-resistant oscillations, the results are compatible with an involvement of inherent, oscillatory membrane properties during fictive locomotion in the lamprey spinal cord.
Single-unit response of noradrenergic neurons in the locus coeruleus of freely moving cats. I. Acutely presented stressful and nonstressful stimuli
Authors: Abercrombie ED , Jacobs BL
Published: March 2018

The present experiment was designed to explore the stress-relatedness of activity in noradrenergic neurons of the locus coeruleus (LC) of behaving cats. A stressor was defined as a stimulus that elicited a significant sympathoadrenal activation as measured by plasma norepinephrine level and heart rate. According to this definition, exposure to 15 min of 100 dB white noise or 15 min of restraint was stressful in cats. In contrast, exposure to inaccessible rats for 15 min was behaviorally activating but nonstressful. The single-unit activity of noradrenergic neurons in the LC of behaving cats was examined under these conditions. The stressful stimuli elicited a significant increase in LC neuronal activity for the entire 15 min stressor duration, whereas the behaviorally activating but nonstressful stimulus elicited no significant change in the activity of these neurons. These results provide evidence that behavioral activation per se is not sufficient to evoke a tonic activation of these neurons. Rather, these data support the hypothesis that the LC is involved in the CNS response to stress and provide additional evidence that the activity of LC noradrenergic neurons increases in association with sympathoadrenal activation.
Single-unit response of noradrenergic neurons in the locus coeruleus of freely moving cats. II. Adaptation to chronically presented stressful stimuli
Authors: Abercrombie ED , Jacobs BL
Published: March 2018

The preceding paper described a stress-related tonic activation of noradrenergic neurons of the locus coeruleus (LC) of behaving cats. The present study examined the degree to which adaptation to stress was reflected in LC unit activity. Adaptation was defined as a reduction in the magnitude of the physiological stress response of the animal, as reflected in plasma norepinephrine level and heart rate. Adaptation of the physiological stress response occurred after 5 repeated hourly presentations of 100 dB white noise and after 2 hr of restraint. When these stimuli ceased to elicit significant sympathoadrenal activation, they likewise ceased to elicit activation of LC single-unit activity. These results provide further support for the hypothesis that tonic elevations in LC neuronal activity are stress related and that the LC is involved in the CNS response to challenges to the organism.
Spinal monoaminergic receptors mediate the antinociception produced by glutamate in the medullary lateral reticular nucleus
Authors: Janss AJ , Gebhart GF
Published: March 2018

Focal electrical stimulation and microinjection of the excitatory amino acid glutamate in the lateral reticular nucleus (LRN) both inhibit the heat-evoked tail flick (TF) reflex in rats. The stimulation-produced inhibition from the LRN has previously been demonstrated to be mediated by spinal monoaminergic receptors. In the present study, inhibition of responses to noxious thermal stimuli by glutamate microinjected into the LRN was examined and characterized; this study is the first to examine the spinal receptors mediating inhibition produced by selective activation of cell bodies in the LRN. Microinjection of glutamate (100 mM) into the LRN in rats lightly anesthetized with pentobarbital produced a transient (less than 5 min) inhibition of the heat-evoked TF reflex, the magnitude of which increased with the volume of glutamate injected (100, 200, or 400 nl). This glutamate-produced inhibition of the TF reflex was antagonized by the intrathecal administration of phentolamine (30 micrograms), yohimbine (15 and 30 micrograms), or methysergide (15 and 30 micrograms) to the level of the lumbar spinal cord, but was not antagonized by prazosin (30 micrograms) or naloxone (20 micrograms). Yohimbine (15 and 30 micrograms) administered to the level of the cervical spinal enlargement did not significantly alter inhibition of the TF reflex produced by glutamate microinjected into the LRN. Microinjection of glutamate (100 mM, 400 nl) into the LRN elevated TF latencies and hindpaw lick latencies in the hot plate test performed on conscious rats. This inhibition of responses to noxious thermal stimuli in conscious rats was short-lasting (less than 5 min), and was also attenuated by intrathecal administration of yohimbine (30 micrograms) or methysergide (30 micrograms), but not by prazosin (30 micrograms) or naloxone (20 micrograms). While it has previously been established that cell bodies in the LRN mediate descending inhibition of spinal nociceptive reflexes, the present results establish that spinal alpha 2-adrenoceptors and serotonin receptors mediate LRN- produced antinociception and extend our understanding of LRN-mediated modulation of nociceptive responses integrated spinally and supraspinally.
Coordinated release of ATP and ACh from cholinergic synaptosomes and its inhibition by calmodulin antagonists
Authors: Schweitzer E
Published: March 2018

Isolated cholinergic synaptosomes from elasmobranch electric organ release both ACh and ATP when depolarized in the presence of calcium. The conditions that trigger ATP release are the same as those known to stimulate neurosecretion. The ratio of ACh to ATP released is the same as that found in purified elasmobranch synaptic vesicles. Both ACh and ATP release are inhibited either by the removal of extracellular calcium or the addition of the “calmodulin antagonist” trifluoperazine (TFP). Taken together, these data suggest that both ACh and ATP are released by exocytosis from synaptic vesicles within nerve terminals. A number of drugs, collectively known as calmodulin antagonists, were examined for their effect on neurosecretion. TFP completely inhibited secretion in a rapid and reversible manner. Other related drugs had similar effects, though with relative efficacies different from those reported for inhibiting calmodulin. It therefore seems likely that a calmodulin-like component of the nerve terminal, distinct from calmodulin itself, is essential for the process of neurosecretion.
Localization of sodium channel subtypes in adult rat skeletal muscle using channel-specific monoclonal antibodies
Authors: Haimovich B , Schotland DL , Fieles WE , Barchi RL
Published: March 2018

Five monoclonal antibodies specific for the 260 kDa subunit of the rat skeletal muscle sodium channel were used to probe the distribution of this channel in adult muscle. All the antibodies reacted with the surface membrane of fast- and slow-twitch fibers in the rat anterior tibial and soleus muscles. Immunoreactivity was also present in the endplate region; this was significantly more intense than that in the surrounding extrajunctional membrane. At the electron microscopic level, this junctional immunoreactivity could be traced uniformly throughout the secondary folds of the post-synaptic membrane. Three of the monoclonal antibodies (A/B2, F/E4, and I/E3) exhibited an additional distinct immunoreactivity pattern, staining the interior of selected fibers in the anterior tibial muscle that were subsequently identified as slow-twitch fibers. An identical reactivity pattern was observed with most of the soleus muscle fibers. In longitudinal sections of slow fibers examined at the light microscopic level, transversely oriented, regularly spaced doublets of fluorescence were localized at the junction of the A and I bands in each sarcomere. In permeabilized slow fibers exposed to A/B2 and examined at the electron microscopic level, internal reactivity was associated exclusively with the membranes of the T-tubular system. A/B2 also strongly stained a transversely oriented pattern within cardiac muscle fibers exhibiting the characteristics of the T-tubular system in that tissue. We conclude that at least 3 subpopulations of sodium channels are present in adult skeletal muscle: those in the sarcolemma of fast and slow fibers, those in slow-twitch fiber T-tubular membranes, and those in the T-tubular system of fast fibers. The channels in the slow fiber T-system apparently share common epitopes with those in the T-system of cardiac fibers.
Representation of interaural time difference in the central nucleus of the barn owl's inferior colliculus
Authors: Wagner H , Takahashi T , Konishi M
Published: March 2018

This paper investigates the role of the central nucleus of the barn owl's inferior colliculus in determination of the sound-source azimuth. The central nucleus contains many neurons that are sensitive to interaural time difference (ITD), the cue for azimuth in the barn owl. The response of these neurons varies in a cyclic manner with the ITD of a tone or noise burst. Response maxima recur at integer multiples of the period of the stimulating tone, or, if the stimulus is noise, at integer multiples of the period corresponding to the neuron's best frequency. Such neurons can signal, by means of their relative spike rate, the phase difference between the sounds reaching the left and right ears. Since an interaural phase difference corresponds to more than one ITD, these neurons represent ITD ambiguously. We call this phenomenon phase ambiguity. The central nucleus is tonotopically organized and its neurons are narrowly tuned to frequency. Neurons in an array perpendicular to isofrequency laminae form a physiological and anatomical unit; only one ITD, the array-specific ITD, activates all neurons in an array at the same relative level. We, therefore, may say that, in the central nucleus, an ITD is conserved in an array of neurons. Array-specific ITDs are mapped and encompass the entire auditory space of the barn owl. Individual space-specific neurons of the external nucleus, which receive inputs from a wide range of frequency channels (Knudsen and Konishi, 1978), are selective for a unique ITD. Space-specific neurons do not show phase ambiguity when stimulated with noise (Takahashi and Konishi, 1986). Space-specific neurons receive inputs from arrays that are selective for the same ITD. The collective response of the neurons in an array may be the basis for the absence of phase ambiguity in space-specific neurons.
MAP2 and tau segregate into dendritic and axonal domains after the elaboration of morphologically distinct neurites: an immunocytochemical study of cultured rat cerebrum
Authors: Kosik KS , Finch EA
Published: March 2018

We sought to determine whether the strict segregation of MAP2 and tau into somatodendritic and axonal compartments in situ was maintained in dissociated neuronal cultures of the rat cerebrum. Cultures grown under serum-free conditions were immunolabeled with monoclonal antibodies specific for MAP2 and tau. At 14 d after plating, a clear distinction between MAP2- and tau-immunoreactive neurites was apparent. MAP2- immunoreactive neurites were relatively short, thick, tapering, and branched. Tau-immunoreactive neurites formed a crisscrossing meshwork of long, fine-caliber neurites, which, in more densely plated cultures, had a tendency to form thick, ropelike fascicles. Unlike the MAP2 pattern, tau antibodies labeled somata only lightly. Since distinct populations of neurites were labeled with the 2 antibodies, we sought to observe the development of the topographically distinct compartments by double-labeled immunocytochemistry with both polyclonal and monoclonal antibodies to MAP2 and tau. Cells observed within the first 8 hr after plating demonstrated equally intense MAP2 and tau immunoreactivity in a coextensive distribution throughout the cell body and initial neurites. By 16 hr, some neurites began to assume dendritic and axonal features; however, many such processes contained reaction product for both MAP2 and tau. Beginning at this time, neurites that appeared axonal showed a progressively weaker reaction with MAP2 antibodies, and neurites that appeared dendritic showed a progressively weaker reaction with tau antibodies. In most neurites the diminution appeared to occur uniformly over the entire extent of the neurite. During this transformation period there were occasional axon-like neurites that contained MAP2 immunoreactivity proximally, while tau immunoreactivity extended over the entire length of the neurite. We conclude that neurons in culture are able to compartmentalize MAP2 and tau into their appropriate processes and only attain an apparently homogeneous population of one of these MAPs after the neuron has assumed dendritic and axonal features. The analysis also lends indirect support to the hypothesis that microtubule-associated proteins (MAPs) form this association at the distal extent of the growing neurite.
Single-unit analysis of postnatal olfactory learning: modified olfactory bulb output response patterns to learned attractive odors
Authors: Wilson DA , Sullivan RM , Leon M
Published: March 2018

Neonatal rats learn to approach odors associated with stimulation normally provided by their mother. The present report describes changes in olfactory bulb single-unit activity following olfactory learning in young rats. Rat pups were exposed from postnatal day 1 to 18 to either (1) peppermint-scented air while receiving tactile stimulation (Pepp- Stroked), (2) peppermint-scented air with no tactile stimulation (Pepp- Only), (3) clean air and tactile stimulation (Stroked-Only), or (4) clean air and no tactile stimulation (Naive). On day 19, single-unit activity was recorded from mitral/tufted cells in urethane- anesthetized, freely breathing pups in response to either peppermint or a novel orange odor. Mitral/tufted cell response patterns to peppermint were significantly altered in Pepp-Stroked animals compared to control pups. Peppermint exposure alone, not associated with tactile stimulation (Pepp-Only), did not affect subsequent single-cell response patterns to that odor. In addition, the modification of response patterns was specific to peppermint and was not associated with a change in respiration rate. Furthermore, Pepp-Stroked pups had a relative behavioral preference for peppermint on day 19 compared to control pups. These results demonstrate that postnatal olfactory learning selectively modifies the subsequent response patterns of olfactory bulb output cells to the attractive odor. Furthermore, these results indicate that the initial coding of an odorxy's attractive value occurs within the olfactory bulb.
Vocalizations by a sexually dimorphic isolated larynx: peripheral constraints on behavioral expression
Authors: Tobias ML , Kelley DB
Published: March 2018

The clawed frog Xenopus laevis uses sexually dimorphic vocalizations, mate calling and ticking, to advertise reproductive state. The basic unit of vocalization is a brief click, produced by the movement of cartilagenous disks located within the larynx. The rate of click production in the male-specific mate call (71 Hz) is an order of magnitude faster than the rate of click production in female typical ticking (6 Hz). To determine if vocalization rate is constrained by the periphery, male and female larynges were isolated and response of the muscles to nerve stimulation was studied. Laryngeal muscle response is markedly dimorphic in the 2 sexes, both in the amplitude potentiation of electromyograms and in the rate at which discrete tension transients can be produced. At 6 Hz (ticking), both sexes generate discrete tension transients in response to each stimulus pulse. In response to nerve stimulation at 71 Hz (mate calling), male laryngeal muscle generates discrete tension transients while female laryngeal muscle does not. Since expression of sex-specific vocalizations is regulated by androgenic hormones, responses of laryngeal muscle to nerve stimulation in androgen-treated adult females and castrated adult males were also examined. The responses of laryngeal muscle from castrated and intact males are similar. Androgen-treated female larynx is partially masculinized but does not produce tension transients at the mate call rate. These physiological results are in close agreement with behavioral observations. Sounds produced by the isolated larynx were nearly identical in spectral properties to those produced by an intact male. We determined that the production of a discrete tension transient is prerequisite to click production. Thus, one reason females do not mate call, even when treated with androgens, is that female laryngeal muscle cannot produce discrete tension transients at a rapid rate.
Androgen regulation of muscle fiber type in the sexually dimorphic larynx of Xenopus laevis
Authors: Sassoon DA , Gray GE , Kelley DB
Published: March 2018

We used histochemical techniques [assays for adenine triphosphatase (ATPase) and succinate dehydrogenase (SDHase) activity] to identify muscle fiber types in the larynx of Xenopus laevis. Male muscle is made up of one fiber type, medium-sized fibers (approximately 9 microns2) that stain lightly for acid-stable ATPase and intensely for SDHase activity. In contrast, the female has 3 fiber types: small fibers (approximately 6 microns2) that stain intensely for ATPase and SDHase, medium-sized fibers (approximately 13 microns2) with moderate staining for ATPase and dark staining for SDHase, and large fibers (approximately 15 microns2) with little SDHase or ATPase activity. Long- term castration (6 months) has no effect on histochemical staining of adult male fibers. Long-term testosterone treatment (5 months) increases the proportion of medium-sized, moderately staining fibers in adult females, and reduces the proportion of both the small, darkly staining fibers and the large, lightly staining fibers. At metamorphosis, both males and females have 3 fiber types whose ATPase activity is similar to that of the adult female. However, no SDHase activity is observed. Treatment of juveniles for 3 weeks with testosterone results in nearly complete masculinization of muscle fibers, as judged by increased cross-sectional area, homogeneous ATPase staining, and a marked increase in SDHase activity. Thus, juvenile muscle is considerably more responsive to testosterone than is adult female muscle. We propose that the uniform metabolic properties of male laryngeal muscle contribute to the production of the rapid (66 Hz) mate call vocalizations characteristic of this species. Further, our results suggest that androgens direct the masculinization of laryngeal muscle fibers during postmetamorphic development.
Determinants of multisensory integration in superior colliculus neurons. I. Temporal factors
Authors: Meredith MA , Nemitz JW , Stein BE
Published: March 2018

One of the most impressive features of the central nervous system is its ability to process information from a variety of stimuli to produce an integrated, comprehensive representation of the external world. In the present study, the temporal disparity among combinations of different sensory stimuli was shown to be a critical factor influencing the integration of multisensory stimuli by superior colliculus neurons. Several temporal principles that govern multisensory integration were revealed: (1) maximal levels of response enhancement were generated by overlapping the peak discharge periods evoked by each modality; (2) the magnitude of this enhancement decayed monotonically to zero as the peak discharge periods became progressively more temporally disparate; (3) with further increases in temporal disparity, the same stimulus combinations that previously produced enhancement could often produce depression; and (4) these kinds of interactions could frequently be predicted from the discharge trains initiated by each stimulus alone. Since multisensory superior colliculus neurons project to premotor areas of the brain stem and spinal cord that control the orientation of the receptor organs (eyes, pinnae, head), they are believed to influence attentive and orientation behaviors. Therefore, it is likely that the temporal relationships of different environmental stimuli that control the activity of these neurons are also a powerful determinant of superior colliculus-mediated attentive and orientation behaviors.
Tight junctions of brain endothelium in vitro are enhanced by astroglia
Authors: Tao-Cheng JH , Nagy Z , Brightman MW
Published: March 2018

The belts of endothelial tight junctions, which impede diffusion between blood and brain, were reduced to fragmentary, small junctions in subcultured brain endothelium. When cocultured with the capillaries' nearest neighbor, the astrocytes, these endothelial tight junctions were enhanced in length, width, and complexity, as seen by en face views of the cell membranes with freeze-fracture electron microscopy. Gap junctions, common in brain endothelium in vitro but absent in mature brain capillaries in vivo, were markedly diminished in area from among the enhanced tight junctions of the cocultures. Thus, astrocytes in vitro play a role in the formation, extent, and configuration of the junctional complexes in brain endothelium, whose diffusion barrier may likewise be influenced by astrocytes in vivo.
Pandinus imperator scorpion venom blocks voltage-gated potassium channels in nerve fibers
Authors: Pappone PA , Cahalan MD
Published: March 2018

We have examined the effects of venom from the scorpion Pandinus imperator on the membrane currents of voltage-clamped frog myelinated nerve fibers using the Vaseline-gap method. Crude venom, applied externally in concentrations from 50 to 500 micrograms/ml, selectively blocked the voltage-gated potassium currents without affecting nodal sodium currents or resting conductances. Block of potassium channels by Pandinus venom was highly dependent on the membrane voltage, being greater at negative potentials than at positive potentials. The blocking effects of Pandinus venom were irreversible on the time scale of our experiments; however, even high concentrations of venom failed to block potassium currents completely at positive potentials. These results suggest that Pandinus venom contains a component(s) that interacts specifically and strongly with a subpopulation of axonal potassium channels.
Connections between layer 4B of area 17 and the thick cytochrome oxidase stripes of area 18 in the squirrel monkey
Authors: Livingstone MS , Hubel DH
Published: March 2018

In area 18 of the primate visual cortex, staining for the mitochondrial enzyme cytochrome oxidase reveals 3 types of stripelike subdivisions running perpendicular to the 17/18 border: thick, thin, and pale stripes. In a previous paper (Livingstone and Hubel, 1984), we described the anatomical connections with area 17 of 2 of these 3 subdivisions, but we did not have any conclusive information on the third subdivision, the thick stripes. Here we report that, in the squirrel monkey, the main input to the thick stripes from area 17 arises from layer 4B. Layer 4B receives its input from the magnocellular division of the lateral geniculate body by way of layer 4C alpha; the thick stripes therefore probably belong to the magnocellular subdivision of the visual pathway.
Segregation of form, color, and stereopsis in primate area 18
Authors: Hubel DH , Livingstone MS
Published: March 2018

Primate visual cortical area 18 (visual area 2), when stained for the enzyme cytochrome oxidase, shows a pattern of alternating dark and light stripes; in squirrel monkeys, the dark stripes are clearly of 2 alternating types, thick and thin. We have recorded from these 3 subdivisions in macaques and squirrel monkeys, and find that each has distinctive physiological properties: (1) Cells in one set of dark stripes, in squirrel monkeys the thin stripes, are not orientation- selective; a high proportion show color-opponency. (2) Cells in the other set of dark stripes (thick stripes) are orientation-selective; most of them are also selective for binocular disparity, suggesting that they are concerned with stereoscopic depth. (3) Cells in the pale stripes are also orientation-selective and more than half of them are end-stopped. Each of the 3 subdivisions receives a different input from area 17: the thin stripes from the blobs, the pale stripes from the interblobs, the thick stripes from layer 4B. The pale stripes are thus part of the parvocellular system, and the thick stripes part of the magnocellular system. The physiological properties of the cells in the thin and pale stripes reflect the properties of their antecedent cells in 17, but nevertheless exhibit differences that suggest the kinds of processing that might occur at this stage.
Terminal arbors of axons projecting to the somatosensory cortex of the adult rat. II. The altered morphology of thalamocortical afferents following neonatal infraorbital nerve cut
Authors: Jensen KF , Killackey HP
Published: March 2018

The organization of the whisker representation within the neocortex of the rat is dependent on an intact periphery during development. To further investigate how alterations in this cortical map arise we examined the organization of thalamocortical afferents to the whisker representation in adult animals in which the infraorbital branch of the trigeminal nerve was cut on the day of birth. The disrupted pattern of thalamocortical projections to the vibrissae representation was apparent in the abnormal pattern of the anterograde transport of horseradish peroxidase from the thalamus, as well as in the abnormal pattern of succinate dehydrogenase activity. To determine the morphology of individual thalamocortical axons associated with this disrupted pattern, terminal arbors were “bulk-labeled” by injections of horseradish peroxidase into the white matter beneath the somatosensory cortex. Terminal arbors were identified by their laminar distribution of boutons corresponding to the specific thalamocortical afferent. The medial to lateral extent of these terminal arbors varied dramatically, from 350 to 1500 microns. In addition, terminal arbors innervating the same local area of cortex appeared to have varying degrees of overlap. Thus, the disruption of the neocortical vibrissae representation appears to involve the abnormal arborization of individual thalamocortical afferents. This finding supports the hypothesis that the fine-grain organization of the somatotopic map is dependent on the morphology and organization of individual thalamocortical arbors, which, in turn, are dependent on the periphery during development.
Cyclic AMP induces changes in distribution and transport of organelles within growth cones of Aplysia bag cell neurons
Authors: Forscher P , Kaczmarek LK , Buchanan JA , Smith SJ
Published: March 2018

This report examines cAMP-induced regulation of directed organelle transport in bag cell neuron growth cones using video-enhanced differential interference contrast (DIC) microscopy (Allen et al., 1981; Inoue, 1981) and digital image analysis techniques. Under control conditions, organelle transport is evident in the central cytoplasmic regions of bag cell neuron growth cones, but not in lamellae. Motility of lamellae takes the form of slow (less than 0.01 micron/sec) extension of margins and ruffling motions that propagate as waves (velocity, approximately 0.07 micron/sec) in a retrograde direction. Application of forskolin and a phosphodiesterase (PDE) inhibitor at concentrations known to induce changes in bag cell protein phosphorylation resulted in (1) rapid extension of directed organelle transport into lamellae, and (2) inhibition of the retrograde ruffling waves. These changes effected transformation of lamellae into neurite endings packed with microtubules and organelles, a large proportion of which appeared to be neurosecretory granules. The effects were reversible, dose-dependent, potentiated by a variety of PDE inhibitors, and mimicked by 6-N-butyl-8-benzyl-thio-cAMP (BT-cAMP). Though forskolin may normally promote depolarization and Ca entry, these changes in growth cone structure are not secondary to influx of external Ca, as they persist in Ca-free/EGTA solutions; furthermore, they do not resemble the effects of depolarization induced by perfusion with elevated K solutions. The cAMP-induced changes in growth cone morphology that we report here suggest a possible role for protein phosphorylation in promoting growth cone differentiation and structural changes accompanying secretion.
Induced disruption in the connectivity of an identified neuron in the Drosophila ts mutant shibire
Authors: Hummon MR , Costello WJ
Published: March 2018

Temperature-sensitive mutants permit the selective expression of mutant genotype. The Drosophila ts mutant shibire (shi) is paralytic at 30 degrees C; the probable primary effect of the mutation is disruption of membrane recycling. In studying the development of the giant fiber (GF) pathway during the pupal period, we find that shi flies exposed to heat pulse during early pupal states exhibit perturbation in the development of an identified neuron that links giant fibers to motoneurons of indirect flight muscles. Concomitantly, latency in activation of these muscles by the giant fiber pathway is significantly increased. Flies exposed to heat pulse during the late pupal period remain similar to control shi and wildtype flies in giant fiber pathway anatomy and muscle latency. Thus, the critical period of development of an identified neuron in a known motor pathway can be defined by its period of sensitivity to the shi defect. The time-dependent defect is apparently specific for cells that are at a developmental stage that is greatly dependent on membrane recycling processes. Use of this mutant will allow us to investigate the possible role of membrane recycling in development and to establish critical periods of neuronal development.
Acidic and basic fibroblast growth factors promote stable neurite outgrowth and neuronal differentiation in cultures of PC12 cells
Authors: Rydel RE , Greene LA
Published: March 2018

Acidic (aFGF) and basic (bFGF) fibroblast growth factors are well- characterized peptide hormones that have potent angiogenic activity and that are mitogenic for a variety of cell types. The present findings demonstrate that FGFs can reproduce the entire spectrum of rat pheochromocytoma PC12 cell responses previously shown to be elicited by NGF. These include responses that are rapid (cell flattening, enhanced phosphorylation of tyrosine hydroxylase) or delayed (neurite outgrowth, induction of phosphorylated MAP 1.2, regulation of NILE and Thy-1 glycoproteins, cessation of mitosis, elevation of AChE activity), as well as responses that have been shown to be either transcription- independent (neurite regeneration, promotion of survival) or transcription-dependent (priming, regulation of NILE and Thy-1 glycoproteins, elevation of AChE activity). The only responses for which the FGFs and NGF consistently showed quantitative differences were in the rates for neurite initiation and elongation in serum- containing medium. Thus, while all 3 factors promoted the formation of stable neurites, the network of outgrowth elicited by NGF at any given time of treatment was always of greater density. Togari et al. (1985) have previously reported that bFGF can initiate transient neurite formation in PC12 cell cultures. The present observations describe a variety of additional actions of bFGF on a neuronal cell line, and demonstrate that aFGF is capable of mimicking many, if not all, of these actions. These observations thus extend the range of actions that aFGF and bFGF may potentially exert on nerve cells, either during their development, repair, or maintenance. In addition, this work suggests that the PC12 cell line may serve as a useful model system with which to study the mechanism of action of FGFs on neurons. Since all 3 factors appear capable of eliciting the same wide spectrum of responses, molecular events specifically associated with FGFs and NGF in PC12 cells may prove illuminating of the causal steps involved in neuronal differentiation.
Metabolites of arachidonic acid in the nervous system of Aplysia: possible mediators of synaptic modulation
Authors: Piomelli D , Shapiro E , Feinmark SJ , Schwartz JH
Published: March 2018

Release of arachidonic acid from membrane phospholipids is receptor- mediated and might generate second messengers in neurons. We tested this idea using the simple nervous system of the marine mollusk, Aplysia californica. Aplysia neural components metabolize arachidonic acid through lipoxygenase and cyclo-oxygenase pathways. We identified 2 major lipoxygenase products, 12- and 5-hydroxyeicosatetraenoic acids (12-HETE and 5-HETE), and 2 cyclo-oxygenase products, PGE2 and PGF2 alpha. These metabolites of arachidonic acid are formed in synaptosomes, as well as in identified nerve cell bodies, indicating that both lipoxygenase and cyclo-oxygenase pathways are active within neurons. Application of the modulatory neurotransmitter histamine to cerebral ganglia that had been labeled with 3H-arachidonic acid induced the formation of 3H-12-HETE. This response was inhibited by the histamine antagonist cimetidine. Furthermore, release of radioactive 5- HETE and 12-HETE was observed after intracellular stimulation of the histaminergic cell C2 in cerebral ganglia labeled with 3H-arachidonic acid. Cimetidine also inhibited this response. Application of serotonin or stimulation of the giant serotonergic cell (GCN) in the cerebral ganglion did not cause detectable amounts of the labeled eicosanoids to be released. We found that intracellular stimulation of putative histaminergic neurons in the L32 cluster of the abdominal ganglion, which produces presynaptic inhibition in L10 neurons, also elicited the release of 3H-12-HETE and 3H-PGE2. Thus, for the first time we provide evidence that synaptic stimulation promotes turnover of arachidonic acid in neurons. We suggest that metabolites of arachidonic acid are likely to participate in some postsynaptic responses to histamine and may be second messengers for presynaptic inhibition.
Membrane properties and adrenergic responses in locus coeruleus neurons of young rats
Authors: Williams JT , Marshall KC
Published: March 2018

Intracellular recordings were made from locus coeruleus neurons in slices taken from rats 8–26 d of age. Neurons from these animals exhibited spontaneous action potentials, which were superimposed on slow (0.3–3 Hz) rhythmic depolarizations. The frequency of these potentials was closely related to the age of the animals from which the slice was taken, the slowest frequencies being observed in tissues from the youngest animals. In adult animals, such rhythmic activity was only rarely observed under normal recording conditions. The rhythmic depolarizations had a slow rate of rise and fall, were 3–15 mV in amplitude, were not affected by tetrodotoxin, and were abolished in solutions that contained elevated magnesium content. When the membrane potential was hyperpolarized by passing current through the recording electrode, the depolarizing rhythmic activity persisted even at very negative potentials (-120 mV). These depolarizations appear to be generated by the inward movement of calcium ions, probably in dendritic regions of the neuron. Superfusion of phenylephrine caused membrane depolarizations, increased the frequency of action potentials and of the slow, rhythmic depolarizations in about 80% of the cells from young rats, whereas it had no effect or a depressant action on cells from adults. Noradrenaline hyperpolarized the cells through an alpha 2- adrenoceptor and abolished the slow depolarizations. In cells from young rats, the hyperpolarization produced by noradrenaline reached a maximum and then declined, such that there was a “sag” in the membrane potential toward the resting potential following the peak of the hyperpolarization. Following the washout of noradrenaline, the membrane potential repolarized before moving toward the resting level.(ABSTRACT TRUNCATED AT 250 WORDS)
Nondirected axonal growth on basal lamina from avian embryonic neural retina
Authors: Halfter W , Reckhaus W , Kroger S
Published: March 2018

The vitreous surface of the embryonic avian retinal neuroepithelium was isolated by mechanical disruption of the retina mounted between 2 adhesive substrata. The 200-micron-thick sheath covered an area of up to 1 cm2 and consisted of the vitreal basal lamina with a lamina densa, 2 laminae rarae, and a carpet of ventricular cell endfeet on top of the lamina. The vitreal endfeet were removed by detergent treatment and an extracellular basal lamina was obtained. The laminae were further characterized by immunohistochemistry and immunoblotting. A 190 kDa laminin protein was detected in laminae with and without vitreal endfeet, whereas the membrane-bound neural cell adhesion molecule (N- CAM) was detectable only on the endfeet of the ventricular cells and was absent in the detergent-treated basal laminae. Neither immunoblotting nor immunostaining revealed fibronectin in these preparations. Explants of retina, sensory ganglia, and cerebellum from chick, quail, and mouse were cultured on the basal lamina as a substratum. In all cases axonal outgrowth was excellent, with a growth rate similar to that in situ. Outgrowing axons from sensory ganglia and cerebellar explants were accompanied by migratory cells, which, in the case of sensory ganglia, were flat cells and, in the case of cerebellar explants, resembled granular neurons. Optic axons grew on the laminae in an asymmetric, explant-inherent pattern specific for the position of origin of the explant. On detergent-treated basal laminae, as well as on laminin, the retinal axons grew in a clockwise orientation. This axonal growth pattern was specific for retinal tissue and was not observed with axons from other neural explants. In spite of the excellent substrate properties provided by the substratum, cues for growing axons (toward or away from the optic disk) were not detectable in the basal lamina preparations.
Quantitative distribution of the glycine receptor in the auditory brain stem of the gerbil
Authors: Sanes DH , Geary WA , Wooten GF , Rubel EW
Published: March 2018

The concentration and relative distribution of glycine receptors were determined for gerbil brain stem auditory nuclei using 3H-strychnine and quantitative autoradiographic techniques. Significant binding was observed in the anteroventral cochlear nucleus, the dorsal cochlear nucleus, the lateral superior olivary nucleus, and the inferior colliculus. A non-uniform distribution of binding was seen in 3 of these nuclei, such that the greatest concentration of glycine receptors was located in the high-frequency regions. An analysis of neuron soma density suggested that the amount of post-synaptic membrane could partially explain the distribution of receptor.
Development of glycine receptor distribution in the lateral superior olive of the gerbil
Authors: Sanes DH , Wooten GF
Published: March 2018

The concentration and relative distribution of glycine receptors were determined for the gerbil lateral superior olive at several postnatal ages. Quantitative autoradiographic techniques revealed significant 3H- strychnine binding to all regions of the nucleus from 4 to 90 d. However, during the first 20 d, a nonuniform distribution of binding emerged, such that the greatest concentration of receptor was found in the high-frequency region of the nucleus. An analysis of neuron packing density showed an approximate 2-fold distribution along the same axis at all ages. This evidence is consistent with an elimination of glycine receptors in the ventral region of the lateral superior olive as maturation progresses.
Cholinergic innervation of the smooth muscle cells in the choroid coat of the chick eye and its development
Authors: Meriney SD , Pilar G
Published: March 2018

The mechanical and pharmacological characteristics of the cholinergic activation of the smooth muscle in the choroidal coat of the chick eye have been assessed in tissues isolated from birds 1 d posthatching using histological, electrophysiological, and immunological techniques. The choroidal coat is innervated by a dense network of cholinergic nerves that make en passant synapses with smooth muscle. Thirty-hertz stimulation of these nerves initiates red blood cell (RBC) movement in the vessels of the choroidal coat, and this activation is blocked by muscarinic ACh receptor (AChR) antagonists. Force-transducer recordings of nerve-induced contractions of this tissue have a slow onset and relaxation time course similar to those of smooth muscle contractions. Furthermore, since nearly half the cholinergic neurons innervating the choroid die within a defined period during development, the onset and pharmacology of this innervation were studied during embryogenesis. With a neural cytoskeletal-like immunostain, we demonstrated that choroid axons are present in peripheral tissue by stage (St) 29. Extracellular electrical recordings made after choroid nerve stimulation allowed us to distinguish axon from muscle responses. These procedures permitted us to examine the time course of the innervation of the smooth muscle. However, to visualize the postsynaptic smooth muscle response, it was necessary to treat the isolated preparation with tetraethylammonium chloride (TEA). Accordingly, TEA-enhanced electrical smooth muscle responses to single-nerve stimuli could be recorded only after St 39. Treatment of the nerve-muscle preparation with prostigmine allowed the recording of TEA-enhanced electrical activity as early as St 36 (1 d after the beginning of the normal choroid neuron death period). This synaptic activation was completely blocked by atropine or quinuclidinyl benzylate (QNB), and was not affected by alpha bungarotoxin (alpha BTX), indicating that, as in the posthatching tissue, neuromuscular transmission is mediated by muscarinic receptors. These results show that cholinergic muscarinic activation of the choroidal coat can occur as early as St 36, but that it is not as efficient as transmission later in embryogenesis.