bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncrossed and crossed inhibition in the inferior colliculus of the cat: a combined 2-deoxyglucose and electrophysiological study
Authors: Webster WR , Serviere J , Martin R , Brown M
Published: March 2018

The cat inferior colliculus (IC) was studied with 2-deoxyglucose (2- DG). By presenting high-frequency tone bursts to one ear and white noise bursts simultaneously to the other, a band of reduced or inhibitory labeling was revealed in the central nucleus (ICC) of the IC ipsilateral to the ear receiving the tone bursts. It was concluded that this ipsilateral inhibition might be related to the organization of excitatory/inhibitory units in ICC. In the opposite ICC, narrow bands of increased labeling were seen. In some animals, the positions of single units were marked, and tone frequencies were presented under 2- DG, which were the same as these units' characteristic frequencies (CFs). The positions of the units coincided with the position of the inhibitory bands, indicating that they were functional isofrequency- inhibitory contours. Unlike higher auditory centers, the binaural inhibitory areas were in register with and not orthogonal to the excitatory isofrequency contours. The inhibitory contours were generally larger than the excitatory contours and became even larger in more caudal sections. Both the inhibitory and excitatory contours extended into dorsal cortex areas of IC. In two other cats, high- frequency tone bursts and white noise bursts were presented to the same ear, and both a band of increased and a band of reduced labelling were found in the IC contralateral to this ear. The inhibitory band was always lateral to the excitatory band and was often smaller. They did not become larger in more caudal sections. The position of a unit in one cat was marked by pontamine sky blue, and the position of the unit coincided with the position of the excitatory band. It was concluded that this lateral inhibitory band represents high-frequency inhibitory sidebands of cells with CFs lower than the stimulating tone. It is concluded that the 2-DG method might reveal hitherto unknown inhibitory systems if stimuli could be combined with diffuse stimuli that raised the general background activity of sensory systems.
Serotonin and cyclic adenosine 3':5'-monophosphate modulate the potassium current in tail sensory neurons in the pleural ganglion of Aplysia
Authors: Pollock JD , Bernier L , Camardo JS
Published: March 2018

Tail sensory neurons in the pleural ganglion that mediate the afferent portion of the tail withdrawal reflex in Aplysia californica undergo heterosynaptic facilitation of transmitter release during sensitization. As in the siphon sensory neurons, the transmitter serotonin produces facilitation and also elicits a slow, decreased conductance excitatory postsynaptic potential (EPSP) in these neurons. Using voltage clamp and biochemical analyses, we have found that the slow EPSP in the pleural sensory neurons is due to a decrease in a potassium conductance identical to the S potassium current characterized in siphon sensory neurons. Like the S current, the current modulated by serotonin in the pleural sensory neurons is a non- inactivating potassium current, and it contributes to both the resting and action potentials. The current reverses in 120 mM external K+ at - 20 mV, close to the predicted Nernst equilibrium potential. Intracellular cesium blocks the serotonin response, but the current is not blocked by equimolar substitution of barium for calcium, nor by 50 mM tetraethylammonium chloride. The effect of serotonin is cAMP dependent, since serotonin elevates cAMP and both cAMP injection and forskolin mimic the serotonin response. These results indicate that the mechanism associated with sensitization of the siphon-gill withdrawal reflex, a slow decreased potassium conductance, is also a component of the neuronal circuitry underlying modulation of another reflex, the tail withdrawal reflex. Therefore, two distinct populations of neurons subserving similar behavioral functions have related biophysical and biochemical properties.
Structure and expression of the egg-laying hormone gene family in Aplysia
Authors: Mahon AC , Nambu JR , Taussig R , Shyamala M , Roach A , Scheller RH
Published: March 2018

Transcription of the egg-laying hormone (ELH) gene family was examined by characterizing homologous cDNA clones from abdominal ganglion and atrial gland cDNA libraries. All cDNAs contain an exon that spans the coding region (exon III) and one or two additional exons. The tissue- specific expression of the ELH gene family was confirmed by the observation that exon III encodes the ELH precursor protein in the bag cell transcripts and either the A or B precursor proteins in the atrial gland transcripts. The cDNA clones also contain 5′ untranslated exons not present in the previously isolated genomic clones. One type of transcript has a 40-base pair segment, designated exon I, contiguous with exon III. A second type of transcript has an additional 149 base pairs of DNA, designated exon II, located between exons I and III. Several genomic clones containing exons I and II were isolated. DNA sequence analysis reveals that exons I and II are directly linked and that they are separated from exon III by an intervening sequence of at least 5 kilobases (kb). Consensus sequences for a putative promotor region and also for RNA splicing and polyadenylation were identified. From this work we can describe a prototype ELH gene complete with identified sequences necessary for the proper initiation of transcription and the subsequent processing of the transcript.
Effect of intrafusal muscle mechanics on mammalian muscle spindle sensitivity
Authors: Poppele RE , Quick DC
Published: March 2018

Sensitivity differences between primary and secondary endings of mammalian muscle spindles under various conditions of stretch and fusimotor activation may be due to differences in their respective mechanoelectric transducers or to mechanical properties of the intrafusal muscle supporting those endings. This study of isolated cat muscle spindles examines the strain in individual intrafusal muscle fibers resulting from stretch and fusimotor stimulation. The degree of local stretch occurring at the sensory endings under these conditions was measured. The results support the hypothesis that the sensitivities of primary and secondary endings are quite similar. They are directly related to the local stretch of the underlying muscle which may be altered by changes in muscle stress and stiffness.
The effects of a myasthenic serum on the acetylcholine receptors of C2 myotubes. II. Functional inactivation of the receptor
Authors: Maricq AV , Gu Y , Hestrin S , Hall Z
Published: March 2018

We have investigated the effect of antibodies from a myasthenic serum on the physiological properties of acetylcholine receptors (AChRs) in myotubes of a mouse muscle cell line, C2. The antibodies in this serum blocked the binding of 125I-alpha-bungarotoxin to the myotubes to an extent of about 50%. The antibodies also inhibited the increase in 22Na influx caused by carbamylcholine (CARB). At a concentration of antibody that blocked about 50% of toxin binding, greater than 80% of the AChR- mediated 22Na influx was blocked. The apparent KD for CARB, estimated from the dose-response curve for 22Na influx, was unaffected. The effect of the antibodies was further examined by patch-clamp recording. In greater than 30% of the patches from antibody-treated cells, no channel activity in response to acetylcholine was seen; in contrast, every patch from control cells showed activity. The channels that were seen after antibody treatment were indistinguishable from those seen in normal cells, both in their single-channel conductance and in the kinetic constants used to describe channel opening and closing. We conclude that the antibodies in this serum inhibit the functional response of AChRs in C2 myotubes to acetylcholine and do so by inactivating individual receptors.
Regulation of the concentration of adenosine 3',5'-cyclic monophosphate and the activity of tyrosine hydroxylase in the rat superior cervical ganglion by three neuropeptides of the secretin family
Authors: Ip NY , Baldwin C , Zigmond RE
Published: March 2018

Preganglionic nerve stimulation leads to an acute elevation of tyrosine hydroxylase (TH) activity in the rat superior cervical ganglion. This effect is mediated in part by acetylcholine, acting via nicotinic receptors, and in part by a noncholinergic neurotransmitter. As a first step in an attempt to identify this noncholinergic transmitter, we have examined a number of biogenic amines, purine nucleotides, neuropeptides, and other compounds for their ability to increase TH activity. Secretin, vasoactive intestinal peptide (VIP), and PHI (a 27- amino acid peptide with an NH2-terminal histidine and a COOH-terminal isoleucine amide), all members of the secretin family of peptides, increased TH activity acutely. Human pancreatic growth hormone- releasing factor, glucagon, and gastric inhibitory peptide (three other members of this peptide family) and all other transmitter candidates tested had no effect on this enzyme activity. We have examined the possibility that this peptidergic regulation of TH activity is mediated via changes in adenosine 3′,5′-cyclic monophosphate (cAMP) levels. When the six members of the secretin family were tested for their ability to increase cAMP levels in the ganglion, secretin, VIP, and PHI significantly increased this cyclic nucleotide, whereas growth hormone- releasing factor, glucagon, and gastric inhibitory peptide produced no significant effects. The rank orders of potency and of efficacy of secretin, VIP, and PHI in altering TH activity and cAMP levels were identical. Furthermore, a strong correlation was found between the cAMP level and the TH activity in individual ganglia exposed to these peptides. Finally, 8-bromoadenosine 3′,5′-cyclic monophosphate and forskolin also increased TH activity.
Projections from the ventral respiratory group to phrenic and intercostal motoneurons in cat: an autoradiographic study
Authors: Feldman JL , Loewy AD , Speck DF
Published: March 2018

Anterograde transport of tritiated amino acids (leucine, lysine, and proline) was used to examine the spinal projections of respiratory premotor neurons in the ventral respiratory group (VRG) of cats. This population of neurons corresponds anatomically with the nucleus ambiguus-retroambigualis. Small volumes (20 to 50 nl) of tritiated amino acids were pressure ejected into the middle of the VRG through a micropipette which permitted simultaneous recording of respiratory modulated activity. In two cats injections were made caudal to the obex in regions which contained expiratory modulated neurons. In five cats injections were made rostral to the obex in regions containing inspiratory neurons. After a 2-week survival period, cats were anesthetized and perfused. The entire neuraxis was removed and processed using standard autoradiographic techniques. Transport of tritiated amino acids revealed a marked bilateral projection to lamina IX of the spinal cord at the C4 to C6 level and a primarily contralateral projection to laminae VIII and IX in the thoracic spinal cord. Distinct descending pathways to the phrenic motor neurons were observed in the lateral funiculus and in the ventral funiculus; descending fibers to the intercostal motoneurons in the thoracic cord appeared to be restricted to the ventral funiculus. Labeling of axon terminals in both the cervical and thoracic cords was confined to ventral horn regions which contain motoneurons. These results suggest that monosynaptic projections from brainstem bulbo-spinal neurons to spinal motoneurons are important in controlling respiratory movements of the diaphragm and intercostal muscles.
Nonsynaptic characteristics of neurotransmission mediated by egg-laying hormone in the abdominal ganglion of Aplysia
Authors: Mayeri E , Rothman BS , Brownell PH , Branton WD , Padgett L
Published: March 2018

The bag cell neurons of the marine mollusk Aplysia are a putative multitransmitter system which utilizes two or more neuropeptides that are enzymatically cleaved from a common precursor protein. It has been proposed that one of the neuropeptides, egg-laying hormone (ELH), acts nonsynaptically as a neurotransmitter in the abdominal ganglion by diffusing long distances to target neurons compared to conventional transmitters acting at synapses. To test this idea further, we investigated the physiological properties of neurotransmission mediated by ELH. We found that ELH acts directly to duplicate two types of responses produced by a burst discharge of the bag cells: prolonged excitation of LB and LC cells, and the previously described effect of ELH, burst augmentation of cell R15. Analysis of perfusate collected after electrical stimulation of the bag cells showed that the peptide is released in sufficient quantity to diffuse long distances within the ganglion without being completely inactivated. To mimic the way the peptide is thought to be released physiologically, ELH was arterially perfused into the ganglion. The response normally produced by bag cell activity was duplicated by 0.5 to 1.0 microM concentrations of ELH and showed no rapid desensitization. ELH had no effect on cells that are unaffected by bag cell activity and no effect on cells that are inhibited (LUQ cells) or transiently excited (cells L1 and R1) by bag cell activity. Acidic peptide, another peptide encoded on the ELH precursor protein, was found to be synthesized and released by the bag cells, but it had no effect on the cells we tested. We conclude that the combined properties of ELH neurotransmission resemble the properties of transmission at autonomic nerve endings on cardiac and smooth muscle rather than those of conventional synaptic transmission. ELH released from bag cells is dispersed throughout the interstitial and vascular spaces of the ganglion to produce responses in the cells that have receptors for the peptide. The results also suggest that ELH mediates only a subset of the responses induced by bag cell activity; they are consistent with data indicating that the other responses are mediated by other bag cell peptides derived from the same precursor protein as ELH.
Depletion of norepinephrine, but not serotonin, reduces long-term potentiation in the dentate gyrus of rat hippocampal slices
Authors: Stanton PK , Sarvey JM
Published: March 2018

Long-term potentiation (LTP) in the hippocampus is a long-lasting enhancement of synaptic efficacy produced by a brief, high frequency repetitive stimulation of afferents. LTP has generated a great deal of interest as a candidate mechanism in learning and memory. A recent in vivo study has shown that depletion of norepinephrine (NE) or serotonin (5-hydroxytryptamine, 5-HT) reduced LTP in the dentate gyrus produced by stimulation of the perforant path. However, it was impossible to tell whether this resulted from depletion in the hippocampus, itself, or was secondary to depletion of other brain areas, and no comparison between hippocampal cell fields was done. Therefore, we have examined the effects of depletion of NE or 5-HT on LTP in the dentate and field CA1 of the isolated in vitro hippocampal slice preparation. We report here that NE depletion markedly reduces the occurrence and amplitude of LTP in the dentate, but not in field CA1. In contrast, depletion of 5- HT does not prevent occurrence of LTP in either area. Furthermore, pharmacologic data indicate that beta-receptor stimulation of adenylate cyclase is probably the mechanism of NE's action in the production of LTP in the dentate. These results suggest that endogenous hippocampal NE is more important to LTP in the dentate than is endogenous 5-HT.
Trophic effects on the contractile and histochemical properties of rat soleus muscle
Authors: Spector SA
Published: March 2018

Contractile and histochemical properties of rat soleus muscle were studied bilaterally after 2 or 4 weeks of denervation (DEN), which eliminates activity and non-activity-related influences, and chronic application of tetrodotoxin (TTX) to the motor nerve, which produces a completely inactive innervated muscle. After 2 or 4 weeks of disuse, the percentages of slow twitch oxidative fibers in both DEN- and TTX- treated soleus were reduced significantly and to similar extents. The dynamic contractile properties of TTX-treated and denervated muscles were similar to those of control muscle after 2 weeks, but by 4 weeks, parallel increases were seen in normalized rate of tension development and maximal shortening speed of these muscles. After either period of disuse, the atrophy of TTX-treated soleus was significantly less than that of denervated muscle. Atrophy was associated with correspondingly diminished capacity of denervated or TTX-disused muscles to generate tension after 2 weeks. By 4 weeks of treatment, the reduction in tension of denervated soleus was greater than its diminished size. These results imply the existence of a non-activity-related stimulus in TTX-inactivated muscles which slows the reductions in muscle mass and specific tension observed in denervated soleus muscle. In contrast, the similarities in dynamic speed-related properties and fiber type profiles between DEN- and TTX-treated rat soleus may be explained simply by the absence of neuromuscular activity.
Gating properties of acetylcholine receptors at developing rat endplates
Authors: Vicini S , Schuetze SM
Published: March 2018

The gating properties of acetylcholine receptors (AChRs) change during the development of rat soleus endplates. During the first 3 weeks after birth, the apparent mean channel open time (tau) decreases severalfold and the single-channel conductance (gamma) increases 50%. To better understand this phenomenon, we used a combination of noise analysis, analysis of miniature endplate currents (MEPCs), and single-channel recordings to quantify the relative levels of fast and slow AChR activity at developing soleus endplates. When the same endplates were studied with both noise analysis and MEPC analysis, results obtained with the two techniques were strongly correlated, but MEPC analysis yielded higher estimates of the relative amount of slow channel activity. Experiments designed to examine the distribution of fast and slow channels gave no evidence for a gradient of either channel type within individual endplates; rather, fast and slow channels appeared to be mixed together. However, the relative amount of fast and slow channel activity did vary markedly among different endplates within individual muscles. In agreement with earlier studies, we found a progressive decrease in the relative amount of slow channel activity during the first 3 weeks after birth. However, our data indicate that this process begins sooner than reported previously and takes longer to complete. Some of the same endplates that were studied physiologically were also examined in the electron microscope to test the hypothesis that changes in AChR gating might be related to ultrastructural changes such as the formation of folds. The physiological and ultrastructural results were essentially uncorrelated.
Biochemical characterization of a filtered synaptoneurosome preparation from guinea pig cerebral cortex: cyclic adenosine 3':5'-monophosphate- generating systems, receptors, and enzymes
Authors: Hollingsworth EB , McNeal ET , Burton JL , Williams RJ , Daly JW , Creveling CR
Published: March 2018

A particulate preparation was obtained by low speed centrifugation of guinea pig cerebral cortical homogenates prepared with a Krebs- Henseleit buffer. Light microscopic examination, using a reflected light differential interference contrast system, reveals the presence of intact neurons, axonal fragments, glial cells, and erythrocytes along with an abundance of small spherical entities (diameter about 1.1 micron) and snowman-shaped entities (diameter of larger sphere about 1.1 micron, diameter of attached smaller sphere about 0.6 micron). Many unattached smaller spherical entities are also present (diameter about 0.6 micron). Pressure filtration through 5- or 10-micron Millipore filters, followed by low speed centrifugation and resuspension, removes most of the larger entities to afford a suspension composed mainly of the small spherical and snowman-shaped entities. Electron microscopic examination reveals the presence of many synaptosomes with attached resealed postsynaptic entities. It is proposed that these correspond to the snowman-shaped entities to be termed synaptoneurosomes. Accumulations of cyclic AMP elicited by 2-chloroadenosine and histamine, and by combinations of 2-chloroadenosine, histamine, norepinephrine, and forskolin, are lower in filtered than in unfiltered preparations, whereas accumulations elicited by forskolin are unchanged. Levels of adenylate cyclase are reduced by filtration, whereas levels of phosphodiesterase are unchanged. Filtration reduces levels of markers for whole cells and endothelial cells, whereas neuronal markers such as acetylcholinesterase activity and norepinephrine uptake are increased. Levels of S-100 protein, a marker for glial cells, are not significantly decreased. There is no apparent change in the density of many receptors or ion channels. Levels of A1- adenosine and H1-histamine receptors are increased, whereas levels of so-called peripheral benzodiazepine-binding sites are decreased.
Independent steroid control of the fates of motoneurons and their muscles during insect metamorphosis
Authors: Weeks JC , Truman JW
Published: March 2018

The metamorphosis of insects is controlled by the blood titers of a small number of developmental hormones including a class of steroids, the ecdysteroids. We have studied the developmental fates of several muscles and their motoneurons during the larval-pupal transformation of the tobacco hornworm, Manduca sexta. The endocrine events which trigger pupal development are first, a fall in the blood titer of juvenile hormone, followed by two subsequent elevations of blood ecdysteroids. The small “commitment pulse” of ecdysteroids commits tissues to pupal development, whereas the sustained “prepupal peak” causes the new pupa to be formed (Riddiford, L. M. (1980) In Progress in Ecdysone Research, J.A. Hoffmann, ed., pp. 409–430, Elsevier/North-Holland Biomedical Press, Amsterdam). In the present experiments we were able to correlate specific aspects of the changing blood steroid titers with the degeneration of larval muscles, and with the dendritic regression and death of their motoneurons. The abdominal prolegs, which are the principal locomotory appendages of the caterpillar, are lost during the larval-pupal transformation. We have followed the fates of a proleg retractor muscle, PPRM, and its single motoneuron, PPR. Two other differently fated abdominal muscles not associated with the proleg were also studied. Surgical and endocrinological manipulations showed that PPRM degenerates in response to the rising phase of the prepupal ecdysteroid peak and that interactions with its motoneuron are not involved in the muscle's death. Motoneuron PPR responds to the rising prepupal peak by first reducing its dendritic arbor by 40% and then dying. Other proleg motoneurons regress but do not die, indicating that dendritic regression is programmed separately from neuronal death. Neither the dendritic reduction nor the death of PPR involves interactions with its target muscle. These results indicate that ecdysteroids have independent and parallel effects in the periphery, where they cause muscle degeneration, and in the central nervous system, where they cause dendritic regression and death of motoneurons.
FMRF-amide-like substances in the leech. I. Immunocytochemical localization
Authors: Kuhlman JR , Li C , Calabrese RL
Published: March 2018

FMRF-amide-like immunoreactivity (FLI) was localized to approximately 50 neurons in each segmental ganglion of the medicinal leech using immunocytochemical techniques. Although most of these neurons were iterated in each segmental ganglion, some were more restricted in their segmental distribution. The head and tail ganglia likewise contained numerous FMRF-amide-like immunoreactive cells. In addition to cell bodies, many nerve processes and varicosities were also immunoreactive throughout the ganglion. All labeling of FLI was blocked by preabsorption of the anti-FMRF-amide antiserum with synthetic FMRF- amide. Using a combination of Lucifer Yellow cellular injection and indirect immunofluorescence techniques, we identified several of the neurons possessing FLI. Identified neurons included excitatory motor neurons (HE, RPE, LPE, AE, and L), the HA modulatory neuron, interneuron cell 204, and cells of unknown function (AP). The processes of HE motor neurons and HA modulatory neurons which innervate the heart tubes were also immunoreactive. These results indicate a role for FMRF- amide-like substances as neurochemical signals in the leech.
Is a nicotinic influence involved in denervation-induced depolarization of muscle?
Authors: Rochel S , Robbins N
Published: March 2018

The neurotrophic role of acetylcholine (ACh) in the denervation- dependent decline of muscle resting membrane potential (RMP) was evaluated. Freshly dissected rat hemidiaphragms with short or long (2 cm) nerve stumps attached (“-N” and “+N” preparations, respectively) were incubated in organ culture in the presence or absence of the nicotinic blockers, alpha-bungarotoxin (alpha-BTX) or d-tubocurarine (curare). Subsequently, RMPs and miniature endplate potentials (MEPPs) of the junctional region were measured. Spontaneous MEPPs disappeared with a half-life of 12 and 20 hr in -N and +N preparations, respectively. A 10- to 15-mV depolarization of RMP was observed between 15 and 20 hr in -N muscles and between 24 and 28 hr in +N muscles. This time course of disappearance of spontaneous potentials and of membrane depolarization agrees well with that observed in vivo. Although nicotinic transmission was blocked from the initiation of the incubation period in alpha-BTX- or curare-treated muscles, no acceleration of RMP decline in -N muscles in vitro was observed. Moreover, in +N preparations the effect of the nerve stump in delaying RMP depolarization persisted despite the continuous presence of alpha- BTX or curare. Since excess ACh triggers a lysosomal proteolytic response at the nerve-muscle junction and since this may occur early in denervation, the possible role of a nicotinic-induced proteolytic mechanism was tested in vitro with the potent protease inhibitor leupeptin. This inhibitor did not delay or prevent the denervation- dependent alterations.(ABSTRACT TRUNCATED AT 250 WORDS)
Growth cone morphology and trajectory in the lumbosacral region of the chick embryo
Authors: Tosney KW , Landmesser LT
Published: March 2018

We quantitatively analyzed several features of orthogradely labeled peripheral growth cones in the lumbosacral region of the chick embryo. We compared motoneuron growth cones in regions where they appear to express specific directional preferences (the plexus region and regions where muscle nerves diverge from main nerve trunks), which we operationally defined as “decision regions,” to motoneuron growth cones in other pathway regions (the spinal nerve, nerve trunk, and muscle nerve pathways) which we termed, for contrast, “non-decision region.” We found that motoneuron growth cones are larger, more lamellepodial, and have more complex trajectories in decision regions. Sensory growth cone populations, which are thought to be dependent upon motoneurons for outgrowth (Landmesser, L., and M. Honig (1982) Soc. Neurosci. Abstr. 8: 929), do not enlarge or become more lamellepodial in motoneuron decision regions, suggesting that this local environment does not affect all species of growth cones equally and that the alterations in motoneuron growth cones in these regions may be relevant to their specific guidance. In addition, the resemblance between the sensory population and other closely fasciculating growth cones lends support to the suggestion that sensory neurons utilize motoneuron neurites as a substratum. We suggest that the convoluted trajectories, enlarged size, and more lamellepodial morphology of motoneuron growth cones in decision regions is either related directly to the presence of specific cues that guide motoneurons or to some aspect of this environment that allows them to respond to specific cues.
Dendritic reorganization of abdominal motoneurons during metamorphosis of the moth, Manduca sexta
Authors: Levine RB , Truman JW
Published: March 2018

During metamorphosis in the hawkmoth Manduca sexta, muscles of the abdominal body wall undergo a reorganization. Many die at the end of larval life and are replaced in the adult by newly generated muscles. We have identified several of the motoneurons innervating these muscles and followed them through metamorphosis. The morphology of larval motoneurons is correlated with their target location. Those with medial targets have bilateral dendritic fields, whereas those with lateral targets have dendrites restricted to one side of the segmental ganglion. Some motoneurons innervate the same muscle in all stages of life, but the majority lose their larval targets following entry into the pupal stage. Although some of the latter group also die at this time, most survive to innervate a new adult target. These “respecified” motoneurons undergo a period of dramatic dendritic growth during metamorphosis. The results demonstrate that these identified neurons are capable, under the appropriate conditions of existing in more than one stable morphology.
The postnatal development of the association projection from visual cortical area 17 to area 18 in the cat
Authors: Price DJ , Blakemore C
Published: March 2018

The postnatal development of the association projection from area 17 to area 18 was studied in normal and binocularly deprived kittens between 1 and 28 days of age, using retrograde transport of horseradish peroxidase conjugated with wheat germ agglutinin. The positions of injection sites in the visual cortex, defined in relation to the borders of visual areas 17, 18, and 19 located in Nissl- and cytochrome oxidase-stained sections, were confirmed by observing the patterns of labeling of cells in the lateral geniculate nucleus. The association projection is present and is arranged at least roughly topographically from birth onward; at all ages it arises from cells in both the superficial layers (II, III, and the upper part of IV) and the deep layers (V and VI). In older kittens (20 days or more), however, the origin of the pathway is principally from the upper layers, as in adult cats, whereas in younger animals the projection arises roughly equally from cells in superficial and deep laminae. Initially, the association neurons in area 17 are distributed uniformly along each lamina. Periodic clustering of labeled cells in the upper layers can just be discerned at 10 days, and this patchiness has reached its adult clarity by 20 days, at which stage the projection from the lower layers is greatly diminished. Binocular deprivation until the age of 28 days did not prevent these developmental changes in the projection. Various controls established that the patterns of labeling seen in this study were not due to direct spread of tracer into area 17, to uptake of tracers by fibers-of-passage, or to transcellular transport via the thalamus.
Ontogenetic changes in the cyclic adenosine 3',5'-monophosphate- stimulatable phosphorylation of cat visual cortex proteins, particularly of microtubule-associated protein 2 (MAP 2): effects of normal and dark rearing and of the exposure to light
Authors: Aoki C , Siekevitz P
Published: March 2018

Based on a theory that a norepinephrine-stimulated cascade of events resulting in an increase of intracellular cyclic adenosine 3′,5′- monophosphate (cAMP) modulates the state of plasticity for the receptive field property of visual cortical neurons, we have followed the ontogenetic changes in cAMP-stimulated phosphorylation of proteins in whole homogenates obtained from developing visual cortices of cats. In vitro phosphorylation was assayed with and without cAMP and the cAMP- dependent protein kinase, and the phosphoproteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were counted for 32P incorporated from [gamma-32P]ATP. It was found that the regulatory subunits of the cAMP-dependent protein kinase are present and fully active by birth, whereas the synapsin content increases at a rate concomitant with synaptogenesis. These ontogenetic developments are not influenced by dark rearing (DR) from birth, a procedure which postpones the onset of the critical period (CP) for plasticity. By contrast, the cAMP-stimulatable phosphorylation of microtubule-associated protein 2 (MAP 2), which under normal rearing conditions increases from birth to the second month, is strongly modulated by the presence of light in the environment. After DR for various periods, kittens were subsequently exposed to light so as to trigger the onset of the CP that had been postponed. A few hours of light were sufficient to cause a large increase in the in vitro phosphorylation of MAP 2. This effect is not observed in the auditory cortex or the lateral geniculate nucleus of the same animals, or in the visual cortex of normally reared cats which were then dark reared in adulthood. But this effect was seen in the visual cortices of cats following 5 months of DR from birth, animals which by chronological age have passed the CP, presumably because the onset of the CP was extended by the DR procedure. The cAMP-dependent phosphorylation of MAP 2 (and its dephosphorylation) may be an important factor for determining the state of plasticity in the CP through its affecting the dendritic cytoskeletal organization involving tubulin and actin.
The electrical circuitry of an olfactory sensillum in Antheraea polyphemus
Authors: de Kramer JJ
Published: March 2018

The aim of this study was to obtain a better insight into the distribution of active and passive electrical properties of the membranes of al olfactory sensillum. Such a sensillum is composed of three accessory cells which envelope the somata of two receptor neurons which have long (300 micron) dendrites that are incorporated in cuticular protuberances (hairs). An electrical equivalent circuit of this organ is reconstructed which is based upon the response of sensilla to current transients, the shape of extracellularly recorded spikes, and the effects of lesions on these signals. A strong influence of membrane capacitances on the overall response and on the shape of spikes becomes apparent. From the combination of electrical and morphometric data it follows that the resistance of the apical membranes of the accessory cells in much higher than the resistance of their basolateral membranes. Neither in simultaneous tip and sidewall recordings nor in the hair (dendrite) amputation experiments could antidromic propagation of action potentials into the dendrite be demonstrated. The commonly accepted retrograde propagation explanation for the biphasic waveform of the spike is, therefore, rejected. Dendrite amputation experiments showed that the impedance of the dendrite does not limit the spike amplitude and that the dendrite contributes slightly to the duration of the positive phases of spikes. Both of these observations indicate that the dendrite is also involved in the generation of the leading phase of the spike. Consequently the proposition is made that action potentials are initiated at a dendritic location.
Possible mechanisms by which repeated clozapine administration differentially affects the activity of two subpopulations of midbrain dopamine neurons
Authors: Chiodo LA , Bunney BS
Published: March 2018

Extracellular single-cell recording techniques were employed to study the mechanism of action of repeated oral clozapine administration on the in vivo spontaneous activity of substantia nigra (A9) and ventral tegmental area (A10) dopamine (DA)-containing neurons in the rat. Clozapine was observed to affect DA neurons differentially within these two regions when compared to haloperidol. Acute treatment (1 hr) with both drugs increased the number of spontaneously firing neurons in both A9 and A10. Chronic (21 day) treatment with haloperidol decreased the number of cells encountered in both regions, whereas repeated treatment with clozapine reduced the number of DA cells per track only in A10. In all cases, the silent DA neurons were inferred to be in a state of depolarization inactivation since they could be induced to discharge normally by the microiontophoretic application of the inhibitory neurotransmitter gamma-aminobutyric acid. These effects were not due to an effect of chloral hydrate anesthesia since they were also observed in gallamine-paralyzed, artificially respired animals. Chronic co- administration with haloperidol of either an anticholinergic (trihexyphenidyl) or the alpha 1-norepinephrine (NE) receptor antagonist, prazosin, but not an alpha 2-NE antagonist, RX781094, resulted in a differential effect on A9 and A10 DA neurons identical to that observed with repeated clozapine administration alone. Thus, chronic treatment with these combinations of drugs resulted in the depolarization inactivation of only A10 cells. These data suggest that anticholinergic and/or alpha 1-NE-blocking properties of clozapine may, in part, mediate its differential effects on A9 and A10 midbrain DA neurons.
Reorganization of actin in depolarized synaptosomes
Authors: Bernstein BW , Bamburg JR
Published: March 2018

Depolarization of whole brain synaptosomes, which stimulates transmitter release, also affects regulation of the assembly of actin microfilaments. Lysates of depolarized synaptosomes contain 20% less cytoskeletal actin than lysates of unstimulated synaptosomes. Parameters affecting the assembly of actin are modified before lysis, but release of actin from the Triton-insoluble cytoskeleton does not occur until after lysis. Actin released from the cytoskeleton is not precipitated with myosin, indicating that it consists of monomers and/or short oligomers. Synaptosomes were incubated for 12 sec in one of three solutions of identical ionic strength but of different salt mixtures: 75 mM KCl-2 mM CaCl2, 5 mM KCl-2mM CaCl2, or 75 mM KCl-0.1 mM EGTA. Synaptosomes were then lysed in an F-actin stabilizing buffer containing 1% Triton X-100. Control synaptosomes (no incubation) were lysed directly into the same lysis buffer containing one of the three different salt mixtures. The cytoskeletal and noncytoskeletal actin pools were separated 25 sec after lysis by centrifugation at 10(4) X g for 1 min, and the actin in each pool was quantitated by the DNase I inhibition assay. The drop in cytoskeletal actin induced by depolarization is maximized by including Ca2+ in the depolarizing buffer, and it is blocked completely by adding a neutral thiol protease inhibitor, leupeptin, to either the pre- or post-lysis buffer. The drop is also completely reversed by repolarizing the synaptosomes.
Evidence for shifting connections during development of the chick retinotectal projection
Authors: McLoon SC
Published: March 2018

The pattern in which optic axons invade the tectum and begin synaptogenesis was studied in the chick. The anterogradely transported marker, horseradish peroxidase, was injected into one eye of embryos between 5 and 16 days of development (E5 to E16). This labeled the optic axons in the brain. The first retinal axons arrived in the most superficial lamina of the tectum on E6. They entered the tectum at the rostroventral margin. During the next 6 days of development the axons grew over the tectal surface. First they filled the rostral tectum, the oldest portion of the tectum, and then they spread to the caudal pole. Shortly after the first axons entered the tectum on E6, labeled retinal axons were found penetrating from the surface into deeper tectal layers. In any given area of the tectum, optic axons were seen penetrating deeper layers shortly after arriving in that area. Electron microscopic examination showed that at least some of the labeled axons in rostral tectum formed synapses with tectal cells by E7. These results show two things which contrast with results from previous studies. First, there is no delay between the time the retinal axons enter the tectum and the time they penetrate into synaptic layers of the tectum. Second, the first retinotectal connections are formed in rostral tectum and not central tectum. Retrograde tracing showed the first optic axons that arrived in the tectum were from ganglion cells in central retina. Previous studies have shown that the ganglion cells of central retina project to the central tectum in the mature chick. This opens the possibility that the optic axons from central retina, which connect to rostral tectum in the young embryo, shift their connections to central tectum during subsequent development. As they enter the tectum the growth cones of retinal axons appear to be associated with the external limiting membrane. During the time that connections would begin to shift in the tectum a second population of axons appears at the bottom of stratum opticum, some with characteristics of growth cones. This late-appearing population may represent axons shifting their connections. These results have implications for theories on how the retinotopic pattern of retinotectal connections develops.
Localization of sodium/potassium adenosine triphosphatase in multiple cell types of the murine nervous system with antibodies raised against the enzyme from kidney
Authors: Ariyasu RG , Nichol JA , Ellisman MH
Published: March 2018

This report describes the development and characterization of a battery of highly specific antibodies to sodium/potassium (Na+ + K+)-ATPase and their use in localizing this enzyme in nervous tissue. The immunolabeling characteristics of polyclonal antibodies and monoclonal antibodies (Schenk, D. B., and H. L. Leffert (1983) Proc. Natl. Acad. Sci. U. S. A. 80: 5281–5285) raised against rat renal (Na+ + K+)-ATPase were compared. The interspecies cross-reactivity of the polyclonal anti- rat antibodies was examined by determining their binding to purified rat, eel, or dog enzyme. The immunostaining characteristics of the IgG fraction of the polyclonal antibody preparations, their affinity- purified derivatives, and the monoclonal antibodies were compared. The results obtained with each of these were similar, providing information about where focal concentrations of the enzyme exist within nervous tissue. The IgG fraction of the polyclonal antibody preparations provided the most sensitive probe, facilitating localization of the (Na+ + K+)-ATPase in the tissue sections from various regions of the nervous system. (Na+ + K+)-ATPase-like immunoreactivity was observed along the plasmalemma of alpha-motor neurons and at the nodal axolemma of myelinated axons from the central or peripheral nervous system. It was determined that the absence of labeling for the enzyme along the paranodal or internodal regions of the axolemma was not an artifact due to a limited accessibility of antibody to these regions. Some central nervous system glial cells demonstrated abundant amounts of plasmalemmal and intracellular (Na+ + K+)-ATPase-like immunoreactivity. These cells were identified as astroglia by positive labeling of cells in serial sections for glial fibrillary acid protein immunoreactivity in the soma and radial processes in optic nerve, or velous processes in the cerebellum. Astrocyte processes overlying the nodal axolemma also stained positively for the enzyme. (Na+ + K+)-ATPase-like immunoreactivity was not observed in association with oligodendroglia cell bodies or their processes forming myelin sheaths. In contrast, the plasmalemma of myelinating Schwann cells showed greatest immunoreactivity in the region of the node of Ranvier. Although a focal concentration of immunoreactivity was observed along node- and paranode- associated regions of Schwann cells, a lower level of uniform staining was noted along the entire Schwann cell surface membrane.(ABSTRACT TRUNCATED AT 400 WORDS)
Localization of glutaminase-like and aspartate aminotransferase-like immunoreactivity in neurons of cerebral neocortex
Authors: Donoghue JP , Wenthold RJ , Altschuler RA
Published: March 2018

The distribution of glutaminase (GLNase)- and aspartate aminotransferase (AATase)-immunoreactive cells was examined in the cerebral neocortex of rat and guinea pig and in the somatic sensorimotor and primary visual cortex of the Macaca fascicularis monkey. These enzymes are involved in the metabolism of glutamate and aspartate, two amino acids thought to be excitatory amino acid transmitters for cortical neurons. In each of the species examined a large percentage of layer V and VI pyramidal neurons have pronounced glutaminase-like immunoreactivity (GLNase IR). In contrast, neurons in layers I, II, and IV show little GLNase IR. Layer III in the rat and guinea pig contains only a few, densely labeled GLNase-like- immunoreactive (GLNase-Ir) pyramidal neurons, whereas in the monkey the number of GLNase-Ir cells in layer III varies between cytoarchitectonic fields. Area 3b of the primary somatic sensory cortex and area 17 (primary visual cortex) contain few GLNase-Ir cells in layer III. However, layer III contains moderate numbers of GLNase IR in cells in areas 3a, 1, 2, 5, and in the primary motor cortex. Within the motor cortex the largest pyramidal (“Betz”) cells are not labeled. In marked contrast to the results with antibody to GLNase, antibody to AATase labels cells that appear nonpyramidal in form, and these cells are in all cortical layers in each of the species examined. This distribution is roughly similar throughout all areas of rodent neocortex, but in monkey visual cortex AATase-immunoreactive neurons are more numerous in layers II-III, IVc, and VI. When combined with the findings of other studies, our results suggest that GLNase IR marks pyramidal neurons that use an excitatory amino acid transmitter. Antibody to AATase appears to mark intrinsic cortical neurons. The AATase immunoreactivity of these cells could indicate that they use an excitatory amino acid transmitter. However, their form and distribution in cortex suggest that this antibody labels GABAergic neurons.
Subcellular distribution of calcium- and calmodulin-dependent myosin light chain phosphorylating activity in rat cerebral cortex
Authors: Edelman AM , Hunter DD , Hendrickson AE , Krebs EG
Published: March 2018

The subcellular distribution of Ca2+- and calmodulin-dependent myosin light chain phosphorylating activity in rat cerebral cortex was studied. The activity showed a high degree of association to nerve endings (either crude or purified by discontinuous sucrose density gradient centrifugation). After osmotic shock of the nerve endings, the activity was largely membrane associated and could not be released from membranes by freeze-thawing, dilution, 75 mM NaCl or 4 mM EDTA. The association of Ca2+/calmodulin-dependent myosin light chain phosphorylating activity with synaptosomal membranes suggests a role for calcium-dependent myosin phosphorylation in events relating to neurotransmission.