bluuebunny/crossref_metadata_2025 huggingface dataset:
Retinal projections and functional architecture of cortical areas 17 and 18 in the tyrosinase-negative albino cat
Authors: Leventhal AG , Creel DJ
Published: March 2018

The visual field representation and functional architecture of cortical areas 17 and 18 in albino cats were studied. In the same animals the distributions of ipsilaterally and contralaterally projecting retinal ganglion cells were determined by injecting horseradish peroxidase into the dorsal lateral geniculate nucleus or optic tract. All cats were tyrosinase-negative albinos (cc), not deaf white cats (W). The proportion of ipsilaterally projecting ganglion cells in the temporal retina of the albino cat was found to be much smaller than in the normal cat or in the Siamese cat. In the albino cat less than 5% of ganglion cells in temporal retina project ipsilaterally. Recordings from areas 17 and 18 provided evidence of a substantial representation of the ipsilateral hemifield in albino visual cortex; cells representing the contralateral and ipsilateral hemifields were often segregated into alternating zones in area 17 and were always segregated in area 18. Cells recorded at the borders of zones representing the ipsilateral and contralateral hemifields often had abnormal properties. Some border cells had two receptive fields separated by as much as 60 degrees of azimuth; one field subserved the contralateral hemifield (contralateral nasal retina) and the other subserved the mirror- symmetric part of ipsilateral hemifield (contralateral temporal retina). Receptive fields of cells subserving the two hemifields did not differ in size. The preferred orientations, preferred velocities, and other characteristics of the two fields were approximately the same; preferred orientation changed gradually and systematically across the borders of zones representing the two hemifields. Our results indicate that afferents representing nasal and temporal regions of retina of the same eye can segregate and form “hemiretina” domains in albino visual cortex. These afferents can also converge upon individual cortical cells in a fashion reminiscent of convergence of afferents from the two eyes upon binocular cells in the normal cortex. The organization of albino visual cortex is therefore different from the organization of Siamese visual cortex. This may be because, in the albino cat but not the Siamese cat, nearly all cells in temporal retina project contralaterally; afferents representing contralateral temporal retina are not at a significant competitive disadvantage in the albino.
Temperature dependence of intrinsic membrane properties and synaptic potentials in hippocampal CA1 neurons in vitro
Authors: Thompson SM , Masukawa LM , Prince DA
Published: March 2018

The temperature dependence of intrinsic membrane conductances and synaptic potentials in guinea pig hippocampal CA1 pyramidal neurons were examined in vitro as they were cooled from 37 degrees C to between 33 and 27 degrees C. Cooling reversibly increased resting input resistance in a voltage-independent manner (Q10 = 0.58 to 0.75). The amplitude and duration of orthodromically evoked action potentials were increased by cooling (Q10 = 0.87 and 0.52 to 0.53, respectively), whereas the maximum rates of rise and fall were reduced (Q10 = 1.27 to 1.49 and 2.19 to 2.44, respectively). The amplitude and duration of the afterhyperpolarization which follows a directly evoked train of action potentials were substantially increased at low temperatures. It is possible to attribute this increase to an augmentation of Ca2+ influx during the train and also to a slowing of Ca2+ removal from the cytoplasm. Spike frequency adaptation during prolonged depolarizing pulses was enhanced at low temperatures. In addition, there was a decrement in spike amplitude during the train of action potentials. These observations all suggest an increase in Ca2+-activated K+ conductance at low temperature. A late, slow, hyperpolarizing synaptic potential in response to orthodromic stimulation became apparent at low temperature. This potential had an apparent reversal potential more negative than the early inhibitory postsynaptic potential, suggesting that it was mediated by a K+ conductance, possibly activated by Ca2+ influx. We conclude that reductions in temperature of as little as 5 to 10 degrees C from normal can significantly alter the intrinsic and synaptic physiology of hippocampal neurons and should, therefore, be considered an important variable in in vitro brain slice experiments.
Calcium channels in rat brain synaptosomes: identification and pharmacological characterization. High affinity blockade by organic Ca2+ channel blockers
Authors: Turner TJ , Goldin SM
Published: March 2018

Rat brain synaptosomes are shown to contain functional voltage- sensitive Ca2+ channels that are inhibited by organic Ca2+ channel blockers. Depolarization of synaptosomes with high K+ stimulates uptake of 45Ca2+ which is biphasic in its time course. Replacement of external Na+ with choline eliminates the slower phase of depolarization- stimulated Ca2+ uptake, leaving only a rapid uptake process which terminates within 1 sec. This rapid, tetrodotoxin-insensitive Ca2+ uptake can be inactivated by prior depolarization of the synaptosomes. Depolarization has no effect on the rate of synatptosomal 22Na+ efflux. These results are interpreted as ruling out Na+/Ca2+ exchange as a mediator of the rapid phase of depolarization-stimulated Ca2+ uptake. A portion (30 to 50%) of the rapid phase of depolarization-stimulated Ca2+ uptake is inhibited by nitrendipine, as is depolarization- stimulated [3H]norepinephrine release from synaptosomes. In external Na+, the inhibition constant (Kapp) for nitrendipine inhibition of Ca2+ uptake is 56 nM. The potency of nitrendipine is increased in the absence of external Na+ (Kapp = 1.7 nM), such that inhibition correlates more closely with the equilibrium dissociation constant for [3H] nitrendipine binding to synaptosomes (Kd = 0.35 nM). Other organic channel blockers (nifedipine, verapamil, D600, and dilitiazem) inhibit the rapid Ca2+ uptake. The potencies of all Ca2+ channel blockers tested by us are in reasonable agreement with their potencies, observed in other laboratories, as blockers of Ca2+ channels in smooth and cardiac muscle. These data demonstrate the existence of active voltage- sensitive Ca2+ channels in synaptosomes.(ABSTRACT TRUNCATED AT 250 WORDS)
The neural circuit for touch sensitivity in Caenorhabditis elegans
Authors: Chalfie M , Sulston JE , White JG , Southgate E , Thomson JN , Brenner S
Published: March 2018

The neural pathways for touch-induced movement in Caenorhabditis elegans contain six touch receptors, five pairs of interneurons, and 69 motor neurons. The synaptic relationships among these cells have been deduced from reconstructions from serial section electron micrographs, and the roles of the cells were assessed by examining the behavior of animals after selective killing of precursors of the cells by laser microsurgery. This analysis revealed that there are two pathways for touch-mediated movement for anterior touch (through the AVD and AVB interneurons) and a single pathway for posterior touch (via the PVC interneurons). The anterior touch circuitry changes in two ways as the animal matures. First, there is the formation of a neural network of touch cells as the three anterior touch cells become coupled by gap junctions. Second, there is the addition of the AVB pathway to the pre- existing AVD pathway. The touch cells also synapse onto many cells that are probably not involved in the generation of movement. Such synapses suggest that stimulation of these receptors may modify a number of behaviors.
Treatment with 6-hydroxydopamine and colchicine decreases nerve growth factor levels in sympathetic ganglia and increases them in the corresponding target tissues
Authors: Korsching S , Thoenen H
Published: March 2018

A two-site enzyme immunoassay was used to determine the nerve growth factor (NGF) contents of sympathetic ganglia and their corresponding target tissues in adult rats. The destruction of sympathetic nerve terminals by 6-hydroxydopamine (6-OHDA) and the blockade of axonal transport by colchicine resulted in a rapid increase in the NGF levels of sympathetically innervated organs and a rapid decrease in the sympathetic ganglia. NGF levels in heart atrium, heart ventricle, submandibular gland, and iris increased 2- to 4-fold 12 hr after injection of 6-OHDA, whereas the NGF contents of stellate and superior cervical ganglia dropped to a minimal level of 3 to 4% of control 24 hr after injection. Twelve hours after treatment with colchicine the NGF levels in sympathetically innervated organs increased 2- to 3-fold, whereas the NGF contents of sympathetic ganglia fell to one-third of control values. The half-lives of NGF in the superior cervical and stellate sympathetic ganglia were 4.5 and 4.8 hr, respectively, as determined by the decrease of NGF content after treatment with 6-OHDA. These results indicate that the synthesis of NGF is normally confined to the innervated target organs with no significant contribution of ganglionic cells. This is consistent with the concept that NGF acts as a retrograde messenger between target organs and innervating sympathetic neurons.
Intracellular acetylcholine receptors in skeletal muscles of the adult rat
Authors: Pestronk A
Published: March 2018

We have examined the localization and numbers of acetylcholine receptors (AChRs) within adult mammalian skeletal muscle using 125I- alpha-bungarotoxin (125I-alpha-BuTx). Intracellular AChRs were exposed to 125I-alpha-BuTx by permeabilizing the muscle membrane with the detergent saponin. Our results show that, in muscles of young adult rats, internal AChRs occur in a number and pattern of distribution similar to that for surface membrane AChRs. Internal AChRs are found only in perijunctional regions of normally innervated muscles, but they appear all along the length of muscle fibers after denervation. A minority of internal AChRs may be newly synthesized AChRs en route to insertion in the surface membrane; however, most internal AChRs appear to be antigentically different from and to behave independently of surface membrane AChRs. With increasing age, internal AChRs decline in number, while surface AChRs remain relatively constant. In older animals, internal AChRs may reappear in muscles that have undergone degeneration and regeneration. We conclude that a significant proportion of AChRs in skeletal muscle may be intracellular. Internal AChRs are a useful marker for young muscle cells. Their distribution may provide information about the intracellular pathways of AChR metabolism.
Eye-specific segregation requires neural activity in three-eyed Rana pipiens
Authors: Reh TA , Constantine-Paton M
Published: March 2018

The addition of a third eye primordium to the forebrain region of a Rana pipiens embryo invariably results in the development of a series of periodic, mutually exclusive eye-specific bands in tectal lobes dually innervated by the host and supernumerary fibers. A number of investigators have proposed that such source-specific segregation arises as a compromise between two mechanisms that are normally involved in retinotectal map formation: one which is dependent on cell surface affinities to align the map and produce a rough retinotopy and a second that “fine tunes” the map by stabilizing adjacent terminals from neighboring retinal ganglion cell bodies at the expense of terminals from non-neighboring cells. In this study we have tested the idea that this second “fine-tuning” mechanism is dependent on neural activity by blocking impulse activity in the optic nerves of three-eyed tadpoles. To assess the requirement for activity on the formation of bands, both normal optic nerves of 17 three-eyed tadpoles were crushed intraorbitally. Two weeks after this operation, the supernumerary retinal projection had debanded and spread to cover the entire tectum in a continuous fashion. By 4 weeks, however, the host optic fibers regenerated back to the tecta and began to form segregated stripes with the fibers from the third eye. Six to 7 weeks after the optic nerve crush the periodic pattern of eye-specific segregation characteristic of dually innervated tecta was again pronounced. When activity in all three optic nerves was eliminated with tetrodotoxin (TTX; embedded in a slow release plastic) during the last 3 weeks of this process, the fibers from the two competing eyes failed to segregate and, instead, formed two completely overlapping, continuous projections across the tectal surface. To test for the requirement of activity in the maintenance of segregation, we also subjected three-eyed tadpoles without optic nerve crush to TTX blockade for 2, 3, and 4 weeks. Animals sacrificed at 2 weeks show overlap of the projections in the rostral tectum but distinct interdigitating stripes in other regions of these lobes. After 3 weeks of blockade, segregation of the projections was less distinct in the central tectum as well. After 4 weeks of TTX blockade the terminals from both eyes spread to form continuous overlapping projections throughout the tectum. Examination of well isolated, individual retinal ganglion cell terminal arbors during this period reveals that they occupy a significantly greater area of tectum following the TTX treatment.
Genetic modifications of voltage-sensitive sodium channels in Drosophila: gene dosage studies of the seizure locus
Authors: Jackson FR , Gitschier J , Strichartz GR , Hall LM
Published: March 2018

We have identified a genetic locus in Drosophila melanogaster whose product appears to have a structural role in the formation of functional voltage-sensitive sodium channels. This locus, designated seizure, is defined by two temperature-sensitive alleles (seits-1 and seits-2), each of which causes convulsive seizures followed by a rapid but reversible paralysis of adults at restrictive temperatures above 38 degrees C. Previous work had shown that seits-2 extracts display an altered pH dependence and an abnormally high Kd for [3H]-saxitoxin binding at high temperatures, suggesting that sodium channels in seits- 2 mutants have an altered structure (Jackson F. R., S. D. Wilson, G. R. Strichartz, and L. M. Hall (1984) Nature 308: 189–191). These binding studies have now been extended to extracts of seits-1 which have a Kd not significantly different from wild-type at all assay temperatures. However, seits-1 extracts show a reduced number of saxitoxin binding sites (Bmax) relative to wild-type. This reduction is only 5 to 18% at 0 degree C but is 17 to 37% at 39 degrees C, suggesting that under certain conditions sodium channels in the seits-1 mutant are more labile than those of wild-type. Cytogenetic studies demonstrate that the seizure locus maps within region 60A to 60B8–10 on the second chromosome. Gene dosage analysis of approximately 99.7% of the genome, including this second chromosome region, failed to detect a wild-type locus whose dose affected saxitoxin-binding activity. Nevertheless, the mutant seits-2 allele has codominant and dose-dependent effects on paralytic behavior and saxitoxin-binding activity.
Stimulation of denervated rat soleus muscle with fast and slow activity patterns induces different expression of acetylcholinesterase molecular forms
Authors: Lomo T , Massoulie J , Vigny M
Published: March 2018

The relative amount and distribution of acetylcholinesterase (AChE) molecular forms were studied in slow soleus and (less extensively) in fast extensor digitorum longus (EDL) muscles of the rat before and after denervation and direct stimulation. Normal EDL muscles showed higher total and specific AChE activity than normal soleus muscles and contained essentially three different molecular AChE forms (G1, G4, and A12) as opposed to six forms (G1, G2, G4, A4, A8, and A12) in the soleus. Denervation reduced AChE activity in both muscles. In the soleus direct stimulation starting 2 to 3 weeks after denervation increased the specific AChE activity markedly. The increase started 12 to 24 hr after the onset of stimulation, reached 3 to 5 times normal values after 2 to 7 days, and then declined gradually toward normal values over the next 2 weeks. Furthermore, the effect on the different molecular forms depended strongly on the stimulus pattern. Thus, intermittent 100 Hz stimulation (fast pattern) induced essentially the three forms typical of the normal EDL, whereas continuous 10 Hz stimulation induced the six forms characteristic of normal soleus muscles but with some differences in their relative proportions. In the EDL, 2 days of continuous 10 Hz stimulation (the only duration and pattern examined) failed to induce a similar increase in AChE activity.
Ultrastructural correlates of transmitter release in presynaptic areas of lamprey reticulospinal axons
Authors: Wickelgren WO , Leonard JP , Grimes MJ , Clark RD
Published: March 2018

The ultrastructure of presynaptic areas of lamprey reticulospinal axons was studied before, during, and after periods of elevated transmitter release produced either by repetitive action potential activity or depolarization by elevated extracellular potassium. Controls for possible effects of these procedures per se were done by replacing extracellular Ca with Mg to block transmitter release. In some experiments the time course of ultrastructural changes during K depolarization and subsequent recovery were studied by fixing tissue samples at various times. Transmitter release produced by action potential activity (20/sec for 15 min) in the presence of extracellular Ca significantly and reversibly decreased the number of synaptic vesicles, the area occupied by the vesicles, and the density of synaptic vesicles. An unexpected finding was a reversible decrease in the length of the differentiated membrane during periods of increased transmitter release. Transmitter release significantly and reversibly increased the number of coated vesicles, expanded the presynaptic membrane, and increased the number of pleomorphic vesicles. K depolarization (50 mM K for 15 min) produced identical, reversible effects, except that the expansion of the presynaptic membrane, although significant, was relatively small and there was no change in the number of pleomorphic vesicles. Raising the temperature of the saline from 2 degrees C (K depolarization experiments) or 7 degrees C (action potential experiments) to 20 degrees C did not change the results qualitatively but did produce somewhat larger effects during stimulation and appeared to increase the speed of recovery. Action potential activity or K depolarization in control experiments with the Ca in the saline replaced by Mg had little or no effect on synaptic ultrastructure. Synaptic vesicles in lamprey reticulospinal axons never contacted the axonal membrane anywhere other than at the differentiated membrane. During periods of elevated transmitter release, although the absolute number of vesicles in contact with the differentiated membrane decreased, the percentage of total vesicles in contact with the differentiated membrane increased dramatically. This suggests that the differentiated membrane is the site of vesicle release and there is an active process of vesicle movement to this membrane. In the course of this work it was observed that presynaptic areas closer than approximately 2 mm to the site of axonal transection, regardless of the composition of the saline or the experimental conditions, showed ultrastructural changes typical of increased transmitter release.
Characterization and segmental distribution of 125I-Bolton-Hunter- labeled substance P binding sites in rat spinal cord
Authors: Charlton CG , Helke CJ
Published: March 2018

Substance P (SP) is widely distributed in the spinal cord and has been implicated as a neurotransmitter in several spinal cord neuronal systems. To investigate SP receptors in the spinal cord, 125I-Bolton- Hunter-SP (125I-BH-SP) was used to identify and characterize spinal cord binding sites for the peptide. The binding of 125I-BH-SP had the following characteristics: high affinity; time, temperature, and membrane concentration dependent; reversible; and saturable. The IC50 of SP in whole spinal cord was 0.46 nM as compared with 0.95, 60, and 150 nM for physalaemin, eledoisin, and kassinin. Four putative antagonists of SP were less than 0.0001 times as potent as SP in inhibiting 125I-BH-SP binding. IC50s were 5, 7.5, 7.0, and 45 microM for D-Pro2, D-Trp7,9-SP; D-Pro2, D-Phe7, D-Trp9-SP; D-Arg1, D-Pro2, D- Trp7,9, Leu11-SP; and D-Pro4, D-Trp7,9,10-SP(4–11), respectively. The lumbosacral section bound 3 times more SP than the cervical and thoracic sections, although IC50 for the cervical section was 0.06 of that for the lumbosacral and thoracic sections. The data suggest more than one class of binding site for SP in the spinal cord and indicate a direct role for SP in spinal cord functions.
Noradrenergic modulation of sensorimotor processes in intact rats: the masseteric reflex as a model system
Authors: Morilak DA , Jacobs BL
Published: March 2018

The masseteric jaw closure reflex was utilized as a model system with which to gauge the functional activity of central noradrenergic neurons. This system was chosen because it is a simple monosynaptic reflex the neuronal substrate of which receives a dense noradrenergic input. The modulatory effects of norepinephrine (NE) on this response in the intact, chloral hydrate-anesthetized rat were studied with a variety of pharmacological strategies. Initially, a reflex facilitation was obtained with the catecholamine precursor L-DOPA. Manipulations with greater specificity of action on the noradrenergic system were then employed. First, we used the presynaptic alpha-2 noradrenergic agonist clonidine, which acts to decrease noradrenergic transmission. Clonidine attenuated the amplitude of the reflex, and this suppression was blocked by pretreatment with the alpha-2 antagonist yohimbine. The effects of yohimbine itself were then examined, and a biphasic effect was obtained. At low doses, at which it preferentially acts as an antagonist at presynaptic alpha-2 receptors and increases noradrenergic transmission, yohimbine enhanced the reflex. At higher doses, at which it also displays postsynaptic alpha-1 antagonist activity, yohimbine depressed the reflex. This reflex modulation by yohimbine was blocked by pretreatment with the alpha-1 antagonist prazosin. The anatomical site of the observed effect was then localized to the direct noradrenergic innervation of the reflex circuitry by locally destroying, with 6-hydroxydopamine, the noradrenergic terminals in the trigeminal motor nucleus mediating the response. This significantly attenuated the reflex modulation by yohimbine, without affecting elicitation of the reflex itself.
Nicotinic binding in rat brain: autoradiographic comparison of [3H]acetylcholine, [3H]nicotine, and [125I]-alpha-bungarotoxin
Authors: Clarke PB , Schwartz RD , Paul SM , Pert CB , Pert A
Published: March 2018

Three radioligands have been commonly used to label putative nicotinic cholinoceptors in the mammalian central nervous system: the agonists [3H]nicotine and [3H]acetylcholine ([3H]ACh--in the presence of atropine to block muscarinic receptors), and the snake venom extract, [125I]-alpha-bungarotoxin([125I]BTX), which acts as a nicotinic antagonist at the neuromuscular junction. Binding studies employing brain homogenates indicate that the regional distributions of both [3H]nicotine and [3H]ACh differ from that of [125I]BTX. The possible relationship between brain sites bound by [3H]nicotine and [3H]ACh has not been examined directly. We have used the technique of autoradiography to produce detailed maps of [3H]nicotine, [3H]ACh, and [125I]BTX labeling; near-adjacent tissue sections were compared at many levels of the rat brain. The maps of high affinity agonist labeling are strikingly concordant, with highest densities in the interpeduncular nucleus, most thalamic nuclei, superior colliculus, medial habenula, presubiculum, cerebral cortex (layers I and III/IV), and the substantia nigra pars compacta/ventral tegmental area. The pattern of [125I]BTX binding is strikingly different, the only notable overlap with agonist binding being the cerebral cortex (layer I) and superior colliculus. [125I]BTX binding is also dense in the inferior colliculus, cerebral cortex (layer VI), hypothalamus, and hippocampus, but is virtually absent in thalamus. Various lines of evidence suggest that the high affinity agonist-binding sites in brain correspond to nicotinic cholinergic receptors similar to those found at autonomic ganglia; BTX- binding sites may also serve as receptors for nicotine and are possibly related to neuromuscular nicotinic cholinoceptors.
Morphological and functional types of neurons in cat ventral posterior thalamic nucleus
Authors: Yen CT , Conley M , Jones EG
Published: March 2018

Neurons in the thalamic ventral posterior (VB) nucleus of the cat were investigated by extracellular and intracellular recording and by anatomical methods involving either the retrograde transport of horseradish peroxidase (HRP) or the intracellular injection of HRP. Two morphological types of neurons could be detected by retrograde labeling from small injections of HRP in the internal capsule adjacent to VB. These two and one other type, judged to be an interneuron, could also be identified by intracellular staining. Type I cells are large, have thick proximal dendrites which branch in a tuft-like manner, and thick, rapidly conducting axons. They possess few or no dendritic appendages. Type II cells are smaller and have slender proximal dendrites which branch dichotomously and thin, slower conducting axons. Those injected intracellularly are covered in fine, hair-like dendritic appendages. Type III cells are small and have thin processes that give rise to many bulbous dilatations and no obvious axon. Type I and type II cells give off slender axon collaterals in the thalamic reticular nucleus but not in VB. Examples of both types of cell could be antidromically activated from the somatic sensory cortex. Type I and type II cells recovered histologically after intracellular recording included examples of most types of receptive field, including several forms of cutaneous and deep fields, as classified by us in a parallel intra- and extracellular study of unit responses. All but one type I cell, however, responded in a transient manner to peripheral stimulation. The remaining type I cell and all members of an admittedly small sample of type II cells responded in a sustained manner. The sample of recovered interneurons and of units that could not be driven antidromically from the cerebral cortex suggested that they, too, included all receptive field types. We conclude that submodality specificity in VB is not represented by morphological specificity in thalamocortical relay cells or interneurons. Some other functional parameter, such as tonic or phasic responsiveness, may be more obviously correlated with relay cell morphology.
Nerve growth cones isolated from fetal rat brain. II. Cyclic adenosine 3':5'-monophosphate (cAMP)-binding proteins and cAMP-dependent protein phosphorylation
Authors: Ellis L , Katz F , Pfenninger KH
Published: March 2018

Cyclic adenosine 3′:5′-monophosphate (cAMP)-binding proteins and cAMP- dependent protein phosphorylation were examined in growth cone particles (GCPs) prepared from fetal rat brain. Several major proteins which specifically bind a photoactivatable analogue of cAMP are observed in GCPs and correspond to isoelectric variants of the regulatory subunits of the cAMP-dependent protein kinase described in adult brain. We found no evidence for differential compartmentalization of specific cAMP-binding proteins in subcellular fractions of fetal brain or within GCPs. cAMP-stimulated phosphoproteins of GCPs are similar to cAMP-dependent protein kinase substrates characterized in nerve terminals (synaptosomes) of adult brain and include the nerve terminal-specific protein, synapsin I. However, as shown in the companion paper (Katz, F., L. Ellis, and K. H. Pfenninger (1985) J. Neurosci. 5: 1402–1411), this synaptic phosphoprotein is not the major kinase substrate in the GCP fraction. The finding of synapsin I in a subcellular fraction prepared from fetal brain suggests that components of the mature nerve terminal are already present in fetal brain during neuronal sprouting and prior to synaptogenesis.
Changes from enkephalin-like to gastrin/cholecystokinin-like immunoreactivity in snail neurons
Authors: Gesser BP , Larsson LI
Published: March 2018

Coexistence of regulatory peptides is reported with increasing frequency in the mammalian neuroendocrine system. We have investigated the possible presence of such coexistence in the invertebrate Lymnaea stagnalis and have found evidence for concurrence of enkephalin- and gastrin/cholecystokinin (CCK)-like peptides in identified neurosecretory neurons. Our immunocytochemical studies reveal, however, that some of these neurons show variations in their content of immunoreactive peptides depending upon season or age. Thus, the light green cells of the Lymnaea cerebral ganglion, known to produce a body growth-stimulating hormone, contain enkephalin-like immunoreactivity during spring and gastrin/CCK-like immunoreactivity during fall. During winter, these cells contain both enkephalin-like and gastrin/CCK-like immunoreactivities. In another group of neurosecretory neurons, the caudodorsal cells, known to produce an ovulation hormone, age-dependent changes were noted. Thus, in young animals, these cells contain enkephalin-like immunoreactivity; in animals of intermediate age, they contain both enkephalin- and gastrin/CCK-like immunoreactivity and, in older animals, only gastrin/CCK-like immunoreactivity can be detected in these cells. Interestingly, the mediodorsal bodies, which are endocrine organs also implicated in regulating sexual function of Lymnaea, show age-dependent variations in immunocytochemically detectable enkephalin- and gastrin/CCK-like immunoreactivity which parallels that found in the caudodorsal cells. The changes noted in the light green cells and the caudodorsal cells are detected both in the cell bodies and in the terminals of these cells, suggesting that the immunoreactivity represents secretory material. The relation, if any, between the immunoreactivities detected and the growth and reproduction of Lymnaea remains to be established, as do the factors responsible for the observed age- and season-dependent variations.
Conjugate and disjunctive saccades in two avian species with contrasting oculomotor strategies
Authors: Wallman J , Pettigrew JD
Published: March 2018

We have recorded with the magnetic search coil method the spontaneous saccades of two species of predatory birds, which differ in the relative importance of panoramic and foveal vision. The little eagle (Haliaetus morphnoides) hunts from great heights and has no predators, whereas the tawny frogmouth (Podargus strigoides) hunts from perches near the ground, is preyed upon, and frequently adopts an immobile camouflage posture. We find that both birds spend most of the time with their eyes confined to a small region of gaze, the primary position of gaze; in this position, the visual axes are much more diverged in the frogmouth than in the eagle, thereby giving it a larger total field of view at the expense of its binocular field. Both species, however, can align their visual axes, thereby gaining a binocular view of targets in the frontal visual field. The eagle makes saccades 10 times as frequently as the frogmouth, and in most of its saccades the eyes move in the same direction, although the eye movements are generally not conjugate; in most frogmouth saccades, on the other hand, the eyes move in opposite directions. We discuss these phenomena in terms of their saccadic mechanisms and their possible adaptiveness. We also report two incidental observations: in certain circumstances, the frogmouth shows no sign of having a vestibulo-ocular reflex, and the eagle, although the quintessential foveate animal, shows extreme directional asymmetries of monocularly evoked optokinetic nystagmus.
Dipeptides of glutamate and aspartate may be endogenous neuroexcitants in the rat hippocampal slice
Authors: Bernstein J , Fisher RS , Zaczek R , Coyle J
Published: March 2018

The dipeptide N-acetylaspartylglutamate (NAAG), and possibly the related dipeptide aspartylglutamate (AG), have been found in high concentrations in rat brain, and have been shown to bind avidly and selectively to a subset of glutamate (GLUT) receptors. Certain observations regarding GLUT and aspartate might be explained if the endogenous transmitter were a compound composed of both amino acids. We therefore examined the electrophysiological actions of NAAG and AG in the rat in vitro rat hippocampal slice model. NAAG or AG and GLUT were applied locally to cells by a dual-barrel pressure technique. Intracellular recordings from 34 CA1 pyramidal neurons showed depolarizations and conductance increases resembling evoked excitatory postsynaptic potential in 15 of 20 cells exposed to NAAG, and 14 of 14 exposed to AG. Many GLUT-responsive sites did not respond to AG, and most did not respond to NAAG. Responses to NAAG were usually too small to induce cell firing; they were best detected, therefore, by intracellular recording. With extracellular unit recordings, GLUT was equally excitatory in stratum radiatum and pyramidale of CA1 (N = 19; p greater than 0.10, one-way analysis of variance). In contrast, AG was considerably more potent (N = 21; p less than 0.01) in stratum radiatum. NAAG was not noted to excite cells when applied to stratum pyramidale. The region of maximal responsiveness to AG in CA1 coincided with the area of the dendritic tree receiving Schaffer collateral- commissural afferents. This spatial profile, together with other neuropharmacological evidence, support the candidacy of glutamate- containing peptides as endogenous excitatory compounds in certain pathways of hippocampus.
Development and subsequent neural tube effects on the excitability of cultured Xenopus myocytes
Authors: DeCino P , Kidokoro Y
Published: March 2018

We examined both the development of electrical excitability in cultured Xenopus muscle over a period of 7 days, and the effects of neural tube on the muscle action potential. During muscle development, delayed and anomalous rectification were present in most cases within 24 hr. The action potential was dependent on Na at all times examined, and the rate of rise of the action potential (Vmax) increased substantially (seven-fold) from the first 2 days to 6 to 7 days in vitro, reflecting an increase in Na current density. In order to determine the mechanism for the increase in Vmax, we examined single-channel Na currents using the gigaseal technique. Single-channel conductance (gamma) did not increase substantially when measured using the patch clamp technique: gamma = 24 pS at 1 to 2 days, and gamma = 28 pS at 4 to 6 days. The channel open time at 14 degrees C was 0.6 msec for 1- to 2-day-old cells and 0.5 msec in 4- to 6-day-old cells at a step potential 40 mV from rest. The time constant for current decay as well as the time-to- peak current also did not change over time. Thus, channel kinetics appear unchanged. The maximum inward current from summed records was statistically greater for older cells, and the frequency of patches displaying single-channel events increased from 75 to 98%. Thus, we conclude that during development in vitro, Na current density increases as a result of an increase in channel density without detectable alterations in single-channel properties. Neural tube addition led to a further increase in Vmax (two-fold), even in muscle cells with no apparent nerve contact. Single channel analysis of cells in coculture revealed gamma to be 28 pS in three cells displaying a single amplitude peak for individual Na currents. In the majority of cases (9/12), however, there appeared to be two classes of Na channels present which were difficult to separate. The larger conductance channel likely corresponds to the 28 pS class. The smaller channels, when present, did not contribute substantially to the population of events comprising the amplitude histogram. Other single-channel kinetic parameters also did not change. We, therefore, conclude that neural tube addition does not effect activation or inactivation kinetics but likely causes a further increase in channel density and possibly the induction of a second type of Na channel.
Cyclic adenosine 3':5'-monophosphate and cytosolic calcium exert opposing effects on biosynthesis of tetrodotoxin-sensitive sodium channels in rat muscle cells
Authors: Sherman SJ , Chrivia J , Catterall WA
Published: March 2018

We have previously presented evidence that electrical activity and increased cytosolic calcium reduce the density of sarcolemmal tetrodotoxin (TTX)-sensitive sodium channels in cultured rat muscle cells (Sherman, S. J., and W. A. Catterall (1984) Proc. Natl. Acad. Sci. U. S. A. 81: 262–266). We show here that growth of cells in ryanodine has a biphasic effect on sodium channel number. At low concentrations (0.3 to 10 microM) where this drug releases calcium from the sarcoplasmic reticulum into the cytoplasm, sodium channel number is reduced 62%; whereas, at higher concentrations where total cellular calcium is depleted, the density of sodium channels is increased 40% above control. These results provide further evidence for modulation of sodium channel number by cytosolic calcium. Growth of muscle cells in the presence of agents that mimic cyclic AMP (cAMP) action or increase intracellular cAMP levels including 8-bromo-cyclic AMP (8-BrcAMP), cyclic nucleotide phosphodiesterase inhibitors, and forskolin increased sodium channel density up to 125%. This action did not involve changes in spontaneous electrical activity. Dibutyryl cGMP had no effect. Measurement of the turnover rate of sodium channels after block of channel accumulation by tunicamycin (1.5 micrograms/ml) gave a half- time of 18 hr for exponential decay of TTX-sensitive sodium channels in cultured rat muscle cells after an initial 6-hr lag period. Treatments which modulate sodium channel number through changes in cytosolic calcium or cAMP had no effect on the rate of channel turnover. The increase of sodium channel number after inhibiton of electrical activity or treatment with 8-BrcAMP was half-maximal at 17 hr, consistent with an increase in the rate of sodium channel biosynthesis and/or incorporation into the sarcolemma without a change in channel turnover time. We conclude that cytosolic calcium decreases and cAMP increases sodium channel number by modulating the rate of biosynthesis and/or processing of channel components. The biochemical mechanisms of these regulatory effects are considered.
Injured neurons in the olfactory bulb of the adult rat grow axons along grafts of peripheral nerve
Authors: Friedman B , Aguayo AJ
Published: March 2018

Certain neurons in the central nervous system (CNS) of adult mammals extend axons for several cm along peripheral nerve grafts inserted into the brain or spinal cord. It is not clear, however, if these nerve cells constitute a special population or are examples of a general capacity of the injured mammalian CNS to regrow processes under these experimental conditions. Furthermore, because the new axons could originate by collateral sprouting from uninjured neurons, it is important to prove that the interruption of a central axonal projection can be followed by extensive fiber regrowth from the damaged neurons. In this anatomical study, we examined whether: (1) nerve cell type; and (2) axotomy, influence CNS axon regrowth along peripheral nerve grafts. For this purpose, we grafted segments of sciatic nerve into the olfactory bulb (OB) of adult rats and used combinations of neuroanatomical tracers (horseradish peroxidase and the fluorescent dyes True Blue and Nuclear Yellow) to investigate axonal regrowth from the different neurons that normally populate the OB. We demonstrate that OB axons extending along peripheral nerve grafts originate from mitral and tufted cells near the graft tip, rather than from the smaller OB neurons (periglomerular, short axon, and granule cells). Most of the mitral and tufted cells that extend new axons in grafted peripheral nerve segments lose their normal projections through the lateral olfactory tract because of axotomy at the time of grafting. Neuronal type, damage, and proximity to the graft appear to be prerequisites of this regenerative response from the OB.
Selective damage to large cells in the cat retinogeniculate pathway by 2,5-hexanedione
Authors: Pasternak T , Flood DG , Eskin TA , Merigan WH
Published: March 2018

The neurotoxic hexacarbon 2,5-hexanedione (2,5-HD), which produces transport abnormalities and swellings in the large diameter fibers of the peripheral nervous system, was administered to cats in an attempt to produce similar selective effects in the optic tract. Anatomical findings indicate damage to one type of retinal ganglion cell, the large (alpha) or Y-cell class, both during dosing and after a long recovery period. This selective involvement of the large ganglion cells during dosing was shown by decreased retrograde transport of HRP in these cells relative to smaller cells. Such selectivity was not apparent in axonal swellings and neurofilament accumulations which were present in fibers of all diameters in the distal optic tract. Visual threshold studies during dosing showed a loss of flicker resolution with preservation of visual acuity, a result consistent with the different physiological properties of alpha and beta ganglion cells. In one cat, which survived dosing for a period of 8 months, there was a dramatic reduction in the number of large cells and a pronounced shrinkage of those that remained, but no observed changes in other cell types. Thus, this intoxication caused (1) axonal swellings which were not selective for fiber size; (2) a selective defect in axonal transport with later neuronal degeneration and shrinkage that were limited to large cells; and (3) a loss of flicker resolution that may reflect dysfunction of large ganglion cells.
Insulin promotes electrical coupling between cultured sympathetic neurons
Authors: Wolinsky EJ , Patterson PH , Willard AL
Published: March 2018

Placing neurons in tissue culture is one way to study how environmental factors affect their differentiation. Replacement of serum- supplementation of the culture medium with defined ingredients extends the experimenter's control of the culture environment; however it also introduces additional potential influences. In this report, we confirm the observation of Higgins and Burton (Higgins, D., and H. Burton (1982) Neuroscience 7:2241–2253) of increased frequency of electrical coupling in serum-free compared to serum-supplemented cultures of rat sympathetic neurons. In addition, experiments were performed to determine whether this effect results from the removal of serum or from the addition of the defined medium components to the culture environment. The results of testing individual ingredients of the defined medium recipe adapted for use on sympathetic neurons (Bottenstein, J.E., and G. H. Sato (1979) Proc. Natl. Acad. Sci. U. S. A. 76:514–517) show that insulin is capable of inducing electrical coupling in serum-free cultures. Thus, the formation of electrical synapses by sympathetic neurons can be hormonally regulated.
Fast and slow nerve growth factor binding sites in human neuroblastoma and rat pheochromocytoma cell lines: relationship of sites to each other and to neurite formation
Authors: Sonnenfeld KH , Ishii DN
Published: March 2018

We studied (a) the distribution and properties of fast and slow 125I- nerve growth factor (125I-NGF) binding sites in cultured human neuroblastoma (NB) cell lines that were categorized as responsive (N+) or unresponsive (N-) to NGF by neurite outgrowth, (b) whether fast or slow sites mediate actions of NGF, and (c) whether NGF-mediated conversion of fast to slow sites occurs in human NB and pheochromocytoma PC 12 cells. In human NB SH-SY5Y cells, the slow sites were trypsin resistant and binding was of high affinity. Loss of binding to the slow sites had a half-time of 25 to 30 min at 37 degrees C and was very slow at 4 degrees C. In contrast, the fast sites were trypsin sensitive and binding was of lower affinity; its dissociation half-time was less than 1 min at 4 degrees C and 37 degrees C. The association rate constants of both sites were about 0.8 to 1.2 X 10(7) M-1 sec-1. Some human NB cells had both fast and slow sites. The N+ human NB lines SH-SY5Y and LA-N-5 had only slow sites. Despite the virtual elimination of fast sites by trypsin in NB MC-IXC cells, remaining slow sites could still efficiently bind 125I-NGF. These observations showed that fast sites are not required for slow site binding, neurite outgrowth, or other demonstrated actions of NGF in some NB cells. In PC 12 cells, 125I-NGF initially bound to fast sites was not directly transferred to slow sites as required for NGF-mediated conversion. The association rate constants of fast and slow sites in PC12 cells were both about 2 X 10(7) M-1 sec-1. The association kinetics were consistent with simple bimolecular reactions in both NB and PC12 cells. The combined evidence in NB and PC12 cells did not support the hypothesis of NGF-mediated conversion of fast to slow sites.
Peripheral nerves in shiverer----dystrophic mouse chimeras: evidence that a non-Schwann cell component is required for axon ensheathment in vivo
Authors: Peterson AC
Published: March 2018

Peripheral nerves in dystrophic mice express multiple axon ensheathment abnormalities. If an intrinsic deficiency expressed within the Schwann cells themselves were to account for this neuropathy, then such cells, existing in a chimera preparation, would be expected to express the same ensheathment abnormalities, whereas a coexisting population of non- dystrophic Schwann cells should not be similarly affected. The genotype of myelinated Schwann cells in shiverer----dystrophic chimera was established with immunocytochemical techniques. Shiverer myelin lacks the P1 component of myelin basic protein (MBP), whereas dystrophic myelin appears to contain normal levels of MBP. No correlation between the ensheathment characteristics of the chimera spinal roots and the genotype of the local Schwann cell population was found; both dystrophic Schwann cell populations expressing normalized ensheathment characteristics and shiverer Schwann cells failing to respond to the local presence of naked axons were observed. These results require that a defective extra Schwann cell component is involved in the pathogenesis of the dystrophic neuropathy. Moreover, the normal realization of that component appears to be a necessary prerequisite for shiverer Schwann cells to achieve full ensheathment competence. Although a definitive identification of the cell type(s) that expresses the dy gene locus has not been achieved in this chimera preparation, the observations are consistent with defective endoneurial fibroblast function.