bluuebunny/crossref_metadata_2025 huggingface dataset:
Myelin formation in rotation-mediated aggregating cell cultures: immunocytochemical, electron microscopic, and biochemical observations
Authors: Trapp BD , Webster HD , Johnson D , Quarles RH , Cohen SR , Murray MR
Published: March 2018

Myelination was studied in aggregating cell cultures derived from mechanically 15- to 16-day fetal rat brains. Myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) were localized immunocytochemically in 20-micrometers-thick Vibratome and 1-micrometer- thick Epon sections at 15, 20, 25, and 30 days in vitro. The occurrence of these proteins was correlated with the ultrastructural appearance of oligodendrocytes and myelin sheaths and with biochemical levels of MBP, MAG, and the myelin-related enzyme, 2′,3′-cyclic nucleotide 3′- phosphodiesterase (CNP). MBP appeared in ultrastructurally immature oligodendrocyte cytoplasm at 15 days in vitro. As oligodendrocytes developed a more differentiated fine structure, MBP and MAG antisera stained oligodendrocyte processes and myelin sheaths. Immunostaining in Vibratome sections demonstrated that MBP was detectable in oligodendrocytes and myelin prior to MAG. At 25 days in vitro, all Vibratome sections contained MBP- and MAG-stained oligodendrocytes and myelin sheaths. Radioimmunoassays for MBP and MAG and enzyme assays for CNP in whole homogenates of the aggregates revealed that each of these components increased with the progression of myelination. However, MBP only reached 8% of the level in adult rat brain, while MAG and CNP increased to more than half of the adult level. The protein composition of myelin purified from 30-day aggregates resembled that of myelin purified from immature rat brain.
Conditioned medium increases the rate of neurite elongation: separation of this activity from the substratum-bound inducer of neurite outgrowth
Authors: Collins F , Dawson A
Published: March 2018

Heart cell-conditioned medium supports extensive neurite outgrowth from dissociated parasympathetic neurons of the chicken embryo ciliary ganglion. We have shown previously that neurite outgrowth in this system depends on the deposition of a substratum-conditioning factor from conditioned medium onto the polyornithine culture substratum. However, in the presence of only the substratum-bound material, neurite outgrowth is never as extensive as in whole conditioned medium. The present report demonstrates that a different and soluble component of conditioned medium is required to achieve the rates of neurite elongation normally observed in whole conditioned medium. This second component, while unable by itself to support neurite outgrowth, is able to increase the rate of neurite elongation approximately 3-fold within 30 to 60 min of its addition. This conclusion is based on direct time- lapse observations of the rate of elongation of individual neurites before and after the addition of fractions of conditioned medium previously depleted of the substratum-conditioning factor. Correlated with the effect of such fractions of conditioned medium on the rate of neurite elongation is a change in the morphology of the growth cones, which become larger and more spread. The activity of the soluble, elongation-promoting component of conditioned medium is nondialyzable and is sensitive to treatments known to affect proteins, such as repeated freeze-thawing, heating, and trypsinization. Fractions of conditioned medium which contain the elongation-promoting activity also contain all of the survival factor for parasympathetic neurons previously shown to be present in heart cell-conditioned medium. The methods described here represent a convenient new assay which we have used recently to demonstrate elongation-promoting factors with neuronal specificity in extracts of rat hippocampus.
Electrical development in spinal cord cell culture
Authors: Jackson MB , Lecar H , Brenneman DE , Fitzgerald S , Nelson PG
Published: March 2018

Parallel electrophysiological and neurochemical studies of development are reported for mouse spinal cord cell cultures. The time course of electrical activity and the stage-dependent effects of tetrodotoxin on levels of the neuronal enzyme choline acetyltransferase were compared to establish the presence of spontaneous electrical activity at a time when tetrodotoxin adversely affects development. The extracellular patch electrode makes it possible to examine the ongoing electrical activity of the small cells present in young cultures. A rapid increase in spontaneous electrical activity during the first 2 weeks in culture was found to correlate closely with the onset of tetrodotoxin-induced depression of choline acetyltransferase activity, supporting the idea that ongoing electrical activity plays a role in neuronal development. The development of inhibitory synaptic activity occurs gradually throughout the period of culture, whereas excitatory synaptic activity and action potentials develop in unison, reaching maximal levels during the 2nd week in culture. For all cultures tested, ranging in age from 9 to 45 days old, acute bath application of gamma-aminobutyric acid (GABA) abolished spontaneous electrical activity. Glycine is relatively ineffective in abolishing spontaneous activity in young cultures which have few inhibitory postsynaptic potentials (IPSPs), but glycine becomes as effective as GABA at a later stage of development. This suggests rather different timetables of development for GABA and glycine receptors, with glycine receptors developing in parallel with IPSPs.
Involvement of lateral habenula-dorsal raphe neurons in the differential regulation of striatal and nigral serotonergic transmission cats
Authors: Reisine TD , Soubrie P , Artaud F , Glowinski J
Published: March 2018

The importance of the lateral habenula-dorsal raphe pathway in the control of in vivo [3H]serotonin release in the cat basal ganglia was examined using the push-pull cannula technique and an isotopic method for the estimation of [3H]serotonin continuously formed from [3H]tryptophan. [3H]Serotonin was measured in both caudate nuclei and substantiae nigra and, in some cases, in the dorsal raphe. Electrical stimulation of the lateral habenula decreased [3H]serotonin release in all structures studied. Blockade of the GABA inhibitory pathway to the lateral habenula by the local application of picrotoxin reduced [3H]serotonin release in both substantiae nigra and increased release of the 3H-amine in the dorsal raphe but was without effect on [3H]serotonin release in either caudate nucleus. This inhibition of nigral [3H]serotonin release was antagonized by simultaneous application of picrotoxin to the dorsal raphe. Substance P delivery to the dorsal raphe produced the same effects on [3H]serotonin release as described for picrotoxin application to the lateral habenula except that inhibition of nigral [3H]serotonin release was not prevented by local co-administration of picrotoxin. These results suggest that the lateral habenula can control serotonergic transmission in the basal ganglia and that this regulation may be different for those serotonergic neurons innervating the caudate nucleus versus those projecting to the substantia nigra.
Characterization of acetylcholinesterase in individual neurons in the leech central nervous system
Authors: Wallace BG , Gillon JW
Published: March 2018

Acetylcholinesterase (AChE) activity was measured in cholinergic and non-cholinergic neurons in the central nervous system of the leech. Intracellular AChE was assayed by pretreating intact ganglia with echothiophate to inhibit selectively extracellular enzyme. The concentration of intracellular AChE in cholinergic neurons was 3- to 24- fold higher than that in non-cholinergic cells. The properties of AChE in extracts of leech ganglia were similar to those of “true” acetylcholinesterase, although butyrylthiocholine was almost as good a substrate as acetylthiocholine. There was also cholinesterase activity in leech blood; this enzyme resembled butyrylcholinesterase. Sucrose gradient velocity sedimentation of Triton X-100 extracts of leech ganglia revealed a major peak of AChE activity at 6.5 S and a small peak at 4.3 S. The pattern of activity in the gradient was the same when intact ganglia were pretreated with echothiophate, although the total activity was reduced by 98%. Intact leech ganglia were stained for AChE activity with and without echothiophate pretreatment. In ganglia that had not been exposed to echothiophate, cholinesterase reaction product was deposited primarily on the ganglionic sheath. In pretreated ganglia, on the other hand, cholinesterase activity was concentrated within neuronal cell bodies. Electrophysiological identification and intracellular injection of the fluorescent dye Lucifer Yellow prior to staining were used to confirm that most AChE- positive cells were cholinergic motoneurons. Two previously unidentified neurons staining for AChE were shown to be motoneurons. These results demonstrate that cholinergic motoneurons can be differentiated from other cells in the leech nervous system by their high intracellular concentration of AChE.
Proportional secretion of opioid peptides and catecholamines from adrenal chromaffin cells in culture
Authors: Wilson SP , Chang KJ , Viveros OH
Published: March 2018

Bovine adrenal medullary chromaffin cells were used to study the relationship between opioid peptide and catecholamine secretion from the adrenal medulla. Stimulation of chromaffin cells by acetylcholine, nicotine, veratridine, barium, or Ionomycin produced secretion of opioid peptides and catecholamines which was proportional to the cellular content of these substances. Nicotine-evoked secretion of opioid peptides and catecholamines was dependent on extracellular calcium and was blocked by d-tubocurarine. Increased cellular content of opioid peptides and decreased catecholamine content induced by treatment of chromaffin cells with reserpine or tetrabenazine were reflected in the secretion of proportionally larger amounts of opioid peptides and smaller amounts of catecholamines when compared with secretion of these substances from untreated cells. Peptides of up to 25,000 daltons that express opiate activity only following digestion with enzymes, such s trypsin and carboxypeptidase B, also are secreted from chromaffin cells in the same proportion of their cellular content as are catecholamines and opioid peptides. Opioid peptides were secreted in proportion to total catecholamines but not in proportion to either epinephrine or norepinephrine alone, suggesting that the peptides are secreted from both epinephrine- and norepinephrine- containing cells in the cultures. The results are consistent with the co-storage of opioid peptides and opiate receptor-inactive peptides containing enkephalin sequences in chromaffin vesicles and with the all- or-none exocytotic secretion of chromaffin vesicles content in response to stimulation of the adrenal medulla.
Auditory and visual maps of space in the optic tectum of the owl
Authors: Knudsen EI
Published: March 2018

The receptive field properties and functional organization of visual and auditory responses were studied in the optic tectum of the barn owl (Tyto alba). Most units throughout the depth of the tectum responded to both visual and auditory stimuli. The entire visual field of each eye was represented topographically in the contralateral tectum. In the portion of the tectal map representing the zone of binocular vision, 50% of the superficial layer units and 100% of the deep; layer units were driven binocularly. The representation of the frontal binocular region of space was greatly expanded in the map; the average magnification factor was 3 times greater for the frontal binocular zone than for the monocular zone. The responses of the superficial and deep tectal units to auditory stimuli were space specific; they responded only when a sound source was located in a particular region of space, or receptive field, regardless of the intensity or type of sound used. Most auditory receptive fields contained a distinct “best area” where a sound source was most effective in driving the unit. Auditory space, as defined by receptive fields and best areas, was represented topographically in the tectum. The auditory and visual maps of space had the same orientations, positions, magnification factors, and termination coordinates at the anterior and dorsal edges of the tectum. Yet the maps lost their registry near the posterior and ventral margins where the most peripheral regions of space were represented. These characteristics suggest that the spatiotopic organization in the tectum is a compromise between a tendency for the space representations of different modalities to align and for the representation of each modality to fill the entire tectum.
Binding of developing mouse cerebellar cells to fibronectin: a possible mechanism for the formation of the external granular layer
Authors: Hatten ME , Furie MB , Rifkin DB
Published: March 2018

The role of the matrix glycoprotein fibronectin in the formation of the external granular layer of the developing mouse cerebellum was investigated by in vitro studies of the binding of cerebellar cells to a fibronectin-coated culture substratum and by in vivo immunocytochemical localization of antiplasma fibronectin antiserum in cerebellar tissue. The adhesion of cells dissociated from embryonic and early postnatal mouse cerebellum is developmental stage-specific when the cells are plated on tissue culture substrata derivatized with human plasma fibronectin. Cells dissociated from mouse cerebellum at embryonic day 13 form cellular aggregates on insoluble plasma fibronectin. In contrast, cells dissociated from embryonic day 16 through postnatal day 7 cerebellum form a monolayer. Time-lapse video recordings reveal extensive cell movement of late embryonic and early postnatal cerebellar cells on insoluble plasma fibronectin. Late embryonic and early postnatal cerebellar cells bind to fibronectin but do not degrade the fibronectin substratum. Immunocytochemical studies of the binding of antiplasma fibronectin antisera to cryostat sections of intact embryonic and early postnatal cerebellar tissue reveal a brightly stained region of endogenous fibronectin along the route of granule cell migration from the lateral caudal part of the neuroepithelium lining the fourth ventricle up onto the external surface of the cerebellar anlage. When the formation of the external granular layer is completed, the intense region of fibronectin is no longer visible.
Studies on the control of myelinogenesis. IV. Neuronal induction of Schwann cell myelin-specific protein synthesis during nerve fiber regeneration
Authors: Politis MJ , Sternberger N , Ederle K , Spencer PS
Published: March 2018

The temporal sequence of axon-Schwann cell interaction during regeneration is examined in cat tibial nerves surgically denervated for 8 weeks and, subsequently, coated to a freshly severed peroneal nerve for 3 weeks. Prior to association with regenerating axons, Schwann cells resident in denervated and reinnervated stumps failed to synthesize proteins co-migrant with P0, P1, and P2 myelin proteins in contrast to normal nerves. Axonal association with Schwann cells stimulated synthesis of amino acid-labeled proteins co-migrating with myelin-specific proteins prior to elaboration of myelin lamellae. Radioactivity from these peaks was precipitated by antibodies raised against myelin-specific proteins. The synthesis of P1 and P2 proteins was evident before P0 synthesis in reinnervated stumps. Immunocytochemical staining with antibody to P0, P1, P2, and myelin- associated glycoprotein (MAG) appeared only after myelin lamellae had been formed. These data suggest that Schwann cells: (a) synthesize proteins co-migrant with P1, P2, P0, and MAG in normal cat nerves; (b) cease detectable manufacture of these proteins after axonal loss; (c) regain their capacity to synthesize these proteins upon re- establishment of axonal association; and (d) during regeneration, express the synthesis of P1 and P2 before that of P0.
Recovery of myelination in rat optic nerve after developmental retardation by cortisol
Authors: Bohn MC , Friedrich VL
Published: March 2018

Oligodendrocyte formation and myelination in the optic nerve of rats treated with cortisol on postnatal days 7 and 18 were investigated at 21 and 60 days by autoradiographic and morphometric methods. At 21 days, the amount of myelin in the optic nerve of treated rats was reduced by 42%. This reduction was accompanied by a 39% decrease in the number of myelinated axons. In addition, the myelin/axon area ratio was reduced 22% for those axons which were myelinated. At 60 days, the amount of myelin, the number of axons myelinated, the average axonal size, and the average amount of myelin per axon had completely recovered to normal values. Tritiated thymidine-labeling experiments showed that the genesis of oligodendrocytes was enhanced following the cessation of treatment. Since the number of oligodendrocytes in the optic nerve of treated rats was normal at 60 days, it is suggested that the retarding effect of cortisol on myelination in the optic nerve may be mediated, at least in part, by inhibited formation of oligodendrocytes during treatment.
Regulation of calcium entry into the extracellular environment of the rat brain
Authors: Barkai AI , Meltzer HL
Published: March 2018

Since neuronal activity is critically related to both intra- and extracellular calcium ion concentrations, there must be a mechanism for regulating the transfer of calcium from the blood into the extracellular environment of the brain. The data presented here support the hypothesis that, within or close to the site of passive permeation of calcium in the choroid plexus, there is a calcium pump capable of recycling the filtered calcium back into the capillary circulation. This pump can be blocked by ruthenium red, a known inhibitor of active calcium transport. The activity of the calcium pump is shown to increase in proportion to the concentration of calcium in the cerebroventricular fluid. Its physiological role therefore would be to insure that the calcium concentration available to the brain will be maintained within a narrow range even in the presence of severe hypercalcemic states.
The human spinal cord: substance P and methionine-enkephalin immunoreactivity
Authors: de Lanerolle NC , LaMotte CC
Published: March 2018

The distribution of substance P-like (SPLI) and methionine-enkephalin- like (MELI) immunoreactivity in the thoracic, lumbar, and sacral human spinal cord was studied in sections stained by the indirect antibody peroxidase-antiperoxidase method. The laminar distributions of SPLI and MELI were somewhat similar. Immunoreactive axons and terminal-like processes were found in the marginal zone and substantia gelatinosa, although SPLI was heavier than MELI in Lissauer's tract and the marginal zone. Laterally, both SPLI and MELI extended along the entire dorsal horn border, including laminae IV and V. Isolated, fine fiber bundles also extended deep into the central regions of laminae IV and V. Heavy SPLI and MELI also were found in the intermediolateral column region (IML), while lesser amounts were observed in the intercalatus and intermediomedial (IMM) regions of lamina VII. In lamina IX, SPLI was moderate, and less MELI was found. The distribution of SPLI fibers and terminal-like profiles in the human spinal cord is similar to that in other mammals, whereas that of MELI suggests some differences, particularly in laminae I, II, and III. Many terminal-like structures were in close apposition to neurons in several laminae. Based upon correlations of the three-dimensional organization of both the labeled terminals and the dendritic trees of the cells, the types of neurons in apposition to SPLI and MELI could be tentatively identified. These may include (1) marginal cells resembling the pyramidal and multipolar types; (2) gelatinosal cells resembling islet and stalked cells; (3) spinothalamic cells in laminae I, V, VI, VII, and VIII; (4) autonomic neurons in the IML and IMM; and (5) motoneurons in lamina IX. In the sacral cord, neurons resembling dorsal band (lamina V) and lateral band (lamina VII) parasympathetic neurons also were outlined by SPLI and MELI, with more SPLI in the region of the lateral band neurons. Often, in many of the laminae, the same neuron was surrounded by both SPLI and MELI. The variety of possible neuronal types supplied by SPLI and MELI processes and the fairly wide distribution of these substances within the spinal cord suggest that they may be involved in a number of spinal functions.
Cerebellar Purkinje cells are descended from a small number of progenitors committed during early development: quantitative analysis of lurcher chimeric mice
Authors: Wetts R , Herrup K
Published: March 2018

Previous analysis of lurcher in equilibrium wild type aggregation chimeras revealed that the degeneration of cerebellar Purkinje cells (PCs) in lurcher mutants is due to a defect intrinsic to the PCs themselves. Thus, all of the PCs remaining in lurcher chimeric mice are descended from only the wild type embryo. In this study, we have determined the number of PCs in four lurcher chimeras and three wild type mice. The low number of wild type PCs (10,200) in half of the cerebellum of one chimera (chi 11) suggested that these cells might be descended from a single progenitor. This idea is strongly supported by the quantitative analysis of the PCs in the other animals. These numbers are integral multiples of the number of PCs in chi 11. We believe that each stepwise increase in the number of PCs in the chimeras is due to the addition of a single wild type cell to the progenitor pool. The existence of integral multiples implies that no other cells can contribute to the PC population after the progenitors become committed to forming PCs. We cannot know, however, whether the PC progenitors also give rise to other cell populations. The values of the integrals in wild type mice indicate that the entire PC population descends from a small number of progenitors (8 in C3H/HeJ mice). We calculate that these progenitors are committed during the neural plate to neural fold stage of development. Thus, the fate of the progenitors of the cerebellar PCs is restricted very early in neural development.
Characterization of [3H]desipramine binding associated with neuronal norepinephrine uptake sites in rat brain membranes
Authors: Lee CM , Javitch JA , Snyder SH
Published: March 2018

A variety of evidence indicates that [3H]desipramine can label neuronal norepinephrine uptake sites in brain membranes. Pretreatment of rat cerebral cortical membranes with 0.3 M KCl increases the ratio of high affinity to low affinity saturable [3H]desipramine binding. With this improved tissue preparation, we have confirmed our earlier observation that the high affinity [3H]desipramine binding component (KD = 2 to 4 nM) is associated with norepinephrine neuronal uptake sites. The potencies of various antidepressant drugs in reducing [3H]desipramine binding correlate with their inhibition of neuronal [3H]norepinephrine accumulation. Like the norepinephrine uptake system, high affinity [3H]desipramine binding is dependent both on sodium and chloride, with half-maximal stimulation by 10 mM chloride. Although bromide can substitute for chloride to stimulate binding, other anions, including iodide, fluoride, acetate, citrate, and phosphate, are inactive. Comparable sodium and anion regulation of [3H]imipramine binding to serotonin uptake recognition sites also is observed. The association of [3H]desipramine binding sites with neuronal norepinephrine uptake sites is supported further by the selective abolition of high affinity [3H]desipramine binding following the destruction of central norepinephrine neurons by intraperitoneal administration of DSP-4 (N-(2- chloroethyl)-N-ethyl-2-bromobenzylamine). In vitro incubation of cerebral cortical membranes with DSP-4 also selectively abolishes the high affinity [3H]desipramine binding, an effect which cannot be reversed by repeated washing of the membranes, suggesting that DSP-4 alkylates neuronal norepinephrine uptake sites.
On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex
Authors: Georgopoulos AP , Kalaska JF , Caminiti R , Massey JT
Published: March 2018

The activity of single cells in the motor cortex was recorded while monkeys made arm movements in eight directions (at 45 degrees intervals) in a two-dimensional apparatus. These movements started from the same point and were of the same amplitude. The activity of 606 cells related to proximal arm movements was examined in the task; 323 of the 606 cells were active in that task and were studied in detail. The frequency of discharge of 241 of the 323 cells (74.6%) varied in an orderly fashion with the direction of movement. Discharge was most intense with movements in a preferred direction and was reduced gradually when movements were made in directions farther and farther away from the preferred one. This resulted in a bell-shaped directional tuning curve. These relations were observed for cell discharge during the reaction time, the movement time, and the period that preceded the earliest changes in the electromyographic activity (approximately 80 msec before movement onset). In about 75% of the 241 directionally tuned cells, the frequency of discharge, D, was a sinusoidal function of the direction of movement, theta: D = b0 + b1 sin theta + b2cos theta, or, in terms of the preferred direction, theta 0: D = b0 + c1cos (theta - theta0), where b0, b1, b2, and c1 are regression coefficients. Preferred directions differed for different cells so that the tuning curves partially overlapped. The orderly variation of cell discharge with the direction of movement and the fact that cells related to only one of the eight directions of movement tested were rarely observed indicate that movements in a particular direction are not subserved by motor cortical cells uniquely related to that movement. It is suggested, instead, that a movement trajectory in a desired direction might be generated by the cooperation of cells with overlapping tuning curves. The nature of this hypothetical population code for movement direction remains to be elucidated.
Intraneuronal injection of horseradish peroxidase labels glial cells associated with the axons of the giant metacerebral neuron of Aplysia
Authors: Goldstein RS , Weiss KR , Schwartz JH
Published: March 2018

After injecting the cell body of the giant serotonergic neuron (GCN) in the cerebral ganglion of Aplysia with horseradish peroxidase (HRP), we found that some glial cells were labeled along the cerebrobuccal connective and posterior lip nerve, the two nerves that contain the major axon branches of the injected neuron. Starting at a distance of about 3 mm from the site of the injection, only glial cells in the nerve that are close to an axon branch of the GCN contained HRP. Labeling appears to be selective because, at most, only one out of three glial cells was labeled within an area of 20 micrometer of the axon. Moreover, no HRP was detected in any of the many glial cells within the cerebral ganglion. Reaction product diffusely labeled the cytoplasm of glial cell bodies and processes after intraneuronal injection of HRP. This distribution was markedly different from that observed in glial cells after the uptake of HRP from the extracellular space; HRP, presumed to be taken up by endocytosis, was found to be localized to vesicles, tubules, and multivesicular bodies.
Distribution of calcium-activated protease activity and endogenous substrates in the squid nervous system
Authors: Pant HC , Gallant PE , Gould R , Gainer H
Published: March 2018

Calcium-activated protease (CAP) activity was studied in various neural tissues of the squid using endogenous (neurofilament protein) and exogenous ([14C]casein) substrate assays. Both assays demonstrated a significant CAP activity in perikarya from stellate ganglia, in axoplasm extruded from the giant axon, and in squid retinal fibers. The endogenous protein substrates in the perikarya and axons were 60,000 and 200,000 daltons, respectively. The Km for the CAP degradation of [14C] casein in axoplasm was about 2 x10–6 m. In contrast, both assays detected no CAP activity nor endogenous substrate in nerve terminals (synaptosomes from squid optic lobe). The absence of both CAP activity and endogenous substrate in nerve endings suggests that the axonal neurofilaments are degraded by CAP at the axon-nerve ending junction, followed by an autoinactivation of the CAP. Consistent with this hypothesis is that exposure of axoplasmic CAP to calcium leads to a rapid degradation of axonal neurofilament protein (t 1/2 less than 2 min) and a slower inactivation of the CAP (t 1/2 = 90 min). Axonal CAP requires a relatively high concentration of CA2+ sensitivity form of CAP found in other tissues.
Chronic effects of a monoamine oxidase-inhibiting antidepressant: decreases in functional alpha-adrenergic autoreceptors precede the decrease in norepinephrine-stimulated cyclic adenosine 3': 5'- monophosphate systems in rat brain
Authors: Cohen RM , Ebstein RP , Daly JW , Murphy DL
Published: March 2018

Various antidepressant drugs (monoamine oxidase inhibitors and tricyclics) enhance norepinephrine availability and lead to adaptive changes in brain noradrenergic systems, namely, decreases in the number of beta receptors and in the responsiveness of adenylate cyclase to norepinephrine monamine oxidase inhibitor, but not after 3 days, there is an increase in norepinephrine release from rat brain microsacs in response to 43 mM KCl stimulation. Microsacs prepared from 21-day clorgyline-treated animals also show a marked decrease in the inhibition of norepinephrine release caused by the alpha 2-selective agonist clonidine. These functional changes in norepinephrine release mechanisms are accompanied by a 53% reduction in brainstem alpha 2 receptor density as measured by [3H]clonidine binding. At the same time, despite findings of a decrease in beta receptor number as determined by [3H]dihydroalprenolol binding data, no significant decrease in the responses of cyclic adenosine 3′: 5′-monophosphate (cyclic AMP) systems to norepinephrine stimulation is observed. Decreases in the cyclic AMP response are observed by day 35 of clorgyline treatment. The results provide direct physiological support for a change in the norepinephrine release mechanism and an effect on autoreceptors, specifically, preceding postsynaptic adaptive changes in the instance of one antidepressant, clorgyline. Difficulties in observing such changes with other antidepressants may result from the multiple nature of alpha-adrenergic receptors, especially as measured by radioactive ligand techniques; the lack of a direct relationship between physiological changes and receptors as measured by radioligand techniques; the large doses of monoamine oxidase inhibitors used in some studies; and the possible multiplicity of antidepressant molecular mechanisms.
"Increased" sensory stimulation leads to changes in energy-related enzymes in the brain
Authors: Dietrich WD , Durham D , Lowry OH , Woolsey TA
Published: March 2018

The facial whiskers of mice project through several synapses to anatomically distinct structures called barrels in the contralateral cerebral cortex. With appropriate illumination, individual barrels can be recognized and dissected from unfixed, freeze-dried tissue sections taken parallel to the plane of layer IV. The tissue then can be analyzed using quantitative microhistochemical techniques to determine the level of various substances of biological importance (W.D. Dietrich, D. Durham, O. H. Lowry, and T. A. Woolsey (1981) J. Neurosci. 1: 929–935). The present paper describes results obtained in this way from adult mice subjected to a chronic “sensory deprivation” by repeatedly clipping all of the whisker hairs on one side of the face and during the recovery from this deprivation in which the whisker hairs were allowed to grow back. Sensory deprivation for 60 days leads to significant changes in the levels of the three energy-related enzymes studied--citrate synthase, malate dehydrogenase, and glycogen phosphorylase. surprisingly, during clipping, the enzyme levels in the barrels of the contralateral cortex are essentially normal, whereas enzyme levels in the barrels of the ipsilateral cortex are increased significantly. Specifically, activities expressed as a percentage of levels in normal animals were: citrate synthase, 135%; malate dehydrogenase, 130%; and glycogen phosphorylase, 170%. Forty-five days after the deprivation is reversed, the levels return to normal. These significant changes occurred in adult mice several synapses away from the sensory periphery. The data are in contrast to our earlier results in which damage to the primary afferents reduced the levels of the enzymes citrate synthase and malate dehydrogenase contralateral to the manipulation. A possible explanation for the enzymatic changes observed in the cortex ipsilateral to the clipped whiskers is an increased utilization of the intact sensory periphery by the animals; this has some behavioral support.
Prenatal development of gabaergic, glycinergic, and dopaminergic neurons in the rabbit retina
Authors: Fung SC , Kong YC , Lam DM
Published: March 2018

The main findings from our studies on the emergence and maturation of neurotransmitter systems in the rabbit retina are that, during normal development: (1) the commitments for certain neurons to become GABAergic, glycinergic, or dopaminergic are made prenatally; the maturation of these neurons, however, occurs postnatally; (2) specific accumulations of exogenously supplied transmitters by presumed retinal neurons were first observed autoradiographically around embryonic day 22 (E22) for gamma-aminobutyric acid (GABA), E25 for glycine, and E27 for dopamine, suggesting that putative GABAergic, glycinergic, and dopaminergic neurons are determined phenotypically at least by these days; (3) based upon the three transmitter-specific properties--uptake, synthesis, and release--the uptake property is generally the first to emerge, while the appearance of the other properties follows a precise and distinct temporal pattern for each of the transmitters studied; (4) for GABAergic and glycinergic systems, the emergence of K+-stimulated, Ca2+-dependent release mechanisms occurs many days after the first appearance of the uptake properties; in contrast, the mechanisms for dopamine uptake and release emerge at about the same time; and (5) by our criteria, putative GABAergic and glycinergic amacrine cells are mature between postnatal day 10 (P10) and P12, around the time when the eyes first open and direction-selective ganglion cells can first be recorded; however, the dopaminergic neurons probably are not mature until about P24.
Immunocytochemical analysis of serotonergic axons in laminae I and II of the lumbar spinal cord of the cat
Authors: Ruda MA , Coffield J , Steinbusch HW
Published: March 2018

Serotonergic axons in the superficial dorsal horn were examined at the light and electron microscopic levels using an antibody specific for serotonin (5-HT). Immunoreactive 5-HT axons were most numerous in lamina I and fewest in lamina IIb. The 5-HT axons tended to orient rostrocaudally as they traveled long distances in the gray matter. Based on the size of the 5-HT varicosities along a strand of axon, at least three different types of 5-HT axons were observed at the light microscopic level. Ultrastructurally, 5-HT immunoreactive axonal endings contained either a mixture of flattened and small oval agranular vesicles or a relatively homogeneous population of oval vesicles. 5-HT endings synapsed primarily on small caliber dendritic shafts. They also were found synapsing on large caliber dendritic shafts, dendritic spines, and neuronal cell bodies. Based on the laminar location of 5-HT axosomatic synapses and the presence of 5-HT synapses on different morphological types of dendrites, we propose that 5-HT modulates the response properties of at least three different types of neurons in the superficial dorsal horn.
Inhibitor of adenosine 3':5'-monophosphate-dependent protein kinase blocks presynaptic facilitation in Aplysia
Authors: Castellucci VF , Nairn A , Greengard P , Schwartz JH , Kandel ER
Published: March 2018

Sensitization of the gill withdrawal reflex results from presynaptic facilitation at the excitatory synapses made by sensory neurons on gill motor neurons. Facilitation is accompanied by an increase in the duration of the action potential in sensory cells because of the depression of a K+ current. This results in an increasd influx of CA2+ and a greater release of transmitter from sensory neurons. There is evidence that serotonin is the facilitating transmitter and that the depression of the K+ current by serotonin mediated by cAMP-dependent protein phosphorylation. To test further the role of the cAMP-dependent protein kinase and of protein phosphorylation in sensitization, we have attempted to prevent or reverse the development of the electrophysiological correlates that accompany sensitization. We have pressure-injected sensory neurons with a specific and a stable protein inhibitor of the cAMP-dependent protein kinase both before and after the application of serotonin or the activation of the facilitator neurons. The increase in spike broadening that accompanies facilitation was prevented or diminished by injection of the inhibitor. Moreover, injection of the inhibitor could reverse fully the developed spike broadening produced by prior application of serotonin. These observations strenthen the evidence for the involvement of protein phosphorylation in presynaptic facilitation. Phosphorylation of the substrate protein evidently is quite labile and does not persist after the kinase is inhibited. Thus, the time course of short term sensitization appears to be determined by an active kinase. We think that it is likely that the mechanism for maintaining the kinase in an active form resides in the slow decay of the cAMP produced by the action of serotonin or the facilitator neurons on the sensory cells.
Facilitatory transmitter causes a selective and prolonged increase in adenosine 3':5'-monophosphate in sensory neurons mediating the gill and siphon withdrawal reflex in Aplysia
Authors: Bernier L , Castellucci VF , Kandel ER , Schwartz JH
Published: March 2018

Sensitization of the gill and siphon withdrawal reflex in the marine mollusc, Aplysia california, is a simple form of learning Underlying this behavioral changes is a cascade of biochemical events. The first step in this cascade is postulated to be an increase in cAMP within the sensory neurons of the abdominal ganglion. We have developed a labeling protocol with 32Pi which permits us to measure the synthesis of cAMP within a single sensory neurons. Application of serotonin for 5 min was found to triple the content of [32P]cAMP in sensory neurons. The response is specific to serotonin: dopamine, a transmitter that does not produce sensitization, did not increase cAMP. Physiological stimulation of facilitator neurons also resulted in a 3.5-fold increase of cAMP in sensory neurons but not in other cells of the ganglion. We studied the time course of the increase of cAMP in sensory cells stimulated with serotonin and found that it parallels closely the time course of the short term form of presynaptic facilitation. We also have determined the effects of transmitters on the synthesis of cAMP in other identified neurons of the ganglion. The bag cells responded specifically to serotonin. R15, which has been shown to be hyperpolarized both the serotonin and by dopamine, responded to both transmitters by increased synthesis synthesis of cAMP. Thus, the dopamine- and serotonin-sensitive cyclase can be localized to both the same and different cells. Other cells did not respond to serotonin or to dopamine, indicating that a transmitter-sensitive adenylate cyclase is a specific property and is not present in all neurons.
Loss of axons in the cat optic nerve following fetal unilateral enucleation: an electron microscopic analysis
Authors: Williams RW , Bastiani MJ , Chalupa LM
Published: March 2018

Between the 48th day of gestation (E-48) and maturity, the number of axons in the cat optic nerve is reduced by approximately 50%. On the basis of an electron microscopic assay, the axon population of the E-48 nerve was estimated to be 328,000. In contrast, estimates from two normal adults were 159,000 and 158,000. In utero unilateral enucleation (at E-45 and E-46) attenuated the severity of this loss since the optic nerves of the experimental animals contained 200,000 and 198,000 fibers. These results indicate that prenatal binocular competition is involved in the elimination of ganglion cell axons during the normal development of the cat's visual system. The increased number of axons in the optic nerve of the prenatally enucleated animals could be due to reduced ganglion cell death or a failure to retract supernumerary axon collaterals. It is suggested that the former explanation is more consistent with what is currently known about the development of retinofugal projections.
Protection of opiate receptors in NG108-15 against modification by N- ethylmaleimide
Authors: Mullikin-Kilpatrick D , Larsen NE , Blume AJ
Published: March 2018

Two different -SH groups associated with the opiate receptors of the mouse neuroblastoma X rat glioma hybrid NG108–15 have been identified. Modification of these by N-ethylmaleimide (NEM) (presumed to be via alkylation) or by para-chloromercuribenzoic acid (presumed to be via formation of mercury adducts) decreases the binding of both opiate agonists and antagonists to these receptors. Agonist binding is more sensitive than antagonist binding to modification by NEM. Losses in antagonist binding are accounted for totally by decreases in the number of binding sites; there are no corresponding losses in antagonist affinity. Losses of antagonist binding exhibit a pseudo-first order rate constant; the modification of only one such group completely destroys the binding site. Both agonists and antagonists protect against modification of this group by NEM. Sodium and lithium, but not GTP, also protect this group, indicating that the action of these monovalent cations is directly on the receptor moiety. Losses in agonist binding stem not only from decreases in receptor number but also from selective losses in affinity. This -SH group appears to be different from the one at the binding site as sodium, GTP, and antagonist ligands do not protect against losses in agonist affinity. Agonist high affinity also is lost in a pseudo-first order fashion indicating that an alteration of only one -SH group per receptor complex is sufficient to produce this effect. The possible roles of two sulfhydryls in opiate receptor function are discussed.
Neural projections from nucleus accumbens to globus pallidus, substantia innominata, and lateral preoptic-lateral hypothalamic area: an anatomical and electrophysiological investigation in the rat
Authors: Mogenson GJ , Swanson LW , Wu M
Published: March 2018

The anatomical organization and electrophysiological characteristics of a projection from the nucleus accumbens to anteroventral parts of the globus pallidus and to a subpallidal region that includes the substantia innominata (SI), the lateral preoptic area (LPO), and anterior parts of the lateral hypothalamic area (LHA) were investigated in the rat. Autoradiographic experiments, with injections of 3H-proline into different sites in the nucleus accumbens and adjacent caudoputamen, indicate that the descending fibers are organized topographically along both mediolateral and dorsoventral gradients, although labeled fibers from adjacent regions of the nucleus accumbens overlap considerably in the ventral globus pallidus and subpallidal region. Injections confined to the caudoputaman only labeled fibers in the globus pallidus. Retrograde transport experiments with the marker true blue confirmed that only the nucleus accumbens projects to the subpallidal region and that the caudoputamen projects upon the glubus pallidus in a topographically organized manner. In electrophysiological recording experiments single pulse stimulation (0.1 to 0.7 mA; 0.15 msec duration) of the nucleus accumbens changed the discharge rate of single neurons in the ventral globus pallidus and in the SI, LPO, and LHA. Typically, the responses were inhibition of neuronal discharge with latencies of 6 to 18 msec. Single pulse stimulation of the dorsolateral caudoputamen altered the discharge rate of single neurons in dorsal regions of the globus pallidus, with inhibition being the most frequently observed response. The results of these anatomical and electrophysiological experiments are complementary and indicate that fibers from the nucleus accumbens innervate the anteroventral region of the globus pallidus as well as the subpallidal region, while most fibers of the caudoputamen innervate the globus pallidus but not the subpallidal region. It appears, therefore, that these two components of the striatum have different output connections. The possible functional significance of these findings is discussed in relation to the projections of the subpallidal region, which may include an output to the mesencephalic locomotor region, and in relation to the nucleus accumbens afferents from the amygdala and hippocampal formation.