bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophysiological properties of identified cells in the in vitro olfactory epithelium of the tiger salamander
Authors: Masukawa LM , Hedlund B , Shepherd GM
Published: March 2018

An in vitro preparation of the salamander olfactory epithelium has been developed for electrophysiological analysis. Intracellular measurements of membrane properties of the main epithelial cell types have been carried out, combined with Lucifer Yellow injections. The most prevalent type of cell had a high resting membrane potential and relatively low input resistance. This cell never discharged impulses, either spontaneously or to injected current. Lucifer Yellow injections identified this cell type as a supporting cell. A less frequent type had a medium resting potential and a very high input resistance. This type always discharged impulses in response to injected depolarizing current. Lucifer Yellow injections identified this cell type as an olfactory receptor neuron. The least frequent type had a medium resting potential and a high input resistance. It never generated action potentials. This nonspiking type was tentatively identified as an immature receptor neuron in the process of differentiating from basal stem cells in the epithelium. These are the first results to document physiological properties for the main cell types and morphological identification of two of the types in the same preparation of the olfactory epithelium. Our results support previous suggestions regarding the glial-like properties of the supporting cells. The membrane properties of the receptor neurons appear to be well suited for mediating the olfactory sensory response of these cells.
Autoradiographic localization of thyrotropin-releasing hormone receptors in the rat central nervous system
Authors: Manaker S , Winokur A , Rostene WH , Rainbow TC
Published: March 2018

We employed quantitative autoradiography to examine the distribution of thyrotropin-releasing hormone (TRH) receptors in the rat CNS. The binding of [3H]3-methyl-histidine-TRH [( 3H]MeTRH) to TRH receptors in frozen rat brain sections was saturable, of a high affinity (Kd = 5 nM), and specific for TRH analogs. Autoradiograms of [3H]MeTRH binding showed highest concentrations of TRH receptors in the rhinencephalon, including accessory olfactory bulb, nuclei of the amygdala, and the ventral dentate gyrus and subiculum of the hippocampus. Moderate TRH receptor concentrations were found within the thalamus and hypothalamus, in most regions of the rhombencephalon, such as the cranial nerve nuclei, and in the substantia gelatinosa of the spinal cord. Neocortex and basal ganglia contained low densities of TRH receptors. This distribution correlates well with the sensitivity of brain regions to the known effects of TRH, and suggests that TRH receptors may mediate the actions of TRH in the rat CNS.
Noradrenergic responses of spinal neurons in locus coeruleus-spinal cord co-cultures
Authors: Pun RY , Marshall KC , Hendelman WJ , Guthrie PB , Nelson PG
Published: March 2018

Locus coeruleus (LC) explants were co-cultured with dissociated spinal neurons of mice. Nerve fibers exhibiting catecholamine fluorescence radiated from the explants and frequently invested spinal cord (SC) neurons close to the explants. Electrical stimulation of the explant and iontophoretic application of norepinephrine evoked a spectrum of slow depolarizing, hyperpolarizing, and biphasic responses in the SC cells. The responses to LC stimulation and to application of norepinephrine were usually similar in a given cell. The depolarizing responses were associated with an increase in apparent input resistance and pharmacologic tests indicated that the responses were mediated by alpha-receptors. Neurons in regions innervated by catecholamine- containing fibers usually gave depolarizing responses to LC stimulation and such neurons had a very high probability of exhibiting depolarizing responses to applied norepinephrine. It would appear that either locus coeruleus explants favored the survival of cells with alpha-receptors or expression of these receptors in SC neurons was induced by innervation of the neurons by locus coeruleus axons.
Specific changes in axonally transported proteins during regeneration of the frog (Xenopus laevis) optic nerve
Authors: Szaro BG , Loh YP , Hunt RK
Published: March 2018

Labeled proteins in intact and regenerating optic nerves of juvenile Xenopus clawed frogs were examined at three different time points (2 to 4 hr, 18 hr, and 5 to 9 days) following [35S]methionine injection into the eye. The distal axon tips of optic nerves were transected at the margin of the tectal lobe and regeneration of the nerve was followed by three methods: autoradiography, tissue section counting following [3H]proline injection into the eye, and electrophysiological mapping of the visual field projection. By these methods, regrowth was found to occur 2 weeks after transection, but the fibers had not yet sorted their retinotopic pattern. Two-dimensional gel separation of labeled nerve proteins revealed 250 to 300 identifiable proteins, 89 of which (including all spots which differed consistently upon direct comparison of regenerating versus normal nerves) were selected for quantitative treatment. Nine of these spots (240, 135, 65, 64, 58, 54, 56, 31, and 26 kilodaltons) were shown to increase and six (56, 49, 42, 29, 17, and 15 kilodaltons) were shown to decrease significantly in regenerating nerves. By using a crush control and tracking the labeled proteins into the tectum over time, these proteins were shown to be axonally transported proteins. In addition, four other nonaxonally transported proteins also changed during regeneration.
Conditioned modification of phototactic behavior in Hermissenda. II. Differential adaptation of B-photoreceptors
Authors: Crow T
Published: March 2018

Changes in the response of B-type photoreceptors to illumination were examined in the isolated nervous systems of Hermissenda following the conditioning procedures described in the preceding paper. Analysis of the transient peak amplitude of the depolarizing generator potential at the onset of two of the three light intensities used in the behavioral studies did not reveal an enhanced photoresponse to the light. However, when the activity of the same B-photoreceptors was examined after 5 min of continuous light, there was a significant decrease in the light- adapted discharge rate and a decreased generator potential amplitude in conditioned animals as compared to the random controls. An examination of the light adapted photoresponse in preparations where spike generation and synaptic interactions were eliminated showed that the decreased photoresponse of conditioned animals was due to factors that are intrinsic to the B-photoreceptors. These results are consistent with previous work suggesting that conditioning produces substantial adaptation effects in B-photoreceptors (Crow, T. (1982) Soc. Neurosci. Abstr. 8: 824). Since the cellular changes qualitatively follow the behavioral changes and are observed at times and light intensities that are similar to those where the suppression of phototactic behavior is expressed, phototactic suppression may be directly related to the changes in the B-photoreceptors and may not require the previously proposed complex network interactions within the eyes of Hermissenda.
Dopamine release and metabolism in awake rats after systemic neuroleptics as studied by trans-striatal dialysis
Authors: Imperato A , Di Chiara G
Published: March 2018

The method of trans-striatal dialysis has been applied here to the study of the release and metabolism of dopamine (DA) in the awake rat. DA and its acidic metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), present in the dialysates were separated by high performance liquid chromatography on reverse phase columns and estimated by electrochemical detection. In the awake rat, DA, DOPAC, and HVA could be recovered and quantitated in the dialysates for at least 4 days from the time of implantation of the dialysis tube. At a constant 2-microliters/min flow of Ringer in the dialysis tube, the output of the substances recovered in 20-min samples 24 hr after the implantation was as follows: DA, 0.318 +/- 0.035; DOPAC, 41.3 +/- 4.84; HVA, 32.98 +/- 3.79 (mean picomoles +/- SEM of six 40-microliters samples). The output of DA, DOPAC, and HVA decreased slowly so that 4 days after the implantation the output of DA was reduced by about 35% in respect to the 24-hr values. After a 24-hr recovery, drugs were administered and their effect on DA release and metabolism was investigated. Drugs of different chemical structure and spectrum, but having in common the property of blocking DA receptors and being effective neuroleptics such as haloperidol, sulpiride, and flupentixol, stimulated DA release and DOPAC and HVA output. Threshold doses for this effect were very low, being 0.012 mg/k, s.c., for haloperidol, 2.5 mg/kg, s.c., for (-)-sulpiride, and 0.025 mg/kg, s.c., for cis- flupentixol. This effect was stereospecific as the (+) form of sulpiride and the trans- form of flupentixol were at least 10 to 100 times less potent than their enantiomer. The stimulation of DA release was shorter-lasting than the stimulation of DA metabolism and sedation or catalepsy. Moreover, whereas DA release did not increase by more than 100% over basal values, DOPAC and HVA increased by more than 3 times after maximally effective doses of neuroleptics. gamma- Butyrolactone (200 mg/kg, i.p.) reversed haloperidol (0.1 mg/kg, s.c.), and sulpiride (20 mg/kg, s.c.) induced stimulation of DA release while it potentiated the stimulation of DOPAC and HVA output. These data indicate that stimulation of DA release by neuroleptics is strictly dependent upon stimulation of DA firing and that different mechanisms underline their effects on DA release and on DA metabolism.
Norepinephrine and histamine potentiate the increases in cyclic adenosine 3':5'-monophosphate elicited by vasoactive intestinal polypeptide in mouse cerebral cortical slices: mediation by alpha 1- adrenergic and H1-histaminergic receptors
Authors: Magistretti PJ , Schorderet M
Published: March 2018

We have examined the interactions, in eliciting cAMP accumulation, between vasoactive intestinal polypeptide (VIP) and the three monoamines norepinephrine (NE), histamine (HIS), and serotonin (5- hydroxytryptamine, 5-HT) in mouse cerebral cortical slices. We have observed that NE and HIS, but not 5-HT, act synergistically with VIP to increase cAMP levels. The rank-order of potency of several adrenergic agonists in potentiating the effect of VIP on cAMP levels is the following: epinephrine greater than NE greater than phenylephrine much greater than clonidine, with EC50 of 2.2, 5, and 10 microM, respectively (clonidine being only marginally effective). This pharmacological profile is characteristic of the activation of alpha 1- adrenergic receptors. This contention is substantiated by the observation that the potentiating effect of NE is antagonized by the selective alpha 1-adrenergic antagonist prazosin at nanomolar concentrations. The potentiating effect of HIS is mediated by H1- histaminergic receptors since it is antagonized by the selective H1- receptor antagonist mepyramine but not by cimetidine, a selective H2- receptor antagonist. The synergistic interaction between VIP and NE is also observed in the presence of the adenosine antagonist theophylline, thus discarding the possibility of a mediation of the synergism by adenosine released by VIP.(ABSTRACT TRUNCATED AT 250 WORDS)
Autoradiographic localization of (125I-Tyr4)bombesin-binding sites in rat brain
Authors: Zarbin MA , Kuhar MJ , O'Donohue TL , Wolf SS , Moody TW
Published: March 2018

The binding of (125I-Tyr4)bombesin to rat brain slices was investigated. Radiolabeled (Tyr4)bombesin bound with high affinity (Kd = 4 nM) to a single class of sites (Bmax = 130 fmol/mg of protein); the ratio of specific to nonspecific binding was 6/1. Also, pharmacology studies indicated that the C-terminal of bombesin was important for the high affinity binding activity. Autoradiographic studies indicated that the (125I-Tyr4)bombesin-binding sites were discretely distributed in certain gray but not white matter regions of rat brain. Highest grain densities were present in the olfactory bulb and tubercle, nucleus accumbens, suprachiasmatic and periventricular nuclei of the hypothalamus, central medial thalamic nucleus, medial amygdaloid nucleus, hippocampus, dentate gyrus, subiculum, nucleus of the solitary tract, and substantia gelatinosa. Moderate grain densities were present in the parietal cortex, deep layers of the neocortex, rhinal cortex, caudate putamen, stria terminalis, locus ceruleus, parabrachial nucleus, and facial nucleus. Low grain densities were present in the globus pallidus, lateral thalamus, and midbrain. Negligible grain densities were present in the cerebellum, corpus callosum, and all regions treated with 1 microM unlabeled bombesin. The discrete regional distribution of binding suggests that endogenous bombesin-like peptides may function as important regulatory agents in certain brain loci.
Evidence for differential localization of noradrenaline and neuropeptide Y in neuronal storage vesicles isolated from rat vas deferens
Authors: Fried G , Terenius L , Hokfelt T , Goldstein M
Published: March 2018

Using the technique of homogenization and subsequent density gradient centrifugation combined with ultrastructural analysis, the subcellular localization of noradrenaline and neuropeptide Y (NPY) was studied in vas deferens of castrated male rats. Noradrenaline showed two peaks in the gradient: one major peak at low density and another at high density. Only one NPY peak was seen, which coincided with the high density peak of noradrenaline. Electron microscopic analysis revealed high proportions of small and large vesicles in the light and heavy fractions, respectively. The present results indicate a differential subcellular localization of noradrenaline and NPY in the noradrenergic nerve endings of vas deferens. Thus, small vesicles seem to contain only noradrenaline, whereas the large vesicles may contain both noradrenaline and NPY.
Neuropharmacological antagonism of the beta-carboline-induced "anxiety" response in rhesus monkeys
Authors: Crawley JN , Ninan PT , Pickar D , Chrousos GP , Linnoila M , Skolnick P , Paul SM
Published: March 2018

A behavioral and physiological syndrome of stress-related responses was reported in primates following treatment with the benzodiazepine receptor antagonist, beta-carboline-3-carboxylic acid ethyl ester (beta- CCE). The behavioral and physiological effects of beta-CCE are similar to those observed during stressful or “anxiety”-related conditions characterized in rhesus monkeys under natural conditions. Pharmacological agents which are known to antagonize anxiety responses in other paradigms were tested for their ability to antagonize the actions of beta-CCE. Diazepam (1 mg/kg) completely blocked the effects of beta-CCE (200 micrograms/kg) on anxiety-related behaviors, heart rate and blood pressure, plasma catecholamines, cortisol, and adrenocorticotrophic hormone. A presynaptically active dose of the alpha-adrenoreceptor agonist, clonidine (10 micrograms/kg), significantly attenuated the effects of beta-CCE on all parameters, whereas the beta-adrenoreceptor agonist, propranolol (3 mg/kg), failed to alter the increases in plasma catecholamines, cortisol, or ACTH. In addition to these adrenergic agents, the serotonin antagonist, cyproheptadine (1 mg/kg), and the GABA-mimetic, 4,5,6,7- tetrahydroisoxazolo(5,4-C)pyrindin-3-ol (1 mg/kg), partially blocked the behavioral, physiological, and biochemical changes after beta-CCE. Manifestation of the complete “anxiety” syndrome evoked by beta-CCE in primates may require the functional activity of several neurotransmitter systems.
The complete pattern of ocular dominance stripes in the striate cortex and visual field of the macaque monkey
Authors: LeVay S , Connolly M , Houde J , Van Essen DC
Published: March 2018

Ocular dominance stripes in the striate cortex of a macaque monkey were labeled by autoradiography after injection of [3H]proline into one eye. The stripes were reconstructed on a representation of the flattened cortical surface by two independent techniques: one used computer graphics, and the other was the manual unfolding procedure of Van Essen and Maunsell (VanEssen, D. C., and J. H. R. Maunsell (1980) J. Comp. Neurol. 191: 255–281). The two reconstructions differed in many details of the pattern but were in agreement on its general features. As described in earlier studies, the stripes formed a system of parallel bands, with numerous branches and islands. They were roughly orthogonal to the V1/V2 border throughout the binocular segment of the cortex. In the lateral part of the operculum, where the fovea is represented, the stripes were less orderly than elsewhere. In the calcarine fissure the stripes ran directly across the striate cortex from its dorsal to its ventral margin. In the far periphery the stripes for the ipsilateral eye became progressively narrower, eventually fragmenting into small islands at the edge of the monocular segment. The overall periodicity (width of a left- plus right-eye pair of stripes) averaged 0.88 mm but decreased by a factor of about 2 from center to periphery. This decrease was not accounted for solely by shrinkage of the ipsilateral eye stripes. The flattened cortical reconstruction was transformed back into visual field coordinates, using information about visual field topography obtained from the detailed mapping study of Van Essen et al. (Van Essen, D.C., W.T. Newsome, and J.H.R. Maunsell (1984) Vision Res. 24: 429–448), as well as from more limited mapping done in the same monkey that was used for the reconstruction. In the transformed map, the stripes increased in width about 40-fold from the fovea to the far periphery. As deduced previously (LeVay, S., D. H. Hubel, and T. N. Wiesel (1975) J. Comp. Neurol. 159: 559–576; Hubel, D. H., and D. C., Freeman (1977) Brain Res. 122: 336–343), there were portions of the map in which the stripes followed curves approximating isoeccentricity lines, but this relationship was not very exact or consistent. The pattern of stripes appears to be more meaningfully related to the geometry of the cortical surface. This has significant implications for understanding the developmental mechanisms involved in stripe formation.
Autoradiographic localization of adenosine uptake sites in rat brain using [3H]nitrobenzylthioinosine
Authors: Bisserbe JC , Patel J , Marangos PJ
Published: March 2018

The adenosine uptake site has been localized in rat brain by an in vitro light microscopic autoradiographic method, using [3H]nitrobenzylthioinosine ( [3H]NBI) as the probe. The binding characteristics of [3H]NBI on slide-mounted sections are comparable to those seen in studies performed on brain homogenates. A very high density of uptake sites occurs in the nucleus tractus solitarius, in the superficial layer of the superior colliculus, in several thalamic nuclei, and also in geniculate body nuclei. A high density of sites are also observed in the nucleus accumbens, the caudate putamen, the dorsal tegmentum area, the substantia nigra, and the central gray. The localization of the adenosine uptake site in brain may provide information on the functional activity of the site and suggests the involvement of the adenosine system in the central regulation of cardiovascular function.
Starburst amacrine cells: morphological constancy and systematic variation in the anisotropic field of rabbit retinal neurons
Authors: Famiglietti EV
Published: March 2018

Starburst amacrine cells of rabbit retina have been characterized previously in terms of their highly distinctive and regular dendritic geometry. They have been identified as probable cholinergic neurons of the retina and have been shown to direct output solely to ganglion cells. The objectives of this paper are to chart the variation of starburst amacrine cells across the retina, to register the morphological features which are held constant for individual cells, and to examine factors which may remain invariant for the population with change in retinal position. Starburst amacrine cells occur as two completely segregated mirror-symmetrical populations, type a and type b cells, separately serving OFF and ON pathways, respectively. They are treated here as two distinct subpopulations with very similar features. A characteristic morphological feature of both types, related to branching pattern and best seen in flat view, is the location of boutons in the distal annular zone. This is the effective zone of synaptic output, which is constant at 50 to 60% of dendritic field area, regardless of the cell's retinal location. Both type a and type b cells exhibit systematic increase in cell body size and dendritic field diameter, and systematic decrease in frequency of branching and of synaptic boutons with perpendicular distance from the visual streak. These rates of increase or decrease fall off considerably at distances greater than about 1.5 mm dorsal and ventral to the visual streak, but at this distance, the dendritic field diameters of cells in dorsal retina are about 65% larger than the diameters of cells in ventral retina. When type a and type b cells are closely compared, they are seen to differ in several respects. Branching patterns of type a and type b cells differ slightly, the latter being more highly branched, and the normalized branching frequency histograms, characteristic for each type, remain constant with changing retinal position. At the same retinal location type a cells always have larger dendritic field diameters than type b cells. This difference is significant in ventral retina, out to a distance of at least 4.5 mm from the streak. The maximum percentage difference in size occurs not at mid-visual streak, but about 1.5 mm ventral to the streak. The population statistics of dendritic field overlap and areal dendritic coverage have been calculated using published data on cell densities. It is concluded that overlap is extraordinarily high (k greater than 25), more than 10 times that calculated for retinal ganglion cells.(ABSTRACT TRUNCATED AT 400 WORDS)
How straight do axons grow?
Authors: Katz MJ
Published: March 2018

Detailed growth paths of embryonic frog and chick axons were measured as the axons elongated in dispersed cultures on acid-rinsed glass surfaces. Mathematical analyses demonstrate that, under these conditions, axons do not grow randomly but tend to grow straight. Growth cones appear to actively alternate sides--right and left from the straight line of growth--and the growth cone neck exhibits all possible angles, but the axon itself maintains a fairly constant orientation. It appears that an axonal resistance to bending may be the cause of the intrinsic tendency for relatively straight axonal growth. The natural straightness of axonal growth may be an important developmental determinant of certain in vivo axon patterns.
Monoclonal antibodies which distinguish certain classes of neuronal and supporting cells in the nervous tissue of the nematode Caenorhabditis elegans
Authors: Okamoto H , Thomson JN
Published: March 2018

Monoclonal antibodies were generated using mice immunized with total homogenates of Caenorhabditis elegans adults or early larvae. Two of them were shown to distinguish a certain class of neuronal or supporting cells in the nervous tissue of this animal. Their histological specificities were studied in detail by indirect immunofluorescence on a whole mount preparation of animal head (or tail); for one of the antibodies further analysis was done by immunoelectron microscopy with the aid of a colloidal gold probe. An application of this antibody to a mutant of C. elegans is also described.
Development of the rat superior cervical ganglion: ganglion cell maturation
Authors: Rubin E
Published: March 2018

The development of superior cervical ganglion cells has been studied in the fetal rat. Sympathetic cells appear first in thoracic sites and, one day later, in cervical sites; localized proliferation among these cells gives rise to the superior cervical and stellate ganglia. The maturation of superior cervical ganglion cells was examined by staining these neurons with horseradish peroxidase in fetal preparations maintained in vitro. This method showed that cells begin to extend processes at widely different times, without regard to a given cell's position in the ganglion. Postganglionic axons appear as early as day 12 of gestation (E12), when only a small number of ganglion cells have emerged from the mitotic cycle. The axon generally originates from a point on the ganglion cell body that is oriented toward the route of subsequent axon extension. As the postganglionic axons grow, they do not branch within the superior cervical ganglion and branch only to a slight extent, if at all, within developing peripheral nerves. Axonal growth is rapid, and fibers reach relatively remote sympathetic targets as early as E15. Dendrites first appear on E14 and are elaborated by ganglion cells that have already extended their axons. By the end of gestation, the number of primary dendrites found on some cells already falls within the range found in maturity.
Motor nerve terminal outgrowth and acetylcholine receptors: inhibition of terminal outgrowth by alpha-bungarotoxin and anti-acetylcholine receptor antibody
Authors: Pestronk A , Drachman DB
Published: March 2018

Motor nerves undergo extensive terminal outgrowth when the muscles they supply are “functionally denervated.” In this study, we have investigated the role of the acetylcholine receptors (AChRs), newly appearing in such muscles, in promoting nerve terminal outgrowth. The amount of outgrowth was determined by morphometric measurement of nerve terminal branching, endplate length, and ultraterminal sprouts, in cholinesterase-silver-stained neuromuscular junctions. Presynaptic neuromuscular blockade with botulinum toxin induced pronounced nerve terminal outgrowth in both the rat and mouse soleus muscles, although ultraterminal sprouts did not occur in the rat soleus. By contrast, postsynaptic neuromuscular blockade with alpha-bungarotoxin (alpha- BuTx) induced little or no terminal outgrowth, although it caused “functional denervation.” Moreover, alpha-BuTx and anti-AChR antibody inhibited the terminal outgrowth otherwise induced by botulinum toxin. Other types of motor nerve growth, such as nerve regeneration, were unaffected by these agents. Our results are consistent with the concept that extrajunctional AChRs in skeletal muscle play an important role in the control of motor nerve terminal outgrowth at neuromuscular junctions.
Longitudinal topography and interdigitation of corticostriatal projections in the rhesus monkey
Authors: Selemon LD , Goldman-Rakic PS
Published: March 2018

Anterograde tracing methods were used to examine the topographic organization and interrelationship of projections to the neostriatum arising from various areas of association cortex. In contrast to the currently accepted topographic schema, all cortical areas examined project to longitudinal territories that occupy restricted medial- lateral domains of the neostriatum. The posterior parietal and superior arcuate cortices project to dorsolateral portions of the neostriatum; the dorsolateral and dorsomedial frontal cortices project centrally; and the orbitofrontal, anterior cingulate, and superior temporal projections are distributed to ventromedial regions of the caudate nucleus and putamen. In coronal section, cortical terminal fields form a diagonal strip, extending from the dorsal, ventricular border of the caudate nucleus, through the fiber bundles of the internal capsule, to the ventral margin of the putamen. Double labeling studies, in which two cortical areas were injected in the same animal, indicated that convergence of input within neostriatal domains is not governed by reciprocity of corticocortical connectivity. Thus, the interrelationship of projections arising from connectionally linked cortical areas ranged from nearly complete segregation of terminal fields (e.g., from dorsolateral prefrontal and orbital cortices) to extensive overlap of terminal domains (e.g., from frontal and temporal cortices). In the latter case, detailed analysis revealed that frontal and temporal terminals actually were interdigitated rather than intermixed within the zone of overlap. The present findings suggest a new conceptualization of corticostriatal topography in the primate which emphasizes the longitudinal arrangement of cortical terminal domains. Additionally, these findings provide a map for functional parcellation of the neostriatum on the basis of its cortical innervation which may prove useful to understanding normal striatal function, as well as the symptomatology associated with neostriatal injury and disease.
Opioid pathways in an avian retina. II. Synaptic organization of enkephalin-immunoreactive amacrine cells
Authors: Watt CB , Su YY , Lam DM
Published: March 2018

Peroxidase-antiperoxidase immunocytochemistry was utilized to investigate the synaptic organization of enkephalin-like immunoreactive amacrine (Enk-amacrine) cells in the chicken retina. An initial light microscopic analysis revealed that immunostained cell bodies were situated in either the second or third tier of cells from the border of the inner nuclear and inner plexiform layers. The processes of such cells extended into the inner plexiform layer where they ramified as a fine plexus in sublaminae 1 and 3 to 5. At the ultrastructural level, enkephalin-positive somas exhibited a rather dense and evenly distributed peroxidase reaction product throughout their cytoplasm. Furthermore, the nucleus of Enk-amacrine cells was characterized by a round, unindented nuclear membrane. Immunoreactive processes of such cells were found to receive synaptic input from unstained amacrine and bipolar cells. Immunolabeled varicosities formed conventional synaptic contacts onto other vesicle-filled, nonimmunoreactive profiles tentatively suggested to originate from amacrine cells. Bipolar cell terminals did not receive synaptic input from stained varicosities of enkephalin-immunoreactive amacrine cells. Moreover, each of the above synaptic relationships were identified in each of sublaminae 1, and 3 to 5 of the inner plexiform layer. In addition, labeled varicosities of Enk-amacrine cells synapsed upon unstained processes which lacked synaptic vesicles and possibly arise from ganglion cells. Enkephalin- positive processes were also observed to synapse upon the vitreal pole of unstained somas situated in the innermost cell row of the inner nuclear layer. Lastly, large immunoreactive varicosities of Enk- amacrine cells were often characterized by the presence of large dense- core vesicles in addition to typical, small agranular synaptic vesicles.
Metabolic alterations in rat somatosensory cortex following unilateral vibrissal removal
Authors: Dietrich WD , Ginsberg MD , Busto R , Smith DW
Published: March 2018

Local cerebral metabolic rates for glucose were studied by [14C]-2- deoxyglucose autoradiography in adult rats following acute and chronic unilateral deafferentation, with particular attention to the barrel field regions of the primary somatosensory cortex. Deafferentation was produced by permanently removing all of the large whiskers (vibrissae) on one side of the face. Data from experimental animals were then compared to data from sham-operated controls at 1, 5, 10, 15, 30, and 60 days after deafferentation. The rate of glucose utilization was maximally depressed at day 1 in the deafferented barrel field. After that, there was a progressive recovery of glucose utilization toward control levels at each subsequent time point. In contrast, glucose utilization in the barrel field associated with the intact set of whiskers increased by day 5 and remained elevated throughout the duration of the experiment. Similar patterns of altered cerebral metabolism were observed following unilateral infraorbital nerve transection. These results demonstrate that interference with normal somatosensory input causes a transient decrease in glucose metabolism of the contralateral cortical barrel-field and, in addition, causes long-term increments in glucose metabolism in the ipsilateral cortical barrel field--a structure not normally influenced by acute manipulation.
Accessory abducens nucleus and conditioned eye retraction/nictitating membrane extension in rabbit
Authors: Disterhoft JF , Quinn KJ , Weiss C , Shipley MT
Published: March 2018

The role of accessory abducens nucleus neurons in the conditioned eye retraction/nictitating membrane extension response was defined in the rabbit. Horseradish peroxidase injections into the retractor bulbi muscle showed that accessory abducens nucleus is the principal location of its motor-neurons. Single and multiple unit recording in accessory abducens indicated that these motor neurons show a marked responsiveness to corneal and periorbital stimulation and fire in close correlation with conditioned, unconditioned, or spontaneous eye retraction/nictitating membrane extension. Complete lesions of accessory abducens showed, at most, a partial reduction of the conditioned and unconditioned eye retraction response. Section of the extraocular muscles, other than retractor bulbi, also caused a partial reduction of the eye retraction response. Accessory abducens lesions, combined with extraocular muscle section, were necessary to dramatically reduce the eye retraction response permanently. These experiments demonstrated that accessory abducens is a primary controller of eye retraction through its axons to retractor bulbi. The other extraocular muscles act in concert with retractor bulbi to elicit conditioned and unconditioned eye retractions.
Retrograde axonal transport of endogenous phospholipids in rat sciatic nerve
Authors: Armstrong R , Toews A , Ray RB , Morell P
Published: March 2018

Anterograde axonal transport of phospholipids occurs at a rate of several hundred millimeters per day. However, although labeled precursors are incorporated into phospholipids in the neuronal cell bodies within several hours, these newly synthesized phospholipids are committed to transport over a much longer period of time. Thus, maximal accumulation of radioactive lipids in axons and nerve endings does not occur for several days (e.g., 4 to 7 days in rat optic tract and sciatic nerve). We have now investigated the retrograde axonal transport of endogenous phospholipid molecules in sensory neurons of rat sciatic nerve. Labeled phospholipids were delivered to axons and nerve endings of these cells by anterograde axonal transport following injection of [2–3H] glycerol into the L5 dorsal root ganglion. At various times following precursor injection two ligatures, 9 mm apart, were applied to the mid-thigh region of the sciatic nerve. Animals were sacrificed 3 to 48 hr after nerve ligation, nerves were dissected and sectioned into 5-mm segments, and phospholipid radioactivity in each segment was determined. The time-dependent accumulation of labeled phospholipids distal to the distal ligature demonstrated their retrograde axonal transport. The time course of retrograde transport for these phospholipids was more prolonged and peaked several days later than the time course for the anterograde transport phase. Further information regarding the relationship between radioactive phospholipids arriving at the nerve endings by anterograde transport, and their subsequent “turn-around” and retrograde transport back to the nerve cell bodies, was obtained by analyzing the phospholipid class label distribution of both of these transport phases at various times following precursor injection.
Evidence of functional mossy fiber sprouting in hippocampal formation of kainic acid-treated rats
Authors: Tauck DL , Nadler JV
Published: March 2018

In the rat hippocampal formation, degeneration of CA4-derived afferent fibers provokes the growth of mossy fiber collaterals into the fascia dentata. These aberrant fibers subsequently form granule cell-granule cell synapses. The hippocampal slice preparation was employed to determine whether these recurrent connections are electrophysiologically functional. Hippocampal slices were prepared 12 to 21 days after the bilateral destruction of CA4 neurons with either intracerebroventricular or intravenous kainic acid (KA). In slices from control rats, antidromic stimulation of the mossy fibers elicited a single population spike in the granular layer of the fascia dentata. In contrast, when slices from some KA-treated rats were similarly tested, antidromic stimulation elicited multiple population spikes. This effect was not reproduced by blocking inhibitory transmission with bicuculline methiodide. Slices from other KA-treated rats fired a single population spike, but an antidromic conditioning volley increased the amplitude of a subsequent antidromic population spike by 5 to 15%. In slices from control rats, on the other hand, an antidromic conditioning volley always either decreased or failed to alter the amplitude of an antidromic test response. Superfusion with Ca2+-free medium containing 3.8 mM Mg2+ reversibly abolished all effects of KA administration. Abnormal responses to antidromic stimulation correlated with the loss of CA4 neurons and the growth of supragranular mossy fiber collaterals in the same animals. These results suggest that supragranular mossy fiber collateral sprouts form a functional recurrent excitatory circuit. These aberrant connections may further compromise hippocampal function already disrupted by neuronal degeneration, such as by facilitating seizure activity.
Release of acetylcholine from embryonic neurons upon contact with muscle cell
Authors: Chow I , Poo MM
Published: March 2018

When a spherical muscle cell (myoball) was manipulated into contact with either the soma or the neurite of an isolated neuron in 2-day-old Xenopus nerve-muscle cultures, depolarizations similar to miniature endplate potentials (MEPPs) were frequently detected in the muscle cell. These depolarizations occurred within minutes after myoball-soma contact and within seconds after myoball-neurite contact. They had time course and amplitude distribution similar to those of the MEPPs recorded from naturally occurring neuromuscular synapses between neurites and muscle cells found in the same cultures, but they occurred at a lower frequency and had smaller average amplitudes. These depolarizations were induced by acetylcholine (ACh) since they were reversibly blocked by addition of d-tubocurarine into the culture, and they were abolished in muscle cells pretreated with alpha-bungarotoxin before contact with the neuron. Greater than 60% of the neuronal population in these cultures released ACh upon this direct muscle contact. The appearance of MEPP-like potentials in the myoball upon contact with an isolated neuron suggests that the cellular machinery responsible for ACh release is present throughout the neuron and that packages of ACh molecules are available for release prior to nerve- muscle synapse formation. We also found that neurons which had previously made synapse with other muscle cells in the culture all failed to release ACh from the soma and showed reduced release capability at the neurite for the first 30 min to 1 hr of contact with a myoball. This finding suggests that, during synapatogenesis, there is a depletion of ACh molecules and/or substances responsible for the triggering of their release in the extrasynaptic regions of the neuron.
Characterization of muscarinic cholinergic receptors in the brains of copper-deficient rats
Authors: Farrar JR , Hoss W , Herndon RM , Kuzmiak M
Published: March 2018

In order to assess a possible role for copper as a regulator of muscarinic receptors in vitro, the receptor was characterized in rats made copper deficient by a dietary regimen. In forebrain regions there was a decrease in both the affinity of the receptors for [3H]-1- quinuclidinyl benzilate and the density of receptors in the copper- deficient animals compared with control animals. Copper treatment in vitro of homogenates from deficient animals did not reverse the in vivo effects on antagonist binding but, rather, decreased receptor occupancy and ligand affinity in a manner similar to copper treatment of control homogenates. Minimally deficient rats displayed very similar changes in receptor properties compared with the more severely deficient animals. Minimal copper deficiency produced robust effects on the binding of agonists, increasing ID50 and derived dissociation constants. The addition of copper to the assay medium caused an apparent reversal of the in vivo effect of copper deficiency on agonist binding, decreasing ID50 and derived dissociation constants to values near those observed with homogenates from normal animals in the presence of copper. Since copper deficiency has dramatic effects on both receptor number and the binding of agonists to muscarinic receptors in the central nervous system, it is suggested that copper, because of its ability to form complexes with some proteins, may have an endogenous role in the regulation of the receptor.
Prolonged glucocorticoid exposure reduces hippocampal neuron number: implications for aging
Authors: Sapolsky RM , Krey LC , McEwen BS
Published: March 2018

The hippocampus of the rat loses neurons with age, a loss which may eventuate in some of the functional impairments typical of senescence. Cumulative exposure to corticosterone (CORT) over the lifespan may be a cause of this neuronal loss, as it is prevented by adrenalectomy at mid- age. In this study, we demonstrate that prolonged exposure to CORT accelerates the process of cell loss. Rats were injected daily with sufficient CORT to produce prolonged elevations of circulating titers within the high physiological range. Animals treated for 3 months (chronic subjects) resembled aged rats in a number of ways. First, both groups had extensive and persistent depletions of CORT receptors in the hippocampus; in the case of chronic rats, no recovery of receptor concentrations occurred 4 months after the end of steroid treatment. Second, autoradiographic analysis revealed that the receptor depletion was due, in part, to a loss of CORT-concentrating cells, especially in the CA3 cell field. Remaining cells bound significantly less [3H]corticosterone than did those of control rats. Finally, analysis of size distributions of hippocampal cell bodies indicated that chronic subjects lost neurons of the same size as those lost in the aged hippocampus. Furthermore, chronic subjects also had increased numbers of small, darkly staining cells of CA3; these corresponded in size to the dark glia whose numbers increase in the aged hippocampus, and which are thought to infiltrate in response to neuronal damage or destruction. Thus, this study supports the hypothesis that cumulative exposure to CORT over the lifespan may contribute to age-related loss of neurons in the hippocampus, and that prolonged stress or exposure to CORT accelerates this process.
A mechanism for glucocorticoid toxicity in the hippocampus: increased neuronal vulnerability to metabolic insults
Authors: Sapolsky RM
Published: March 2018

Glucocorticoids appear capable of damaging or destroying hippocampal neurons. There is a progressive loss of such neurons with age, and the process can be prevented by adrenalectomy at mid-age or accelerated by prolonged exposure to high circulating titers of glucocorticoids. The present study examines possible mechanisms for this steroid action. Rats were either adrenalectomized, intact, or treated with corticosterone (CORT) sufficient to produce prolonged elevations of titers in the high physiological range. After 1 week, unilateral hippocampal microinfusions were made with either kainic acid (KA) or 3- acetylpyridine (3-AP). Doses of these hippocampal neurotoxins were chosen to produce small-sized lesions. Treatment with CORT exacerbated the extent of damage following neurotoxin infusion, whereas adrenalectomy attenuated the damage. Additional studies eliminated some potential mechanisms for this phenomenon. CORT did not directly alter the intrinsic toxicity of the compounds but, rather, altered the sensitivity of target cells to them. As evidence, no potentiation of damage in CORT-treated animals occurred in KA-sensitive brain regions lacking CORT receptors. Since CORT did not increase the diffusion or binding of [3H]KA in the hippocampus, it appears unlikely that CORT potentiated toxin-induced damage by influencing the specific mechanism of action of any toxin. Finally, the general nature of the CORT potentiation of damage was supported by the markedly different postulated mechanisms of toxicity of KA and 3-AP. We hypothesize that CORT exerts its extensive catabolic effects upon target cells to produce generalized metabolic vulnerability in hippocampal neurons possessing high concentrations of CORT receptors, thereby sensitizing them to varied metabolic insults.
Regulation of synthesis of the neurosecretory egg-laying hormone of Aplysia: antagonistic roles of calcium and cyclic adenosine 3':5'- monophosphate
Authors: Bruehl CL , Berry RW
Published: March 2018

The potential role of cyclic nucleotides and calcium as regulators of neuropeptide biosynthesis was examined in the bag cell neurons of Aplysia, which produce and secrete a peptide egg-laying hormone (ELH). Elevated external potassium, which stimulates ELH biosynthesis, increased bag cell cAMP levels when assayed in the presence of a phosphodiesterase inhibitor. Dopamine and serotonin, which increase bag cell cAMP levels, both stimulated ELH synthesis, as did the phosphodiesterase inhibitor isobutylmethylxanthine, the specific adenylate cyclase activator forskolin, and the phosphodiesterase- resistant cAMP analogue 8-benzylthio-cAMP. The stimulatory effect on peptide biosynthesis appears to be specific for cAMP, as bag cell cGMP levels were not altered significantly by high potassium or forskolin, and 8-bromo-cGMP did not stimulate ELH synthesis. In contrast to cAMP, intracellular calcium inhibits ELH production: biosynthesis of the peptide was elevated in a 0 Ca2+/EGTA medium and reduced in the presence of the Ca2+ ionophore A23187. Synthesis was also elevated in the presence of the calmodulin inhibitor calmidazolium. Treatment of intact bag cells with 0 Ca2+/EGTA or A23187 did not alter cAMP levels significantly, suggesting that calcium exerts its effect on peptide synthesis independently of cAMP. The antagonistic effects of cAMP and calcium on ELH synthesis parallel their effects on bag cell excitability, suggesting that, in these cells, neuropeptide synthesis and secretion are co-regulated by the same intracellular messengers.