bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of endogenous opioid peptides on acetylcholine release from the cat superior cervical ganglion: selective effect of a heptapeptide
Authors: Araujo DM , Collier B
Published: March 2018

The present experiments show the presence of both metenkephalin-like and met-enkephalin-Arg6-Phe7-like immunoreactivity in the superior cervical ganglion of the cat; this was determined by radioimmunoassay after high-pressure liquid chromatography separation of tissue extracts. There was measurable efflux of both peptides, as determined by radioimmunoassay of ganglionic perfusates; this measure was increased by thiorphan, an enkephalinase inhibitor. The effect of the 2 peptides on ACh release was determined: The stable analog of methionine- enkephalin, D-Ala2-methionine-enkephalinamide, did not affect ACh release from the ganglion; in contrast, methionine-enkephalin-Arg6-Phe7 significantly depressed evoked ACh release. The effect of met- enkephalin-Arg6-Phe7 to decrease ACh release was antagonized, although only partially, by the opioid antagonist naloxone. Thus, it appears that methionine-enkephalin-Arg6-Phe7 alters ACh release from the superior cervical ganglion by acting, at least in part, on a presynaptic opioid receptor. The results suggest that in the cat superior cervical ganglion, the heptapeptide enkephalin might have a significant role in the regulation of synaptic transmission, which is unrelated to its potential function as a precursor for methionine- enkephalin.
Acetylation of alpha-tubulin in cultured neurons and the induction of alpha-tubulin acetylation in PC12 cells by treatment with nerve growth factor
Authors: Black MM , Keyser P
Published: March 2018

alpha-Tubulin of cultured neurons undergoes a posttranslational modification that lowers its p/(Black and Kurdyla, 1983a). We show here that this modification is due to acetylation. Incubation of cultures with 3H-acetate results in the prominent labeling of a protein that comigrates with alpha-tubulin in 1-dimensional SDS gels, and in 2- dimensional isoelectric focusing X SDS gels, it comigrates with the more acidic alpha-tubulin forms. The labeled material can be immunoprecipitated by monoclonal antibodies to alpha-tubulin but not by antibodies to beta-tubulin. The reaction occurs to equal extent in the presence or absence of 0.1 mM cycloheximide or unlabeled amino acids. These observations indicate that the reaction is posttranslational and is not secondary to conversion of isotopic acetate into amino acids. The posttranslational nature of tubulin acetylation was further established by the demonstration that acetate is incorporated into alpha-tubulin in neurites, which lack the capacity for cytoplasmic protein synthesis. Finally, a monoclonal antibody that is specific for acetylated alpha-tubulin (Piperno and Fuller, 1985) recognizes the acidic variants of alpha-tubulin of cultured neurons that can be labeled by incubation with 3H-acetate. Collectively, these observations indicate that alpha-tubulin of cultured sympathetic neurons undergoes a posttranslational acetylation. Immunofluorescence analyses using a monoclonal antibody specific for acetylated alpha-tubulin revealed that it was present throughout the neuron and showed no obvious regional compartmentalization. We have also shown that alpha-tubulin is acetylated in the NGF-responsive PC12 line of pheochromocytoma cells using biochemical and immunological criteria. However, this modification was detected only in long-term (14 d) NGF-treated cells. The results are discussed in terms of the possible role of acetylation as a local mechanism for regulating microtubule stability.
Glutamate-positive neurons in the somatic sensory cortex of rats and monkeys
Authors: Conti F , Rustioni A , Petrusz P , Towle AC
Published: March 2018

The morphology and laminar distribution of neurons labeled with an antiserum prepared against glutamic acid (Glu) conjugated to keyhole limpet hemocyanin have been studied in the somatic sensory cortex of rats and monkeys. In both species, the vast majority of immunostained neurons are pyramidal; some nonpyramidal neurons are also present. Positive neurons are observed in all cortical layers, although variations are found in the percentage of Glu-positive neurons in the different layers. In rats they are most numerous in layer V (36%), followed by layer II (33%), layer III (32%), and layer VI (29%). In layer IV, 13% of all neurons are positive. Immunoreactive neurons are very sparse in layer I. In monkeys, Glu-positive neurons represent 51% of all neurons in layer V, 49% in layer III, 40% in layers II and VI, and 19% in layer IV. No differences are evident in the laminar distribution of Glu-positive neurons among cytoarchitectonic areas 3a, 3b, 1, and 2. As in rats, Glu-positive neurons are very sparse in layer I. Since Glu and GABA metabolisms are closely related, double-labeling experiments were performed in which thin, adjacent paraffin sections were stained alternately with the anti-Glu serum and with an anti-GABA serum. The 2 populations are almost completely segregated, even though a small fraction of neurons (less than 5%) are labeled by the antisera against both antigens.(ABSTRACT TRUNCATED AT 250 WORDS)
Cell death during gangliogenesis in the leech: bipolar cells appear and then degenerate in all ganglia
Authors: Stewart RR , Gao WQ , Peinado A , Zipser B , Macagno ER
Published: March 2018

The bipolar cells can be recognized very early during gangliogenesis in the leech central nervous system by their expression of antigens that are recognized by the monoclonal antibody Laz1–1. They are the first cells to express these antigens, which are later shared with a distinct set of other cells in the leech nervous system. Their processes extend several segments rostrally and caudally along the forming interganglionic connective nerves; they are first found in anterior segments and gradually appear in more posterior ones over the course of 2–3 d. At about the time bipolar cells appear in the neuromeres of the tail ganglion, those in the most anterior segmental ganglia begin to degenerate. Degeneration proceeds caudally over the next 3 d, until all bipolar cells have disappeared. Bipolar cells are, thus, members of that class of cells that exists for only a short period in neurogenesis and then presumably disappears once its functions are no longer required. These cells' morphology and appearance at the earliest stages in the formation of the interganglionic connective nerves are suggestive of a role in the establishment of these longitudinal pathways in the leech CNS.
The effects of changes in the environment on the spatial firing of hippocampal complex-spike cells
Authors: Muller RU , Kubie JL
Published: March 2018

Using the techniques set out in the preceding paper (Muller et al., 1987), we investigated the response of place cells to changes in the animal's environment. The standard apparatus used was a cylinder, 76 cm in diameter, with walls 51 cm high. The interior was uniformly gray except for a white cue card that ran the full height of the wall and occupied 100 degrees of arc. The floor of the apparatus presented no obstacles to the animal's motions. Each of these major features of the apparatus was varied while the others were held constant. One set of manipulations involved the cue card. Rotating the cue card produced equal rotations of the firing fields of single cells. Changing the width of the card did not affect the size, shape, or radial position of firing fields, although sometimes the field rotated to a modest extent. Removing the cue card altogether also left the size, shape, and radial positions of firing fields unchanged, but caused fields to rotate to unpredictable angular positions. The second set of manipulations dealt with the size and shape of the apparatus wall. When the standard (small) cylinder was scaled up in diameter and height by a factor of 2, the firing fields of 36% of the cells observed in both cylinders also scaled, in the sense that the field stayed at the same angular position and at the same relative radial position. Of the cells recorded in both cylinders, 52% showed very different firing patterns in one cylinder than in the other. The remaining 12% of the cells were virtually silent in both cylinders. Similar results were obtained when individual cells were recorded in both a small and a large rectangular enclosure. By contrast, when the apparatus floor plan was changed from circular to rectangular, the firing pattern of a cell in an apparatus of one shape could not be predicted from a knowledge of the firing pattern in the other shape. The final manipulations involved placing vertical barriers into the otherwise unobstructed floor of the small cylinder. When an opaque barrier was set up to bisect a previously recorded firing field, in almost all cases the firing field was nearly abolished. This was true even though the barrier occupied only a small fraction of the firing field area. A transparent barrier was effective as the opaque barrier in attenuating firing fields. The lead base used to anchor the vertical barriers did not affect place cell firing.(ABSTRACT TRUNCATED AT 400 WORDS)
Pattern formation in the striatum: developmental changes in the distribution of striatonigral neurons
Authors: Fishell G , van der Kooy D
Published: March 2018

The striatum of the mammalian forebrain can be divided into 2 compartments, the patches and the matrix. We have investigated embryonic events involved in the formation of these compartments in rats. Early in development, dopamine fibers from the substantia nigra selectively innervate the patches. In the perinatal striatum, we observed a close match between the distributions of striatal cell bodies with axonal projections to the substantia nigra and patches of afferent dopamine fibers. Striatal cells projecting to the nigra are first seen in the ventrolateral striatum at embryonic day (E) 17. Striatonigral cell bodies are distributed homogeneously through the striatum from E18 to 19. At E20 and until postnatal day 4, these cell bodies are organized into discrete patches. After this time, striatonigral cell bodies assume the dense and homogeneous distribution characteristic of the adult striatum. A retrograde tracer injection in the nigra at E18 (during the early period of homogeneous striatonigral distribution) produces a patchy striatonigral distribution if the embryo is not sacrificed until E21. The number of retrogradely labeled striatonigral cell bodies in a midstriatal section, at times immediately before and after the early homogeneous to patchy changeover did not differ significantly. We suggest that the neurons of the patch compartment of the striatum are born first and project to the substantia nigra first. The patch neurons only become restricted to “patchy” areas as the later-born matrix neurons migrate out into the striatum.
A highly abundant transcript in adult murine cerebellar granule cells contains repetitive sequences homologous to L1
Authors: Schaal H , Goldowitz D , Heinlein UA , Unterbeck A , Ruppert C , Papenbrock T , Muller-Hill B , Vielmetter W , Wille W
Published: March 2018

Cloned cDNA from adult mouse cerebellum composed of subsequences homologous to the L1Md consensus sequence (long interspersed repetitive element “LINE” family of the mouse) hybridizes specifically with large nuclear poly(A)+RNAs that are highly concentrated in the murine and rat cerebellum. These homogeneous L1-related transcripts were localized in the mouse CNS by in situ hybridization with 3H- and biotin-labeled DNA probes. They were found to hybridize to cerebellar granule cells specifically.
Postsynaptic inhibition mediates high-frequency selectivity in the cricket Teleogryllus oceanicus: implications for flight phonotaxis behavior
Authors: Nolen TG , Hoy RR
Published: March 2018

The frequency selectivity of the identified auditory interneuron, Int- 1, in the cricket Teleogryllus oceanicus was examined using intracellular recording and staining techniques. Previous behavioral assays showed that crickets discriminate the low frequencies of the species calling song (4-5 kHz) from the high frequencies contained in the vocalizations of insectivorous bats (Nolen and Hoy, 1986a). Int-1 was excited by frequencies between 3 and 40 kHz, being similar, therefore, to the tympal organ (ear) in its broad range sensitivity; however, it responded differentially to high and low frequencies in terms of the number of action potentials evoked per stimulus tone pulse, the average discharge rate, and the latency of response. It was especially responsive to ultrasound (greater than 20 kHz), discharging at rates up to 400 spikes/sec (average rate), with 10 msec latencies; its response to pulses of the calling song was less than 150 spikes/sec, with 30 msec latencies. Int-1's dynamic range for ultrasound was also quite large, about 50 dB, compared to 20 dB for the calling song frequency. In addition, it responded well to trains of short, batlike pulses of ultrasound. These results are consistent with previous behavioral experiments showing that during flight, Int-1 was both necessary and sufficient for the ultrasound avoidance steering behavior (Nolen and Hoy, 1984), as long as it discharged above a rate of 180 spikes/sec. Ultrasound readily produced such high rates, whereas calling song rarely did; ultrasound reliably evoked avoidance steering over a wide dynamic range, while tone pulses of the calling song rarely did so (Nolen and Hoy, 1986a). A unique source of ipsilaterally mediated inhibition, tuned to the calling song frequency, accounted for the poor response to calling song and hence the neuron's high-frequency selectivity, and the behavioral and physiological effects of 2-tone suppression of high frequencies by the calling song (Nolen and Hoy, 1986b). These results further strengthen Int-1's proposed role as a “bat-detector” during flight and suggest only a limited role in other contexts such as social behavior.
Multiple mechanisms of bursting in a conditional bursting neuron
Authors: Harris-Warrick RM , Flamm RE
Published: March 2018

The anterior burster (AB) neuron in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus, is a conditional burster in the pyloric motor circuit. Bath application of the monoamines dopamine, serotonin, and octopamine induces rhythmic bursting pacemaker potentials in a silent, synaptically isolated AB cell. However, each amine produces a unique and characteristic burst shape, resulting from different ionic dependences of the burst mechanisms. Bursting induced by serotonin or octopamine is critically dependent upon sodium entry through tetrodotoxin-sensitive channels; dopamine-induced bursting is not TTX-sensitive. Dopamine-induced bursting is abolished when extracellular calcium is reduced to 25% of normal; serotonin- and octopamine-induced bursts continue in this saline, although they are abolished in salines with calcium reduced to 10% or less of normal. Quantitative differences between the amines are also seen in the tetraethylammonium (TEA) sensitivity of the burst amplitude and in the dependence of the interburst hyperpolarization on extracellular potassium. These experiments demonstrate that there are both quantitative and qualitative differences in the ionic currents underlying every phase of the bursts induced by the 3 amines. Thus, a single neuron can burst via more than one ionic mechanism.
Transient and chronic neonatal denervation of murine muscle: a procedure to modify the phenotypic expression of muscular dystrophy
Authors: Moschella MC , Ontell M
Published: March 2018

The extensor digitorum longus muscles of 14-d-old normal (129 ReJ ++) and dystrophic (129 ReJ dy/dy) mice were denervated by cutting the sciatic nerve. One denervation protocol was designed to inhibit reinnervation of the shank muscles, the other to promote reinnervation. Chronically denervated muscles (muscles that remained denervated for 100 d after nerve section) exhibited marked atrophy, but the number of myofibers in these muscles (1066 +/- 46 and 931 +/- 62 for the denervated normal and dystrophic muscles, respectively) was similar to the number of myofibers found in age-matched, unoperated normal muscles [922 +/- 28 (Ontell et al., 1984)] and was significantly greater than the number of myofibers found in age-matched dystrophic muscles [547 +/- 45 (Ontell et al., 1984)]. Similar effects on myofiber number were obtained when denervated muscles were allowed to reinnervate. Reinnervation of both normal and dystrophic muscles mitigated the marked atrophy that characterized chronically denervated muscles. The dystrophic reinnervated muscles appeared “healthier” than age-matched, unoperated dystrophic muscles, having 70% more myofibers, less myofiber diameter variability, substantially less connective tissue infiltration, and a greater amount of contractile tissue at their widest girths. The present study demonstrated that it is possible to alter the phenotypic expression of the histopathological changes associated with murine dystrophy, in dystrophic myofibers that are formed during fetal development, by subjecting the muscle to neonatal denervation.
Ultrastructural distribution of 125I-toxin F binding sites on chick ciliary neurons: synaptic localization of a toxin that blocks ganglionic nicotinic receptors
Authors: Loring RH , Zigmond RE
Published: March 2018

Although alpha-bungarotoxin (BGT), a common probe for nicotinic ACh receptors from vertebrate skeletal muscle, binds tightly to many autonomic ganglia, it fails to block nicotinic transmission in most of these ganglia. Recently, we have isolated a second toxin, toxin F, that blocks transmission in several autonomic ganglia, including the chick ciliary ganglion. 125I-Toxin F binds to 2 sites in the ciliary ganglion: one site that is also recognized by BGT and one site that is not. Since the presence of BGT fails to prevent the blocking effect of toxin F, the toxin F site not recognized by BGT most likely represents the neuronal nicotinic receptor. Accordingly, we have localized the binding of 125I-toxin F to both sites, using electron-microscopic autoradiography. After a 45 min incubation, 125I-toxin F binding sensitive to BGT was primarily localized extrasynaptically on the neuronal plasma membranes; however, by 4 hr, much of this site had been internalized. In contrast, the 125I-toxin F binding site not recognized by BGT was highly concentrated near synaptic membranes at both times. Pretreatment of ganglia with the classic nicotinic antagonists dihydro- beta-erythroidine (DHBE) and d-tubocurarine (DTC) significantly reduced 125I-toxin F binding to the toxin F-specific site. The average density of these sites on synaptic membranes was approximately 600 sites/micron 2. We conclude that toxin F binds to 2 pharmacologically distinct sites in the ciliary ganglion and that these sites are distributed differently over the plasma membrane of ciliary neurons. On the basis of the density of the toxin F-specific binding sites at synaptic membranes, we infer that the density of synaptic nicotinic receptors on these neurons is at least 20-fold lower than the density of nicotinic receptors at the vertebrate neuromuscular junction, as determined by BGT binding. These findings are consistent with those of electrophysiological studies, which also suggest low nicotinic receptor densities on ganglionic neurons.
Sinusoidal movement of a grating across the monkey's fingerpad: temporal patterns of afferent fiber responses
Authors: Morley JW , Goodwin AW
Published: March 2018

Responses were recorded from cutaneous afferents innervating mechanoreceptors in the monkey's fingerpad, while gratings of alternating grooves and ridges were moved sinusoidally across their receptive fields. The gratings were specified by their spatial period and the movement by its peak speed: together these determined the peak temporal frequency at which grating ridges passed over the receptive field. During the central 42 degrees of each half cycle of movement, the speed and thus the temporal frequency of the grating ridges remained constant to within 6.6% of their peak values. In this region the responses of all afferents were phase-locked to the temporal sequence of grating ridges. The number of impulses elicited by each grating ridge was a function of the stimulus variables. For all 3 afferent classes--namely, slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs)--the number of impulses per grating ridge increased as the spatial period of the grating increased (while the peak speed of movement was held constant). Similarly, for all 3 classes, the number of impulses per ridge decreased as the peak speed of movement increased (while the spatial period of the grating remained constant). When the peak temporal frequency of the grating ridges was held constant, for SAs and RAs the number of impulses per ridge increased with an increase in the spatial period of the grating and thus with an increase in the peak speed. These phase-locked responses provided information about the peak temporal frequency of the grating ridges independent of the grating spatial period and of the peak speed of movement. The shape of the response profile during a half cycle of movement was different for different afferents. Many of the RA response profiles were close to sinusoidal. The SA and PC profiles tended to have reduced peaks or raised troughs, resulting in flatter profiles. Other departures from sinusoidal profiles were also seen.
The role of depolarization in the survival and differentiation of cerebellar granule cells in culture
Authors: Gallo V , Kingsbury A , Balazs R , Jorgensen OS
Published: March 2018

Cultures greatly enriched in granule cells from early postnatal cerebellum (P8) were grown in a medium containing fetal calf serum. Under the conditions used, nerve cells died, usually within a week, unless the K+ concentration in the medium was greater than or equal to 20 mM. The requirement for elevated [K+]e was manifested by about 3 d in vitro, and after this time continuous exposure to high [K+]e was essential for the survival of the granule cells. The initial morphological and biochemical maturation of the granule cells was similar in the presence and the absence of elevated [K+]e, suggesting that the dependence on depolarizing conditions develops in parallel with the expression of the differentiated characteristics of the cells. The positive effect of elevated [K+]e on granule cell survival was not influenced by preventing bioelectric activity in the cultures with TTX and xylocaine. On the other hand, depolarization-induced transmembrane Ca2+ flux was essential in securing the maintenance of the granule cells. Depolarized nerve cells were compromised when Ca2+ entry was blocked by elevated Mg2+, EGTA, or organic Ca2+ antagonists, while dihydropyridine Ca2+ agonists [BAY K 8644, (+)-(S)-202 79 1 and CGP 28392] were potent agents preventing nerve cell loss in the presence of 15 mM [K+]e, which was ineffective on its own. Calmodulin inhibitors (1 microM trifluoperazine or calmidazolium) blocked the beneficial effect of K+-induced depolarization on granule cells. The comparison of the timing of the differentiation and innervation of the postmitotic granule cells in vivo with the development of the K+ dependence in vitro would indicate that depolarization of the granule neurons in culture mimics the influence of the physiological stimulation in vivo through excitatory amino acid receptors, including N-methyl-D-aspartate receptors, involving Ca2+ entry and the activation of a Ca2+/calmodulin- dependent protein kinase.
Morphological changes in leech Retzius neurons after target contact during embryogenesis
Authors: Jellies J , Loer CM , Kristan WB
Published: March 2018

Segmental variation in identified neurons may provide an opportunity to examine extrinsic influences on neuronal phenotype, since segmentally homologous neurons must contain much the same intrinsic information, having arisen from very similar or identical precursors. Two large serotonergic Retzius (Rz) cells are found in each segmental ganglion of the leech Hirudo medicinalis. While most Rz cells innervate the body wall in their own segment and, by way of axons in the interganglionic connectives, the body wall of adjacent segments, the Rz cells in ganglia 5 and 6 [Rz(5,6)] lack interganglionic axons and innervate only the reproductive tissue (Glover and Mason, 1986). Here we describe and quantify the development of differences between Rz(5,6) and other Rz cells in peripheral innervation, neuropilar arborization, and soma size. We filled individual Rz cells with Lucifer yellow or HRP in adults and in staged embryos. During the first 72 hr of outgrowth of Rz cell processes, the morphology of Rz(5,6) was indistinguishable from that of other Rz cells. Only after the processes of Rz(5,6) reached the reproductive tissue did they begin to differ from their segmental homologs. This temporal correlation suggests that these morphological differences arise because of some interaction between Rz(5,6) and their target tissue.
Segment-specific morphogenesis of leech Retzius neurons requires particular peripheral targets
Authors: Loer CM , Jellies J , Kristan WB
Published: March 2018

In most segments of the leech, a pair of Retzius (Rz) cells innervate the body wall musculature and skin; however, in the segments specialized for reproduction (midbody segments 5 and 6), these neurons innervate the reproductive tissue instead. Whereas all Rz cells have the same morphology early in embryogenesis, those in the reproductive segments [Rz(5,6)] become considerably different from their segmental homologs. Unlike standard Rz cells, Rz(5,6) do not have axons in the interganglionic connectives or in the body wall (Glover and Mason, 1986). Rz(5,6) also have significantly smaller somata and fewer branches in the ganglionic neuropil than do standard Rz cells (Jellies et al., 1987). Since these differences between Rz cells do not become apparent until after Rz(5,6) processes appear to contact the reproductive tissue primordia, interactions between Rz(5,6) processes and the reproductive tissue may determine the segmental specializations of these neurons. We have tested this possibility by ablating the reproductive tissue primordia early in embryogenesis and subsequently examining Rz(5,6) morphology. In the absence of reproductive tissue, Rz(5,6) became more like standard Rz cells: they retained axons in the interganglionic connectives, they projected into the body wall, and the density of their arborization within the neuropil increased. These results indicate that the development of some segmental specializations of Rz(5,6) involves an interaction with their unique target tissue.
Medial preoptic sexual dimorphisms in the guinea pig. II. An investigation of medial preoptic neurogenesis
Authors: Byne W , Warren JT , Siggelkow I
Published: March 2018

Neurogenesis was studied in the medial preoptic area of the guinea pig by the method of tritiated thymidine autoradiography. Eight cytoarchitectonic divisions were examined, 4 of which display sexual dimorphism and 4 that do not. Neurogenesis in the nonsexually dimorphic divisions was found to end at embryonic day (E) 27, while in each of the sexually dimorphic divisions neurogenesis continued after this and persisted until at least E31 in the central compact and principal portions of the medial preoptic nucleus. Since the testes become active at E25 in the guinea pig (Resko, 1970), it is possible that gonadal secretions influence the proliferation and subsequent developmental processes of neurons destined for the sexually dimorphic nuclei.
Tyrosine hydroxylase immunoreactivity in the rhesus monkey retina reveals synapses from bipolar cells to dopaminergic amacrine cells
Authors: Hokoc JN , Mariani AP
Published: March 2018

The synaptic organization of dopamine-containing amacrine cells in the rhesus monkey retina was studied using immunohistochemistry of tyrosine hydroxylase (TH), the rate-limiting enzyme in the catecholamine synthetic pathway. Cell bodies of the TH-containing neurons were primarily in the innermost tier of the inner nuclear layer. Their synaptic processes, confined to the outermost stratum of the inner plexiform layer, contained mostly small, clear vesicles and were presynaptic to unlabeled amacrine cell processes and cell bodies at junctions that were symmetrical. Synapses onto the TH-immunoreactive neurons were from bipolar cell axon terminals, nonimmunoreactive amacrine cell processes, and other TH-containing amacrine cells in a decreasing order of predominance. The bipolar cells were presynaptic to the TH-containing neuronal processes at ribbon synapses. The size, structure, and position of the bipolar cell axon terminals, which, like the TH-reactive processes, were narrowly confined to the outermost stratum of the inner plexiform layer, indicate that they are recently described giant bistratified bipolar cells. The identification of this bipolar cell input now provides evidence for a pathway from the outer plexiform layer to dopaminergic amacrine cells in the inner plexiform layer via a type of cone bipolar cell.
Electrophysiologically identified nigral dopaminergic neurons intracellularly labeled with HRP: light-microscopic analysis
Authors: Tepper JM , Sawyer SF , Groves PM
Published: March 2018

Intracellular recordings were obtained in vivo from neurons of the rat substantia nigra, pars compacta. Neurons that were identified as dopaminergic by a variety of electrophysiological criteria, including antidromic activation from ipsilateral neostriatum or globus pallidus, were microiontophoretically injected with horseradish peroxidase and examined at the level of the light microscope. Dopaminergic neurons were of medium size and had ovoid, polygonal, or fusiform cell bodies that emitted from 3-6 primary dendrites. Much of the sparse and relatively unbranched dendritic arborization of these neurons remained within pars compacta, except for 1 or 2 large dendrites that were directed ventrally or ventrolaterally into pars reticulata, roughly perpendicular to the plane of the pars compacta. In coronal sections, the dendrites of ovoid- or polygonal-shaped pars compacta neurons were oriented mainly along the dorsoventral axis, whereas fusiform-shaped neurons had dendrites that were oriented primarily mediolaterally. Although some of the dendrites of dopaminergic neurons exhibited variations in diameter, most were not markedly varicose. Dendrites were sometimes sparsely invested with spinelike appendages or other dendritic extrusions, particularly along their distal portions. The axons of dopaminergic pars compacta neurons were emitted from primary or proximal secondary dendrites, and were extremely fine processes, 0.5 micron or less in diameter. No local axon collaterals were observed.
Adaptation of mechanoelectrical transduction in hair cells of the bullfrog's sacculus
Authors: Eatock RA , Corey DP , Hudspeth AJ
Published: March 2018

Adaptation in a vestibular organ, the bullfrog's sacculus, was studied in vivo and in vitro. In the in vivo experiments, the discharge of primary saccular neurons and the extracellular response of saccular hair cells were recorded during steps of linear acceleration. The saccular neurons responded at the onset of the acceleration steps, then adapted fully within 10-50 msec. The extracellular (microphonic) response of the hair cells adapted with a similar time course, indicating that the primary sources of the neural adaptation are peripheral to the afferent synapse--in the hair cell, its mechanical inputs, or both. Evidence for hair cell adaptation was provided by 2 in vitro preparations: after excising the sacculus and removing the accessory structures, we recorded either the extracellular hair cell response to displacement of the otolithic membrane or the intracellular hair cell response to hair bundle displacement. In both cases the response to a step stimulus adapted. The adaptation involved a shift in the displacement-response curve along the displacement axis, so that the cell's operating point was reset toward the static position of its hair bundle. This displacement shift occurred in response to both depolarizing and hyperpolarizing stimuli. Its time course varied among cells, from tens to hundreds of milliseconds, and also varied with the concentration of Ca2+ bathing the apical surfaces of the hair cells. Voltage-clamp experiments suggested that the displacement shift does not depend simply on ion entry through the hair cell's transduction channels and can occur at a fixed membrane potential. The possible role of the displacement-shift process in the function of the frog's sacculus as a very sensitive vibration detector is discussed.
Distribution of synaptic specializations along isolated motor units formed in Xenopus nerve-muscle cultures
Authors: Cohen MW , Rodriguez-Marin E , Wilson EM
Published: March 2018

The capacity of individual muscle cells and neurons to establish synaptic specializations along the entire extent of their neurite- muscle contacts was assessed in culture. Spinal cord neurons derived from embryos of Xenopus laevis were plated at low density in cultures of Xenopus myotomal muscle cells in order to obtain isolated motor units whose neuron and muscle cells were not contacted by any other neuron. These isolated motor units were examined for localization of acetylcholine receptors (AChRs) after staining with fluorescent alpha- bungarotoxin and, in some cases, for localization of a synaptic vesicle antigen by immunofluorescence. The neurite-muscle contacts formed by competent neurons exhibited discontinuous sites of AChR localization occupying about 25% of the contact length as compared with 2% for incompetent neurons. Competent neurons, unlike incompetent ones, established these neurite-associated receptor patches (NARPs) on virtually all the muscle cells they contacted and functionally innervated them. These and other observations on the distribution of NARPs throughout the isolated motor units indicate that the capacity of competent neurons to establish NARPs extends to the limits of growth of most if not all of their neurites, that this capacity is least in the most proximal portions of initial neuritic segments, and that the overall capacity of muscle cells to generate NARPs can be saturated by long lengths of neurite-muscle contact. The results also suggest that even in the absence of competitive interactions between neurons there are spatial discontinuities in neuritic action and/or muscle response during the establishment of NARPs. Synaptic vesicle antigen patches (SVAPs) occurred along the neuritic arbor of all neurons, but their distribution in competent neurons (those which established NARPs) and in incompetent ones differed. For competent neurons the percentage of neurite length occupied by SVAPs was 4.8-fold greater on muscle cells than off, whereas the corresponding value for incompetent neurons was only 1.5-fold. This large preferential localization of SVAPs along neurite-muscle contacts of competent neurons was further associated with a colocalization of SVAPs and NARPs that was greater than predicted by chance. These results suggest that muscle cells are much more effective in influencing the distribution of synaptic vesicles along the neuritic arbor of competent neurons than along the arbor of incompetent neurons and that this influence is greatest at sites of postsynaptic differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)
Selective D1 and D2 dopamine agonists differentially alter basal ganglia glucose utilization in rats with unilateral 6-hydroxydopamine substantia nigra lesions
Authors: Trugman JM , Wooten GF
Published: March 2018

he relative roles of D1 and D2 dopamine receptor stimulation in mediating the antiparkinsonian effects of dopaminergic drugs remain unclear. To determine the functional metabolic consequences of selective dopamine receptor stimulation, we used 2-deoxyglucose (2-DG) autoradiography to examine the effects of the D1 agonist SKF-38393 and the D2 agonist LY-171555 on regional cerebral glucose utilization (RCGU) in rats with unilateral 6-hydroxydopamine (6-OHDA) substantia nigra lesions. SKF-38393 (0.5-25.0 mg/kg) and LY-171555 (0.01-5.0 mg/kg) produced indistinguishable behavioral responses, including vigorous contralateral rotation. Treatment with each drug similarly increased glucose utilization, dose-dependently, in the parafascicular thalamus, subthalamic nucleus, deep layers of the superior colliculus, and lateral midbrain reticular formation ipsilateral to the nigral lesion; glucose utilization was decreased in the ipsilateral lateral habenula. By contrast, the D1 and D2 agonists differentially altered glucose utilization in the entopeduncular nucleus (EP) and the substantia nigra pars reticulata (SNr). SKF-38393, 5.0 and 25.0 mg/kg, increased glucose utilization 127 and 275%, respectively, in the pars reticulata ipsilateral to the lesion. LY-171555, 1.0 and 5.0 mg/kg, caused maximal contralateral turning, yet did not alter glucose utilization in the ipsilateral SNr. The glucose utilization response of the ipsilateral EP paralleled that of the SNr demonstrating large increases following administration of SKF-38393 and minimal change following the use of LY-171555. The results demonstrate that the selective D1 agonist reproduces the marked glucose utilization increases (2-3-fold above control values) in the EP and SNr that were previously observed using L-DOPA and apomorphine in this model, whereas the selective D2 agonist does not.(ABSTRACT TRUNCATED AT 250 WORDS)
Inhibition of in vitro peripheral myelin formation by monoclonal anti- galactocerebroside
Authors: Ranscht B , Wood PM , Bunge RP
Published: March 2018

This work investigates the role of galactocerebroside (GalC) in peripheral myelin formation. A monoclonal antibody against GalC was introduced into a myelinating culture system consisting of rat sensory neurons and Schwann cells, without other cell types. At levels that saturated Schwann cell surface GalC, anti-GalC IgG prevented by more than 99% the appearance of myelin sheaths. Ensheathment and basal lamina deposition were unaffected and many Schwann cells were in the 1:1 relationship that typically develops between Schwann cells and axons prior to myelination. Thus, the anti-GalC antibody did not interfere with the formation of the mesaxon but prevented its elongation. When experimentally restrained from myelination, Schwann cells did not accumulate the myelin proteins PO and basic protein; only low levels were expressed. The proposed mechanism of inhibition is the removal of GalC from Schwann cell surfaces by internalization of the GalC-anti-GalC antigen-antibody complex. This apparently prevented the interaction of adjacent cell surfaces during the elongation of Schwann cell membranes that constitute the myelin lamellae.
Autoradiographic localization and biochemical characterization of peripheral type CCK receptors in rat CNS using highly selective nonpeptide CCK antagonists
Authors: Hill DR , Campbell NJ , Shaw TM , Woodruff GN
Published: March 2018

Two potent and highly selective nonpeptide antagonists, L-365,031 [1- methyl-3-(4-bromobenzoyl)amino-5-phenyl-3H-1,4 benzodiazepin-2-one] and 3H-L-364,718 [1-methyl-3-(2-indoloyl)amino-5-phenyl-3H-1,4 benzodiazepin-2-one] were used to localize “peripheral” CCK receptors in rat brain. In autoradiographic experiments, L-365,031 displaced 125I- Bolton Hunter CCK-8 binding from the interpeduncular nucleus (IPN) (IC50 = 7 X 10(-8) M), the area postrema (AP), and the nucleus tractus solitarius (NTS) without influencing specific binding to other areas, such as the cerebral cortex or the spinal tract of the trigeminal nerve. Desulfated CCK preferentially inhibited 125I-CCK binding to cerebral cortex (IC50 = 7 X 10(-8) M) rather than IPN (IC50 greater than 1 X 10(-6) M) or AP-NTS. In the medulla the localization of 3H-L- 364,718 binding was similar to L-365,031-sensitive 125I-CCK-8 binding and was found in the AP and medial, but not lateral, aspects of the NTS. In membranes prepared from IPN, NTS, and AP, 3H-364,718 binding was of high affinity (Kd = 0.14 nM), saturable (Bmax = 20 fmol/mg protein), and inhibited by compounds previously shown to act at pancreatic CCK receptors. The receptors labeled by 3H-364,718 were modulated by guanyl nucleotide, which reduced agonist affinity 10-fold without affecting antagonist binding. The localization and high density of CCK receptors in AP and NTS suggest that these receptors may play an important role in processing sensory afferent information.
The role of spiking local interneurons in shaping the receptive fields of intersegmental interneurons in the locust
Authors: Laurent G
Published: March 2018

Intracellular recordings were made simultaneously from pairs of spiking local and intersegmental interneurons in the mesothoracic ganglion of the locust Schistocerca gregaria (Forskal). The spiking local interneurons belong to a midline group, and the intersegmental interneurons to a lateral-posterior population that projects ipsilaterally to the metathoracic ganglion. Both respond to mechanosensory inputs from one middle leg. The receptive fields of both types of interneurons were plotted and the contribution of the local interneurons to the shaping of the receptive fields of the intersegmental interneurons was studied. The spiking local interneurons are excited by specific arrays of exteroreceptors and proprioceptors of one leg. They make inhibitory connections with specific intersegmental interneurons which thus have corresponding inhibitory regions to their receptive fields. For example, inhibition from local interneurons with inputs from hairs or campaniform sensilla on the tarsus could sharpen the boundaries of the excitatory receptive field of an intersegmental interneuron by lateral inhibition. Inhibition from local interneurons with inputs from joint proprioceptors suppresses the excitation of an intersegmental interneuron during the antipreferred direction of movement. Rapid alternate movements about one joint can in this way be signaled by an intersegmental interneuron in a phase-locked manner. Certain intersegmental interneurons are excited by exteroreceptive inputs and inhibited by proprioceptive signals, or vice versa. The inhibition could become significant during walking, where the excitatory and inhibitory inputs to an interneuron are likely to be evoked during the different phases of a step cycle. The inhibitory regions of the receptive field of an intersegmental interneuron have never been found to be smaller than the excitatory regions of the receptive field of a presynaptic local interneuron and can result from converging inhibitory inputs from several spiking local interneurons. The inhibitory connections are highly specific: Several local interneurons may be excited by a particular stimulus that also inhibits an intersegmental interneuron, but only a small proportion of the former are the cause of the inhibition in the intersegmental interneuron.
Serotonergic afferents to the rat olfactory bulb: I. Origins and laminar specificity of serotonergic inputs in the adult rat
Authors: McLean JH , Shipley MT
Published: March 2018

This is a study of the chemoanatomical organization of the projection from the raphe nuclei to the main olfactory bulb in the rat. A heavy projection from the dorsal and median raphe nuclei to the main olfactory bulb was shown by both retrograde and anterograde tracing techniques. Following injections of 1% wheat germ agglutinin- horseradish peroxidase (WGA-HRP) into the main olfactory bulb, up to 1300 neurons were retrogradely labeled in the dorsal and median raphe nuclei, a much larger number than has been suggested by previous studies. By combining 5-HT immunofluorescence with True blue retrograde fluorescent labeling, it was determined that the vast majority of raphe neurons that project to the olfactory bulb contain serotonin. Injections of WGA-HRP into dorsal and/or median raphe produced dense anterograde labeling in the glomeruli, while fewer labeled fibers were observed in the external plexiform layer, internal plexiform layer, and granule cell layer. In contrast to the number of other centrifugal afferents to the bulb, a significant contingent of fibers from the raphe nuclei enters the main olfactory bulb (MOB) from outside in, i.e., via the olfactory nerve layer. Serotonergic fibers in MOB were visualized by immunocytochemistry, and the distribution of specific 5- HT fibers closely matched the distribution of anterograde terminal label resulting from injections of WGA-HRP in the raphe nuclei. The serotonergic fibers have a specific laminar distribution and morphology in MOB. Thus, the density of the serotonergic innervation to the glomerular layer is 2–3 times that of any other layer in MOB. In addition to their preferential innervation of the glomeruli, glomerular and infraglomerular serotonergic fibers are morphologically different. Serotonergic fibers located in the glomerular layer are generally thick (0.25–0.60 micron) compared to the thinner (0.25–0.35 micron) fibers that predominate in infraglomerular layers. Another difference is that the glomerular fibers often contain varicosities that are greater than 1 micron in diameter, while varicosities along infraglomerular fibers are usually barely larger than the axonal diameter. Finally, glomerular fibers are much more intensely stained than infraglomerular fibers. Electrolytic lesions of the dorsal and median raphe caused a total depletion of serotonin fiber staining in the bulb, demonstrating that the raphe nuclei are the sole source of the serotonergic input to the main olfactory bulb. Thus, it has been demonstrated that serotonergic neurons in dorsal and median raphe project very heavily to glomeruli and less heavily to other layers in the main olfactory bulb.(ABSTRACT TRUNCATED AT 400 WORDS)
Serotonergic afferents to the rat olfactory bulb: II. Changes in fiber distribution during development
Authors: McLean JH , Shipley MT
Published: March 2018

The present studies have defined the developmental time course and distribution patterns of serotonergic fibers in the main olfactory bulb (MOB) using immunocytochemistry, anterograde tracing and image analysis. The results indicate that the deployment of serotonergic fibers to the main olfactory bulb is essentially a postnatal event in the rat. During the first 4 d after birth, 5-HT fibers infiltrate and begin to arborize in the MOB. The density of fibers in each layer is sparse during this period, but increases rapidly. By postnatal day 8 all layers are much more heavily innervated by 5-HT fibers. The surge of fiber growth into all layers is rapid; the fibers arborize earlier at caudal than at rostral levels. This may be related to the increased metabolic activity that is reported to occur selectively in the caudal parts of the immature olfactory bulb. After the second postnatal week, 5-HT fiber density increases much more gradually in all layers except the glomerular layer; in the glomerular layer, 5-HT fiber density continues to increase rapidly. It is also during this time that the olfactory bulb begins to grow substantially in volume. Bulb volume increases from the second week into adulthood (greater than 60 d); during the same period, the density of 5-HT remains relatively constant in the infraglomerular layers. Thus, from the second week onward, the growth of 5-HT fibers appears to be closely linked to the increasing volumes of these layers. The density of 5-HT fibers in the glomerular layer, however, continues to increase from the second postnatal week. Thus, the density of fibers in the glomerular layer increases more than the increase in glomerular size, indicating that the glomerular 5-HT fibers are proliferating more than could be accounted for by simple glomerular expansion. In the adult, 5-HT fibers are 2–3 times denser in the glomerular than the infraglomerular layers (McLean and Shipley, 1987). This preferential innervation of glomeruli may be the result of a protracted period of arborization by glomerular versus infraglomerular fibers. This could be due to the prolonged focal release of a trophic factor by glomerular-associated neurons or to the earlier production of an inhibitory factor by infraglomerular neurons.