bluuebunny/crossref_metadata_2025 huggingface dataset:
Systemic morphine suppresses noxious stimulus-evoked Fos protein-like immunoreactivity in the rat spinal cord
Authors: Presley RW , Menetrey D , Levine JD , Basbaum AI
Published: March 2018

Previous experiments have shown that noxious stimulation increases expression of the c-fos proto-oncogene in subpopulations of spinal cord neurons. c-fos expression was assessed by immunostaining for Fos, the nuclear phosphoprotein product of the c-fos gene. In this study, we examined the effect of systemic morphine on Fos-like immunoreactivity (FLI) evoked in the formalin test, a widely used model of persistent pain. Awake rats received a subcutaneous 150 microliters injection of 5% formalin into the plantar aspect of the right hindpaw. The pattern of nuclear FLI was consistent with the known nociceptive primary afferent input from the hindpaw. Dense labeling was recorded in the superficial dorsal horn (laminae I and IIo) and in the neck of the dorsal horn (laminae V and VI), areas that contain large populations of nociceptive neurons. Sparse labeling was noted in lamina IIi and in the nucleus proprius (laminae III and IV), generally considered to be nonnociceptive areas of the cord. Fos immunoreactivity was also evoked in the ventromedial gray, including laminae VII, VIII, and X. There was no labeling in lamina IX of the ventral horn. Since FLI was time dependent and distributed over several spinal segments, we focused our analysis where maximal staining was found (L3-L5) and at the earliest time point of the peak Fos immunoreactivity (2 hr). Twenty minutes prior to the formalin injection, the rats received morphine (1.0, 2.5, 5.0, or 10 mg/kg, s.c.) or saline vehicle. Two hours later, the rats were killed, their spinal cords removed, and 50 microns transverse sections of the lumbar enlargement were immunostained with a rabbit polyclonal antiserum directed against Fos. Prior treatment with morphine sulfate profoundly suppressed formalin-evoked FLI in a dose- dependent and naloxone-reversible manner. The dose-response relationship of morphine-induced suppression of FLI varied in different laminae. To quantify the effect of morphine on FLI, labeled neurons in sections taken from the L4/5 level of each rat were plotted with a camera lucida and counted. Staining in the neck of the dorsal horn (laminae V and VI) and in more ventral laminae VII, VIII, and X, was profoundly suppressed by doses of morphine which also suppress formalin- evoked behavior. Although the labeling was also significantly reduced in laminae I and II, at the highest doses of morphine there was substantial residual labeling in the superficial dorsal horn. These data indicate that analgesia from systemic opiates involves differential regulation of nociceptive processing in subpopulations of spinal nociceptive neurons.
The effects of postembryonic receptor cell addition on the response properties of electroreceptive afferents
Authors: Sanchez DY , Zakon HH
Published: March 2018

The weakly electric fish Sternopygus detects electric fields with a receptor organ called a tuberous electroreceptor. Previous studies have shown that an electroreceptive afferent fiber innervates a single organ in small fish and that as fish grow some of these organs divide, giving rise to daughter organs; these divide in turn to produce a cluster of organs. All of the organs in a cluster are innervated by the original afferent, which sprouts new terminals to accommodate them. Other organs, however, seldom divide. Thus, the distribution of the number of tuberous organs per afferent becomes increasingly bimodal with fish body length (Zakon, 1984a). In order to investigate the effect of organ addition on neural coding within the afferent fiber, activity was recorded from single units within the anterior branch of the anterior lateral line nerve in fish of a range of sizes. It was found that, as fish increase in body length, the best frequency, sharpness of tuning, and sensitivity increase in a subset of afferents, while others remain essentially unchanged. This results in an increasingly bimodal distribution of these physiological measures with increasing fish body length. These results suggest that the afferents that innervate multiple receptor organs are more sensitive and possess higher best frequencies than those that innervate 1 or 2 organs. This was confirmed by dye injections of electroreceptive fibers with Lucifer yellow.(ABSTRACT TRUNCATED AT 250 WORDS)
Fictive locomotion in the fourth thoracic ganglion of the crayfish, Procambarus clarkii
Authors: Chrachri A , Clarac F
Published: March 2018

Bath application of muscarinic agonists induced rhythmic motor activity in an in vitro preparation of the thoracic nervous system of the crayfish, Procambarus clarkii. In 70% of the cases, the rhythm was organized into 1 of the 2 normal patterns: “backward” walking or “forward” walking. In the rest (30%), the ganglion produced either a series of bursts of impulses or no rhythm at all, just an increase in the tonic activity. When it was isolated from all ascending and descending afferents, the fourth thoracic ganglion was still able to generate rhythmic motor output during bath application of muscarinic agonists. In certain motor neurons, muscarinic agonists induced plateau potentials. Under these conditions, some of these motor neurons were able to change the period of the motor pattern, which might suggest that these motor neurons were part of the central pattern generator (CPG) for locomotion. In the presence of 5 x 10(-6)M TTX, the membrane potential of these motor neurons continued to oscillate with organized rhythmic membrane potential oscillations into 1 of the 2 patterns. Under these conditions, current injection into certain motor neurons demonstrated that they continued to affect the CPG. Two classes of walking leg interneurons have been found. First, there are those with a sustained membrane potential: injection of a steady depolarizing current into some of these interneurons induced rhythmic activity in all thoracic motor nerves, even in the absence of any pharmacological activation. Second, there are those with an oscillating membrane potential: these seemed to enable silent motor neurons to be involved in an ongoing rhythm.
Chronic naltrexone treatment increases expression of preproenkephalin and preprotachykinin mRNA in discrete brain regions
Authors: Tempel A , Kessler JA , Zukin RS
Published: March 2018

Long-term blockade of brain opioid receptors by the opiate antagonist naltrexone increases methionine-enkephalin content in the striatum and nucleus accumbens (Tempel et al., 1984). To determine whether these changes in peptide levels reflect increased peptide synthesis, we examined preproenkephalin mRNA content in discrete brain regions of control (placebo-treated) and chronic naltrexone-treated animals by Northern analysis. Chronic naltrexone treatment (8 d) led to an approximately 12-fold increase in the striatal content of preproenkephalin mRNA relative to that of control animals. In contrast, no statistically significant change was observed in striatal mRNA for cyclophilin (1B15) or actin. Small increases in preproenkephalin mRNA content occurred in the hippocampus (+40%) and hypothalamus (+19%). No significant changes occurred in the frontal cortex. Increases in levels of the mRNA were seen as early as 24 hr after antagonist treatment. In contrast, changes in opioid receptor density required 3–4 d to reach half-maximal up-regulation after chronic antagonist treatment. Recent evidence has suggested that substance P is regulated by opioid peptides. To determine whether substance P synthesis is altered by chronic antagonist treatment, the mRNA corresponding to the precursor for substance P was examined using a probe for exon-7 of the preprotachykinin gene. Preprotachykinin mRNA content in the striatum was increased 6-fold after chronic antagonist treatment relative to that of control animals. Substance P content was increased 3-fold after chronic antagonist treatment. These data suggest that chronic blockade of brain opioid receptors leads to the increased synthesis of both enkephalin and substance P in the striatum and that these changes are relatively specific.(ABSTRACT TRUNCATED AT 250 WORDS)
Evaluation of long-term potentiation of small compound and unitary EPSPs at the hippocampal CA3-CA1 synapse
Authors: Friedlander MJ , Sayer RJ , Redman SJ
Published: March 2018

Long-term potentiation (LTP) was evaluated for small monosynaptic CA3- mediated EPSPs in CA1 neurons in the guinea pig hippocampal slice. Small EPSPs included those elicited by stimulation of Schaffer axon collaterals of several CA3 neurons (160–480 microV amplitude, n = 40 EPSPs in 40 neurons) and those elicited by stimulation of an individual CA3 neuron (89–563 microV amplitude, n = 14 EPSPs in 11 neurons). Various protocols were employed to induce LTP and were deemed successful as evaluated by recording sustained enhancement of the mean peak amplitude of conventionally elicited large compound EPSPs and extracellular field potentials. However, in 47 of 54 cases, tetanization did not lead to a potentiation of the small or unitary EPSPs. In 9 cases, it was possible to directly evaluate the compound EPSP (elicited by stimulating a group of CA3 neuron's axons) and the unitary EPSP (elicited by stimulating a single CA3 neuron) in the same CA1 neuron. The tetanization protocol was successful in inducing LTP in 7 of 9 of these CA1 neurons as evaluated by the compound EPSP but resulted in LTP for only 1 of 9 of the unitary EPSPs for the same neurons. One explanation for these results is a threshold mechanism controlling the expression of LTP. Although LTP induction occurred in most cases, it is proposed that a critical level of depolarization (achieved by the test activation of a sufficient number of CA3 neurons) is necessary so that the enhancement at the modified synapse is expressed.
Insect olfactory neurons in vitro: morphological and immunocytochemical characterization of male-specific antennal receptor cells from developing antennae of male Manduca sexta
Authors: Stengl M , Hildebrand JG
Published: March 2018

Sex-pheromone components released by Manduca sexta females are detected solely by male-specific olfactory receptor neurons that innervate long sensilla trichodea on the male antennae. To facilitate studies of the development and physiology of these receptor cells, we have produced primary in vitro cultures of cells dissociated from pupal male antennae. These cultures comprise several morphological types of cells, 2 of which have been characterized immunocytochemically with a pair of monoclonal antibodies that were shown previously to recognize certain antigens in olfactory receptor neurons at defined stages of development. The good correlation between in vivo and in vitro expression of these antigens suggests that the immunocytochemically recognized cells are olfactory receptor neurons that follow at least partially their normal course of differentiation in vitro.
Correlation between GAP43 and nerve growth factor receptors in rat sensory neurons
Authors: Verge VM , Tetzlaff W , Richardson PM , Bisby MA
Published: March 2018

In mature rat sensory neurons, expression of the gene for the growth- associated protein, GAP43, was studied by in situ hybridization with a cDNA probe. Among neurons in normal lumbar dorsal root ganglia, labeling for GAP43 mRNA was heterogeneous, approximately one-half of the neurons being densely labeled. To characterize the latter population, individual neurons were examined in adjacent sections processed either for GAP43 hybridization or NGF-receptor radioautography. Virtually all neurons with high-affinity NGF binding sites had high basal levels of GAP43 mRNA and most GAP43-positive neurons bore NGF receptors. Another NGF-responsive population, sympathetic neurons in the superior cervical ganglion, also had high basal concentrations of GAP43 mRNA. Further co-localization studies in dorsal root ganglia were performed with immunohistochemistry for somatostatin and enzyme histochemistry for acid phosphatase. The latter 2 groups of sensory neurons have been previously shown to lack high- affinity receptors and were here shown to have low basal concentrations of GAP43 mRNA. From this and earlier studies, it can be assumed that substance P-immunoreactive neurons and strongly positive CGRP neurons synthesize GAP43 at high basal rate. One week following peripheral nerve transection, almost all neurons had high concentrations of GAP43 mRNA without correlation with NGF binding. Intrathecal infusion of NGF after the sciatic nerve was cut did not strongly influence this post- traumatic elevation in GAP mRNA. In normal dorsal root ganglia, neurons that have high-affinity NGF binding sites and are therefore potentially responsive to NGF also have high basal rates of synthesis of GAP43.(ABSTRACT TRUNCATED AT 250 WORDS)
The organization and connections of somatosensory cortex in marmosets
Authors: Krubitzer LA , Kaas JH
Published: March 2018

Microelectrode mapping methods were used to define and describe 3 representations of the body surface in somatosensory cortex of marmosets: S-I proper or area 3b of anterior parietal cortex, S-II, and the parietal ventral area (PV) of the upper bank of the lateral sulcus. In the same animals, injections of anatomical tracers were placed into electrophysiologically determined sites in area 3b or S-II. Mapping results and patterns of connections were later related to architectonic fields that were delimited in sections cut parallel to the surface of manually flattened cortex and stained for myelin. There were several major results. (1) Recordings from area 3b revealed a characteristic somatotopic organization of foot to face in a mediolateral sequence as previously reported in other members of the marmoset family (Carlson et al., 1986). (2) Multiple injections of WGA-HRP in area 3b demonstrated dense, patchy interconnections with ipsilateral S-II, PV, area 3a, and area 1, less dense interconnections with primary motor cortex (M-I), the supplementary motor area (SMA), limbic cortex of the medial wall (L), and rostrolateral parietal cortex of the lateral sulcus (PR), and callosal connections with areas 3b, S-II, and PV. Injections of 3 different tracers into the representation of 3 body regions in area 3b indicated that the connections with areas 3a, 3b, 1, S-II, and PV are topographically organized. (3) Recordings from cortex on the upper bank of the lateral sulcus demonstrated a somatotopic representation of the body surface that matches that of S-II of other mammals. S-II immediately adjoined areas 3b along the dorsal lip of the lateral sulcus. The face representation in S-II was adjacent to the face representation in 3b while the trunk, hindlimb, and forelimb were represented in a caudorostral sequence deeper in the sulcus. (4) Injections in S-II revealed ipsilateral connections with areas 3a, 3b, 1, a presumptive area 2, PV, PR, M-I, SMA, limbic cortex, the frontal eye fields, and the frontal ventral visual area. Dense callosal connections were with S-II and PV. (5) The recordings also revealed a systematic representation just rostral to S-II that has not been previously described in primates.(ABSTRACT TRUNCATED AT 400 WORDS)
Sex differences and thyroid hormone sensitivity of hippocampal pyramidal cells
Authors: Gould E , Westlind-Danielsson A , Frankfurt M , McEwen BS
Published: March 2018

In an effort to determine if sex differences exist in the morphologic characteristics of pyramidal cells and granule cells of the hippocampal formation and whether sex plays a role in determining thyroid hormone sensitivity of these neuronal populations, we used single-section Golgi impregnation to examine the effects of neonatal thyroid hormone administration on hippocampal cells from the brains of adult rats of both sexes. Quantitative analyses of control brains revealed sex differences in the number of primary dendrites and the number of spines on the apical dendritic shaft of CA3 pyramidal cells. These differences showed opposite trends; females possessed more primary dendrites, whereas males showed more apical excrescences. Neonatal treatment with thyroid hormone resulted in long-lasting and dramatic changes of the entire CA3 pyramidal cell. CA3 pyramidal cells from thyroid hormone- treated animals showed significantly larger cell body areas, greater numbers of dendritic branchpoints, and longer dendrites. In addition, CA3 pyramidal cells from thyroid hormone-treated animals showed changes in the morphological characteristics which were shown to be sexually dimorphic; treatment resulted in significantly greater numbers of both primary dendrites and apical excrescences. These treatment differences occurred in both sexes and were of equal magnitude, regardless of sex. On the other hand, no sex differences in the morphologic parameters examined were detected for pyramidal cells in the CA1 region. Moreover, neonatal thyroid hormone treatment did not affect the cell body area, dendritic branch points, or the length of dendrites of these cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Selective expression of an endogenous lactose-binding lectin gene in subsets of central and peripheral neurons
Authors: Hynes MA , Gitt M , Barondes SH , Jessell TM , Buck LB
Published: March 2018

Cellular interactions in a variety of vertebrate non-neural tissues are thought to be mediated by cell surface carbohydrate structures. The detection of cell-specific surface carbohydrates and carbohydrate- binding proteins within the embryonic nervous system has raised the possibility that carbohydrate recognition may also contribute to the interactions of developing neurons. Soluble lactose-binding lectins constitute one class of carbohydrate-binding proteins expressed in the vertebrate nervous system. We describe here the isolation of cDNAs from rat brain libraries encoding one of these lectins, RL-14.5, and demonstrate that this protein is not only homologous to other soluble lectins, but also identical in primary sequence to a lectin present in at least one non-neural tissue. RNA blot analysis and in situ hybridization reveal a restricted pattern of expression of RL-14.5 mRNA within the rat nervous system. High levels of RL-14.5 mRNA are present in primary sensory neurons and motoneurons in the spinal cord and brain stem. Moreover, expression of RL-14.5 mRNA in sensory and motoneurons is detectable soon after neuronal differentiation. These findings, together with previous studies demonstrating the selective expression of oligosaccharide ligands for RL-14.5 on the same neurons, are consistent with the idea that carbohydrate-mediated interactions contribute to the development of this subset of mammalian neurons.
Immunolocalization of G protein alpha-subunits in the Drosophila CNS
Authors: Wolfgang WJ , Quan F , Goldsmith P , Unson C , Spiegel A , Forte M
Published: March 2018

In order to uncover the role of G proteins in the integrative functioning and development of the nervous system, we have begun a multidisciplinary study of the G proteins present in the fruit fly, Drosophila melanogaster. In this report, we describe the distribution of 3 different G protein alpha-subunits in the adult Drosophila CNS as determined by immunocytochemical localization using affinity-purified antibodies generated to synthetic oligopeptide sequences unique to each alpha-subunit. Western blot analysis of membranes prepared from Drosophila heads indicates that antibodies specific for the Drosophila Go alpha and Gs alpha homologs recognize the appropriate protein species predicted by molecular cloning (Quan et al., 1989; Thambi et al., 1989). The Gi alpha homolog could not be detected in head membranes by Western blotting, consistent with the negligible levels of expression observed for Gi alpha on Northern blots of head mRNA (Provost et al., 1988). However, a Drosophila Gi alpha fusion protein could be detected by these antibodies following expression in E. coli. Immunolocalization studies revealed that the Go alpha and Gs alpha homologs are expressed at highest levels in neuropils and at intermediate levels in the cortex of all brain and thoracic ganglion areas. Only the lamina contained low levels of these alpha-subunits in the CNS. Additionally, Gs alpha appears to be associated with the cell membranes of neuronal cell bodies, while Go alpha has a more diffuse distribution, suggesting its presence in the cytoplasm as well as cell membranes. In contrast to the wide distribution of Go alpha and Gs alpha, Gi alpha has a surprisingly restricted distribution in the CNS. It is present at high levels only in photoreceptor cell terminations, glomerulae of the antennal lobes, and the ocellar retina. Little or no Gi alpha was detected in other brain regions or in the thoracic ganglion. Gi alpha, then, appears to be uniquely associated with some primary sensory afferents and their terminations, suggesting the presence of specific receptor and/or effector systems which mediate the transmission of primary sensory information in Drosophila.
Unit responses evoked in the amygdala and striatum by electrical stimulation of the medial geniculate body
Authors: Clugnet MC , LeDoux JE , Morrison SF
Published: March 2018

Unit activity was recorded from cells and cell clusters in the amygdala and striatum in response to electrical stimulation of the medial geniculate body (MGB) in rats anesthetized with chloral hydrate. Responses were mostly excitatory and were evoked against a relatively silent background (i.e., the units seldom fired between stimuli). The shortest latency responses were recorded in the caudate putamen (CPU), lateral amygdaloid nucleus (AL), and amygdalostriatal transition area (AST). Longer latency responses were obtained from neurons in the basolateral (ABL), basomedial (ABM), and central (ACE) nuclei of the amygdala. Moreover, while responses were evoked in AL, AST, and CPU with 300–500 microA stimuli delivered once every 10 sec, more intense and higher-frequency stimuli were required to obtain responses in ABL, ABM, and ACE. These findings are consistent with anatomical tracing studies showing that AL, AST, and CPU receive direct projections from the MGB and related acoustic processing areas of the thalamus but that ACE, ABL, and ABM do not.
Spatial firing properties of hippocampal theta cells
Authors: Kubie JL , Muller RU , Bostock E
Published: March 2018

Previous studies have shown that complex-spike cells, the most common cell type recorded in the hippocampus of freely moving rats, have the property of spatial firing--that is, a cell will fire rapidly only when the animal is in a particular part of its environment (O'Keefe and Dostrovsky, 1971). In the current study, we analyze the spatial firing of theta cells, the second major class of cells in the hippocampus, which are thought to correspond to nonpyramidal neurons (Fox and Ranck, 1975, 1981). Our purposes were to extend findings from earlier spatial analyses (McNaughton et al., 1983; Christian and Deadwyler, 1986), and to determine whether the spatial firing is cell specific and independent of behavior. Theta cells were recorded from rats in a cylindrical enclosure using techniques previously used for the analysis of spatial firing in complex-spike cells (Muller et al., 1987). The spatial firing patterns of individual neurons appeared as a complex surface with several regions of high and low firing. The ratio of firing from high- to low-rate regions averaged 2.5. These spatial firing patterns were smooth and reproducible, but less so than for complex-spike cells. When a cue card on the wall was moved, theta cell firing patterns remained in register with the cue. Two analyses were performed to determine whether spatial firing patterns were secondary to spatial distributions of behavior. When only locomotor data segments were selected, spatial variations were more clear-cut. In an attempt to test whether theta cells had cell-specific patterns of firing, pairs of theta cells were recorded simultaneously. On all occasions, the firing distribution for each of the cells in a pair was clearly distinctive. These findings support the conclusions that theta cell activity contains a spatial signal that is cell specific and not secondary to other firing correlates.
Cyclic GMP levels and guanylate cyclase activity in pheromone-sensitive antennae of the silkmoths Antheraea polyphemus and Bombyx mori
Authors: Ziegelberger G , van den Berg MJ , Kaissling KE , Klumpp S , Schultz JE
Published: March 2018

Female sex pheromones applied to freshly isolated, living antennae of male Antheraea polyphemus and Bombyx mori led to an increase of cGMP. A 1:1 mixture of 2 pheromone components of Antheraea polyphemus blown for 10 sec in physiological concentrations over their antennal branches raised cGMP levels about 1.34-fold (+/- 0.08 SEM, n = 23) from a basal level of 3.0 +/- 0.6 (SEM, n = 20) pmol/mg protein. Similarly, bombykol elicited a 1.29-fold (+/- 0.13 SEM, n = 23) cGMP increase in antennae of male Bombyx mori from a basal level of 2.7 +/- 0.5 (SEM, n = 24) pmol/mg protein. No cross-sensitivity was found with respect to pheromones from either species. In antennae of female silkmoths, the cGMP response was missing upon stimulation with their own respective pheromones according to the known lack of pheromone receptor cells in the female. cAMP levels in the male antennae of 14.2 +/- 2.9 (SEM, n = 4) pmol/mg protein in A. polyphemus and 15.0 +/- 3.0 (SEM, n = 5) pmol/mg protein in B. mori were not affected by pheromone stimulation. Within 1–60 sec, the extent of cGMP increase in B. mori was independent of the duration of pheromone exposure. The levels of cGMP in pheromone- stimulated antennae of both species remained elevated for at least 10 min, i.e., much longer than the duration of the receptor potential measured in single-cell recordings. Guanylate cyclase activity was identified in homogenates of male and female antennae from both species. The Km of the guanylate cyclase from male B. mori for the preferential substrate MnGTP was 175 microM.(ABSTRACT TRUNCATED AT 250 WORDS)
Nerve growth factor-dependence of herpes simplex virus latency in peripheral sympathetic and sensory neurons in vitro
Authors: Wilcox CL , Smith RL , Freed CR , Johnson EM
Published: March 2018

Previously, we reported that nerve growth factor (NGF) is required to maintain herpes simplex virus (HSV) latency in cultures of rat sympathetic neurons (Wilcox and Johnson, 1987, 1988). Here, we extend these results by showing that NGF was also required to maintain HSV latency in cultures of sensory neurons obtained from dorsal root ganglia of rats, monkeys, and humans. The interruption of the neuronal supply of NGF for 1 hr reactivated HSV, indicating that the latent virus was exquisitely sensitive to perturbations in the concentration or binding of NGF. A species-specific monoclonal antibody directed against the human NGF-receptor, which blocks NGF binding, reactivated latent HSV in human, but not rat, sensory neurons. In contrast, a monoclonal antibody against the rat NGF-receptor, which binds the receptor without blocking NGF action, did not produce reactivation. These results indicate that the effects of NGF on HSV latency are mediated via NGF binding to the NGF receptor. In addition, treatments that interfere with specific steps in the transduction of the NGF signal, including treatment with 6-hydroxydopamine and colchicine, reactivated latent HSV. Further, in neurons harboring latent virus, interruption of protein synthesis or RNA transcription for 1 hr resulted in viral reactivation, suggesting that a short-lived factor may be present in neurons which represses viral reactivation.
Pathfinding by identified growth cones in the spinal cord of zebrafish embryos
Authors: Kuwada JY , Bernhardt RR , Chitnis AB
Published: March 2018

The spinal cord of early (18–20 hr) zebrafish embryos consists of a small number of neurons per hemisegment. The earliest neurons are identified and project growth cones that follow stereotyped, cell- specific pathways to reach their termination sites. We have studied the pathways taken by 4 of the early neurons in order to delineate the cells and structures their growth cones encounter during pathfinding. These neurons are 3 classes of commissural neurons (CoPA, CoSA, and CoB), which have contralateral longitudinal axons, and the VeLD neuron, which has an ipsilateral longitudinal axon. These growth cones encounter a defined set of cells and structures. Commissural growth cones appear to bypass the longitudinal axons of several identified neurons, including those from contralateral commissural neurons they encounter immediately following projection from the cell bodies. In contrast, these growth cones appear to extend in association with the longitudinal axons of commissural cells after crossing the ventral midline. Another set of cells of interest are the floor plate cells, a row of cells that constitute the ventral floor of the cord. At the floor plate growth cones exhibit cell-specific behaviors which may be influenced by the floor plate. (1) The floor plate may attract specific growth cones. The CoPA, CoSA, CoB, and VeLD growth cones all extend to the floor plate while other identified growth cones do not. (2) The floor plate may mediate cell-specific turns and induce some growth cones to cross the midline while inhibiting others from doing so. The commissural growth cones extend directly under the floor plate to cross the midline and turn anterior (CoPA and CoSA) or bifurcate (CoB); the VeLD growth cone turns away from the midline and extends posteriorly. (3) The floor plate may mediate changes in the substrate affinities of growth cones. Commissural growth cones bypass longitudinal pathways before they have encountered the floor plate, but not after. The description of pathfinding by these growth cones suggests that some elements in their environment are ignored while others are not. Most interestingly, a single structure (the floor plate) may mediate multiple, cell-specific effects on spinal growth cones.
Postsynaptic changes at a sensory-to-motoneuron synapse contribute to the developmental loss of a reflex behavior during insect metamorphosis
Authors: Jacobs GA , Weeks JC
Published: March 2018

The larval-pupal transformation of the tobacco hornworm, Manduca sexta, involves the loss of many larval-specific behaviors, including a simple withdrawal reflex of the abdominal prolegs. This reflex is mediated by monosynaptic excitatory connections between afferents that innervate mechanosensory hairs on the proleg [the planta hairs (PHs)] and motoneurons that innervate proleg retractor muscles. In response to hormonal cues during the final days of larval life, the dendritic arbors of proleg retractor motoneurons regress extensively. Intracellular recordings indicate that the synaptic depolarization evoked in proleg motoneurons by electrical stimulation of PH afferents decreases by 78% during the larval-pupal transformation, over the same time course that the motoneuron dendrites regress. During the same period the number of PH afferents and the extent of their central projections may decrease slightly. To test the relative contributions of developmental changes in the presynaptic afferents and postsynaptic motoneurons to the weakening of the reflex pathway, we generated heterochronic mosaic pupae that retained one larval proleg. The PH afferents on the retained proleg retained their larval characteristics while their postsynaptic targets, the proleg motoneurons, appeared to regress normally. In the mosaic hemisegments, electrical stimulation of PH afferents evoked only a small synaptic depolarization of the proleg motoneurons, similar in amplitude to that recorded in normally developing pupae; thus, the developmental status of the afferents was irrelevant to the loss of the reflex. These findings suggest that postsynaptic changes, e.g., structural regression of motoneuron dendrites, may cause the weakening of the reflex pathway. This is the first demonstrated correlation between the hormonally mediated regression of motoneuron dendrites and the loss of a specific behavior during metamorphosis.
Distinct patterns of expression of two VAMP genes within the rat brain
Authors: Trimble WS , Gray TS , Elferink LA , Wilson MC , Scheller RH
Published: March 2018

VAMPs are synaptic vesicle-specific proteins composed of a carboxy- terminal hydrophobic membrane anchor and an approximately 100 amino acid domain oriented towards the cytoplasm. In rat, two 77% homologous VAMP genes are expressed in the CNS. To precisely localize the neurons expressing these 2 forms of VAMP, we have used RNA blotting and in situ hybridization histochemistry with RNA probes specific for the 3′ untranslated regions of the transcripts. These experiments revealed that the 2 genes are expressed in distict, but slightly overlapping, patterns in the rat brain. VAMP-1 expression is localized to a limited number of nuclei, particularly those involved in modulating somatomotor functions, while VAMP-2 expression is more ubiquitous, being found in nuclei associated with autonomic, sensory, and integrative roles. These data suggest that the specific structural features of individual VAMPs may play an important role in synaptic vesicle metabolism.
Factors influencing GAP-43 gene expression in PC12 pheochromocytoma cells
Authors: Costello B , Meymandi A , Freeman JA
Published: March 2018

We have studied factors controlling message levels for the neuronal growth- and plasticity-associated protein, GAP-43. Following exposure of PC12 cells to various effectors, cytoplasmic RNA was isolated and analyzed by Northern transfer and autoradiography using a GAP-43 cDNA probe. Induction by NGF is apparent after 3 hr exposure and reaches maximal levels at 24 hr. Beyond 24 hr, levels remain constant in the continued presence of NGF. Induction is insensitive to variations in culture conditions, such as plating density or substrate, which influence NGF-induced neurite outgrowth. Other inducers, in order of decreasing efficacy, are FGF, dBcAMP, TPA, K+, and EGF. Insulin and retinoic acid are ineffective. Dexamethasone partially inhibited basal expression as well as induction by NGF, FGF, dBcAMP, and TPA. The methyltransferase inhibitor 5′-S-(2-methyl-propyl)adenosine completely inhibited induction by NGF, FGF, and dBcAMP. Inhibition of protein synthesis by cycloheximide partially decreased induction by NGF, FGF, and TPA but slightly enhanced dBcAMP induction. Complete down- regulation of protein kinase C by chronic TPA treatment completely eliminated the TPA response but slightly enhanced induction by NGF. These findings and the results of additivity experiments in which cells were stimulated with various combinations of NGF, dBcAMP and TPA suggest that NGF induction of GAP-43 RNA (1) does not involve activation of protein kinase C but (2) may be mediated partially via activation of protein kinase A.
Visibility of synaptically induced conductance changes: theory and simulations of anatomically characterized cortical pyramidal cells
Authors: Koch C , Douglas R , Wehmeier U
Published: March 2018

A recent report has provided evidence that there are no significant increases in the neuronal input conductance during the response of cortical cells in cat visual cortex to non-preferred visual stimuli (Douglas et al., 1988). A criticism of experiments of this kind is that changes in the membrane conductance occurring in the dendritic tree may not be visible from electrodes that impale the soma. Our paper describes theoretical and numerical results concerning the visibility of synaptically induced conductance changes from intracellular electrodes, in both ideal and anatomically well-characterized cortical neurons. Based on earlier work by Rall (1967), we here derive theoretical expressions for the change in input conductance at any location in a passive dendritic tree resulting from activation of a single synapse and obtain bounds for the effects of multiple synapses. We find that the conductance change measured at the cell body is always less than the sum of the synaptic conductance changes and that this observed conductance change does not depend on the synaptic reversal potential. For the case of an infinite dendritic cylinder, the change in input resistance due to a single synaptic input decays exponentially with distance of the synapse from the recording site. Numerical simulations of synaptic inputs that change approximately as fast as the membrane time-constant produce an increase in input conductance that is only slightly less visible than that of a constant input. We also compute the changes in somatic input conductance of 2 morphologically identified pyramidal cells from cat visual cortex during activity of a single inhibitory basket cell with known synaptic input locations. We find that the increase in conductance due to the activity of the inhibitory basket cells is clearly visible from the cell body of the pyramidal cells and that a 70% reduction in the amplitude of excitation is associated with at least a 30% increase in somatic input conductance, which would be visible in intracellular recordings. Taken together with the negative experimental evidence of Douglas et al. (1988), our results cast doubt on a large class of models of direction selectivity that rely on synaptically mediated inhibitory conductance increases to veto or block excitatory conductances increases.
Serotonin regulates type II corticosteroid receptor binding in hippocampal cell cultures
Authors: Mitchell JB , Rowe W , Boksa P , Meaney MJ
Published: March 2018

Previous work from our laboratory has shown that early postnatal handling of rat pups permanently increases hippocampal type II, but not type I, corticosteroid receptor binding. Handling also increases hippocampal 5-HT turnover, and the effect of handling on type II corticosteroid receptor binding is blocked by concurrent administration of the 5-HT2 receptor antagonist ketanserin. In view of these findings, the present studies examined the effects of 5-HT on type I ([3H]corticosterone) and type II ([3H]RU 28362) corticosteroid receptor binding in dispersed hippocampal cell cultures derived from animals killed at E19–20 in order to verify that 5-HT can act directly on hippocampal cells to alter corticosteroid receptor binding. Both type I and type II receptors were measurable in cultured hippocampal cells and the apparent affinity (Kd) for [3H]corticosterone (0.4 +/- 0.1 nM) and [3H]RU 28362 (0.8 +/- 0.1 nM) was similar to that from studies with intact animals. 5-HT increased type II, but not type I, corticosteroid receptor binding capacity in a dose-related manner, with the maximal effect (+188%) observed at 10 nM 5-HT and no change in the affinity of the receptor for [3H]RU 28362. The effect of 10 nM 5-HT on [3H]RU 28362 binding required a minimum of 4 d exposure and persisted for at least 7 d following the removal of 5-HT. The effect of 10 nM 5-HT on [3H]RU 28362 binding was completely blocked by the 5-HT2 receptor antagonists ketanserin and mianserin. There were no effects of the 5-HT1a antagonist, BMY 7378, or the 5-HT3 antagonist, MDL 72222.(ABSTRACT TRUNCATED AT 250 WORDS)
Physiological differences between strong and weak frog neuromuscular junctions: a study involving tetanic and posttetanic potentiation
Authors: Pawson PA , Grinnell AD
Published: March 2018

This paper describes the extent of release and terminal variability among normal frog sartorius neuromuscular junctions and seeks physiological correlates for these differences. Terminal length varied over approximately a 10-fold range, quantal content and release per unit terminal length (“release efficacy”) over much larger ranges. For purposes of comparison of different junctions, release efficacy in a Ringer's containing 0.25 mM Ca2+ was determined in all cases. In a Ringer's containing 0.1 mM Ca2+, tetanic stimulation causes a buildup of evoked release and of miniature endplate potential (mEPP) frequency. The mEPP frequency at the end of the tetanus is proportional to the evoked release level. Following the tetanus, the mEPP frequency declines in a multiexponential fashion, with the 2 longest decay phases, representing augmentation and posttetanic potentiation (PTP), both having time constants that are positively linearly correlated with the synaptic release efficacy. Longer or higher-frequency tetanic stimulation resulted in a longer time course of decay of mEPP frequency. In a Ca2(+)-free/EGTA Ringer's, tetanic stimulation causes no evoked release, but does lead to an increased mEPP frequency, presumably due to a buildup of free Ca2+ displaced from internal stores by the Na+ influx. Following the tetanus, the mEPP frequency declines to resting level with a time constant that is essentially the same for all junctions, regardless of their release efficacy in Ca2(+)- containing Ringer's. These findings indicate that stronger terminals have a greater influx of Ca2+ per unit length during action potential invasion, but that in the absence of external Ca2+, tetanic stimulation results in comparable release of Ca2+ from internal stores in all terminals and comparable accumulation of Ca2+ in some large compartment, the subsequent emptying of which determines the time course of PTP.
In situ hybridization histochemistry of Ca2+/calmodulin-dependent protein kinase in developing rat brain
Authors: Burgin KE , Waxham MN , Rickling S , Westgate SA , Mobley WC , Kelly PT
Published: March 2018

Oligonucleotide DNA probes were used to determine the distribution of mRNAs encoding the alpha- and beta-subunits of Ca2+/calmodulin- dependent protein kinase type II (CaM-KII) in developing rat brain. The regional and temporal distribution of these mRNAs closely paralleled the distribution and developmental appearance previously reported for their respective protein subunits. alpha-Subunit mRNA was barely detectable in sagittal sections at 4 d postnatal but increased as much as 10-fold in frontal cortex by day 16. beta-Subunit mRNA, on the other hand, was readily detected at 4 d postnatal and changed only slightly during development. Telencephalic structures exhibited the highest levels of CaM-KII mRNA and the brain stem displayed the least. alpha- Subunit mRNA was not observed in cerebellar granule cells and was barely detectable in Purkinje cells, while the beta-mRNA was easily detected in both neuronal types. mRNAs for both alpha- and beta- subunits were present in many neuronal cell bodies; however, only the alpha-subunit mRNA was localized to molecular layers of the hippocampus and lamina I of the frontal cortex. These layers of neuropil are relatively cell sparse and contain extensive dendritic arborizations and synaptic contacts. Since polyribosomes have been observed near hippocampal dendritic spines, the localization of alpha-subunit mRNA to dendrites of pyramidal and dentate granule cells suggests that this subunit is synthesized in situ at postsynaptic sites. The co- localization of translational machinery and high concentrations of CaM- KII in postsynaptic elements suggests an important relationship between alpha-subunit synthesis and the maintenance and plasticity of postsynaptic structures.
Distributed processing of sensory information in the leech. I. Input- output relations of the local bending reflex
Authors: Lockery SR , Kristan WB
Published: March 2018

Sensory processing in the local bending reflex of the leech (Hirudo medicinalis) was studied by examining the input-output relations of the reflex. Sensory cells (P cells) were stimulated singly and in pairs and the responses of the longitudinal muscle motor neurons were recorded. Each pattern of single and paired P cell stimulation produced a unique pattern of motor neuron response. In general, motor neuron response patterns were consistent with the behavioral response of the whole animal.
A quantitative description of NMDA receptor-channel kinetic behavior
Authors: Jahr CE , Stevens CF
Published: March 2018

Currents evoked in neurons of the vertebrate CNS by the glutamate agonist N-methyl-D-aspartate (NMDA) exhibit a marked voltage dependence in the presence of extracellular Mg. At the single-channel level, the addition of external Mg alters single-channel openings from long-lived events to many very short events grouped into bursts of openings. These bursts apparently result from short interruptions of current flow during periods when the channel is in the open configuration. Single- channel currents evoked by NMDA have been studied in outside-out patches of membrane taken from hippocampal CA 1 neurons grown in dissociated cell culture. The effects of changing external Mg concentration and holding potential on the single-channel parameters of open time, closed time, and burst length have been successfully described assuming a 3- or 4-state model with 1 open state, 1 or 2 “blocked” states, and 1 absorbing closed state. Evaluation of the blocking rates over Mg concentrations from 0.2–200 microM indicate that a single “blocking” mechanism cannot account for the short closed states and that a second voltage-dependent but Mg-independent “blocked” state is necessary to explain the data especially at low Mg concentrations.
Changes in striatal dopamine neurotransmission assessed with microdialysis following recovery from a bilateral 6-OHDA lesion: variation as a function of lesion size
Authors: Castaneda E , Whishaw IQ , Robinson TE
Published: March 2018

Intracerebral microdialysis was used to measure the extracellular concentration of striatal dopamine (DA) and its metabolites in freely moving rats depleted of DA by the bilateral infusion of 6- hydroxydopamine into the substantia nigra approximately 1 month earlier. It was found that the basal extracellular concentration of DA remained within the same range as seen in control animals until the size of the lesion exceeded 80% (estimated by the postmortem tissue concentration of DA). In animals with an 80–95% lesion there was only a modest decrease in basal extracellular DA, but as lesion size exceeded 95% there was a marked drop in the basal extracellular concentration of DA. In contrast, the basal extracellular concentration of the DA metabolites showed a more steady decline as a function of lesion size. To determine the ability of the residual population of DA terminals to further increase DA release upon increased demand, animals were given a challenge injection of 1.5 mg/kg of d-amphetamine. Amphetamine-evoked DA release remained within the control range until lesion size exceeded 95%. These results provide direct confirmation for the hypothesis that following recovery from partial bilateral damage to the nigrostriatal DA system in adulthood, there are presynaptic compensatory changes in the remaining population of DA neurons sufficient to “normalize” the extracellular concentration of striatal DA. It is suggested that this normalization of extracellular DA is responsible for the sparing of function seen following the loss of up to 80% of the DA innervation to the striatum and contributes to the recovery of function seen after even more extensive damage (80–95%).(ABSTRACT TRUNCATED AT 250 WORDS)
Serotonin enhances a low-voltage-activated calcium current in rat spinal motoneurons
Authors: Berger AJ , Takahashi T
Published: March 2018

Calcium currents and the effects of 5-HT on these currents were investigated in visually identified motoneurons using whole-cell recording in the neonatal rat spinal cord slice preparation. In current- clamp recording, step depolarizations from a holding potential of about -90 mV produced a low-threshold transient depolarizing response and a high-threshold long-lasting spike. In voltage-clamp recording, low (LVA) and high (HVA) voltage-activated Ca2+ currents were recorded in response to depolarizing voltage steps. Low concentration of Cd2+ (50 microM) did not reduce the amplitude of the LVA current but markedly diminished the HVA current. Bath application of 5-HT (10–50 microM) markedly increased the amplitude of the LVA current without causing a shift in the current (I)-voltage (V) relation. In contrast, 5-HT did not appreciably affect the amplitude of the HVA current. We conclude that 5-HT specifically enhances the LVA Ca2+ current and that this effect together with the previously reported 5-HT-induced inward current (Takahashi and Berger, 1990), would facilitate the excitation of motoneurons.