bluuebunny/crossref_metadata_2025 huggingface dataset:
N-methyl-D-aspartate receptor antagonists reduce synaptic excitation in the hippocampus
Authors: Hablitz JJ , Langmoen IA
Published: March 2018

The hypothesis that synaptic excitation in the CA1 region of the hippocampus is mediated in part by N-methyl-D-aspartate (NMDA) receptors was tested using intra- and extracellular recording techniques. Synaptic potentials elicited by stratum radiatum stimulation were examined in individual neurons before and after bath application of the NMDA receptor antagonist, DL-2-amino-5- phosphonovalerate (APV). This antagonist reduced both excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs). When IPSPs were suppressed by the addition of picrotoxin, EPSPs were seen in isolation. APV reduced these EPSPs but did not block synaptic transmission. This antagonist demonstrated anticonvulsant actions when tested against picrotoxin-induced epileptiform activity. These results suggest that, as in the spinal cord and neocortex, synaptic excitation in the CA1 region of the hippocampus is partially mediated by APV-sensitive NMDA receptors. The fact that synaptic activity is not blocked by NMDA antagonists indicates that EPSPs in CA1 neurons are not mediated solely by this receptor.
A time-comparison circuit in the electric fish midbrain. I. Behavior and physiology
Authors: Carr CE , Heiligenberg W , Rose GJ
Published: March 2018

Behavioral experiments show that the weakly electric fish, Eigenmannia, detects differences in timing as small as 400 nsec between electric signals from different parts of its body surface. The neural basis of this remarkable temporal resolution was investigated by recording from elements of the phase-coding system, a chain of electrotonically connected neurons devoted to the processing of temporal information. Each element of this system fires a single action potential for every cycle of the electric signal (either the fish's own electric organ discharge or a sinusoidal signal of similar frequency). For phase- coding primary afferents and midbrain neurons, the temporal resolution was determined by measuring each unit's capacity to lock its spike to a particular phase of the stimulus cycle. The jitter of a neuron's response (measured as the standard deviation of the timing of the spikes with respect to the stimulus) decreases from the level of the primary afferent (mean = 30 microsec) to the midbrain torus (mean = 11 microsec); these results can be correlated with morphological measures of convergence. The temporal resolution of single neurons is still inferior to that displayed at the behavioral level.
Cellular physiology of the turtle visual cortex: distinctive properties of pyramidal and stellate neurons
Authors: Connors BW , Kriegstein AR
Published: March 2018

The electrophysiological properties of neurons in the three-layered dorsal cortex of the turtle, Pseudemys scripta elegans, have been studied in vitro. Intracellular recordings suggested two distinct classes of neuronal behavior. Cell labeling with either Lucifer Yellow or horseradish peroxidase revealed that these behaviors correlated with the two morphological classes of cortical neurons: pyramidal cells and stellate cells. Examination of Golgi-stained neurons of dorsal cortex did not uncover any other obvious classes. Pyramidal cells had their somata in the cell layer, and extended several densely spined apical dendrites through the molecular layer to the pia. They also had spiny basilar dendrites directed through the subcellular layer toward the ependymal border. Physiologically, pyramidal cells had relatively prolonged action potentials that showed marked frequency adaptation during a sustained suprathreshold current pulse. Their most striking characteristic was a tendency to fire two discrete sizes of action potential, one small (mean = 34 mV) and of relatively low threshold, the other large (mean = 76 mV) and of higher threshold. We hypothesize that at least some small spikes arise from distal dendritic sites, whereas large spikes are somatically generated. Both spikes were tetrodotoxin-sensitive, although calcium-dependent electrogenesis occurred when potassium channels were blocked. In contrast to pyramidal cells, the somata of stellate cells were found in the molecular and subcellular zones. Their dendrites tended to be horizontally oriented and spine-free. Stellate cells had relatively brief action potentials, each of which was followed by a large but short-lasting undershoot of membrane potential. Stellate cells showed little or no spike frequency adaptation. Spike amplitudes were always relatively uniform and large (mean = 73 mV). Thus, in the dorsal cortex of turtles, the pyramidal cells, which are projection neurons, and stellate cells, which are local GABAergic inhibitory neurons, have distinctly different membrane characteristics. The physiological properties of the two types of turtle cortical neurons are very similar to their counterparts in cortical structures of the mammalian telencephalon.
Cellular physiology of the turtle visual cortex: synaptic properties and intrinsic circuitry
Authors: Kriegstein AR , Connors BW
Published: March 2018

We have examined the synaptic physiology of the isolated dorsal cortex of the turtle, Pseudemys scripta elegans. Electrical stimulation of afferent pathways elicited distinct, stereotyped responses in pyramidal and stellate neurons. Single shocks evoked a long-lasting barrage of excitatory postsynaptic potentials (EPSPs) in stellate cells, and led to a burst of several action potentials. Under the same circumstances, pyramidal cells displayed a small amount of short-latency excitation, but this was accompanied by a profound and prolonged set of inhibitory post-synaptic potentials (IPSPs). Synaptic excitation of the distal dendrites of pyramidal cells could evoke dendritic action potentials that were visible at the soma as small all-or-none spikes rising from the hyperpolarized level of the IPSP. There appeared to be two mechanistically different types of IPSPs in pyramidal cells. The first occurred at short latency, could produce a very large conductance increase, reversed polarity at -71 mV, and was chloride-dependent. The second was generally smaller and more protracted, had a relatively negative reversal potential of -85 to -95 mV, and was insensitive to chloride injection. Focal application of small doses of the putative inhibitory neurotransmitter gamma-aminobutyric acid (GABA) onto the somata of pyramidal cells caused a conductance increase and hyperpolarization. This response had features in common with the short- latency IPSP, including an identical reversal potential. Application of large doses of GABA to the somata of pyramidal cells or smaller doses to their dendrites elicited multiphasic or purely depolarizing responses that were at least partly due to time- or space-dependent shifts of the equilibrium potential of the response. Bicuculline methiodide, a potent GABA antagonist, depressed both the responses to GABA and the short-latency IPSP, but not the long-latency IPSP; synchronized epileptiform burst discharges also resulted. These findings, together with responses to locally applied electric shocks and the excitatory amino acid glutamate, suggested that inhibition of pyramidal cells was generated intrinsically by stellate cells, and that the cortical circuit provides pathways for both feedforward and feedback GABAergic inhibition. The data also suggest that pyramidal cells are mutually excitatory. These features are similar to the basic intrinsic circuitry in the telencephalic cortices of mammals.
Heterogeneous localization of protein kinase C in rat brain: autoradiographic analysis of phorbol ester receptor binding
Authors: Worley PF , Baraban JM , Snyder SH
Published: March 2018

Protein kinase C is a calcium- and phospholipid-stimulated enzyme present in high concentration in the brain. Phorbol esters are potent tumor promoters that bind to specific receptors with high affinity. Several lines of evidence indicate that the phorbol ester receptor is identical to protein kinase C. To determine the distribution of protein kinase C, we have localized phorbol ester receptors in the rat brain by autoradiography, using [3H]phorbol 12,13-dibutyrate ([3H]PDBu) and have performed a variety of lesions to assess the nature of the cellular elements possessing the binding sites. The [3H]PDBu binding sites in the rat brain are discretely localized and primarily associated with neurons. Evidence is presented for localization to intrinsic neurons of the cortex and hippocampus, terminals of the striatonigral projection, a projection to the molecular layer of the dentate gyrus, and to dendrites of Purkinje cells.
Development of choline acetyltransferase (CAT) in the sympathetic innervation of rat sweat glands
Authors: Leblanc G , Landis S
Published: March 2018

It has been postulated that the developing sympathetic innervation of rat eccrine sweat glands changes from adrenergic to cholinergic under the influence of its target. In agreement with previous evidence that the sympathetic innervation of adult rat sweat glands is cholinergic, we found that choline acetyltransferase (CAT)-immunoreactive nerve fibers are present in adult glands, and that gland-rich chunks of adult footpads contain CAT enzyme activity. We were therefore interested in determining when CAT activity is first expressed in the developing gland innervation. Low levels of acetylating activity were observed in rat footpads as early as postnatal day 4, when sympathetic fibers first contact the glands. A greater than fourfold increase in CAT specific activity occurred between postnatal days 11 and 21. Neonatal treatment of rats with the adrenergic neurotoxin 6-hydroxydopamine (6-OHDA) eliminated most of the CAT activity in 14 and 19 d footpads. In contrast, the acetylating activity observed prior to day 11 was unaffected by neonatal 6-OHDA treatment, and only slightly reduced by the selective CAT inhibitor, naphthylvinylpyridine. These results indicate that the sympathetic fibers that innervate rat sweat glands do not acquire detectable levels of CAT activity until a full week after they contact the glands.
Sensitivity to painful and nonpainful electrocutaneous stimuli in monkeys: effects of anterolateral chordotomy
Authors: Greenspan JD , Vierck CJ , Ritz LA
Published: March 2018

Four Macaca nemestrina monkeys were trained to pull a manipulandum to escape electrocutaneous stimulation (ES) applied to either leg. The intensities of stimulation which the monkeys chose to escape were those that humans identify as painful. The duration of escape trials was inversely related to stimulus intensity, and the force of escape responses was directly related to ES intensity. Reflexive responses were elicited by stimulus intensities below and above the escape threshold, and the force of the flexion reflexes was a negatively accelerating function of stimulus magnitude. The monkeys were also trained to respond, for water reinforcement, to cued, low-intensity ES. The stimulus intensities detected for water reinforcement were 50–100 X less than the escape thresholds. Following unilateral, anterolateral chordotomy, all monkeys demonstrated a large reduction in percentage of escape responding to stimulation of the contralateral leg. When the animals did escape contralateral stimulation, the latencies to respond were longer than preoperatively. The percentage and latency of escape responses to stimulation of the ipsilateral leg were not changed following chordotomy. Despite the depression of contralateral pain reactivity, the animals continued to respond to low levels of stimulation on the detection task, demonstrating that anterolateral chordotomy reduced the painfulness of strong stimulation without eliminating sensibility for low levels of stimulation. However, postoperative detection thresholds were consistently higher contralaterally than ipsilaterally. This effect resulted from slight contralateral decreases and significant ipsilateral increases in sensitivity to low levels of ES (relative to preoperative values). Thus, contralateral axons in the anterolateral column contribute to detection of light cutaneous stimulation, and chordotomy appears to disinhibit inputs from large myelinated afferent fibers to ipsilateral neurons in the spinal gray matter caudal to the lesion. The strictly contralateral slowing and reduction in percentage of pain reactivity by chordotomy correlated with reports from human patients. However, reflexive measures did not suffice as indicants of pain sensitivity. The chordotomies produced bilateral attenuations of reflexive amplitudes. Also, the force of operant escape responses was reduced with stimulation of either side. Thus, the disfacilitation of motoric reactions extended both rostral and caudal to the spinal lesions that interrupted propriospinal axons in the vicinity of the ventral horns.
Protein-synthetic machinery at postsynaptic sites during synaptogenesis: a quantitative study of the association between polyribosomes and developing synapses
Authors: Steward O , Falk PM
Published: March 2018

Previous studies have revealed dramatic accumulations of polyribosomes under growing spine synapses, suggesting a critical role for protein synthesis at the postsynaptic site during synaptogenesis. The present study quantitatively analyzes the distribution of polyribosomes under synapses during developmental synaptogenesis in the rat's dentate gyrus. The middle molecular layer of the suprapyramidal blade of the dentate gyrus was examined electron-microscopically at 1, 4, 7, 10, 15, 20, and 28 d of age. At each age, we evaluated (1) synapse density (the number of synapses/100 micron2 of neuropil), (2) the width of the molecular layer, (3) the proportion of spine synapses with underlying polyribosomes, and (4) the number of polyribosome-containing synapses/1000 micron2 of neuropil. From the first two measures, an estimate was obtained of the total extent of synaptogenesis, taking into account both the increase in synapse density and the increase in total area of neuropil. At 1 d of age, very few synapses were found in the molecular layer of the dentate gyrus, and those that were present were quite immature in appearance. Synapse density increased about 140- fold between 1 and 28 d of age, from an average of 0.36 synapses/100 micron2 at 1 d of age to 49 synapses/100 micron2 at 28 d of age. An inverse relationship was found between synapse density and the proportion of synapses with polyribosomes. Between 1 and 7 d of age, about 60% of the spine synapses had one or more polyribosomes under the spine base. Thereafter, the proportion of spines with polyribosomes decreased as synapse density increased. Similarly, the proportion of shaft synapses with underlying polyribosomes was greatest between 1 and 7 d postnatal, and decreased thereafter. While the proportion of synapses with polyribosomes was greatest between 1 and 7 d, the actual number of polyribosome-containing synapses/1000 micron2 of neuropil was negligible at 1 d, increased to a peak at 7 d of age, and then decreased as synapse density increased. Qualitatively, the most dramatic accumulations of polyribosomes were also found at 7 d of age. We conclude that spine-associated polyribosomes represent a structural specialization of dendrites at sites of synapse construction and as such may represent a marker for growing synapses. We propose that these elements produce protein(s) that are critically involved in the formation of the synaptic contact.
Selective effects of skeletal muscle extract fractions on motoneuron development in vitro
Authors: Smith RG , Vaca K , McManaman J , Appel SH
Published: March 2018

In vivo labeling of motoneurons with retrogradely transported wheat germ agglutinin, and in situ staining of cholinergic neurons with a monoclonal antibody against CAT, have been used as methods to identify motoneurons in cultures of dissociated 14 d embryonic rat ventral spinal cord. With these two different labeling techniques, we demonstrate that skeletal muscle extracts maintain motoneuron survival, and induce motoneuron morphologic and cholinergic differentiation in vitro. Further, we show that several partially purified muscle extract- derived proteins separately augment each of these specific parameters of motoneuron development. A 55,000 Da neutral glycoprotein specifically induces both ACh synthesis and motoneuron-selective process outgrowth and elongation, while a 1200–1500 Da peptide selectively augments both apparent motoneuron survival and ACh synthesis. A third trophic agent, a 33,000–35,000 Da acidic glycoprotein, induces process outgrowth in both motoneurons and nonmotoneurons of the ventral spinal cord, but has no effect on ACh synthesis.
Functional metabolic mapping during forelimb movement in rat. II. Stimulation of forelimb muscles
Authors: Santori EM , Der T , Collins RC
Published: March 2018

Repetitive electrical stimulation of wrist extensor muscles in rat was combined with quantitative 14C-deoxyglucose autoradiography to study sensory systems functionally activated during forelimb movement. Metabolism increased ipsilaterally in the wrist extensors, the dorsal horn of the cervical spinal cord, the cuneate nucleus and cerebellar hemisphere. The metabolic activation in cerebellum occurred in cortex surrounding the primary fissure anteriorly (lobules simplex and V), and the prepyramidal fissure posteriorly (lobules paramedian and copula pyramis). Metabolism was increased in both granule cell and molecular layers and was uniform throughout the zone of activation. Hindlimb stimulation primarily activated the medial aspect of copula pyramis, demonstrating the somatotopic specificity of changes. Forelimb stimulation also activated contralateral sites in the dorsal accessory nucleus of the inferior olive, ventrobasal thalamus, and SI and SII in cortex. Studies of the relationship between the magnitude of the response and the frequency of the stimulation revealed a positive correlation in muscle, dorsal horn and cuneate nucleus. Other activated sites only showed a significant change at the highest rates of stimulation. Comparison of the pattern of metabolic activation during forelimb movements induced centrally (Collins et al., 1986) with the pattern induced peripherally revealed overlap primarily in the paramedian zone of anterior and posterior cerebellum, and the granular cortex of SI and SII. These studies suggest that forelimb movement initiated centrally would have considerable influence on feedback sensation from the moving limb in these sites.
Monoclonal antibodies specific to the beta and gamma subunits of the Torpedo acetylcholine receptor inhibit single-channel activity
Authors: Blatt Y , Montal MS , Lindstrom JM , Montal M
Published: March 2018

The functional role of individual ACh receptor subunits in the mechanism of the nicotinic ACh receptor channel was examined using subunit-specific monoclonal antibodies (mAbs) as probes. Single-channel recordings from the Torpedo californica purified ACh receptor reconstituted in planar lipid bilayers were used as the assay to evaluate the influence of distinct mAbs on the ion conduction and gating characteristics of the ACh receptor channel. The mAbs that bind to the main immunogenic region on an extracellular domain of the alpha subunits do not perturb the open-channel conductance or lifetimes. A mAb that binds to extracellular domains of alpha and beta subunits and two mAbs that bind to the cytoplasmic surface of the beta and gamma subunits inhibit single-channel activity. Thus, mAbs with primary specificity for beta and gamma subunits affect channel gating. This approach may specify the functional roles of distinct structural domains in the ACh receptor molecule.
Glutamic acid decarboxylase (GAD) immunocytochemistry of developing rabbit hippocampus
Authors: Kunkel DD , Hendrickson AE , Wu JY , Schwartzkroin PA
Published: March 2018

Immunocytochemical techniques were used to examine the synaptic relations of inhibitory interneurons in the developing rabbit hippocampus. Glutamic acid decarboxylase (GAD), the synthesizing enzyme for the inhibitory neurotransmitter GABA, was found in interneurons of immature (8 d old) as well as mature (30 d old) tissue. GAD- immunoreactivity was seen in somata, dendrites, and axon terminals of interneurons at both ages. Electron-microscopic examination revealed that GAD-positive “terminals” in immature tissue were often not associated with the usual synaptic specializations, but were rather in simple apposition to the “postsynaptic” element. In mature tissue, GAD- positive terminals made symmetric contacts primarily with pyramidal cell somata, initial segments, and proximal dendrites. In addition, GAD- positive terminals synapsed onto both GAD-positive and GAD-negative interneuron profiles.
Long-term enhancement of hippocampal synaptic transmission and the acquisition of spatial information
Authors: McNaughton BL , Barnes CA , Rao G , Baldwin J , Rasmussen M
Published: March 2018

The hypothesis that memories are stored as a specific distribution of strengths in a population of modifiable synapses was examined by the bilateral induction of long-term enhancement in synapses of the main afferent fiber system to the hippocampal formation in rats. Brief, high- frequency activation of the perforant pathway in chronically prepared animals resulted in a persistent increase in the field EPSP and population spike, measured extracellularly in fascia dentata. This treatment resulted in a profound and persistent deficit in the acquisition of new spatial information in a task requiring spatial “reference” memory, and disruption of recently acquired spatial information. Well-established spatial memory was completely unaffected, however, as was the acquisition of spatial information into short-term “working” memory. These results support the hypothesis that, during the formation of “cognitive maps,” spatial information must be temporarily stored at modifiable synapses at the input stage to the hippocampal formation, but that this information is not needed once the representation of the environment is well established. Spatial working memory, in a familiar environment, appears not to depend on the distribution of synaptic strengths in this system at all.
Elimination of preexistent acetylcholine receptor clusters induced by the formation of new clusters in the absence of nerve
Authors: Peng HB
Published: March 2018

Acetylcholine receptors (AChRs) form clusters spontaneously in cultured Xenopus myotomal muscle cells in the absence of innervation. Innervation causes a dispersal of these clusters, as well as the formation of new clusters along the neuromuscular contact. To examine whether this dispersal process is dependent upon the presence of the nerve or can be effected by the formation of new clusters alone, we examined the stability of the preexistent clusters during the formation of new AChR clusters induced by basic polypeptide-coated latex beads. These beads cause a rapid development of clusters in cultured Xenopus muscle cells, and the size and the number of clusters can be experimentally manipulated by varying the size and number of beads applied to the culture. Accompanying the bead-induced formation of new clusters was an observed suppression of preexistent clusters, as shown by fluorescence microscopy after staining with rhodamine-conjugated alpha-bungarotoxin. This process of extra-bead cluster removal can be speeded up by treating the cultures with more beads or using beads of larger diameter. Furthermore, if the beads are applied before the spontaneous AChR clustering, no extra-bead clusters are formed. Thus, the latex beads can mimic the nerve in both causing the formation of new clusters and the dispersal of preexistent clusters. Although the receptor clusters are dispersed by the beads, the density of diffuse receptors, as shown by autoradiography with 125I-conjugated alpha- bungarotoxin does not decrease in the short-term cultures under study. This indicates that the dispersal of preexistent clusters is not due to a depletion of the surface pool of AChRs.(ABSTRACT TRUNCATED AT 250 WORDS)
Analysis of a glycinergic inhibitory pathway in the cat retina
Authors: Wassle H , Schafer-Trenkler I , Voigt T
Published: March 2018

Incubation of cat retinas with 3H-glycine in vitro, followed by horizontal sectioning and autoradiography, showed labeling of 10–12% of bipolar cells and 45% of amacrine cells. To ascertain the effects of glycine-accumulating bipolar and amacrine cells on the response properties of retinal ganglion cells, in vivo iontophoretic studies were performed in the cat eye. Glycine inhibited all ganglion cells, and this action was blocked by strychnine. Aminophosphonobutyric acid (APB) suppressed ON-ganglion cells, but activated OFF-ganglion cells. The influence of APB upon OFF-ganglion cells could be completely blocked by strychnine. In the mudpuppy, APB suppressed ON-bipolar cells without affecting OFF-bipolar cells and without direct effects on other retinal neurons (Slaughter and Miller, 1981, 1985). If APB has the same mode of action in the cat retina, the present results suggest a glycinergic inhibitory input of the ON-channel upon OFF-ganglion cells.
Modification of the discharge of lateral geniculate neurons during visual learning
Authors: Gibbs CM , Cohen DH , Broyles JL
Published: March 2018

Visually conditioned heart rate change in the pigeon has been developed as a vertebrate model system for cellular analysis of associative learning. Previous studies have characterized the behavior, largely delineated the neural circuitry mediating the conditioning, and estimated the central processing time for the conditioned response. Most recently, this system has been used to investigate neuronal activity during conditioning along the visual pathways that transmit the conditioned stimulus (CS) information. It was first shown that neither maintained nor CS-evoked discharge of retinal ganglion cells changes during conditioning. Subsequently, we found that the thalamic and telencephalic components of the ascending tectofugal pathway show associative modification. We report here studies of the thalamofugal pathway, the avian homolog of the mammalian geniculocortical system. Single-cell activity was recorded in the thalamic relay of this pathway, the dorsal lateral geniculate equivalent (LGNe). This provided an opportunity to evaluate the generality of the training-induced modification found along the tectofugal pathway, and to determine if such modification occurs as peripherally as retinorecipient neurons. The results show that almost all LGNe neurons (97%) respond phasically to the onset of whole-field illumination. Most (94%) also respond to the unconditioned stimulus (US), footshock, some with increased and others with decreased discharge. Of cells receiving convergent input, those responding with decreased discharge to the US showed associative change (52%). Neurons that did not respond to both the CS and US, or that responded to the US with increased discharge, did not show associative modification. These findings suggest that the visual pathways transmitting CS information are not merely input lines, but undergo training-induced modification; such modification can occur as peripherally as the retinorecipient neurons of these pathways; and CS- US convergence is necessary but not sufficient for associative modification, since modifiability is apparently contingent on specific US response properties.
Dynorphin- and enkephalin-like immunoreactivity is altered in limbic- basal ganglia regions of rat brain after repeated electroconvulsive shock
Authors: Kanamatsu T , McGinty JF , Mitchell CL , Hong JS
Published: March 2018

In an attempt to determine whether the opioid peptides derived from prodynorphin participate in the effects of electroconvulsive shock (ECS), we used radioimmunoassay and immunocytochemistry to measure dynorphin-like immunoreactivity (DN-LI) in various rat brain regions after repeated ECS treatments. Ten daily ECSs caused a significant increase in dynorphin A (1–8)-LI in most limbic-basal ganglia structures, including hypothalamus (50%), striatum (30%), and septum (30%). No significant change was found in the frontal cortex or the neurointermediate lobe of the pituitary. In contrast, 10 ECS treatments depleted DN-LI in hippocampal mossy fibers by 64%. A detailed time- course study revealed that a single shock caused a small but significant increase in hippocampal DN-LI, whereas three consecutive shocks depleted DN-LI by 30%. The maximal decrease in DN-LI was reached after six daily ECSs. The level of DN-LI in the hippocampus partly recovered, but remained lower than the control value 4, 7, and 14 d after the cessation of six daily ECSs (50, 77, and 83% of control value, respectively). In contrast with the ECS-induced depletion of hippocampal dynorphin, 10 daily ECSs caused a significant increase (40%) in (Met5)-enkephalin-LI in the hippocampus, as well as in other limbic-basal ganglia structures. Immunocytochemistry revealed that enkephalin-LI was increased in the perforant pathway, which is presynaptic to the dynorphin-containing mossy fiber pathway in the hippocampus. These observations suggest that different mechanisms may regulate these two opioid peptide systems in the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)
Morphology of HRP-injected spinocervical tract neurons: effect of dorsal rhizotomy
Authors: Sedivec MJ , Capowski JJ , Mendell LM
Published: March 2018

Twenty-five physiologically identified spinocervical tract (SCT) neurons in the sixth lumbar segment of the cat were filled with HRP by intracellular injection. All were reconstructed from sagittal sections using the camera lucida, and a subset (n = 18) was also reconstructed using a computer reconstruction system. Thirteen cells were in intact preparations, nine were in spared root preparations (L5, L6, S1, S2 cut; L7 spared), and three were in preparations with L5 through S2 cut. Analysis of the dendritic tree of these neurons revealed little change in gross morphology after partial deafferentation despite increased proportions sensitive to nociceptive input (Sedivec et al., 1983). The dendrites still largely respected the lamina II-III border, and relatively few dendrites were directed ventrally from the cell body, although the ratio of ventral to dorsal dendrites was greater than normal. The major change was an increase in surface area and volume caused by changes in diameter (but not length) of the dendrites. Larger- than-usual maximum branch order of individual dendritic trees of some cells was also observed after chronic deafferentation. Thus, SCT cells in deafferented segments do not undergo atrophy, but show, rather, limited signs of growth and the possibility of dendritic reorganization. We have also computed correlations between different parameters of these cells (cell body size, number and size of primary dendrites, total area and length of individual dendrites) and have found that, as in motoneurons, diameter of the primary dendrite measured 30 micron from the soma is significantly correlated with total dendritic surface area and length. SCT neurons tend to have more dendrites than spinal alpha-motoneurons, but total surface area is smaller for a given diameter of a proximal dendrite.
Localization of acetylcholine receptors and cholinesterase on nerve- contacted and noncontacted muscle cells grown in the presence of agents that block action potentials
Authors: Davey DF , Cohen MW
Published: March 2018

The possible role of nerve activity in triggering changes in the localization of acetylcholine receptors (AChRs) and cholinesterase (ChE) on nerve-contacted Xenopus muscle cells has been assessed. The localization of these molecules was examined on nerve-contacted and noncontacted muscle cells in cultures of spinal cord and myotomal muscle derived from Xenopus embryos. Sites of high AChR density were revealed by staining with fluorescent alpha-bungarotoxin and sites of ChE localization were revealed histochemically. Localization of AChRs and ChE at sites of nerve-muscle contact occurred when the culture medium contained 1.2 micron tetrodotoxin (TTX), 1.2 micron TTX, 10 mM magnesium, and no calcium salts, 1.2 micron TTX and 2 mM manganese, or 106 mM potassium methyl sulfate instead of sodium chloride. The nerve- contacted muscle cells in each of these modified culture media also exhibited a reduced incidence of AChR and ChE patches away from the site of contact. It is concluded that the neural factor(s) that triggers the local and remote changes in AChR and ChE distribution can be supplied to the neurites and externalized in the absence of nerve impulses, and that the nerve and muscle cells can interact even when they are largely depolarized.
Immunocytochemical localization of tubulin and microtubule-associated protein 2 during the development of hippocampal neurons in culture
Authors: Caceres A , Banker GA , Binder L
Published: March 2018

n dissociated-cell cultures prepared from the embryonic rat hippocampus, neurons establish both axons and dendrites, which differ in geometry, in ultrastructure, and in synaptic polarity. We have used immunocytochemistry with monoclonal antibodies to study the regional distribution of beta-tubulin and micro-tubule-associated protein 2 (MAP2) in hippocampal cultures and their localization during early stages of axonal and dendritic development. After development for a week or more in culture, when axons and dendrites were well- differentiated, the distribution of these two proteins was quite different. Beta-tubulin was present throughout the nerve cell, in soma, dendrites, and axon. It was also present in all classes of non-neuronal cells, astrocytes, fibroblasts, and a presumptive glial progenitor cell. In contrast, MAP2 was preferentially localized to nerve cells; within neurons, MAP2 was present in soma and dendrites, but little or no immunostaining was detectable in axons. Both beta-tubulin and MAP2 were present in nerve cells at the time of plating. From the earliest stages of process extension, beta-tubulin was present in all neuronal processes, both axons and dendrites. Surprisingly, MAP2 was also initially present in both axons and dendrites, extending as far as the axonal growth cone. With subsequent development, MAP2 staining was selectively lost from the axon so that after 1 week in vitro little or no axonal staining remained. Taken together with earlier results (Caceres et al., 1984a), these data indicate that the establishment of neuronal polarity, as manifested by the molecular differentiation of the axonal and dendritic cytoskeleton, occurs largely under endogenous control, even under culture conditions in which cell interactions are greatly restricted.(ABSTRACT TRUNCATED AT 250 WORDS)
Reinnervation of the extraocular muscles in goldfish is nonselective
Authors: Scherer SS
Published: March 2018

The selectivity of axonal regeneration to the extraocular muscles in teleosts has been reinvestigated by mapping, with retrogradely transported HRP, the motor pools of the muscles innervated by the oculomotor nerve. In normal goldfish, the motoneurons of the superior rectus, inferior rectus, and inferior oblique muscles formed discrete, nonoverlapping motor pools; the motor pool of the medial rectus muscle overlapped with those of the inferior oblique and inferior rectus muscles. In fish whose oculomotor nerve had regenerated (after intracranial transection), in contrast, many motoneurons in other, inappropriate motor pools reinnervated the superior rectus and inferior oblique muscles (the only muscles examined in lesioned animals). Furthermore, these inappropriate motoneurons continued to project to these muscles for at least 1 year. The oculomotor nerve and its molecular branches were examined by light and electron microscopy to determine the pathway by which axons regenerated to their muscles. Axons regenerated within the basal laminae of Schwann cells, which persisted in the distal nerve-stump after a lesion. After labeling the inferior oblique nerve with HRP in regenerated nerves, there were labeled axons in all of the muscular branches; this indicates that regenerating axons branched, which was confirmed by finding an increased number of myelinated axons in other, regenerated inferior oblique nerves. Thus, different branches of the same axons sometimes reinnervated different muscles. These results demonstrate that regenerating axons in the oculomotor nerve are misdirected to inappropriate muscles, and do not selectively reinnervate individual muscles, as had been previously suggested (Sperry and Arora, 1965).
Multiple components of delayed potassium current in peptidergic neurons of Aplysia: modulation by an activator of adenylate cyclase
Authors: Strong JA , Kaczmarek LK
Published: March 2018

The neurosecretory bag cell neurons of the mollusk, Aplysia, control egg-laying behavior in the animal. In these cells, elevation of cAMP greatly enhances the height and width of action potentials. A similar enhancement of action potentials is seen during the bag cell afterdischarge, a 30 min period of repetitive activity that may be triggered by peptides from the reproductive tract or by brief extracellular stimulation. The enhancement of action potentials during an afterdischarge is well correlated with the observed elevations of cAMP. In the present study, we have examined the effects of forskolin (an activator of adenylate cyclase) and theophylline (a phosphodiesterase inhibitor) on the delayed outward currents that are likely to control repolarization of the action potential. Isolated bag cell neurons, maintained in primary culture, were studied with a whole- cell patch clamp technique. High intracellular concentrations of EGTA were used to block potassium current activated by calcium entry. Analysis of the remaining voltage-dependent delayed outward current revealed two major components, which could be separated on the basis of their different kinetic properties. Both currents (IK1 and IK2) were carried by potassium. IK1, which did not inactivate during 100 msec depolarizations, was reduced in amplitude by application of forskolin and theophylline. Ik2, a current defined by its faster kinetic properties, partially inactivated during 100 msec depolarizations. This inactivation was markedly speeded by application of forskolin and theophylline. It is suggested that such changes in outward current in response to cAMP could explain the enhancement of spike width seen during an afterdischarge in vivo.
Effect of monensin on deoxyglucose uptake in cultured astrocytes: energy metabolism is coupled to sodium entry
Authors: Yarowsky P , Boyne AF , Wierwille R , Brookes N
Published: March 2018

This study was undertaken to measure the effect of maximal stimulation of sodium pump activity on the rate of energy metabolism in mouse cerebral astrocytes. The rate of uptake of 3H-2-deoxyglucose (3H-2-DG) was measured in astrocyte cultures sodium-loaded either by incubation in a K+-deficient solution or by use of the carboxylic sodium ionophore monensin. Sodium-loading by the first method caused 3H-2-DG uptake to increase by 80%, but the effect was brief (about 5 min) compared with the period of uptake measurement (20 min). In contrast, the presence of monensin (20 microM) caused a sustained 3.4-fold increase in the rate of 3H-2-DG uptake. The concentration-response relationship for monensin indicated a Kd of 1.5 microM and a maximum uptake enhancement of approximately fourfold. The monensin-stimulated uptake of 3H-2-DG was totally inhibited by incubation of the cultures in either K+-free or Na+-free solutions, or in the presence of ouabain (0.4 mM), indicating that the enhancement of uptake was the result of Na+ influx and sodium pump activation. These results raise the possibility that astroglia contribute significantly to regional variations in glucose consumption associated with functional activity in the brain. Ultrastructural analysis showed that sodium-loading in K+-free solution caused swelling confined to the trans face of Golgi stacks. However, monensin (5 microM) caused swelling of the entire Golgi stack, with progressively more severe swelling from cis to trans cisternae and formation of cytoplasmic vacuoles.(ABSTRACT TRUNCATED AT 250 WORDS)
Tyrosine hydroxylase immunoreactive neurons throughout the hypothalamus receive glutamate decarboxylase immunoreactive synapses: a double pre- embedding immunocytochemical study with particulate silver and HRP
Authors: van den Pol AN
Published: March 2018

Silver-intensified gold (SIG) particles were used for light- and electron-microscopic immunocytochemical localization of neuronal antigens, and the SIG method was compared with related heavy-metal methods for the purpose of dual ultrastructural localization of neurotransmitter-related antigens. SIG immunostaining was combined with peroxidase immunostaining to allow simultaneous study of differentially labeled tyrosine hydroxylase and glutamate decarboxylase immunoreactive neurons in the medial hypothalamus. A number of electron-dense markers that might be of use in double immunostaining for light and electron microscopy were examined, either with a simple nitrocellulose dot-blot method or on Formvar-coated slot grids. Of these, silver-intensified 5 nm colloidal gold was the most effective. Silver intensification of colloidal silver and of peroxidase reaction product also showed promise for combined LM and EM double-immunolabeling studies. Since the silver- intensification procedure used here intensifies both gold and peroxidase, in experiments involving, double staining, the silver- intensified gold procedure should be used for the first antigen and nonintensified HRP for the second. Presumptive dopaminergic neurons containing the enzyme tyrosine hydroxylase were located throughout the hypothalamus with SIG immunostaining. In the same areas where frequent tyrosine hydroxylase immunoreactive neurons were found, many axons and bouton terminals were also found with antisera against GABA or against the GABA-synthesizing enzyme glutamate decarboxylase. Areas containing cells immunoreactive for tyrosine hydroxylase and stained with SIG and axons immunoreactive for glutamate decarboxylase and stained with peroxidase included the periventricular area (A14), the arcuate nucleus (A12), the dorsomedial hypothalamus/zona incerta area (A13), the posterior hypothalamus (A11), the medial paraventricular nucleus, and dorsal to the supraoptic nucleus, in addition to the preoptic area near the third ventricle and dorsally adjacent to the anterior commissure. For comparison, the SIG procedure was also used to stain dopaminergic neurons outside the hypothalamus in the substantia nigra and ventral tegmental area. Double immunocytochemical staining of two different neurotransmitter-related antigens allowed examination with both light and electron microscopy. By virtue of a large silver shell formed around the colloidal gold particle and its adsorbed immunoglobulin or protein A, cross-reactivity of the first set of immunoreagents stained with particulate silver and a second set stained with peroxidase could be reduced or eliminated.(ABSTRACT TRUNCATED AT 400 WORDS)
Binaural response organization within a frequency-band representation of the inferior colliculus: implications for sound localization
Authors: Wenstrup JJ , Ross LS , Pollak GD
Published: March 2018

The auditory system of the mustache bat (Pteronotus parnellii) contains a disproportionately large representation of a narrow frequency band, corresponding to the dominant, 60 kHz component of its echolocation signal. In the inferior colliculus (IC), the 60 kHz representation comprises an architectonically distinct region called the dorsoposterior division (DPD), which is accessible for detailed physiological study. We examined the topographic distribution of binaural responses within this one frequency-band representation of the inferior colliculus. We describe two primary results. First, neurons with different binaural response properties are spatially segregated into one of four binaural response-specific regions of the DPD: a large region of monaural (EO) responses; two regions containing neurons excited by sound from both ears (EE); and a region containing neurons excited by one ear and inhibited by the other (EI). Regions dominated by 60 kHz EI responses are also found in the lateral extremity of the IC, probably within the external nucleus. These results demonstrate functionally defined subdivisions in a single frequency-band representation of the IC. Moreover, they suggest that brain stem auditory projections to the DPD and/or intrinsic connections within the DPD are highly organized. Second, within the EI region of the DPD, there is a systematic shift in the sensitivity of EI multiunit responses to interaural intensity disparities (IIDs). Dorsally, EI neurons are suppressed only by relatively loud ipsilateral sounds, and there is a systematic decrease in the relative ipsilateral intensity required for suppression at more ventral recording sites. This result demonstrates that neurons sensitive to a sound localization cue are systematically organized within a frequency-band representation of the inferior colliculus. It has implications for the manner in which the location of a sound source is encoded within the primary auditory pathway.
In vivo comparison of the regulation of releasable dopamine in the caudate nucleus and the nucleus accumbens of the rat brain
Authors: Kuhr WG , Bigelow JC , Wightman RM
Published: March 2018

In vivo voltammetry has been used to measure the release of dopamine evoked by electrical stimulation of the medial forebrain bundle (MFB). Simultaneous measurements have been made with voltammetric-sensing electrodes ipsilateral to the stimulating electrode in the nucleus accumbens and the caudate nucleus of the anesthetized rat. During the stimulation, the species observed in both regions is voltammetrically identical to dopamine. Further evidence for the identity of dopamine is provided by anatomical, physiological, pharmacological, and postmortem data. Postmortem analysis of these brain regions after a single stimulation demonstrates that dopamine levels are unchanged, while dihydroxyphenylacetic acid (DOPAC) levels are increased in both regions. Systemic application of synthesis inhibitors results in a decrease in evoked release for each brain region. Amfonelic acid results in a restoration of stimulated release after synthesis inhibition. Evoked release is affected differently by pargyline in the two brain regions. The evoked release of dopamine is significantly elevated in the nucleus accumbens as a result of pargyline administration, but similar effects are not seen in the caudate nucleus. Tissue levels of dopamine are increased in both brain regions by pargyline, but the increase is significantly greater in the accumbens. Electrolytic lesions of the striatonigral pathway or systemic administration of picrotoxin eliminates the pargyline-induced difference in evoked release of dopamine. Amphetamine causes a reduction in stimulated release in the caudate nucleus with little effect on that observed in the nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)