bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmitter-operated channels in rabbit retinal astrocytes studied in situ by whole-cell patch clamping
Authors: Clark B , Mobbs P
Published: March 2018

Glutamate and GABA open ion channels in the membranes of astrocytes found on the vitreal surface of the rabbit retinal visual streak. The glutamate-operated channels are opened by kainate, quisqualate, and AMPA, but not by NMDA, aspartate, or the metabotropic agonist 1- aminocyclopentane-1 S,3R-dicarboxylic acid. The effects of glutamate and its analogs can be blocked by 20 microM 6-cyano-7-nitroquinoxaline- 2,3-dione. The conductance increase evoked by 10 microM glutamate, a concentration of this transmitter near to that found in the vitreous humor that bathes these cells, was equivalent to 22% of the cell's resting conductance. The conductance increase evoked by 1 microM GABA, a concentration near that found in the vitreous, was equivalent to 131% of the cell's resting conductance. The effects of GABA can be blocked by bicuculline. These data show that GABA, and non-NMDA-type glutamate receptors play an important part in determining the resting potential of visual streak astrocytes in situ and that these channels may be of general importance for the functions of astrocytes in vivo.
Transient calbindin-D28k-positive systems in the telencephalon: ganglionic eminence, developing striatum and cerebral cortex
Authors: Liu FC , Graybiel AM
Published: March 2018

Calbindin-D28k (calbindin) is a member of the superfamily of calcium- binding proteins implicated in the regulation of intracellular calcium. In the mature brain, calbindin is widely expressed in neurons of the forebrain and the hindbrain, and in the telencephalon calbindin-like immunoreactivity is particularly strongly expressed by medium-sized neurons of the striatum and by certain other neurons in the cortex and subcortex. We have traced the development of calbindin expression in the forebrain of the rat, and report here that in addition to the steady development of these calbindin-positive neuronal systems, transient waves of calbindin expression occur in cells of the ventricular zones of the basal ganglia and cortex and in cells of the telencephalic regions derived from these ventricular zones including radial glia of the developing striatum. In the striatum and its ventricular zone (the ganglionic eminence, or GE) we identified four transient calbindin-positive systems in the perinatal period. First, calbindin-immunoreactive cells began to appear in the GE by embryonic day (E)18, and by E20 an extensive dorsal and lateral part of the GE was marked by dense calbindin-like immunoreactivity in the ventricular zone. This calbindin system peaked at postnatal day (P)0-P3 and disappeared by P15. Its presence suggests that the GE is divisible on a molecular basis into lateral and medial districts that may correspond to derivatives of the lateral and medial ventricular ridges. Second, a system of calbindin-positive processes appeared in the dorsal and lateral caudoputamen with temporal and spatial distributions matching the germinal zone system. Many of these processes could be traced from calbindin-positive cells in the ventricular zone of the GE, including processes stretching across the full width of the dorsal caudoputamen. Double-staining experiments demonstrated that these radial processes were Rat.401-positive, suggesting that they form a subset of radial glia in the developing telencephalon. These findings demonstrate that during development calbindin is expressed in glial as well as neural cells. They further suggest that the radial glia associated with the GE form heterogeneous populations, the transient calbindin-positive radial glia being associated with the lateral ridge of the GE and its derivatives. Third, a scattered population of calbindin-positive cells with morphologies different from the common medium-sized calbindin- immunoreactive neurons of the striatum appeared in the dorsal and lateral striatum from about E20 to P15. Some of these cells were close to the transient calbindin-positive radial processes in the same region, but others were not.(ABSTRACT TRUNCATED AT 400 WORDS)
Neural-vascular relationships in central retina of macaque monkeys (Macaca fascicularis)
Authors: Snodderly DM , Weinhaus RS , Choi JC
Published: March 2018

The relationship of the vasculature to the neuronal layers was studied in whole-mounts and in sections of macaque retinas. Like other central nervous structures, primate retinas have local variations in vascularity that reflect local variations in metabolism, rather than simply tissue thickness or volume. A special feature of the retina is a dense vascular plexus in the nerve fiber layer, which is unmyelinated and hence must generate a substantial metabolic demand for ion pumping. Much of the retinal vasculature is laminated and located at specific layer boundaries. Throughout the central retina, two planes of capillaries bracket the inner nuclear layer to form a sclerad capillary network. In some regions, especially near the fovea, a second, more vitread network brackets the ganglion cell layer with another pair of capillary planes. Wherever the nerve fiber layer is thick, the vitread network becomes less planar and is multilayered. When surrounded by nerve fibers, capillaries tend to orient parallel to the fibers; when adjacent to ganglion cell bodies, the capillaries are less systematically oriented. At the border between the nerve fiber layer and the ganglion cell layer, rows of ganglion cells often interdigitate with nerve fiber bundles, resulting in local perturbations of capillary orientation. The volume of the sclerad capillary network is relatively constant at different locations, but the volume of the vitread network increases dramatically where the nerve fiber layer is thick. As a result, the vascularity of the retina is greatest in the peripapillary region near the optic disk, even though the total thickness of the peripapillary retina is comparable to the retinal thickness near the foveal crest. As many as 60–70% of the photons passing through the retina in the peripapillary region will encounter one or more capillaries before reaching a photoreceptor. Median capillary diameter increases with retinal depth from 4.5–4.7 microns in the nerve fiber layer to 5.0 microns at the sclerad border of the inner nuclear layer. Capillary diameter in the nerve fiber layer also increases near the optic disk.
EPSP-IPSP interactions in cat visual cortex studied with in vivo whole- cell patch recording
Authors: Ferster D , Jagadeesh B
Published: March 2018

Postsynaptic inhibition can operate by two distinct mechanisms: (1) membrane hyperpolarization and (2) shunting of excitatory postsynaptic currents. The arithmetic operations--either addition or multiplication-- that synapses are able to perform during neuronal computations are determined by which of these two inhibitory mechanisms predominates. Hyperpolarizing IPSPs interact linearly with EPSPs; their negative and positive synaptic currents sum to produce a net change in membrane potential (Eccles, 1961). Shunting synapses interact nonlinearly with EPSPs; the shunt-induced increase in membrane conductance directly reduces the amplitude of EPSPs by a constant multiplicative factor (Fatt and Katz, 1953; Blomfield, 1974). This property of shunting inhibition has provided the basis for models of synaptic interaction in which shunting inhibition acts as an AND-NOT gate for excitatory inputs (Torre and Poggio, 1978; Koch et al., 1983). Using an in vivo variant of the whole-cell patch technique (Blanton et al., 1989), we have examined the effect of visually evoked inhibition on the size of EPSPs in cortical simple cells and found that the predominant inhibitory mechanism is hyperpolarization. We conclude that these inhibitory synapses operate primarily in the linear mode.
Cellular analogs of visual cortical epigenesis. II. Plasticity of binocular integration
Authors: Shulz D , Fregnac Y
Published: March 2018

Two differential pairing procedures were applied in the primary visual cortex of anesthetized and paralyzed kittens and cats, to produce changes in ocular dominance and interocular orientation disparity (IOD) during the time of recording of a single neuron. A first experiment was devised to demonstrate plasticity in the balance of monocular responses. The visual activity of the cell was driven iontophoretically to either a “high” or a “low” level, depending on the ocularity of the visual stimulation. Ocular dominance measurements before and after pairing revealed significant long-lasting changes in 33% of cases. Relative ocular preference shifted in most cases (87.5%) in favor of the reinforced eye. Similar proportions of significant changes were observed in kitten and adult cortex. The amplitude of the functional modifications was not significantly related with age, although the largest changes in ocular dominance were recorded at the peak of the critical period. The second experiment more specifically addressed the plasticity of binocular interaction. The activity of a binocular cell was driven iontophoretically to either a “high” or a “low” level, depending on the orientation disparity between two oriented stimuli, presented simultaneously and separately in the receptive field of each eye. Significant long-lasting changes in binocular responses were induced in 40% of cases. The relative IOD preference generally shifted (67%) in favor of the reinforced disparity. In half of the modified cells, functional changes were expressed only in the dichoptic viewing condition used during the pairing procedure. These functional modifications of binocular integration, demonstrated at the cellular level, are analogous to those induced by global manipulations of the visual environment (Hubel and Wiesel, 1970; Shinkman and Bruce, 1977). They are interpreted as evidence for synaptic plasticity. Our results support the hypothesis that covariance levels between pre- and postsynaptic activities determine the sign and the amplitude of changes in synaptic efficacy.
Functional classes of cortical projection neurons develop dendritic distinctions by class-specific sculpting of an early common pattern
Authors: Koester SE , O'Leary DD
Published: March 2018

We demonstrate in rat neocortex that the distinct laminar arrangements of the apical dendrites of two classes of layer 5 projection neurons, callosal and corticotectal, do not arise de novo, but are generated later in development from a common tall pyramidal morphology. Neurons of each class initially elaborate an apical dendrite in layer 1. Layer 5 callosal neurons later lose the segments of their apical dendrite superficial to layer 4, generating their characteristic short pyramidal morphology. The apical dendrite of layer 5 callosal neurons later lose the segments of their apical dendrite superficial to layer 4, generating their characteristic short pyramidal morphology. The apical dendrite of layer 5 callosal neurons is actively eliminated, rather than passively displaced, as superficial cortical layers expand. Corticotectal neurons and callosal neurons superficial to layer 5 maintain their apical dendrite to layer 1. Therefore, this selective dendritic loss occurs in a neuron class-specific manner and, within the callosal population, in a lamina-specific manner. Based on our additional observations and other studies, this phenomenon can be extended to other types of cortical projection neurons. These findings show that selective dendritic elimination plays a major role in shaping the functional architecture characteristic of the adult cortex.
Mesencephalic dopaminergic neurons in primary cultures express functional neurotensin receptors
Authors: Brouard A , Pelaprat D , Dana C , Vial M , Lhiaubet AM , Rostene W
Published: March 2018

The cellular distribution and functional aspects of neurotensin (NT) binding sites in rat mesencephalic cells in primary culture were investigated by an original approach combining anatomical and biochemical studies. Using a double-labeling protocol combining 125I-NT receptor radioautography and tyrosine hydroxylase (TH) immunocytochemistry, we obtained the first direct visualization of NT binding sites on TH-immunoreactive neurons. Eighty percent of the TH neurons were endowed with NT binding sites, which can be observed on both cell bodies and processes. TH-immunoreactive neurons were characterized as dopaminergic neurons by their ability to take up dopamine in a benztropine- and nomifensine-sensitive manner. In the mesencephalic cultures, NT increased potassium-evoked release of tritiated dopamine, and the relative potencies of various NT-related peptides to increase dopamine release were in good agreement with their abilities to bind to NT sites. These results show for the first time that cultured rat mesencephalic dopaminergic cells express functional NT receptors. Finally, the specificity and distribution of NT receptors on dopaminergic neurons in primary culture are quite similar to what was observed in the adult rat brain using pharmacological and radioautographic approaches. These data indicate that NT can influence the activity of dopaminergic neurons at very early stages of the rat brain development.
Periodic-pattern-selective cells in monkey visual cortex
Authors: von der Heydt R , Peterhans E , Dursteler MR
Published: March 2018

To study the visual processing of periodic and aperiodic patterns, we have analyzed neuronal responses in areas V1 and V2 of the visual cortex of alert monkeys during behaviorally induced fixation of gaze. Receptive field eccentricities ranged between 0.5 degrees and 4 degrees. We found cells that responded vigorously to gratings, but weakly or not all to bars and edges. In some cells the aperiodic stimuli even reduced the activity below the spontaneous level. The distribution of a bar-grating response index indicated a discrete population of “grating cells” characterized by more than 10-fold superiority of gratings. We estimated that these cells have a frequency of 4% in V1 and 1.6% in V2, and that about 4 million grafting cells of V1 subserve the central 4 degrees of vision. The converse, cells that responded to isolated bars but not to gratings of any periodicity, was also observed. The grating cells of V1 were mostly (23 of 26) found in layers 2, 3, and 4B. They preferred spatial frequencies between 2.6 and 19 cycles/degree (median, 9.3), with tuning widths at half-amplitude between 0.4 and 1.4 octaves (median, 1.0). Their tunings were narrower, and their preferred frequencies higher, than those of other cells on average. Grating cells were also narrowly tuned for orientation. Those of V2 were similarly selective. The responses of grating cells depended critically on the number of cycles of the gratings. With square waves of optimum periodicity responses required a minimum of 2–6 grating cycles and leveled off at 4–14 (median, 7.5). The corresponding receptive field widths were 0.34–2.4 degrees (median, 0.78 degrees) for V1 and 0.72–2.4 degrees (median, 1.4 degrees) for V2. Grating cells typically gave unmodulated responses to drifting gratings, were unselective for direction of motion, and were strongly activated also by stationary gratings. Half of those of V1 were monocular, the others binocular, some showing strong binocular facilitation and disparity sensitivity. Length summation was usually monotonic, but strong end- inhibition was also observed. In contrast to other cells, grating cells were not activated by harmonic components. Spatial-frequency response curves for sine-wave, square-wave, and line gratings were similar. Square-wave gratings of one-third the preferred frequency failed to excite the cells, while the isolated 3f component (f = the fundamental of the square wave) of these gratings evoked strong responses. In spite of the nonlinear features, grating cells had low contrast thresholds.(ABSTRACT TRUNCATED AT 400 WORDS)
Reliability and effectiveness of transmission from exteroceptive sensory neurons to spiking local interneurons in the locust
Authors: Burrows M
Published: March 2018

Mechanosensory information from exteroceptive hairs on the legs of a locust is first processed in a segmental ganglion by a midline population of spiking local interneurons for use in adjustments of posture and locomotion. Each interneuron receives excitatory inputs from a characteristic array of these receptors so that the surface of a leg is mapped onto the whole population of interneurons as a series of overlapping receptive fields. The properties of this first synaptic connection, and the contributions of individual afferents forming the receptive fields of the interneurons are examined. The gain of the excitatory synaptic connection between the hair afferents and the interneurons is often high, so that a single afferent spike can lead directly to a spike in the interneuron. Repetitive spikes in a hair afferent evoke EPSPs in an interneuron that decline in amplitude but that may summate. The first EPSP in any sequence is always the largest. The high frequencies of afferent spikes that are evoked by a normal deflection of a hair saturate the synaptic connection so that the amplitude of depolarization is no greater than to a single spike. The EPSPs from two hairs in a receptive field can summate but lead to no heterosynaptic facilitation. High-frequency bursts of spikes in one afferent can reduce the postsynaptic effect of another afferent. The amplitude of the EPSPs and the gain of the synaptic connections differ markedly between the hairs that comprise the receptive field of an interneuron. There are gradients of effectiveness, generally according to the axes of the leg, with one group of adjacent hairs producing the largest-amplitude EPSPs and having the highest gains. Individual hairs may contribute to the receptive field of more than one interneuron, and the gain of these connections may differ. The complexity of a receptive field is further accentuated by the specificity of connections made by the different physiological types of hair receptors. High-threshold hairs may make synaptic connections with an interneuron, but adjacent low-threshold hairs may not. This organization of the receptive fields means that the interneurons are sensitive to certain inputs and can reliably pass on a signal from one hair. It also implies that greater weighting is given to inputs from certain regions.
Zinc, a neurotoxin to cultured neurons, contaminates cycad flour prepared by traditional guamanian methods
Authors: Duncan MW , Marini AM , Watters R , Kopin IJ , Markey SP
Published: March 2018

We have used cultured ventral mesencephalic and cerebellar granule cells to test the toxicity of extracts of cycad seeds (genus Cycas) and cycad-derived flours traditionally prepared in Guam. There was no significant difference in the toxicity of extracts prepared from the female gametophyte tissue of C. circinalis, C. revoluta, and C. media, common wheat flour, and 13 of 17 cycad flour samples. However, extracts prepared from 4 of 17 Guamanian flour samples exhibited marked dose- dependent neurotoxicity to mesencephalic and granule cell cultures. There was no correlation between toxicity and 2-amino-3-(methylamino)- propanoic acid (BMAA) content, and the concentration of BMAA in the medium arising from these extracts was far below that required to be neurotoxic. Toxicity of extracts was not blocked by the NMDA receptor antagonist MK-801 or the non-NMDA receptor antagonist 6-cyano-7- dinitroquinoxaline-2,3-dione, indicating that toxicity was not mediated by excitatory amino acid receptors. Analysis of the four toxic processed flour samples indicated high zinc content. Zinc produced a concentration-dependent neurotoxic response in mesencephalic and granule cell cultures that paralleled the calculated concentrations of zinc in the cultures derived from the four toxic flour samples. When sliced C. circinalis gametophyte tissue was “processed” in our laboratory by soaking in a galvanized container, there was a time- dependent increase in zinc content.
Development of retinal displaced ganglion cells in the chick: neurogenesis and morphogenesis
Authors: Prada C , Medina JI , Lopez R , Genis-Galvez JM , Prada FA
Published: March 2018

The time of birth of displaced ganglion cells (DGCs) was determined by autoradiography. DGCs start to leave the cell cycle early, on embryonic day 3, in the central and peripheral retina, and end on embryonic day 8, also in both areas of the retina. During the period of neurogenesis, unlabeled (born) DGCs do not appear distributed in spatial gradients as do the ganglion, amacrine, and other cell types in the retina (Prada et al., 1991). Our results show characteristic spatial and temporal patterns of DGC neurogenesis, which differ from those of the other retinal cell types. The morphogenesis of DGCs was studied by means of Golgi preparations. After leaving the cycle, DGC neuroblasts detach from the ventricular lining; they then move their soma through the vitreal process toward the final position at the same time that they emit the axon. Also during soma translocation, a transient sprouting of a few short processes is emitted from the vitreal process of the cell, close to where the soma is later located, suggesting that the “abnormal” position of DGCs could be specifically marked during the process of migration.
Developmental regulation of leucine-enkephalin expression in adrenal chromaffin cells by glucocorticoids and innervation
Authors: Henion PD , Landis SC
Published: March 2018

Most catecholaminergic cells derived from the sympathoadrenal lineage of the neural crest contain one or more neuropeptides. Although a great deal is known about the development and regulation of catecholaminergic properties in these cells, relatively little is known about the developmental control of their neuropeptidergic properties. We have investigated the possible role of glucocorticoids and preganglionic innervation in the regulation of leucine-enkephalin (L-Enk) expression in cultures of embryonic and neonatal adrenal chromaffin cells and in mature chromaffin cells in vivo. Exposure of embryonic and neonatal chromaffin cells to the synthetic glucocorticoid dexamethasone increases L-Enk content. Neonatal chromaffin cells grown in medium containing elevated levels of potassium to mimic depolarization also exhibited increased L-Enk levels. The depolarization-induced increase in L-Enk was selectively inhibited by treatment with the enkephalin analog [D-Ala, d-Leu]-enkephalin to mimic the enkephalinergic component of the preganglionic innervation. Denervation of the adrenal gland in vivo resulted in a dramatic increase in L-enk expression that could be partially mimicked by selectively blocking enkephalinergic transmission with administration of the opiate receptor antagonist naloxone. Taken together with the developmental time course and pattern of L-Enk expression in vivo, our results suggest that glucocorticoids and the preganglionic innervation regulate the developmental expression of this peptide in adrenal chromaffin cells and therefore participate in the generation of the mature neurochemical phenotypes present in the adrenal medulla. Further, in adult chromaffin cells similar factors appear to regulate the expression of L-Enk, which could in turn participate in physiological responses to stress.
A time course for the focal elevation of synthesis of basic fibroblast growth factor and one of its high-affinity receptors (flg) following a localized cortical brain injury
Authors: Logan A , Frautschy SA , Gonzalez AM , Baird A
Published: March 2018

Traumatic injury to the CNS initiates transient and unsuccessful regeneration of damaged neural pathways, accompanied by reactive gliosis, angiogenesis, and deposition of a dense fibrous glial/meningeal scar at the wound site. Basic fibroblast growth factor (basic FGF) is a CNS protein with potent effects on neurons, glia, fibroblasts, and vascular endothelial cells. Hybridization and immunocytochemical methods were used to examine temporal and spatial changes in distribution and levels of basic FGF protein and mRNA and also of its receptor mRNA (flg), following a defined wound to the cerebral cortex of adult rat brains. In the injured brain, a rapid, transient increase in basic FGF mRNA and protein is readily detectable within 7 d of surgery and thereafter declines in the tissues bordering the lesion. The increased expression is localized to multiple cell types including macrophages, neurons, astrocytes, and vascular endothelial cells. The changes in immunoreactive basic FGF parallel changes in the bioactivity of extracted heparin-binding proteins, which include basic FGF. Focal increases in flg mRNA appear 7 d after injury and subside by 14 d. The changes in local basic FGF synthesis, concentration, localization, and bioactivity suggest that this growth factor may contribute to the cascade of cellular events that occur in CNS wound repair.
The downregulation of growth-associated proteins in motoneurons at the onset of synapse elimination is controlled by muscle activity and IGF1
Authors: Caroni P , Becker M
Published: March 2018

Axonal growth during development and regeneration coincides with the expression of growth-associated proteins (GAPs), including GAP-43 and tubulin-alpha 1. Following contact with the target region and synaptogenesis, GAPs are downregulated. However, high levels of GAP-43 are expressed in some neurons in the adult CNS, indicating that its function may not be restricted to axonal growth. To define the type of signals that regulate GAP levels during development, we have determined whether GAP downregulation coincides with a defined phase of synapse development and whether it is controlled by the postsynaptic target. Levels of GAP-43 mRNA in spinal motoneurons and protein at the neuromuscular junction were analyzed in the developing neuromuscular system of chick and rat. In both species, GAP-43 mRNA declined rapidly at a time corresponding to the onset of synapse elimination, and nerve terminal GAP-43 immunoreactivity became undetectable with a delay of 2- 3 d. In rat motoneurons, GAP-43 and tubulin-alpha 1 mRNA levels declined with a similar time course, indicating that at least two GAPs are downregulated at the same time. Blockade of neuromuscular transmission with either a pre- or a postsynaptically acting toxin prevented GAP downregulation, indicating that target activity affects GAP mRNA levels in motoneurons. Finally, counteracting the activity- dependent decline of muscle insulin-like growth factors during synapse elimination by local subcutaneous injections prevented motoneuron GAP downregulation, suggesting that these growth factors may be involved in the regulation of motoneuron GAPs by the muscle. These results demonstrate that motoneurons undergo target-sensitive changes in GAPs at the onset of synapse elimination. In addition, these results raise the possibility that termination of a presynaptic growth mode may be a prerequisite for synapse elimination.
Olfactory sensory neurons are trophically dependent on the olfactory bulb for their prolonged survival
Authors: Schwob JE , Szumowski KE , Stasky AA
Published: March 2018

In most neural systems, developing neurons are trophically dependent on contact with their synaptic target for their survival and for some features of their differentiation. However, in the olfactory system, it is unclear whether or not the survival and differentiation of olfactory sensory neurons depend on contact with the olfactory bulb (normally the sole synaptic target for these neurons). In order to address this issue, we examined neuronal life-span and differentiation in adult rats subjected to unilateral olfactory bulb ablation at least 1 month prior to use. Life-span of a newly generated cohort of olfactory neurons was determined by labeling them at their “birth” via the incorporation of 3H-thymidine. In the absence of the bulb, neurons are continually produced at a twofold greater rate. However, the epithelium on the ablated side is thinner, indicating that average neuronal life-span must be reduced in the targetless epithelium. Indeed, nearly 90% of the labeled neurons disappear from the bulbectomized side between 5 d and 2 weeks of neuronal age. Moreover, on electron microscopic examination, olfactory axons are degenerating in large numbers on the ablated side. Since labeled neurons migrate apically through the width of the epithelium during this same period, it appears that most, if not all, neurons on the ablated side have a life-span on the order of 2 weeks or less. In contrast, there is a more moderate degree of neuronal loss on the unoperated side of the same animals during the first 2 weeks after tracer injection, and that occurs while the neurons are concentrated in the deeper half of the epithelium, suggesting that there is a preexisting population of neurons in the control epithelium that does not die during this period. Likewise, degenerating axons are much less frequent on the unoperated side. We conclude that life-span is significantly shorter for olfactory neurons born in the targetless epithelium and that olfactory neurons are trophically dependent on the presence of the bulb for their prolonged survival. Neuronal differentiation in the absence of the bulb was assessed according to ultrastructural criteria and the pattern of protein expression using antisera to the growth associated protein GAP-43 and the olfactory marker protein. By both measures, most neurons in the epithelium on the bulbectomized side, but not all, are immature.(ABSTRACT TRUNCATED AT 400 WORDS)
Trigeminal ganglion cell processes are spatially ordered prior to the differentiation of the vibrissa pad
Authors: Erzurumlu RS , Jhaveri S
Published: March 2018

The rodent trigeminal system is characterized by the punctate organization of its afferents and neurons that replicate the distribution of mystacial vibrissae and sinus hairs on the snout. We have examined the development of topographic equivalence between the sensory periphery on the snout and the brainstem trigeminal nuclei in rats. Lipophilic tracers Dil (1,1′-dioctodecyl-3,3,3′,3′- tetramethylindocarbocyanine perchlorate) and DiA [4-(4- dihexadecylaminostyryl)-N-methylpyridinium iodide] were used to label trigeminal ganglion cells and their processes differentially from discrete regions of the presumptive vibrissa field in fixed embryos. Our results show that trigeminal ganglion cell processes are spatially ordered as they reach their peripheral and central targets on embryonic day 12 (E12). Peripheral processes of dorsomedially situated ganglion cells course dorsally toward the presumptive vibrissa field, and those of ventrolaterally situated ganglion cells project ventrally. On E13, the central processes of dorsomedially situated ganglion cells enter the brainstem medially whereas those of ventrolaterally situated ganglion cells enter laterally. This spatial order of trigeminal ganglion cell processes precedes the emergence of vibrissa rows in the periphery and the differentiation of brainstem trigeminal nuclei. Thus, the subsequent transfer of the vibrissa-related pattern to the brainstem trigeminal nuclei occurs along a preexisting, spatially aligned bridge formed by the trigeminal ganglion cells.
Cek5, a membrane receptor-type tyrosine kinase, is in neurons of the embryonic and postnatal avian brain
Authors: Pasquale EB , Deerinck TJ , Singer SJ , Ellisman MH
Published: March 2018

Cek5 is a recently identified receptor-type tyrosine kinase of the Eph subclass that is nearly ubiquitously expressed during embryonic development (Pasquale, 1991). Cek5 is predominantly expressed in the avian CNS throughout development, and high levels remain apparent in adult neurons. By means of immunofluorescence microscopy and high- resolution immunoelectron microscopy, Cek5 was found to be expressed in many regions of the chicken brain at various developmental stages, most notably in the hippocampus and cerebellum. The highest concentration of Cek5 was observed in the molecular layer of the cerebellum, associated within the axons of mature granule cells (parallel fibers) and with the cell bodies of immature granule cells. In the axons of parallel fibers, Cek5 was concentrated in the fasciculated nonsynaptic portions. This localization, together with the “adhesion” motifs present in the Cek5 extracellular region suggest that Cek5 may interact with other cell surface-associated molecules and be involved in the growth, guidance, and/or bundling of certain unmyelinated axonal processes. Alternatively (or in addition), Cek5 may represent the receptor for a neurotrophic substance, similar to several other neuronal transmembrane tyrosine kinases.
Denervation of the motor endplate results in the rapid expression by terminal Schwann cells of the growth-associated protein GAP-43
Authors: Woolf CJ , Reynolds ML , Chong MS , Emson P , Irwin N , Benowitz LI
Published: March 2018

Developing and regenerating neurons express high levels of the growth- associated phosphoprotein GAP-43. This membrane protein is not confined to neurons, however, as a number of studies have demonstrated GAP-43 immunoreactivity in central and peripheral glia in vitro and in vivo. We have found that the Schwann cells overlying the terminal motor axon at adult rat skeletal muscle endplates, and the motor axons themselves, are normally not GAP-43 immunoreactive. Within 24 hr of denervation, however, the terminal Schwann cells are positive for a GAP-43 mRNA in situ hybridization signal and are GAP-43 immunoreactive. The immunoreactive GAP-43 cells possess elaborate processes that branch from the endplate region into the perisynaptic zone and stain with defined Schwann cell markers: the calcium binding protein S100 and the low-affinity NGF receptor (NGFr), but not with a fibroblast marker, Thy- 1. Reinnervating motor axons are GAP-43 positive, with an appearance quite different from the GAP-43-positive Schwann cells. The reappearance of nerve endings at the motor endplate is followed by the disappearance of GAP-43 labeling in the Schwann cells and of a retraction of their processes. GAP-43 expression in Schwann cells is therefore state dependent, apparently regulated by neural contact. This protein, which is associated in neurons with neurite formation, may participate in the elaboration of processes by Schwann cells when their contact with axons is disrupted.
A confocal laser microscopic study of enkephalin-immunoreactive appositions onto physiologically identified neurons in the rostral ventromedial medulla
Authors: Mason P , Back SA , Fields HL
Published: March 2018

Neurons in the rostral ventromedial medulla (RVM) are important in the opioid modulation of dorsal horn nociceptive transmission. Systemically administered morphine inhibits one class of RVM cells, the on-cells; excites a second class of RVM cells, the off-cells; and has no effect on a third class, neutral cells. In contrast, iontophoretic application of morphine inhibits on-cells but does not alter the activity of either off- or neutral cells. The present study addresses whether the differential sensitivity to exogenous opioids is correlated with a differential termination pattern onto the three classes of RVM neurons by afferents containing endogenous opioids. Intracellular recordings were made from RVM neurons in rats under light halothane anesthesia. Physiologically characterized neurons were injected with Neurobiotin and then subsequently visualized with a Texas red fluorophore. Thick (50 microns) sections containing labeled RVM cells were processed for enkephalin immunoreactivity (ENK-IR) using an FITC fluorophore and then optically sectioned at 1.5 micron intervals using a dual-channel confocal laser scanning microscope. ENK-IR appositions were found on the somata and dendrites of all on-cells. Although ENK-IR varicosities were also apparently apposed to off- and neutral cells, the density of such appositions was significantly less than the density of ENK-IR appositions onto on-cells. The greater overall density of ENK-IR appositions onto on-cells was apparently due to a concentration of appositions on the soma and proximal dendrites of these neurons. These results support a model of RVM function in which endogenous opioid peptides produce an antinociceptive action by a direct inhibitory action on on-cells that facilitate nociceptive transmission. This on- cell inhibition may produce an additional antinociceptive effect by removing a possible on-cell inhibition of off-cells, which are thought to inhibit nociceptive transmission.
Structural determinants of barium permeation and rectification in non- NMDA glutamate receptor channels
Authors: Dingledine R , Hume RI , Heinemann SF
Published: March 2018

A single site in recombinant glutamate receptor channels of the GluR1- GluR4 family has been previously identified as a key regulator of ion permeation. The natural amino acid at this position (arginine in GluR2 but glutamine in GluR1, GluR3, and GluR4) determines both the ability to pass outward current and the divalent cation permeability of kainate- activated receptor channels. By mutagenesis of GluR6, we demonstrated that the same site also controls the ability to pass outward current in another non-NMDA receptor family. Additional mutations at and near this site in GluR3 indicated that the position of the arginine is critical to function, that the ability to pass outward current is not necessarily linked to low barium permeability, and that the size as well as the charge of the side chain at this position influences barium permeation. These results provide evidence that this site forms part of the selectivity filter of glutamate receptor channels.
Evidence for conditional neuronal activation following exposure to a cocaine-paired environment: role of forebrain limbic structures
Authors: Brown EE , Robertson GS , Fibiger HC
Published: March 2018

The reinforcing properties of cocaine can readily become associated with salient environmental stimuli that acquire secondary reinforcing properties. This form of classical conditioning is of considerable clinical relevance as intense craving can be evoked by the presentation of stimuli previously associated with the effects of cocaine. To understand better the neurobiology of cocaine-induced environment- specific conditioning, Fos expression was examined in the forebrain of rats exposed to an environment in which they had previously received cocaine. These results were compared to those observed following an acute injection of cocaine. Consistent with its stimulant actions, cocaine produced an increase in locomotion that was accompanied by an increase in Fos expression within specific limbic regions (cingulate cortex, claustrum, piriform cortex, lateral septal nucleus, paraventricular nucleus of the thalamus, lateral habenula, and amygdala) as well as the basal ganglia (dorsomedial striatum and nucleus accumbens). Exposure of rats to the cocaine-paired environment also produced an increase in locomotion, as compared to various control groups. In addition to this behavioral effect, conditioned subjects exhibited a significant increase in Fos expression within the cingulate cortex, claustrum, lateral septal nucleus, paraventricular nucleus of the thalamus, lateral habenula, and the amygdala, suggesting increased neuronal activity within these regions. In contrast to the dramatic effects observed within these structures, no conditional activation was observed within the piriform cortex, nucleus accumbens, or dorsal striatum, suggesting that these brain areas are not involved in the conditioned response. The present findings indicate that specific limbic regions exhibit increased neuronal activation during the presentation of cocaine-paired cues and may be involved in the formation of associations between cocaine's stimulant actions and the environment in which the drug administration occurred. Although the nucleus accumbens is necessary for the reinforcing and locomotor effects of cocaine, it does not exhibit a conditional Fos response, suggesting that different neural circuits are involved in the unconditioned and conditioned effects of cocaine.
Postsynaptic spike firing reduces synaptic GABAA responses in hippocampal pyramidal cells
Authors: Pitler TA , Alger BE
Published: March 2018

Using intracellular recording techniques in CA1 cells in the hippocampal slice, we studied the responses of cells to synaptically released and iontophoretically applied GABA. With high-resistance, Cl(- )-filled electrodes, which inverted and enlarged the responses at normal resting potentials, we examined spontaneous GABA-mediated IPSPs. Usually we recorded the spontaneous events in the presence of carbachol (10–25 microM), which significantly increased IPSP frequency and blocked potentially confounding K+ conductances. Following a train of action potentials, spontaneous IPSPs were transiently suppressed. This suppression could not be accounted for by membrane conductance changes following the train or activation of a recurrent circuit. Whole-cell voltage-clamp recordings in the slice indicated that the amplitudes of the spontaneous GABAA inhibitory postsynaptic currents (IPSCs) were also diminished following the action potential train. In some cases BAY K 8644, a Ca2+ channel agonist, enhanced the suppression of IPSPs, while buffering changes in [Ca2+]i with EGTA or BAPTA prevented it. The monosynaptically evoked IPSC in the presence of 6-cyano-7- nitroquinoxaline-2,3-dione (CNQX) and dl-2-amino-5-phosphonovaleric acid (APN) was also diminished following a train of action potentials; however, iontophoretically applied GABA responses did not change significantly. These studies suggest that localized physiological changes in postsynaptic [Ca2+]i potently modulate synaptic GABAA inputs and that this modulation may be an important regulatory mechanism in mammalian brain.
Temporal and harmonic combination-sensitive neurons in the zebra finch's HVc
Authors: Margoliash D , Fortune ES
Published: March 2018

Song learning shapes the response properties of auditory neurons in the song system to become highly selective for the individual bird's own (“autogenous”) song. The auditory representation of autogenous song is achieved in part by neurons that exhibit facilitated responses to combinations of components of song. To understand the circuits that underlie these complex properties, the combination sensitivity of single units in the hyperstriatum ventrale, pars caudale (HVc) of urethane-anesthetized zebra finches was studied. Some neurons exhibited nonlinear temporal summation, spectral summation, or both. The majority of these neurons exhibited low spontaneous rates and phasic responses. Most combination-sensitive neurons required highly accurate copies of sounds derived from the autogenous song and responded weakly to tone bursts, combinations of simple stimuli, or conspecific songs. Temporal combination-sensitive (TCS) neurons required either two or more segments of a single syllable, or two or more syllables of the autogenous song, to elicit a facilitated, excitatory response. TCS neurons integrated auditory input over periods ranging from 80 to 350 msec, although this represents a lower limit. Harmonic combination- sensitive (HCS) neurons required combinations of two harmonics with particular frequency and temporal characteristics that were similar to autogenous song syllables. Both TCS and HCS neurons responded much more weakly when the dynamical spectral features of the autogenous song or syllables were modified than when the dynamical amplitude (waveform) features of the songs were modified. These results suggest that understanding the temporal dynamics of auditory responses in HVc may provide insight into neuronal circuits modified by song learning.
Pharmacological characterization of calcium currents and synaptic transmission between thalamic neurons in vitro
Authors: Pfrieger FW , Veselovsky NS , Gottmann K , Lux HD
Published: March 2018

We recorded from pairs of cultured, synaptically connected thalamic neurons. Evoked excitatory postsynaptic currents (EPSCs) reversed at +17 mV and were blocked reversibly by 1 mM kynurenic acid, a glutamate receptor antagonist. NMDA and non-NMDA receptors mediated excitatory post-synaptic responses, as shown by selective block of EPSC components with 50 microM (+/-)-2-amino-5-phosphonopentanoic acid and 10 microM 6,7-dinitroquinoxaline-2,3-dione, respectively. Inhibitory postsynaptic responses were evoked less frequently and were blocked by the GABAA receptor antagonist (-)-bicuculline methochloride. The pharmacological profiles of whole-cell calcium currents and evoked EPSCs were compared. With 50 microM cadmium chloride (Cd), whole-cell low voltage-activated (LVA) calcium currents were reduced in amplitude and high voltage- activated (HVA) calcium currents and excitatory synaptic transmission were completely blocked. This suggests that the residual calcium influx through LVA channels into the presynaptic terminal does not suffice to trigger transmitter release. A saturating concentration of omega- conotoxin GVIA (omega-CgTx) (2.5 microM) blocked one-third of whole- cell HVA calcium currents and evoked EPSCs. The dihydropyridine nifedipine (50 microM) reversibly reduced whole-cell HVA calcium currents in a voltage-dependent manner but not excitatory synaptic transmission. Cd and omega-CgTx did not alter amplitude distributions of miniature EPSCs, demonstrating that the inhibition of synaptic transmission was due to block of presynaptic calcium channels. We conclude that excitatory glutamatergic transmission in thalamic neurons in vitro was mediated mainly by HVA calcium currents, which were insensitive to omega-CgTx and nifedipine.
Inhibition of calcium channels in rat CA3 pyramidal neurons by a metabotropic glutamate receptor
Authors: Swartz KJ , Bean BP
Published: March 2018

L-Glutamate rapidly and reversibly suppressed Ca channel current in freshly dissociated pyramidal neurons from the CA3 region of the rat hippocampus. L-Glutamate inhibition of Ca channel current could be distinguished from activation of background conductance by appropriate ionic conditions and by distinct pharmacological profiles. Ca channel inhibition by glutamate was mimicked by quisqualate, ibotenate, racemict-ACPD and 1S,3R-ACPD but not by kainate, AMPA, L-aspartate, NMDA, L-2-amino-4-phosphonobutyric acid, or 1R,3S-ACPD; 6-cyano-7- nitroquinoxaline-2,3-dione did not inhibit the response. All agonists inhibited a similar fraction of high-voltage-activated Ca channel current, typically approximately 30%. Concentration-response relations for the agonists were consistent with mediation by a metabotropic glutamate receptor. The stereospecific agonist 1S,3R-ACPD was especially useful since it did not activate background conductances. The fraction of Ca channel current sensitive to 1S,3R-ACPD was partially blocked by omega-conotoxin GVIA but was not sensitive to dihydropyridine antagonists or agonists. The suppression of Ca channels by 1S,3R-ACPD became irreversible when cells were dialyzed with GTP- gamma-S. 1S,3R-ACPD suppressed Ca channel currents in outside-out membrane patches but not in cell-attached patches when applied outside the patch. These results suggest that metabotropic glutamate receptors suppress the activity of N-type Ca channels in CA3 neurons by a mechanism involving G-proteins but not readily diffusible second messengers.