bluuebunny/crossref_metadata_2025 huggingface dataset:
Inositol 1,4,5-trisphosphate-gated channels in cerebellum: presence of multiple conductance states
Authors: Watras J , Bezprozvanny I , Ehrlich BE
Published: April 2018

The mechanism by which inositol 1,4,5-triphosphate (InsP3) induces calcium (Ca) release from the reticulum of canine cerebellum was examined. Reticular membrane vesicles used in these experiments accumulated Ca in the presence of ATP and then released approximately 30% of the accumulated Ca upon addition of micromolar concentrations of InsP3. When these membrane vesicles were incorporated into planar lipid bilayers, InsP3-gated Ca channels were observed. Up to four current amplitudes were observed at a given voltage, yielding conductances of 20, 40, 60, and 80 pS with 50 mM Ca as the current carrier. Thus, the cerebellar InsP3-gated Ca channel exhibits four conductance levels that are multiples of a unit conductance step. Moreover, examination of the single-channel records showed both openings directly to each of the current levels and rapid transitions between current levels. These four conductance steps may reflect the interaction among the four InsP3 receptors thought to comprise the InsP3-gated Ca channel in these tissues. Examination of the InsP3 dependence of channel openings and Ca release from vesicles, however, yielded Hill coefficients of 1-1.3. Thus, we hypothesize that it takes only one molecule of InsP3 to open the channel. The observation that the conductance of the InsP3-gated Ca channel assumes four levels that are multiples of a unit conductance suggests that the number of interacting InsP3 receptors in one complex can vary from one to four and supports the hypothesis that the channel is a tetramer.
Regulation of neuropeptide stoichiometry in neurosecretory cells
Authors: Hekimi S , Fischer-Lougheed J , O'Shea M
Published: April 2018

Peptidergic neurons and neurosecretory cells often contain multiple peptides, where they may be present in characteristic ratios. In this article, we describe how a set of five colocalized and coreleased peptides, two adipokinetic hormones (AKH I and AKH II), and three dimeric peptides (APRP 1, 2, and 3) are synthesized by the neurosecretory cells of the corpora cardiaca of the locust Schistocerca gregaria. We show that the five peptides are produced from two prohormones called pro-AKH I, or A-chain, and pro-AKH II, or B-chain. The amino acid sequences as determined by direct protein sequencing are given for both. Prior to processing, the two prohormones form the three possible dimers by the oxidation of the single cysteine residues found in each. The dimers, not the prohormones, are the direct precursors of the peptides. The dimeric precursors are called P1 (A-A), P2 (A-B), and P3 (B-B). Processing results in the generation of the two AKH peptides and the three dimers called adipokinetic hormone precursor-related peptides, or APRPs. Throughout postembryonic development, we show that the ratios of the AKHs and APRPs change dramatically and systematically. We show that these changes can be explained by the differential regulation of the synthesis of the two prohormones and their random association into dimers that are then completely processed. Regulation of peptide stoichiometry may expand the potential information content of the signals generated by multipeptide-producing neurons.
Multiple cholinergic markers are unexpectedly not altered in the rat dentate gyrus following entorhinal cortex lesions
Authors: Aubert I , Poirier J , Gauthier S , Quirion R
Published: April 2018

Since major cholinergic deficits are observed in Alzheimer's disease, the development of models to study possible cholinergic plasticity has generated great interest. In this regard, it has been shown that lesions of the entorhinal cortex, which sends glutamatergic projections to the hippocampus, promote the sprouting and plasticity of presumptive cholinergic septohippocampal fibers in the dentate gyrus, as revealed by AChE histochemistry. This sprouting was reported to be evident at 8 d and up to 30 d postlesion (DPL) and is now widely used as a model of cholinergic neuronal plasticity. In the present study, unilateral lesions of the entorhinal cortex were made in adult rats, and the status of various putative pre- and postsynaptic cholinergic markers was assessed after 2, 4, 8, 14, and 30 DPL. As expected, AChE was increased in the outer molecular layer of the ipsilateral dentate gyrus from 8 to 30 DPL. In contrast, the activity of ChAT, the enzyme responsible for the synthesis of ACh, and the densities of specific binding sites for 3H-AH5 183/vesamicol (blocker of the ACh vesicular transport sites), 3H-hemicholinium-3 (blocker of the high-affinity choline uptake sites), muscarinic-M2 (3H-AF-DX 384 and 3H-ACh), muscarinic-M1 (3H-pirenzepine), and nicotinic (3H-N- methylcarbamylcholine) cholinergic receptors were not increased on the ipsilateral molecular layer of the dentate gyrus, as compared to their contralateral controls. We conclude that the increase in AChE staining in the molecular layer of the dentate gyrus following entorhinal cortex lesions may be due to changes in noncholinergic neurons.
Medial lemniscal and spinal projections to the macaque thalamus: an electron microscopic study of differing GABAergic circuitry serving thalamic somatosensory mechanisms
Authors: Ralston HJ , Ralston DD
Published: April 2018

The synaptic relationships formed by medial lemniscal (ML) or spinothalamic tract (STT) axon terminals with neurons of the somatosensory ventroposterolateral thalamic nucleus of the macaque monkey have been examined quantitatively by electron microscopy. ML and STT axons were labeled by the anterograde axon transport of WGA-HRP following injection of the tracer into the contralateral dorsal column nuclei, or the dorsal horn of the spinal cord, respectively. Thalamic tissue was histochemically reacted for the presence of HRP. Serial thin sections were stained with a gold-labeled antibody to GABA, to determine which neuronal elements exhibited GABA immunoreactivity (GABA- ir). Serially sectioned thalamic structures were recorded in electron micrographs and reconstructed in three dimensions by computer. Individual ML axon terminals form multiple synaptic contacts with segments of the proximal dendritic trees of thalamocortical relay neurons and also synapse upon the dendritic appendages of GABA-ir interneurons (local circuit neurons). These GABA-ir dendritic appendages contain synaptic vesicles and are presynaptic (presynaptic dendrites) to the same segments of relay neuron dendrites that receive ML contacts. When analyzed in serial sections and reconstructed by computer, the ML terminals form triadic relationships (ML, GABA appendage, and relay neuron dendrite) or more complex glomerular arrangements involving multiple appendages, all of which then contact the relay neuron dendritic segment. In contrast, multiple STT terminals make synaptic contacts along segments of projection neuron dendrites and are usually the only type of profile to contact that segment of dendrite. More than 85% of the spinal afferents form simple axodendritic synapses with relay cells and do not contact GABA-ir appendages. The thalamic synaptic relationships of ML terminals are fundamentally different from those formed by the STT. Because STT neurons predominatly transmit information about noxious stimuli, the simple axodendritic circuitry of the majority of these spinal afferents suggests that the transmission of noxious information is probably not subject to GABAergic modulation by thalamic interneurons, in contrast to the GABAergic processing of non-noxious information carried by the ML afferents. The differences in the GABAergic circuits of the thalamus that mediate ML and STT afferent information are believed to underlie differential somatosensory processing in the forebrain. We suggest that changes in thalamic GABAergic dendritic appendages and GABA receptors following CNS injury may play a role in the genesis of some central pain states.
Developmental regulation of voltage-gated K+ channel and GABAA receptor expression in Bergmann glial cells
Authors: Muller T , Fritschy JM , Grosche J , Pratt GD , Mohler H , Kettenmann H
Published: April 2018

Bergmann glial cells are closely associated with neurons: during development they provide guiding structures for migrating granule cells and in the adult cerebellum they display intimate interactions with Purkinje cells. In this study, we have addressed the question of whether such changes in neuronal-glial interactions during development are accompanied by variations in the membrane properties of Bergmann glial cells. We used a mouse cerebellum slice preparation to study membrane currents of the Bergmann glial cells at various stages of development in situ using the patch-clamp technique. The distinct morphology of Bergmann glial cells was revealed by Lucifer yellow injections during recording. While Bergmann glial cells in mice of postnatal day 20 (P20) to P30 have thick processes with arborized, irregularly shaped leaf-like appendages, the processes of cells from younger mice (P5-P7) are thinner and smoother. This morphological maturation is accompanied by a variation in voltage-gated currents. In cells from P5 to P7, delayed outward- and inward-rectifying K+ currents were recorded, while older Bergmann glial cells were characterized by, large, voltage- and time-independent K+ currents. In addition, application of GABA induces two effects, a rapid activation of a Cl- conductance and a longer-lasting decrease in the (resting) K+ conductance. Both effects were mediated by benzodiazepine-insensitive GABAA receptors. Responses in cells of P5-P7 mice were large as compared to the small or even undetectable responses in P20-P30 cells. These GABAA receptors were characterized immunohistochemically in mice and rat brain sections with five subunit-specific antibodies. Bergmann glial cells exhibit a distinct but transient immunoreactivity for the GABAA receptor alpha 2-, alpha 3-, and delta-subunits. Staining is maximal between P7 and P10 and decreases gradually thereafter. In contrast, antibodies to the alpha 1- and beta 2,3-subunits fail to decorate Bergmann glial cells, although they yield a prominent staining of both the Purkinje cells and the granule cells. These changes in the Bergmann glial cell membrane properties and GABAA receptor expression suggest a transition between functional states during development of the Bergmann glial cells.
Overproduction of corticotropin-releasing factor in transgenic mice: a genetic model of anxiogenic behavior
Authors: Stenzel-Poore MP , Heinrichs SC , Rivest S , Koob GF , Vale WW
Published: April 2018

Corticotropin-releasing factor (CRF) is released in response to various stressors and regulates adrenocorticotropin secretion and glucocorticoid production. In addition to its endocrine functions, CRF acts as a neuromodulator in extra-hypothalamic systems and has been shown to play a role in behavioral responses to stress. CRF overproduction has been implicated in affective disorders such as depression and anorexia nervosa. A transgenic mouse model of CRF overproduction has been developed in order to examine the endocrine and behavioral effects of chronic CRF excess. CRF transgenic animals exhibit endocrine abnormalities involving the hypothalamic-pituitary- adrenal axis such as elevated plasma levels of ACTH and glucocorticoids. The present series of experiments tested the hypothesis that chronic overproduction of CRF throughout the life-span of these animals may lead to an anxiogenic behavioral state. CRF transgenic mice and normal littermate controls were tested by measuring locomotor activity in a novel environment and through the use of an elevated plus-maze as indices of anxiety. CRF transgenic animals exhibited an increase in anxiogenic behavior, an effect known to occur following central administration of CRF in mice and rats. Injection of the CRF antagonist alpha-helical CRF 9–41 into the lateral cerebral ventricles reversed the anxiogenic state observed in the CRF transgenics. This finding supports the possibility that central CRF overproduction may mediate the anxiogenic behavior exhibited in this animal model. Thus, CRF transgenic mice represent a genetic model of CRF overproduction that provides a valuable tool for investigating the long-term effects of CRF excess and dysregulation in the CNS.
Early peripheral nerve regeneration after crushing, sectioning, and freeze studied by implanted electrodes in the cat
Authors: Fugleholm K , Schmalbruch H , Krarup C
Published: April 2018

Regeneration of axons after Wallerian degeneration is influenced by various factors localized to the distal nerve stump. We have examined elongation of axons to assess the relative influence of basal lamina and of Schwann cells in lesions with and without interruption of the Schwann cell tubes. In particular, we wanted to follow the growth of axons throughout the same distal nerve stump. Silicone cuff and patch electrodes with multiple contacts were therefore implanted around hindlimb nerves proximal and distal to the lesion. The tibial nerve was cut and sutured (15 nerves) or crushed (10 nerves). A 20–25-mm-long segment distal to the lesion was in addition frozen in four crushed and in seven sectioned nerves to eliminate the Schwann cells. Six unlesioned tibial nerves from four cats served as control. Reinnervation of plantar muscle occurred 42–54 d after nerve crushing and 42–84 d after nerve sectioning (P < 0.01). Regeneration was followed by weekly electrophysiological observations that allowed serial identification of the fastest-growing individual axons, with conduction velocities of 0.5–3 m/sec and amplitudes of 0.15–0.5 microV. Unmyelinated axons were present at the most distal lead of the electrode array from which action potentials were identified. The rate of elongation after both crushing and crush+freeze was 3–4 mm/d, and after sectioning only 2.5 mm/d (P < 0.01). Freezing in addition to sectioning was associated with even slower elongation of 1.2 mm/d. Distal to the frozen portion of the nerve elongation accelerated. Our findings suggest that regeneration was slowed throughout the nerve distal to a sectioning compared with a crushing lesion, and that depletion of Schwann cells only influenced axonal elongation after interruption of the basal lamina. This suggests that the basal lamina tubes at the lesion site may facilitate the action of neurotropic factors of distal origin.
Coactivation of prefrontal cortex and inferior parietal cortex in working memory tasks revealed by 2DG functional mapping in the rhesus monkey
Authors: Friedman HR , Goldman-Rakic PS
Published: April 2018

Functional studies of the dorsolateral prefrontal cortex and the inferior parietal lobe of the rhesus monkey have implicated the former in spatial mnemonic function and the latter in visuospatial processing. We used the 14C-2-deoxyglucose (2DG) method to assess the contribution of these cortical regions to the cognitive performance of monkeys on working memory tasks. In these experiments, one group of monkeys (WORK) was trained to perform tasks (delayed spatial alternation, spatial delayed response, or delayed object alternation) that specifically engaged working memory processing. Local cerebral glucose utilization (LCGU) rates in the WORK group was compared with LCGU rates for a second group of monkeys (CONT) tested on one of two tasks (visual pattern discrimination or sensory-motor) that relied upon associative memory. The results showed that in comparison to the CONT group, working memory performance significantly enhanced LCGU by 19% in the principal sulcus region of prefrontal cortex and by 11–20% in regions of the inferior parietal cortex corresponding to areas 7A, 7B, 7IP, and 7M. By contrast, LCGU in the auditory cortex was similar for both groups. In all areas examined, metabolic activation peaked in lower layer III where the majority of associational and callosal neurons lie. Correlation analyses of LCGU and behavioral task parameters indicated that LCGU in the parietal subdivisions was significantly related either to the accuracy of performance or to the number of trials completed on the 2DG test. In contrast, LCGU in the principal sulcus was positively correlated with task difficulty. These findings suggest that the enhancement of LCGU in the principal sulcus was primarily influenced by the mnemonic components of the tasks whereas LCGU in the inferior parietal cortex was influenced by their sensory-motor demands. These are the first results showing concurrent metabolic activation of the prefrontal and parietal cortex in monkeys performing working memory tasks and they support the suggestion that these cortical regions represent two important nodes in a neural network mediating spatial working memory in the monkey (Goldman-Rakic, 1988). Further, the present report reinforces the power of the 2DG method for functional mapping as these areal and laminar results could not be readily appreciated at this resolution in any other methodological context.
Overexpression of a potassium channel gene perturbs neural differentiation
Authors: Jones SM , Ribera AB
Published: April 2018

Functional regulation of potassium currents in developing neurons is pivotal for changes in excitability and action potential waveform. Here, we test whether an excess of potassium channel transcripts is sufficient to drive functional expression of potassium current and shortening of the duration of the action potential. Injection of Shaker- like potassium channel transcripts into two-cell stage embryos achieves increases in RNA levels. The elevated levels of potassium channel RNA produce larger delayed-rectifier currents. Action potential durations are briefer, indicating that larger potassium currents are not compensated by changes in inward currents. Strikingly, overexpression of potassium current RNA leads to a reduction in the number of morphologically differentiated neurons in culture. We suggest that, by prematurely reducing the duration of the impulse, early overexpression of potassium channel activity suppresses normal developmental cues.
A novel epitope of entactin is present at the mammalian neuromuscular junction
Authors: Chiu AY , Ko J
Published: April 2018

The extracellular matrix (ECM) at the neuromuscular junction (NMJ) is biochemically and functionally specialized, and bears molecules that can regulate both the formation and function of this peripheral synapse. We have previously purified one synaptic component of the muscle ECM--a unique laminin isoform named s-laminin--from a rat schwannoma cell line (Chiu et al., 1992). To develop new probes for the ECM, monoclonal antibodies were generated against other components produced by this cell line. One of these new antibodies, 9H6, binds selectively at the synaptic cleft of NMJs in adult rats, but not at extrasynaptic sites on the muscle surface. On Western blots, 9H6 recognizes a 150 kDa band that colocalizes, and copurifies with the laminin-binding, ECM glycoprotein entactin under both reducing and nonreducing conditions. N-terminal sequence analysis also indicates that the 9H6 antigen is related to entactin. However, polyclonal antibodies to entactin stain both synaptic and extrasynaptic sites. Thus, 9H6 appears to identify an entactin epitope with a very restricted distribution. Treatment with N-glycanase reduces the molecular mass of entactin and eliminates 9H6 binding, suggesting that the 9H6 epitope at synapses is dependent on glycosylation. Recent studies have shown that novel isoforms of laminin, collagen IV, agrin, and AChE are selectively sequestered at the NMJ. Our results indicate that the entactin present at the synaptic cleft also differs from entactin present outside the synapse. The synaptic form of entactin may contribute to the unique functions of the ECM at the neuromuscular synapse.
Synaptic plasticity in the rat supraoptic nucleus during lactation involves GABA innervation and oxytocin neurons: a quantitative immunocytochemical analysis
Authors: Gies U , Theodosis DT
Published: April 2018

The hypothalamic supraoptic nucleus (SON) is known to undergo synaptic remodeling in response to physiological stimuli, such as lactation. We here investigated the involvement of the GABAergic innervation in such plasticity by carrying out comparative ultrastructural analyses after postembedding immunogold labeling for GABA on sections of the SON from virgin and lactating rats. Using random single-section analysis to estimate the numerical density of synapses (from areal measurements of the anterior, mid, and posterior portions of the nucleus), we found that the overall density in either group was about 35 x 10(6) synapses/mm3, of which over one-third were GABA immunoreactive. The GABAergic terminals formed mainly symmetrical synaptic contact on neurosecretory somata and dendrites; the density of axodendritic contacts was twice that of axosomatic contacts. Despite hypertrophy of the neurosecretory neurons in lactating rats, the overall synaptic density did not diminish and was similar to that evaluated in virgin rats. When we estimated synaptic densities in the neuropil (by subtracting the proportion of sampled areas occupied by soma profiles), we found a statistically significant increase in the density of GABAergic synapses, in particular in the mid and posterior portions of the SON in lactating animals. On the other hand, the density of GABA- immunonegative synapses did not differ in the two groups. Terminals contacting more than one postsynaptic element in the same plane of section (“shared” synapses) were visible in the nuclei of virgin and lactating rats and about half in each group were GABAergic. They were comparatively rare but their incidence doubled in lactating animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Basal cortisol levels and cognitive deficits in human aging
Authors: Lupien S , Lecours AR , Lussier I , Schwartz G , Nair NP , Meaney MJ
Published: April 2018

A group of 19 healthy elderly subjects previously shown to differ in terms of their cortisol levels over a 4 year period were administered a neuropsychological test battery assessing memory, attention, and language. Correlational analyses performed on various corticosteroid measures showed that the slope of the change in cortisol levels over time predicted cognitive deficits in this elderly population. Aged subjects showing a significant increase in cortisol levels with years and with high current basal cortisol levels were impaired on tasks measuring explicit memory and selective attention when compared to aged subjects presenting either decreasing cortisol levels with years or increasing cortisol levels with moderate current basal cortisol levels. We further showed that subjects presenting a decrease in cortisol levels with years performed as well as young healthy subjects with regard to cognitive performance. Thus, impaired cognitive performance was associated with recent evidence of hypothalamic-pituitary-adrenal (HPA) dysregulation and elevated basal cortisol levels. These results are consistent with recent animal studies showing the existence of subpopulations of aged rats that differ in HPA activity and cognitive performance. Finally, the pattern of cognitive results related to the cortisol history of subjects is in agreement with a role played by the hippocampus in age-related HPA dysfunction and cognitive performance.
Heterogeneous subregional binding patterns of 3H-WIN 35,428 and 3H-GBR 12,935 are differentially regulated by chronic cocaine self- administration
Authors: Wilson JM , Nobrega JN , Carroll ME , Niznik HB , Shannak K , Lac ST , Pristupa ZB , Dixon LM , Kish SJ
Published: April 2018

We examined the influence of chronic cocaine exposure, in an unlimited access self-administration paradigm, on density of the dopamine transporter (3H-WIN 35,428 and 3H-GBR 12,935 binding) and concentration of monoamine (dopamine, serotonin, noradrenaline and metabolites) neurotransmitters in rat brain. In normal rodent striatum 3H-WIN 35,428 and 3H-GBR 12,935 binding to the dopamine transporter, although generally similar, showed different subregional rostrocaudal and mediolateral gradients, suggesting that the two ligands might bind to different subtypes or states of the dopamine transporter. Following chronic, unlimited access cocaine self-administration, binding of 3H- WIN 35,428 was significantly elevated in whole nucleus accumbens (+69%, p < 0.001) and striatum (+65%, p < 0.001) on the last day of cocaine exposure (“on-cocaine group”); whereas in the 3 week withdrawn animals (“cocaine-withdrawn group”), levels were either normal (striatum) or reduced (-30%, p < 0.05, nucleus accumbens). Although similar changes in 3H-GBR 12,935 binding were observed, this dopamine transporter ligand showed a smaller and highly subregionally dependent increase in binding in striatal subdivision of the on-cocaine group, but a more marked binding reduction in the cocaine-withdrawn animals. As compared with the controls, mean dopamine levels were reduced in striatum (-15%, p < 0.05) of the on-cocaine group and in nucleus accumbens (-40%, p < 0.05) of the cocaine-withdrawn group. These data provide additional support to the hypothesis that some of the long-term effects of cocaine exposure (drug craving, depression) could be consequent to reduced nucleus accumbens dopamine function. Our data also suggest that dopamine transporter concentration, and perhaps function, might undergo up- or downregulation, either as a direct effect of cocaine, or indirectly as part of a homeostatic response to altered synaptic dopamine levels, and therefore might participate in the neuronal events underlying cocaine-induced behavioral changes.
Astrocytes inhibit Schwann cell proliferation and myelination of dorsal root ganglion neurons in vitro
Authors: Guenard V , Gwynn LA , Wood PM
Published: April 2018

Schwann cells promote the regrowth of nerve fibers in both the PNS and CNS and might thus be of value in strategies to promote repair following injury or demyelination in the CNS. The effectiveness of Schwann cells in promoting repair could, however, be limited by interactions with reactive astrocytes that are prominent at lesioned and demyelinated sites. To investigate this possibility, experiments were performed to determine the influence of cortical astrocytes on Schwann cell proliferation and myelination of dorsal root ganglion (DRG) neurons in vitro. DRG neurons from embryonic rats and Schwann cells, astrocytes, and fibroblasts isolated from the sciatic nerve, cerebral cortex, and cranial periosteum, respectively, of neonatal rats were purified and then recombined to provide neuron-Schwann cell, neuron-Schwann cell-astrocyte, and neuron-Schwann cell-fibroblast cultures. Astrocytes inhibited both neuron-dependent Schwann cell proliferation and the myelination of axons by Schwann cells. The expression of galactocerebroside, but not of the O4 antigen, was inhibited by astrocytes, suggesting that astrocytes blocked Schwann cell differentiation prior to the onset of myelination. Ultrastructural analysis of the cultures also indicated that both axonal ensheathment and the segregation of large axons into 1:1 relationships were decreased in the presence of astrocytes. Astrocytes did not affect the expression of the basal lamina components type IV collagen and laminin, and basal lamina formation assessed by electron microscopy was only slightly decreased. Some of these inhibitory effects appear to be mediated by diffusible factors since astrocyte-conditioned medium also reduced Schwann cell myelination. Fibroblasts or fibroblast-conditioned medium did not induce such inhibitory effects, indicating that the effects were astrocyte specific. We conclude that cortical astrocytes release a soluble factor(s) that inhibits specific aspects of neuron- Schwann cell interactions leading to myelination.
Muscarinic modulation of a pattern-generating network: control of neuronal properties
Authors: Bal T , Nagy F , Moulins M
Published: April 2018

The aim of this article is to investigate the cellular mechanisms underlying cholinergic modulation of the pyloric network in the stomatogastric ganglion (STG) of the Cape lobster Jasus Ialandii. Bath application of the muscarinic agonists muscarine, oxotremorine, and pilocarpine on the STG activates a rhythmic pattern from a quiescent pyloric network. The mechanisms of this modulation were investigated on individual pyloric neurons isolated both from synaptic interactions within the network (by photoinactivation of most of the presynaptic neurons and pharmacological blockade of the remaining synapses) and from central inputs (by a sucrose block of the input nerve). All three muscarinic agonists activated bursting and plateau properties of all the neurons comprising the pyloric network. The activation was dose dependent, and was blocked by the muscarinic antagonists atropine, pirenzepine, and scopolamine. The oscillatory behavior triggered by the muscarinic stimulation was specific to each type of pyloric neuron. The isolated neuron AB had the shortest oscillation period and depolarizing phase. The constrictor neurons (LP, PY, IC) were the slowest oscillators, and only oscillated upon hyperpolarizing current injection. Under muscarinic modulation, the individual bursting activities of the isolated pyloric neurons were of the same type as their activities when isolated from the network but modulated by central inputs (Bal et al., 1988). The VD neuron is an exception since it was a rapid oscillator in the latter situation and became a slow oscillator when modulated by a single muscarinic agonist. To determine the relative importance of the muscarinic-dependent bursting properties of the individual pyloric neurons in the operation of the intact network, a progressive reconstruction of the synaptic circuitry was attempted. We found that under certain conditions of muscarinic modulation a new composite pacemaker could be created, composed of the electrically coupled VD, AB, and PD neurons. This can result in the generation of new pyloric patterns that were very sensitive to the membrane potential of individual network neurons. The data also confirmed that, in a rhythmic “pattern-generating network,” the pacemaker role may not be definitely attributed to a given neuron but instead could be assigned to other neurons by modulation of their respective oscillatory capabilities.
An animal model of early-treated PKU
Authors: Diamond A , Ciaramitaro V , Donner E , Djali S , Robinson MB
Published: April 2018

Phenylketonuria (PKU) is a genetic disorder in which the hydroxylation of phenylalanine (Phe) to tyrosine is severely disrupted. If PKU is left untreated, severe mental retardation results. The accepted treatment is to restrict dietary intake of Phe. It has generally been thought that cognitive impairments are prevented if levels of Phe in plasma are maintained at or below five times the normal level. However, we recently documented that children treated early and continuously for PKU or children mildly hyperphenylalaninemic, who have levels of Phe in plasma approximately three to five times normal, still have cognitive impairments. These impairments are specific to the functions of frontal cortex (A. Diamond, W. Hurwitz, E. Lee, W. Grover, and C. Minarcik, unpublished observations). To investigate the mechanism underlying these cognitive deficits, an animal model of this condition was developed and characterized. Thirty-six rat pups were divided into three groups. The first group was treated pre- and postnatally with Phe and alpha-methylphenylalanine (a phenylalanine hydroxylase inhibitor). The second group was injected postnatally with Phe and alpha- methylphenylalanine. The third group received postnatal control injections. The mild plasma Phe elevations in the two experimental groups produced significant behavioral and neurochemical effects. Both experimental groups were impaired on a task dependent on frontal cortex, delayed alternation. Levels of dopamine, homovanillic acid (HVA), norepinephrine, and 5-hydroxyindole acetic acid (5-HIAA) were measured in medial prefrontal cortex, anterior cingulate cortex, striatum, and nucleus accumbens. The largest neurochemical reductions observed were in HVA and were in the two frontal cortical areas (medial prefrontal cortex and anterior cingulate cortex). There were modest reductions in HVA in the nucleus accumbens but no significant changes in HVA, or in any other metabolite or neurotransmitter, in the striatum. The levels of 5-HIAA were also reduced in all brain regions examined. There was no effect on norepinephrine in any of the four regions examined. Reduced levels of HVA in medial prefrontal cortex were the only neurochemical effect that significantly correlated with every measure of performance on the delayed alternation task. This study provides evidence of deleterious effects from mild elevations in the levels of Phe in plasma previously considered small enough to be safe. These effects include impaired performance on a cognitive task dependent on frontal cortex and reduced HVA levels in frontal cortex.(ABSTRACT TRUNCATED AT 400 WORDS)
Neuronal loss induced in limbic pathways by kindling: evidence for induction of hippocampal sclerosis by repeated brief seizures
Authors: Cavazos JE , Das I , Sutula TP
Published: April 2018

Repeated kindled seizures induce long-lasting physiological and morphological alterations in the hippocampal formation. In the dentate gyrus (DG), the morphological alterations induced by kindled seizures include loss of polymorphic neurons in the hilus, mossy fiber axon sprouting, and synaptic reorganization of the mossy fiber pathway. In this study, quantitative stereological methods were used to determine the distribution and time course of neuronal loss induced by 3, 30, or 150 kindled generalized tonic-clonic seizures in hippocampal, limbic, and neocortical pathways. Neuronal loss was observed in the hilus of the DG and CA1 after three generalized tonic-clonic seizures, and progressed in these sites to 49% and 44% of controls after 150 seizures. Neuronal loss was also observed in CA3, entorhinal cortex, and the rostral endopyriform nucleus after 30 seizures, and was detected in the granule cell layer and CA2 after 150 seizures. There was no evidence of neuronal loss in the somatosensory cortex after 150 seizures. The time course of the neuronal loss demonstrated selective vulnerability of hippocampal neuronal populations to seizure-induced injury, and suggests that even brief seizures may induce excitotoxic injury in vulnerable neuronal populations. Repeated brief seizures induced neuronal loss in a distribution that resembled hippocampal sclerosis, the most common lesion observed in human epilepsy. The results demonstrated that kindling induces alterations in neural circuitry in a variety of locations in the limbic system, and suggest that hippocampal sclerosis may be acquired in human epilepsy as a consequence of repeated seizures.
Morphologic and biochemical analysis of the intracellular trafficking of the Alzheimer beta/A4 amyloid precursor protein
Authors: Caporaso GL , Takei K , Gandy SE , Matteoli M , Mundigl O , Greengard P , De Camilli P
Published: April 2018

Abnormal metabolic processing of the beta/A4 amyloid precursor protein (APP) has been implicated in the pathogenesis of Alzheimer disease. Several aspects of normal APP processing have been elucidated, but the precise cellular trafficking of APP remains unclear. To investigate APP trafficking pathways further, we have examined the subcellular distribution of APP in rat brain tissue and a variety of cultured cell types, and correlated this distribution with the biochemical processing of APP. In immunofluorescence microscopy of rat brain sections, APP immunoreactivity was concentrated in the Golgi complex and in proximal axon segments. In addition, a lower level of punctate fluorescence was visible throughout the neuropil. By immunoelectron microscopy of rat brain tissue fragments, APP was found associated with Golgi elements and with medium-sized, invaginated vesicles in both axons and dendrites. Prominent localization of APP to the Golgi complex was also found in primary cultures of rat hippocampal neurons and in non- neuronal cell lines. When cultured cells were treated with brefeldin A (BFA), APP immunoreactivity changed from a Golgi-like to an endoplasmic reticulum-like distribution. No APP was detected in the BFA-induced reticulum identified by the transferrin receptor, indicating that concentration of APP in the Golgi does not reflect recycling between the trans-Golgi network and early endosomal system. In immunoblots of BFA-treated cells, there was an accumulation of full-length APP and inhibition of APP secretory processing. Treatment with phorbol ester resulted in a marked elevation of APP secretion, but no obvious redistribution of APP immunoreactivity was apparent at the light microscope level. The lysosomotropic drug chloroquine induced accumulation of APP in cell lysates, as seen by immunoblotting. Immunofluorescence microscopy of chloroquine-treated cells demonstrated a colocalization of APP with the lysosomal marker Igp 120, whereas no colocalization was seen in untreated cells. Taken together, these results support a scheme in which APP is concentrated in the Golgi complex as it travels through the central vacuolar system en route to the plasma membrane for secretion of its amino-terminal domain and/or to lysosomes for degradation.
Induction of a cellular defense reaction is accompanied by an increase in sensory neuron excitability in Aplysia
Authors: Clatworthy AL , Castro GA , Budelmann BU , Walters ET
Published: April 2018

The complexity of vertebrate immune and nervous systems makes detailed cellular analysis of neuroimmune interactions a challenging prospect. The immune systems of invertebrates, although much less complex than their vertebrate counterparts, share basic cellular defense responses to wounded self or nonself. We have developed a simple model system to study neuroimmune interactions using an invertebrate preparation well suited to detailed cellular analysis. Loose ligation of peripheral nerves in Aplysia induced a cellular defense reaction evidenced by the accumulation of large numbers of amebocytes at the ligation site. From 5 to 30 d after ligation, the excitability of the soma of sensory neurons having axons in ligated nerves was increased compared to contralateral sensory neurons with axons in nonligated nerves. Spike threshold and afterhyperpolarization were reduced, and spike amplitude and duration were increased. Spike accommodation was also decreased such that sensory neurons on the ligated side fired more spikes to a 1 sec intracellular depolarizing pulse than control sensory neurons. These effects are unlikely to be accounted for by ligation-induced injury of sensory axons since both morphological and electrophysiological evidence indicated that the axons in ligated nerves were healthy and able to conduct action potentials. Amebocytes activated by the presence of nonself may release factors that lead to a central sensitization of sensory neurons with axons in close proximity to the amebocytes.
Single odors differentially stimulate dual second messenger pathways in lobster olfactory receptor cells
Authors: Boekhoff I , Michel WC , Breer H , Ache BW
Published: April 2018

Quench-flow measurements are used to determine the subsecond kinetics of odor-induced changes in second messenger concentrations in lobster olfactory receptor neurons. Individual odors transiently and differentially increase the production of both adenosine cAMP and inositol 1,4,5-trisphosphate (IP3) within 50 msec of odor stimulation. The ability of two different odors to stimulate cAMP and IP3 correlates with the odors' ability to excite and inhibit receptor cells physiologically. These results strengthen the proposition, heretofore based largely on evidence from cultured cells, that dual second messenger pathways mediate excitatory and inhibitory input to lobster olfactory receptor cells.
A cyclic AMP-dependent form of associative synaptic plasticity induced by coactivation of beta-adrenergic receptors and metabotropic glutamate receptors in rat hippocampus
Authors: Gereau RW , Conn PJ
Published: April 2018

Recent studies suggest that increases in intracellular cAMP increase evoked synaptic responses in area CA1 of the hippocampus. We recently reported that activation of metabotropic glutamate receptors (mGluRs) in hippocampal slices potentiates cAMP responses to activation of other receptors that are positively coupled to adenylyl cyclase through Gs. It is possible that by enhancing cAMP responses, mGluRs could markedly potentiate the ability of agonists of Gs-coupled receptors to potentiate synaptic responses in area CA1. Such synergistic activation of a second messenger system could be involved in an associative form of neuronal plasticity in which simultaneous activation of two independent inputs to a cell is required for induction of a given change in synaptic transmission or neuronal excitability. We therefore tested the hypothesis that coactivation of mGluRs and a Gs-coupled receptor (the beta-adrenergic receptor) could lead to large increases in cAMP accumulation in hippocampus and thereby increase synaptic responses in area CA1. We report that coactivation of mGluRs and beta- adrenergic receptors leads to a lasting (> 30 min) increase in the amplitude of evoked population spikes at the Schaffer collateral-CA1 synapse. This effect is not accompanied by an increase in excitatory postsynaptic currents or by a decrease in synaptic inhibition in area CA1, suggesting that it is not mediated by a lasting change in excitatory or inhibitory synaptic transmission. However, coactivation of these receptors leads to a persistent depolarization of CA1 pyramidal cells with a concomitant increase in input resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
Distribution of m1-m4 muscarinic receptor proteins in the rat striatum: light and electron microscopic immunocytochemistry using subtype- specific antibodies
Authors: Hersch SM , Gutekunst CA , Rees HD , Heilman CJ , Levey AI
Published: April 2018

Muscarinic ACh receptors mediate complex and clinically important effects in the striatum. To better understand the roles of the different muscarinic receptor subtypes (m1-m4), we have determined the cellular and subcellular distribution of the m1-m4 receptor proteins in the rat neostriatum using subtype-specific antibodies and avidin-biotin- peroxidase immunocytochemistry for light and electron microscopy. m1 receptor protein is expressed in 78% of neurons and is enriched in spiny dendrites and at postsynaptic densities. A small number of m1- immunoreactive axon terminals were observed, all forming asymmetrical synapses. About 2.5% of striatal neurons express m2 receptor protein with reaction product evident, by light microscopy in scattered large oval neurons with enfolded nuclei and long aspiny dendrites. By electron microscopy, m2 immunocytochemistry labeled somata, aspiny dendrites, and many axon terminals. Most axon terminals containing m2 make symmetrical synapses with somata, and dendritic shafts and spines. In addition, many m2-immunoreactive axon terminals formed asymmetrical synapses with spines or dendrites. m3 receptor protein was not evident in somata by light microscopy but was present in a distinct population of small-caliber spiny dendrites as well as in axon terminals forming asymmetrical synapses with spines. m4 receptor protein was heterogeneously distributed in the neostriatum and localized to 44% of striatal cells. m4-positive neurons had the ultrastructural features of medium spiny neurons with reaction product particularly concentrated in spines, often at postsynaptic densities. Axon terminals containing m4 form asymmetrical synapses, primarily with spines. These findings indicate that the muscarinic receptor proteins occur in distinct populations of striatal neurons; that the receptor proteins concentrate postsynaptically at synapses, including many considered to be noncholinergic; that m2 is the predominant muscarinic autoreceptor in the striatum; and that each receptor subtype may be a presynaptic heteroceptor in the striatum modulating extrinsic striatal afferents.
Fetal NGF augmentation preserves excess trigeminal ganglion cells and interrupts whisker-related pattern formation
Authors: Henderson TA , Johnson EM , Osborne PA , Jacquin MF
Published: April 2018

In the developing nervous system, precisely patterned connections result from mechanisms that remodel initially diffuse connections. For example, ocular dominance column formation depends upon activity-based competitive interactions. In the developing trigeminal (V) somatosensory system, injury to afferent inputs prevents somatotopic pattern formation; however, afferent impulse blockade does not. What establishes central V patterns remains unclear. As a first step in assessing the role of neurotrophins in naturally occurring death of V ganglion cells and whisker-related pattern formation, the consequences of prenatal NGF injections were evaluated. Fetal rats given NGF on both embryonic day (E) 15 and E18 had 36% more V ganglion cells than normal and lacked whisker-related patterns in the V brainstem complex at birth and through postnatal day 3, as determined by cytochrome oxidase histochemistry. Rats injected with NGF on E16 or on E18, or with vehicle had normal ganglion cell numbers and brainstem patterns. Animals injected with antibodies to NGF or an NGF receptor had reduced ganglion cell numbers and normal brainstem patterns. These findings suggest that naturally occurring cell death in the V ganglion is neurotrophically regulated and that this process impacts upon somatotopic pattern formation in the V brainstem complex. Results of anterograde tracing experiments in NGF-augmented animals suggest that pattern disruptions are due to an absence of whisker-related patterning in the central projections of V ganglion cells. Moreover, single primary afferent collaterals labeled by Neurobiotin injections in the V ganglion did not have widespread or unusually complex arbors. Thus, NGF may affect V pattern formation by preserving or inducing projections to brainstem regions that normally come to lack such projections, such as the spaces normally demarcating neighboring whisker primary afferent projections.
Homosynaptic long-term depression in the visual cortex
Authors: Kirkwood A , Bear MF
Published: April 2018

We have investigated the characteristics and mechanism of activity- dependent decreases in synaptic effectiveness in visual cortex. Repetitive, low-frequency stimulation (LFS) of either layer IV or the white matter of visual cortical slices was shown to result in a long- term depression (LTD) of intra- and extracellularly recorded synaptic responses in layer III. In preparations in which responses to stimulation of two independent pathways could be monitored, LFS of one pathway produced LTD of responses to test stimulation of that input only, showing that this form of LTD is homosynaptic. This form of LTD was dependent on the frequency and/or pattern of conditioning stimulation and on activation of NMDA receptors. Okadaic acid, an inhibitor of protein phosphatases 1 and 2a, inhibited LTD, but had no effect on induction of long-term potentiation. In all of these respects, LFS-induced LTD in visual cortex closely resembles what has been recently documented in hippocampus. The combined data support a model in which LTD is triggered by a modest elevation in postsynaptic Ca2+ and activation of protein-serine, threonine phosphatases.