bluuebunny/crossref_metadata_2025 huggingface dataset:
The Representation of Illusory and Real Contours in Human Cortical Visual Areas Revealed by Functional Magnetic Resonance Imaging
Authors: Mendola Janine D. , Dale Anders M. , Fischl Bruce , Liu Arthur K. , Tootell Roger B. H.
Published: April 2018

Illusory contours (perceived edges that exist in the absence of local stimulus borders) demonstrate that perception is an active process, creating features not present in the light patterns striking the retina. Illusory contours are thought to be processed using mechanisms that partially overlap with those of “real” contours, but questions about the neural substrate of these percepts remain. Here, we employed functional magnetic resonance imaging to obtain physiological signals from human visual cortex while subjects viewed different types of contours, both real and illusory. We sampled these signals independently from nine visual areas, each defined by retinotopic or other independent criteria. Using both within- and across-subject analysis, we found evidence for overlapping sites of processing; most areas responded to most types of contours. However, there were distinctive differences in the strength of activity across areas and contour types. Two types of illusory contours differed in the strength of activation of the retinotopic areas, but both types activated crudely retinotopic visual areas, including V3A, V4v, V7, and V8, bilaterally. The extent of activation was largely invariant across a range of stimulus sizes that produce illusory contours perceptually, but it was related to the spatial frequency of displaced-grating stimuli. Finally, there was a striking similarity in the pattern of results for the illusory contour-defined shape and a similar shape defined by stereoscopic depth. These and other results suggest a role in surface perception for this lateral occipital region that includes V3A, V4v, V7, and V8.
Membrane Potential Oscillations in Dorsal Root Ganglion Neurons: Role in Normal Electrogenesis and Neuropathic Pain
Authors: Amir Ron , Michaelis Martin , Devor Marshall
Published: April 2018

Abnormal afferent discharge originating at ectopic sites in injured primary sensory neurons is thought to be an important generator of paraesthesias, dysaesthesias, and chronic neuropathic pain. We report here that the ability of these neurons to sustain repetitive discharge depends on intrinsic resonant properties of the cell membrane and that the prevalence of this characteristic increases after nerve injury. Recording from primary sensory neurons in excised rat dorsal root ganglia, we found that some cells show subthreshold oscillations in their membrane potential. The amplitude, frequency, and coherence of these oscillations were voltage sensitive. Oscillations gave rise to action potentials when they reached threshold. Indeed, the presence of oscillations proved to be a necessary condition for sustained spiking both at resting membrane potential and on depolarization; neurons without them were incapable of sustained discharge even on deep depolarization. Previous nerve injury increased the proportion of neurons sampled that had subthreshold oscillations, and hence the proportion that generated ectopic spike discharge. Oscillatory behavior and ectopic spiking were eliminated by [Na+]osubstitution or bath application of lidocaine or tetrodotoxin (TTX), under conditions that preserved axonal spike propagation. This suggests that a TTX-sensitive Na+conductance contributes to the oscillations. Selective pharmacological suppression of subthreshold oscillations may offer a means of controlling neuropathic paraesthesias and pain without blocking afferent nerve conduction.
Cortical Involvement in the Induction, But Not Expression, of Thalamic Plasticity
Authors: Parker Jayson L. , Dostrovsky Jonathan O.
Published: April 2018

The present study examined the role of the somatosensory cortex in the plasticity of thalamic sensory maps. Thalamic plasticity was induced by the disruption of hindlimb input by unilateral destruction of nucleus gracilis. Unilateral somatosensory cortex lesions were performed either on the same day as or a week after the removal of hindlimb input. Multiple electrode penetrations enabled us to measure the volume of somatosensory thalamus devoted to hindlimb, forepaw, and shoulder body regions.

Cortical lesions alone did not change the volume of the shoulder, forepaw, or hindlimb representations in the thalamus relative to controls. However, these lesions blocked the increase in shoulder representation resulting from the nucleus gracilis lesion. In contrast, if thalamic reorganization caused by removal of hindlimb input was allowed to occur, subsequent somatosensory cortex lesions 1 week later did not prevent reorganization. Thus, an intact somatosensory cortex is necessary for the occurrence of sensory map reorganization at the thalamic level (induction) in response to nucleus gracilis lesions, but not for the maintenance of such changes once they are present (expression).
Neurotoxic Basolateral Amygdala Lesions Impair Learning and Memory But Not the Performance of Conditional Fear in Rats
Authors: Maren Stephen
Published: April 2018

We examined the influence of extensive overtraining (75 trials) on the impact of neurotoxic basolateral amygdala (BLA) lesions on Pavlovian fear conditioning in rats. As we have shown previously,pretrainingBLA lesions yielded severe deficits in the acquisition of conditional freezing in rats trained with either 1 or 25 conditioning trials. However, extensive overtraining (50 or 75 trials) mitigated deficits in conditional freezing. Under these conditions the rats with BLA lesions expressed normal and robust freezing behavior, although they required at least 10 times as much training as control rats to reach this level of performance. The ability of rats with BLA lesions to acquire and express conditional freezing after extensive overtraining was modality-specific; conditional freezing in individual rats was acquired to contextual, but not acoustic, conditional stimuli. These results suggest that neural circuitry outside of the amygdala can mediate contextual fear conditioning under some conditions. In contrast to pretraining lesions,post-trainingBLA lesions eradicated the memory for Pavlovian fear in rats trained with either 1 or 75 trials; this deficit was not modality-specific. Together, these results reveal that impairments in the acquisition and expression of conditional fear in rats with BLA lesions are not attributable to deficits in the performance of the freezing response but are attributable to disruptions in the learning and memory of Pavlovian fear conditioning.
Time-Dependent Reversal of Long-Term Potentiation in Area CA1 of the Freely Moving Rat Induced by Theta Pulse Stimulation
Authors: Stäubli Ursula , Scafidi Joey
Published: April 2018

Previous studies in slices have shown that low-frequency stimulation at 5 Hz, i.e., theta pulse stimulation (TPS), completely reverses long-term potentiation (LTP) in area CA1 when delivered within 1–2 min after induction but produces progressively less depotentiation at longer delays, until it has no longer any impact at 30 min after induction. The present study examined whether LTP in the freely moving rat exhibits a similar time-dependent susceptibility to reversal. Adult male Long–Evans rats with bilateral stimulating electrodes activating collateral/commissural projections to area CA1 were used. A 1 min episode of TPS, ineffective when applied to naive pathways, was found to permanently erase LTP when delivered to the test pathway either 30 sec or 15 min after induction. Administered at a delay of 30 min, however, the same treatment no longer had any impact on established LTP. Additional experiments examined the ability of shorter TPS episodes to erase LTP and found that a 30 sec treatment was effective at 30 sec but not 15 min after induction. When the duration of TPS was further reduced to 15 sec, a reversal was no longer obtained at any delay. These results provide the first demonstration that the limited vulnerability of LTP to reversal by TPS, originally observedin vitro, also holds true for LTP in the awake animal and occurs along the same time frame, supporting the notion that LTP stabilization mechanisms take less than 30 min to be complete.
Somatostatin Modulates Voltage-Gated K+and Ca2+Currents in Rod and Cone Photoreceptors of the Salamander Retina
Authors: Akopian Abram , Johnson Juliette , Gabriel Robert , Brecha Nicholas , Witkovsky Paul
Published: April 2018

We investigated the cellular localization in the salamander retina of one of the somatostatin [or somatotropin release-inhibiting factor (SRIF)] receptors, sst2A, and studied the modulatory action of SRIF on voltage-gated K+and Ca2+currents in rod and cone photoreceptors. SRIF immunostaining was observed in widely spaced amacrine cells, whose perikarya are at the border of the inner nuclear layer and inner plexiform layer. sst2Aimmunostaining was seen in the inner segments and terminals of rod and cone photoreceptors. Additional sst2Aimmunoreactivity was expressed by presumed bipolar and amacrine cells. SRIF, at concentrations of 100–500 nm, enhanced a delayed outwardly rectifying K+current (IK) in both rod and cone photoreceptors. SRIF action was blocked in cells pretreated with pertussis toxin (PTX) and was substantially reduced by intracellular GDPβS. Voltage-gated L-type Ca2+currents in rods and cones were differently modulated by SRIF. SRIF reduced Ca2+current in rods by 33% but increased it in cones by 40%, on average. Both effects were mediated via G-protein activation and blocked by PTX. Ca2+-imaging experiments supported these results by showing that 500 nmSRIF reduced a K+-induced increase in intracellular Ca2+in rod photoreceptor terminals but increased it in those of cones. Our results suggest that SRIF may play a role in the regulation of glutamate transmitter release from photoreceptors via modulation of voltage-gated K+and Ca2+currents.
Kinetic Differences between Synaptic and Extrasynaptic GABAAReceptors in CA1 Pyramidal Cells
Authors: Banks Matthew I. , Pearce Robert A.
Published: April 2018

GABAA-mediated IPSCs typically decay more rapidly than receptors in excised patches in response to brief pulses of applied GABA. We have investigated the source of this discrepancy in CA1 pyramidal neurons. IPSCs in these cells decayed rapidly, with a weighted time constant τDecayof ∼18 msec (24°C), whereas excised and nucleated patch responses to brief pulses of GABA (2 msec, 1 mm) decayed more than three times as slowly (τDecay, ∼63 msec). This discrepancy was not caused by differences between synaptic and exogenous transmitter transients because (1) there was no dependence of τDecayon pulse duration for pulses of 0.6–4 msec, (2) responses to GABA at concentrations as low as 10 μmwere still slower to decay (τDecay, ∼41 msec) than IPSCs, and (3) responses of excised patches to synaptically released GABA had decay times similar to brief pulse responses. These data indicate that the receptors mediating synaptic versus brief pulse responses have different intrinsic properties. However, synaptic receptors were not altered by the patch excision process, because fast, spontaneous IPSCs could still be recorded in nucleated patches. Elevated calcium selectively modulated patch responses to GABA pulses, with no effect on IPSCs recorded in nucleated patches, demonstrating the presence of two receptor populations that are differentially regulated by intracellular second messengers. We conclude that two receptor populations with distinct kinetics coexist in CA1 pyramidal cells: slow extrasynaptic receptors that dominate the responses of excised patches to exogenous GABA applications and fast synaptic receptors that generate rapid IPSCs.
The Electrogenic Sodium Bicarbonate Cotransporter: Developmental Expression in Rat Brain and Possible Role in Acid Vulnerability
Authors: Giffard Rona G. , Papadopoulos Marios C. , van Hooft Johannes A. , Xu Lijun , Giuffrida Raffaela , Monyer Hannah
Published: April 2018

The electrogenic sodium bicarbonate cotransporter (NBC) is expressed in glial cells in the brain and plays an important role in the regulation of both intracellular and extracellular pH. Differential vulnerability to acidosis between neurons and glia has been noted and may contribute to infarction after cerebral ischemia. Ionic substitution studies and inhibition of injury by 4,4′-di-isothiocyanostilbene-2,2′-disulfonic acid suggest that NBC is involved in astrocyte vulnerability to acidic injury. Recently two NBC cDNAs differing in 5′-untranslated and N-terminal coding sequence have been cloned from kidney and pancreas. We cloned one of these cDNAs from rat brain and demonstrate here that the clone is functional by expression inXenopusoocytes. We determined the developmental and regional expression of NBC in the brain byin situhybridization. Expression was observed in the spinal cord at embryonic day 17, whereas expression in brain was first seen at approximately postnatal day 0 (P0), increased at P15, and persisted in the adult brain. Expression was widespread throughout the cerebellum, cortex, olfactory bulb, and subcortical structures. Cellular resolution of thein situhybridization signal and double labeling for glial fibrillary acidic protein were consistent with a glial localization for NBC. Expression of NBC in 3T3 cells that do not normally express this transporter rendered them vulnerable to acid injury. The expression profile suggests that this transporter is critical during the later stages of brain development and could be one of the factors contributing to the different patterns of injury seen in perinatal versus adult cerebral ischemia.
Identification of an Invariant Response: Stable Contact with Schwann Cells Induces Veil Extension in Sensory Growth Cones
Authors: Polinsky Michael , Balazovich Kenneth , Tosney Kathryn W.
Published: April 2018

Growth cones sense cues by filopodial contact, but how their motility is altered by contact remains unclear. Although contact could alter motile dynamics in complex ways, our analysis shows that stable contact with Schwann cells induces motility changes that are remarkably discrete and invariant. Filopodial contact invariably induces local veil extension. Even when contacts are brief, veils always extend before the filopodia retract. Contact at filopodial tips suffices for induction. Moreover, veils extend significantly sooner than on filopodia contacting laminin, which often detach without extending veils. The overall behavioral responses of the growth cone, such as increased area and turning, result from integrating multiple discrete responses. Cycles of veil induction enlarge the growth cone and often lead it onto the cell. Invariant veil induction is abolished by blockingN-cadherin signaling. We propose an axonal guidance model in which different guidance cues act by inducing different but discrete and invariant responses.
The Pattern of Avian Intramuscular Nerve Branching Is Determined by the Innervating Motoneuron and Its Level of Polysialic Acid
Authors: Rafuse Victor F. , Landmesser Lynn T.
Published: April 2018

Most skeletal muscles are composed of a heterogeneous population of fast and slow muscle fibers that are selectively innervated during development by fast and slow motoneurons, respectively. It is well recognized that, in both birds and mammals, fast and slow motoneurons have substantially different intramuscular branching patterns, a difference critical for proper motor function. However, the cellular mechanisms regulating these differences in motoneuron branching are unknown. In a previous study, we showed that the fast and slow pattern of intramuscular branching, in a chick muscle containing distinct fast and slow muscle regions, was remarkably similar to normal when formed by foreign motoneurons. Whether this was attributable to some property of the innervating “fast” or “slow” motoneurons or to some property of the developing fast–slow muscle fibers was not determined. To distinguish between these two possibilities, we performed chick–quail hindlimb chimeras to force slow chick plantaris motoneurons to innervate a fast quail plantaris muscle. The pattern of intramuscular nerve branching in the fast plantaris of these chimeras closely resembled the slow branching pattern normally observed in chick slow plantaris muscles. Enzymatic removal of polysialic acid (PSA) from nerve and muscle during normal quail plantaris development dramatically changed the normal fast pattern to more closely resemble a slow pattern. In contrast, removal of PSA from chick plantaris motoneurons and muscle fibers had little effect on the pattern of nerve branching. Together, these results indicate that the pattern of intramuscular nerve branching is determined by the level of PSA on the innervating motoneurons.
Structured Long-Range Connections Can Provide a Scaffold for Orientation Maps
Authors: Shouval Harel Z. , Goldberg David H. , Jones Judson P. , Beckerman Martin , Cooper Leon N.
Published: April 2018

In the visual cortex of the cat and ferret, it is established that maturation of orientation selectivity is shaped by experience-dependent plasticity. However, recent experiments indicate that orientation maps are remarkably stable and experience-independent. We present a model to account for these seemingly paradoxical results. In this model, a scaffold consisting of non-isotropic lateral connections is laid down in horizontal circuitry before visual experience. These lateral connections provide an experience-independent framework for the developing orientation maps by inducing a broad orientation tuning bias in the model neurons. Experience-dependent plasticity of the thalamocortical connections sharpens the tuning while the preferred orientation of the neurons remains unchanged. This model is verified by computer simulations in which the scaffolds are generated both artificially and inferred from experimental optical imaging data. The plasticity is modeled by the BCM synaptic plasticity rule, and the input environment consists of natural images. We use this model to provide a possible explanation of the recent observation in which two eyes without common visual experience develop similar orientation maps. Finally, we propose an experiment involving the disruption of lateral connections to distinguish this model from models proposed by others.
Do Centrally Administered Neuropeptides Access Cognate Receptors?: An Analysis in the Central Corticotropin-Releasing Factor System
Authors: Bittencourt Jackson C. , Sawchenko Paul E.
Published: April 2018

To determine the extent to which centrally administered corticotropin-releasing factor (CRF) activates neurons that express CRF receptors (CRF-Rs), we followed the kinetics and distribution (relative to those of CRF-Rs) of Fos induction seen in response to intracerebroventricular (icv) injection of the peptide (1–10 μg). CRF provoked widespread Fos expression: its strength was dose-related, it peaked at 2 hr after injection, and it was antagonized in a dose-dependent manner by coinjection of CRF-R antagonists. The activation pattern closely mimicked the distribution of CRF-R1 mRNA, in including widespread Fos induction throughout the cortical mantle, in cell groups involved in sensory information processing, and in the cerebellum and several of its major afferents and targets. Dual labeling revealed extensive correspondence of CRF-stimulated Fos-immunoreactivity (Fos-ir) and CRF-R1 mRNA at these and other loci. Unique sites of CRF-R2 expression were relatively unresponsive to CRF but were more so after icv administration of urocortin (UCN), a new mammalian CRF-related peptide. Both CRF and UCN elicited activational responses in cell groups that are involved in central autonomic control but that express neither CRF-R, including the central amygdaloid and paraventricular hypothalamic nuclei, and brainstem catecholaminergic cell groups. The results support an ability of CRF-related peptides in the ventricular system to access receptor-expressing cells directly but leave open questions as to the basis for the recruitment of central autonomic structures, many of which have been identified as stress-related sites of CRF action.
Specificity of Projections from Wide-Field and Local Motion-Processing Regions within the Middle Temporal Visual Area of the Owl Monkey
Authors: Berezovskii Vladimir K. , Born Richard T.
Published: April 2018

The middle temporal visual area (MT) of the owl monkey is anatomically organized with respect to both preferred direction of motion and different types of center–surround interaction. The latter organization consists of clusters of neurons whose receptive fields have antagonistic surrounds that render them unresponsive to wide-field motion (local motion columns) interdigitated with groups of neurons whose receptive fields have additive surrounds and thus respond best to wide-field motion (wide-field motion columns).

To learn whether the information in these regions remained segregated further along the visual pathways, we made injections of retrograde tracers into two visual areas to which MT projects [the medial superior temporal area (MST) and fundus of the superior temporal sulcus (FST)] and then labeled the wide-field and local organization using 2-deoxyglucose. In complementary experiments, we injected anterograde tracers into regions of MT that we had mapped using microelectrode recordings.

Injections into both dorsal FST and ventral MST labeled clusters of cell bodies in MT that were concentrated within wide-field motion columns, whereas injections into dorsal MST labeled neurons predominantly within local motion columns. Results from the anterograde tracer experiments corroborated these findings. The high degree of specificity in the connections reinforces a model of functional organization for wide-field versus local motion processing within MT. Our data support the previously reported division of FST into separate dorsal and ventral areas, and they also suggest that MST of the owl monkey is, like MST of the macaque, functionally organized with respect to local versus wide-field motion processing.
Opioids Suppress IPSCs in Neurons of the Rat Medial Septum/Diagonal Band of Broca: Involvement of μ-Opioid Receptors and Septohippocampal GABAergic Neurons
Authors: Alreja Meenakshi , Shanabrough Marya , Liu Weimin , Leranth Csaba
Published: April 2018

The medial septum/diagonal band region (MSDB), which provides a major cholinergic and GABAergic input to the hippocampus, expresses a high density of opioid receptors. Behaviorally, intraseptal injections of opioids produce deficits in spatial memory, however, little is known about the electrophysiological effects of opioids on MSDB neurons. Therefore, we investigated the electrophysiological effects of opioids on neurons of the MSDB using rat brain slices. In voltage-clamp recordings with patch electrodes, bath-applied met-enkephalin, a nonselective opioid receptor agonist, decreased the number of tetrodotoxin and bicuculline-sensitive inhibitory synaptic currents in cholinergic- and GABA-type MSDB neurons. A similar effect occurred in brain slices containing only the MSDB, suggesting that opioids decrease GABA release primarily by inhibiting spontaneously firing GABAergic neurons located within the MSDB. Accordingly, in extracellular recordings, opioid-sensitive, spontaneously firing neurons could be found within the MSDB. Additionally, in intracellular recordings a subpopulation of GABA-type neurons were directly inhibited by opioids. All effects of met-enkephalin were mimicked by a μ receptor agonist, but not by δ or κ agonists. In antidromic activation studies, μ-opioids inhibited a subpopulation of septohippocampal neurons with high conduction velocity fibers, suggestive of thickly myelinated GABAergic fibers. Consistent with the electrophysiological findings, in double-immunolabeling studies, 20% of parvalbumin-containing septohippocampal GABA neurons colocalized the μ receptor, which at the ultrastructural level, was found to be associated with the neuronal cell membrane. Thus, opioids, via μ receptors, inhibit a subpopulation of MSDB GABAergic neurons that not only make local connections with both cholinergic and noncholinergic-type MSDB neurons, but also project to the hippocampus.
Mechanisms of Ionotropic Glutamate Receptor-Mediated Excitotoxicity in Isolated Spinal Cord White Matter
Authors: Li Shuxin , Stys Peter K.
Published: April 2018

Spinal cord injury involves a component of glutamate-mediated white matter damage, but the cellular targets, receptors, and ions involved are poorly understood. Mechanisms of excitotoxicity were examined in anin vitromodel of isolated spinal dorsal columns. Compound action potentials (CAPs) were irreversibly reduced to 43% of control after 3 hr of 1 mmglutamate exposure at 37°C. AMPA (100 μm) and kainate (500 μm) had similar effects. Antagonists (1 mmkynurenic acid, 10 μmNBQX, 30 μmGYKI52466) were each equally protective against a glutamate challenge, improving mean CAP amplitude to ∼80% versus ∼40% without antagonist. Joro spider toxin (0.75 μm), a selective blocker of Ca2+-permeable AMPA receptors, was also protective to a similar degree. Ca2+-free perfusate virtually abolished glutamate-induced injury (∼90% vs ∼40%). MK-801 (10 μm) had no effect. Glutamate caused damage (assayed immunohistochemically by spectrin breakdown products) to astrocytes and oligodendrocytes consistent with the presence of GluR2/3 and GluR4 in these cells. Myelin was also damaged by glutamate likely mediated by GluR4 receptors detected in this region; however, axon cylinders were unaffected by glutamate, showing no increase in the level of spectrin breakdown. These data may guide the development of more effective treatment for acute spinal cord injury by addressing the additional excitotoxic component of spinal white matter damage.
Coding of Sound-Source Location by Ensembles of Cortical Neurons
Authors: Furukawa Shigeto , Xu Li , Middlebrooks John C.
Published: April 2018

We examined the coding of sound-source location by ensembles of neurons in the auditory cortex. Broadband noise bursts were presented from loudspeakers throughout 360° in the horizontal plane. Sound levels varied from 20 to 40 dB above neural thresholds. We recorded temporal spike patterns simultaneously at 16 recording sites in area A2 of α-chloralose-anesthetized cats. Spike patterns of individual units varied in spike counts and in spike timing as a function of sound-source location. Ensembles of up to 19 units recorded simultaneously demonstrated additional location sensitivity in the form of relative spike counts and relative spike timing among neurons. We used an artificial neural network (ANN) algorithm to recognize ensemble spike patterns and, thereby, to infer the locations of sound sources. The ANN could estimate stimulus locations based on ensemble responses to single-stimulus presentations. Median errors (MEs) averaged 49.2 ± 11.9° (mean ± SD;n= 34; chance level, 90°). The ANN maintained better-than-chance performance even when input spike patterns were expressed as relative spike counts across units (i.e., no information available from absolute spike counts of individual units; ME, 63.0 ± 11.8°) or when spike latencies were represented as time relative to the first spike for each trial (i.e., no external time reference available; ME, 54.3 ± 12.4°). The ANN performance improved monotonically as the sizes of ensemble patterns were increased by combining patterns across the entire unit sample. The performance by ensembles of 128 units approached the level of localization performance of behaving cats.
Behavioral Evidence of Depolarization Block of Dopamine Neurons after Chronic Treatment with Haloperidol and Clozapine
Authors: Boye Sandra M. , Rompré Pierre-Paul
Published: April 2018

Electrophysiological studies have shown that chronic treatment with haloperidol causes depolarization block (DB) of dopamine cells in anesthetized and paralyzed rats. It has been proposed that the emergence of DB underlies the therapeutic and side effects of this drug. However, the relevance of DB to the clinical actions of haloperidol has been questioned on the grounds that chronic drug-induced DB has not yet been demonstrated in freely moving animals. In this study, responding for rewarding electrical brain stimulation was used to assess the occurrence of DB in rats chronically treated with haloperidol or clozapine. The time course of the effects of acute haloperidol (7.8–500 μg/kg) and clozapine (5–40 mg/kg) and of withdrawal from chronic drug treatment on reward and performance measures were also characterized. Haloperidol and clozapine dose-dependently attenuated reward and performance, haloperidol producing a predominant suppression of performance, and clozapine preferentially attenuating reward. Chronic (21 d) treatment with haloperidol (500 μg/kg) caused responding to cease in the six rats tested, and repeated injection with apomorphine restored the behavior in all of them; such an effect of apomorphine was observed in only two of six rats treated acutely with the same dose of haloperidol. Chronic treatment with clozapine (20 mg/kg) increased reward thresholds, an effect that was reversed by apomorphine in chronically, but not acutely, treated rats. The times at which chronic haloperidol-treated rats resumed responding was positively correlated with indices of behavioral supersensitivity after withdrawal, suggesting that the effect of apomorphine was not caused by direct stimulation of upregulated postsynaptic receptors. These findings constitute the first behavioral evidence of DB in unanesthetized, freely moving animals treated chronically with antipsychotics. They also demonstrate that the neural substrates mediating reward and performance are functionally independent and differentially sensitive to haloperidol and clozapine.
Chronic Administration of the Triazolobenzodiazepine Alprazolam Produces Opposite Effects on Corticotropin-Releasing Factor and Urocortin Neuronal Systems
Authors: Skelton Kelly H. , Nemeroff Charles B. , Knight David L. , Owens Michael J.
Published: April 2018

In view of the substantial preclinical evidence that supports a seminal role of central corticotropin-releasing factor (CRF) neuronal systems in the physiology and pathophysiology of stress and anxiety, it is reasonable to suggest that the anxiolytic properties of benzodiazepines are mediated, at least in part, via regulation of CRFergic function. To begin to test this complex hypothesis, we examined the effects of acute and chronic administration of the triazolobenzodiazepine agonist alprazolam on CRF peptide concentrations, receptor-binding density, and mRNA expression in the CNS. Additionally, we measured mRNA expression for urocortin, a recently discovered neuropeptide that is generally considered to be a second endogenous ligand for CRF receptors. Both acute and chronic alprazolam administration was found to decrease CRF concentrations within the locus coeruleus. Furthermore, chronic alprazolam decreased basal activity of the hypothalamic–pituitary–adrenal axis, CRF mRNA expression in the central nucleus of the amygdala, and CRF1mRNA expression and receptor binding in the basolateral amygdala. In marked contrast, urocortin mRNA expression in the Edinger-Westphal nucleus and CRF2Areceptor binding in the lateral septum and ventromedial hypothalamus were increased. Similar findings of an inverse relationship between the CRF1and CRF2Areceptor systems have been reported in an anxiety model based on adverse early-life experience, suggesting the intriguing possibility that CRF neuronal systems may be comprised of two separate, but interrelated, subdivisions that can be coordinately and inversely regulated by stress, anxiety, or anxiolytic drugs.
A Developmental Change in NMDA Receptor-Associated Proteins at Hippocampal Synapses
Authors: Sans Nathalie , Petralia Ronald S. , Wang Ya-Xian , Blahos Jaroslav , Hell Johannes W. , Wenthold Robert J.
Published: April 2018

The membrane-associated guanylate kinases [Chapsyn-110/postsynaptic density-93 (PSD-93), synapse-associated protein-90 (SAP-90)/PSD-95, and SAP-102] are believed to cluster and anchor NMDA receptors at the synapse and to play a role in signal transduction. We have investigated the developmental changes in expression of these proteins in rat hippocampus using biochemical analyses and quantitative immunogold electron microscopy. At postnatal day 2 (P2), SAP-102 was highly expressed, whereas PSD-93 and PSD-95 were low. SAP-102 expression increased during the first week, stayed stable through P35, and showed a reduced expression at 6 months. From P2 through 6 months, PSD-93 and PSD-95 increased. For PSD-95, the percent of labeled synapses increased almost threefold with age, whereas the number of gold particles per labeled synapse did not change significantly, suggesting that the increase in PSD-95 is attributable primarily to an increase in the number of synapses containing PSD-95. In contrast, for SAP-102, both percent labeled synapses and the number of gold particles per labeled synapse decreased during this time. From Western blots of hippocampus and immunogold analysis of CA1 synapses, the high expression of NR2B at P2 coincides with the high level of SAP-102 at synapses, whereas the later expression of NR2A coincides with that of PSD-93 and PSD-95. To determine whether the changes in PSD-93/95 and SAP-102 reflect preferred associations with NR2A and NR2B, respectively, we measured co-immunoprecipitation in the adult hippocampus. These studies suggest that there is a preference for complexes of NR2A/PSD-93/95 and NR2B/SAP-102. These results indicate that individual receptor-associated proteins may have specific functions that are critical to synapse development.
Local Morphine Withdrawal Increases c-fosGene, Fos Protein, and Oxytocin Gene Expression in Hypothalamic Magnocellular Neurosecretory Cells
Authors: Johnstone Louise E. , Brown Colin H. , Meeren Hanneke K. M. , Vuijst Chrétienne L. , Brooks Philip J. , Leng Gareth , Russell John A.
Published: April 2018

We measured stimulation of c-fosand oxytocin gene expression during excitation of oxytocin cells induced by systemic or local morphine withdrawal. Female rats were made morphine-dependent by intracerebroventricular morphine infusion over 5 d. Morphine withdrawal, induced by systemic injection of the opioid antagonist naloxone (5 mg/kg) in conscious or anesthetized rats, increased the density of c-fosmessenger RNA and of oxytocin heterogeneous nuclear RNA in supraoptic nucleus cells compared with those of nonwithdrawn rats; c-fosmessenger RNA was also increased in the magnocellular and parvocellular paraventricular nuclei of withdrawn rats. Morphine withdrawal increased the number of Fos-immunoreactive cells in the supraoptic and magnocellular paraventricular nuclei of conscious or pentobarbitone-anesthetized rats. Morphine withdrawal also increased Fos-immunoreactive cell numbers in the parvocellular paraventricular nucleus of conscious but not anesthetized rats. Central administration of the α1-adrenoreceptor antagonist benoxathian (5 μg/min) did not prevent morphine withdrawal-induced increases in the numbers of Fos-immunoreactive neurons in the supraoptic or magnocellular paraventricular nucleus. Unilateral microdialysis administration of naloxone (10−5m) into the supraoptic nucleus of anesthetized morphine-dependent rats increased Fos-immunoreactive cell numbers compared with the contralateral nucleus. Finally, we investigated whether dependence could be induced by chronic unilateral infusion of morphine into a supraoptic nucleus; systemic naloxone (5 mg/kg) increased Fos-immunoreactive cell numbers in the morphine-infused nucleus compared with the contralateral nucleus. Thus, morphine withdrawal excitation increases c-fosand oxytocin gene expression in supraoptic nucleus neurons. This occurs independently from excitation of their ascending noradrenergic inputs, and both dependence and withdrawal can be induced within the supraoptic nucleus.
The Products of theDrosophila stonedLocus Interact with Synaptic Vesicles via Synaptotagmin
Authors: Phillips A. Marie , Smith Michiko , Ramaswami Mani , Kelly Leonard E.
Published: April 2018

Thestonedlocus ofDrosophila melanogasterencodes two novel proteins, stonedA (STNA) and stonedB (STNB), both of which are expressed in the nervous system. Flies with defects at thestonedlocus have abnormal behavior and altered synaptic transmission. Genetic interactions, in particular with theshibire(dynamin) mutation, indicated a presynaptic function forstonedand suggested an involvement in vesicle cycling. Immunological studies revealed colocalization of the stoned proteins at the neuromuscular junction with the integral synaptic vesicle protein synaptotagmin (SYT). We show here thatstonedinteracts genetically withsynaptotagminto produce a lethal phenotype. The STNB protein is found by co-immunoprecipitation to be associated with synaptic vesicles, and glutathioneS-transferase pull-downs demonstrate anin vitrointeraction between the μ2-homology domain of STNB and the C2B domain of the SYTI isoform. The STNA protein is also found in association with vesicles, and it too exhibits anin vitroassociation with SYTI. However, we find that the bulk of STNA is in a nonmembranous fraction. By using theshibiremutant to block endocytosis, STNB is shown to be present on some synaptic vesicles before exocytosis. However, STNB is not associated with all synaptic vesicles. We hypothesize that STNB specifies a subset of synaptic vesicles with a role in the synaptic vesicle cycle that is yet to be determined.
Molecular and Functional Diversity of Neural Connexins in the Retina
Authors: Dermietzel R. , Kremer M. , Paputsoglu G. , Stang A. , Skerrett I. M. , Gomès D. , Srinivas M. , Janssen-Bienhold U. , Weiler R. , Nicholson B. J , Bruzzone R. , Spray D. C.
Published: April 2018

Electrical synapses (gap junctions) in neuronal circuits have become a major focus in the study of network properties such as synchronization and oscillation (Galarreta and Hestrin, 1999;Gibson et al., 1999). Despite the recent progress made in unraveling the contribution of gap junctions to network behavior, little is known about the molecular composition of the junctional constituents. By cloning gap junction proteins [connexins (Cxs)] from zebrafish retina and through functional expression, we demonstrate that the retina possesses a high degree of connexin diversity, which may account for differential functional properties of electrical synapses. Three new Cxs, designated as zebrafish Cx27.5 (zfCx27.5), zfCx44.1, and zfCx55.5, and the carp ortholog of mammalian Cx43 were cloned. Byin situhybridization andin situRT-PCR, we demonstrate that the four fish connexin mRNAs show differential localization in the retina. Transient functional expression in pairedXenopusoocytes and in the neuroblastoma N2A cell line indicate an extreme range of electrophysiological properties of these connexins in terms of voltage dependence and unitary conductance. For instance, the new zfCx44.1 exhibited high sensitivity to voltage-induced closure with currents decaying rapidly for transjunctional potentials >10 mV, whereas zfCx55.5 channels showed an opposite voltage dependence in response to voltage steps of either polarity. Moreover, although zfCx44.1 channels showed unitary conductance as high as any previously reported for junctional channels (nearly 300 pS), zfCx55.5 and zfCx27.5 exhibited much lower unitary conductances (<60 pS).
Inositol 1,4,5-Trisphosphate (IP3)-Mediated Ca2+Release Evoked by Metabotropic Agonists and Backpropagating Action Potentials in Hippocampal CA1 Pyramidal Neurons
Authors: Nakamura Takeshi , Nakamura Kyoko , Lasser-Ross Nechama , Barbara Jean-Gaël , Sandler Vladislav M. , Ross William N.
Published: April 2018

We examined the properties of [Ca2+]ichanges that were evoked by backpropagating action potentials in pyramidal neurons in hippocampal slices from the rat. In the presence of the metabotropic glutamate receptor (mGluR) agonistst-ACPD, DHPG, or CHPG, spikes caused Ca2+waves that initiated in the proximal apical dendrites and spread over this region and in the soma. Consistent with previously described synaptic responses (Nakamura et al., 1999a), pharmacological experiments established that the waves were attributable to Ca2+release from internal stores mediated by the synergistic effect of receptor-mobilized inositol 1,4,5-trisphosphate (IP3) and spike-evoked Ca2+. The amplitude of the changes reached several micromoles per liter when detected with the low-affinity indicators fura-6F, fura-2-FF, or furaptra. Repetitive brief spike trains at 30–60 sec intervals generated increases of constant amplitude. However, trains at intervals of 10–20 sec evoked smaller increases, suggesting that the stores take 20–30 sec to refill. Release evoked by mGluR agonists was blocked by MCPG, AIDA, 4-CPG, MPEP, and LY367385, a profile consistent with the primacy of group I receptors. At threshold agonist concentrations the release was evoked only in the dendrites; threshold antagonist concentrations were effective only in the soma. Carbachol and 5-HT evoked release with the same spatial distribution ast-ACPD, suggesting that the distribution of neurotransmitter receptors was not responsible for the restricted range of regenerative release. Intracellular BAPTA and EGTA were approximately equally effective in blocking release. Extracellular Cd2+blocked release, but no single selective Ca2+channel blocker prevented release. These results suggest that IP3receptors are not associated closely with specific Ca2+channels and are not close to each other.
Selective and Protracted Apoptosis in Human Primary Neurons Microinjected with Active Caspase-3, -6, -7, and -8
Authors: Zhang Yan , Goodyer Cynthia , LeBlanc Andréa
Published: April 2018

We have shown previously that caspase-6 is activated in serum deprivation-mediated human neuronal cell death and correlates with increased production of Alzheimer's disease (AD) amyloid β peptide (Aβ). Here, we show by direct microinjection of recombinant active enzymes that caspase-6 (>0.5 pg/cell) induces a protracted course of apoptosis in neurons in a caspase-specific, dose- and time-dependent manner in the presence of serum. Only transient activation of caspase-6 is required to initiate apoptosis. Caspase-6 induces apoptosis directly without the activation of other caspase effectors. Doses of caspase-6 of <0.25 pg/cell induce only 20% cell death within 16 d but render neurons vulnerable to oxidative stress, indicating that caspase activation affects neurons despite the absence of cell death. Caspase-3 induces neuronal apoptosis in 20% of the cells, whereas caspase-7 or -8 do not induce apoptosis. In contrast, astrocytes undergo apoptosis within 24 hr when microinjected with caspase-3 but not caspase-6, -7, or -8. These results show cell type-specific vulnerability to caspases in the CNS. The results suggest that activation of caspases in human neurons does not lead to an immediate and rapid process of cell death but provokes a protracted form of apoptosis. Activation of caspases in human neurons may participate in the long-term overproduction of Aβ and other potential toxic fragments resulting from caspase-mediated proteolysis. These results are consistent with the protracted and age-dependent nature of AD.
Neuronal Apoptosis by Apolipoprotein E4 through Low-Density Lipoprotein Receptor-Related Protein and Heterotrimeric GTPases
Authors: Hashimoto Yuichi , Jiang Hong , Niikura Takako , Ito Yuko , Hagiwara Akari , Umezawa Kazuo , Abe Yoichiro , Murayama Yoshitake , Nishimoto Ikuo
Published: April 2018

The ε4 genotype of apolipoprotein E (apoE4) is the most established predisposing factor in Alzheimer's disease (AD); however, it remains unclear how apoE4 contributes to the pathophysiology. Here, we report that the apoE4 protein (ApoE4) evokes apoptosis in neuronal cells through the low-density lipoprotein receptor-related protein (LRP) and heterotrimeric GTPases. We examined neuron/neuroblastoma hybrid F11 cells and found that these cells were killed by 30 μg/ml ApoE4, but not by 30 μg/ml ApoE3. ApoE4-induced death occurred with typical features for apoptosis in time- and dose-dependent manners, and was observed in SH-SY5Y neuroblastomas, but not in glioblastomas or non-neuronal Chinese hamster ovary cells. Activated, but not native, α2-macroglobulin suppressed this ApoE4 toxicity. Suppression by the antisense oligonucleotide to LRP and inhibition by low nanomolar concentrations of LRP-associated protein RAP provided evidence for the involvement of LRP. The involvement of heterotrimeric GTPases was demonstrated by the findings that (1) ApoE4-induced death was suppressed by pertussis toxin (PTX), but not by heat-inactivated PTX; and (2) transfection with PTX-resistant mutant cDNAs of Gαirestored the toxicity of ApoE4 restricted by PTX. We thus conclude that one of the neurotoxic mechanisms triggered by ApoE4 is to activate a cell type-specific apoptogenic program involving LRP and the Giclass of GTPases and that the apoE4 gene may play a direct role in the pathogenesis of AD and other forms of dementia.
Glossopharyngeal Nerve Regeneration Is Essential for the Complete Recovery of Quinine-Stimulated Oromotor Rejection Behaviors and Central Patterns of Neuronal Activity in the Nucleus of the Solitary Tract in the Rat
Authors: King Camille T. , Garcea Mircea , Spector Alan C.
Published: April 2018

The peripheral, central, and behavioral consequences of glossopharyngeal nerve transection (GLX), regeneration, and the prevention of regeneration on the quinine-elicited responses of adult rats were concurrently examined. Oromotor taste reactivity (TR) was videotaped during intraoral infusion of 7 ml of either quinine (3 mm) or distilled water at 17, 52, or 94 d after surgery. We confirmed previous findings by showing that 17 d after neurotomy, (1) the number of circumvallate (CV) and foliate taste buds, (2) gapes (a characteristic aversive TR response), and (3) the number of Fos-like immunoreactive (FLI) neurons in the gustatory NST (gNST), particularly in the medial portion (subfield 5) of the rostral central subdivision (RC), were all severely attenuated in GLX rats. We extended these findings by showing that these lesion-induced effects were enduring when the GL did not regenerate (up to 94 d). In contrast, when the GL regenerated, as few as 52 d were sufficient to re-establish quinine-elicited TR, especially gaping, and FLI expression in RC, particularly within subfield 5, to values comparable with quinine-stimulated sham-operated rats. Evidently, the gNST maintains its potential to restore accurately the organization of neural activity that is disrupted by nerve injury, as assessed by FLI, ultimately leading to the return of normal protective oromotor responses, provided the nerve regenerates. This recovery was complete despite the reappearance of a reduced population of CV taste buds (∼75% control values) and may relate to peripheral and/or central changes that occur in tandem with regeneration of the GL.