bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoperiodically Driven Changes in Fos Expression within the Basal Tuberal Hypothalamus and Median Eminence of Japanese Quail
Authors: Meddle Simone L. , Follett Brian K. 
Published: April 2018

The rapid photoperiodic response in Japanese quail is so precise that it allows neural analyses of how photoperiodic information is transduced into an endocrine response. After transfer from short [SD; 6L:18D (6:18 hr light/dark cycle)] to long (LD; 20L:4D) days, luteinizing hormone (LH) first rises 20 hr after dawn. Using Fos immunocytochemistry, we examined the basal tuberal hypothalamus (BtH) to determine the relationship between brain cell activation and the first endocrine changes. Two separate cell populations within the BtH expressed Fos-like immunoreactivity (FLI) by hour 18 of the first LD. Importantly, this activation occurred before the LH rise. Median eminence activation appeared within glial cells, whereas activated infundibular nucleus cells were neuronal, providing support to the view that gonadotropin-releasing hormone (GnRH) release can be controlled at the terminals by glia. The FLI induction parallels LH changes, suggesting that gene expression may be involved in events preceding photostimulation and is the earliest photoperiodically stimulated physiological change yet reported.Additional experiments provided further support for this hypothesis. First, photoperiodically induced activation is not a result peculiar to castrates because intact birds displayed similar results. Second, the critical length of 14 hr of light had to be exceeded to cause both BtH activation and a LH rise 30 hr from dawn. Finally, valuable evidence of the response specificity was provided by using a unique property of the quail photoperiodic clock in which exposure to 10L:26D, but not 10L:14D, causes photoinduction. The 36 hr paradigm increased both plasma LH and BtH activation.
An Alternate Pathway for Visual Signal Integration into the Hypothalamo-Pituitary Axis: Retinorecipient Intergeniculate Neurons Project to Various Regions of the Hypothalamus and Innervate Neuroendocrine Cells Including Those Producing Dopamine
Authors: Horvath Tamas L. 
Published: April 2018

Using tract tracing and immunocytochemistry, this study explored the connectivity between lateral geniculate efferents and neurons of the hypothalamus, including those producing dopamine, that have direct access to fenestrated capillaries. It was also determined whether the intergeniculate neurons that give rise to hypothalamic projections are targeted by retinal axons.Within the hypothalamus,Phaseolus vulgarisleucoagglutinin-labeled, lateral geniculate efferents were observed in the suprachiasmatic nucleus, subparaventricular area, periventricular nuclei, medial preoptic areas, and between the arcuate and ventromedial nuclei. In these sites, intergeniculate efferents contacted populations of neurons that were retrogradely labeled from fenestrated capillaries by the intraperitoneal injection of fluorogold. Hypothalamic dopamine neurons, a population of which was neuroendocrine, were also synaptic targets of lateral geniculate efferents. After injection of the retrograde tracer fluorogold into these hypothalamic projection sites in parallel with bilateral enucleation, retrogradely labeled perikarya were restricted to the intergeniculate leaflet. All of the labeled perikarya contained infolded nuclei, and their distal dendrites were frequently found to be contacted by degenerated, retinal fibers.This study provides morphological evidence for a signaling pathway from the retina through the intergeniculate leaflet to hypothalamic cells that participate in neuroendocrine regulations. These observations raise the possibility that visual signals independent of the circadian clock may also influence the hypothalamo-pituitary axis. In light of the overlapping distribution of intergeniculate and suprachiasmatic efferents in the hypothalamus and their similar relationship with neuroendocrine cells, it is suggested that integration of circadian and visual signals can occur outside of the suprachiasmatic nucleus to regulate endocrine rhythms.
Behavioral Studies of Sound Localization in the Cat
Authors: Populin Luis C. , Yin Tom C. T. 
Published: April 2018

Using the magnetic search coil technique to measure eye and ear movements, we trained cats by operant conditioning to look in the direction of light and sound sources with their heads fixed. Cats were able to localize noise bursts, single clicks, or click trains presented from sources located on the horizontal and vertical meridians within their oculomotor range. Saccades to auditory targets were less accurate and more variable than saccades to visual targets at the same spatial positions. Localization accuracy of single clicks was diminished compared with the long-duration stimuli presented from the same sources. Control experiments with novel auditory targets, never associated with visual targets, demonstrated that the cats localized the sound sources using acoustic cues and not from memory.The role of spectral features imposed by the pinna for vertical sound localization was shown by the breakdown in localization of narrow-band (one-sixth of an octave) noise bursts presented from sources along the midsagittal plane. In addition, we show that cats experience summing localization, an illusion associated with the precedence effect. Pairs of clicks presented from speakers at (±18°,0°) with interclick delays of ±300 μsec were perceived by the cat as originating from phantom sources extending from the midline to approximately ±10°.
Extensive Divergence and Convergence in the Thalamocortical Projection to Monkey Somatosensory Cortex
Authors: Rausell Estrella , Bickford Lincoln , Manger Paul R. , Woods Timothy M. , Jones Edward G. 
Published: April 2018

This study examined the extent of thalamocortical divergence as a potential determinant of activity-dependent representational plasticity in area 3b of adult monkey somatosensory cortex. Single or paired injections of anterogradely transported tracers, of varying anteroposterior extent, were made horizontally from behind in defined parts of the body representation in the ventral posterior lateral (VPL) and/or ventral posterior medial (VPM) thalamic nuclei, and the distribution and density of labeled thalamocortical terminations were mapped in cortex. Injections of increasing size in any dimension of VPL or VPM resulted in increasing accumulation of labeled terminals within the region of projection, implying extensive convergence of individual axons. Anteroposteriorly elongated injections labeled mediolaterally extended but anteroposteriorly restricted zones in cortex. Dorsoventral placement of an injection in VPL or VPM determined anteroposterior location of labeling in cortex.Dual injections separated mediolaterally or dorsoventrally by ∼1 mm, and in different parts of the thalamic body or head–face representation gave rise to labeled thalamocortical terminations that overlapped extensively. For injection sites at different anteroposterior levels in VPL or VPM, the area of cortical convergence was related to their extent of anteroposterior coincidence. Labeled terminations arising from injections in immediately adjacent parts of VPL and VPM did not overlap in cortex.The extent of thalamocortical divergence and convergence revealed by these experiments is greater than that predictable from labeling of single axons and is sufficiently great to account for representational plasticity that exceeds the 1.5 mm cortical “distance limit.”
Single-Cell Correlates of a Representational Boundary in Rat Somatosensory Cortex
Authors: Hickmott Peter W. , Merzenich Michael M. 
Published: April 2018

In primary somatosensory cortex (S1), the transition from one representation to the next is typically abrupt when assayed physiologically. However, the extent of anatomical projections to and within the cortex do not strictly respect these physiologically defined transitions. Physiological properties, such as synaptic strengths or intracortical inhibition, have been hypothesized to account for the functionally defined precision of these representational borders. Because these representational borders can be translocated across the cortex by manipulations or behaviors that change the activity patterns of inputs to the cortex, understanding the physiological mechanisms that delimit representations is also an important starting point for understanding cortical plasticity.A novelin vivoandin vitropreparation has been developed to examine the cellular and synaptic mechanisms that underlie representational borders in the rat.In vivo, a short segment of the border between the forepaw–lower jaw representations in rat S1 was mapped using standard electrophysiological methods and was visibly marked using iontophoresis of pontamine sky blue dye. Slices were then obtained from this marked region and maintainedin vitro.Intracellularly recorded responses to electrical stimulation of supragranular cortex were obtained from single neurons near the border in response to stimulation within the representational zone or across the border. Both excitatory and inhibitory responses were smaller when evoked by stimuli that activated projections that crossed borders, as compared with stimuli to projections that did not. These findings indicate that intracortical network properties are contributing to the expressions of representational discontinuities in the cortex.
On the Action of the Anti-Absence Drug Ethosuximide in the Rat and Cat Thalamus
Authors: Leresche Nathalie , Parri H. Rheinallt , Erdemli Gül , Guyon Alice , Turner Jonathan P. , Williams Stephen R. , Asprodini Eftihia , Crunelli Vincenzo 
Published: April 2018

The action of ethosuximide (ETX) on Na+, K+, and Ca2+currents and on tonic and burst-firing patterns was investigated in rat and cat thalamic neuronsin vitroby using patch and sharp microelectrode recordings. In thalamocortical (TC) neurons of the rat dorsal lateral geniculate nucleus (LGN), ETX (0.75–1 mm) decreased the noninactivating Na+current,INaP, by 60% but had no effect on the transient Na+current. In TC neurons of the rat and cat LGN, the whole-cell transient outward current was not affected by ETX (up to 1 mm), but the sustained outward current was decreased by 39% at 20 mV in the presence of ETX (0.25–0.5 mm): this reduction was not observed in a low Ca2+(0.5 mm) and high Mg2+(8 mm) medium or in the presence of Ni2+(1 mm) and Cd2+(100 μm). In addition, ETX (up to 1 mm) had no effect on the low-threshold Ca2+current,IT, of TC neurons of the rat ventrobasal (VB) thalamus and LGN and in neurons of the rat nucleus reticularis thalami nor on the high-threshold Ca2+current in TC neurons of the rat LGN.Sharp microelectrode recordings in TC neurons of the rat and cat LGN and VB showed that ETX did not change the resting membrane potential but increased the apparent input resistance at potentials greater than −60 mV, resulting in an increase in tonic firing. In contrast, ETX decreased the number of action potentials in the burst evoked by a low-threshold Ca2+potential. The frequency of the remaining action potentials in a burst also was decreased, whereas the latency of the first action potential was increased. Similar effects were observed on the burst firing evoked during intrinsic δ oscillations.These results indicate an action of ETX onINaPand on the Ca2+-activated K+current, which explains the decrease in burst firing and the increase in tonic firing, and, together with the lack of action on low- and high-threshold Ca2+currents, the results cast doubts on the hypothesis that a reduction ofITin thalamic neurons underlies the therapeutic action of this anti-absence medicine.
Alternative RNA Splicing of the NMDA Receptor NR1 mRNA in the Neurons of the Teleost Electrosensory System
Authors: Bottai Daniele , Maler Leonard , Dunn Robert J. 
Published: April 2018

The sequence for cDNA encoding the NMDA receptor subunit 1 (aptNR1) of the weakly electric fishApteronotus leptorhynchushas been determined. The deduced amino acid sequence is ∼88% identical to other vertebrate NR1 proteins, with sequence homology extending to the alternatively spliced cassettes N1 and C1. The fish and mammalian N1 and C1 splice cassettes are identical at 20 of 21 and 30 of 37 amino acid positions, respectively. We did not detect a C2 splice cassette in aptNR1 mRNA, but we did find two novel C-terminal alternative splice cassettes labeled C1′ and C1".The relative levels of NR1 transcripts containing the N1 and C1 splice cassettes were determined by using RNase protection andin situhybridization analysis. N1-containing mRNAs are more abundant in caudal brain regions, similar to the patterns reported for mammalian brain. In contrast, the relative levels of transcripts containing the C1 splice cassette are much lower in fish than in mammals, averaging only 9% for the whole brain. The levels of C1 splicing increased in more rostral brain regions.In situhybridizations with N1- and C1-specific probes demonstrated that N1 cassette splicing occurs in most neurons but that C1 splicing is heterogeneous and is restricted to a subset of neuronal types in the electrosensory system.
Biochemical and Morphometric Analyses Show that Myelination in the Insulin-like Growth Factor 1 Null Brain Is Proportionate to Its Neuronal Composition
Authors: Cheng Clara M. , Joncas George , Reinhardt Rickey R. , Farrer Robert , Quarles Richard , Janssen Jeremy , McDonald Michael P. , Crawley Jacqueline N. , Powell-Braxton Lynn , Bondy Carolyn A. 
Published: April 2018

To elucidate the role of insulin-like growth factor 1 (IGF1) in the normal development of brain myelination, we used behavioral, biochemical, and histological analyses to compare the myelination of brains fromIgf1−/−and wild-type (WT) littermate mice. The studies were conducted at postnatal day 40, at which time theIgf1−/−mice weighed ∼66% less than wild-type mice. However, theIgf1−/−brain weight was only reduced by ∼34%. Formal neurological testing showed no sign of central or peripheral myelinopathy inIgf1−/−mice. Myelin composition was not significantly different, and myelin concentration, normalized to brain weight or protein, was equal inIgf1−/−and WT mice. Likewise, concentrations of myelin-specific proteins (MBP, myelin proteolipid protein, MAG, and 2′,3′-cyclic nucleotide,3′-phosphodiesterase) were not significantly different inIgf1−/−and WT mice. The myelin-associated lipids galactocerebroside and sulfatide were modestly reduced inIgf1−/−brains. Regional oligodendrocyte populations and myelin staining patterns were comparable inIgf1−/−and WT brains, with the notable exception of the olfactory system. TheIgf1−/−olfactory bulb was profoundly reduced in size and was depleted of mitral neurons and oligodendrocytes, and its efferent tracts were depleted of myelin.In summary, this study shows that myelination of theIgf1−/−brain is proportionate to its neuronal composition. Where projection neurons are preserved despite the deletion of IGF1, as in the cerebellar system, oligodendrocytes and myelination are indistinguishable from wild type. Where projection neurons are depleted, as in the olfactory bulb, oligodendrocytes are also depleted, and myelination is reduced in proportion to the reduced projection neuron mass. These data make a strong case for the primacy of axonal factors, not including IGF1, in determining oligodendrocyte survival and myelination.
Synaptic Regulation of Action Potential Timing in Neostriatal Cholinergic Interneurons
Authors: Bennett Ben D. , Wilson Charles J. 
Published: April 2018

Action potentials in neostriatal cholinergic interneurons recordedin vivoare triggered by summation of two or three discrete synaptic depolarizations (Wilson et al., 1990). The ability and precision with which EPSPs and IPSPs regulate action potential timing was therefore investigatedin vitro. Cholinergic interneurons were identified on the basis of morphological and electrophysiological characteristics in neostriatal slices taken from 2- to 3-week-old postnatal rats recorded at 24–26°C.During periods of induced regular firing, intrastriatal stimuli were used to evoke pharmacologically isolated monosynaptic AMPA receptor-mediated EPSPs or GABAAreceptor-mediated IPSPs. EPSPs evoked during the interspike interval (ISI) produced a phase-dependent decrease in the ISI, whereas IPSPs produced a phase-independent prolongation of the ISI. Injection of brief depolarizing currents mimicked the action of EPSPs and revealed an alteration in the input resistance during the ISI. In contrast to IPSPs, the ability of brief hyperpolarizing current injections to delay spike generation was phase-dependent. After blockade of GABAergic and glutamatergic synaptic transmission, stimuli failed to produce a detectable conductance change but could still prolong the subsequent ISI primarily through a D1 dopamine receptor-mediated enhancement of the afterhyperpolarization (AHP).Hence, EPSPs are ideally suited to provide a precise regulation of spike timing in cholinergic cells, whereas IPSPs are more likely to influence the overall level of excitability. The D1-mediated modulation of the AHP may contribute to the prolonged ISI seen in tonically active neuronsin vivoin monkeys trained to respond to a sensory cue.
Silent Synapses in the Developing Rat Visual Cortex: Evidence for Postsynaptic Expression of Synaptic Plasticity
Authors: Rumpel Simon , Hatt Hanns , Gottmann Kurt 
Published: April 2018

In the developing visual cortex activity-dependent refinement of synaptic connectivity is thought to involve synaptic plasticity processes analogous to long-term potentiation (LTP). The recently described conversion of so-called silent synapses to functional ones might underlie some forms of LTP. Using whole-cell recording and minimal stimulation procedures in immature pyramidal neurons, we demonstrate here the existence of functionally silent synapses, i.e., glutamatergic synapses that show only NMDA receptor-mediated transmission, in the neonatal rat visual cortex. The incidence of silent synapses strongly decreased during early postnatal development. After pairing presynaptic stimulation with postsynaptic depolarization, silent synapses were converted to functional ones in an LTP-like manner, as indicated by the long-lasting induction of AMPA receptor-mediated synaptic transmission. This conversion was dependent on the activation of NMDA receptors during the pairing protocol.The selective activation of NMDA receptors at silent synapses could be explained presynaptically by assuming a lower glutamate concentration compared with functional ones. However, we found no differences in glutamate concentration-dependent properties of NMDA receptor-mediated PSCs, suggesting that synaptic glutamate concentration is similar in silent and functional synapses. Our results thus support a postsynaptic mechanism underlying silent synapses, i.e., that they do not contain functional AMPA receptors. Synaptic plasticity at silent synapses might be expressed postsynaptically by modification of nonfunctional AMPA receptors or rapid membrane insertion of AMPA receptors. This conversion of silent synapses to functional ones might play a major role in activity-dependent synaptic refinement during development of the visual cortex.
Dopamine Modulates the Susceptibility of Striatal Neurons to 3-Nitropropionic Acid in the Rat Model of Huntington’s Disease
Authors: Reynolds David S. , Carter Rebecca J. , Morton A. Jennifer 
Published: April 2018

Huntington’s disease (HD) is a progressive neurodegenerative disorder characterized by chorea, psychiatric disturbances, and dementia. The striatum is the primary site of neuronal loss in HD; however, neither the mechanism of neurodegeneration nor the underlying cause of the selectivity for the striatum is understood. Chronic systemic injection of 3-nitropropionic acid (3-NP) into rats induces bilateral striatal lesions with many neuropathological features of HD and is widely used as a model of HD. In this study we examine the role striatal dopamine plays in 3-NP-induced striatal toxicity.The effect of elevated striatal dopamine levels on 3-NP toxicity was examined by using acute administration of methamphetamine. After 7 d of 3-NP treatment, a single low dose of methamphetamine markedly increased the frequency of striatal lesion formation. This effect was mediated via dopamine receptors because it could be blocked by the administration of dopamine receptor antagonists. The effect of decreased striatal dopamine on 3-NP toxicity was examined by lesioning the nigrostriatal dopamine input to one striatum 7 d before 3-NP treatment was started. Removal of the dopamine input protected the denervated striatum from the neurotoxic effects of systemic 3-NP but did not prevent the formation of lesions in the intact striatum. Thus the formation of 3-NP lesions is critically dependent on an intact dopamine input.Our data show that dopamine plays an important role in the formation of 3-NP lesions. We suggest that modulation of the dopaminergic system should be reevaluated as a potential drug target in the treatment for HD.
Regeneration of Adult Rat Corticospinal Axons Induced by Transplanted Olfactory Ensheathing Cells
Authors: Li Ying , Field Pauline M. , Raisman Geoffrey 
Published: April 2018

Precisely localized focal stereotaxic electrolytic lesions were made in the corticospinal tract at the level of the first to second cervical segments in the adult rat. This consistently destroyed all central nervous tissue elements (axons, astrocytes, oligodendrocytes, microglia, and microvessels) in a highly circumscribed area.In a group of these rats immediately after lesioning, a suspension of cultured adult olfactory ensheathing cells was transplanted into the lesion site. Within the first week after transplantation, the cut corticospinal axons (identified by anterograde transport of biotin dextran) extended caudally along the axis of the corticospinal tract as single, fine, minimally branched sprouts that ended in a simple tip, often preceded by a small varicosity. By 3 weeks, the regenerating axons, ensheathed by P0-positive peripheral myelin had accumulated into parallel bundles, which now extended across the full length of the lesioned area and reentered the caudal part of the host corticospinal tract.The transplants contained two main types of cells: (1) p75-expressing S cells, which later formed typical peripheral one-to-one myelin sheaths around individual ensheathed axons, and (2) fibronectin-expressing A cells, which aggregated into tubular sheaths enclosing bundles of myelinated axons. The point of reentry of the axons into the central nervous territory of the caudal host corticospinal tract was marked by the resumption of oligodendrocytic myelination. Thus the effect of the transplant was to form a “patch” of peripheral-type tissue across which the cut central axons regenerated and then continued to grow along their original central pathway.