bluuebunny/crossref_metadata_2025_split huggingface dataset:
Excitatory Amino Acid Pathway from the Hippocampus to the Prefrontal Cortex. Contribution of AMPA Receptors in Hippocampo‐prefrontal Cortex Transmission
Authors: Jay Thérèse M. , Thierry Anne‐Marie , Wiklund Leif , Glowinski Jacques 
Published: April 2006

AbstractPrevious experiments in the rat have demonstrated that field CA1 and the subiculum project to the prefrontal cortex and that this direct unilateral pathway is excitatory. In the present study, anatomical and electrophysiological approaches were used to determine the transmitter mediating the excitatory responses in prefrontal cortex neurons to low‐frequency stimulation of the hippocampus. The method of selective retrograde d‐[3H]aspartate labelling was used to identify putative glutamatergic and/or aspartatergic hippocampal afferent fibres to the prefrontal cortex. Unilateral microinjection of d‐[3H]aspartate into the prelimbic area of the prefrontal cortex resulted in the retrograde labelling of a fraction of hippocampal neurons. Some labelled cell bodies were distributed in field CA1 and the subiculum but larger numbers of neurons were detected in the ventral and intermediary subiculum. In a second series of experiments, the excitatory transmission from the hippocampus to the prefrontal cortex was pharmacologically analysed to provide further evidence for the involvement of glutamate and/or aspartate in the pathway. All prefrontal cortex neurons responding to the stimulation of the hippocampus were activated by selective agonists of the glutamate receptor subtypes α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionic acid (AMPA) and N‐methyl‐d‐aspartate (NMDA), and these effects were selectively antagonized by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and 2‐amino‐5‐phosphonopentanoic acid (APV) respectively. Most of the excitatory responses of prefrontal cortex neurons to single and paired‐pulse stimulation of the hippocampus were antagonized by CNQX. APV only affected the excitatory response in a few cells. These results suggest that the hippocampal input to the prefrontal cortex utilizes glutamate and/or aspartate as a transmitter. Even though prefrontal cortex neurons responding to the stimulation of the hippocampus appear to have both AMPA and NMDA receptors, low‐frequency stimulation of the hippocampo‐prefrontal cortex pathway activates cortical neurons mostly through AMPA receptors.
Inferotemporal‐frontal Disconnection: The Uncinate Fascicle and Visual Associative Learning in Monkeys
Authors: Eacott M. J. , Gaffan David 
Published: April 2006

AbstractWe report a series of six experiments in which we examined the behavioural effects of disconnecting the inferior temporal cortex from the prefrontal cortex in cynomolgus monkeys by sectioning the direct cortico‐cortical pathway between them, the uncinate fascicle. In experiment 1, monkeys with bilateral section of the uncinate fascicle showed a marked deficit in learning visuomotor conditional problems. Experiments 2 and 3 demonstrated that this deficit was not the result of a mild motor impairment, nor of a visual discrimination impairment. However, experiment 4 showed that the impairment extended to visual – visual conditional learning. In contrast, following bilateral section of the uncinate fascicle monkeys were unimpaired at two other tasks of visual associative learning: a reward – visual associative task (experiment 5), in which the presence or absence of a food reward served as a cue to the correct choice between two visual stimuli, and a time – visual associative task (experiment 6), in which the cue to the correct choice was the length of the intertrial interval. Thus, animals with uncinate fascicle section showed no impairment in learning to choose between visual stimuli based on their differential association with food reward or other non‐visual cues, but were unable to learn to choose between visual stimuli based on their differential association with another visual stimulus. They were equally unable to choose between two motor responses on the basis of the visual cue.
Post‐crucial Period Effects of Auditory Experience and Deprivation on the Guinea‐pig Superior Collicular Map of Auditory Space
Authors: Binns K. E. , Withington D. J. , Keating M. J. 
Published: April 2006

AbstractThe auditory space map in the superior colliculus of the guinea‐pig requires for its normal emergence at 32 days after birth (DAB) bimodal, auditory and visual experience during a 4‐day crucial period (26–30 DAB) (Withington‐Wray et al., Neurosci. Lett., 116, 280–286, 1990d). The need for auditory experience has been proposed to be linked to the rapid changes in the cues for auditory localization brought about by head growth. Head growth is particularly rapid during the first postnatal month but continues more slowly until ∼70 DAB. This suggests that sensory experience may be required beyond the initial crucial period to accommodate later growth. In this paper the role of auditory experience beyond the crucial period has been investigated. Deprivation of ordinary auditory experience was effected by placement of the animals in an environment in which continuous omnidirectional noise obscured the cues of sound direction. Animals deprived of auditory experience during the crucial period and then allowed normal experience showed limited ability to construct an auditory space map and the resulting map was less accurate than that found in normally reared animals. Auditory deprivation following normal experience during the crucial period caused a profound degradation, of both spatial tuning and topography, of auditory multi‐unit receptive fields in the superior colliculus. The spatial tuning and topography of auditory fields from older animals (100 DAB) deprived of ordinary auditory cues for a 4‐week period were normal. Thus, in the guinea‐pig, susceptibility of the superior collicular space map to deprivation of auditory cues is limited by the age of the animal. The timing of the cessation of vulnerability may, in part, be due to the stabilization of directional cues affected by head growth.
The Somatotopic Organization Within the Rabbit's Thalamic Reticular Nucleus
Authors: Crabtree John W. 
Published: April 2006

AbstractThe organization of the somatosensory representation within the rabbit's thalamic reticular nucleus (TRN) was studied. Focal injections of horseradish peroxidase (HRP), wheatgerm agglutinin conjugated to HRP, or [3H]proline were made into somatosensory cortical area 1 (S1). The resultant labelling in the thalamus was analysed. Single injections into S1 result in single zones of terminal labelling in TRN that are restricted to the centroventral part of the sheet‐like nucleus. In reconstructions from horizontal sections these zones of labelling resemble ‘slabs’, which lie in the plane of the nucleus parallel to its borders, occupy only a fraction of the thickness of the reticular sheet, and are elongated in the dorsoventral and oblique rostrocaudal dimensions. Thus, the slabs of S1 terminals, which represent various loci of the body surface, and the main distribution of the reticular dendrites have a similar orientation. In comparisons of the zones of labelling following single or double injections at different cortical sites in S1, an inner (medial) to outer (lateral) shift in labelling in the ventrobasal complex (VB) is accompanied by an inner (medial) to outer (lateral) shift in labelling along the thickness of the reticular sheet; a rostral to caudal shift in labelling in VB is accompanied by a rostral to caudal shift in labelling along the plane of the reticular sheet. Thus, like VB, the reticular nucleus receives a topographically accurate projection from S1. Further, the somatotopic map conveyed from S1 to TRN lies perpendicular to the plane of the nucleus and repeats the spatial organization of the map in VB. These findings, together with those for the visual sector of the rabbit's TRN, indicate that the representation of the cortical sheet is broken up into significant parcels at the inner and outer borders of the reticular sheet.
The Somatotopic Organization Within the Cat's Thalamic Reticular Nucleus
Authors: Crabtree John W. 
Published: April 2006

AbstractThe organization of the somatosensory representation within the cat's thalamic reticular nucleus (TRN) was studied. Focal injections of horseradish peroxidase (HRP), wheatgerm agglutinin conjugated to HRP, and/or [3H]proline were made into somatosensory cortical areas 1 (S1) and 2 (S2). The resultant labelling in the thalamus was analysed. Single injections into S1 result in single zones of terminal labelling in TRN that are restricted to the centroventral part of the sheet‐like nucleus. In reconstructions from horizontal sections these zones of labelling resemble thin ‘slabs’, which lie in the plane of the nucleus parallel to its borders, occupy only a fraction of the thickness of the reticular sheet, and are broadly elongated in the dorsoventral and oblique rostrocaudal dimensions. Thus, the slabs of S1 terminals, which represent large loci of the body surface, and the main distribution of the reticular dendrites have a similar orientation. In comparisons of the zones of labelling following single or double injections at different cortical sites in S1, an inner (medial) to outer (lateral) shift in labelling in the ventrobasal complex (VB) is accompanied by an inner (medial) to outer (lateral) shift in labelling along the thickness of the reticular sheet. Thus, like VB the reticular nucleus receives a topographically accurate projection from S1. Further, the somatotopic map conveyed from S1 to TRN is orientated perpendicular to the plane of the nucleus and repeats the spatial organization of the map in VB. S2 injections result in zones of terminal labelling in that part of TRN that receives S1 inputs. On the basis of these findings, together with those in other mammalian species, two conclusions can be reached about corticoreticular relations. First, although there can be continuity in individual maps of cortical inputs to TRN, there are discontinuities in cortical representations at the inner and outer borders of the reticular sheet. Second, TRN can receive a significant convergence of inputs from different cortical areas.
Relationship Between Intracellular Free Calcium Concentration and NMDA‐induced Cerebellar Granule Cell Survival In Vitro
Authors: Pearson Heather , Graham Margaret E. , Burgoyne Robert D. 
Published: April 2006

AbstractThe survival of cerebellar granule cells in culture is stimulated by activation of the N‐methyl‐d‐aspartate (NMDA) class of glutamate receptors. Activation of these receptors at the key period for cell survival in vitro (3 days; 3DIV) resulted in a sustained elevation of intracellular free calcium concentration [Ca2+]i over the same concentration range of NMDA that led to granule cell survival. Agents that release Ca2+ from intracellular stores led to only small, transient elevations of [Ca2+]i and were unable to stimulate granule cell survival. Addition of the Ca2+ ionophore ionomycin to granule cell cultures at 3DIV resulted in increased granule cell number at 7DIV. The ability of ionomycin to stimulate granule cell survival was related to the [Ca2+]i elicited, indicating that a rise in [Ca2+]i is sufficient to activate the processes leading to granule cell survival and that the extent of the elevation in [Ca2+]i is crucially important in determining granule cell fate.
Synaptic Currents in Thalamo‐cortical Neurons of the Rat Lateral Geniculate Nucleus
Authors: Leresche N. 
Published: April 2006

AbstractThalamo‐cortical neurons were identified in slices of the rat dorsal lateral geniculate nucleus and whole‐cell currents were recorded using the patch‐clamp technique. Postsynaptic currents occurring spontaneously, or elicited by extracellular stimulation in the vicinity of the recorded neuron, were analysed. Spontaneous postsynaptic currents were observed in every recorded neuron. At a holding potential of –60 mV, and with a high internal Cl−, the currents were inward and had amplitudes ranging from <10 to 425 pA. All the spontaneous currents were blocked by 10 μM bicuculline, indicating that they were due to the activation of postsynaptic α‐aminobutyric acid (GABAA) receptors. The 10–90% rise time of these spontaneous GABAergic currents was 0.86 ± 0.19 ms. Their time course of decay could be fitted to an exponential function with one time constant of 18.19 ± 3.02 ms (mean ± SD), or two time constants of 4.47 ± 0.77 and 33.27 ± 3.74 ms. This activity was frequently organized in bursts. Stimulus‐evoked postsynaptic currents were recorded and shown to be due to the activation of glutamatergic receptors. Under similar experimental conditions a bicuculline‐sensitive component was also recorded. These stimulus‐evoked GABAergic currents had a 10–90% rise time of 1.93 ± 0.54 ms. Their time course of decay could also be fitted to an exponential function with one time constant of 24.42 ms or two time constants of 10.26 ± 2.46 and 49.30 ± 10.98 ms. The difference in the time course between spontaneous and evoked GABAergic currents suggests that these responses may arise from synapses having different locations.
An Organotypic Co‐culture of Embryonic Rat Brainstem and Tongue or Skeletal Muscle
Authors: Gueritaud J. P. , Seyfritz N. 
Published: April 2006

AbstractTransverse sections of rat embryo brainstem (embryonic age 18–19 days) containing the brainstem motor nuclei were explanted, together with a small piece of tongue or skeletal muscle, in a plasma clot and maintained in culture for 2–3 weeks using the roller tube technique. The results show that brainstem motoneurons survived, differentiated and innervated newly formed multinucleated myotubes which displayed large synchronized contractions after 1 week in culture. Muscle fibre contractions could be induced by excitatory amino acid applications and suppressed by curarization. Muscle fibres differentiated normally. During the first week they showed diffuse acetylcholinesterase positivity and multi‐innervation. During the second and third weeks the number of motor end‐plates was greatly reduced and transverse striation was observed. In the presence of muscle fibres, the brainstem thinned out and spread, becoming one or two cell layers thick, and the motoneurons tended to migrate towards the muscle fibres, becoming clearly observable in the living culture. When the muscle explant was not present, the brainstem explant did not spread and remained several cell layers thick, while acetylcholinesterase‐positive cells, presumed to be motoneurons, tended to disappear. The preparation described is well suited for electrophysiological studies of differentiating motoneurons and offers direct access to their dendritic tree, a most desirable feature for patch‐clamp or multisite optical recording.
The L2/HNK‐1 Carbohydrate Epitope is Involved in the Preferential Outgrowth of Motor Neurons on Ventral Roots and Motor Nerves
Authors: Martini R. , Xin Y. , Schmitz B. , Schachner M. 
Published: April 2006

AbstractBased on the observation that in adult mice the carbohydrate epitope L2/HNK‐1 is detectable on Schwann cells in ventral spinal roots, but only scarcely in dorsal roots (Martini et al., Dev. Biol., 129, 330–338, 1988), the possibility was investigated that the carbohydrate is involved in the outgrowth of regenerating motor neuron axons on peripheral nerve substrates expressing the epitope. To monitor whether the L2 carbohydrate remains present during the time periods in which regenerating axons penetrate the denervated distal nerve stumps, the expression of L2 in motor and sensory branches of the femoral nerve was investigated in normal animals and after a crush lesion. During the first two postoperative weeks, L2 immunoreactivity remained high in the myelinating Schwann cells of the motor branch, whereas L2 immunoreactivity was virtually absent in the sensory branch. In a first experimental approach, cryosections of ventral and dorsal spinal roots and of motor and sensory nerves of adult rats and mice were used as substrates for neurite outgrowth. Neurites of motor neurons from chicken embryos were ∼35% longer after 30 h of maintenance on ventral roots than on dorsal roots. Neurites from sensory neurons had the same length on dorsal as on ventral motors and were as long as neurites from motor neurons grown on dorsal roots. L2 antibodies reduced neurite outgrowth of motor neurons on ventral roots but not on dorsal roots. Neurite outgrowth of sensory neurons on both roots was not altered by the antibodies. Neurite outgrowth of motor neurons on a mixture of the extracellular matrix glycoprotein laminin and the L2 carbohydrate‐carrying glycolipid was significantly higher than on the laminin substrate mixture with GD1b ganglioside or sulphatide. L2 antibodies reduced neurite outgrowth of motor neurons by 50% on the L2 glycolipid, but not on GD1b or sulphatide. These observations indicate that the L2 carbohydrate promotes neurite outgrowth of motor neurons in vitro and may thus contribute to the preferential reinnervation of motor nerves by regenerating motor axons in vivo.
Intrastriatal Dopamine‐rich Implants Reverse the Increase of Dopamine D2 Receptor mRNA Levels Caused by Lesion of the Nigrostriatal Pathway: A Quantitative In Situ Hybridization Study
Authors: Chritin M. , Savasta M. , Mennicken F. , Bal A. , Abrous D. N. , Le Moal M. , Feuerstein C. , Herman J. P. 
Published: April 2006

AbstractChanges in striatal dopamine D2 receptor mRNA levels provoked by unilateral 6‐hydroxydopamine‐induced lesion of the nigrostriatal dopamine pathway were studied by in situ hybridization. The influence of embryonic dopaminergic neurons implanted into the dopamine‐depleted striatum on the lesion‐induced changes was also examined. Changes in D2 mRNA levels were compared with changes in D2 receptor densities measured in the same animals by receptor autoradiography using [3H]spiperone or [3H]SDZ 205–501 as ligands. The distribution of D2 mRNA in the striatum of control animals closely paralleled that of the D2 receptor itself, as assessed by autoradiography, and the highest density of D2 mRNA occurred in the lateral part of the striatum. One month after lesion, levels of D2 mRNA were 34% higher in the dorsolateral part of the dopamine‐depleted striatum than in the corresponding region of the contralateral control striatum. D2 receptor density in this region was increased by 40% relative to the control level. No significant increases could be measured in the medial part of the striatum. The increases in the lateral part were similar at 7 months post‐lesion; however, at this time the increase in both D2 mRNA and receptor levels had spread to the medial part of the striatum as well. In the graft‐bearing striatum levels of both D2 mRNA and D2 receptors reverted to control levels. This study shows that the post‐lesion increase in striatal dopamine receptor and mRNA level is a biphasic phenomenon with a late‐occurring component in the medial striatum. It also shows that once the increase in striatal D2 receptor gene expression is accomplished, it is maintained unchanged for long periods, similar to that of D2 receptor levels themselves. Moreover, grafts of embryonic dopaminergic neurons are able to modulate the expression of the dopamine D2 receptor gene.
The Relative Contribution of NMDA Receptor Channels in the Expression of Long‐term Potentiation in the Hippocampal CA1 Region
Authors: Asztely Fredrik , Wigström Holger , Gustafsson Bengt 
Published: April 2006

AbstractLong‐term potentiation (LTP) was studied in the hippocampal CA1 region of guinea‐pigs using a solution containing 0.1 mM magnesium and 10 μM of the non‐N‐methyl‐d‐aspartate (non‐NMDA) antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), leaving an NMDA‐mediated field excitatory postsynaptic potential (EPSP). Brief high‐frequency afferent tetanization induced a substantial synapse‐specific potentiation of the NMDA EPSP with a time course closely resembling that previously described for LTP of the non‐NMDA‐mediated EPSP. This NMDA EPSP potentiation was occluded by prior induction of LTP in normal solution. Using a solution containing 0.1 mM magnesium and 1 μM CNQX, the EPSP was composed of both a non‐NMDA‐ and an NMDA‐mediated component which could be measured separately and in parallel. Manipulations that cause increased transmitter release, such as phorbol ester application and changes in stimulation frequency, enhanced the two measures nearly equally. Afferent tetanization induced an increase of both EPSP components, with a similar time course, the NMDA component showing a relative increase of about one‐third of that of the non‐NMDA one. These results suggest that, to the extent that LTP is based on an increased release of transmitter, the mechanism exhibits features distinct from those underlying other forms of enhanced release.
Adult Retinofugal Axons Regenerating Through Peripheral Nerve Grafts Can Restore the Light‐induced Pupilloconstriction Reflex
Authors: Thanos Solon 
Published: April 2006

AbstractTo investigate the ability of mature regenerating retinal axons to form functional connections within central targets, severed axons were guided into the primary visual centres which subserve the pupillary constriction reflex in response to light. The ocular stump of the transected optic nerve of adult rats was connected by means of an autologous peripheral nerve graft with the pretectal region which contains the relay nucleus of pupillary constriction, the olivary pretectal nucleus. This nucleus is efferently connected with preganglionic neurons in the oculomotor nuclear complex which innervates parasympathetically the muscle constrictors of the iris. Six to sixteen weeks after optic nerve transection and peripheral nerve transplantation, brisk responses were observed in the pupils upon illumination of the transplanted eye. Recovery of the pupil responses indicated that retinal neurons used the peripheral nerve ‘bridge’ to access the pretectum, in which they established synaptic contacts in sufficient density and with appropriate specificity to reconstitute the function of the traumatically interrupted neuronal circuitry.