bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterotopic Cortical Afferents to the Medial Prefrontal Cortex in the Rat. A Combined Retrograde and Anterograde Tracer Study
Authors: van Eden C. G. , Lamme V. A. F. , Uylings H. B. M.
Published: April 2006

Cortical afferent projections towards the medial prefrontal cortex (mPFC) were investigated with retrograde and anterograde tracer techniques. Heterotopical afferent projections to the medial prefrontal cortex arise in secondary, or higher order, sensory areas, motor areas and paralimbic cortices. On the basis of these projections three subfields can be discriminated within the mPFC. (1) The ventromedial part of mPFC, comprising the pre‐ and infralimbic areas, receives mainly projections from the perirhinal cortex. (2) The caudal two‐thirds of the dorsomedial PFC, comprising frontal area 2 and the dorsal anterior cingulate area, receives projections from the secondary visual areas, the posterior agranular insular area and the retrosplenial areas. (3) The rostral one‐third of the dorsomedial PFC is the main recipient of projections from the somatosensory and motor areas and the posterior agranular insular area. The laminar distribution of cells projecting to the mPFC varies considerably in the different cortical areas, just as the laminar distribution of termination of their fibres within the mPFC does. It is concluded that the corticocortical connections corroborate with subcortical connectivity in attributing to the mediodorsal projection cortex of the rat functions which are comparable to those of certain prefrontal, premotor and anterior cingulate areas in the monkey.
Two GTP‐binding Proteins Control Calcium‐dependent Exocytosis in Chromaffin Cells
Authors: Sontag Jean‐Marie , Aunis Dominique , Bader Marie‐France
Published: April 2006

The effect of guanosine triphosphate analogues on catecholamine secretion from permeabilized bovine chromaffin cells was examined. Guanosine 5′‐[γ‐thio]triphosphate was demonstrated to produce a dual effect on calcium‐evoked secretion, enhancing the release through a mechanism involving protein kinase C and inhibiting secretion by a protein kinase C‐independent pathway. We propose that two functionally distinct G‐proteins control the stimulus ‐ secretion coupling in chromaffin cells.
Triple Immunofluorescence Evidence for the Coexistence of Acetylcholine, Enkephalins and Calcitonin Gene‐related Peptide Within Efferent (Olivocochlear) Neurons of Rats and Guinea‐pigs
Authors: Safieddine Saaid , Eybalin Michel
Published: April 2006

The efferent (olivocochlear) nerve supply to the cochlea is subdivided into a lateral and a medial innervation according to several criteria, e.g. locus of origin in the superior olivary complex and type of synaptic connections established in the organ of Corti. We have used a triple immunofluorescence colocalization approach to determine whether putative cholinergic neurons from the lateral innervation contain both metenkephalin and calcitonin gene‐related peptide (CGRP), and whether those from the medial innervation also contain CGRP. About 80% of the choline acetyltransferase (ChAT)‐like immunostained lateral efferent neurons within the lateral superior olive were CGRP‐ and metenkephalin‐like immunostained. In the organ of Corti, colocalization of the three antigens within the inner spiral bundle was also found. This bundle contains the lateral efferent synapses, with the dendrites of the primary auditory neurons innervating the sensory inner hair cells. Most of the medial efferent neurons in the ventral nucleus of the trapezoid body were only immunoreactive for ChAT. However, in the rostral part of the nucleus, a minority of ChAT‐like immunostained neurons were also CGRP‐like immunostained. None of the ChAT‐like immunostained medial efferent neurons presented metenkephalin‐like immunostaining. In agreement with these brainstem data, partial colocalization of the ChAT‐ and CGRP‐like immunostaining and a lack of metenkephalin immunoreactivity was noted below the sensory outer hair cells, which are the synaptic targets of medial efferent terminals in the organ of Corti. This distinction in the coexistence pattern of the two efferent innervations probably reflects distinct modes of action for acetylcholine in the cochlea. In one case, the effects of acetylcholine on the primary auditory neurons innervating the inner hair cells may require balanced modulation by metenkephalin and CGRP. In the other case, modulation of the effects of acetylcholine on the outer hair cells by neuropeptides would be less critical.
GABAB Receptors in the Parallel Fibre Pathway of Rat Cerebellum
Authors: Batchelor Andrew M. , Garthwaite John
Published: April 2006

Binding studies indicate that the molecular layer of the cerebellum has a high concentration of γ‐aminobutyric acid type B (GABAB) receptors. In order to elucidate the function of these receptors we have recorded from Purkinje cells in biplanar slices of immature (14‐day‐old) and adult rat cerebellum using a low‐noise, non‐invasive, gap technique. The responses of Purkinje cells to parallel fibre stimulation in slices from both immature and adult rats contained a wave that could be inhibited by the GABAA antagonist, bicuculline. In slices from immature animals, application of 30–50 μM bicuculline revealed a slow (400 ms to peak) and very long‐lasting (up to 1 s) hyperpolarizing wave which was inhibited by GABAB antagonists. Activation of GABAB receptors on Purkinje cells with an exogenous agonist, baclofen, also generated a hyperpolarization. Baclofen additionally inhibited the synaptic potentials generated in Purkinje cells on stimulating parallel fibres, an effect which could be reversed by GABAB antagonists. The potency of baclofen in this respect was similar in adult and immature tissue but another excitatory pathway in the cerebellar cortex, the mossy fibre to granule cell synapse, proved to be much less sensitive. We conclude that, at least in the immature rat, there are GABAB receptors on Purkinje cell dendrites and that these receptors can be activated following parallel fibre stimulation; there are also GABAB receptors on presynaptic terminals within the molecular layer of immature and adult cerebellum that, when stimulated, inhibit transmitter release.
Neurophysiological Correlates of Colour Induction on White Surfaces
Authors: Kastner Sabine , Crook John M. , Pei Xing , Creutzfeldt Otto D.
Published: April 2006

Coloured light surrounding a white surface of about equal luminance makes the white surface appear illuminated with an unsaturated light of the complementary colour. In an attempt to discover the neurophysiological basis of such colour induction, we recorded from spectrally opponent cells of the parvocellular layers of the lateral geniculate nucleus (P‐LGN) of anaesthetized macaques. Only cells with wide‐band (W) spectral sensitivity in the short (S) or long wavelength (L) part of the spectrum (WS, WL) are excited by white spots of light centred on their receptive field. Cells with narrow‐band (N) spectral sensitivity (NS, NL) and light‐inhibited (L1) cells are inhibited by white light. Therefore, it is likely that the code for white is contained in a balanced excitation of the W cells. The effects of continuous illumination of remote surrounds with different wavelengths on the responses to achromatic light stimuli were investigated. Responses [on minus maintained discharge rate (MDR) or on‐minus‐off] were determined for white spots (1–3° diameter) flashed on the receptive field centre, presented either alone or in the presence of an annular surround of equal luminance (inner diameter 5°; outer diameter 20°). During red surround illumination the responses of WL cells to white spots tended to be reduced as were those of WS cells during blue surround illumination. Surround illumination with the opponent colour had more variable effects, neither WS nor WL cells showing a significant alteration of their mean response to white during surround illumination with opponent light. Response alterations were to a large extent due to changes in MDR, which increased in WS cells during blue surround illumination and in WL cells during red surround illumination. It is argued that the surround effects on centre responses are due to intraocular stray light rather than lateral connections in the retina. The surround effects also depended to some extent on the size of the test spot. L1 cells and the very rare parvocellular panchromatic on‐cells showed no chromatic response changes during coloured surround illumination. Inasmuch as the excitation of WS cells, either alone or in combination with NS cell activation, is involved in coding for green and blue, and that of WL cells, in combination with NL cell activation, is involved in coding for red and yellow in perception, the shift of excitation towards one or the other W cell group indicates relatively more red or green signals in the white response, consistent with and in the same direction as colour induction. In addition, the summed population response of WS and WL cells is decreased during surround illumination with any colour including white. This is related to brightness decrease during surround illumination in perception.
Neonatal Anti‐NGF Treatment Reduces the Aδ‐ and C‐Fibre Evoked Vasodilator Responses in Rat Skin: Evidence That Nociceptor Afferents Mediate Antidromic Vasodilatation
Authors: Lewin Gary R. , Lisney Stephen J. W. , Mendell Lorne M.
Published: April 2006

Electrical stimulation of cutaneous nerve Aδ‐fibres can lead to increases in skin blood flow (Jänig and Lisney, J. Physiol. (Lond.), 415, 477–486, 1989). Here we have examined this phenomenon in adult rats treated neonatally with antisera to nerve growth factor between postnatal days 2 and 14. This treatment forces many Aδ nociceptor afferents to take on the phenotype of low‐threshold D‐hair afferents (Lewin et al., J. Neurosci., 12, 1896–1905, 1992). In animals treated this way we found a parallel decrease in the ability of Aδ‐fibres to increase skin blood flow. The increase in blood flow evoked by C‐fibre stimulation was also reduced, but no change was seen in the ability of C‐fibres to elicit neurogenic extravasation in skin. These data may be taken as evidence that in rats, amongst the cutaneous Aδ‐fibres, nociceptor but not D‐hair afferents are capable of producing blood flow changes in the skin.
Synaptic Contacts and the Transient Dendritic Spines of Developing Retinal Ganglion Cells
Authors: Wong R. O. L. , Yamawaki R. M. , Shatz C. J.
Published: April 2006

The dendrites of ganglion cells in the mammalian retina become extensively remodelled during synapse formation in the inner plexiform layer. In particular, after birth in the cat, many short spiny protrusions are lost from the dendrites of ganglion cells during the time when ribbon, presumably bipolar, synapses appear in the inner plexiform layer and when conventional, presumed amacrine, synapses increase significantly in number. It has therefore been postulated that these transient spines may be the initial or preferred substrates for competitive interactions between amacrine or bipolar cell terminals that subsequently result in the formation of appropriate synapses onto the ganglion cells. If so, the majority of synapses made onto developing ganglion cells should be found on these dendritic spines. To test this hypothesis, we determined the synaptic connectivity of identified ganglion cells in the postnatal cat retina during the period of peak spine loss and synapse formation. The dendritic trees of ganglion cells were intracellularly filled with Lucifer yellow that was subsequently photo‐oxidized into an electron‐dense product suitable for electron microscopy. In serial reconstructions of the dendrites of a postnatal day 11 (P11) alpha ganglion cell and a P14 beta ganglion cell, conventional and ribbon synapses were found predominantly on dendritic shafts. Only three out of a total of 341 dendritic spines from the two cells received direct presynaptic input, all of which were conventional synapses. Thus, our observations suggest that the transient dendritic spines are not the preferred postsynaptic sites as previously suspected. However, it is possible that these structures play a different role in synaptogenesis, such as mediating interactions between retinal neurons that may lead to cell‐cell recognition, a necessary step prior to synapse formation at the appropriate target sites (Cooper and Smith, Soc. Neurosci. Abstr., 14, 893, 1988).
7‐Chlorokynurenate Ameliorates Neuronal Injury Mediated by HIV Envelope Protein gp120 in Rodent Retinal Cultures
Authors: Lipton Stuart A.
Published: April 2006

Prior studies with in vitro model systems have suggested that at least part of the neurological manifestations of AIDS may stem from neuronal injury involving the HIV‐1 coat protein gp120. This form of neuronal damage is most probably mediated indirectly by a complex set of cellular interactions among macrophages, astrocytes, and neurons, resulting in a final common pathway of overstimulation of N‐methyl‐d‐aspartate (NMDA) receptors. We studied the neuroprotective effect from gp120‐induced neuronal injury of an antagonist of the glycine site of the NMDA receptor, 7‐chlorokynurenate. In identified rat retinal ganglion cells in culture, we found that 50 μM 7‐chlorokynurenate significantly abrogated the injury engendered by 20 pM gp120. Addition of 300 μM exogenous glycine prevented this protective effect of 50 μM 7‐chlorokynurenate. These data suggest that glycine site antagonists of the NMDA receptor may have therapeutic potential for ameliorating neuronal damage associated with gp120.
Effect of Nucleus Basalis Magnocellularis Ablation on Local Brain Glucose Utilization in the Rat: Functional Brain Reorganization
Authors: Soncrant Timothy T. , Holloway Harold W. , Horwitz Barry , Rapoport Stanley I. , Lamour Yvon A.
Published: April 2006

After unilateral destruction of the nucleus basalis magnocellularis (NBM) in 3‐month‐old rats, which reduces cholinergic inputs to the ipsilateral frontoparietal neocortex, regional cerebral metabolic rates for glucose (rCMRglc) of denervated cortex are initially reduced, but nearly normalize by 2 weeks. To examine functional reorganization of the brain after unilateral destruction of the NBM, a correlation analysis of rCMRglc was performed on two groups of 16 young rats 2 weeks after stereotaxic ablation of the right NBM with ibotenate or sham surgery. rCMRglc was measured in 117 brain regions of awake rats with the [14C]deoxyglucose method. For each region pair, a partial correlation coefficient was calculated for rCMRglc across animals. Most correlations between cholinergic nuclei of both left and right forebrain (medial septum and diagonal band) and right (66/72, mean increase 0.44) but not left (39/72) frontoparietal cortical regions were larger (P < 0.001) in lesioned rats, as were those between most frontoparietal region pairs (516/630, P < 0.001). These results suggest that, after unilateral NBM ablation, (1) functional interactions are established between the remaining cholinergic forebrain and the deafferented cortex, (2) the neocortex becomes more integrated, and (3) functional reorganization involves both cortical hemispheres. These changes do not correspond to those reported to occur in Alzheimer's disease.
Reduction of Potassium Conductances Mediated by Metabotropic Glutamate Receptors in Rat CA3 Pyramidal Cells Does Not Require Protein Kinase C or Protein Kinase A
Authors: Gerber U. , Sim J. A. , Gähwiler B. H.
Published: April 2006

Metabotropic glutamate receptors, unlike ionotropic receptors, exert their actions on ion channels via G‐proteins coupled to second messenger systems. In the hippocampus stimulation of metabotropic receptors can lead to decreased potassium channel conductance, decreased accommodation of cell firing and inhibition of the slow calcium‐dependent afterhyperpolarizing current (IAHP). Using the single‐electrode voltage‐clamp technique in hippocampal slice cultures of the rat, the role of protein kinases in mediating these metabotropic glutamate responses was investigated. In the presence of staurosporin, protein kinase C activation by phorbol esters and protein kinase A activation by 8‐bromo‐cyclic adenosine monophosphate were blocked. Under these conditions, the inhibition of IAHB by 1‐aminc‐cyclopentyl‐trans‐dicarboxylate (ACPD), a metabotropic agonist, was unchanged, whilst the inward current elicited by ACPD was enhanced. These results demonstrate that, in the hippocampus, metabotropic glutamate responses persist during inhibition of protein kinase A and C activation. Furthermore, these responses are insensitive to pertussis toxin, confirming previous observations.
Tonotopic Order in the Adult and Developing Auditory System of the Rat as Shown by c‐fos Immunocytochemistry
Authors: Friauf Eckhard
Published: April 2006

Immediate éarly genes such as the proto‐oncogene c‐fos can be expressed in neurons following synaptic excitation by sensory stimulation. C‐fos immunocytochemistry has subsequently been shown to be a very sensitive marking technique for neuronal activity. Here, antibodies against the c‐fos protein product Fos were used to map the tonotopic organization in the auditory system of adult and developing rats. After stimulating adult rats with pure‐tone pulses, bands of Fos‐immunoreactive neurons revealed the frequency representation in seven brainstem nuclei: all three subdivisions of the cochlear nucleus, the lateral superior olive, the medial nucleus of the trapezoid body, the ventral nucleus of the trapezoid body, the rostral periolivary nucleus, the dorsal nucleus of the lateral lemniscus and the inferior colliculus. With the exception of the dorsal cochlear nucleus and the inferior colliculus, tonotopicity has not been previously demonstrated in the brainstem nuclei of the rat. During development two striking results were obtained. First, beginning at postnatal day 14 (i.e. ∼2 days after physiological hearing begins in rats), not only low but also high frequencies were able to induce strong Fos immunoreactivity, indicating that gradual recruitment of formerly unresponsive high‐frequency sites does not occur in the rat. Second, a gradual age‐related shift of the position of isofrequency bands was not seen in any of the nuclei, suggesting that changes in frequency‐place code do not occur after 2 weeks postnatally. These results indicate that the rat's auditory brainstem nuclei achieve their adult‐like tonotopic organization early on, implying a somewhat different developmental time course than is found in other mammalian species.
Temporal Patterns in Spontaneous and Odour‐evoked Mitral Cell Discharges Recorded in Anaesthetized Freely Breathing Animals
Authors: Chaput M. A. , Buonviso N. , Berthommier F.
Published: April 2006

This study investigates in detail how mitral cell activity is distributed during the respiratory cycle in freely breathing animals and how this temporal pattern changes under odour stimulation. Results were obtained from 1408 sequences composed of a 30‐s period of spontaneous activity followed by a 10‐s period of stimulation. Spontaneously, a majority of the patterns did not show any clear relationship with respiration and were categorized as unsynchronized. Stimulations evoked a high proportion of synchronized patterns. About 40% displayed a single period of firing rate increase superimposed on no background activity or on sustained background activity, and were categorized as simple excitatory synchronized patterns. Thirty‐six per cent showed a single inhibitory trough, and were categorized as simple suppressive synchronized patterns, whereas the remaining 24% showed a succession of peaks and troughs, and were categorized as complex synchronized patterns. Under pure air delivery, the position in time of the firing peak in simple excitatory synchronized patterns was found to be generally phase‐locked on late inhalation and early exhalation. During stimulation, its position did not change in patterns which originated from spontaneous patterns having the same type whereas it was shifted towards earlier portions of the cycle in patterns originating from another type. Lastly, the possibilities of transition between spontaneous and odour‐evoked patterns seemed to follow general rules. Whereas any type of spontaneous patterns may transform into any other type under stimulation, a majority of synchronized odour response patterns originated from unsynchronized spontaneous patterns. This may reflect some potential of cells having a non‐modulated spontaneous activity to be more responsive to peripheral inputs.
Axonal Growth on Solubilized and Reconstituted Matrix from the Embryonic Chicken Retina Inner Limiting Membrane
Authors: Halfter W. , Von Boxberg Y.
Published: April 2006

Basal laminae, thin sheets of extracellular matrix covering the basal side of all neuroepithelia, are strongly supportive for neurite outgrowth in vitro and may provide a permissive environment for growing neurites in vivo. To gain information about the biological activity and composition of in situ‐derived basal laminae the inner limiting membranes from embryonic day (E) 7 to E11 chick and quail retinae were isolated. The basal laminae were solubilized with high‐molar guanidine hydrochloride or urea, and the solubilized proteins reconstituted by dialysis. The matrix proteins were spotted or dried onto nitrocellulose or polylysine‐coated dishes. When explants from retina or from dorsal root ganglia were incubated on the protein spots, neurite extension was very robust, at a level as high as on authentic basal lamina. Extracts from the pigment epithelial basement membrane did not support neurite extension. Western blot analysis showed that the explant from the retinal inner limiting membrane contained predominantly basal lamina‐type proteins, such as laminin, collagen type IV and heparan sulphate proteoglycan, whereas the matrix extract from the pigment epithelium contained predominantly mesenchymal‐type proteins, like collagen type I and tenascin. JG22, a β1 integrin antibody that inhibited neurite extension on EHS tumour laminin substrate, had no effect on neurite outgrowth on retinal basal lamina matrix, indicating that embryonic basal laminae contain other or additional growth promoting substrate molecules.
GABAergic Interneurons are the Major Postsynaptic Targets of Median Raphe Afferents in the Rat Dentate Gyrus
Authors: Halasy K. , Miettinen R. , Szabat E. , Freund T. F.
Published: April 2006

The termination pattern of median raphe axons was studied in the rat dentate gyrus using Phaseolus vulgaris leucoagglutinin as an anterograde tracer, in combination with postembedding immunostaining for γ‐amino‐butyric acid (GABA), and pre‐embedding immunostaining for calbindin D28k, parvalbumin and GABA. Postembedding immunogold staining for GABA revealed that the majority (73.7%) of anterogradely labelled median raphe boutons make synaptic contacts with GABA‐immunoreactive postsynaptic targets, mainly with dendritic shafts and perikarya. Pre‐embedding immunocytochemical double staining for the anterograde tracer and GABA confirmed the electron microscopic results and showed that varicose median raphe axons establish multiple contacts with fusiform interneurons in the hilus and different types of basket cells in the granule cell layer. Some of the innervated cells were shown to contain calbindin D28k, whereas GABAergic interneurons containing another calcium‐binding protein, parvalbumin, were never seen to receive multiple contacts from axons of raphe origin. Our results suggest that serotonergic median raphe fibres influence the firing of dentate granule cells via local inhibitory interneurons. The mechanism of using these interneurons with extensive local connections as monosynaptic targets may explain the great efficacy of this pathway in the control of hippocampal electrical activity.
Learning of Sequential Finger Movements in Man: A Combined Kinematic and Positron Emission Tomography (PET) Study
Authors: Seitz Rüdiger J. , Roland Per E.
Published: April 2006

The cerebral structures participating in learning of a manual skill were mapped with regional cerebral blood flow (rCBF) measurements and positron emission tomography in nine healthy volunteers. The task was a complicated right‐hand finger movement sequence. The subjects were examined at three stages: during initial practice of the finger movement sequence, in an advanced stage of learning, and after they had learnt the finger movement sequence. Quantitative evaluation of video tapes and electromyographic records of the right forearm and hand muscles demonstrated that the finger movements significantly accelerated and became more regular. Significant mean rCBF increases were induced in the left motor hand area, the left premotor cortex, the left supplementary motor area, the left sensory hand area, the left supplementary sensory area and the right anterior lobe of the cerebellum. During the learning process significant depressions of the mean rCBF occurred bilaterally in the superior parietal lobule, the anterior parietal cortex and the pars triangularis of the right inferior frontal cortex. The mean rCBF increases in these structures during the initial stage of learning were related to somatosensory feedback processing and internal language for the guidance of the finger movements. These activations disappeared when the subjects had learnt the finger movement sequence. Conversely, the mean rCBF significantly rose during the course of learning in the midsector of the putamen and globus pallidus on the left side. It is suggested that during the learning phase of this movement sequence, the basal ganglia were critically involved in the establishment of the final motor programme.
Widespread Horizontal Connections Arising from Layer 5/6 Border Inverted Cells in Rabbit Visual Cortex
Authors: Reblet Conceptión , López‐Medina Antonio , Gómez‐Urquijo Sonia M. , Bueno‐López José L.
Published: April 2006

Herein we describe the inverted cells [defined as those projection neurons having a major dendritic shaft abpially oriented (Bueno‐López et al., Eur. J. Neurosci., 3, 415, 1991)] originating a unique set of cortical connections characterized by extraordinarily widespread horizontal distribution. Single and multiple injections of wheatgerm agglutinin ‐ horseradish peroxidase were made in areas 17 and 18 and the resulting retrograde labelling in the cortex was analysed. The findings were assessed in independent control experiments in which Fluoro‐Gold was used as retrograde tracer. Following single injections in area 17 several separate patches of labelled cells comprising layers 2–6 were consistently found in area 18. In addition to these associational cells a number of labelled cells appeared at the layer 5/6 border but were distributed over most of the tangential extent of the visual occipital cortex. This widespread pattern was particularly striking in brains after multiple injections. In these brains a conspicuous band of labelled cells at the 5/6 border radiated from the injection sites, making up an apparently continuous horizontal sheet that intersected the striate ‐ extrastriate boundary and merged with the patches of labelled cells in area 18 and beyond. Most of the cells in the 5/6 border band were inverted cells (82%; n= 2081). Injections in area 18 failed to produce such a widespread set of labelled cells in area 17. The functional significance of these connections furnished by the 5/6 border inverted cells remains to be determined, but their distribution would allow for convergent/divergent binding interactions both intra‐areally (within area 17) and inter‐areally (from area 18 to area 17).
Increase in GABAergic Cells and GABA Levels in the Spinal Cord in Unilateral Inflammation of the Hindlimb in the Rat
Authors: Castro‐Lopes J. M. , Tavares Isaura , Tölle T. R. , Coito Ana , Coimbra A.
Published: April 2006

The effects of chronic peripheral inflammation on spinal cord γ‐aminobutyric acid (GABA) were examined in the rat. Following the injection of complete Freund's adjuvant in the left hindlimb footpad an increased number of immunoreactive cells occurred in ipsilateral laminae I‐III of the dorsal horn from L3 to L5. GABA‐immunoreactive cells were more numerous than contralaterally 1 week after the onset of the inflammation, reached maximal numbers after 3–4 weeks, and declined thereafter. Differences from control sides were statistically significant except at week 6. GABA levels in homogenates of the ipsilateral lumbar enlargement were increased significantly at 4 weeks. Since increases in GABA occurred in the spinal cord zone of projection of the nerves supplying the inflamed foot, the central response is surmised to result from the increased nociceptive input arriving from the periphery. However, the transmission from primary axons to GABA interneurons is not likely to be monosynaptic since profiles containing glutamate decarboxylase or GABA immunoreactivity are known to be predominantly presynaptic, and rarely postsynaptic, to primary afferent endings in electron micrographs in the rat. The findings support the function attributed to spinal GABA in modulating nociceptive input at segmental level.
Antagonists of the Platelet‐activating Factor Receptor Block Long‐term Potentiation in Hippocampal Slices
Authors: Arai Amy , Lynch Gary
Published: April 2006

The effects of antagonists and agonists of the platelet‐activating factor (PAF) receptor on the formation of long‐term potentiation (LTP) were examined in slices of rat hippocampus. The antagonist trans‐BTD (trans‐2,5‐bis‐(3,4,5‐trimethoxyphenyl)‐1,3‐dioxolane) at concentrations of 8–16 μM blocked LTP in field CA1 while the same concentration of a stereo isomer (cis‐BTD) with low affinity for PAF receptors was without effect. CV3988, an antagonist structurally related to PAF, also attenuated LTP. The blockade of LTP by trans‐BTD was partially reversed by simultaneous application of the non‐metabolizable receptor agonist carbamyl‐PAF. Trans‐BTD did not change the following physiological measures: (i) paired‐pulse facilitation, (ii) responses occurring during the short bursts given to induce LTP, (iii) N‐methyl‐d‐aspartate receptor‐mediated responses, and (iv) potentiation measured during the first minute after high‐frequency stimulation. It thus appears that trans‐BTD interferes with LTP at some step after induction and initial expression. These results suggest that activation of PAF receptors contributes to the stabilization of LTP, possibly via an effect on intracellular calcium levels.
A Role for Nitric Oxide in Long‐term Potentiation
Authors: Bon Christelle , Böhme Georg Andrees , Doble Adam , Stutzmann Jean‐Marie , Blanchard Jean‐Charles
Published: April 2006

Nitric oxide production in the cerebellum and induction of long‐term potentiation (LTP) in the hippocampus have some characteristics in common: both phenomena are induced by activation of N‐methyl‐D‐aspartate receptors and both are highly dependent on calcium‐mediated processes. Here we provide evidence that endogenous nitric oxide production is necessary for synaptic plasticity in the CA1 hippocampus of the rat. LTP recorded in slices was blocked in a concentration‐dependent manner by the nitric oxide synthase inhibitors L‐NG‐nitroarginine and L‐NG‐nitroarginine methyl ester, but L‐NG‐monomethylarginine was only marginally active. Bathing the slices with haemoglobin, a protein that scavenges nitric oxide, also resulted in a concentration‐dependent blockade of LTP. Nitric oxide released locally from hydroxylamine produced a stable potentiation of synaptic transmission that was not additive with LTP induced by high‐frequency stimulation. These results are fully consistent with the presumed retrograde messenger role of nitric oxide in LTP.
The Role of Ca2+ in the Elimination of Polyneuronal Innervation of Rat Soleus Muscle Fibres
Authors: Zhu Pei‐Hong , Vrbová G.
Published: April 2006

The mechanism by which nerve ‐ muscle contacts are reduced during postnatal development of the rat soleus muscle was investigated using electrophysiological methods. Between days 7 and 9 after birth, soleus muscle fibres lose 0.19–0.24 terminals per muscle fibre within 24 h. A much more rapid loss of contacts is seen when muscles are exposed in vitro to acetylcholine (10−3 g/ml). In this case 0.67–0.87 terminals per muscle fibre lose contact within 2 h. The loss of neuromuscular contacts induced by acetylcholine can be reduced by preincubating the muscles in solutions containing acetoxymethyl ester of 1,2‐bis(2‐amino‐phenoxylethane‐N,N1;N1‐tetraacetic acid (BAPTA‐AM), a Ca2+ chelating agent that enters cells and reduces the Ca2+ transients inside the cell. Treatment of muscles with nifedipine, which blocks dihydropyridine‐sensitive (L‐type) Ca2+ channels, also reduced the acetylcholinesterase‐induced loss of neuromuscular contacts. The results indicate that transient increases in Ca2+ inside nerve terminals contribute to loss of neuromuscular contacts, and that these increases occur by Ca2+ entry through L‐type channels.
Heterogeneity in the Membrane Current Pattern of Identified Glial Cells in the Hippocampal Slice
Authors: Steinhaüser C. , Berger T. , Frotscher M. , Kettenmann H.
Published: April 2006

Glial cells, acutely isolated or in tissue culture, have previously been shown to express a variety of voltage‐gated channels. To resolve the question whether such channels are also expressed by glial cells in their normal cellular environment, we have applied the patch‐clamp technique to study glial cells in hippocampal slices of 10–12‐day‐old mice. Based on the membrane current pattern, we distinguished four glial cell types. One was characterized by passive, symmetrical K+ currents activated in depolarizing and hyperpolarizing directions. A second population showed a similar current pattern, but with a marked decay of the current during the 50‐ms voltage jumps. In a third population, the decaying passive currents were superimposed with a delayed rectifier outward current and, in some cases, with a slow inward current activated by depolarization. The fourth population expressed delayed rectifying outward currents, an inward rectifier K+ current and fast inward currents activated by depolarization. To unequivocally identify the glial cells we combined electrophysiological and ultrastructural characterizations. Therefore, cells were filled with the fluorescent dye lucifer yellow during characterization of their membrane currents, the fluorescence of the dye was used to convert diaminobenzidine to an electron‐dense material, and subsequently slices were inspected in the electron microscope. Recordings were obtained from cells in the stratum radiatum and were identified as glial by their size, the characteristic chromatin distribution, and the lack of synaptic membrane specializations.
Characterization of L‐2‐Amino‐4‐Phosphonobutanoate Action Following Sensitization by Quisqualate in Rat Hippocampal Slice Cultures
Authors: Charpak Serge , Thompson Scott M. , Gähwiler Beat H. , Gerber Urs
Published: April 2006

An excitatory action of l‐2‐amino‐4‐phosphonobutanoate (l‐AP4), a glutamate analogue, is observed following pre‐exposure of tissue to quisqualate. We have studied the mechanism of sensitization of l‐AP4 responses by quisqualate in voltage‐clamped CA3 pyramidal cells in rat hippocampal slice cultures in the presence of tetrodotoxin. Prior to quisqualate addition, CA3 cells did not respond to l‐AP4 (50–1000μM). Following brief application of quisqualate (500 nM for 30 s), l‐AP4 (50–200 μM) induced a complex excitatory response which could be obtained for >1 h. l‐AP4 caused an ionotropic inward current associated with a conductance increase. This response was in part sensitive to 6‐cyano‐7‐nitro‐quinoxaline‐2,3‐dione (CNQX) and in part sensitive to d‐2‐amino‐5‐phosphonovalerate (d‐AP5) and Mg2+ ions. At depolarizing potentials, in the presence of CNQX and d‐AP5, l‐AP4 caused excitation by depressing K+ currents, mimicking the metabotropic action of glutamate. This indicates that the action of l‐AP4 is mediated by three different receptor types: N‐methyl‐D‐aspartate (NMDA) receptors, α‐amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionate (AMPA) receptors, and glutamatergic metabotropic receptors. The l‐AP4 response persisted in solutions containing low Ca2+ and high Mg2+ concentrations or 100–200 μM Cd2+, suggesting that it is independent of extracellular Ca2+. We were unable to identify any substance other than quisqualate capable of sensitizing the l‐AP4 action. This effect also occurred when quisqualate was applied in Ca2+‐free solution or in solutions containing low concentrations of Na+ or Cl−. Sensitization of l‐AP4 responses by quisqualate was not observed in acutely dissociated pyramidal cells recorded by means of the whole‐cell recording mode, although ionotropic quisqualate responses were present. Sensitization was readily reversed by short applications of the endogenous excitatory amino acids glutamate, aspartate and homocysteate at concentrations of 10–100 μM. Our data are consistent with the hypothesis that the excitatory action of l‐AP4 results from a Ca2+‐independent release of endogenous excitatory amino acids from some presynaptic neuronal or glial site.
Quisqualate Metabotropic Receptors Modulate NMDA Currents and Facilitate Induction of Long‐Term Potentiation Through Protein Kinase C
Authors: Aniksztejn Laurent , Otani Satoru , Ben‐Ari Yehezkel
Published: April 2006

Using intracellular and extracellular recordings in rat hippocampal slices, we have investigated the interactions between the quisqualate metabotropic receptor (QP) and currents mediated by N‐methyl‐d‐aspartate (NMDA) and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA). We found that trans‐ (t)‐1‐amino‐1,3‐cyclopentanedicarboxylic acid (trans‐ACPD) and 1S,3R‐aminocyclopentane‐1,3‐dicarboxylic acid (1S,3R‐ACPD) potentiated NMDA but not AMPA‐mediated currents. Intracellular injections of selective protein kinase C inhibitors prevented the up‐regulation of the NMDA response. The physiological consequence of the up‐regulation by ACPD of the NMDA response on the threshold of long‐term potentiation induction was tested. We found that a subthreshold train of electrical stimulation that produced short‐term potentiation generated long‐term potentiation when coupled with ACPD application, an effect which was not produced by AMPA or NMDA. This effect was blocked by an inhibitor of protein kinase C. These results demonstrate for the first time that one subtype of glutamate receptor (QP) can regulate another subtype of glutamate receptor (NMDA) through the activation of protein kinase C. Our results also suggest that the NMDA receptor is regulated by protein kinase C, and that the intracellular level of protein kinase C may determine the threshold for induction of long‐term potentiation.
Parallel Circuits from Cones to the On‐Beta Ganglion Cell
Authors: Cohen Ethan , Sterling Peter
Published: April 2006

Neural integration depends critically upon circuit architecture; yet the architecture has never been established quantitatively (numbers of cells and synapses) for any vertebrate local circuit. Here we describe circuits in the cat retina that connect cones to the on‐beta ganglion cell. This cell type is important because on‐ and off‐beta cells contribute about 50% of the optic nerve fibres and the major retinal input to the striate cortex. Three adjacent on‐beta cells in the area centralis and their bipolar connections to cones were reconstructed from electron micrographs of 279 serial sections. The beta dendritic field is 34±2 μm in diameter and encompasses 35 cones. All of these cones connect to the beta cell via 14–17 bipolar cells. These bipolar cells were shown previously by cluster analysis to be of four types (b1‐b4); three of these types (b1′ b2 and b3) provided 97% of the bipolar contacts to the beta cell, in the ratio 4:2:1. On average, bipolar cells nearest the centre of the beta dendritic field contribute more synapses than those towards the edge, but the peaked distribution of bipolar synapses across the dendritic field is only slightly broader than the optical pointspread function of the cat's eye, and is narrower by half than the centre of the ganglion cell receptive field. This implies that the distribution of bipolar synapses across the beta cell dendritic field contributes little to the extent or shape of the receptive field. Since all three bipolar circuits connect to the same set of cones, they must carry the same spatial and chromatic information; they might convey different temporal frequencies. The numbers of bipolar synapses (mean ± SD = 154±8) and amacrine synapses (59±5) converging on three adjacent beta cells are remarkably constant (SD=±5% of the mean). Thus, as the circuits repeat locally, the fundamental design is accurately reproduced.
Expression of the Neural Recognition Molecule L1 by Cultured Neural Cells is influenced by K+ and the Glutamate Receptor Agonist NMDA
Authors: Scherer Martin , Heller Martin , Schachner Melitta
Published: April 2006

To investigate the influence of neuronal activity on the expression of neural recognition molecules, cultures of neural cell lines and dissociated cells of early postnatal mouse cerebellum were maintained in the presence of elevated concentrations of K+ and the glutamate agonist N‐methyl‐D‐aspartate (NMDA). Levels of expression of the neural adhesion molecules L1 and N‐CAM at the cell surface were measured by an enzyme‐linked immunosorbent assay. Expression of L1 was up‐regulated in neuroblastoma N2A cells after 1 day of maintenance in 40 and 60 mM K+, but not in phaeochromocytoma PC12 cells. Expression levels of N‐CAM and antigens recognized by the monoclonal antibody A2B5 or by polyclonal antibodies to crude membrane fractions of liver were not significantly altered by elevated K+ concentrations in these two cell lines. In monolayer cultures of early postnatal mouse cerebellum, an increase of 60% in expression of L1, but not N‐CAM or A2B5, was seen at 20 and 40 mM K+. This increase in L1 expression was specifically inhibitable by the Ca2+ channel blocker nicardipine. NMDA at a concentration of 100 μM increased levels of L1, but not of N‐CAM. This increase was inhibitable by the NMDA antagonists 2‐amino‐5‐phosphonovalerate and MK‐801, but not significantly by the kainate/quisqualate antagonist 6‐cyano‐7‐nitroquinoxaline‐2, 3‐dione. The increase in L1 expression at higher K+ concentrations was not inhibitable by the NMDA antagonists, indicating that the K+‐mediated increase in L1 expression is not due to release of glutamate by cerebellar neurons. These observations indicate that compounds influencing neuronal membrane properties, and thus neuronal excitability, are capable of regulating the expression of L1. In a more general context, these findings suggest that previously observed changes in synaptic connectivity in situ, resulting from activity‐dependent fine tuning of neuronal morphology, may be mediated by alterations in the expression of recognition molecules.
Relationships of the Dendritic Arborizations of Ventral Striatomesencephalic Projection Neurons With Boundaries of Striatal Compartments. An In Vitro Intracellular Labelling Study in the Rat
Authors: Arts Monique P. M. , Groenewegen Henk J.
Published: April 2006

We studied the relationships of the dendrites of ventral striatomesencephalic projection neurons with the compartmental structure of the ventral striatum, as revealed by enkephalin immunohistochemistry. Lightly fixed slices were employed in which Lucifer yellow was intracellulary injected into neurons that were retrogradely labelled following Fast Blue injections in the ventral tegmental area. Double immunohistochemical staining was carried out using antisera to Lucifer yellow and Leu‐enkephalin. Most of the 226 injected cells were located in the core region of the nucleus accumbens. All these neurons were of the small‐ to medium‐sized spiny type. The dendritic arborizations of over 90% of the cells remained within the compartment in which the parent cell bodies resided. The dendrites of most of these neurons abutted the border of the compartment, whereas a smaller number of neurons had dendrites that were distant from any compartmental boundary. The dendrites of fewer than 10% of the neurons crossed the borders of compartments. Only a few cells were injected in the shell region of the nucleus accumbens. None of these neurons extended its dendrites into the core region of the nucleus or into the territory of the clusters of small cells which characterize the shell. The present results demonstrate that the dendrites of the great majority of ventral striatomesencephalic neurons comply with the boundaries of ventral striatal enkephalin compartments. Together with the results of previous studies showing that such compartments are selectively innervated by thalamic and cortical afferents, and have outputs to different areas in the ventral mesencephalon, the present data suggest the existence of discrete channels through the ventral striatum.
Transient Association of the HNK‐1 Epitope with 5′‐Nucleotidase during Development of the Cat Visual Cortex
Authors: Vogel M. , Zimmermann H. , Singer W.
Published: April 2006

During early postnatal development of the kitten visual cortex the ectoenzyme 5′‐nucleotidase undergoes a characteristic redistribution. Until about postnatal week 6 it is essentially confined to synaptic contacts in input layer IV and its expression is related to the use‐dependent segregation of thalamic afferents into ocular dominance columns. Subsequently, 5′‐nucleotidase becomes distributed uniformly throughout all layers and is then associated selectively with glial cells. Here we describe an age‐dependent alteration in the expression of a carbohydrate epitope of 5′‐nucleotidase which correlates with the developmental change of the enzyme's localization. We have isolated 5′‐nucleotidase from the occipital cortex of kittens of varying age and from adult cats and investigated by immunoblotting the association of the HNK‐1 carbohydrate epitope with the protein. 5′‐Nucleotidase carries the HNK‐1 epitope in kittens of 3–9 weeks but the epitope is absent from 12‐week‐old kittens or adult cats. Thus, the appearance of the HNK‐1 epitope correlates with the transient localization of the enzyme at synapses. The HNK‐1 carrying 5′‐nucleotidase may be involved in synaptogenesis and use‐dependent modifications of synaptic connections.
Brain‐derived Neurotrophic Factor is a Survival Factor for Cultured Rat Cerebellar Granule Neurons and Protects them Against Glutamate‐induced Neurotoxicity
Authors: Lindholm Dan , Dechant Georg , Heisenberg Carl‐Philipp , Thoenen Hans
Published: April 2006

We have studied the effects of different neurotrophins on the survival and proliferation of rat cerebellar granule cells in culture. These neurons express trkB and trkC, the putative neuronal receptors for brain‐derived neurotrophic factor (BDNF) and neurotrophin‐3 (NT‐3) respectively. Binding studies using iodinated BDNF and NT‐3 demonstrated that both BDNF and NT‐3 bind to the cerebellar granule neurons with a similar affinity of ˜ 2x10‐9 M. The number of receptors per granule cell was surprisingly high, ∼30x10‐4 and 2x 105 for BDNF and NT‐3, respectively. Both NT‐3 and BDNF elevated c‐fos mRNA in the granule neurons, but only BDNF up‐regulated the mRNA encoding the low‐affinity neurotrophin receptor (p75). In contrast to NT‐3, BDNF acted as a survival factor for the granule neurons. BDNF also induced sprouting of the granule neurons and significantly protected them against neurotoxicity induced by high (1 mM) glutamate concentrations. Cultured granule neurons also expressed low levels of BDNF mRNA which were increased by kainic acid, a glutamate receptor agonist. Thus, BDNF, but not NT‐3, is a survival factor for cultured cerebellar granule neurons and activation of glutamate receptor(s) up‐regulates BDNF expression in these cells.