bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensory Excitatory Postsynaptic Potentials Mediated by NMDA and non‐NMDA Receptors in the Thalamus in vivo
Authors: Salt T. E. , Eaton S. A.
Published: April 2006

Excitatory amino acid neurotransmitters, such as l‐glutamate, act at several receptors in the brain, which are sometimes referred to as N‐methyl‐d‐aspartate (NMDA) and non‐NMDA receptors. Extensive in vitro work indicates that both NMDA receptors and non‐NMDA receptors contribute to excitatory postsynaptic potentials (epsps). The contribution of NMDA receptors to epsps in vivo under physiological conditions is, however, almost unknown. The receptors that mediate the epsps evoked in thalamic relay cells by natural stimulation of sensory afferents have been investigated in anaesthetized rats, and we report the first pharmacological characterization of an excitatory amino acid receptor‐mediated epsp in vivo involving both non‐NMDA receptors and, in particular, NMDA receptors.
Regeneration of Lesioned Septohippocampal Acetylcholinesterase‐positive Axons is Improved by Antibodies Against the Myelin‐associated Neurite Growth Inhibitors NI‐35/250
Authors: Cadelli D. , Schwab M. E.
Published: April 2006

Two oligodendrocyte membrane proteins, NI‐35 and NI‐250, have been shown to be highly inhibitory for neurite growth. Upon neutralization of these components with the specific monoclonal antibody IN‐1, lesioned corticospinal tract fibres were able to regenerate over long distances. In the present study, we have investigated the behaviour of regenerating cholinergic septohippocampal tract fibres. Large fimbria/fornix aspiration lesions were bridged by human amnion extracellular matrix material containing nerve growth factor, and the inhibitor‐neutralizing antibody IN‐1 or a control antibody were applied. After 3–5 weeks survival time, acetylcholinesterase (AchE)‐positive fibres had crossed the bridge and, upon entering the hippocampus, had developed a profuse fibre plexus. In the controls (antibody against peroxidase) the fibre growth within the hippocampal tissue remained limited to maximally 1 mm in the caudal and lateral directions. In the presence of the antibody IN‐1, however, AchE‐positive fibres were seen to grow for 2–4 mm both in the caudal and lateral directions. Interestingly, the regenerated fibres preferably grew to their original terminal areas in the infra‐ and suprapyramidal layers of the hippocampus proper and the hilus, and in the supragranular layer of the dentate gyrus. These data show that the neurite growth inhibitors severely impede regenerative axon growth also for the cholinergic fibres in the hippocampus, and that their neutralization increases axon growth and leads to partial reconstitution of the original anatomical fibre distribution.
Loss of Calbindin‐28K Immunoreactivity in Hippocampal Slices from Aged Rats: a Role for Calcium?
Authors: Dutar P. , Potier B. , Lamour Y. , Emson P. C. , Senut M. C.
Published: April 2006

Calbindin‐28K (CaBP) is a calcium‐binding protein widely distributed in the brain. This protein appears to be involved in the sequestration and the translocation of intracellular free calcium. In this study, we have examined the distribution pattern of the structures immunoreactive for CaBP in the hippocampal formation from slices of young (4 months) and aged (24–27 months) rats previously submitted to electrophysiological measurements. We demonstrated a marked loss in the number of pyramidal cells immunoreactive for CaBP in aged rats as compared to young rats. A consistent decrease in the staining intensity was also revealed by optical density measurements. Some experiments have suggested that calcium homeostasis is modified in hippocampal neurons of aged rats. The loss of CaBP‐like immunoreactivity (CaBP‐LI) labelling could result from an increase in intracellular calcium concentrations. To support this hypothesis, we showed that in young rats (i) the CaBP‐LI was enhanced in pyramidal neurons when the slice was preincubated in a calcium‐free medium, and (ii) CaBP‐LI was strongly decreased when the slice was preincubated in a high‐calcium medium (5 mM) and when the entry of calcium into the cell was increased by a short application of an excitatory amino acid in the medium. Our results suggest that the loss of CaBP‐LI in the hippocampus of aged rats could be due to an increase in intracellular calcium concentration. Preliminary observations of hippocampal slices at different times after induction of long‐term potentiation (LTP) failed to show significant changes in CaBP immunoreactivity, suggesting that this calcium‐binding protein is not directly involved in LTP processes.
Long‐term Potentiation of NMDA Receptor‐mediated EPSP in Guinea‐pig Hippocampal Slices
Authors: Berretta N. , Berton F. , Bianchi R. , Brunelli M. , Capogna M. , Francesconi W.
Published: April 2006

Hippocampal slices from guinea‐pigs were used to examine the long‐term potentiation (LTP) of the N‐methyl‐D‐aspartate (NMDA)‐mediated excitatory postsynaptic potential (EPSP). lntracellular recordings were performed from CA1 pyramidal neurons in the presence of 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 5–10 μM) and picrotoxin (50 μM). In these experimental conditions test stimuli applied at low frequency (0.1 Hz) to the Schaffer collateral ‐ commissural pathway evoked a prolonged EPSP (150–200 ms). To obtain this CNQX‐resistant EPSP, stimulus intensities had to be raised above the level required to evoke an EPSP of comparable amplitude in physiological solution. Tetanic stimulation (two trains of 100 Hz, 1 s every 20 s) led to a potentiation of the CNQX‐resistant EPSP, and this potentiated response was abolished with d‐(‐)‐2‐amino‐5‐phosphonovaleric acid (50μM). The potentiation of the NMDA receptor‐mediated EPSP was more pronounced for strong than for weak test stimuli, and was suppressed when test EPSPs were evoked during membrane hyperpolarization. These results suggest that NMDA receptor‐mediated responses can undergo LTP, and hence can contribute to the maintenance of LTP.
In Vitro Development of Rat Cerebellar Neurons of Early Embryonic Origin. An Anatomical and Electrophysiological Study
Authors: Hamon Brigitte , Condé Françoise , Jaillard Danielle , Thomasset Monique , Crépel Francis
Published: April 2006

The development of the major morphological and electrophysiological properties of presumptive Purkinje cells (PCs) was studied in primary cultures of rat cerebellum dissociated on the 14th embryonic day, when PCs are minimally differentiated and migrate in vivo PCs were identified with a specific antibody to calbindin D‐28K (CaBP), which allowed visualization of the different morphological types of PCs between 3 and 29 days in vitro (DIV). CaBP‐immunopositive cells were first detected at 3 DIV. Thereafter, the shape of these cells resembled some of those described in viva After 20 DIV, 95% of the CaBP‐immunopositive cells had characteristic PC dendritic trees, although they were very atrophic. Glial cells immunopositive for the glial fibrillary acidic protein (GFAP) were first seen at 3 DIV. Thereafter GFAP‐immunopositive cells resembled Bergmann cells or velate astrocytes. Neurons regarded as PCs were studied electrophysiologically using the patch‐clamp whole‐cell configuration. Voltage‐dependent, tetrodotoxin‐sensitive fast inward currents were virtually absent at 2–4 DIV, but increased between 7 and 14 DIV to reach two‐thirds of the amplitude obtained after 15 DIV. These currents were large enough to give rise to overshooting spikes as early as 7 DIV in the current‐clamp mode. This time schedule is in keeping with that of PCs developed in situ. The tetraethylammonium‐sensitive, slowly inactivating outward currents had reached two‐thirds of the amplitude obtained after 15 DIV by 3–4 DIV. Their amplitude remained stable between 4 and 7 DIV, and increased to their maximal value during 7–14 DIV, with a marked shortening of action potentials. 4‐Aminopyridine‐sensitive, fast‐inactivating outward currents might also be associated with development, since they were present in 66% of the cells between 7 and 14 DIV but in only 39% from 15 to 29 DIV; however, their amplitude did not vary with time. Presumptive PCs bore l‐glutamate‐activated receptors, which preceded the emergence of kynurenate‐sensitive, spontaneous synaptic currents at 7 DIV. These currents were sometimes intermingled with inhibitory currents, although presumptive PCs were sensitive to γ‐aminobutyrate at 7 DIV. The present model represents some unequivocal features of PC development, although the PCs used had undergone minimal differentiation in vivo and were cultured in a very disturbed cellular environment.
Projections from the Cerebral Cortex to the Red Nucleus of the Guinea‐pig. A Retrograde Tracing Study
Authors: Giuffrida R. , Aicardi G. , Rapisarda C.
Published: April 2006

The origin and the topographic distribution of corticorubral (CR) projections in the guinea‐pig were studied by using the retrograde axonal transport of a tracer, colloidal gold‐labelled, enzymatically inactive horseradish peroxidase conjugated to wheat‐germ agglutinin (WGAapoHRP‐Au), which was injected in the red nucleus (RN). It was found that the bulk of the CR projections arise from layer V neurons of the agranular frontal cortex in both its medial (Agm) and lateral (Agl) subdivisions; in the Agm labelled neurons are preferentially located in the upper part of layer V, whereas in the Agl they are more concentrated in the central band of the layer. Fewer projections originate from areas of the granular parietal and the agranular cingulate and retrobulbar cortices. CR projections have a bilateral origin, with a large ipsilateral predominance. The pattern of retrograde cortical labelling observed after injection of WGAapoHRP‐Au in different portions of the RN indicates that CR projections are distributed throughout the entire rostrocaudal extent of the nucleus, but are slightly more concentrated in the rostral parvocellular area. The morphological arrangement of CR projections in the guinea‐pig, as demonstrated in the present study, shows several analogies with other mammals. The functional characteristics of the cortical areas in which CR neurons are located indicate that CR projections may play a significant role in the central organization of movement.
Down‐regulation of GAP‐43 During Oligodendrocyte Development and Lack of Expression by Astrocytes In Vivo: Implications for Macroglial Differentiation
Authors: Curtis Rory , Hardy Rebecca , Reynolds Richard , Spruce Barbara A. , Wilkin Graham P.
Published: April 2006

The discovery of molecular markers which are selectively expressed during the development of specific classes of rat central nervous system macroglia has greatly advanced our understanding of how these cells are related. In particular, it has been shown in tissue culture that oligodendrocytes and some astrocytes (type‐2) may be derived from a common progenitor cell (O‐2A progenitor). However, the existence of type‐2 astrocytes in vivo has yet to be unequivocally established. Recently, it has been reported that the neural‐specific growth‐associated protein‐43 (GAP‐43, otherwise known as 8–50, F1, pp46 and neuromodulin) may be expressed by cells of the O‐2A lineage in vitro. We set out to examine the cellular specificity of GAP‐43 in O‐2A progenitors and their descendants in vitro and in vivo. Using a polyclonal antiserum against a GAP‐43 fusion protein we have shown the presence of immunoreactive GAP‐43 in the membranes of bipotential O‐2A glial progenitor cells and type‐2 astrocytes by Western blotting and immunocytochemistry of cells in culture. In contrast to previous studies, double labelling with mature oligodendrocyte markers showed that GAP‐43 is down‐regulated during oligodendrocyte differentiation in vitro. Immunohistochemical staining of sections of developing rat brain demonstrated the same developmental regulation of GAP‐43, suggesting that oligodendrocytes only express GAP‐43 at immature stages. In addition, normal and reactive astrocytes in tissue sections were not labelled with GAP‐43.
Distribution of mRNAs for Chromogranins A and B and Secretogranin II in Rat Brain
Authors: Mahata S. K. , Mahata M. , Marksteiner J. , Sperk G. , Fischer‐Colbrie R. , Winkler H.
Published: April 2006

The mRNA distribution of chromogranins A and B and secretogranin II was determined in rat brain. In Northern blots the oligonucleotide probes used hybridized with single mRNA species of the expected sizes. With tissue hybridization the mRNA signals for these three proteins were found throughout the brain. However, each of the three messages had a distinct distribution, which was exemplified by the fact that in the various regions either all three proteins, a combination of two or only one of them were apparently synthesized. Significant levels of all three mRNAs were found in several regions of the hippocampus and of the amygdala, in some thalamic nuclei and in the pyriform cortex. On the other hand the subiculum contained only the message for chromogranin A, the granule cell layer of the cerebellum only that for chromogranin B, and in posterior intralaminar thalamic and medial geniculate nuclei and in the nucleus of the solitary tract only secretogranin II mRNA was found. The distinct distributions of mRNAs for the chromogranins in various brain regions support the concept that these proteins are propeptides giving rise to functionally active components.
The Desheathed Periphery of Aplysia Giant Neuron. Fine Structure and Measurement of [Ca2+]o Fluctuations with Calcium‐selective Microelectrodes
Authors: Keicher E. , Bilbaut A. , Maggio K. , Hernandez‐Nicaise M. L. , Nicaise G.
Published: April 2006

The visceral ganglion of Aplysia was mechanically desheathed after protease softening of the connective tissue to permit the positioning of ion‐selective electrodes in the vicinity of the neuronal membrane. The effects of this treatment on satellite glia and neuronal cytology were observed by electron microscopy. The intracellular alterations were not suggestive of serious membrane damage but the cohesion between glial and neuronal membranes was affected—the glial processes appeared to retract from the trophospongium and in some cases the neuronal membrane was completely naked. The external calcium activity [Ca2+]o at the surface of identified giant neuron, R2, was measured using double‐barrelled calcium‐selective microelectrodes. A decrease of ∼1 mM in [Ca2+]o could be recorded only during trains of action potentials induced by intracellular depolarizing current injection, and when the electrode was pushed firmly against the neuron surface. A recovery from this decrease in [Ca2+]o could sometimes, but not always, be observed during the phase of induced neuronal activity.
Neurodegenerative Effects Induced by Chronic Infusion of Quinolinic Acid in Rat Striatum and Hippocampus
Authors: Vezzani A. , Forloni G. L. , Serafini R. , Rizzi M. , Samanin R.
Published: April 2006

In this study we examined whether the potency of quinolinic acid (Quin) in inducing neurodegeneration in vivo was dependent on the exposure time of the tissue to the excitotoxin. The effect of chronic infusion of Quin into rat striatum and hippocampus was examined at the light microscopic level and by cell count on 40 μm Cresyl violet stained brain sections. Continuous infusion was at a constant speed (0.5 μl/h) for various times (15 h–2 weeks) by osmotic minipumps (Alzet 2002). No build up of [3H]Quin occurred in the tissue during infusion; this was assessed by measuring the radioactivity 3–14 days after minipump placement. Intrastriatal infusion of 6 and 10 nmol/h Quin, but not of nicotinic acid, for 1 week induced a dose‐dependent neurodegeneration (70 and 90% loss of neurons, respectively, compared to the contralateral striatum) extending 1.2–2 mm from the centre of the injection. The onset of the neurotoxicity caused by 10 nmol/h Quin was >24 h. One week's infusion of 4 nmol/h Quin did not induce neurotoxicity, but a 40% drop of neurons, compared to the contralateral side, occurred after 2 weeks. One week's intrahippocampal infusion of 2.4 and 6 nmol/h Quin, but not of nicotinic acid, caused a dose‐dependent neurodegeneration with a radius of ∼1–1.5 mm around the injection track. The onset of the neurotoxicity induced by 2.4 nmol/h Quin was <15 h. The pattern of nerve cell loss induced by 1.2 nmol/h Quin after 1 week (CA4 cells lost in 50% of the rats) did not differ from that observed after 2 weeks of infusion. Nerve cell loss caused by Quin in the striatum and in the hippocampus was restricted to the injected area and antagonized by coinfusion with d(–)‐2‐amino‐7‐phosphonoheptanoic and kynurenic acids in molar ratios of 1:0.1 and 1:3, respectively. These data show that Quin's potency in inducing neurodegeneration in the striatum, but not in the hippocampus, depends on the exposure time of the tissue to the excitotoxin. In addition, neurodegeneration is induced faster by Quin in the hippocampus than in the striatum. The usefulness of this model to study the sequelae of the neurotoxic process in vivo will be discussed.
Evidence of a Monosynaptic Pathway Between Cells of the Ventromedial Medulla and the Motoneuron Pool of the Thoracic Spinal Cord in Rat: Electron Microscopic Analysis of Synaptic Contacts
Authors: Zagon A. , Bacon S. J.
Published: April 2006

Previous electrophysiological and anatomical data have suggested the existence of a descending pathway from the ventromedial medulla into the thoracic motoneuron pool. However, systematic light and electron microscopic analysis have not yet been done to reveal such a projection. In the present study, the anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA‐L) was injected into several discrete regions of the medioventral medulla and descending PHA‐L‐labelled axons were investigated in the thoracic ventral horn using both light and electron microscopy. Light microscopic analysis of descending projections from 20 distinct areas of the medioventral medulla showed that neurons that project predominantly to the intermediate and ventral regions of the thoracic spinal grey matter are located caudal to the facial nucleus. Monosynaptic contacts were found between axons originating from five distinct regions of the medioventral medulla (containing raphé and/or gigantocellular reticular neurons) and cells in the thoracic motoneuron pool. PHA‐L‐labelled boutons formed synaptic contacts with large calibre dendrites and with somata. Seventy‐two per cent of the investigated 32 boutons appeared to have symmetrical synaptic membrane specializations. The majority of the boutons contained only small, pleomorphic vesicles. Our findings show the existence of a direct monosynaptic pathway between the neurons of the ventromedial medulla and thoracic motor nuclei, providing anatomical support for previous physiological data.
Very Slow Retrograde and Wallerian Degeneration in the CNS of C57BL/Ola Mice
Authors: Perry V. H. , Brown M. C. , Lunn E. R.
Published: April 2006

Wallerian degeneration following peripheral nerve transection in C57BL/Ola mice is very slow in comparison to other strains of mice. We show that following optic nerve transection, the axons of retinal ganglion cells in C57BL/Ola mice undergo very slow Wallerian degeneration and that retrograde degeneration of the ganglion cell bodies is much slower than in other strains of mice. The results suggest that the gene product affecting Wallerian degeneration in the peripheral nervous system (PNS) also confers a greater resistance to degeneration on central nervous system (CNS) neurons.
Modulation of GABA‐mediated Synaptic Potentials by Glutamatergic Agonists in Neonatal CA3 Rat Hippocampal Neurons
Authors: Gaiarsa Jean‐Luc , Corradetti Renato , Cherubini Enrico , Ben‐Ari Yehezkel
Published: April 2006

Intracellular recordings were made from slices of adult and neonatal hippocampal neurons. During the first 2 weeks of life the majority of pyramidal cells exhibited spontaneous gamma‐aminobutyric acid (GABA)‐mediated synaptic potentials, which were depolarizing at birth and became hyperpolarizing by the end of the first postnatal week. These synaptic potentials were reduced in frequency or blocked by the N‐methyl‐d‐aspartate (NMDA) receptor antagonist d(‐)2‐amino‐5‐phosphonovalerate (AP‐5, 50 μM) (13/15 cells). The non‐NMDA antagonist, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 5–10μM) abolished the GABA‐mediated synaptic potentials in all the cells tested (n= 12), Superfusion of l‐glutamate (up to 100 μM) increased the frequency of both depolarizing and hyperpolarizing GABA‐mediated synaptic potentials. This effect was reduced by AP‐5 or dl‐2‐amino‐7‐phosphonoheptanoate (AP‐7, 50 μM) and fully blocked by concomitant application of AP‐5 (50 μM) and CNQX (5–10 μM). NMDA (0.5–2 μM) increased the frequency of the GABA‐mediated synaptic potentials. These effects were blocked by AP‐5 (50 μM) and by bicuculline (10 μM). Quisqualate (100–300 nM), (RS)‐alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐izopropionate (AMPA, 100–300 nM) and kainate (100 nM) also increased the frequency of the GABA‐mediated synaptic potentials. These effects were blocked by CNQX (5–10 μM) and by bicuculline (10 μM) but not by AP‐5 (50 μM). In the presence of tetrodotoxin (TTX, 1 μM), quisqualate (up to 300 nM), AMPA (up to 500 nM) and kainate (100 nM) had no effect on membrane potential or input resistance. In conclusion, our experiments suggest that, in early postnatal life, NMDA and non‐NMDA receptors located on GABAergic interneurons modulate GABAergic synaptic potentials.
Expression and Developmental Regulation of a GABAA Receptor in Cultured Murine Cells of the Oligodendrocyte Lineage
Authors: von Blankenfeld G. , Trotter J. , Kettenmann H.
Published: April 2006

The inhibitory neurotransmitter GABA activated Cl− currents in oligodendrocytes and their precursor cells. Most of the pharmacological features of these GABA‐evoked currents matched those described for the neuronal GABAA/benzodiazepine receptor complex, such as the blockade by picrotoxin and bicuculline and the enhancement by barbiturates and benzodiazepines. In contrast to the astrocytic GABA receptor, but similar to the neuronal GABAA receptor, the inverse benzodiazepine agonist DMCM decreased GABA‐induced current responses. A further similarity to the neuronal receptor is the strong run‐down of the current in the absence of ATP in the pipette. A difference between oligodendroglial receptors and receptors expressed on neurons and astrocytes was revealed by the dose ‐ response curve, which indicated only one binding site for GABA or weak allosterical interactions between two putative binding sites. Thus, GABAA receptors of precursor cells and oligodendrocytes might represent a third class of GABAA receptors, in addition to those expressed by neurons and astrocytes. The density of these receptors in the membrane, as calculated on the basis of whole cell currents and membrane capacitance, decreased by a factor of 100 when cells matured along the oligodendrocyte lineage, indicating a developmental regulation of the expression of the GABA receptor.
Afferent and Efferent Connections of Temporal Association Cortex in the Rat: A Horseradish Peroxidase Study
Authors: Vaudano E. , Legg C. R. , Glickstein M.
Published: April 2006

We studied the afferent and efferent connections of the caudal temporal cortex in rat using the tracer wheat germ agglutinin – horseradish peroxidase (WGA–HRP). This area is reciprocally connected with primary and secondary visual and auditory areas of cortex. The connections with primary visual cortex are restricted to the ventral and caudal parts of the caudal temporal area. Caudal temporal cortex has reciprocal connections with the perirhinal cortex and projects to the caudate ‐ putamen and lateral and basolateral nuclei of the amygdala. It also has reciprocal connections with the nucleus lateral is posterior, the dorsal and medial divisions of the medial geniculate nucleus and the caudal part of the posterior nucleus of the thalamus. It projects to the deep layers of the superior colliculus, the pericentral nucleus of the inferior colliculus and to the ventral nucleus of the basilar pons. Our results suggest that the rat caudal temporal cortex forms part of a pathway that connects visual and auditory cortex with the limbic system, by the way of the amygdala and perirhinal cortex.
Peptide‐containing Neurons Projecting to the Tongue of the Rat: Retrograde Tracing and Immunocytochemistry
Authors: Luts Anders , Uddman Rolf , Grunditz Torsten , Montavon Phillippe , Lindstrand Kaj , Sundler Frank
Published: April 2006

The origin and neuropeptide content of nerve fibres in the rat circumvallate papilla was studied by retrograde tracing in combination with immunocytochemistry. An injection of the retrograde tracer True Blue into the circumvallate papilla resulted in the appearance of labelled nerve cell bodies in the superior cervical, the stellate, the thyroid, the nodose, the jugular, the petrosal, the otic, the trigeminal and the dorsal root ganglia at level C2. Most of the True Blue‐labelled nerve cells in the superior cervical ganglia contained neuropeptide Y. The majority of labelled cell bodies in the thyroid ganglia contained vasoactive intestinal peptide. In the jugular and trigeminal ganglia, the majority of the labelled nerve cell bodies stored calcitonin gene‐related peptide. A small number of neurons in the medial reticular formation of the central nervous system was labelled. Tracer injections deep into the tongue tissue beneath the circumvallate papilla gave rise to True Blue‐labelled neurons in the hypoglossal nucleus.
Differential Regulation of Calcitonin Gene‐related Peptide (CGRP) in Regenerating Rat Facial Nucleus and Dorsal Root Ganglion
Authors: Dumoulin F. L. , Raivich G. , Streit W. J. , Kreutzberg G. W.
Published: April 2006

The content of calcitonin gene‐related peptide (CGRP) and CGRP‐mRNA were determined in axotomized rat facial motor nucleus and sensory fifth lumbar dorsal root ganglion (L5 DRG) using radioimmunoassay and Northern blot analysis. After facial nerve transection CGRP levels in the facial nucleus showed a biphasic, five‐fold increase. A first peak occurred at postoperative day 3 and, after a transient decrease to normal levels at day 9, another increase was observed reaching a peak around the time of reinnervation (postoperative day 21). CGRP‐mRNA showed a similar, biphasic increase. The first peak in CGRP mRNA preceded the peptide peak by 2 days, the second peak was day 21. In contrast, a decrease in CGRP levels is seen in L5 DRG after sciatic nerve section, reaching minimal levels of 45% of control during the second postoperative week. CGRP‐mRNA in axotomized DRG also decreases preceding the decrease in peptide levels. No recovery to normal levels is seen for either peptide or mRNA levels in regenerating DRG up to 45 days after injury. Thus, axotomy leads to a differential regulation of both CGRP and CGRP‐mRNA in regenerating facial motor nucleus and sensory L5 DRG. This difference may be due to different regulating factors present in both the respective target tissues and the CNS regions and could reflect different functions of CGRP in regenerating motor and sensory neurons.
Climbing Fibre Responses in Olivo‐cerebellar Slice Cultures. II. Dynamics of Cytosolic Calcium in Purkinje Cells
Authors: Knöpfel T. , Vranesic I. , Staub C. , Gähwiler B. H.
Published: April 2006

The generation of climbing fibre responses in cerebellar Purkinje cells has been analysed in co‐cultured slices of rat cerebellum and inferior olive. Complex spikes were evoked in Purkinje cells by climbing fibre activation or by intrasomatic injection of depolarizing current pulses. Microfluorometric measurements of cytosolic free calcium ([Ca2+]i) by means of intracellularly injected fura‐2 combined with intracellular recordings revealed that both types of complex spikes were accompanied by a transient rise in [Ca2]i, which was most prominent at dendritic locations. Synaptically induced Ca2+ transients were completely and reversibly abolished by 6‐cyano‐7‐nitroquinoxaline‐2–3‐dione (CNQX, 5 μM), an antagonist of the ionotropic action mediated by non‐N‐methyl‐d‐aspartate excitatory amino acid receptors. Ca2+ transients evoked by injections of depolarizing current pulses were not affected by CNQX. These observations indicate that Ca2+ transients induced by climbing fibre activity are generated by voltage‐gated Ca2+ channels, which are activated by a CNQX‐sensitive synaptic depolarization.
Endothelin Opens Potassium Channels in Glial Cells
Authors: Supattapone Surachai , Ashley Christopher C.
Published: April 2006

Endothelin‐1 (ET‐1), an autocrine hormone synthesized by astrocytes, and endothelin‐3 (ET‐3), a highly homologous peptide produced by neurons, have both been shown previously to cause proliferation of these astrocytes in culture [Supattapone et al. (1989) Biochem. Biophys. Res. Commun., 165, 1115–1122; MacCumber et al. (1990) Proc. Natl. Acad. Sci. USA, 87, 2359–2363]. We now demonstrate, using 86Rb+ influx assays and single channel patch‐clamp recording, that both endothelins–ET‐3 and ET‐1–can also open a charybdotoxin‐sensitive, calcium‐activated K+ channel of 15–40 pS in glial cells. The opening of this channel may be important for the regulation of [K+] in the brain microenvironment. Thus, the endothelins may be a general mediator of astroglial response to neuronal injury.
Divalent Cations Modulate the Inhibitory Substrate Properties of Murine Glia‐derived J1‐160 and J1‐180 Extracellular Matrix Glycoproteins for Neuronal Adhesion
Authors: Pesheva Penka , Probstmeier Rainer , Spiess Eberhard , Schachner Melitta
Published: April 2006

J1–160 and J1–180 are developmentally late appearing J1 extracellular matrix glycoproteins derived from oligodendrocytes. They prevent adhesion of neurons (but not of astrocytes or fibroblasts) when offered as a substrate in mixture with laminin (Pesheva et al., J. Cell Biol., 109, 1765–1778, 1989). In the present study we have examined the influence of divalent cations on the inhibitory substrate properties of J1‐160/180 glycoproteins towards adhesion of neurons. By metal chelate affinity chromatography, we show that J1‐180, but not J1‐160, binds Ca2+, while both J1 components are capable of binding Zn2+ and other divalent metal ions. Divalent cation binding was observed by gel filtration, aggregation assays with coated latex beads and electron microscopic examination to elicit aggregation of the molecules. Divalent cation binding also affects their non‐permissive substrate properties towards neurons from early postnatal mouse cerebellum. Without divalent cations, J1–160 and J1–180 are inhibitory for substrate adhesion of neurons independently of the adhesive substrate present (laminin or poly‐l‐lysine). This effect is neutralized when J1–180 is preincubated with Ca2+ or Zn2+ prior to coating as substrate. In contrast, preincubation with Ca2+ ions does not affect the inhibitory substrate properties of J1–160 under these conditions. These observations show that J1‐160/180 molecules may undergo self‐aggregation in a divalent cation‐dependent mechanism, which correlates with the neutralization of their inhibitory effect on neuronal adhesion. The aggregation state of the molecules may thus influence the process of myelination by a homophilic binding mechanism and determine the effectiveness of neurite extension during central nervous system development and under traumatic conditions in the adult.
Climbing Fibres as a Source of Nitric Oxide in the Cerebellum
Authors: Southam Eric , Garthwaite John
Published: April 2006

Exposure of adult rat cerebellar slices to a moderately raised K+ concentration (15 mM) caused a large (30‐fold) rise in the levels of cyclic GMP. Excitatory amino acid antagonists failed to inhibit this response, nor could it be mimicked by agonists active at a number of other transmitter receptors. It was, however, inhibited by the nitric oxide (NO) synthase antagonist, l‐methylarginine (lC50= 10 μM), and also by tetrodotoxin (1 μM) implying that underlying the cyclic GMP response was an action potential‐dependent formation of NO. Prelesioning of climbing fibres resulted in a loss of ∼50% of the response to K+ but failed to influence the effects of glutamate receptor agonists or the NO‐donor, nitroprusside. These findings point to a new mechanism for the formation of NO in the central nervous system and suggest that, in the cerebellum, climbing fibres are a source of NO.
Catecholamine Metabolism in Locus Coeruleus Neurons: A Study of its Activation by Sciatic Nerve Stimulation in the Rat
Authors: Brun P. , Suaud‐Chagny M. F. , Lachuer J. , Gonon F. , Buda M.
Published: April 2006

Sciatic nerve stimulation, which strongly activates noradrenergic locus coeruleus (NA‐LC) neurons, was used in anaesthetized rats as a model to study the transneuronal control of catechol metabolism in this nucleus. We show, using in vivo electrochemistry and biochemical post‐mortem assays, that a prolonged (20 min) unilateral sciatic nerve electrical stimulation led to a reversible enhancement (80 – 130%) of both endogenous and in vivo extracellular levels of 3,4‐dihydroxyphenylacetic acid (DOPAC) within the contralateral LC region. An elevation in DOPAC levels was also observed in the ipsilateral nucleus but was always significantly lower. The response was abolished by a pretreatment with kynurenic acid, a non‐selective excitatory amino acid (EAA) antagonist known to block footshock‐induced excitations of NA‐LC neurons: in antagonist‐treated rats, the stimulation induced a non‐significant effect (+ 30%) on endogenous DOPAC levels, which contrasted with the highly significant effect (+ 113%) observed in vehicle‐treated animals. As the major source of EAA afferents to the LC originates in the nucleus paragigantocellularis, we made an attempt to suppress activation by a section of these fibres. An incision performed obliquely (45°) between LC and PGi greatly and significantly attenuated, but did not totally suppress, the increase in DOPAC endogenous content due to the stimulation. These experiments indicate that a peripheral stimulus provokes an activation of catecholamine metabolism within the soma ‐ dendritic region of the NA‐LC cells. They suggest that this effect may be mediated, at least in part, by afferent pathways originating from the medulla which utilize an EAA as transmitter.
Taste Buds and Neuromasts of Astyanax jordani: Distribution and Immunochemical Demonstration of Co‐localized Substance P and Enkephalins
Authors: Bensouilah M. , Denizot J.‐P.
Published: April 2006

The distribution and some immunohistochemical aspects of the taste buds and free neuromasts of the blind cave fish Astyanax jordani were investigated using serial sections of whole fish. Taste buds are restricted to the skin of the lips and the lower jaw. Neuromasts are widely distributed over the whole epidermis except the lips and are particularly numerous in the opercular region and the caudal fin; they are absent from all other fins. The histological structure of the taste buds and the free neuromasts is similar to that described in other fish. The former are composed of two types of cells. The free neuromast, as seen under the electron microscope, is also constituted by two types of cell: dark supporting cells and clear sensory cells whose basal cytoplasm contains presynaptic bodies. Immunohistochemical results obtained with the peroxidase antiperoxidase method revealed the presence of different peptides in the taste buds and the free neuromasts. The former contain substance P (SP) and enkephalins (leu‐ and metenkephalin); the latter contain SP and leuenkephalin, but no metenkephalin. These peptides are localized in the cytoplasm of the accessory and sensory cells but not in the nervous fibres. None of these peptides occur in the olfactory epithelium of A.jordani. These immunohistochemical results raise the question of whether SP, leuenkephalin or metenkephalin play a role in transmission between the sensory cells and the afferent fibre.
Targets and Laminar Distribution of Projection Neurons with ‘Inverted’ Morphology in Rabbit Cortex
Authors: Bueno‐López José L. , Reblet Concepción , López‐Medina Antonio , Gómez‐Urquijo Sonia M. , Grandes Pedro , Gondra Juan , Hennequet Leonor
Published: April 2006

This study examines the axonal projections of so‐called inverted pyramids and other neurons with their major dendritic shaft oriented in the direction of the white matter (‘inverted cells’) in the adult rabbit cortex. Single injections of horseradish peroxidase wheat germ agglutinin were made into cortical or subcortical sites. The resulting retrograde labelling in the cortex was analysed and the distribution across areas and layers of inverted cells contributing to each of these projections was estimated. In addition, the radial distribution of inverted cells was independently determined from rapid Golgi‐impregnated and Nissl‐stained material. All three procedures revealed that inverted cells lay overwhelmingly in infragranular layers, but congregated at the border between layers 5 and 6. Inverted cells, identified by retrograde labelling, seldom furnished non‐telencephalic centres; in contrast, these cells constituted a major source for the projections to the ipsi‐ or the contralateral cortex, the claustrum or the nucleus caudatus. In general, each set of inverted cells (when defined by its specific destination as a group) was located below the typically oriented cells whose axons were aimed at the same target. Thus, the inverted cells of the rabbit cortex are characterized not only by their unique morphology and their corticocortical, corticoclaustral and corticostriatal projections, but also by their distinctive radial locations. These findings suggest that inverted cells, even though possibly composed of different cell types, are a specific class of projection neurons.
Brain Spectrins 240/235 and 240/235E: Differential Expression During Development of Chicken Dorsal Root Ganglia in vivo and in vitro
Authors: Barakat‐Walter I. , Reiderer B. M.
Published: April 2006

Brain spectrin, a membrane‐related cytoskeletal protein, exists as two isoforms. Brain spectrin 240/235 is localized preferentially in the perikaryon and axon of neuronal cells and brain spectrin 240/235E is found essentially in the neuronal soma and dendrites and in glia (Riederer et al., 1986, J. Cell Biol., 102, 2088–2097). The sensory neurons in dorsal root ganglia, devoid of any dendrites, make a good tool to investigate such differential expression of spectrin isoforms. In this study expression and localization of both brain spectrin isoforms were analysed during early chicken dorsal root ganglia development in vivo and in culture. Both isoforms appeared at embryonic day 6. Brain spectrin 240/235 exhibited a transient increase during embryonic development and was first expressed in ventrolateral neurons. In ganglion cells in situ and in culture this spectrin type showed a somato – axonal distribution pattern. In contrast, brain spectrin 240/235E slightly increased between E6 and E15 and remained practically unchanged. It was localized mainly in smaller neurons of the mediodorsal area as punctate staining in the cytoplasm, was restricted exclusively to the ganglion cell perikarya and was absent from axons both in situ and in culture. This study suggests that brain spectrin 240/235 may contribute towards outgrowth, elongation and maintenance of axonal processes and that brain spectrin 240/235E seems to be exclusively involved in the stabilization of the cytoarchitecture of cell bodies in a selected population of ganglion cells.
Localization and Synaptic Release of N‐acetylaspartyl‐glutamate in the Chick Retina and Optic Tectum
Authors: Williamson Lura C. , Eagles Douglas A. , Brady Meghan J. , Moffett John R. , Namboodiri M. A. Aryan , Neale Joseph H.
Published: April 2006

The neuropeptide, N‐acetylaspartylglutamate (NAAG), was identified in the chick retina (1.4 nmol/retina) by HPLC, radioimmunoassay and immunohistochemistry. This acidic dipeptide was found within retinal ganglion cell bodies and their neurites in the optic fibre layer of the retina. Substantial, but less intense, immunoreactivity was detected in many amacrine‐like cells in the inner nuclear layer and in multiple bands within the inner plexiform layer. In addition, NAAG immunoreactivity was observed in the optic fibre layer and in the neuropil of the superficial layers of the optic tectum, as well as in many cell bodies in the tectum. Using a newly developed, specific and highly sensitive (3 fmol/50 μI) radioimmunoassay for NAAG, peptide release was detected in isolated retinas upon depolarization with 55 mM extracellular potassium. This assay also permitted detection of peptide release from the optic tectum following stimulation of action potentials in retinal ganglion cell axons of the optic tract. Both of these release processes required the presence of extracellular calcium. Electrically stimulated release from the tectum was reversibly blocked by extracellular cadmium. These findings suggest that NAAG serves an extracellular function following depolarization‐induced release from retinal amacrine neurons and from ganglion cell axon endings in the chick optic tectum. These data support the hypothesis that NAAG functions in synaptic communication between neurons in the visual system.
Functional Properties of Neurons in the Anterior Bank of the Parieto‐occipital Sulcus of the Macaque Monkey
Authors: Galletti C. , Battaglini P. P. , Fattori P.
Published: April 2006

Extracellular recordings were made in the anterior bank of the parieto‐occipital sulcus of two waking monkeys trained to perform fixation tasks in normal illumination or in complete darkness. Of the recorded neurons, 73% (251/343) were responsive to visual stimulation, but their overall organization did not conform to a simple, continuous retinotopic map. Most of the visual neurons showed a high degree of orientation and direction sensitivity, higher than that found in areas V1, V2 and V3A under the same experimental conditions. Whether they had a resolvable receptive field or not, the discharge rate of many neurons in the anterior bank of the parieto‐occipital sulcus was influenced by oculomotor activity. The animals were required to execute pursuit or saccadic eye movements in darkness. Saccadic eye movements were found to influence 19% of the neurons tested (29/156); by contrast, pursuit eye movements were without effect (0/64). Saccade responses were direction‐tuned and, in several cases, the neuronal discharge started before the onset of eye movement. The animals were also required to gaze, in darkness, at nine different positions on the screen they faced. Of the neurons tested, 59% (102/174) were affected by the direction of gaze. Higher discharge rates were generally observed when the animals looked towards the lower part of the field of view. Given the functional properties of its neurons, its connections with area V3A—where neural signals appropriate for building an objective map of the visual space are present (Galletti and Battaglini, 1989, J. Neurosci., 9, 1112–1125)—and its output to the visuomotor centres involved in the generation of saccades (frontal eye fields and superior colliculus), we infer that the cortex of the anterior bank of the parieto‐occipital sulcus might be part of the network involved in the control of gaze in order to locate objects in visual space.
Somatosensory Discrimination of Shape: Tactile Exploration and Cerebral Activation
Authors: Seitz Rüdiger J. , Roland Per E. , Bohm Christian , Greitz Torgny , Stone‐Elander Sharon
Published: April 2006

This study of somatosensory discrimination of rectangular parallelepipeds with the right hand had three purposes: (i) to describe the exploratory finger movements; (ii) to reveal the anatomical brain structures specifically engaged in the production of exploratory finger movements; and (iii) to reveal the anatomical structures specifically engaged in the discrimination of tactually sensed shape. The thumb was the most active finger, moving with a mean exploration frequency of 2.4 Hz, as evident from videotape records of the exploratory finger movements. The cerebral structures activated during somatosensory discrimination were mapped by measurements of regional cerebral blood flow (rCBF) in six healthy male volunteers with positron emission tomography (PET) and the use of the computerized brain atlas of Greitz et al. (1991, J. Comp. Ass. Tomogr., 15, 26–38). The rCBF changes caused by somatosensory discrimination were compared point‐to‐point to a PET‐study on right‐hand finger movements and a PET‐study on vibration stimulation of the right hand. From these results the following conclusions were drawn. The rCBF increase in the left superior parietal lobule indicated the site engaged in the analysis of shape. The rCBF increases in the left supplementary sensory area, bilaterally in premotor areas, in the left putamen, the right dentate nucleus and bilaterally in the posterior cerebellum were related to the control of the tactile exploratory finger movements. The rCBF increases in the right homologue of Broca's area, bilaterally in the superior prefrontal cortex and in the right midfrontal cortex probably resulted from working memory, the direction of attention, and the discrimination process.
Ultrastructural Relationships Between GABAergic Terminals and Cardiac Vagal Preganglionic Motoneurons and Vagal Afferents in the Cat: A Combined HRP Tracing and Immunogold Labelling Study
Authors: Maqbool Azhar , Batten Trevor F. C. , McWilliam Peter N.
Published: April 2006

The ultrastructural relationships between γ‐aminobutyric acid‐immunoreactive (GABA‐ir) neurons and other neurons of the nucleus tractus solitarius (NTS) and motoneurons of the nucleus ambiguus (NA) and dorsal motor vagal nucleus (DMVN), were examined by electron microscopic (EM) immunogold labelling with an anti‐GABA antiserum on brain stem sections in which vagal motoneurons and vagal afferent fibres were labelled with horseradish peroxidase (HRP). HRP was applied to the cervical vagus or the cardiac vagal branch of anaesthetized cats. After 24–48 h survival, brains were glutaraldehyde‐fixed and a stable HRP‐tetramethylbenzidine reaction product compatible with EM processing was revealed on 250 μm vibratome sections. Following osmium postfixation, dehydration and resin embedding, GABA‐ir was localized on ultrathin sections by an immunogold technique. GABA‐ir axon terminals, heavily and specifically labelled with gold particles, were very numerous within NTS, DMVN and NA. All terminals contained small, clear, pleomorphic vesicles and a few also contained larger dense cored vesicles. The density of gold particles over clear vesicles, dense cored vesicles and mitochondria was significantly greater than over the cytoplasm of these terminals. GABA‐ir synapses were found on the soma and dendrites of neurons, but rarely on other axon terminals within NTS, where GABA‐ir cell bodies and dendrites were also seen. These received synaptic contacts from both GABA‐ir terminals and from HRP‐labelled vagal afferents. In both the DMVN and NA, similar GABA‐ir synapses were present on both the soma and dendrites of HRP‐labelled motoneurons. GABA synapses were also present on other cell types in DMVN. These observations provide an anatomical basis for a GABAergic inhibition of neurons forming the central pathways of cardiovascular and other autonomic reflexes.