摘要:

AbstractIntracellular 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 theN‐methyl‐d‐aspartate (NMDA) receptor antagonistd(‐)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 ofl‐glutamate (up to 100 μM) increased the frequency of both depolarizing and hyperpolarizing GABA‐mediated synaptic potentials. This effect was reduced by AP‐5 ordl‐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,

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00816.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe 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 GABAAreceptor, 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, GABAAreceptors of precursor cells and oligodendrocytes might represent a third class of GABAAreceptors, 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

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00817.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractWe 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 c

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00818.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe 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 nu

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00819.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe 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 sens

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00820.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe 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‐sensi

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00821.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractEndothelin‐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 [Supattaponeet al.(1989)Biochem. Biophys. Res. Commun., 165, 1115–1122; MacCumberet al.(1990)Proc. Natl. Acad. Sci. USA, 87, 2359–2363]. We now demonstrate, using86Rb+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

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00822.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractJ1–160 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 (Peshevaet 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 tr

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00823.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe pattern of glutamate‐like immunoreactivity was investigated in the pigeon optic tectum. The most impressive aspect of the labelling pattern was an accumulation of immunoreactive terminal‐like elements restricted to those superficial tectal layers that correspond to the termination zone of the retinal afferents. These immunoreactive puncta occurred frequently in small clusters. At the level of electron microscopy, many of the labelled nerve endings showed the characteristics of retinal terminals. Moreover, following unilateral retinal ablation a drastic loss of immunoreactive terminal‐like puncta was observed in the retinorecipient layers of the tectum contralateral to the lesion. The remaining glutamate‐immunoreactive terminal‐like elements had the light and electron microscopic features typical of the afferents from the nucleus isthmi, pars parvocellularis (lpc). The relation between the latter result and the transmitter specificity of the afferents from this subtectal nucleus is unclear at present. On the other hand, the light and electron microscopic labelling patterns and the effect of retinal ablation suggest that afferents from retina and from lpc are the only major sources for glutamate‐immunoreactive terminals in the pigeon optic tectum. Furthermore, the results are well in line with previous data indicating glutamate as neurotransmitter at least in part of the retinal afferents to the pigeon o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractExposure 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 s

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY