摘要:

AbstractTo assess the role of subunits for channel function and drug modulation in recombinant GABAAreceptors, the α3β1γ2 subunits and the dual combinations α3β1, β1γ2 and α3γ2 were expressed by transfection of human embryonic kidney cells and by RNA injection inXenopusoocytes (α3β1γ2 combination). GABA‐induced chloride currents were recorded using the whole‐cell configuration of the patch‐clamp technique (transfected cells) or the voltage‐clamp technique (oocytes). The currents recorded from the α3β1Γ2 subunit combination in transfected cells were reduced by bicuculline and picrotoxin, enhanced by flunitrazepam in a flumazenil‐sensitive manner and reduced by β‐carboline‐3‐carboxylic acid methyl ester (β‐CCM). The GABA‐induced current was reduced by β‐CCM in all combinations containing the γ2 subunit, but potentiation by flunitrazepam was only obtained when the 72 subunit was coexpressed in the presence of the α3 subunit (α3β1γ2 or α3γ2). The GABA sensitivities of the receptors were similar when the α3β1γ2 combination was expressed in oocytes (half‐maximum effective concentration = 240 μM) or in the kidney cell line (270 μM). However, the currents were less potentiated by flunitrazepam in oocytes (129% of controls) than in transfected cells (189%). These results suggest that the α3β1γ2 subunit combination, which is coexpressed in various brain regions as shown byin situhybridization histochemistry, may repres

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00103.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCerebellar long‐term depression (LTD) is produced when conjunctive stimulation of parallel fibre (PF) and climbing fibre (CF) inputs to a Purkinje neuron (PN) results in a prolonged decrease in the strength of the PF‐PN synapse. In cultured PNs, LTD may be induced by substituting depolarization of the PN and iontophoretic glutamate pulses for CF and PF stimulation, respectively, allowing an unambiguous analysis of post‐synaptic processes (Lindenet al., Neuron,7, 81–89, 1991). Recent studies have suggested that release of the newly described second messenger, nitric oxide, in the cerebellar molecular layer, is necessary for LTD produced in the slice preparation by PF/CF conjunctive stimulation (Shibuki and Okada,Nature,349, 326–328, 1991) or PF/depolarization conjunctive stimulation (Crepel and Jaillard,NeuroReport,1, 133–136, 1990). We report that LTD of glutamate currents produced without synaptic stimulation in cultured PNs is unaffected by reagents that stimulate (sodium nitroprusside) or inhibit (haemoglobin, NG‐nitro‐l‐arginine) nitric

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00104.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIntracellular recordings with K‐acetate‐filled microelectrodes were performed in slices of the adult rat hippocampus maintainedin vitroat 35–36°C to analyse the potentials associated with the orthodromic inhibitory sequence generated by CA1 pyramidal cells. In 43 of 72 cells, stimuli that were delivered in the stratum radiatum induced (i) an initial excitatory postsynaptic potential (EPSP), (ii) an early, hyperpolarizing inhibitory postsynaptic potential (IPSP) (peak latency from the stimulus artefact 20 ms), (iii) an intermediate depolarizing component (peak latency = 60–120 ms; duration = 60‐150 ms, and (iv) a late, long‐lasting hyperpolarizing IPSP (peak latency = 120–160 ms, duration>400 ms). In the remaining cells the orthodromic inhibitory response lacked the intermediate depolarization. The depolarizing component was selectively blocked by local applications of bicuculline or picrotoxin on the apical dendrites of pyramidal cells. This pharmacological procedure induced an increase in the amplitude of the EPSP that was capable of triggering 2–3 action potentials, but no reduction of the recurrent IPSP which is caused by GABAAreceptors located close to the soma. The amplitude and duration of the depolarizing component was enhanced by lowering the temperature in the tissue chamber to 29–31°C or by application of the GABA uptake blocker nipecotic acid, further indicating that the depolarizing component represented an active phenomenon mediated through GABA. Application of the CI‐pump blocker furosemide reduced and eventually blocked the early IPSP and the depolarizing component. These data demonstrate that under physiological conditions rat hippocampal pyramidal cells generate a depolarization that is presumably caused by an outwardly directed CI‐movement due to the activation of GABAAreceptors located on the apical dendrites. This novel mechanism might modulate hippocampal excitability in both physiological and pathop

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00105.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA commissural system of ‘intertectal’ connections inXenopusmediates the registration of binocular visual maps at the midbrain optic tectum. Following surgical eye rotation in larval animals, the system can completely alter its pattern of connectivity to restore binocular visual registration at the tectum. This experimentally induced plasticity is known to require visual experience and thought to be subject to an age‐related restriction: eye rotation in adult animals is reported to provoke no subsequent intertectal alteration. In this paper we describe the detailed age‐dependence of this plasticity. One eye was rotated in 238 animals of various developmental stages between mid‐larval and adult life. At each age, different animals received rotations of different sizes, ranging from 20 to 180°. The pattern of intertectal connectivity was mapped electrophysiologically 1–2 years postoperatively. A ‘critical’ period was defined around the time of metamorphosis: the vast majority of animals receiving a rotation in larval life (up to ‐2 weeks before metamorphic climax) showed altered intertectal connections, whereas none of the animals operated upon at 3 months or more postmetamorphosis displayed the plasticity. At intervening ages, altered intertectal connections were found only in response to progressively smaller eye rotations. The profile of this critical period was further shown to mirror temporal features of the changes in eye position that occur inXenopusas natural consequences of head growth, and which themselves impose a normal developmental requirement for intertectal plasticity. We conclude that the capacity of theXenopusintertectal system for plasticity in response to abnormal experience undergoes a progressive age‐dependent decline, and that the profile of this decline is delimited by

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00106.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractFollowing surgical rotation of an eye, theXenopus‘intertectal’ system is capable of a vision‐dependent alteration of its connectivity, that restores spatial registration of binocular maps on the optic tectum. In the preceding paper (Keating and Grant,Eur. J. Neurosci.,4, 27–36, 1992), we reported that this capacity undergoes a progressive, age‐dependent restriction during a critical period around the time of metamorphosis, so that rotations produced in animals aged 3 months postmetamorphosis normally evoke no such alteration of the system. Here we examine whether this restriction is rigidly age‐dependent or whether vision can influence its profile. We report that in animals dark‐reared from embryonic stage 35 through the critical period to 3 months, 1 year or even 2 years after metamorphosis, rotations instituted at those ages now result in intertectal reorganization if a period of normal vision is allowed after the operation. Similarly, intertectal alteration was also seen in animals eye‐rotated at larval stage 58, then dark‐reared just for the duration of the critical period, and subsequently returned, at 3 months of age, to a normal visual environment. We conclude, therefore, that the normal developmental restriction in the plasticity of theXenopusintertectal system is not strictly age‐dependent, but that vision contributes to the process by activating the underlying pl

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00107.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA simple method for high‐resolution immunocytochemical colocalization of different antigens in semithin sections 1 ‐ 3 μm thick was used to study the colocalization of the calcium binding protein calbindin D‐28k (calbindin) with γ‐aminobutyric acid (GABA) in double bouquet cells of monkey(Macaca fuscata)somatosensory cortex. Double bouquet cells were first visualized in vibratome sections by pre‐embedding immunocytochemical staining for calbindin. Sections containing calbindin‐immunoreactive somata and double bouquet cell axons were then osmicated, embedded in Araldite, resectioned at 1–3μm and stained for GABA by postembedding immunocytochemistry after elution of the bound anti‐calbindin antibodies. Other semithin sections adjacent to those eluted and still containing calbindin immunoreactive somata and processes were resectioned at 60–70 nm for electron microscopy and stained immunocytochemically for GABA by the postembedding immunogold procedure. Calbindin‐positive cells are most numerous in layer II and upper layer III, where they outnumber those in all other layers combined. In layers II and upper III, ‐30% of the stained cells are pyramidal and do not colocalize GABA. Only approximately two‐thirds of the calbindin‐stained nonpyramidal cells in these layers colocalize GABA, but among these virtually all the calbindin‐positive double bouquet cells and their axons are GABA‐immunoreactive. In deeper layers all calbindin‐positive cells are nonpyramidal and all colocalize GABA. At the electron microscopic level, however, significant numbers of calbindin‐positive axon terminals making symmetrical synapses are not GABA‐immunoreactive. These results suggest the calbindin cells of monkey somatosensory cortex are a heterogeneous population that includes

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00108.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis study concerns the involvement of calbindin‐D28K (CaBP28k)‐containing neurons in the efferent projections of both the trigeminal nucleus caudalis and the dorsal vagal complex (nucleus of the solitary tract and area postrema) in rats. Recent evidence has shown that these projections are particularly important for the processing of visceroception and/or nociception at central levels. The trigeminal nucleus caudalis has dense projections to both the nucleus of the solitary tract and the parabrachial area; the dorsal vagal complex is intimately connected to the parabrachial area. CaBP28k is a calcium‐binding protein the function of which could be a determining factor in controlling the excitability of cells by acting on intrinsic calcium metabolism. CaBP28k content of projections was ascertained using a double labelling approach that combined the retrograde transport of a protein ‐ gold complex to identify projection cells and immunocytochemistry to identify CaBP28k‐positive cells. The trigeminal nucleus caudalis is rich in both CaBP28k‐immunoreactive cells and cells projecting to the parabrachial area or the nucleus of the solitary tract. Cells containing both the protein and the retrograde tracer, however, were mostly restricted to the superficial layers (laminae I and outer II) and to their rostral extensions, the dorsal paramarginal and paratrigeminal nuclei. These trigeminal subdivisions are targets for nociceptive, visceroceptive and thermal inputs of peripheral origins. The dorsal vagal complex is rich in CaBP28k. Dense populations of immunoreactive cells are observed in the ventrolateral part of the area postrema and all of the three main subdivisions of the nucleus of the solitary tract (rostral gustatory, ventrolateral respiratory and medial cardiovascular subregions). The subnucleus commissuralis, subnucleus centralis and dorsal subnuclei are particularly densely stained. The subnucleus centralis, which is involved in regulating food and water intake, does not project to the parabrachial area. The area postrema, subnucleus commissuralis and dorsal subnuclei, which are implicated in cardiovascular and/or ingestive behaviours, have dense projections to the parabrachial area, many of which contain CaBP28k. The present results demonstrate that CaBP28k‐containing cells form a major part of the solitary and trigeminal projection systems, including subregions that are involved in visceroception and/or nociception processing. The location of solitary nucleus projection cells overlaps those of some neuropeptidergic projecting populations, suggesting colocalization. Consequently, certain neuropeptidergic actions may be CaBP

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00109.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis study concerns the involvement of calbindin‐D28K (CaBP28k)‐containing neurons in ascending spinal projections to the brainstem (nucleus of the solitary tract, lateral reticular nucleus area), pontine (parabrachial area) and mesencephalic (periaqueductal grey) structures. All these central structures are important in the processing of visceroception and visceronociception and all are targets for spinal efferents from similar areas. CaBP28k controls the excitability of cells by acting on intrinsic calcium metabolism. Results refer to the caudal spinal areas where the visceroceptive regions are concentrated. Experiments were performed through a double labelling approach that combined the retrograde transport of a protein ‐ gold complex to identify the projection cells and immunohistochemistry to identify the CaBP28k‐positive cells. The caudal spinal cord is rich in both CaBP28k‐containing and projection cells. Cells colocalizing the protein and the retrograde tracer were quite numerous, with a particularly high concentration in the superficial layers of the dorsal horn (laminae I and outer II) and the lateral spinal nucleus. The other spinal areas containing immunoreactive projection cells were the reticular part of the neck of the dorsal horn, the medial laminae VII and VIII, lamina X and the sacral parasympathetic nucleus. The superficial layers and the neck of the dorsal horn are targets for nociceptive, visceroceptive and thermal inputs; the sacral parasympathetic column and lamina X are involved in visceroceptive integration. A functional role for the lateral spinal nucleus has not yet been established. Quite similar results were obtained for each of the ascending pathways under study. The high incidence of CaBP28k in spinal pathways suggests that calbindin has a major role in controlling the excitability of spinal cells subserving the processing of visceroception and/or visceronociception information to supraspinal levels. The participation of CaBP28k‐immunoreactive cells in spinal ascending tract cells largely outnumbers those previously reported for various neuropeptides (Leahet al., Neuroscience,24, 19

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00110.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCortical 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 m

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00111.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe 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 ch

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00112.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY