摘要:

AbstractThe effects of apomorphine, a D1–D2 dopamine receptor agonist, on the extracellular concentrations of glutamate and GABA were investigated in the striatum of young, middle‐aged and aged rats.In vivointracerebral perfusions were undertaken in the conscious rat using a concentric push‐pull cannula system. Amino acid concentrations in samples were determined by HPLC with fluorometric detection. Apomorphine produced a concentration‐related rise in striatal glutamate and GABA concentrations in young rats. Maximal increases were obtained at 20 μM apomorphine, and concentrations reached 184 and 191% of the basal value for glutamate and GABA respectively. Apomorphine failed to produce similar increases in glutamate concentration in middle‐aged and aged rats. Apomorphine, at 10 μM, also failed to produce an increase in GABA concentration in the aged rat. However, at 20 μM apomorphine produced increases in GABA concentration in middle‐aged and aged rats similar to those produced in young rats. These data are indicative of a change in threshold for GABA release induced by dopamine receptor stimulation in the aged rat. These results indicate that an interaction among dopamine, glutamate and GABA exists in the striatum of the rat, and that this type of interaction deterio

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00640.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA large variety of potassium channels is involved in regulating integration and transmission of electrical signals in the nervous system. Different types of neurons, therefore, require specific patterns of potassium channel subunit expression and specific regulation of subunit coassembly into heteromultimeric channels, as well as subunit‐specific sorting and segregation. This was investigated by studying in detail the expression of six different α‐subunits of voltage‐gated potassium channels in the rat hippocampus, cerebellum, olfactory bulb and spinal cord, combiningin situhybridization and immunocytochemistry. Specific polyclonal antibodies were prepared for five α‐subunits (KV1.1, KV1.2, KV1.3, KV1.4, KV1.6) of theShaker‐related subfamily of rat Kvchannels, which encode delayed‐rectifier type and rapidly inactivating A‐type potassium channels. Their distribution was compared to that of an A‐type potassium channel (KV3.4), belonging to theShaw‐related subfamily of rat Kvchannels. Our results show that these Kvchannel α‐subunits are differentially expressed in rat brain neurons. We did not observe in various neurons a stereotypical distribution of Kvchannel α‐subunits to dendritic and axonal compartments, but a complex differential subcellular subunit distribution. The different Kvchannel subunits are targeted either to presynaptic or to postsynaptic domains, depending on neuronal cell type. Thus, distinct combinations of Kv1 α‐subunits are co‐localized in different neurons. The implications of these findings are that both differential expression and assembly as well as subcellular targeting of Kvchannel α‐subunits may contribute to Kvchannel diversity and thereby to presynaptic and p

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00641.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractHippocampal ‘place cells’ discharge when a rat occupies a location that is fixed in relation to environmental landmarks. A principal goal of this study was to determine whether hippocampal place cell activity could be influenced by inertial cues. Water‐deprived rats were trained in a square‐walled open field in a dark room. The behavioural task required alternating visits to water reservoirs in the centre and in the four corners of the arena. The rat and arena were rotated in total darkness through ±90, 180 or 270°. The next water reward was then presented in the corner at the same position relative to the outside room as before the rotation. A cue card was later illuminated in this corner as a visual cue for the extra‐arena (room) reference frame. Fifteen out of 97 recorded hippocampal CA1 complex spike cells had spatially selective discharges in non‐central parts of the arena. After arena rotations, the firing fields of three units shifted between corners of the arena to maintain a fixed orientation relative to the room. This indicates that the hippocampus updated its representation of the position and heading direction of the rat using vestibular‐derived inputs concerning rotation angle. Other spatially selective discharges were guided to landmark cues (cue card or position of the reward: two units) or arena‐locked ‘substratal’ cues (eight units). In six cells, place cell activity suddenly ceased or appeared following rotations. These results provide evidence for contributions of inertial as well as substratal and landmark information to hippocampal sp

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00642.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThis study examined the influence of fibronectin conduits joining two halves of a sectioned sciatic nerve, with and without preimpregnation with nerve growth factor, on regeneration in rats with streptozotocin‐induced diabetes mellitus. Regeneration, measured morphometrically in fibres containing immunoreactivity to calcitonin gene‐related peptide (CGRP) and GAP‐43, was significantly less (P<0.0001 for all comparisons) in diabetic rats with fibronectin mat grafts without nerve growth factor compared to similarly treated controls. Regeneration distances in diabetic rats were reduced to 43% (CGRP‐reactive fibres) and 44% (GAP‐43‐reactive fibres) of controls, and the total amounts of immunoreactivities in the conduits were also reduced, though by lesser amounts (55 and 61% of controls respectively). Impregnation of the conduits with nerve growth factor before implantation increased the distance and amounts of regenerating immunoreactivity in both control and diabetic rats for both CGRP and GAP‐43, such that these regeneration parameters were similar in nerve growth factor‐treated diabetic rats to those in control rats implanted with untreated fibronectin mat conduits. These findings implicate impaired neurotrophic support in the defective regeneration characteristic of diab

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00643.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe large majority of mammalian retinal ganglion cells degenerate following section of their axons in the optic nerve. It has been suggested that some axotomized retinal ganglion cells die because of toxic agents produced within their immediate environment. Our hypothesis was that nitric oxide might be one of the toxic factors implicated in the death of adult retinal ganglion cells post‐axotomy. In the first instance, we determined whether there were any changes in the retinal expression of NADPH diaphorase both 3 and 14 days following intraorbital section of the optic nerve in adult rats. Secondly, if nitric oxide was indeed implicated in the death of ganglion cells, then trophic factors which rescue these neurons might do so by decreasing the expression of nitric oxide synthase. Recently, we found that a collicular proteoglycan purified from the major target of retinal ganglion cells, the superior colliculus, rescued a greater proportion of adult ganglion cells from axotomy‐induced death than most other known trophic factors. We thus injected this proteoglycan intraocularly after section of the optic nerve and examined its effect on the expression of NADPH diaphorase in the retina. Thirdly, an inhibitor of nitric oxide synthetase was repeatedly injected into the eye following the section of the optic nerve in order to determine if such a treatment might improve the survival of retinal ganglion cells. The present results indicate that section of the optic nerve does not alter the overall levels of NADPH diaphorase within the adult rat retina. Intraocular injections of the collicular proteoglycan actually increased the number of neurons expressing NADPH diaphorase, particularly in the ganglion cell layer. Finally, inhibition of nitric oxide synthetase following axotomy resulted in increased loss of retinal ganglion cells over a 2 week period when compared with controls. Our findings indicate that, rather than being toxic, small amounts of nitric oxide may be important for the survival of a proportion of injured retinal ganglion ce

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00644.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe high concentration and the localization of nitric oxide synthase in the olfactory system of both vertebrates and invertebrates suggest that the diffusible messenger nitric oxide plays a central role in the processing of chemosensory information. This paper describes the nitric oxide releasing system in the antenna and the antennal lobes ofApis melliferausing the NADPH diaphorase technique, and analyses the contribution of the nitric oxide system in the neuronal processing of chemosensory signals using a behavioural assayin vivo.In the antenna the strongest NADPH diaphorase staining is found in non‐neuronal auxiliary and/or epithelial cells, while the sensory cells and the antennal nerve are stained at a low level. At the major site of chemosensory signal integration, the antennal lobes, the highest nitric oxide synthase activity is located in the glomeruli, which are ideally suited to act as diffusion compartments. We demonstrate that inhibition of nitric oxide synthase in the antennal lobes specifically interferes with neuronal processing of repetitive chemosensory stimuli but does not affect the response to single stimuli, and is independent of parameters such as satiation level, stimulus strength, interstimulus interval and duration of sensory stimuli. Since inhibition of the soluble guanylate cyclase, a major target of nitric oxide, also particularly affects the adaptive component, the physiological effects of nitric oxide appear to be mediated by the action of cGMP. These findings suggest that the nitric oxide/cGMP system in the antennal lobes is a component of the molecular machinery involved in adaptive and/or integrative mechanisms during chemosensory information processingin viv

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00645.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractBrain cytoplasmic 1 (BC1) RNA is a small non‐translated RNA polymerase III transcript. Because this RNA can be detected in the rat posterior pituitary with35Sin situhybridization autoradiography, it has been hypothesized that this RNA might be transported in the axons of hypothalamo‐neurohypophyseal neurons. In the present study, we aimed to determine the cellular localization of BC1 more precisely by using non‐radioactivein situhybridization of BC1 RNA at both the light and electron microscopic levels. Our studies revealed that BC1 RNA was indeed located intra‐axonally. Furthermore, BC1 RNA was abundant within a subset of axonal swellings and/or terminals, and was also found in discrete cytoplasmic domains of undilated axonal segments. Using a semiquantitativein situhybridization approach, we have measured and compared the changes in BC1 RNA and arginine vasopressin (AVP) mRNA during dehydration (chronic salt‐loading) and rehydration. Chronic salt‐loading significantly increased both BC1 RNA and AVP mRNA. The increase in BC1 RNA labelling (2.5‐fold), however, was modest and somewhat less enduring than the increase in AVP mRNA labelling (13‐fold). Upon rehydration, both the BC1 and vasopressin transcripts in the posterior pituitary rapidly returned to control values. In conclusion, like vasopressin mRNA, BC1 RNA is transported in axons of the hypothalamo‐neurohypophyseal system where it aggregates in a subset of axonal swellings, and its axonal transport is similarly regulated. Therefore, we propose that BC1 RNA might be involved in the axonal targeting, docking and/or transport of AVP or o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00646.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effects of circumscribed lesions of the superior temporal cortical motion areas on speed discrimination were tested in three macaque monkeys using both moving random‐textured patterns and moving bars. The lesions, which included the middle temporal visual area, the adjacent medial superior temporal visual area and the fundus superior temporal visual area, produced a severe and lasting deficit in speed discrimination when tested with the random patterns. In contrast, deficits were smaller when tested with moving bars. Control lesions of the inferior temporal cortex in two monkeys had little effect on speed discrimination. There was no clear deficit following inferior temporal or superior temporal sulcus lesions on a vernier acuity task. These experiments indicate that the middle temporal and adjacent areas play a crucial role in speed discrimination and that lesion effects depend on the cues available to the animal

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00647.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractRadial columnar organization of cell clones is a characteristic feature of vertebrate retinae that is structurally not understood. Here we providein vitroevidence that Müller glia processes stabilize cells within columns. Dissociated embryonic chick retinal plus pigmented cells regeneratein vitrointo fully laminated stratospheroids. After reaggregating chick and quail cells, quail‐derived spheroid areas are detected as isolated sectors, as shown by a quail‐specific antibody. Each sector contains one or multiple cell columns. The radial borders separating chick and quail sectors are fully congruent with the extension of 3A7‐labelled Müller glia processes. While cell somata do not show any lateral interspecies mixing, quail‐derived neuropil extends within the inner plexiform areas far into chick sectors. After selective damage of Müller cells by the gliotoxindl‐α‐aminoadipic acid, the columnar organization is destabilized, as evidenced by a decrease in vimentin expression and by the migration of individual neurons out of their cell column. These data demonstrate that Müller cells actively stabilize cells within their columns, while neuritic growth

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00648.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe envelope glycoprotein gp120 of the human immunodeficiency virus HIV‐1 has been proposed to cause neuron death in developing murine hippocampal cultures and rat retinal ganglion cells. In the present study, cultured human embryonic cerebral and spinal neurons from 8‐ to 10‐week‐old embryos were used to study the neurotoxic effect of gp120 and gp160. Electrophysiological properties as well asN‐methyl‐d‐aspartate (NMDA)‐induced currents were recorded from neurons maintained in culture for 10–30 days. Neither voltage‐activated sodium or calcium currents nor NMDA‐induced currents were affected by exposure of neurons to 250 pM gp120 or gp160. In contrast, when neurons were subjected to photometric measurements using the calcium dye indo‐1 to monitor the intracellular free Ca2+concentration ([Ca2+]i), gp120 and gp160 (20–250 pM) potentiated the large rises in [Ca2+]iinduced by 50 μM NMDA. The potentiation of NMDA‐induced Ca2+responses required the presence of Ca2+in the medium, and was abolished by the NMDA antagonistd‐2‐amino‐5‐phosphonovalerate (AP5) and the voltage‐gated Ca2+channel inhibitor nifedipine. Moreover, exposure of a subpopulation of spinal neurons (25% of the cells tested) to 20–250 pM gp120 or gp160 resulted in an increase in [Ca2+]ithat followed three patterns: fluctuations not affected by AP5, a single peak, and the progressive and irreversible rise of [Ca2+]i. The neurotoxicity of picomolar doses of gp120 and gp160 cultures was estimated by immuno‐fluorescence and colorimetric assay. Treatment of cultures with AP5 or nifedipine reduced gp120‐

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1995.tb00649.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY