摘要:

AbstractThalamo‐cortical neurons were identified in slices of the rat dorsal lateral geniculate nucleus and whole‐cell currents were recorded using the patch‐clamp technique. Postsynaptic currents occurring spontaneously, or elicited by extracellular stimulation in the vicinity of the recorded neuron, were analysed. Spontaneous postsynaptic currents were observed in every recorded neuron. At a holding potential of –60 mV, and with a high internal Cl−, the currents were inward and had amplitudes ranging from<10 to 425 pA. All the spontaneous currents were blocked by 10 μM bicuculline, indicating that they were due to the activation of postsynaptic α‐aminobutyric acid (GABAA) receptors. The 10–90% rise time of these spontaneous GABAergic currents was 0.86 ± 0.19 ms. Their time course of decay could be fitted to an exponential function with one time constant of 18.19 ± 3.02 ms (mean ± SD), or two time constants of 4.47 ± 0.77 and 33.27 ± 3.74 ms. This activity was frequently organized in bursts. Stimulus‐evoked postsynaptic currents were recorded and shown to be due to the activation of glutamatergic receptors. Under similar experimental conditions a bicuculline‐sensitive component was also recorded. These stimulus‐evoked GABAergic currents had a 10–90% rise time of 1.93 ± 0.54 ms. Their time course of decay could also be fitted to an exponential function with one time constant of 24.42 ms or two time constants of 10.26 ± 2.46 and 49.30 ± 10.98 ms. The difference in the time course between spontaneous and evoked GABAergic currents suggests that these responses may arise from syna

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00168.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe relationship between the development of the pupilloconstriction response to changes in light levels and retinal maturation was studied in normal rats and rats that had received intracranial retinal transplants at birth. A pupillary response to light was first observed between postnatal days 7 and 9 in normal rats, and was typically of small amplitude and sluggish. By the time the eyelids first open, 2 weeks after birth, the pupillary response had improved to near adult levels. The inception of the pupillary response correlates with the first appearance of conventional synaptic contacts in the inner and outer plexiform layers of the retina, while improved responses correlate with maturation of photoreceptor outer segments and formation of synaptic ribbons in the inner plexiform layer. When embryonic retinae were transplanted to intracranial locations in newborn hosts and the transplants later illuminated as the host matured, the onset of a pupillary response to transplant illumination was delayed in proportion to the developmental disparity between the transplant and the host. The pattern of anatomical development in transplanted retinae was also similar, but delayed in time, compared to normal retinae. This indicates that the limiting factors for expression of light‐activated pupilloconstriction exist within the retina, rather than being intrinsic to the central nuclei or to the output pathway subserving the respons

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00169.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTransverse sections of rat embryo brainstem (embryonic age 18–19 days) containing the brainstem motor nuclei were explanted, together with a small piece of tongue or skeletal muscle, in a plasma clot and maintained in culture for 2–3 weeks using the roller tube technique. The results show that brainstem motoneurons survived, differentiated and innervated newly formed multinucleated myotubes which displayed large synchronized contractions after 1 week in culture. Muscle fibre contractions could be induced by excitatory amino acid applications and suppressed by curarization. Muscle fibres differentiated normally. During the first week they showed diffuse acetylcholinesterase positivity and multi‐innervation. During the second and third weeks the number of motor end‐plates was greatly reduced and transverse striation was observed. In the presence of muscle fibres, the brainstem thinned out and spread, becoming one or two cell layers thick, and the motoneurons tended to migrate towards the muscle fibres, becoming clearly observable in the living culture. When the muscle explant was not present, the brainstem explant did not spread and remained several cell layers thick, while acetylcholinesterase‐positive cells, presumed to be motoneurons, tended to disappear. The preparation described is well suited for electrophysiological studies of differentiating motoneurons and offers direct access to their dendritic tree, a most desirable feature for patch‐clamp or multisite optica

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00170.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractBased on the observation that in adult mice the carbohydrate epitope L2/HNK‐1 is detectable on Schwann cells in ventral spinal roots, but only scarcely in dorsal roots (Martiniet al., Dev. Biol.,129, 330–338, 1988), the possibility was investigated that the carbohydrate is involved in the outgrowth of regenerating motor neuron axons on peripheral nerve substrates expressing the epitope. To monitor whether the L2 carbohydrate remains present during the time periods in which regenerating axons penetrate the denervated distal nerve stumps, the expression of L2 in motor and sensory branches of the femoral nerve was investigated in normal animals and after a crush lesion. During the first two postoperative weeks, L2 immunoreactivity remained high in the myelinating Schwann cells of the motor branch, whereas L2 immunoreactivity was virtually absent in the sensory branch. In a first experimental approach, cryosections of ventral and dorsal spinal roots and of motor and sensory nerves of adult rats and mice were used as substrates for neurite outgrowth. Neurites of motor neurons from chicken embryos were ∼35% longer after 30 h of maintenance on ventral roots than on dorsal roots. Neurites from sensory neurons had the same length on dorsal as on ventral motors and were as long as neurites from motor neurons grown on dorsal roots. L2 antibodies reduced neurite outgrowth of motor neurons on ventral roots but not on dorsal roots. Neurite outgrowth of sensory neurons on both roots was not altered by the antibodies. Neurite outgrowth of motor neurons on a mixture of the extracellular matrix glycoprotein laminin and the L2 carbohydrate‐carrying glycolipid was significantly higher than on the laminin substrate mixture with GD1b ganglioside or sulphatide. L2 antibodies reduced neurite outgrowth of motor neurons by 50% on the L2 glycolipid, but not on GD1b or sulphatide. These observations indicate that the L2 carbohydrate promotes neurite outgrowth of motor neuronsin vitroand may thus contribute to the preferential reinnervation of motor nerves by regenerating motor axons

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00171.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractNeuronal death in the inferior olivary complex (IOC) was studied in control and unilaterally pedunculotomized newborn rats, from postnatal day 1 (P1) to P30, in order to test whether the approximately two‐fold increase in available specific targets (i.e. Purkinje cells) that is theoretically provided by sectioning one inferior cerebellar peduncle to the developing climbing fibres of the remaining IOC could prevent the loss of inferior olivary neurons taking place during the first 2 weeks of postnatal life in the rat. Numerical estimation of the number of inferior olivary neurons in control and experimental rats showed that (i) in pedunculotomized rats, the number of inferior olivary neurons of the remaining inferior olivary complex was always greater than that encountered in control rats, (ii) the consistent decrease in the number of inferior olivary neurons observed in control animals between P2 and P8 was absent in cell counts of the pedunculotomized rats, and (iii) the increase in olivary cell number following the phase of cell decrease was also absent in pedunculotomized rats. It is concluded that the increase of available Purkinje cells during early postnatal development of the olivocerebellar projection prevents neuronal death in the remaining inferior olivary complex following pedunculotom

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00172.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractRecent studies indicate that the nociceptive withdrawal reflexes to individual muscles are evoked by separate reflex pathways. The present study examines whether nociceptive withdrawal reflexes to different muscles are subject to differential supraspinal control in rats. A distant noxious stimulus was used to activate a bulbospinal system which selectively inhibits ‘multireceptive’ neurons (i.e. neurons receiving excitatory tactile and nociceptive inputs) in the dorsal horn of the spinal cord. Withdrawal reflexes, recorded with electromyographic techniques in single hindlimb muscles, were evoked by standardized noxious pinch. Thirty‐seven rats, anaesthetized with halothane and nitrous oxide, were used. Whereas withdrawal reflexes to the extensor digitorum longus and brevis, tibialis anterior and biceps posterior muscles were strongly inhibited, reflexes to interossei muscles were potentiated during noxious pinch of the nose. Reflexes to peronei muscles were not significantly changed. The effects on the reflexes usually had an onset latency of<0.5 s and outlasted the conditioning stimulation by up to 2 s. The monosynaptic la reflex to the deep peroneal nerve, innervating dorsiflexors of the digits and ankle, was not significantly changed during noxious pinch of the nose. Hence, the inhibitory effects on the hindlimb withdrawal reflexes induced by the conditioning stimulation were presumably exerted on reflex interneurons. It is concluded that nociceptive withdrawal reflexes to different hindlimb muscles are differentially controlled by descending pathways activated by a distant noxious stimulus. The results support our previous conclusion that there are separate nociceptive withdrawal reflex pathways to different hindlimb mu

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00173.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

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

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00174.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractChanges in striatal dopamine D2receptor mRNA levels provoked by unilateral 6‐hydroxydopamine‐induced lesion of the nigrostriatal dopamine pathway were studied byin situhybridization. The influence of embryonic dopaminergic neurons implanted into the dopamine‐depleted striatum on the lesion‐induced changes was also examined. Changes in D2mRNA levels were compared with changes in D2receptor densities measured in the same animals by receptor autoradiography using [3H]spiperone or [3H]SDZ 205–501 as ligands. The distribution of D2mRNA in the striatum of control animals closely paralleled that of the D2receptor itself, as assessed by autoradiography, and the highest density of D2mRNA occurred in the lateral part of the striatum. One month after lesion, levels of D2mRNA were 34% higher in the dorsolateral part of the dopamine‐depleted striatum than in the corresponding region of the contralateral control striatum. D2receptor density in this region was increased by 40% relative to the control level. No significant increases could be measured in the medial part of the striatum. The increases in the lateral part were similar at 7 months post‐lesion; however, at this time the increase in both D2mRNA and receptor levels had spread to the medial part of the striatum as well. In the graft‐bearing striatum levels of both D2mRNA and D2receptors reverted to control levels. This study shows that the post‐lesion increase in striatal dopamine receptor and mRNA level is a biphasic phenomenon with a late‐occurring component in the medial striatum. It also shows that once the increase in striatal D2receptor gene expression is accomplished, it is maintained unchanged for long periods, similar to that of D2receptor levels themselves. Moreover, grafts of embryonic dopaminergic neurons are able to modulate the expression of the dopam

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00175.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe aim of this study was to test the role of glutamatergic neurotransmission in photic entrainment of the circadian oscillator of the suprachiasmatic nuclei (SCN) in the Syrian hamster. The response of the oscillator to a brief pulse of light was assessed using two independent indices, the phase shift of the free‐running activity rhythm, and the photically induced expression of the immediate‐early gene c‐foswithin neurons of the SCN. The behavioural and the cellular responses to light were compared in animals which received intra‐cerebroventricular (icv) infusions into the region of the SCN of either a vehicle solution or a solution of γd‐glutamyl‐glycine (DGG), a competitive antagonist at bothN‐methyl‐d‐aspartate (NMDA) and non‐NMDA types of glutamate receptor. Infusions of vehicle or DGG (200 nmol) were given 10 min before presentation of a 15‐min light pulse at either circadian time (CT) 14 or CT20 (onset of activity defined as CT12). As anticipated, animals treated with vehicle and light at CT14 exhibited phase delays in the activity rhythm, whereas animals treated at CT20 exhibited phase advances. Central infusion of DGG prior to a light pulse at CT14 blocked the phase‐delaying effect of light, and DGG delivered before a light pulse at CT20 markedly attenuated the phase‐advancing effect of light. In a separate group of animals, the expression of the immediate‐early gene c‐foswas assessed by immunocytochemical staining for its protein product Fos. Exposure of vehicle‐infused animals to light at CT14 caused extensive expression of c‐fosthroughout the retinorecipient region of the SCN. However, when the light pulse was preceded by icv fusion of DGG at a dose which would block the phase‐shifting response to light, the total number of neurons immunopositive for Fos was significantly reduced (∼50%) and the expression was confined to a restricted area of the dorsolateral SCN. The precise correlation between the effects of glutamatergic blockade upon both the behavioural and the cellular responses of the circadian system to light demonstrates that effective glutamatergic neurotransmission within or adjacent to the SCN is a necessary component of the mechanism which mediates photic entrainment of the circadian clock. The results further demonstrate a pharmacological and anatomical compartmentalization of the retinorecipient zone of the SCN, consistent with the view that retinal afferents to the ventral region employ glutamate as a transmitter, whereas more dorsal input may be dependent upon non‐

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00176.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY