摘要:

AbstractThe main efferent axons of pyramidal cells in layer 2/3 in the adult cat striate cortex make collateral connections specifically within layer 2/3 and layer 5 and avoid the intervening layer 4. Intracellular dye injectionsin vitrowere used to determine how, during early postnatal development, this precise pattern of laminar connections was achieved. These investigations revealed that the pattern of collateral outgrowth was specific from the very earliest time that axons began sprouting collaterals. During the first postnatal week, sprouts were seen exclusively within layers 2/3 and 5; no evidence for a transient connection to layer 4 was observed. Furthermore, collaterals emerged simultaneously within layers 2/3 and 5, despite the large difference in the postmigratory ages of the two layers. By the end of the second postnatal week, the adult number of collaterals was achieved. Further elaboration of the local arbors occurred by repeated branching of already existing collaterals, rather than by addition of new collaterals to the main axon. These results demonstrate that the formation of local connectionsbetweencortical layers is highly specific, in contrast to the development of clustered horizontal connections by these same cells within layers 2/3 and 5, which involves extensive remodelling of local connections.

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe visceral ganglion ofAplysiawas 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+]oat the surface of identified giant neuron, R2, was measured using double‐barrelled calcium‐selective microelectrodes. A decrease of ∼1 mM in [Ca2+]ocould 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+]ocould sometimes, but not always, be observed during the phase of induced neuronal

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe complex construction of the joint apparatus of the cat distal forelimb, which allows the paw three degrees of freedom, poses special requirements on the neural signals controlling the paw position. To understand the electromyography (emg) signals of the distal forelimb muscles during locomotion, it is necessary to know the kinematics of the forelimb joints in detail. As no such information is available, we used the pulsed X‐ray technique in trained cats during treadmill locomotion to analyse the angular excursions of the wrist, the metacarpophalangeal (MCP) and the proximal interphalangeal (PIP) joints. X‐ray illuminations were done in either the parasagittal or the frontal plane. At the beginning of the stance phase the wrist (WR) and the MCP joints extended slowly, and the PIP joints flexed. Whereas the WR and the PIP joints maintained a constant angular position of ∼200° and 60°, respectively, throughout the stance phase, extension continued in the MCP joints from 240° at touch‐down to 300° at the end of the stance phase. Slightly before lift‐off (100 ms) the WR and the MCP joints flexed rapidly. This flexion changed ∼150 ms after lift‐off into a slow extension. The PIP joints extended rapidly at the beginning and at the end of the swing phase, during the interposed period of the swing phase they displayed a slow flexion. Rotatory movements of the forelimb in the radioulnar joints were present during the swing and stance phases. During the swing phase the limb first supinated (starting 100 ms after lift‐off); pronation occurred immediately before ground contact. During the stance phase the supination angle was kept constant until 100 ms before lift‐off, when a short pronation was found. The paw was kept in an ulnar deviated position throughout the complete step cycle. Ulnar deviation decreased at the end of the swing and stance phases. The results of this study increase our understanding of how the body weight is transmitted on to the ground. They suggest four main functions for the skeletomotor apparatus and the underlying neural commands to secure the forward movement of the animal during the stance phase: (i) preparation and stabilization of a force‐transmitting platform; (ii) stabilization of the wrist and the carpal/metacarpal joints; (iii) stabilization of the supination angle; (iv) antigravity control of t

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of various neurotransmitter agonists and antagonists on the synthesis and release of methionine enkephalin (mENK) in neuronal cultures of mouse spinal cord and dorsal root ganglia have been measured. Blockade of electrical activity with tetrodotoxin between days 9 and 13 in culture caused a>95% decrease in the number of mENK‐immunoreactive neurons. This effect was also seen upon the blockade of glycine and β‐adrenergic receptors with strychnine and propranolol, respectively, and stimulation of GABA receptors with muscimol. Stimulation of β‐adrenergic receptors with isoproterenol, or blockade of glutamate and GABA receptors with 2‐aminophosphonovalerate and strychnine, respectively, had a qualitatively opposite action on both the number of mENK‐immunoreactive neurons and enkephalin peptide levels measured by radioimmunoassay. Application of substance P also enhanced the mENK cell number. These data suggest that, at least in the spinal cord, characteristics other than the average level of impulse activity in the afferent input may be critical to the regulation of express

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this study we examined whether the potency of quinolinic acid (Quin) in inducing neurodegenerationin vivowas 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 withd(–)‐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 proces

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00809.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractInjection of 0.2–3.0 ng of tetanus toxin into rat parietal neocortex resulted in permanent (>7 months) changes in the local circuit properties of this tissue. It caused excessive synchronization of neuronal activity. This was seen as spontaneous paroxysmal field potentials and/or evoked all‐or‐none population burst discharges. Such activity was recorded widely over the parietal and temporal areas of both the injected and the contralateral hemispheres from as little as 16 h after injection up to the maximum survival time of 7 months. Several observations suggest that the speed with which the hypersynchronous activity spread to the opposite hemisphere reflects transport of the toxin through corticocortical axons, and consequent blockade of synaptic inhibition. However, from what is known of the half life of the peptide in brain, it is unlikely that the persistent, widespread distribution of epileptiform discharge several months after injection was due to the continued presence of toxin. Thus, intracortical application of tetanus toxin provides a good experimental model of chronic focal epilepsies, and raises fundamental questions regarding the long term regulation of local circuit properties in the neoc

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00810.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPrevious 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 vulgarisleucoagglutinin (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 physio

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00811.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractN‐methyl‐d‐aspartate (NMDA) receptors represent a major subtype of excitatory amino acid receptors in the mammalian brain. In addition to their physiological role, NMDA receptors have been linked to the occurrence of nerve cell death in several neurodegenerataive diseases. The hamster neurotropic (HNT) strain of measles virus causes non‐inflammatory encephalopathy in mice. This is associated with neuronal loss in areas CA1 and CA3 of the hippocampus. Systemic treatment with the non‐competitive NMDA receptor antagonist 5‐methyl‐10,11‐dihydro‐5H‐dibenzo(a,d)cyclo‐hepten‐5,10‐imine maleate (MK‐801) prevented this cellular necrosis. Thus, a virus may have indirect neurodegenerative effects in the brain due to a

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00812.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSelective lesions of the dopaminergic nigrostriatal system and embryonic neuron grafts were used to study the mechanism by which exogenous neurons can restore transmitter function and to examine CNS development and plasticity. C57BL mice treated with acetaldehyde/1‐methyl‐4‐phenyl‐1,2,3,6‐tetra‐hydropyridine show irreversible loss of substantia nigra dopaminergic neurons. Implants of embryonic mesencephalic dopaminergic neurons functionally reinnervate the striatum and form a dense network of fibres; ∼20% of the implanted dopaminergic cells survive for several months. However, dopaminergic fibre outgrowth and mesencephalic graft development appear lower in control, non‐lesioned, animals. Moreover, implants of embryonic hypothalamic dopaminergic neurons show little or no survival. These results indicate that interactions between embryonic and adult neurons are selective. We suggest that this specificity may be sustained by the action of still unknown trophic and/or tropic factors, possibly produced by the lesioned striatum and by putative inhibitory mechanisms of cell migration and neu

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00813.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe developmental time‐course and growth characteristics of efferent graft‐to‐host projections were studied from mouse fetal striatal grafts (E13–14) implanted as a cell suspension into the ibotenate‐lesioned striatum of immunosuppressed adult rats. A cell surface monoclonal antibody specific for mouse neurons (M6) was used to identify the donor cells and their projections into the host brain. At 3–5 days after implantation, sparse fascicles of M6‐positive graft‐derived fibres extended for ∼0.3–0.4 mm across the graft‐host border into the surrounding host striatum. From the beginning they were selectively orientated in one direction, i.e. caudally along the myelinated fibre bundles of the internal capsule. At 8 days, the graft‐derived fibres were more numerous and more densely labelled. They ran in dense fascicles inside the myelinated bundles of the host internal capsule and reached the rostral host globus pallidus, a distance of ∼ 1.2 mm from the caudal tip of the graft. Two weeks after grafting, the M6‐positive fibre fascicles were clearly seen to branch within the globus pallidus to form terminal‐like networks. From this time onwards, the immunoreactivity of the outgrowing fibre fascicles gradually diminished, although small but dense terminal‐like networks could be found in the host globus pallidus in most, but not all, of the rats at longer survival times (3–15 weeks). This is consistent with previous work showing that outgrowing axons lose their M6 immunoreactivity as they mature and become myelinated. Control grafts of fetal neocortical and fetal cerebellar tissue were used to assess the tissue‐type specificity of the efferent fibre growth. The neocortical implants projected densely up to about 3 mm into the host brain, along the internal capsule and the corpus callosum and into the overlying cortex. By contrast, although the cerebellar grafts survived well, they showed very little efferent fibre growth. Double immunostaining for DARPP‐32 and M6 revealed that all M6‐positive fibre fascicles extending from the striatal (but not neocortical) grafts also showed DARPP‐32 positivity, and thus that it was the DARPP‐32‐positive regions of the striatal grafts that projected to the host brain. It is concluded that graft‐to‐host projections, running along and inside host myelinated bundles, are formed from intrastriatal striatal grafts within 1–2 weeks of implantation. Grafts of neocortical tissue grew well along the same trajectory, whereas neurons of a type not normally projecting along the internal capsule, i.e. cerebellum, failed to extend axons

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1991.tb00814.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY