摘要:

AbstractIn order to investigate the responses of neurites to myelinin vitro, retinal explants obtained from adult rats were cultured on poly‐L‐lysine and laminin. Regenerating adult ganglion cell axons were confronted with rat central myelin which was adsorbed on culture dishes. When the explants were placed directly on the myelin, axons did not grow out. Alternatively, when the explants were placed at a certain distance from the myelin, massive outgrowth of axons was observed. When axonal growth cones encountered the myelin, they displayed various reactions. All single axons observed immediately stopped growing after encountering the myelin border. All of them remained for at least 4 h at the border. Sixteen per cent of them remained in this ‘resting state’ throughout the time of observation (2–5 days). Nineteen per cent of the axons degenerated following contact with the myelin. The majority of axons were able to circumvent the myelin either by backbranching (21%) or by growing in another direction with the leading growth cone (37%). Eight per cent of the axons were observed to enter the myelin. The results indicate that central myelin represents a non‐permissive obstacle for growing adult axons. This observation is in conformity with the inability to regenerate that is typical of lesioned optic nerve a

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00403.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractEffects of secretagogues and anti‐secretagogues of ACTH secretion on K+permeability in the clonal pituitary cell line AtT‐20 were measured by recording86Rb or42K efflux. Efflux was accelerated by the secretagogues K+, corticotrophin, forskolin, isoprenaline, and the Ca‐ionophore A23187. Efflux was reduced by the inhibitors somatostatin, muscarine, and oxotremorine, or by removing external Ca. Efflux was also reduced by the K+‐channel blocking compound d‐tubocurarine but not by tetraethylammonium. Muscarine, oxotremorine, somatostatin, and 0 Ca2+also reduced intracellular Ca2+measured by quin‐2 fluorescence. It is suggested that most of the resting86Rb or42K efflux measured under these conditions occurs via tubocurarine‐sensitive Ca2+‐dependent K+‐channels, and that changes in efflux rate produced by secretagogues or anti‐secretagogues are secondary to changes in

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00404.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe inhibitory motor innervation of a crustacean leg was studied in the crab,Carcinus maenas.Inin vitropreparations of the central nervous system and the proximal leg nerves, motor nerve recordings demonstrate the presence of a single common inhibitory motor neuron which elicits picrotoxin‐sensitive inhibitory junction potentials in a distal leg muscle, the accessory flexor. This inhibitor is the common inhibitor (CI). Immunohistochemical detection of the inhibitory motor neuron neurotransmitter, gamma‐aminobutyric acid (GABA), allows us to identify three immunoreactive motor neuron axons in sections of the distal leg nerves and of proximal leg nerves. One corresponds to the CI whereas the other two are the specific inhibitors, one to the stretcher and one to the opener muscles. After nickel chloride backfills of the CI in proximal leg nerves, GABA immunodetection fails and thus confirms that CI is the single inhibitor having branches in proximal leg nerves.These results demonstrate that the inhibitory motor innervation of a crab leg comprises three and only three inhibitors: the common inhibitor innervating all leg muscles and the two specific inhibitors, each innervating a single distal leg muscle. Further conclusions can be drawn: first, a muscle innervated by more than one excitatory axon has no specific inhibitor; second, sensory afferents are not mediated by GABA. Finally, during locomotion, the leg muscles receive two very distinct types of motor input: (1) one common to all the muscles coming from the common inhibitor which was previously shown by other authors to prevent build‐up of tension in the muscles, thus allowing each muscle to contract according to (2) the specific motor input it receives from its own exc

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThough most experimental evidence indicates that the corticothalamic (CT) pathway would exert a direct excitatory action on thalamic relay neurons, the electrophysiological features of this excitation have never been clearly described. A methodological problem in previous electrophysiological studies was that direct corticofugal effects on relay cells could not be separated from those mediated by collateral activation of reticular thalamic neurons. In the present study, the reticular complex was lesioned by kainic acid and the CT response of relay neurons of the ventral lateral nucleus was recorded intracellularly in cats under pentobarbital or urethane anaesthesia.Following reticular thalamic lesions, a prominent depolarization was triggered in thalamic relay cells by stimulation of the CT pathway. This depolarization strongly drove spike discharges, and its amplitude augmented when the stimulation rate exceeded 2 Hz. Tetanizing the CT input with short trains (100–200 Hz for 200–300 ms) produced a similar augmentation to test volleys for 15–30 s after the tetanos. The CT excitation and its frequency‐dependent augmentation were depressed by ketamine injection or by local application of N‐methyl‐D‐aspartate (NMDA) antagonists. The augmenting phenomenon appeared strictly homosynaptic. For instance, it did not appear during repetitive stimulation of the cerebellar input, nor did the CT input potentiate subthreshold synaptic potentials of cerebellar origin during a conditioning procedure. Conversely, the cerebellar excitation was depressed when it occurred during the CT depolarization.It is concluded that the direct synaptic responses induced by CT fibres in relay neurons are mediated at least partly by the activation of NMDA receptors. Moreover, the marked non‐linear additivity of cerebellar and CT synaptic potentials raises questions concerning the presumed improvement of thalamic transmission of peripheral informations ensured by the CT input. Instead, both inputs could compete for control of the firing of thalamic neurons. The numerical importance of CT fibres and the strong augmenting mechanism operating at synaptic sites in the thalamus suggest that the role of the thalamus is not only to transfer peripheral informations toward the cortex, but also and mainly to feed back to the cortex a modified copy of its own neur

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00406.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractWe have studied two monoclonal antibodies raised against crude fractions of membrane glycoproteins from adult mouse brain and found them to react with two carbohydrate epitopes expressed on several neural cell adhesion molecules. Other identified and unidentified glycoproteins from different cell types, organs and species were also recognized by these antibodies. Both epitopes are N‐glycosidically linked mannosidic or hybrid type oligosaccharides and co‐expressed on all the glycoproteins so far tested. In spite of their remarkable similarities, the glycan epitopes are different as shown by ELISA competition assays. In microexplant outgrowth and cell adhesion assays, both antibodies interfere with neural cell adhesion, migration, and neurite outgrowth. These observations, together with previous studies on the L2/HNK‐1 glycan (Künemund et al., 1988), indicate that adhesion molecules carry various carbohydrate epitopes mediating different cell interactions inin vitro

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractTo investigate the role of spontaneous retinal activity in map refinement, we studied goldfish kept in darkness during regeneration of a cut optic nerve. In one experiment, such fish (with lenses ablated to blur vision) were maintained for 70 days in stroboscopic light, diurnal light, or total darkness interrupted daily by 15 minutes of stroboscopic light. The retinotectal projection was then assessed for retinotopy by standard methods, using retrograde transport of wheat germ agglutinin—horseradish peroxidase. As in previous work, significantly more refinement was found in diurnal than in stroboscopic light. In darkness, refinement was as complete as in diurnal light. In a second experiment, similar fish were kept in stroboscopic light for 63 days. Some were then assessed to confirm that refinement had been delayed, while others were transferred to darkness or diurnal light for assessment later. After 7 days in either environment, no further refinement was seen; but after 21 days, substantial and significant refinement has occurred in both. Thus the effects of darkness and diurnal light were indistinguishable, and very different from those of stroboscopic light and (in previous studies) tetrodotoxin. Map refinement is evidently activity‐dependent but not experience‐dependent, and can effectively use the correlated spontaneous firing of neighbouring ganglion cells as its basis. Locally correlated spontaneous activity, which appears also to drive eye‐ and class‐specific axon segregation in mammals, occurs widely in the nervous system. It could potentially generate systematic interconnection patterns even between neuronal populations without an overtly topographic org

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00408.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThree genetically distinct isozymes of the catalytic subunit of the Na,K‐ATPase have been detected and have been designated α1, α2, and α3. To determine whether their expression is restricted to identifiable neurons and glia, specific monoclonal antibodies were used for immunofluorescent localization in the rat retina and optic nerve. The patterns of staining were markedly different, suggesting differences in cellular localization. Photoreceptor inner segments and optic nerve fibers expressed predominantly α3. Müller glia in the retina and astrocytes in the optic nerve expressed α1 and α2. Isolated, dissociated bipolar, horizontal, and Müller cells expressed different isozymes separately or in combination. The complexity of staining of neurons and their axons and dendrites suggested that Na,K‐ATPase isozyme expression is not stereotyped, but is tailored to the ion transport needs of individual cell types, and targeted to specified membr

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00409.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractTo examine the possibility that glutamate may be widely used as the transmitter for cerebellar mossy fibres, population responses of granule cells following electrical stimulation of these fibres were recorded in rat cerebellar slices using a gap technique. Several different vermal lobules (II, V, VIb, VIII, IXc and X) whose main mossy fibre afferents originate in different nuclei, were compared. The mossy fibre response was remarkably similar in appearance in all lobules. With 1.2 mM Mg2+in the perfusing solution, and with a low rate of stimulation (0.05 Hz), the N‐methyl‐D‐aspartate (NMDA) antagonist, D‐2‐amino‐5‐phosphonovalerate (APV, 30 μM), had little or no effect but all components of the response could be inhibited by the broad spectrum excitatory amino acid antagonist, kynurenate (3 mM), or by the relatively selective non‐NMDA antagonist, 6‐cyano‐2,3‐dihydroxy‐7‐nitro‐quinoxaline (CNQX, 10 μM). Slow APV‐sensitive components emerged during high frequency stimulation (30 ‐ 150 Hz) or, with a low stimulation rate, on removal of Mg2+or addition of bicuculline (30 μM). The results suggest that an excitatory amino acid, presumably glutamate, is the major mossy fibre transmitter in the cerebellum and that it activates both NMDA and n

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00410.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY