摘要:

AbstractHomotopic and isochronic transplantations of the right dorsal half of the mesencephalic vesicle have been performed between chick and quail embryos at the stage of 10–14 somites. Analysis of the extension of the graft, by means of the quail nucleolar marker, combined with cytoarchitectonic analysis has disclosed that the transplanted neuroepithelium gives rise to isthmic nuclei and to a portion of rostral cerebellum, in addition to the optic tectum and mesencephalic dorsal grisea. These results show that the rostral portion of the cerebellar primordium is located in the so‐called ‘mesencephalic’ alar plate, thus considerably more rostrally than previously supposed. This has been confirmed by two other types of chimeric embryos resulting from homotopic transplantation of either: (i) the quail right alar plate of the first rhombencephalic vesicle, which gives rise to caudal but not rostral cerebellum in the operated side, or (ii) the right alar portion of a segment of the quail neural tube including both the caudal third of the mesencephalic vesicle and the rostral half of the first rhombencephalic vesicle, which gives rise to the whole hemicerebellum in the operated side. Moreover, in chimeric embryos with transplants restricted to the mesencephalic alar plate, the grafted portion of the cerebellar primordium gives rise both to deep cerebellar neurons and to all types of cortical neurons. Among the quail cortical neurons, the Purkinje cells, although intermingled with host Purkinje cells, are organized, at E18, in a characteristic longitudinal band which is strongly reminiscent of the longitudinal functional and morphological organization of the cerebellum. Other types of quail cortical neurons, that is, Golgi cells, granule cells, and molecular layer interneurons, are also observed within this sagittal band. In addition, quail granule cells and molecular layer interneurons as well as quail glial cells, extend over a larger territory on both sides of the longitudinal band containing quail Purkinje cells and even cross the midline and invade the contralateral hemicerebellum. In all types of chimeric embryos, the proliferation, migration, and differentiation of quail transplanted neurons, both in the isthmic region and in the cerebellum, evolve asynchronously from the host homologous ones, following a more precocious and faster developmental schedule. This asynchrony in the development of grafted and host isthmic and cerebellar homologous areas confirms and extends previous findings concerning the proliferation and migration of quail tectal cells in chick quail chimeric embryos (Senut and Alvarado‐Malla

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00362.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRecent investigations into the neural basis for swimming inXenopusembryos have pointed to central roles played by N‐methyl‐D‐aspartate (NMDA) receptor‐mediated excitation actingwithinand glycinergic reciprocal inhibition actingbetweenmotor systems for the muscular antagonists on the two sides of the CNS. A ‘reduced’ preparation consisting of only one half of the CNS divided sagittally along its midline is used here to examine the basis for rhythmicity within each side in the absence of reciprocal connections. Divided preparations transected rostrally at levels between the otic capsule and the obex can all generate a rhythmic pattern of motor discharge similar to that which underlies swimming. All rhythm generation is blocked by the NMDA antagonist (+/ ‐)‐2‐amino‐5‐phosphonovaleric acid (APS) at 20 μM. However, neither glycinergic nor GABAergic inhibition is required for a basic rhythmicity since some rhythm persists in the presence of 10 μM strychnine and 50 μM bicuculline, though it is no longer sustained. In the divided spinal cord alone, rhythm generation requires extracellular Mg2+. If the most caudal segment of the divided hindbrain is left attached, extracellular Mg2+is required only if strychnine is present. If more of the hindbrain is included, extracellular Mg2+is no longer necessary for rhythm generation even in the presence of strychnine.It seems that rhythm generation by a single side of the spinal cord requires NMDA receptor‐mediated excitation together with the voltage dependency conferred on it by extracellular Mg2+, but not inhibition in order to occur. As more of the hindbrain is left attached, the requirement for extracellular Mg2+becomes progressively less strong. For sustained rhythm generation, one side of the CMS requires both excitation

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00363.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe spatial and temporal organization of climbing fibre activation of Purkinje cells, the so‐called complex spikes, were studied in the rat cerebellar Crus II folium utilizing a multiple microeletrode recording technique. As many as 32 Purkinje cells could be simultaneously recorded by using a custom‐built electronic amplifier system and a special data storage device. Analysis of the auto‐correlation activity of complex spikes in any given group of Purkinje cells indicated that activation occurs with a particular rhythmicity having a base firing of 10 Hz. Cross‐correlation of spontaneous complex spikes demonstrated, in addition to a particular rhythmicity, an extraordinarily high degree of synchronicity within a particular spatial distribution of Purkinje cells. Thus, Purkinje cells organized in rostra‐caudal rows tend to fire within 1 ms of each other for distances as far as 800 μm (the width of a folium) from the ‘master’ neuron. By contrast, Purkinje cells located medial or lateral to the master neuron showed almost no cross‐correlation. Administration of harmaline to the animal increased the degree of auto‐ and cross‐correlation but did not change the spatial order of the distribution of the cross‐correlation. The results indicate that the olivo‐cerebellar system is organized in such a way that climbing fibre afferents may be activated in a close‐to‐synchronous and rhythmic fashion. The spatial distribution of these afferents over the cortex is such as to activate rostro‐caudal bands of Purkinje cells which tend to fire in

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00364.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractMultiple recordings from Purkinje cells in the rat cerebellum allowed the mechanism responsible for the activation of rows of synchronous complex spikes to be investigated. By determining the spatial distribution of the climbing fibre reflex that follows electrical microstimulation of the cerebellar cortex, it was shown that the mechanism for the simultaneity of firing was the electrotonic interactions between neurons in the inferior olive (IO). The spatial organization of the complex spike activity was shown to be regulated by GABAergic inhibitory input into the IO, probably arising from the cerebellar nuclear neurons. The rostro‐caudal organizion of the complex spike activity following physiological stimulation (tactile stimulation of the upper and lower lip) demonstrated the same spatial distribution of synchronous activity in the cerebellar cortex as did the spontaneous activity and this was also disrupted by GABA blockers. Finally, complex spike responses to physiological stimulation indicate that the IO is capable of gating sensory inputs in accordance with its intrinsic autorhythmicity and that strong peripheral stimuli reset the oscillatory properties of the IO. The functional implications of the synchronicity and of the temporo‐spatial organizion of complex spikes in the cerebellar cortex are discussed in the context of motor coordination and tim

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00365.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe anatomical and physiological properties of GABAergic inhibitory neurotransmission were investigated in organotypic slice cultures of rat hippocampus. Interneurons and terminal‐like elements containing GABA‐like immunoreactivity were numerous in tissue kept for 13–26 days in culture and showed a similar morphology and distribution to those known from investigations on the hippocampal formationin situ.Furthermore, after 8–30 days in culture, spontaneous and evoked IPSPs were observed in all CA3 pyramidal cells tested, resulting from an increase in chloride conductance, and were shown to be mediated by activation of GABA receptors. No functional decrement in the efficacy of GABAergic inhibitory synaptic transmission following chronic isolation and long‐term maintenancein vitrowas noticed. In particular, neither the magnitude of the synaptic conductance underlying the inhibitory postsynaptic currents nor its reversal potential varied with time in culture. Taken together, the present physiological and immunohistochemical data show that GABAergic inhibition is well expressed in organotypic hippocampal slice cultures and is maintained over periods of at least 4 week

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00366.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRat soleus muscles were partially denervated by removal of the L5 ventral ramus at either 4 ‐ 6 days or 17 ‐ 19 days. Local application of leupeptin, a potent inhibitor of the calcium activated neutral protease to these operated muscles, resulted in a significantly greater maximal tetanic tension and motor unit size, when compared to untreated partially denervated muscles. This was achieved in the 4 ‐ 6 day operated animals by an increased number of terminals and in the 17 ‐ 19 day old animals by increased number of axonal sprouts that maintain contact with muscle fibres. In both groups of operated animals in the leupeptin treated muscles large numbers of motor units were able to maintain or achieve an expanded territory, whilst the size of the largest motor unit did not appear to be increased.It is proposed that leupeptin exerts its effect by inhibiting the degradative action of the neuronal calcium activated neutral protease on the axonal cytoskeleton. Such inhibition may act to prevent or decrease the degradation of cytoskeletal structures in the nerve terminal, and so provide protection for weak terminals at a synapse and growth cones of sprouting axons following partial dene

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00367.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn the central nervous system of fish and frogs, some, but not all, axons can regenerate. Retinal ganglion cells are among those that can. The retinae of fish and frogs produce new retinal neurons, including ganglion cells, for months or years after hatching. We have evaluated the hypothesis that retinal axonal regeneration is obligatorily linked to continued production of new ganglion cells.We used bromodeoxyuridine immunocytochemistry to assess retinal neurogenesis in juvenile, yearling, and 10 year oldXenopus laevis.Retinal ganglion cell genesis was vigorous in the marginal retina of the juveniles, but in the yearlings and the 10 year olds, no new ganglion cells were produced there. Cellular proliferation in the central retina was evident at all three ages, but none of the cells produced centrally were in the ganglion cell layer.Regeneration was examinedin vivoby cutting one optic nerve and then, weeks later, injecting the eye with tritiated proline. Autoradiographs of brain sections showed that the optic nerves of all three ages regenerated. Regenerationin vitrowas assessed using retinal explants from frogs of all three ages. In all cases, the cultures produced neurites, with some age‐specific differences in the patterns of outgrowth.We conclude that retinal axonal regeneration is not linked obligatorily to maintained neurogenesi

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00368.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractSpontaneous saccadic eye movements were recorded in seven head‐restrained pigmented rats by means of a phase detection search coil system, both in the light and in the dark. In an illuminated environment, all the rats made numerous spontaneous saccades with an average amplitude of 13.2 deg (±2.2 SD) and a maximal amplitude of 35 deg. In the dark, mean saccadic amplitude was significantly reduced to 9.2 deg (±2.0 SD).Saccadic peak velocity increased linearly as a function of saccadic size, with no saturation at high amplitude values. In the light, peak velocity increase was 32.7 deg/s/deg (±3.5 SD). This value is higher than that described in many other species including man and is similar to that of the monkey. Also saccadic duration increased linearly as a function of size at a rate of 1 ms/deg, which is closer to that of monkey than to that of other species including man. Both peak velocity and duration were not significantly different in the dark from those measured in the light.In the light, following a saccadic gaze shift, the rats were able to maintain a steady eye position for long periods, also at large orbital eccentricities. In the dark, on the contrary, the eye presented a drift towards the central position in the orbit. Such a drift had an exponential‐like time course with a time constant of 1567 ms (±829 SD), a value which is much shorter than that of cat and primates. This indicates that in the absence of a visual input, the rat has a poor gaze holding ability compared to other

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00369.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRats with different degrees of microencephaly were obtained by injecting pregnant mothers with methylazoxymethanol acetate (MAM) at gestational days 13.5 or 16.5. Specific markers for cholinergic (choline acetyltransferase, ChAT), GABAergic (glutamate decarboxylase, GAD), and glutamatergic (D‐3H aspartate high affinity uptake) neurons, were measured in several brain regions (cortex, hippocampus, anterior and posterior striatum, medial septum plus nucleus of the diagonal band, globus pallidus) in young and adult microencephalic rats. In adult rats born to mothers injected with MAM at gestational day 16.5 (G 16.5) ChAT level was increased in the cortex, hippocampus and striatum but decreased in the septal complex; GAD was decreased in the globus pallidus and, to a little extent, in the hippocampus while D‐3H aspartate uptake was decreased in the striatum. One month old rats belonging to the same group showed comparable differences with the exception of larger increase of ChAT in the cortex and striatum. In adult rats born from mothers injected with MAM at gestational day 13.5 (G13.5) differences in the cholinergic marker were in general less pronounced; GAD was not decreased in the globus pallidus and D‐3H aspartate uptake was unchanged in the striatum but significantly decreased in the hippocampus. The results are correlated with morphological brain alterations caused by differentially timed MAM treatment and with available information on the generation time of various neuronal populations. They show that the balance between different neurotransmitter systems can be experimentally altered and suggest that MAM treatment may provide an experimental tool for studying the development of this ba

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00370.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractCalibres and microtubule contents of the non‐medullated and myelinated domains of optic nerve axons of adult rats were studied with the electron microscope. The cross‐sectional areas of the non‐medullated domain was 0.25 μm2, and that of the myelinated domain 0.40 μm2, that is, greater by 59%. The increase in size was uneven across the axonal population; it was marked in fine and medium sized axons, and modest in the largest axons. The number of microtubules increased with axonal size; the density, however, decreased from 85 mirotubules/μm2axons to about 20 in 1.2 μm2axons. In axons of equal cross sectional area, the microtubular density of the myelinated and non‐medullated domains was the same. Microtubular density values of optic axons resemble those of dorsal roots more than those of peripheral nerve axons of equal calibre. The facts that optic axons increase in size and gain microtubules behind the eyeball while the microtubular packing decreases suggest a local regulation of the axonal c

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1989.tb00371.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY