Peripheral maps and synapse elimination in the cerebellum of the rat. II. Representation of peripheral inputs through the climbing fiber pathway in the posterior vermis of X-irradiated adult rats.
The present study gives a detailed description of the functional characteristics and of the topographic distribution of responses mediated through the climbing fiber (CF) pathway in the cerebellum of adult rats which have been repeatedly irradiated from birth so that the Purkinje cells (PCs) in the adult remained innervated by several climbing fibers instead of one. Experiments were carried out under urethane anaesthesia. After electrical stimulation of the contralateral snout, the ipsilateral and contralateral hindlimb or forepad, and the tail, CF-EPSPs were recorded from PCs in an area extending 1000 microns laterally to the midline in the vermal part of lobules VII and VIII. The stepwise variation of CF-EPSP amplitude demonstrated the multiple innervation of the PCs by CFs in these animals. The responses of a given PC through separate CFs were analyzed separately and, using precise micromapping techniques and computer analysis, cells were located on the map of the unfolded PC layer. Taking into account the mean latency of the responses and the probability of discharge of the PCs, restricted areas of projection were found for the snout, the forepads and the tail. Zones of short-latency responses formed compact patches of approximately 1 mm2. Their disposition was very similar to that found in normal rats. The responses evoked through the different CFs converging on a given PC were in general very homogeneous and very similar to those recorded in control rats. There was some overlap of projection zones from tail and snout and from forepads and snout. In this latter case, there was a convergence of several peripheral inputs on some of the PCs tested. No precise projection of the hindlimbs could be detected in the same lobules. These results suggest that, with the type of stimulation used, the representation of peripheral inputs through CF pathway is roughly conserved even though multiple innervation of PCs by CFs is maintained until adulthood.
Mariani
J
J
Laboratoire de Neurophysiologie Ontogénétique et Unité Associée au CNRS No. 1199, Université Pierre et Marie Curie, Paris, France.
Mulle
C
C
Geoffroy
B
B
Delhaye-Bouchaud
N
N
D000200:Action Potentials; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D002452:Cell Count; D002531:Cerebellum / Q000502:physiology / Q000528:radiation effects*; D004558:Electric Stimulation; D009475:Neurons, Afferent / Q000502:physiology*; D011689:Purkinje Cells / Q000502:physiology / Q000528:radiation effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D013569:Synapses / Q000502:physiology / Q000528:radiation effects*