ELECTROPHYSIOLOGICAL ANALYSIS OF CIRCUITRY AND OF CORTICONUCLEAR RELATIONSHIPS IN AGRANULAR CEREBELLUM OF IRRADIATED RATS

  • 1 January 1976
    • journal article
    • research article
    • Vol. 114  (1) , 49-74
Abstract
The cerebellar circuitry and the corticonuclear relationships were studied in the cerebellum of adult rats rendered agranular through 7 successive exposures to X-ray radiations during infancy. Electrical responses induced in Purkinje cells (PC) and neurons of the lateral vestibular nucleus (LVN) by cerebellar and spinal stimulations were recorded. In irradiated rats, PC exhibited antidromic activation with a high axonal threshold and 70% of them also presented typical climbing fiber responses (CFR). They seldom exhibited responses via the mossy fiber (MF)-granule cell pathway, but 2 other classes of responses were identified: short latency single spike responses attributed to a direct excitatory impingement of MF onto PC; and atypical CFR formed of high frequency bursts of simple spikes which were seen in 76% of PC tested. Of these cells, 53% also presented typical CFR, strongly suggesting these PC were innervated by more than 1 CF and confirming previous data on the same type of agranular cerebellum. In the LVN neurons of control and irradiated rats, spinal and cerebellar stimulations evoked clear cut IPSP [inhibitory postsynaptic potential]. On the basis of their shape, latency and occurrence in animals with or without cerebellum and with or without lesion of the CF pathway, they were interpreted as mediated through direct or synaptic activation of PC or through an extracerebellar pathway. In irradiated rats, the quantitative study of these IPSP gave further arguments in favor of multiinnervation of PC by CF and of an important reafferentation of MF onto PC. The functional efficiency of this reafferentation appeared very low, as tested by activation of MF originating in the spinal cord. The intracellular recording of LVN neurons showed that a large majority of PC axons retained normal synaptic connections with nuclear cells in treated animals, indicating that corticonuclear relationships do not markedly depend upon granule cells and normal CF input.