CONDITIONED AND UNCONDITIONED FORELIMB REFLEX SYSTEMS IN THE CAT - INVOLVEMENT OF THE INTERMEDIATE CEREBELLUM

Temporary inactivation of the cerebellar interposed nuclei was used to assess the role of the intermediate cerebellum in the performance of forelimb cutaneomuscular reflexes in the cat. The following types of r eflexive responses were evaluated: the classically conditioned and unc onditioned forelimb withdrawal responses and the forelimb tactile plac ing, hopping and magnet responses. The experiments tested the hypothes is that the intermediate cerebellum is involved in the performance of all the above forelimb reflexes. The forelimb withdrawal reflex was cl assically conditioned in a newly developed paradigm in which animals w ere first operantly conditioned to stand on four elevated platforms. T rained animals were microinjected with a gamma-aminobutyric acid (GABA ) agonist, muscimol, in the interposed nuclei, and the effects of inac tivation of the intermediate cerebellar output on the forelimb reflexe s were examined. The main findings of these experiments are that unila teral muscimol inactivation of the interposed nuclei in the cat abolis hed the expression of the classically conditioned limb flexion reflex, suppressed the performance of the unconditioned withdrawal reflex and , in parallel, downregulated the tactile placing, hopping and magnet p ostural responses in the ipsilateral forelimb. These observations are inconsistent with concepts indicating exclusive involvement of the int ermediate cerebellum in the classically conditioned reflexes elicited by aversive stimuli. On the contrary, they support the hypothesis of a more global involvement of this structure in learned and unlearned de fensive flexion reflexes and in automatic postural response systems.