Conditioned and unconditioned forelimb reflex systems in the cat: involvement of the intermediate cerebellum |
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Authors: | F P Kolb K B Irwin J R Bloedel V Bracha |
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Institution: | (1) Institute of Physiology, University of Munich, Munich, Germany, DE;(2) Barrow Neurological Institute, 350 W. Thomas Road, Phoenix, AZ 85013, USA; Tel: +1 (602) 406 3220, Fax: +1 (602) 406 4172, e-mail: vbracha@mha.chw.edu, US |
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Abstract: | Temporary inactivation of the cerebellar interposed nuclei was used to assess the role of the intermediate cerebellum in
the performance of forelimb cutaneo-muscular reflexes in the cat. The following types of reflexive responses were evaluated:
the classically conditioned and unconditioned forelimb withdrawal responses and the forelimb tactile placing, hopping and
magnet responses. The experiments tested the hypothesis that the intermediate cerebellum is involved in the performance of
all the above forelimb reflexes. The forelimb withdrawal reflex was classically conditioned in a newly developed paradigm
in which animals were first operantly conditioned to stand on four elevated platforms. Trained animals were microinjected
with a γ-aminobutyric acid (GABA) agonist, muscimol, in the interposed nuclei, and the effects of inactivation of the intermediate
cerebellar output on the forelimb reflexes were examined. The main findings of these experiments are that unilateral muscimol
inactivation of the interposed nuclei in the cat abolished 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 postural responses in the ipsilateral forelimb. These observations are inconsistent with concepts indicating exclusive
involvement of the intermediate 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 defensive flexion reflexes
and in automatic postural response systems.
Received: 29 July 1996 / Accepted: 26 September 1996 |
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Keywords: | Withdrawal reflex Classical conditioning Posture Interposed nucleus Cerebellum |
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