The differential effects of baclofen on segmental and descending excitation of spinal interneurones in the cat.

Intravenous baclofen (1-6.25 mg kg-1) substantially reduced the monosynaptic excitation of neurones in the intermediate nucleus of the cat spinal cord by impulses in group I extensor muscle primary afferent fibres, but had little or no effect on excitation by stimulating fibres of the ipsilateral dorsolateral funiculus or the contralateral red nucleus. Relatively low concentrations of baclofen thus appear not to influence the release of excitatory transmitter from the terminals of rubrospinal, corticospinal and long descending propriospinal fibres, in contrast to the reduction of the release of primary afferent transmitters.