Abolition of spinal motor disturbance by injections of dopamine receptor agonists, atropine and GABA into the caudate nucleus

Abstract

Reflex activity of α- and γ-motoneurones was recorded from ventral root filaments in rats. Intravenous reserpine. as well as bilateral injections of nicotine or muscarine, into the caudate nuclei, or of 6-hydroxydopamine (6-OH-DA) into the substantia nigra, increased the α-reflex discharges and reduced the α-reflex latency and the γ-reflex discharges. Bilateral intranigral injections of GABA and procaine produced similar changes in α, but not in γ-reflex activity. Bilateral intracaudate injections of dopamine receptor agonists (dopamine, apomorphine) and of atropine abolished this disturbance of spinal motor activity. In rats injected with 6-OH-DA into the substantiae nigrae of both sides, dimethylaminoadamantane (DMAA) and GABA injected bilaterally into the caudate nuclei normalized only the α-reflex activity. The results may be interpreted in terms of a nigro-striatal feedback system which controls spinal motor activity and consists of dopaminergic, cholinergic and GABA neurones. It seems that α- and γ-motor activity is influenced by more than one outlet from the system and, thus, by different descending pathways.