The ventral spino-olivocerebellar system in the cat. IV. Spinal transmission after administration of clonidine and L-dopa.

1. The transmission from the flexor reflex afferents (FRA) to the spino-olivocerebellar paths ascending through the ventral funiculus (VF-SOCPs; Oscarsson and Sjölund, 1977) was compared with the transmission from the FRA to segmental reflex arcs in cats with the spinal cord transected in the third cervical segment sparing only the ventral funiculus on one side. The climbing fiber responses evoked in Purkinje cells by electrical stimulation of limb nerves were monitored by recording the mass activity at the cerebellar surface simultaneously from several termination zones, while the flexion reflex was recorded from a flexor nerve and the primary afferent depolarization (PAD) from a dorsal root filament. 2. Changes in the segmental reflex responses were produced by i.v. injections of l-Dopa and Clonidine. L-Dopa produced the expected depression of the flexion reflex and the FRA-induced PAD in the FRA, whereas Clonidine depressed only the flexion reflex but did not affect or even enhanced the FRA-induced PAD in the FRA. 3. The changes in transmission to one of the ascending paths, the a-VF-SOCP, parallelled that in the flexion reflex arc. The transmission to another path, the b2-VF-SOCP, parallelled that in the pathway responsible for the FRA-induced PAD in the FRA. 4. The remaining hindlimb paths, the c1- and c3-VF-SOCPs, monosynaptically activated from primary afferents, were little influenced by the changes induced in the segmental reflex arcs. 5. It is suggested that the a- and b2-VF-SOCPs carry information related to interneuronal activity in segmental centers, whereas the c1- and c3-VF-SOCPs forward information mainly related to peripheral events.