The interrelationship between superior colliculus and substantia nigra pars reticulata in programming movements of cats.

Recent electrophysiological and behavioural studies have suggested that the deeper layers of the superior colliculus (dl-SC) are involved in the execution of targeting movements which are elicited but not continuously guided by external stimuli. In the first part of the present study the role of the GABAergic transmission in the dl-SC in the execution of these targeting movements was investigated. Therefore cats, trained to walk from one side of a narrow bar towards the target at the other side of the bar under stroboscopic illumination (2 flashes/s), were injected bilaterally in the dl-SC with picrotoxin (100 ng/0.5 microliter) or muscimol (75 ng/1 microliter). In the second part of this study the role of the GABAergic activity in the substantia nigra pars reticulata (SNR), projecting to the dl-SC through the GABAergic nigrotectal pathway, in the execution of the above-mentioned targeting movements was investigated. Therefore cats, trained to walk from one side of a narrow bar towards the target at the other side of the bar, either under full light or under stroboscopic illumination (2 flashes/s), were bilaterally injected in the SNR with picrotoxin (500 ng/0.5 microliter) or muscimol (200 ng/1 microliter). Under stroboscopic illumination (2 flashes/s) solvent-treated cats either continuously grasped the bar and/or continuously touched the bar with their whiskers, i.e. they executed movements which were continuously guided by external stimuli, while walking towards the target at the other side of the bar.(ABSTRACT TRUNCATED AT 250 WORDS)