Movements of cats on a rotating cylinder: role of the substantia nigra pars reticulata and the deeper layers of the superior colliculus.

Recently it has been shown that the substantia nigra pars reticulata (SNR) is required for adjusting the body position. In this study the role of the SNR in the execution of movements was investigated. Therefore, the effects of bilateral SNR injections of picrotoxin (500 ng/0.5 microliter) and muscimol (200 ng/1 microliter) were investigated on movements of cats which were trained to cross a rotating cylinder. SNR injection of picrotoxin suppressed the movements that were executed by cats injected with distilled water (0.5 microliter), i.e. 'normal movements'. While crossing the rotating cylinder, picrotoxin-injected cats mainly executed movements that almost never occurred in distilled water treated cats. Picrotoxin-injected cats executed 'special movements', i.e. forward locomotion in which the hindlimbs were affected, and 'counter-movements'. While executing the latter movements no forward locomotion occurred at all; the cats solely executed lateral fore- and hindlimb movements opposite to the direction in which the cylinder rotated. SNR application of muscimol enhanced the execution of 'normal movements'. Since the SNR sends information to the deeper layers of the superior colliculus (dl-SC) via GABAergic fibers, it was also investigated whether pharmacological stimulation (muscimol) and inhibition (picrotoxin) of the GABAergic dl-SC activity affected these movements on the rotating cylinder: no changes were observed after injecting otherwise effective doses of muscimol (75 ng/1 microliter) and picrotoxin (100 ng/0.5 microliter). In order to compare the function of the SNR and dl-SC in programming a different type of movements, the effects of GABAergic agents in the dl-SC (picrotoxin 100 ng/0.5 microliter and muscimol 75 ng/1 microliter) and the SNR (picrotoxin 500 ng/0.5 microliter and muscimol 200 ng/1 microliter) were investigated on the feline ability to execute goal-directed movements in an experimental set-up that prevented the occurrence of targeting movements which were continuously guided by external, i.e. auditory, visual, tactile and olfactory stimuli. For that purpose cats were trained to step out of a startbox on a rotating cylinder, i.e. the target. Dl-SC injection of muscimol or SNR application of picrotoxin prevented the cats from stepping out of the startbox on the rotating cylinder. In contrast, cats injected with muscimol into the SNR or picrotoxin into the dl-SC stepped out of the startbox, although dl-SC application of picrotoxin elicited forelimb misplacements: frequently the cats placed their forelimbs alongside of, but not on the cylinder when trying to leave the startbox.(ABSTRACT TRUNCATED AT 400 WORDS)