Behavioral correlates of a progressive dysfunctioning of the deeper layers of the colliculus superior: effects of picrotoxin.

Intracaudate injections of relatively high doses of apomorphine produce a regression in motor behavior of cats collecting food pellets in a treadmill design (25). It has been hypothesized that this regression is partly due to functional disturbances in brain regions receiving (in) directly striatal output signals. In view of this hypothesis it was investigated whether experimentally induced changes in GABAergic activity within the deeper layers of the colliculus superior, which is a second order output station of the caudate nucleus, are also able to elicit a regression in motor behavior. Therefore, motor behavior of cats was tested in the treadmill paradigm before and after intracollicular injections of the GABA antagonist picrotoxin. Picrotoxin produced dose-dependently a regression in motor behavior which was comparable to that elicited by intrastriatally injected apomorphine. The noted effects were GABA-specific since muscimol attenuated the picrotoxin-induced regression. The present data are discussed in view of a model for a hierarchical organization of the brain.