Rate dependent inhibition of self-stimulation by apomorphine.

The effect of three doses of apomorphine 0.125, 0.25 and 0.5 were studied on self-stimulation generated by three levels of current intensity. Eight rats exhibited overall dose dependent decreases in self-stimulation obtained at the two lowest current intensities. Self-stimulation at the highest current intensity, however, was unaffected by even the highest dose level of apomorphine (0.5 mg/kg) despite typical signs of stereotypy exhibited by the rats in their home cages. Additionally, self-stimulation obtained under the 0.5 mg/kg dose of apomorphine under went extinction when reinforcement was discontinued. Thus, brain stimulation can be an effective reinforcement when an animal is given a stereotypy inducing dose of apomorphine if the current intensity is of sufficient magnitude and if the response manipulandum is not compatible with stereotypic responses. These observations appear consistent with a dopaminergic involvement in the response rather than reinforcement aspect of self-stimulation.