The effects of unilateral intranigral injections of substance P and the newly discovered tachykinin, substance K, were compared using a rotometer to measure circling behaviour in rats. Various solutions were injected directly into the right substantia nigra pars reticulata (SNR), via chronically implanted guide cannulae. Substance P, substance K, apomorphine and saline were administered sequentially in each rat. This repeated measures design allowed for comparisons to be made with respect to the effects of each solution on circling. Separate groups were formed so that three different concentrations of substance P and substance K could be tested (Groups A, B, C received 8, 12 16 ug / .5 ul, in that order). Groups A, B, and C were pretreated with d-amphetamine, while Group D was not. All groups also received intranigral injections of apomorphine (15 ug / .5 ul) and saline. At a concentration of 12 ug, substance K significantly increased the amount of contralateral circling when compared with the effects of control administrations. These are the first data to indicate that substance K can elicit contraversive circling when administered unilaterally into the SNR. Concentrations of eight and 16 ug of substance K did not significantly increase contralateral circling. None of the three doses of SP elicited significantly more circling than did the saline. Apomorphine was ineffective at increasing circling in three groups, while it significantly increased contraversive circling in one group. In examining the results of the experiment, the effects of each solution are discussed. Explanations that may serve to clarity inconsistencies are proposed, and an effort is also made to reconcile these results with those reported in the relevant literature
