Neurochemical correlates of differences in responses to psychotropic drugs. I. Apomorphine and morphine effects on locomotor activity of C57/BL and Balb/C mice.

C57/BL mice have higher basal locomotor activity than Balb/C mice and react to apomorphine (4 mg/kg) and morphine (20 mg/kg) with motor stimulation, while in Balb/C mice this dose of apomorphine depressed the basal locomotor activity and morphine did not affect it. No differences in the characteristics of opiate mu and delta receptors in the whole brain of mice of both strains were found, but the responsiveness of the central alpha-adrenoceptor system, as measured with the accumulation of inositol phosphate in brain slices after exposure to noradrenaline was different: the low concentrations of noradrenaline (5 microM) produced stronger effect in Balb/C mice, but the maximum responses tended to be stronger in C57/BL mice.