Intra-accumbal infusions of cholecystokinin and enkephalin modulate amphetamine-induced locomotor behavior

Abstract

Rats receiving intra-accumbal infusions of 10 ng cholecystokinin (CCK) and/or 1 ng met-enkephalin (ENK) were subsequently injected with d-amphetamine (AMPH) and observed for 100 min in an open field. Rears, numbers of lines crossed, and locomotor stereotypy (using the new gamma statistic) were measured. In the absence of AMPH, rats infused with CCK and/or ENK did not differ from AMPH controls on any behavioral measures. AMPH increased the numbers of rears and lines crossed, and also induced stereotypic patterns of locomotions. In AMPH treated rats however, CCK reduced the number of lines crossed and potentiated locomotor stereotypy. ENK had no effect when given with AMPH, but when administered with both CCK and AMPH, ENK blocked the potentiating effect of CCK on AMPH-induced locomotor stereotypy. These results indicate that ENK interacts with CCK in nucleus accumbens to modulate amphetamine-induced locomotor stereotypy. Moreover, the behavioral effects of ENK in nucleus accumbens are limited to specific aspects of locomotor behavior since it produced no changes in lines crossed. The results of this study contribute to an ongoing investigation into locomotor stereotypy and into the behavioral effects of peptide-transmitter interactions in brain.