INVOLVEMENT OF DOPAMINE AND EXCITATORY AMINO-ACID TRANSMISSION IN NOVELTY-INDUCED MOTOR-ACTIVITY

The increase in locomotor activity expressed by rats in a novel enviro nment demonstrates individual variability, and the present study evalu ated an hypothesis that the variability resides, in part, in differenc es in neurotransmission in the nucleus accumbens, ventral tegmental ar ea or ventral pallidum. Rats were divided into equal groups expressing either a high or low response in a novel open field. Subsequently, do pamine, the excitatory amino acid agonist lpha-amino-3-hydroxy-5-methy lisoxazole-4-propionic acid (AMPA) or the mu opioid agonist [D-Ala(2), MePhe(4), Gly-ol(5)] enkephalin (DAMGO) was microinjected into one of the three brain nuclei, and motor activity was monitored. All three d rugs produced a dose-dependent elevation in motor activity in all thre e brain nuclei. However, the motor response elicited by dopamine in th e ventral pallidum and nucleus accumbens was significantly greater in the rats demonstrating a high locomotor response to novelty. Similarly , the motor response elicited by AMPA in the ventral pallidum, nucleus accumbens or ventral tegmental area was enhanced in the high versus l ow responding rats. In contrast, at no dose and in no brain nucleus wa s the motor response to DAMGO different between high and low respondin g rats. These data indicate that alterations in dopamine and excitator y amino acid but not enkephalin neurotransmission in the ventral palli dum, nucleus accumbens and ventral tegmental area are associated with differences in motor activity expressed by animals in a novel environm ent.