Effects of the systemic administration of kainic acid and NMDA on exploratory activity in rats

In spite of growing evidence for the involvement of the glutamatergic system in mammal's locomotion, studies on behavioral effects induced by the systemic administration of excitatory amino acids not associated to convulsions are lacking. In the present work, the effect of one single systemic administration of kainic acid (KA) (9 mg/kg, IP) or NMDA (100 mg/kg, IP) on exploratory activity in the rat during 6 consecutive days was studied. Separation of exploratory activity in fast (FM) and slow movements (SM) and rearings (R), together with the analysis of those variables during both the light and dark periods of the light-dark cycle, allowed finding specific drug-induced effects. KA produced an acute short-lasting increase in exploratory activity, only significant for FM. On the other hand, NMDA produced an acute short-lasting depressant effect on FM, SM, and R, followed during the next 2 days by a long-lasting increase in exploratory activity, only significant for FM during the dark period. These results underline the importance of using repeated testing during both light and dark periods of the light-dark cycle when analyzing drug-induced changes on exploratory activity.