Interictal changes in behavior and cerebral metabolism in the rat: opioid involvement

Interictal changes in locomotor and shock-response behaviors were examined in rats that were kindled unilaterally or bilaterally in the amygdala. 2-Deoxyglucose and naloxone were used to test whether alterations in cerebral glucose metabolism or opioid functioning, respectively, correlated with changes in these behaviors. Bilaterally kindled rats, at 14 to 28 days after their last seizure, displayed increased locomotion (square crossing) in an open field compared with unilaterally kindled or control rats. Bilaterally kindled rats also showed elevated thresholds for the elicitation of a multiple squeak response to tail shocks. Single squeak or tail withdrawal responses to tail shock were not affected by bilateral kindling. Likewise, unilaterally kindled rats did not differ from controls on any of the behavioral measures. Naloxone (10 mg/kg, i.p.) reversed the increase in locomotion and elevation of multiple squeak thresholds in the bilaterally kindled rats. By itself, naloxone did not influence any of the behaviors. Finally, cerebral glucose metabolism was decreased, globally, in the forebrain of the bilaterally kindled rats, and naloxone normalized this change. Cerebral metabolism was not altered in unilaterally kindled rats compared with controls. Thus, changes in cerebral metabolism and opioid functioning may be involved in the mediation of interictal changes in locomotor and emotional behavior in rats.