HIPPOCAMPAL THETA-ACTIVITY AFTER SYSTEMIC ADMINISTRATION OF A NONPEPTIDE DELTA-OPIOID AGONIST IN FREELY-MOVING RATS - RELATIONSHIP TO D-1 DOPAMINE-RECEPTORS

Hippocampal theta activity was acquired and processed off-line from di gitized EEG recordings after subcutaneous (s.c.) administration of the non-opioid delta agonist BW 373U86 (0.5-2.5 mg/kg) in freely-moving r ats. Relative theta power spectral analysis, implemented by a signal p rocessing software, showed that BW 373U86 induced a dose-dependent inc rease in the slow component of theta band (Type 2 theta), while moveme nt-related fast theta band (Type 1 theta) failed to show significant c hanges, Moreover, the increase in relative Type 2 theta power showed a maximal change at 1 mg/kg of BW 373U86, while higher doses, although effective in increasing relative Type 2 theta, induced locomotion and irregularly increased Type 1 hippocampal theta activity. The administr ation of 10.0 mg/kg of the delta antagonist Naltrindole (NLI) 30 min b efore BW 373U86, abolished hippocampal Type 2 theta increase. The rise of relative Type 2 theta power induced by BW 373U86 (1-2.5 mg/kg) was greatly attenuated by 0.1 mg/kg of the selective dopamine (DA) D-1 an tagonist SCH 23390. Administration of 0.1 mg/kg of SCH 23390 alone did not modify hippocampal Type 2 theta. These results indicate that delt a receptors modulate the expression of hippocampal Type 2 theta and do pamine, through D-1 receptors, exerts a permissive role on this influe nce. (C) 1997 Elsevier Science B.V.