Desynchronization of carbachol-induced theta-like activities by alpha-adrenergic agents in guinea pig hippocampal slices

The effect of alpha-adrenergic agents on theta-like activity (TLA) in guine a-pig hippocampal slices was studied. TLA was induced by a cholinergic agen t, carbachol. TLA had a frequency of 4.66 +/- 0.08 Hz (mean +/- S.E.M.) and an amplitude of 96.3 +/- 8.3 mu V in the dentate gyrus (DG). The alpha-adr energic agents epinephrine and clonidine increased the frequency and decrea sed the amplitude of TLA in a concentration-dependent manner. The agents al so increased antidromic and orthodromic population spike (PS) amplitudes of the granule cells, but did not have any effect on population EPSP. Another alpha-adrenergic agent, guanabentz, had the same effect as clonidine. The adenylate cyclase inhibitor SQ22536 suppressed the increase in PS amplitude by clonidine. The results suggest that these alpha(2)-adrenergic agents fa cilitate the activity of granule cells through the activation of the alpha( 2)-adrenoreceptor and cAMP pathway, and the facilitation causes the desynch ronization of TLA. (C) 1999 Elsevier Science Ireland Ltd. All rights reserv ed.