USE-DEPENDENT EFFECTS OF ACUTE AND CHRONIC TREATMENT WITH IMIPRAMINE AND BUSPIRONE ON EXCITATORY SYNAPTIC TRANSMISSION IN THE RAT HIPPOCAMPUS IN-VIVO

The effects of acute and long-term treatment with imipramine and buspi rone on the responses of mt hippocampal neurones to low and high frequ ency electrical stimulation were compared. Whereas acute treatment wit h imipramine (10 mg/kg, i.p.) had no effect on synaptic responses to l ow frequency stimulation, chronic treatment for 14 days significantly reduced the amplitude of the field excitatory postsynaptic potential. Both acute and chronic imipramine treatment markedly reduced the ampli tude of the nerve volley and excitatory postsynaptic potential evoked at high frequency stimulation rates in a use-dependent manner. Buspiro ne (0.5-3 mg/kg, i.p.) produced a significant reduction of the excitat ory postsynaptic potential at high frequencies. This was enhanced afte r repeated administration of a dose of 0.5 mg/kg for 14 days. We previ ously reported a similar effect of buspirone at low frequency stimulat ion. Both compounds therefore share the ability to exert strong depres sant effects on transmission in the hippocampus especially after chron ic treatment.