Frequency-dependent block of field potentials in the rat hippocampal slice caused by tricyclic antidepressants

The effect of the tricyclic antidepressants imipramine and desipramine were studied on field potentials in the rat hippocampal slice. The electrically evoked stratum radiatum nerve volley, excitatory postsynaptic potential (e.p.s.p.) and pyramidal cell layer population spike (PS) were recorded in the CA1 region. At concentrations of 10(-6)M to 10(-5)M, impramine did not affect the amplitude of the nerve volley, e.p.s.p. or PS at low frequencies of stimulation (0.01 Hz). At higher frequencies of stimulation (1-100 Hz), imipramine caused a frequency-dependent block of the nerve volley, e.p.s.p. and PS. The time course of onset of the frequency-dependent block in the presence of imipramine was very slow. Maximum inhibition was reached after 3-4 h treatment with imipramine. Desipramine (10(-6)-10(-5)M) also caused a frequency-dependent block of the hippocampal field potentials. Only slight frequency-dependent block was observed in slices from rats injected in vivo with desipramine (10 mg kg-1) for 14 days.