VOLTAGE-CLAMP ANALYSIS OF THE EFFECTS OF CLASSICAL-CONDITIONING ON THE HIPPOCAMPUS

1. Effects of nictitating membrane conditioning on K+ currents of CAl pyramidal cells of rabbit hippocampus were studied by the use of the single-electrode voltage-clamp (SEVC) technique. 2. I(Q), I(M), I(C), and I(AHP) were recorded in slices from control animals, showing behavior similar to that previously described for other preparations. I(Q) developed as an inward inactivating relaxation during hyperpolarizing pulses, from potentials slightly more positive than the resting potential (approximately -40 mV). Such depolarization is thought to activate the I(M). I(C) was recorded during long depolarizing pulses as a slow outward current. I(AHP) appeared during short depolarizing pulses as an outward current peaking at approximately 200 ms after the pulse. Progressively more positive pulses were accompanied by a linear increase of the peak I(AHP) value. The slope of the I(AHP)-voltage relation was used for comparison of cells between groups of animals that had different training experience. 3. Responses of control cells to cholinergic agents were similar to those previously characterized in other preparations. Specifically, cholinergic agonists blocked I(M) and I(AHP), partially reduced I(C), and did not affect I(Q). 4. Conditioning did not affect I(Q), I(M), and I(C) but reduced the slope values of the I(AHP)-voltage relation. This change is consistent with the conditioning-specific afterhyperpolarization (AHP) reduction previously reported. 5. The effect of conditioning on the I(AHP) but not on the I(C), both Ca2+ -dependent K+ currents, suggests a direct effect on the former, rather than a reduction of I(Ca2+) or a change in the levels of Ca(i)2+.