The transient potassium current, the A-current, is involved in spike frequency adaptation in rat amygdala neurons

Abstract

The possible functional roles of the transient K + current, I A, in basolateral amygdala (BLA) neurons were studied using a rat brain slice preparation and conventional intracellular recording techniques. Conditioning depolarization, which inactivates I A slowed the action potential repolarization while conditioning hyperpolarization accelarated the action potential repolarization. 4-Aminopyridine (4-AP, 100 μM), a specific I A antagonist, also caused a clear delay in spike repolarization similar to the effect of conditioning depolarization suggesting that I A is involved in the action potential repolarization. When BLA neurons were excited by injecting long depolarizing current pulses (500 ms), they responded with an initial rapid discharge of action potentials which slowed or accommodated; an afterhyperpolarization (AHP) followed the depolarizing current pulses. Superfusion of 4-AP (100 μM) blocked accommodation resulting in an increase in action potential discharge in 74% (32 out of 43) neurons tested. The remaining 11 cells responded with an increased frequency of discharge of the first few action potentials. Unlike the effect of cadmium (Cd 2+, 100 μM), a calcium channel blocker, 4-AP did not reduce the AHP. In the presence of norepinephrine (NE, 10 μM), a neurotransmitter which has been shown to block calcium-activated potassuim conductance, 4-AP caused a further increase in the number and frequency of action potential discharge. In addition, in BLA neurons, spontaneous interictal and ictal-like events were observed at low and high concentrations of 4-AP, respectively. We conclude that I A is involved in the action potential repolarization as well as spike frequency adaptation in BLA neurons and that these actionsmay contribute to the convulsant effect of 4-AP