Differential effects of corticosterone on the slow afterhyperpolarization in the basolateral amygdala and CA1 region: possible role of calcium channel subunits.

The stress hormone corticosterone increases the amplitude of the slow afterhyperpolarization (sAHP) in CA1 pyramidal neurons, without affecting resting membrane potential, input resistance, or action potential characteristics. We here examined how corticosterone affects these properties in the basolateral amygdala (BLA). In the amygdala, corticosterone does not change the AHP amplitude, nor any of the passive and active membrane properties studied. The lack of effect on the AHP is surprising since in both areas corticosterone increases high-voltage-activated sustained calcium currents, which supposedly regulate the sAHP. We wondered whether corticosterone targets different calcium channel subunits in the two areas because currents through only one of the subunits (Cav1.3) are thought to alter the AHP amplitude. In situ hybridization studies revealed that CA1 cells express Cav1.2 and Cav1.3 subunits; corticosterone does not transcriptionally regulate Cav1.2 but increases Cav1.3 expression compared with vehicle treatment. In the BLA, Cav1.3 expression was not detectable, both after control and corticosterone treatment. Cav1.2 is moderately expressed. In a modeling study, we examined putative consequences of changes in specific calcium channel subunit expression and calcium extrusion by corticosterone for the AHP in CA1 and amygdala neurons. A differential distribution and transcriptional regulation of Cav1.2 and Cav1.3 in the CA1 area versus BLA partly explain the observed differences in AHP amplitude. The functional implication of these findings could be that stress-induced arousal of activity in the BLA is more prolonged than that in the CA1 hippocampal area, so that information with an emotional component is more effectively encoded.