Differential effects of corticosterone on the sAHP in the basolateral amygdala and CA1 region: Possible role of calcium channel subunits

The stress hormone corticosterone increases the amplitude of the slow afterhyperpolarization 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. In the amygdala, corticosterone does not change the afterhyperpolarization amplitude, nor any of the passive and active membrane properties studied. The lack of effect on the afterhyperpolarization is surprising since in both areas corticosterone increases highvoltage activated sustained calcium currents, which supposedly regulate the slow afterhyperpolarization. We wondered if corticosterone targets different calcium channel subunits in the two areas, as currents through only one of the subunits (Cav1.3) is thought to alter the afterhyperpolarization 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 to vehicle treatment. In the basolateral amygdala, 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 afterhyperpolarization in CA1 and amygdala neurons. A differential distribution and transcriptional regulation of Cav1.2 and Cav1.3 in the CA1 area versus basolateral amygdala partly explains the observed differences on afterhyperpolarization amplitude. The functional implication of these findings could be that stress-induced arousal of activity in the basolateral amygdala is more prolonged than in the CA1 hippocampal area, so that information with an emotional component is more effectively encoded. Page 2 of 40