EFFECT OF ADRENALECTOMY IN KINDLED RATS

It has previously been observed that adrenalectomy (ADX) increases the amplitude of transient Ca currents in CA1 hippocampal neurons. In the present study, the effect of ADX on cellular properties of CA1 neuron s was investigated under conditions that challenge the CA1 network, i. e. in fully kindled rats, 5-6 weeks after the last kindling session. A t this time, adrenally intact kindled rats showed, in comparison to no n-kindled controls, a reduced population spike amplitude evoked in the CA1 area by Schaffer/commissural fiber stimulation, an increased ampl itude of low-threshold, transient Ca currents and a decrease of the hi gh-threshold, sustained Ca currents. As observed before, ADX in non-ki ndled rats increased the amplitude of transient Ca currents while sust ained Ca currents were not affected. In kindled rats, ADX did not incr ease the transient Ca current amplitude beyond the level reached by ki ndling alone. The kindling-induced reduction of the sustained Ca curre nt was partly normalized after ADX. Field responses of kindled rats we re not affected by ADX. These data support the view that lack of adren al hormones does not exacerbate but, to some extent, normalizes the ki ndling-induced changes in cellular properties and network function of the CA1 area. The hormonal effects on kindling may be reciprocal in na ture, since kindling, in turn, was found to affect the stress response and the corticosteroid receptor mRNA expression in the hippocampus.