Abstract
Alcohol during brain development leads to the widespread neuronal death observed in fetal alcohol spectrum disorders (FASD). In comparison, the mature brain is less vulnerable to alcohol. Studies into maturation-acquired alcohol resistance uncovered a protective mechanism that reduces alcohol-induced neuronal death through nitric oxide-cGMP-cyclic GMP-dependent protein kinase (NO-cGMP-cGK) signaling. However, the downstream processes underlying this neuroprotection remain unclear. Alcohol can disrupt levels of intracellular calcium ([Ca(2+)](i)) in vulnerable neuronal populations to trigger cell death in both in vivo and in vitro models of FASD. Since cGK has been demonstrated to regulate and inhibit intracellular Ca(2+) release, we examined the hypothesis that cGK confers alcohol resistance by preventing [Ca(2+)](i) disruptions. Alcohol resistance, determined by neuronal survival after 24 h of alcohol exposure, was examined in primary cerebellar granule neuron (CGN) cultures derived from 5 to 7 day-old neonatal mice with an activator, 8-Br-cGMP, and/or an inhibitor, Rp-8-pCPT-cGMPS, of cGK signaling. Intracellular Ca(2+) responses to alcohol were measured by ratiometric Ca(2+) imaging in Fura-2-loaded CGN cultures after 8-Br-cGMP treatment. Our results indicate that activating cGK with 8-Br-cGMP before alcohol administration provided neuroprotection, which the cGK inhibitor, Rp-8-pCPT-cGMPS, blocked. Alcohol exposure elevated [Ca(2+)](i), whereas 8-Br-cGMP pretreatment reduced both the level of the alcohol-induced rise in [Ca(2+)](i) as well as the number of cells that responded to alcohol by increasing [Ca(2+)](i). These findings associate alcohol resistance, mediated by cGK signaling, to reduction of the persistent and toxic increase in [Ca(2+)](i) from alcohol exposure.