Inhibition of muscarinic receptor- and G-protein-dependent phosphoinositide metabolism in cerebrocortical membranes from neonatal rats by ethanol.

Phosphoinositide (PtdIns) metabolism activated by cholinergic muscarinic receptors appears to play a role in brain development and has been recently suggested as a possible biochemical target for the developmental neurotoxicity of ethanol (EtOH). Recent experimental evidence indicates that, in rat brain, muscarinic receptor stimulation is coupled to PtdIns hydrolysis through regulatory GTP-binding proteins (G-proteins). We investigated the effect of various alcohol concentrations (10-500 mM) on guanine nucleotide-, fluoride-, and muscarinic-dependent PtdIns hydrolysis in [3H]inositol-labelled cerebral cortical membranes from neonatal (7-day-old) and adult rats. At both ages, EtOH exerted slight inhibitory effects on GTP(S) (100 microM)- and NaF (5 mM)-induced [3H]inositol phosphates accumulation. The presence of GTP(S) was necessary to unmask the stimulatory effect of the muscarinic agonist carbachol. Under these experimental conditions EtOH markedly inhibited carbachol (100 microM)-induced PtdIns hydrolysis. This effect was concentration-dependent and was more pronounced in the cortex from immature animals, where a statistically significant inhibition was observed at EtOH concentrations as low as 50 mM, comparable to the hematic concentrations reached following in vivo administration of doses of ETOH able to induce developmental neurotoxicity. These results confirm that EtOH exerts an age-specific inhibition of muscarinic-dependent PtdIns metabolism and suggest that this action might be exerted through an interaction with receptor-G-protein coupling.