INHIBITION BY ETHANOL OF EXCITATORY AMINO-ACID RECEPTORS IN RAT LOCUS-COERULEUS NEURONS IN-VITRO

Intracellular recordings were made in a pontine slice preparation of t he rat brain containing the nucleus locus coeruleus (LC). In a first s eries of experiments, various parameters of spontaneous action potenti als were evaluated. It turned out that ethanol (100 mM) does not alter the firing rate, the spike amplitude and the afterhyperpolarization f ollowing a spike. In subsequent experiments, the generation of action potentials was prevented by passing continuous hyperpolarizing current via the recording electrode. Under these conditions, ethanol (100 mM) had no effect on the membrane potential or input resistance. Pressure -applied N-methyl-D-aspartate (NMDA), lpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA) and alpha,beta-methylene ATP (alpha,bet a-meATP) reproducibly depolarized LC neurons. While ethanol (100 mM) d epressed the NMDA-and AMPA-induced depolarization to a similar extent, it did not interact with alpha,beta-meATP Lower concentrations of eth anol (10 and 30 mM) had no effect on depolarizing responses to NMDA or AMPA. Noradrenaline applied by pressure pulses reproducibly hyperpola rized LC cells. These hyperpolarizations were unchanged by ethanol (10 0 mM). Biphasic synaptic potentials consisting of early depolarizing ( PSP) and late hyperpolarizing (IPSP) components were evoked by electri cal stimulation. Ethanol (100 mM) depressed the PSP and increased the IPSP. Glutamatergic PSPs recorded in the combined presence of picrotox in (100 mu M) and suramin (100 mu M) were also inhibited by ethanol (1 00 mM). However, IPSPs recorded under these conditions were insensitiv e to ethanol (100 mM). In conclusion, ethanol may interfere with the A MPA (or NMDA) receptor-mediated fraction of the PSP and slightly facil itate the alpha(2) adrenoceptor-mediated fraction of the IPSP.