INCREASED RESPONSIVENESS OF PONTINE RETICULAR-FORMATION NEURONS ASSOCIATED WITH AUDIOGENIC-SEIZURE SUSCEPTIBILITY DURING ETHANOL WITHDRAWAL

Susceptibility to audiogenic seizures (AGS) is observed during ethanol withdrawal (ETX). The pontine reticular formation (PRF) is implicated in the propagation pathway for AGS during ETX. The present study exam ined the changes in single PRF neuronal firing patterns produced by et hanol and during ETX following repeated intragastrically administered ethanol. Microwire electrode bundles were implanted into PRF and singl e neuronal responses in freely moving rats were examined. During initi al ethanol administration the animals were stuporous, and spontaneous and acoustically-evoked PRF neuronal firing were reduced significantly . During ETX the animals were susceptible to AGS and displayed agitate d and irritable behavior. At this time a significant increase in spont aneous and acoustically-evoked PRF neuronal firing was observed. Repet ition-induced response attenuation (habituation) of PRF neuronal respo nses was significantly diminished during ETX, leading to an exaggerate d acoustic startle response, which may be a physiological basis for AG S. Previous reports indicate that ethanol enhances the effects of GABA and decreases the effects of glutamate. The PRF neuronal firing incre ases during ETX in the present study may involve the down-regulation o f GABA, receptors and supersensitivity of glutamate receptors reported to occur during ETX, which could contribute to AGS susceptibility. Th e PRF neuronal firing increases observed in the present study in conco rd with previous observation of AGS blockade by PRF microinjections du ring ETX further support an important role of this brain region in the propagation of AGS during ethanol withdrawal.