Ethanol-induced modification of sensory evoked potentials recorded from the caudate nucleus, substantia nigra, hypothalamus, and pineal

Modifications of the averaged sensory acoustic-evoked response (AAER) were examined following intraperitoneal injection of ethanol (1.67 g/kg). Changes in the evoked responses were correlated with blood alcohol concentration. Evoked field potentials from freely behaving rats previously implanted with stainless-steel semimicroelectrodes stereotaxieally were recorded simultaneously from the head of the caudate nucleus, substantia nigra, ventromedial hypothalamus, and pineal. Following ethanol administration, all four regions exhibited a general pattern of initial evoked response suppression (decreased component amplitudes) followed by gradual recovery in which the magnitude of suppression was directly related to the blood ethanol concentration. However, whereas more than 90% of the evoked response recordings from the caudate (P₂ and N₂ components) demonstrated significant amplitude decreases at maximum alcohol levels, fewer than 35% of recordings obtained from the substantia nigra exhibited such decreases. Moreover, the absolute magnitude of amplitude attenuation of the evoked responses was markedly greater in the caudate than in the substantia nigra. The responses recorded from the hypothalamus and pineal exhibited a similar pattern of suppression which was distinct from that recorded from the caudate and substantia nigra. The recovery profile of individual evoked response components (P₂, N₂, and p₂) as compared to alcohol levels was also observed to vary between the different brain areas examined. These results demonstrate a heterogeneous physiological response to acute ethanol exposure in four distinct brain regions mediating motor and neuroendocrine functions.