Interactions between TRH and ethanol in the medial septum.

When rats were pretreated with ethanol (3.0 g/kg, IP), subsequent microinjection of thyrotropin-releasing hormone (TRH) (500 or 1000 ng) into the medial septum, 30 minutes later, significantly shortened the time necessary for the rats to regain their righting reflex. Conversely, microinjection of TRH into the nucleus accumbens (1000 ng/side) or the area of the raphe obscurus (1000 ng) had no effect on ethanol-induced depression, although both of these structures mediate specific TRH effects in the CNS. In order to determine if this antagonism was due to a specific TRH interaction, TRH Fab fragments were microinjected into the medial septum just prior to the microinjection of TRH. Under these conditions, TRH did not alter ethanol's depressant actions. Finally, this TRH antagonism of ethanol-induced depression appears attributable to a net increase in neuronal activity, because electrical stimulation (160 microA, 120 Hz, 1.5 msec duration) of the medial septum antagonized ethanol's impairment of the righting reflex. These results are discussed in relationship to a potential CNS site for the action of ethanol.