Acute ethanol administration induces changes in TRH and proenkephalin expression in hypothalamic and limbic regions of rat brain

Thyrotropin releasing hormone (TRH) present in several brain areas has been proposed as a neuromodulator. Its administration produces opposite effects to those observed with acute ethanol consumption. Opioid peptides, in contrast, have been proposed to mediate some of the effects of alcohol intoxication. We measured TRH content and the levels of its mRNA in hypothalamic and limbic zones 1–24 h after acute ethanol injection. We report here fast and transient changes in the content of TRH and its mRNA in these areas. The levels of proenkephalin mRNA varied differently from those of proTRH mRNA, depending on the time and region studied. Wistar rats were administered one dose of ethanol (intraperitoneal, 3 g/kg body weight) and brains dissected in hypothalamus, hippocampus, amygdala, n. accumbens and frontal cortex, for TRH quantification by radioimmunoassay or for proTRH mRNA measurement by RT-PCR. After 1 h injection, TRH levels were increased in hippocampus and decreased in n. accumbens; after 4 h, it decreased in the hypothalamus, frontal cortex and amygdala, recovering to control values in all regions at 24 h. ProTRH mRNA levels increased at 1 h post-injection in total hypothalamus and hippocampus, while they decreased in the frontal cortex. The effect of ethanol was also studied in primary culture of hypothalamic cells; a fast and transient increase in proTRH mRNA was observed at 1 h of incubation (0.001% final ethanol concentration). Changes in the mRNA levels of proTRH and proenkephalin were quantified by in situ hybridization in rats administered ethanol intragastrically (2.5 g/kg). Opposite alterations were observed for these two mRNAs in hippocampus and frontal cortex, while in n. accumbens and the paraventricular nucleus of the hypothalamus, both mRNA levels were increased but with different kinetics. These results give support for TRH and enkephalin neurons as targets of ethanol and, as possible mediators of some of its observed behavioral effects.