Rapid changes in enkephalin levels in rat striatum and hypothalamus induced by diazepam

The acute treatment of rats with diazepam induces pronounced changes in brain enkephalin concentrations, as was estimated for methionine(met)-enkephalin and in some representative experiments for leucine(leu)-enkephalin, employing highly specific radioimmunoassays. Diazepam selectively increased the enkephalin concentrations in the hypothalamus by about 35%, and lowered it in the corpus striatum by roughly 25%; no changes could be detected in the medulla oblongata/pons or midbrain. The drug-induced changes displayed a rapid onset. Peak effects were reached by 2 to 5 min after injection. Changes observed in the hypothalamus were only short lasting and were apparently parallelled by diazepam concentrations in the brain, whereas the decrease in the striatum was of markedly longer duration. Presently, the mechanism underlying all these changes is unknown. Whereas an increase in enkephalin concentrations in the hypothalamus may be discussed in terms of the anti-stress effect of benzodiazepines, the observed drop in striatal enkephalin is not obviously to be correlated to behavioural changes induced by these drugs.