Distribution of catalase in rat brain: aminergic neurons as possible targets for ethanol effects

Ethanol is metabolized at a slow but measurable rate in rodent brain. Recent studies indicate that this process is mediated mainly by catalase. The spatial distribution of this enzyme in different brain structures is poorly known. To explore possible local imbalances between the production and elimination of ethanol-derived acetaldehyde, we investigated the regional and cellular distribution of catalase, histo- and immunohistochemically, using serial cryostat sections from male Wistar rats. Compared to the strong peroxisomal staining seen in liver, brain catalase staining was weak and was not immunologically detected with an anti-sheep bovine catalase antibody. Activity was observed only in microperoxisomes, mainly in perikaryons of aminergic neurons, in the known groups of adrenergic, nonadrenergic and serotonergic neurons of the brain stem. Little peroxisomal staining was seen in other types of brain structures. This result contrasted to that of aldehyde dehydrogenase, which we previously observed to be widely distributed in brain structures, but with low activity in perikaryons of aminergic (especially catecholaminergic) neurons, as compared to cholinergic neurons. Our data indicate that catalase-mediated oxidation of ethanol to acetaldehyde takes place mainly in aminergic neurons, which seem to have a limited capacity for the subsequent removal via aldehyde dehydrogenase. This suggests that locally produced acetaldehyde could mediate CNS effects of ethanol in these structures.