Early partial maternal deprivation causes long-lasting neurochemical, behavioral and brain structural effects. In rats, it causes a deficit in memory consolidation visible in adult life. Some of these deficits can be reversed by
donepezil and
galantamine, which suggests that they may result from an impairment of brain
cholinergic transmission. One such deficit, representative of all others, is an impairment of memory consolidation, clearly observable in a one-trial inhibitory avoidance task. Recent data suggest a role of brain histaminergic systems in the regulation of behavior, particularly inhibitory avoidance learning. Here we investigate whether
histamine itself, its analog SKF-91844, or various receptor-selective
histamine agonists and antagonists given into the CA1 region of the hippocampus immediately post-training can affect retention of one-trial inhibitory avoidance in rats submitted to early postnatal maternal deprivation. We found that
histamine, SKF-91844 and the H2 receptor agonist,
dimaprit enhance consolidation on their own and reverse the consolidation deficit induced by maternal deprivation. The enhancing effect of
histamine was blocked by the H2 receptor antagonist,
ranitidine, but not by the
H1 receptor antagonist
pyrilamine or by the H3 antagonist
thioperamide given into CA1 at doses known to have other behavioral actions, without altering locomotor and exploratory activity or the anxiety state of the animals. The present results suggest that the
memory deficit induced by early postnatal maternal deprivation in rats may in part be due to an impairment of
histamine mediated mechanisms in the CA1 region of the rat hippocampus.