1. The present study examined the role of the hippocampal histaminergic system in the regulation of spatial memory deficit in rats using the radial arm maze task after
scopolamine injection into the bilateral dorsal (DH) or ventral (VH) hippocampus. 2. Bilateral injection of
scopolamine (5 microg/site) into both the DH and VH impaired spatial memory in the retrieval memory process. Injection of
histamine (50 or 100 ng/site) in the DH and
intraperitoneal injection of
histidine (100 mg/kg) markedly improved working memory and reference
memory deficits induced by
scopolamine injection into the DH. The
histamine H(1) receptor antagonist
pyrilamine (1 microg/site) abolished the ameliorative effects of
histidine on working memory deficits, whereas both
pyrilamine and the H(2) receptor antagonist
cimetidine (0.5 microg/site) abolished the effect of
histidine on reference memory. 3. Local injection of
histamine (25 or 50 ng/site) into the VH and systemic injection of
histidine (50 or 100 mg/kg) markedly improved working memory deficits induced by
scopolamine injection into the VH, but did not improve the deficits in reference memory. Injection of both
pyrilamine (0.2, 0.5 and 1 microg/site) and
cimetidine (0.1 and 0.5 microg/site) into the VH reversed the effects of
histidine. 4. The results of the present study indicate that
histamine has different actions on
cholinergic-related memory in the the DH and VH.
Histamine in the DH ameliorates spatial working memory deficits by acting on
histamine H(1) receptors and reference
memory deficits through both H(1) and H(2) receptors. However,
histamine in the VH ameliorates working memory deficits via an action on both H(1) and H(2) receptors.