Evidence for dopamine as a transmitter in dorsal hippocampus.

Intrahippocampal distribution of dopamine (DA) and its metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), was studied along with those of noradrenaline (NA) and 5-hydroxytryptamine in rats. DA concentration in the dorsal part of the hippocampus was found to be 4--10 times higher than in other parts. A study of metabolite distributions produced similar results, showing a higher concentration in the dorsal part of the hippocampus. A ratio of NA/DA had a value similar to that of the hypothalamus in which apparent dopaminergic innervation has been reported. Haloperidol decreased the DA level, whereas it increased the concentration of metabolites, in whole and dorsal hippocampus. The ratio HVA/DOPAC increased after haloperidol treatment. These findings strongly suggest the presence of dopaminergic innervation in at least the dorsal part of the hippocampus.