Histamine and tyrosine hydroxylase in developing rat brain.

The distribution of histamine and tyrosine hydroxylase in fetal rat brain was investigated immunocytochemically in order to determine possible colocalization of these two substances. Embryonic rat brains were fixed with carbodiimide and processed for immunofluorescence studies with antisera against histamine and tyrosine hydroxylase either in the same sections or in consecutive sections. Histamine and tyrosine hydroxylase showed no colocalisation in the developing rat brain. However, fibre networks immunoreactive for histamine and tyrosine hydroxylase were often found in the same areas. The results of the study suggest that the catecholaminergic and histaminergic neurones develop separately in the rat brain. Based on the location of developing histamine-immunoreactive neurones, a more intimate relationship between histamine- and serotonin-containing neurones in the developing rat brain is plausible.