Ontogenetic development of histamine H1-receptor binding in rat brain

Histamine H1- receptors labeled with [3H]mepyramine in rat brain show an age-dependent development. [3H]Mepyramine receptor density and histidine decarboxylase activity in whole rat brain reach adult levels at 25–30 days after birth and they attain 50% of adult level at day 10 and 17, respectively. The apparently later development of histidine decarboxylase activity in whole rat brain is partly accounted for by a biphasic developmental increase of this enzymatic activity in cerebral cortex. For all other brain regions examined, the development of histamine H1- receptors parallels that of histidine decarboxylase. The increase in [3H]mepyramine binding can be accounted for by an absolute increase in the numbers of the receptor sites, with no change in affinity. Subcellular fractionation studies indicate that histamine H1- receptors are predominantly associated with synaptosomal fractions derived from both newborn and adult rat.