Ontogenesis and regional distribution of histamine and histamine-N-methyltransferase in the guinea pig brain.

Abstract

Abstract—The ontogenetic development and the regional distribution of histamine (HA) and histamine‐N‐methyltransferase (HMT, EC 2.1.1.8) in guinea pig brain and pituitary gland were studied. The samples were taken every fourth day beginning on the 28th foetal day. The HA concentration in the brains of the youngest foetuses was almost undetectable. A significant increase in HA concentrations occurred between days 40 and 44, which coincides with the period of rapid growth of nerve cell processes in this species. After this, a steep increase continued to the end of gestation in the hypothalamus, and to a lesser degree in the medulla‐midbrain and in the forebrain. In all parts of the brain the adult HA levels were reached by the time of birth. The HMT activity increased 15‐fold from the 28th foetal day to the adult and reached ca. 80% of the adult activity by the time of birth. The HMT activity developed earlier in the midbrain than in the forebrain or in the cerebellum, but after the birth the regional distribution of HMT was fairly even. In the pituitary gland the HA concentration and HMT activity increased hundredfold and tenfold, respectively.The developmental patterns of HA and HMT in the guinea pig brain give support to the concept that HA might be a neurotransmitter in the brain.