The distribution of histidine decarboxylase mRNA in the rat brain: an in situ hybridization study using synthetic oligonucleotide probes.

L-Histidine decarboxylase catalyzes the formation of histamine from the amino acid L-histidine. We have studied the distribution of neurons expressing mRNA for histidine decarboxylase in adult rat brain using in situ hybridization with synthetic oligonucleotide probes. The expression of mRNA for histidine decarboxylase was detected in the hypothalamic tuberomammillary nucleus that has been shown to contain histidine decarboxylase-like and histamine-like immunoreactivity, but not in any other brain area. This method may prove useful in studying the physiological role of central histaminergic neurons.