Synaptic responses mediated by identified histamine-containing neurones

Abstract

EFFORTS to prove that histamine has a role in synaptic neurotransmission have been less successful than for other biogenic amines. For example, there has been no convincing physiological or pharmacological evidence to support the transmitter candidacy of this imidazole at any known synapse. In the central nervous system (CNS) of the marine mollusc Aplysia californica chemical measurements of single isolated neurones have revealed large concentrations of histamine within two identified neurones¹. The histamine-containing neurones (HN) uniquely possess a specific histidine decarboxylating enzyme and they can synthesise and store labelled histamine². These biochemical observations prompted the suggestion² that the two identified nerve cells utilise histamine as a neurotransmitter. The physiological studies reported here show that each HN monosynaptically elicits multicomponent excitatory and inhibitory postsynaptic potentials (p.s.ps) in different follower neurones, the somal membranes of which show appropriate potential changes to iontophoretic application of histamine. This suggests that histamine is a neurotransmitter released from the nerve terminals of the HN.