Abstract
Histamine is a putative neurotransmitter in mammals and molluscs, but its role in the nervous systems of other animals is not known. This study examines the possibility that histamine is a neurotransmitter in an arthropod. Results show that first, 14 neurons in the stomatogastric ganglion of the spiny lobster respond to histamine. The response is inhibitory, is mediated by an increased conductance to chloride, and desensitizes with repeated applications of histamine. These same 14 neurons receive one type of synaptic potential from two extrinsic neurons, the “through-fibers” of the inferior ventricular nerve. This synaptic potential is also inhibitory, is mediated by an increased conductance to chloride, and is blocked when histamine receptors are desensitized. Second, assays of endogenous histamine indicate that histamine is distributed nonuniformly throughout the stomatogastric nervous system and that its distribution correlates with the axonal pathways and terminal arborizations of the inferior ventricular nerve through-fibers. Lastly, histamine is present in relatively high concentrations in the cell bodies of the through-fibers, whereas it is not detectable in other neurons in the stomatogastric system. These results suggest that histamine may be a transmitter in the lobster.