Histamine acts directly on calcitonin gene-related peptide- and substance P-containing trigeminal ganglion neurons as assessed by calcium influx and immunocytochemistry.

Primary cultures of rat trigeminal ganglion cells were exposed to histamine, and the intracellular free-calcium concentration, [Ca2+]i, was measured by the calcium-sensitive dye fura-2. Histamine increased the [Ca2+]i of the neurons. Pretreatment of the cells with histamine H1-receptor blocker, or removal of extracellular calcium, abolished the response, however, the response was not altered by pretreatment with H2-blocker. Immunocytochemical analysis showed that these cultured cells that responded to histamine identically showed substance P- or calcitonin gene-related peptide-like immunoreactivity.