2-pyridylethylamine (at a high dose) and dimaprit produced antinociception, whereas immepip produced nociception in two models of trigeminal pain.
These effects were prevented by prior microinjection of mepyramine, ranitidine and thioperamide, respectively.
Post-synaptic histamine H2, and to a lesser extent H1, receptors and pre-synaptic histamine H3 receptor may be involved in VPM modulation of trigeminal pain.