اثر تزریق داخل هیپوکامپی هیستامین و تیوپرامید بر درد تونیک ناحیه دهانی - صورتی در موش صحرایی .

Brain histamine, through H3 receptor, has an important role in central perception of pain. The present study investigated the effects of intra-hippocampal microinjection of histamine and thioperamide (a histamine H3 antagonist) on tonic pain in orofacial region of rats.

Materials & Methods: In 72 male Wistar rats two guide cannulae were implanted into the dorsal hippocampus bilaterally. Orofacial region tonic pain was induced by subcutaneous injection of formalin (50 µl, %1) into the upper lip, and rubbing the injected site (face rubbing) was recorded in 3 min blocks for 45 min.

Results: Subcutaneous injection of formalin in the upper lip produced a marked biphasic (first phase: 0-3 min and second phase: 15-33 min) pain response. The intensity of pain in the first and second phases was significantly (P<0.05) suppressed with intra-hippocampal injection of histamine (1 and 2 µg) and thioperamide (2.5 and 5 µg). Pretreatment with thioperamide before histamine enhanced the antinociceptive effect of histamine.

Conclusion: The results showed that intra-hippocampal injection of histamine and thioperamide suppressed the first and the second phases of orofacial tonic pain. Blockade of histamine H3 receptor with thioperamide enhanced the antinociceptive effect of histamine.