Effects of calcitonin injected into various brain areas on pain threshold and Ca2+ in rats.

AIM: To study the effects of calcitonin (Cal) injected into different brain areas on pain threshold.

METHODS

The analgesic effects of Cal were investigated in rats by the tail-flick test.

RESULTS

Cal injected into lateral cerebral ventricle (LCV) or periaqueductal gray (PAG) increased obviously the pain threshold to 49 +/- 22% or to 68 +/- 12% (P < 0.01), respectively. When PAG was blocked with lidocaine, the analgesic effect of Cal injected into LCV was lowered 41 +/- 9%. Cal injected into habenula (Hab) decreased the pain threshold to -30 +/- 5% (P < 0.01).

CONCLUSION

Cal in different rat brain areas induced different effects on pain responses: analgesia or hyperalgesia, and showed that PAG played an important role in the analgesic effect induced by Cal, and the changing of pain threshold was mediated by the Ca2+ in brain.