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Departments of *Pharmacology and
Anatomy and Neurobiology, Dalhousie University, Halifax, Nova Scotia, Canada
Address correspondence and reprint requests to Jana Sawynok, PhD, Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia B3H 4H7. Address e-mail to Jana.Sawynok{at}Dal.ca
We examined the effects of systemically, spinally, and peripherally administered amitriptyline on formalin-induced Fos immunoreactivity in the lumbar spinal cord. Formalin (2.5%), injected subcutaneously into the rat hindpaw, increased Fos immunoreactivity in laminae III, IIIIV, and VVI of the dorsal L5 spinal cord. Amitriptyline, administered both systemically and spinally before formalin, increased flinching and concurrently decreased biting/licking behaviors, but neither route of administration produced any statistically significant change in Fos immunoreactivity. Amitriptyline coadministered with the formalin reduced both flinching and biting/licking behaviors, and significantly reduced Fos immunoreactivity, particularly in laminae III. These immunohistochemical changes reflect the net behavioral effects observed after the different routes of drug administration. The profile of amitriptyline action after peripheral administration may be of clinical importance because of the potential use of antidepressants as topical analgesics.
IMPLICATIONS: In the formalin test, amitriptyline produces different effects on pain behaviors after systemic, spinal administration and peripheral administration. Fos protein, an indicator of neuronal activity after noxious stimulation, is upregulated after formalin injection. We examined the effects of amitriptyline on such expression and observed a reduction in expression with peripheral administration.
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