1Associate Professor of Biotechnology, Cellular and Molecular Research Center, Qazvin University of Medical Sciences, Qazvin, Iran
2Nursing and Midwifery School, Torbat-e Heydariyeh University of Medical Sciences, Torbat-e Heydariyeh, Iran
3Master of Physiology, Department of Physiology, School of Medicine, Qazvin University of Medical Sciences, Qazvin, Iran
4Assistant Professor of Physiology, Cellular and Molecular Research Center, School of Medicine, Qazvin University of Medical Sciences, Qazvin, Iran
Background and Aims: It is well-recognized that endogenous opioidergic system plays an important role in
pain sensitivity, pain perception, and response to some stressing situations. The present study examined the
probable role of endogenous opioidergic system in effects of food deprivation on formalin-induced
nociceptive behaviors in male and female rats.
Methods: To make short-term food deprivation, the rats did not receive food for 48 hours prior to the
formalin test. However, they could freely access water. Afterward, 50 µl formalin 2% was injected into the
bottom of the rats’ right paw. Naloxone was injected to evaluate the involvement of the endogenous
opioidergic system in effects of food deprivation on formalin-induced nociceptive behaviors.
Results: Formalin injection caused nociceptive behaviors in two phases The first and second
phases were separated by a brief interphase where nociceptive behaviors decreased. As a result of
48-hour food deprivation, nociceptive behaviors in male and female rats were increased and the
second phase was finished with delay. Naloxone administration blocked the pronociceptive effect of
the 48-hour food deprivation in the interphase of male rats and in the first phase of female rats.
Conclusion: The present study indicated that food deprivation increased formalin-induced nociceptive
behaviors through affecting the opioidergic system.