ADOLESCENT NICOTINE EXPOSURE ALTERS THE RESPONSES OF PERIAQUEDUCTAL GRAY MATTER NEURONS TO FORMALIN INJECTION

Background and Aim : Tobacco use is a leading global risk factor for many chronic disorders, preventable death, and disability. Epidemiological reports indicate that the initiation of smoking primarily occurs during adolescence. Evidence suggests that adolescent nicotine exposure results in persistent changes in affect, cognition, drug-related behaviors and neurobiology. The midbrain region ventrolateral periaqueductal gray (vlPAG) is a major component of descending pain inhibitory system. Activation of this system inhibits nociceptive neurons in the spinal dorsal horn. In the present study we investigated the effect of adolescent nicotine exposure on vlPAG neuronal responses to formalin injection during adulthood.Methods : Male Wistar rats received subcutaneous injections of either nicotine or saline during adolescence. Then, during adulthood (70 days old), in vivo extracellular single-unit recording was used for investigating vlPAG neuronal responses to formalin injection into the hind paw.Results : Results showed that adolescent nicotine exposure attenuates the extent of inhibitory response of vlPAG neurons to formalin injection into the hind paw. It also changed the histogram pattern of inter-spike intervals in recorded signal.Conclusion : Our results indicate that prolonged exposure with nicotine during adolescence can Cause long-lasting neuronal changes in vlPAG region in response to formalin injection and this may change the pain modulatory systems and subsequent response to noxious stimuli.

Keywords:

Adolescent , Nicotine , Extracellular single unit recording , vlPAG , Rat