Tobacco smoking is recognized as a life-threatening risk factor worldwide. Initiation of smoking primarily occurs during adolescence which is a critical developmental phase characterized by specific neurobehavioral alterations. The effect of adolescent
nicotine exposure on vulnerability to
opioid addiction has not been previously addressed. Furthermore, lateral paragigantocellularis (LPGi) is a key modulator of
opiate effects. In this study we investigated the effect of adolescent
nicotine treatment on development of
morphine tolerance and dependence as well as LPGi neuronal responses to
morphine during adulthood. Male Wistar rats received
subcutaneous injections of either
nicotine or saline during adolescence and then development of
morphine tolerance and dependence was assessed during adulthood by tail-flick and withdrawal tests, respectively. In vivo single-unit recording was performed to examine the LPGi neuronal activities. Results indicated that adolescent
nicotine exposure significantly facilitates the development of tolerance to
analgesic effect of
morphine and increases the expression of
morphine withdrawal signs in adulthood. Also, it was observed that following adolescent
nicotine treatment, the extent of
morphine-induced excitation is attenuated in LPGi neurons of adult rats. Moreover, the onset of
morphine-induced inhibition was increased in these animals. Neither the baseline, nor the regularity of firing was affected in our observations. It could be concluded that
nicotine challenge during adolescence may enhance the future vulnerability to
opioid addiction through induction of persistent neuroadaptations in LPGi neurons.