Alterations in BDNF and Phospho-Creb Levels Following Chronic Oral Nicotine Treatment and Its Withdrawal in Dopaminergic Brain Areas of Mice

Neuronal changes induced by chronic nicotine in the brain dopaminergic circuits are thought to lead to compulsive nicotine use. When nicotine is given to mice chronically in their drinking water, its intake and effects mimic human smoking. Previously, we have reported that this treatment in mice induces several neurochemical and behavioural changes that are associated with nicotine addiction. Here we studied the effects of chronic oral nicotine treatment and nicotine treatment cessation on two well-characterised markers of neuronal plasticity, brain-derived neurotrophic factor (BDNF) and phosphorylated cAMP-responsive element-binding protein (pCREB), in several dopaminergic brain areas. BDNF levels were not altered by chronic nicotine treatment, but they were significantly increased in the nucleus accumbens (NAc) after 24h and 29 days of nicotine abstinence and in the ventral tegmental area (VTA) and substantia nigra after 29 days of nicotine abstinence. These findings suggest that nicotine abstinence promotes long-lasting neuroadaptations in dopaminergic neurocircuits by inducing BDNF production. Withdrawal from chronic nicotine treatment oppositely affected pCREB levels in the NAc and in the VTA. Thus, in the NAc, the pCREB levels were significantly elevated and in the VTA significantly decreased as compared with the pCREB levels during the nicotine treatment. These alterations could be compensatory and related to increased dopaminergic signalling during nicotine treatment. In conclusion, the current results suggest the involvement of BDNF- and CREB-related neuronal processes in nicotine-induced neurochemical, behavioural, and neuroplastic changes in dopaminergic neurocircuits.