Route-Dependent Behavioral, Dopaminergic, and Transcriptomic Adaptations to Nicotine Aerosol Inhalation and Systemic Injection in Male Mice.

Nicotine is one of the most widely used psychoactive substances, yet most preclinical studies rely on subcutaneous injection, which does not fully model inhalation-based exposure. How different nicotine delivery paradigms shape neurobehavioral adaptations remains unclear. Here, we compared subcutaneous nicotine injection and nicotine aerosol inhalation in male mice across behavioral, dopaminergic, and transcriptomic domains. Nicotine aerosol inhalation produced concentration-dependent modulation of conditioned place preference, accompanied by rapid nicotine absorption and delayed cotinine accumulation. Fiber photometry recordings in the nucleus accumbens revealed distinct dopamine dynamics during nicotine-associated contextual processing, with nicotine-paired contexts eliciting shorter time-to-peak but reduced amplitude and area under the curve. High-dimensional behavioral tracking under mecamylamine-precipitated withdrawal conditions demonstrated that nicotine exposure conditions reshaped behavioral organization rather than producing generalized hyperlocomotion. Subcutaneous nicotine and aerosol exposure produced partially overlapping but compositionally distinct behavioral profiles influenced by nicotine exposure, delivery paradigm, and aerosol formulation. Transcriptomic analyses further revealed region-specific molecular signatures, including metabolic pathways in the ventral tegmental area and synaptic/neuroimmune-related pathways in the nucleus accumbens after aerosol exposure. Together, these findings demonstrate that nicotine delivery paradigms shape distinct neurobehavioral and molecular responses, emphasizing the importance of inhalation-based models in preclinical nicotine research.