Abstract
Nicotine engages dopamine neurons in the ventral tegmental area (VTA) to encode reward and drive the development of nicotine addiction, however how nicotine alters a stress associated VTA population remains unclear. Here, we used male and female CRF1-GFP mice and nicotine vapor exposure to examine the effects of nicotine in VTA corticotropin-releasing factor receptor 1 (CRF1) neurons. We use immunohistochemistry and electrophysiology to examine neuronal activity, excitability, and inhibitory signaling. We found that VTA CRF1 neurons are mainly dopaminergic and project to the nucleus accumbens (NAc; VTA-NAcCRF1 neurons). VTA-NAcCRF1 neurons show greater phasic inhibition in naive females and greater focal nicotine-induced increases in firing in naive males. Following acute nicotine vapor exposure, phasic inhibition was not altered, but focal nicotine-induced tonic inhibition was enhanced in females and diminished in males. Acute nicotine vapor exposure did not affect firing in VTA-NAcCRF1 neurons, but females showed lower baseline firing and higher focal nicotine-induced firing. Activity (cFos) was increased in the CRF1 dopaminergic VTA population in both sexes, but with greater increases in females. Following chronic nicotine vapor exposure, both sexes displayed reduced basal phasic inhibition and the sex difference in tonic inhibition following acute vapor exposure was no longer observed. Additionally, activity of the CRF1 dopaminergic VTA population was no longer elevated in either sex. These findings reveal sex-dependent and exposure-dependent changes in mesolimbic VTA-NAc CRF1 neuronal activity, inhibitory signaling, and nicotine sensitivity following nicotine vapor exposure. These changes potentially contribute to nicotine-dependent behaviors and the intersection between stress, anxiety, and addiction.
SIGNIFICANCE STATEMENT Nicotine is known to engage reward systems in the brain historically centering the neurotransmitter dopamine however, how nicotine impacts other neurons in the reward pathway is less clear. The current study investigates the impact of acute and chronic electronic nicotine vapor exposure in a genetically-defined cell population containing the stress receptor corticotropin-releasing factor 1 (CRF1) that is located in the reward circuitry. This study employs functional measures of neuronal activity and identifies important sex differences in nicotine's effects across time and exposure.
