Effects of Acute Nicotine Exposure on Anxiety-like Behavior in Rats Chronically Exposed to Methylphenidate

Abstract:

Consistent nicotine use through smoking is common among those diagnosed with attention-deficit hyperactivity disorder (ADHD), with upwards of 75% of individuals showing moderate to high use. The connection between ADHD diagnoses and smoking has yet to be fully explained in the literature, but one potential partial explanation is related to the of use of nicotine to relieve anxiety symptoms in ADHD patients. Treatment of ADHD with stimulant medication, particularly methylphenidate, is associated with increased smoking, and it is known to produce anxiogenic effects in rodents. However, the combined effects of nicotine and methylphenidate-exposure on anxiety behavior have not been studied extensively to date. Therefore, this study sought to investigate the effect of acute nicotine administration on anxiety-like behavior in rodents chronically exposed to methylphenidate to better understand their connection. In Experiment 1, following 18 days of chronic methylphenidate exposure, baseline anxiety-like behavior was assessed on the light-dark (LD) test, and nicotine-induced anxiety like behavior was assessed on the elevated plus maze (EPM). Results indicated no differences in baseline anxiety-like behavior but did show increased locomotor activity after chronic exposure to methylphenidate. Following nicotine injection, methylphenidate-exposed rats showed significantly decreased anxiety-like behavior when compared to non-exposed rats. These results suggest that nicotine may have an anxiolytic effect in subjects with a history of methylphenidate use, which may partially explain the elevated smoking patterns in the ADHD population. However, factors such as small sample sizes and a lack of a true control group reduce the generalizability of this finding. Thus, in Experiment 2, additional control groups were added for comparison, including a group exposed to methylphenidate and no nicotine and a group that was entirely drug-naïve. It is expected that the results of the first experiment be replicated in Experiment 2, and the additional control groups will help to solidify the results of Experiment 1.