Effects of nicotine on the human visual system: 1) color perception; 2) processing at the cortical level.

摘要

The visual system is sensitive to various types of chemical substances, including nicotine. Nicotinic acetylcholine receptors (nAChRs) are found in the nervous system, including the retina. These receptors play a role in modulating signals within the visual system. It has been shown that smoking affects color vision, and visual evoked potentials (VEPs). But few studies have been devoted to understanding the effects of nicotine alone.;The purpose of this research was to examine the effects of oral administration of nicotine in human adults, who are non-smokers, on color vision, and visual cortical processing. Previous studies on adult smokers revealed that smokers differ in their color discrimination threshold compared to non-smokers, with higher error scores and thresholds on color tests when compared to light smokers or non-smokers. Also, smoking alters the responses of the cortical visual pathways measured by VEP, showing shorter latencies, and amplitudes increased.;A group of non-smokers participated in this study. Subjects were given a comprehensive eye examination to determine eligibility. All subjects attended a minimum of two visits. Two doses of Nicorette nicotine gum (2 and 4 mg) were given to each subject, one dose per visit. We conducted two separate experiments: 1) color vision; 2) VEP. For each experiment subjects were tested twice at each visit: 1) baseline; 2) 30 minutes after chewing nicotine gum.;Color testing revealed an overall improvement in sensitivity to the Farnsworth-Munsell 100 hue test (FM-100) with nicotine. Total error score (TES) decreased on the FM-100. Also, by using an increment threshold test, sensitivity increased with nicotine. Visual evoked potential recordings revealed no changes in latency or amplitude of the P100 peak of the transient VEP. Nicotine had both inhibitory and excitatory effects on lateral interactions in the cortex (1st and 2nd harmonics). In addition, increases in amplitudes were observed only in the magnocellular pathway. Model fits to the data also indicated in cortical shunting inhibition and initial conductance. We therefore assume that nicotine differentially alters the projected signals from the different visual pathways and systems. Also, the findings demonstrate that nicotine plays an effect in modulating both excitatory and inhibitory responses.