Constant exposure to darkness produces supersensitivity to nicotine

Treatment with full-spectrum bright artificial light produces subsensitivity to the hypothermic effect of nicotine in the rat. The authors hypothesized that prolonged exposure to darkness would produce the opposite effect. The thermic responsiveness of 11 rats to nicotine (base), 0.25 mg/kg IP, was telemetrically measured at baseline, after 7 days of exposure to constant darkness, and 2, 5, and 12 days after being returned to standard vivarium conditions. Exposure to constant darkness enhanced the hypothermic response to nicotine. The sample exhibited a hyperthermic response to nicotine 2 and 5 days after being returned to the standard vivarium conditions with a 12-hour-light/12-hour-dark cycle. The magnitude of the hyperthermia observed is characteristic of the response to the injection of saline. Twelve days after return to standard vivarium conditions the thermic response of the sample was at baseline.