Chronopharmacological effects of nicotine repeated administration on heart rate, body temperature and locomotor activity circadian rhythms in rats

The aim of this study was to compare morning and evening repeated nicotine administration on the circadian rhythms of heart rate (H), body temperature (T) and locomotor activity (A) in unrestrained rats by using implanted radio-telemetry transmitters. The study was divided into three 7- day periods: a control period (P1), a treatment period (P2) and a recovery period (P3). During P2, four rats received nicotine (1 mg.kg^-1) subcutaneously at 09.00 h and four rats received nicotine in the same conditions at 21.00 h. For P1, P2 and P3, a power spectrum analysis was applied in order to determine the dominant period of rhythmicity. If H, T and A circadian rhythms were detected, the characteristics of these rhythms were determined by cosinor analysis, expressed as means+SEM and compared by ANOVA. Our results indicated: (1) a lack of detection of A circadian rhythm during P2 for the morning group while H and T circadian rhythms were detected for the morning and evening group whatever the period. (2) alterations of mesors, amplitudes and acrophases of H and T circadian rhythms for the morning and evening group during P2 and alterations of mesor, amplitude and acrophase of A circadian rhythm for the evening group. Furthermore these alterations were significantly different for the morning and evening group during P2. These results showed that the time of administration of nicotine differently affect H, T and A rhythms. The authors suggest that these effects can be mediated by central cholinergic and/or monoaminergic mechanisms.