The influence of caffeine on nicotine's discriminative stimulus, subjective, and reinforcing effects.

Caffeine may acutely alter the discriminative stimulus and subjective effects of nicotine, perhaps explaining the association of coffee intake with smoking status. In this study, smokers were initially trained to discriminate 20 microg/kg nicotine by nasal spray from placebo (0). Then, generalization of nicotine discrimination was tested, using both 2- and 3-choice ("novel" option) procedures, across a range of doses (0-20 microg/kg) following pretreatment with 0, 2.5, and 5.0 mg/kg caffeine p.o. Nicotine reinforcement was assessed after the end of generalization testing using a choice procedure. Caffeine pretreatment did not alter nicotine discrimination and self-administration. Caffeine and nicotine influenced some subjective and cardiovascular responses, but there were no interaction effects except for diastolic blood pressure. These results do not support the notion that caffeine acutely alters nicotine's discriminative stimulus, subjective, or reinforcing effects.

The consistency of acute responses to nicotine in humans.

Nicotine has many acute subjective, physiological, and behavioral effects in humans, some of which may explain why nicotine produces dependence. Individual differences in the magnitude of these effects (i.e., nicotine sensitivity) are of interest to many researchers, such as those examining vulnerability to dependence and processes related to chronic tolerance. However, such characterization of individual differences depends on the consistency of the observed responses, and the consistency of acute effects of nicotine in humans has not been studied systematically. We examined the consistency of the acute effects of the same dose of nicotine administered by nasal spray across multiple drug administration trials, within as well as between sessions. Subjective (i.e., self-reported effects), cardiovascular, and performance measures were assessed following each of four dosing trials of nicotine (20 microg/kg) on three sessions and of placebo on one session. For those measures in which the main effect of nicotine vs. placebo was significant, intraclass correlations were calculated for different sets of trials across different numbers of sessions. Our objective was to determine whether the consistency of responses declined when those responses were based on smaller numbers of trials or sessions, in an effort to guide future research in this area. Results indicated that the consistency of nicotine effects is generally high, even across trials within just one session. Additional research is needed to determine the generalizability of these findings to other methods of nicotine administration, including smoking, and to clarify the extent to which this consistency reflects characteristic consistency of the pharmacological actions of nicotine per se vs. consistency of nonspecific responses to the drug administration procedure.