Baseline-dependency of nicotine effects: a review

'Rate-dependency', a founding observation of behavioral pharmacology, gener ally indicates that effects of drugs will be inversely related to the rate of operant responding under control conditions (i.e. decrease in high-rate behaviors and increase in low-rate behaviors). 'Baseline-dependency' encomp asses rate-dependency and extends this notion to other drug effects, includ ing those assessed by means other than 'rate' (such as subjective mood self -reports). Although little human research has specifically investigated the effects of nicotine as a function of baseline level of responding, a numbe r of studies suggest baseline-dependent differences in the influence of nic otine on behavioral and cognitive task performance and on subjective mood r esponses. Results of many animal studies also are very consistent with thes e observations. Baseline-dependency, perhaps, is most clearly demonstrated in comparisons between groups selected on the basis of specific characteris tics (e.g. high vs low 'trait hostility'), or within subjects as a result o f acute environmental manipulations (e.g. high vs low 'stress' task). Moreo ver, baseline-dependency of the effects of nicotine may have broader applic ability in explaining individual differences in vulnerability to nicotine d ependence, particularly among those with psychiatric disorders (e.g. depres sion). While individual differences in responses to nicotine may be due to differences in pharmacological sensitivity to nicotine, as commonly assumed , they also may be due partly to individual and situationally determined di fferences in baseline level of responding on the measure of interest. Consi deration of the conditions under which baseline-dependent effects of nicoti ne are observed may clarify both individual difference and situational infl uences on responses to nicotine. (C) 1999 Lippincott Williams C Wilkins.