Effects of urinary pH on the behavioral responses of squirrel monkeys to nicotine

Behavioural studies in humans: anxiety, stress and smoking

Numerous observers have reported that smokers smoke more under stressful conditions. The most frequent explanation is that nicotine reduces anxiety, an intervening variable identified as a negative reinforcer for smoking behaviour. The conditions under which anxiety reduction occurs in response to smoking, however, have not been well defined, nor are underlying mechanisms well understood. There are several possible explanations, including Schachter's theory based on stress-induced changes in urinary pH and the hypothesis of endogenous opioid involvement. The work of Collins and his associates in animals has shown that genetic variations in corticosteroid responsiveness to nicotine are associated with differences in sensitivity to nicotine. Research in our laboratory has extended to humans Collins' findings that sensitivity to nicotine is inversely related to corticosteroid activity. We also found that the combination of a psychological stressor and smoking produced additive effects on cortisol release in humans. These findings suggest a novel way of explaining the interaction between smoking and stress, in that increased nicotine intake in the context of stress may in part reflect behavioural compensation for diminished sensitivity to nicotine when corticosteroid activity is enhanced by the stressor.

Smoking, stress, and negative affect: correlation, causation, and context across stages of smoking

This transdisciplinary review of the literature addresses the questions, Do stress and negative affect (NA) promote smoking? and Does smoking genuinely relieve stress and NA? Drawing on both human and animal literatures, the authors examine these questions across three developmental stages of smoking--initiation, maintenance, and relapse. Methodological and conceptual distinctions relating to within- and between-subjects levels of analyses are emphasized throughout the review. Potential mechanisms underlying links between stress and NA and smoking are also reviewed. Relative to direct-effect explanations, the authors argue that contextual mediator-moderator approaches hold greater potential for elucidating complex associations between NA and stress and smoking. The authors conclude with recommendations for research initiatives that draw on more sophisticated theories and methodologies.

Neuroendocrine responses to nicotine and stress: enhancement of peripheral stress responses by the administration of nicotine

Habitual smokers frequently report that when they are stressed smoking helps them to relax. One potential explanation for the reported stress ameliorating effect of smoking is that cigarette consumption (nicotine self-administration) may decrease the sympathetic autonomic nervous system activity which is associated with the stress response. In the present study, rabbits prepared with chronic vascular cannulae were used to study the effects of nicotine administration on plasma corticosterone, catecholamine (epinephrine, norepinephrine and dopamine) and glucose responses to physical restraint stress. Nicotine (0.025, 0.05 or 0.10 mg nicotine base/kg body weight) was administered for 10 days prior to the "stress test" to allow for the development of habituation/tolerance to its acute toxic effects. Independent administration of nicotine, or the application of the physical restraint stressor, resulted in increases in the plasma concentrations of corticosterone, epinephrine, norepinephrine, and glucose. Nicotine administration during restraint stress enhanced the increase in plasma corticosterone and epinephrine, as compared to the responses induced by either factor alone. The results suggest that the stress ameliorating effect of continued cigarette smoking, as reported by habitual smokers, is not due to a reduction in the activity of the peripheral sympathetic autonomic nervous system.

Pharmacologic characterization of nicotine-induced conditioned place preference

Rats received subcutaneous injections of either nicotine (0.1 to 1.2 mg/kg) or saline (1.0 ml/kg) immediately prior to conditioning sessions in a conditioned place preference (CPP) paradigm. The drug was paired for 3 conditioning sessions with the non-preferred environment of a 3 compartment place preference apparatus; saline was paired with the preferred environment. The animals were then tested for place preference by determining the proportion of time spent in the preferred and non-preferred compartments during a 15 min test session. Using a statistical method developed for the CPP paradigm, dose-response curves were obtained for the rewarding and aversive effects of nicotine as measured by its ability to alter previously determined baseline preferences obtained from the control animals. Nicotine's rewarding and aversive effects were linearly correlated with respect to dosage within the range of 0.1-0.8 mg/kg (reward increased and aversion decreased). A decrease in reward and an increase in aversion was measured at the 1.2 mg/kg treatment level. Mecamylamine hydrochloride and hexamethonium bromide (at 1.0 mg/kg of the base or ion, respectively) were also tested using the CPP paradigm. While neither compound produced place preferences when administered alone, mecamylamine did block the rewarding effects of 0.8 mg/kg of nicotine when administered 30 minutes prior to the nicotine conditioning sessions. Hexamethonium did not alter nicotine-induced reinforcement. The data suggest that nicotine and its rewarding effects as measured by CPP are primarily mediated by central rather than peripheral events.