Acute plasma tryptophan depletion and smoking abstinence: Withdrawal, mood and quantitative EEG correlates and the acute smoking response.

Abstract

Since research has implicated a role for serotonin function in smoking abstinence and in smoking behavior, the present study examined the effects of a tryptophan-depleting amino acid mixture and the subsequent smoking of a single cigarette on the nicotine withdrawal syndrome, mood and quantitative electroencephalography (EEG) in chronic smokers acutely deprived of smoking. In a double-blind, placebo-controlled, repeated measures design, eighteen male smokers were tested on two separate occasions, three days apart. On each occasion they: (a) ingested a nutritionally balanced amino acid mixture containing tryptophan or ingested a similar mixture devoid of tryptophan, and (b) sham smoked and smoked a single cigarette. Nicotine withdrawal symptoms, mood states, EEG and expired-breath carbon monoxide (CO) concentrations were measured four times: (a) immediately before smoking deprivation and ingestion of the amino acid mixtures (baseline); (b) 5 hr after smoking abstinence and ingestion of the amino acid mixtures; (c) immediately after sham smoking, and (d) after cigarette smoking. Total plasma tryptophan levels were measured two times: before and 5 hr after amino acid mixture ingestion. A significant reduction of plasma tryptophan (71%) was achieved by the tryptophan-depletion mixture. Smoking deprivation led to clear time-dependent increases in negative mood state and nicotine withdrawal ratings and reduced EEG activation. While acute tryptophan depletion did not exacerbate this withdrawal in abstinent smokers as evidenced by the absence of change in mood and withdrawal ratings, it was associated with altered brain state arousal as indicated by the reduction in alpha2 amplitude. While the smoking of a cigarette reduced and reversed to baseline some of the smoking abstinence-induced effects, these effects were not influenced by the tryptophan depletion mixture. Localized and lateralized EEG effects in abstinent smokers and following tryptophan depletion were also not observed. These findings suggest that in chronic male smokers reduced serotonin neurotransmission is not an important characteristic of acute smoking withdrawal effects. These results do not support previous research that has implicated altered serotonin function in tobacco withdrawal and in smoking behavior.