EFFECT OF TOBACCO SMOKE ON KNEE-JERK REFLEX IN MAN

The knee-jerk reflex was elicited automatically in human volunteers every 10 sec. Cigarette smoking caused a decrease in the knee-jerk which was more pronounced in non-smokers and light smokers than in heavy smokers. Smoking cigarettes containing an amount of nicotine comparable to commercial cigarettes (2.1%) inhibited the knee-jerk in a significantly greater number of subjects than did smoking cigarettes with a low nicotine content (0.1%). The knee-jerk of some subjects was facilitated by the contemporaneous performance of a task; cigarette smoking depressed the knee-jerks of these subjects more than in subjects who showed little or no facilitation. It is suggested that the depression of the knee-jerk is due to the nicotine present in the cigarette smoke and that the so-called tranquillisation attributed to cigarette smoking may be related to inhibition of reflex mechanisms. © 1968.