FAILURE OF NICOTINE TO AFFECT NEUROACTIVE STEROID CONCENTRATIONS IN THE BRAIN OR PLASMA OF RATS.

Nicotine, one of the most widely used psychotropic substances, is able to induce both anxiolytic and anxiogenic effects. The effect of this drug on the brain and plasma concentrations of neuroactive steroids was examined in the rat. A single intraperitoneal injection of nicotine (0.1 to 3 mg/kg) did not affect the concentrations of 3a-hydroxy-5a-pregnan-20-one (allopregnanolone) or 3a,21-dihydroxy-5a-pregnan-20-one (allotetrahydrodeoxycorticosterone, or THDOC), or those of their precursors progesterone and pregnenolone, in the cerebral cortex, hippocampus, or plasma of rats at various times (15, 30, or 45 min) after drug administration. In contrast, nicotine induced a dose-and time-dependent increase in the plasma concentration of corticosterone, indicating that this drug activates the hypothalamic-pituitary-adrenal axis. These results suggest that the changes in emotional behavior elicited by nicotine, unlike those induced by stressful stimuli or other anxiogenic drugs, are not associated with an increase in neuroactive steroid content of the brain or plasma.