Effect of L-cysteine on acetaldehyde self-administration.

Acetaldehyde (ACD), the first metabolite of ethanol, has been implicated in several behavioural actions of alcohol, including its reinforcing effects. Recently, we reported that L-cysteine, a sequestrating agent of ACD, reduced oral ethanol self-administration and that ACD was orally self-administered. This study examined the effects of L-cysteine pre-treatment during the acquisition and maintenance phases of ACD (0.2%) self-administration as well as on the deprivation effect after ACD extinction and on a progressive ratio (PR) schedule of reinforcement. In a separate PR schedule of reinforcement, the effect of L-cysteine was assessed on the break-point produced by ethanol (10%). Furthermore, we tested the effect of L-cysteine on saccharin (0.2%) reinforcement. Wistar rats were trained to self-administer ACD by nose poking on a fixed ratio (FR1) schedule in 30-min daily sessions. Responses on an active nose-poke caused delivery of ACD solution, whereas responses on an inactive nose-poke had no consequences. L-cysteine reduced the acquisition (40 mg/kg), the maintenance and the deprivation effect (100 mg/kg) of ACD self-administration. Furthermore, at the same dose, L-cysteine (120 mg/kg) decreased both ACD and ethanol break point. In addition, L-cysteine was unable to suppress the different responses for saccharin, suggesting that its effect did not relate to an unspecific decrease in a general motivational state. Compared to saline, L-cysteine did not modify responses on inactive nose-pokes, suggesting an absence of a nonspecific behavioural activation. Taken together, these results could support the hypotheses that ACD possesses reinforcing properties and L-cysteine reduces motivation to self-administer ACD.