Leptin has a prime role in responses to stress and elicits antidepressant like effects.  The present study investigates serum leptin, corticosterone and serotonin responses to noise, restraint and immobilization stress and their relationship with stress-induced behavioral deficits in rats. Animals exposed to 2h noise, restraint or immobilization stress were killed either immediately or 24h after the termination of stress to monitor serum leptin, corticosterone and serotonin. Stress-induced deficits in open field exploration as well as decreases of food intake were also monitored. Acute exposure to noise, restraint or immobilization stress resulted in an increase in serum corticosterone and leptin and a decrease in serum serotonin. The corticosterone response, but not leptin or serotonin response, was greater in rats exposed to immobilization than restraint than noise stress. Animals killed 24 h after the cessation of stress exhibited a decrease in serum leptin but corticosterone and serotonin levels were not altered.  Stress-induced deficits of food intake and open field exploration were greater in rats exposed to immobilization than restraint than noise stress. The present study shows that together with increases in circulating levels of corticosteroids and leptin; decreases in serum serotonin are peripheral marker of acute stress response. A decrease in serum leptin associated with deficits of behavior in animals decapitated 24 h post stress termination suggest that an insufficiency of endogenous leptin contributes to stress-related illnesses.

Key words: Anorexia, Corticosterone, Exploratory activity, Leptin, Serum serotonin, Stress