Effects of restraint stress and serotonin on macronutrient selection: a rat model of stress-induced anorexia

The present study investigated the effects of brief (20 min), acute (2 hr) and chronic restraint stress (2 hr/day for five days) at the time of dark onset on macronutrient selection in female Wistar rats. The role of 5-HT1A receptors in nutrient intake was also examined in a dose-response study (100-700 microg/kg body weight) of 8-hydroxy-2-(di-n-propylamino) tetralin (DPAT) in an acute restraint model. A total of 200 rats aged 6-12 months were tested. In all cases, the restraint stress took the form of confinement within tight-fitting cylinder tubes. In the brief and acute paradigms, the intake of pure carbohydrate (CHO), protein (PRO), and fat was measured for 40 min after a single exposure to stress; in the chronic model, nutrient intake was assessed for 40 min only after the final restraint stress session on day 5. In the DPAT paradigm, intraperitoneal injections of the 5-HT1A agonist were given prior to acute restraint and a 40 min session of nutrient self-selection. Statistical analysis using the t-test for independent samples revealed that neither PRO nor total intake was significantly altered by restraint in the brief, acute or chronic restraint experiments, whereas CHO consumption was suppressed by acute (p=0.02) and chronic restraint (p=0.021), and fat intake was suppressed by brief (p=0.010), acute (p=0.002) and chronic restraint (p=0.001). In the DPAT paradigm, acute restraint stress suppressed CHO (p=0.0001), fat (p=0.000001) and total intake (p=0.003). These effects were not reversed by DPAT, and the administration of 300 pg/kg actually further reduced fat intake. In conclusion, fat intake is more sensitive to the suppressive effects of restraint stress than CHO intake, whereas protein intake is unaffected. Furthermore, 5-HT1A receptors do not seem to play a role in the effects of acute restraint on CHO and fat intake.