STRESS-RELATED BEHAVIOR AND CENTRAL NOREPINEPHRINE CONCENTRATIONS IN THE REM SLEEP-DEPRIVED RAT

Rapid eye movement sleep deprivation (REMd) is a potent stressor in th e rat. Behavioral abnormalities are among the earliest overt symptoms of REMd, the mechanisms for which remain largely unknown. The phenomen a of hyperphagia and weight loss that are associated with REMd may con tribute to its later morbidity; however, little is known about the ons et of these phenomena or the neurotransmitter mechanisms that are invo lved. The aim of this study was to determine whether the earliest effe cts of REMd on consumatory behavior in the rat and its performance in the swimming cylinder of Porsolt are related to changes in norepinephr ine (NE) concentrations in the cerebral cortex and selected areas of t he hypothalamus. Sprague-Dawley rats were divided into three groups (n = 6): the REMd group resided in a water tank on 6.5-cm diameter pedes tals for 96 h; the tank control (TC) group resided in the water tank o n 15-cm pedestals for 96 h; the cage controls (CC) remained in their h ome cages for the duration of the study. In the first series of experi ments, body weights and caloric intake were recorded daily, along with the performance of all animals in the swimming cylinder of Porsolt. I n the second series of experiments, body weights and caloric intake we re recorded, but the Porsolt test was not employed and the brains were dissected after 96 h for NE analysis by HPLC. It was observed that th e REMd group had lower immobility times (p < 0.05) in the Porsolt test after only 24 h, compared to groups TC and CC. Caloric intake in the REMd group was significantly greater than that of the TC group only wh en the rats were not subjected to the additional stress of the Porsolt test. The NE concentrations were significantly diminished in the ante rior hypothalamus of the REMd and TC groups, suggesting activation of central thermogenic mechanisms in rats exposed to the water tank regar dless of pedestal size. In the parietal cortex, NE concentrations were significantly increased in both the REMd and TC groups, suggesting an increase in basal arousal levels in the rats exposed to the water tan k. However, NE concentrations in the lateral hypothalamus of the REMd group were significantly greater than those of the TC group, whereas t he TC and CC groups were not different. The NE concentrations in the l ateral hypothalamus thus correlated with both the caloric intake and P orsolt test data in the REM sleep-deprived rats.