Stress-related behavior and central norepinephrine concentrations in the REM sleep-deprived rat

Abstract

Rapid eye movement sleep deprivation (REMd) is a potent stressor in the rat. Behavioral abnormalities are among the earliest overt symptoms of REMd, the mechanisms for which remain largely unknown. The phenomena of hyperphagia and weight loss that are associated with REMd may contribute to its later morbidity; however, little is known about the onset of these phenomena or the neurotransmitter mechanisms that are involved. The aim of this study was to determine whether the earliest effects of REMd on consumatory behavior in the rat and its performance in the swimming cylinder of Porsolt are related to changes in norepinephrine (NE) concentrations in the cerebral cortex and selected areas of the hypothalamus. Sprague-Dawley rats were divided into three groups ( n = 6): the REMd group resided in a water tank on 6.5-cm diameter pedestals for 96 h; the tank control (TC) group resided in the water tank on 15-cm pedestals for 96 h; the cage controls (CC) remained in their home cages for the duration of the study. In the first series of experiments, body weights and caloric intake were recorded daily, along with the performance of all animals in the swimming cylinder of Porsolt. In the second series of experiments, body weights and caloric intake were 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 the 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 when the rats were not subjected to the additional stress of the Porsolt test. The NE concentrations were significantly diminished in the anterior hypothalamus of the REMd and TC groups, suggesting activation of central thermogenic mechanisms in rats exposed to the water tank regardless 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 tank. However, NE concentrations in the lateral hypothalamus of the REMd group were significantly greater than those of the TC group, whereas the TC and CC groups were not different. The NE concentrations in the lateral hypothalamus thus correlated with both the caloric intake and Porsolt test data in the REM sleep-deprived rats.