Abstract
The difference of amine dynamics in central noradrenergic, dopaminergic and serotonergic systems of adaptive or non-adaptive rats to repeated restraint stress was investigated neurochemically. A single immobilization induced stress responses, such as reductions in growth rate, food intake, water intake and locomotor activity, and an increase in pain threshold. These responses disappeared after repeated immobilization 1 or 2 hr daily for 7 days, but not after 4 hr daily for 7 days. These results suggest that stress adaptation models should include the parameter of repeated exposure to restraint stress 1 or 2 hr daily for 7 days. In the frontal cortex, midbrain-thalamus, striatum, hypothalamus, medulla-pons, cerebellum, cervical cord, thoracic cord and lumbar cord of models with adaptability to repeated restraint stress, a marked increase in serotonin (5-HT) turnover was observed. This neurochemical change was seen in the hypothalamus and lumbar cord of non-adaptive models, but not in the other brain and spinal cord regions. Also, an increase in norepinephrine (NE) turnover in spinal cord regions was observed in adaptive models, but NE turnover was decreased in the frontal cortex, striatum or cervical cord of non-adaptive models. These findings suggest that enhancement of central 5-HT turnover and NE turnover in the spinal cord contribute to the formation of adaptation to repeated restraint stress.
