Abstract
Based upon the previous findings obtained from the several neurochemical studies wherein the rats were subjected, we have proposed the three main neurochemical mechanisms of onset of psychosomatic disorders. We have employed the in vivo microdialysis method and the simultaneous determination of levels of both noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-S0_4) , the major metabolite of NA and the indicative of the released NA, in the rat brain regions. When the rats were exposed to the activity-stress paradign wherein they were kept in a runningwheel activity cage consisting of a wire drum activity wheel and adjoining chamber under a foodrestricted feeding schedule for I hour per day, the number of wheel revolutions was markedly and progressively increased and they revealed the severe gastric lesions and finally resulted in death. Under this situation, the very marked increases in NA release exceeding those caused by other chronic stress situations occurred in the extended brain regions. The finding suggests that one of neurochemical mechanisms of onset of psychosomatic disorders might be the excessive increases in the neurotransmitter release caused by stress. We examined whether or not an aggressive biting response could affect the brain NA release during stress exposure. The rats were restrained in the supine position with or without being allowed to bite a wooden stick. The non-biting rats showed the more marked and persistent increases in brain NA release as compared to those in biting rats. It is suggested that the persistent increases in the neurotransmitter release, even if the degree might be within the range caused by the usual stress situation, might be one of the causative mechanisms of the disorders. When young rats (2 months old) and aged rats (18 months old) were exposed to the repeated immobilization stress for 16 hours daily in 6 days, the brain NA release in the aged rats was markedly and persistently increased, however, no such a phenomenon was observed in the young rats. The finding raises a possibility that the excessive and persistent increases in the transmitter release might also be the causative mechanism. These findings suggest that there might be, at least, the three main neurochemical mechanisms related to onset of psychosomatic disorders ; stress-induced increases in the neurotransmitter release might be excessive, persistent, and excessive and persistent.
