Biopsychological study on characteristics of stress responses associated with appetitive and aversive behaviors

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The aim of the present study was to examine the effects of stress associated with appetitive and aversive behaviors on endocrine, immune and neurochemical functions in rats. Appetitive and aversive stimuli used here were intracranial self-stimulation and immobilization, respectively. The results were as follows : (1) Plasma corticosterone levels were determined using a radioimmunoassay. Both self-stimulation and immobilization stress increased corticosterone levels in the blood to a similar degree. (2) Cellular immune responses of splenic lymphocytes to B-cell and T-cell mitogens were measured by [ィイD13ィエD1H]thymidine uptake, and natural killer cell cytotoxicity in splenic lymphocytes was measured against YAC-1 by a[ィイD151ィエD1Cr] release assay. Immobilization suppressed all of these immune responses, whereas self-stimulation did not have any effect on immune function. (3) The effects of appetitive and aversive stimuli on glutamate (GLU) efflux in the medial prefrontal cortex (mPFC) wer … More e assessed using microdialysis. Self-stimulation caused a small decrease in extracellular GLU concentrations followed by a large increase returning to basal levels after cessation of the appetitive manipulation. Immobilization produced a rapid increase in GLU levels which peaked twice, during the period of the stress and when rats were freed from the aversive manipulation. Thus, we observed a differential time course of changes in GLU efflux from the mPFC in response to appetitive and aversive stimuli. Both appetition- and aversion-evoked GLU effluxes were attenuated, but not abolished, by co-perfusion of tetrodotoxin (TTX), a sodium channel inhibitor. These TTX-insensitive GLU effluxes sustained biphasic changes, comparable to that in the normal stimulated-GLU effluxes. On the other hand, TTX-sensitive components of GLU efflux were estimated to increase monophasically and to be very similar in their time courses. The results suggest that the different time course of GLU effluxes in the mPFC induced by appetitive and aversive behaviors is a result of TTX-insensitive GLU efflux. Less