Analysis of adaptation mechanisms during environmental stress through the neural-immune interaction.

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(1) Amount of c-fos mRNA increased in the medial preoptic area (MPO), lateral hypothalamic area (LHA), and ventromedial hypothalamus (VMH) during cold exposure (4 ℃, 1 hr), while CRF mRNA increased in the MPO and paraventricular hypothalamus (PVN) during heat exposure (33 ℃, 1 hr) and in the MPO and LHA during cold. (2) Intraperitoneal injection of poly I:C (mg/kg) in rats induced suppression of spontaneous running wheel activity for more than one week. During this period IFN-α and serotonin transporter (5-HTT) mRNA increased in the cortex and hypothalamus. (3) Heat exposure induced increase in IL-1β, COX-2 and inhibitor of nuclear factor (NF)-κB-β mRNAs, as well as lipopolysaccharide (LPS) content in the cortex of aged rats. Since pretreatment with an endotoxin inhibitor attenuated the increases in these mRNAs and LPS levels, it was suggested that bacterial translocation induced by heat exposure was one of the mechanisms of the increased expression of IL-1β and its related substances mRNAs in the brain. (4) In vivo brain microdialysis revealed that the extracellular concentration of 5-HT in the prefrontal cortex decreased after poly I:C injection. In addition, the poly I:C-induced suppression of the running wheel activity was attenuated by 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetraline (8-OH-DPAT). (5) Application of a hematopoietic cytokine, stem cell factor (SCF), modulated paired-pulse facilitation in the mossy fiber-CA3 pathway in the mouse hippocampal slices, suggesting that SCF plays a role in the synaptic plasticity in the hippocampus.