| To explore the relationship between PVN-CRH and LC - NE neuronal systems, which are considered as two most important stress systems, we studied the c-fos expression in rats brain after cold stress, including PVN and LC. We also identified the chemical characteristics of neurons expressing Fos by double staining and determined the plasma level of ACTH by radioimmunoassay, in addition, we studied the changes of plasma ACTH level and Fos expression in rats brain induced by cold stress after intracerebroventricular (Lev.) injection of 6-hydroxydopamine(6-OHDA).The experimental results indicated that: 1) Cold stress could induce significant Fos protein expression in many areas of brain, such as hypothalamic paraventricular nucleus, supraoptic nucleus, hypothalamic dorsomedial nucleus, hypothalamic ventromedial nucleus, lateral septal nucleus, central amygdaloid nucleus, medial preoptic nucleus, anterior parvicellular of paraventricular hypothalamic nucleus in forebrain and nucleus of the solitary tract, locus coeruleus, A5 in hindbrain. After i.c.v. 6-OHDA , the c-fos expression of these areas induced by cold stress reduced significantly. 2) Double staining showed that Fos-like immunoreactive positive granules were observed in somevasopressin(AVP)-immunoreactive positive neurons in paraventricular and supraoptic nuclei, as well as in some tyrosine hydroxylase(TH) -immunoreactive positive neurons in NTS and LC nuclei. The number of cells expressing Fos- and AVP-immunoreactivity in PVN were decreased significantly after i.c.v. 6-OHDA. 3) Plasma ACTH level was increased by cold stress significantly, which could be blocked partially after 6-OHDA i.c.v, administration.The results suggested that hypothalamic PVN-AVP neuronal system and LC -NE neuronal stystem in brainstem could be activated by cold stress. Cold stress could also activated HPA axis. The activation of HPA axis could be mediated, at least in part, by NE neuronal system.
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