Long-lasting expression of FosB/ΔFosB immunoreactivity following acute stress in the paraventricular and supraoptic nuclei of the rat hypothalamus

Abstract

We examined expression profiles of FosB/∆FosB immunoreactivity and fosB gene transcripts in the paraventricular nucleus of the hypothalamus (PVH) and the supraoptic nucleus (SON) of rats following acute surgical stress (SS) and restraint stress (RS) and compared them with those of c-Fos immunoreactivity and c-fos mRNA. Following SS, the number of FosB/ΔFosB-ir cells markedly increased, the time course of which was slow-onset and long-lasting, in contrast with rapid-onset and short-lived c-Fos expression. Characteristically long-lasting FosB/ΔFosB expression was also observed following RS. On the other hand, fosB mRNA was short-lived, and its time course not much different from that of c-fos mRNA; thus, the long-lasting expression of FosB/∆FosB immunoreactivity may be attributed to the longer half-life of FosB proteins, and not to the persistent expression of fosB gene transcripts. Following SS, FosB/ΔFosB immunoreactivity was present mainly in PVH corticotropin-releasing factor (CRF) neurons and SON vasopressin (AVP) neurons, while c-Fos immunoreactivity in either PVH CRF neurons, or AVP and oxytocin neurons in PVH and SON. Following RS, FosB/ΔfosB- and c-Fos expression was almost restricted to PVH CRF neurons. The present study raises the possibility that FosB proteins in discrete populations of hypothalamic neuroendocrine neurons may play roles in forming adaptability to and/or resilience against stress, which takes longer than the acute phase response.