NEURONS IN THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS THAT PROJECT TO THE ROSTRAL VENTROLATERAL MEDULLA ARE ACTIVATED BY HEMORRHAGE

The retrogradely-transported tracer, rhodamine-tagged microspheres, wa s injected into the presser region of the rostral ventrolateral medull a (RVLM) to identify paraventricular neurons in the hypothalamus that project to the RVLM. The protein, Fos, was detected immunohistochemica lly and used to highlight neurons that were activated by a hypotensive haemorrhage. Compared to controls, Fos production was increased by ap proximately 3-fold in the paraventricular nucleus (P < 0.009) and ther e was a significant increase in the number of retrogradely-labelled ce lls that expressed Fos. These represented 5% of the retrogradely-label led cell population. The results suggest that a small subpopulation of PVN neurons projecting to the RVLM are activated by haemorrhage and m ay be involved in the reflex responses initiated by that stimulus. (C) 1998 Elsevier Science B.V.