A comparison of hypotensive and non-hypotensive hemorrhage on Fos expression in spinally projecting neurons of the paraventricular nucleus and rostral ventrolateral medulla
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Abstract
The protein, Fos, detected immunohistochemically, was used to identify neurons in
the brain that were activated after hemorrhage in the conscious rat. Spinally projecting
neurons in the paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM)
were identified by the presence of rhodamine-labeled latex beads which had been previously
injected into the upper thoracic spinal cord. On the experimental day, conscious rats
underwent either (1) withdrawal of 4 ml of blood from a carotid cannula (n = 8) which
reduced mean arterial pressure from 96.6 +/- 2.7 to 42.7 +/- 7.1 mmHg, (2) withdrawal
of 2 ml of blood (n = 4) which did not affect mean arterial pressure. Animals that
were not hemorrhaged were used as controls (n = 6). After the 4 ml hemorrhage, dense
concentrations of Fos-positive cell nuclei were found in the lamina terminalis, supraoptic
nuclei (SON), PVN and in the medulla. In contrast, the density of Fos-positive cells
in 2 ml-hemorrhaged rats was not different from controls except in the SON and in
the medial PVN in 2 of 4 rats. After the 4 ml hemorrhage 14.4 +/- 1.2% of the spinally
projecting neurons in the PVN and 22.7 +/- 6.1% in the RVLM expressed Fos (P < 0.001
compared to control). After the 2 ml hemorrhage the proportion was 12.2 +/- 3.1% in
the PVN (P < 0.001 compared control) but only 5.4 +/- 2.2% in the RVLM (P > 0.05 compared
to control). The results suggest that spinally projecting neurons in the PVN and RVLM
participate in the reflex responses to hemorrhage.(ABSTRACT TRUNCATED AT 250 WORDS)