DISTRIBUTION OF ACTIVATED NEURONS IN THE RABBIT BRAIN FOLLOWING A VOLUME LOAD

Immunohistochemical detection of the protein, Fos, was used to identif y neurons in the brain activated following a volume load. The plasma e xpanders, Haemaccel and 6% dextran, were infused intravenously in cons cious rabbits for 60 min. Compared to control animals both stimuli sig nificantly increased right atrial pressure but had no effect on blood pressure. Heart rate was significantly elevated with dextran only. Vol ume expansion with Haemaccel also reduced renal sympathetic nerve acti vity by about 50% from the pre-infusion resting level. Ninety minutes after the start of the infusion, the rabbits were perfusion fixed and the distribution of Fos-positive cell nuclei was examined. Following H aemaccel infusion there were significant increases in the number of Fo s-positive cell nuclei in the organum vasculosum of the lamina termina lis, parvocellular paraventricular nucleus and in specific rostrocauda l levels of the nucleus tractus solitarius and ventrolateral medulla. Following dextran similar effects were observed in the medulla but Fos -positive cell nuclei were not significantly elevated above controls i n the forebrain. After Haemaccel or dextran areas such as the supraopt ic nucleus, the magnocellular paraventricular nucleus, the bed nucleus of the stria terminalis, diagonal band of Broca and amygdala either d id not produce Fos or were not consistently different from the control group. The results suggest that specific brain regions, that are know n to be important in cardiovascular control, are activated by a volume load. These areas are likely to play an important role in the reflex responses initiated by that particular stimulus. (C) 1997 IBRO. Publis hed by Elsevier Science Ltd.