Distribution of neurons in the anterior hypothalamic nucleus activated by blood pressure changes in the rat

Electrophysiological and Fos-like protein immunocytochemical methods were u sed to identify the number and distribution of anterior hypothalamic neuron s that are activated by changes in arterial pressure. First, in anesthetize d, male Sprague-Dawley rats, arterial pressure increases and decreases led to differential activation of neurons in the anterior hypothalamic nucleus. Most of the units that responded to a rise in arterial pressure with a dec rease in activity (pressor units) were located in the central part of the a nterior hypothalamic nucleus, whereas units that increased firing when arte rial pressure rose (the depressor units) were found throughout the nucleus. Second, in awake, male Sprague-Dawley rats, Fos-like protein immunoreactiv ity was mapped following sustained arterial pressure changes. Within the an terior hypothalamus, reduction in arterial pressure increased the number of Fos-labeled neurons primarily in the paraventricular nucleus and to a less er extent in the anterior half of the anterior hypothalamic nucleus. In con trast, elevation in arterial pressure increased Fos labeling throughout the anterior hypothalamic nucleus and to a lesser extent in the paraventricula r nucleus. (C) 1999 Elsevier Science Inc.