Neuronal activation in nucleus tractus solitarius and area postrema of young and aged female rats induced by hypotension

Abstract

It is well documented that blood pressure changes with age, and the effect is particularly pronounced in females. However, few studies have examined blood pressure in aged individuals, and most animal studies have been done with male rats. Our goal was to investigate responses to experimental hypotension in aged females, comparing activity in central nervous system areas implicated in blood pressure control in young and aged female rats. Isoproterenol (ISOP) is a B-adrenergic agonist that produces hypotension, thereby activating the renin-angiotensin system (RAS) and baroreceptors located in the aorta and great veins. Input from baroreceptors terminates in the hindbrain Nucleus of the Solitary Tract (NTS), whereas circulating hormones are detected by the adjacent Area Postrema (AP). Accordingly, we assessed neural activation in these areas using immunohistochemical labeling for the fos protein.

The results showed a marked difference in numbers of fos+ neurons between young and aged female rats across both areas in response to ISOP. Fos in aged females was blunted in both caudal and middle levels of the NTS and throughout the AP. We conclude that aged females have an impaired response to baroreceptor input after hypotension and are less sensitive to hormones, such as Ang II, that are associated with hypotension. Thus, neurons in the hindbrain areas involved in cardiovascular control may play a role in age-related changes in blood pressure in females.