Functional mapping of visceral sympathetic outflow and skeletal muscle blood flow in the hypothalamus of rats

The lateral hypothalamic area, including dorsomedial hypothalamic area (DMH) and it’s marginal area, have been proposed to play a critical role in the defensive cardiovascular response to stress. In the typical defense response, it is recognized that blood flow redistribution is caused sympathetically and is conflicting between abdominal and skeletal muscle blood flows. In this study, we tested that localization of neurons within the DMH and the marginal areas evokes the patterns of cardiovascular response. Arterial pressure, heart rate, renal sympathetic nerve activity (RSNA), and skeletal muscle blood flow (SMF) were recorded simultaneously in urethane-anesthetized rats. Microinjections of very small amounts of bicuculline (BIC, 2.5pmol in 5 nl) were made within sites of the DMH and the marginal areas. Two different patterns of RSNA and SMF were observed in the DMH. The typical "defense response" pattern, which was increases in blood pressure, heart rate, RSNA and SMF, was observed in the caudal and dorsal region of the DMH. In contrast, microinjection of BIC in the DMH caused increase in RSNA and decrease in SMF, though distinct distribution between the 2 patterns was not found. We conclude that there are at least 2 populations of neurons in the DMH to regulate skeletal vascular beds and that the DMH may play key role to redistribute of the blood flow during the stress condition.