Sa. Aicher et Dj. Reis, GIGANTOCELLULAR VASODEPRESSOR AREA IS TONICALLY ACTIVE AND DISTINCT FROM CAUDAL VENTROLATERAL VASODEPRESSOR AREA, American journal of physiology. Regulatory, integrative and comparative physiology, 41(3), 1997, pp. 731-742
The gigantocellular depressor area (GiDA) is a functionally defined su
bdivision of the medullary gigantocellular reticular formation where v
asodepressor responses are evoked by glutamate microinjections (Aicher
, S. A., D. J. Reis, D. A. Ruggiero, and T. A. Milner. Neuroscience 60
: 761-779, 1994). The present experiments sought to determine whether
the GiDA 1) tonically inhibits the sympathetic nervous system; 2) is n
ecessary for baroreflex function; and 3) is functionally distinct from
adjacent vasodepressor regions in the medullary reticular formation,
including the midline raphe nuclei and the caudal ventrolateral medull
a (CVL). Excitotoxic lesions of the GiDA abolished the baroreflex and
significantly increased sympathetic nerve activity in anesthetized rat
s. Equivalent injections into the midline raphe nuclei elevated sympat
hetic activity but did not alter baroreflex responses. Therefore, the
GiDA is functionally distinct from the raphe nuclei, although both con
tain tonically active sympathoinhibitory neurons. Because the effects
of GiDA lesions were identical to those seen after lesions of the CVL,
further studies were required to demonstrate that the GiDA and CVL ar
e functionally and anatomically distinct. First, intramedullary inject
ions of kynurenic acid produced hypertension and blocked the barorefle
x when placed in the CVL, but not when placed in the GiDA. Second, mus
cimol inactivation of the RVL blocked the hypertension produced by exc
itotoxic lesions of the CVL, but failed to block the hypertension prod
uced by similar lesions of the GiDA. Third, CVL neurons project to the
RVL but not the spinal cord, whereas GiDA neurons project to the spin
al cord but not the RVL. These studies show that the CVL and GiDA are
both tonically sympathoinhibitory regions, but they are distinct with
regard to their functional connectivity with other autonomic regions.