Identification of brainstem projections mediating hemodynamic responses to stimulation of the anteroventral third ventricle (AV3V) region.

The anteroventral third ventricle (AV3V) region is necessary for the development of several models of experimental hypertension in rats. Electrical stimulation of the AV3V region produces hindlimb vasodilation, mesenteric and renal vasoconstriction and bradycardia resulting in a depressor response. The effect of selective ablation of diencephalic and mesencephalic sites upon responses to AV3V stimulation was employed earlier to functionally identify descending tracts from the AV3V region through the ventromedial hypothalamus and rostral central gray. This study was performed in a similar manner to identify more caudal projections from the AV3V region to the level of pons and medulla. The vasodilator response to AV3V stimulation was dependent upon sites in and around the nucleus tractus solitarius, although the region receiving primary baroreceptor afferent input was not part of this projection. Visceral vasoconstrictor tracts were less clearly defined suggesting that these projections traverse diffusely through the ventrolateral tegmentum. These data suggest that a topographical differentiation of descending vasomotor tracts from the AV3V region exists in the brainstem of the rat.