CENTRAL INSPIRATION INCREASES BAROSENSITIVITY OF NEURONS IN RAT ROSTRAL VENTROLATERAL MEDULLA

Barosensitive neurons in the rostral ventrolateral medulla (RVLM) ofte n have a respiratory-related modulation of their activity. However, th e extent of the interaction between baroreceptor and respiratory input s is controversial. The main aim of the present study was to determine the effect of central respiratory drive (CRD) on the barosensitivity of RVLM neurons. Extracellular recordings were obtained from 68 barose nsitive neurons in the RVLM of anesthetized, paralyzed, and bilaterall y vagotomized Sprague-Dawley rats. Examination of phrenic-triggered hi stograms revealed five activity patterns among barosensitive neurons: inspiratory depression (type I, n = 20), early inspiratory activation (type II, n = 14), postinspiratory activation (type III, n = 18), expi ratory depression (type IV, n = 5) and no modulation (type V, n = 11). In most neurons (types I and III and 56% of type II) inhibition produ ced by aortic nerve stimulation was greater in inspiration than in exp iration. Cardiac-related modulation, as an index of natural phasic bar oreceptor activation, was also greater in inspiration than expiration in type III neurons. The results demonstrate that CRD modulates the ba roreflex at the level of the RVLM.