Furlan R. Lateralization of expression of neural sympathetic activity to the vessels and effects of carotid baroreceptor stimulation. Am J Physiol Heart Circ Physiol 296: H1758 -H1765, 2009. First published April 10, 2009 doi:10.1152/ajpheart.01045.2008.-Human studies suggest that cardiovascular neural sympathetic control is predominantly modulated by the right cerebral hemisphere. It is unknown whether post-ganglionic sympathetic activity [muscle sympathetic nerve activity (MSNA)] shows any functional asymmetry. Eight right-handed volunteers (3 women and 5 men, 32 Ϯ 2 yr of age) underwent ECG, beat-by-beat blood pressure, respiratory activity, and simultaneous right and left MSNA recordings during spontaneous and controlled breathing (CB, 15 breaths/min, 0.25 Hz). Dynamic carotid baroreceptor stimulation was obtained by 0.1-Hz sinusoidal suction, from 0 to Ϫ50 mmHg, randomly applied to the right, left, and combined right and left sides of the neck during CB. Laterality was assessed by changes in the MSNA burst rate (in bursts/min, and bursts/100 beats), strength [amplitude (A) and area (AA)], and the oscillatory component at 0.1 Hz during baroreceptor stimulation. Amplitude parameters were normalized by CB burst mean amplitude and area of the same side. At rest, the right and left MSNA burst rate and total MSNA activity were similar. Conversely, the right MSNA normalized burst AN (1.36 Ϯ 0.18) and AAN (1.31 Ϯ 0.16) were larger than the left MSNA AN (1.04 Ϯ 0.09) and AAN (1.02 Ϯ 0.08). Unilateral and bilateral carotid baroreflex stimulation abolished the right prevalence of AN and AAN. In conclusion, the right lateralization of sympathetic activity to the vessels is indicated by normalized burst strength parameters of bilateral MSNA recordings at rest during spontaneous breathing. Carotid baroreceptor stimulation disrupted such expression of MSNA lateralization possibly by disturbing the synchronizing action of right cerebral hemisphere. sympathetic control of circulation; muscle sympathetic nerve activity recording; burst amplitude; area; laterality SEVERAL HUMAN STUDIES support the concept that the neural sympathetic activity regulating the cardiovascular system undergoes a predominant modulation exerted by the right cerebral hemisphere (2, 4, 10, 17-19, 33, 34). The right side of the medulla was also found to be involved in cardioacceleration in vagotomized animals (16). However, it has to be pointed out that the large majority of these investigations focused on functional modifications of the sympathetic target organs, i.e., on changes of heart rate and blood pressure and their variability, and did not focus on a direct measure of right and left efferent sympathetic activity.Two studies (27, 28) addressed the problem of the potential dissimilarity between the right and left neural efferent sympathetic activity by recording simultaneously muscle sympathetic nerve activity (MSNA) in both peroneal nerves in humans. Sundlof and Wallin (27) focused on burst rate, which was found to be similar in the right and le...