Interactive effects of trigeminal nerve stimulation and muscle metaboreflex activation on muscle sympathetic nerve activity in healthy humans (1170.5)

Abstract

We investigated the independent and interactive effects of trigeminal cutaneous receptor stimulation and activation of metabolically sensitive skeletal muscle afferents (muscle metaboreflex) on muscle sympathetic nerve activity (MSNA). Heart rate (HR; ECG), blood pressure (BP; Finometer) and MSNA (microneurography) were continuously recorded in eight healthy men (29±2 yr) during three experimental conditions; 1) facial cooling [0°C, trigeminal stimulation, TGS], 2) muscle metaboreflex activation by post‐exercise ischemia [PEI] following isometric handgrip at 30% maximum voluntary contraction, and 3) simultaneous TGS and PEI. Trials were counterbalanced and respiratory rate and tidal volume controlled at baseline, TGS, PEI and TGS+PEI. TGS produced a significant decrease in HR (Δ‐5±2 bpm; mean±SE), and increase in mean BP (Δ14±3 mmHg) and MSNA total activity (Δ353±118% AU). During PEI, HR remained at resting levels (Δ3±2 bpm; mean±SE), while mean BP (Δ25±3 mmHg) and MSNA total activity (Δ234±83% AU) increased. Finally, during combined TGS and PEI, HR was unchanged (Δ0±2 bpm; mean±SE), while mean BP (Δ30±3 mmHg) and MSNA total activity (Δ331±100% AU) were increased. Thus, excitatory inputs from the trigeminal nerve and metabolically sensitive skeletal muscle afferents do not appear to summate algebraically in determining a MSNA response, but rather exhibit neural occlusion.Grant Funding Source: Supported by CAPES, CNPq, FAPERJ.