Circadian variations of stellate ganglion nerve activity in ambulatory dogs

BackgroundThe presence of circadian variations in sympathetic outflow from the stellate ganglia is unclear.ObjectivesThe purpose of this study was to continuously record stellate ganglion nerve activity (SGNA) in ambulatory dogs.MethodsWe performed continuous 24-hour left (N = 3) or bilateral (N = 3) SGNA recordings in normal ambulatory dogs using implanted Data Sciences International transmitters. We also performed simultaneous ECG recording (n = 5) or simultaneous ECG and blood pressure recordings (n = 1).ResultsThe total duration of continuous ambulatory recording averaged 41.5 ± 16.6 days. Five dogs had persistent stable recording, and one dog developed hardware malfunction in week 3. SGNA was followed immediately (<1 second) by heart rate and blood pressure elevation and a reduced standard deviation of consecutive activation cycle length (SDNN) from 236 ± 93 ms to 121 ± 51 ms (P = 0.007). Heart rate correlated significantly with SGNA. When there was a sudden increase of SGNA, the sudden increase occurred bilaterally in 90% of the episodes. Both heart rate and SGNA showed statistically significant (P <.01) circadian variation. Nadolol (20 mg/day for 5 days) reduced average heart rate from 99 ± 8 bpm at baseline to 88 ± 9 bpm (N = 6, P = .001) but did not significantly alter SGNA. Immunohistochemical staining of the stellate ganglia showed tyrosine hydroxylase-positive ganglion cells and nerves at the recording site.ConclusionThere is a circadian variation in sympathetic outflow from canine stellate ganglia. Circadian variation of SGNA is an important cause of circadian variations of cardiac sympathetic tone.