Assessment of heart rate variability (HRV) in SN rotenone-induced lesion Parkinson's disease rat model
Authors: Rapelli Vindhya Rani , Wadolowski Robert , Solomon Irene 
Published: May 2023

Parkinson’s disease (PD) is a progressive neurodegenerative disorder caused by loss of dopaminergic neurons in the substantia nigra (SN). While PD is clinically characterized by motor deficits, non-motor symptoms such as autonomic dysfunction that can lead to deficits in cardiovascular function are common in early PD. Autonomic dysfunction is an imbalance in sympathetic (SNS) and parasympathetic (PNS; vagal) tone, which directly impacts cardiovascular function and responsiveness, leading to alterations in heart rate variability (HRV). HRV is the fluctuation in time intervals between consecutive heartbeats, and reduced HRV has been linked to increased risk for cardiovascular morbidity and mortality in both cardiac and non-cardiac disorders, including those associated with PD. To gain further insight into the influence of PD on autonomic balance, we investigated measures of HRV quantified from a 20-min segment of basal ECG activity recorded in a rat model of PD generated by unilateral injection of the pesticide rotenone (ROT; n=8) into the SN; SN injection of vehicle (VEH) in a separate group of rats (n=7) served as a control. At 2-weeks after SN injection, ECG activity was recorded in urethane-anesthetized adult female Sprague-Dawley rats using needle electrodes inserted into each forepaw, RR interval data were obtained from the ECG records, and HRV was quantified using time-domain analysis to obtain SDRR and RMSSD, frequency-domain analysis to obtain spectral power in the low (LF) and high (HF) frequency bands and the LF/HF ratio, and non-linear Poincaré plot analysis to obtain SD1, SD2, and the SD1/SD2 ratio, with all data presented as mean±SE. Evaluation of mixed SNS/PNS tone measures showed that SDRR (2.89±1.09 vs 2.60±0.98 ms), relative LF power (49.9±18.9 vs 44.8±16.9% (nu)), and SD2 (4.25±1.60 vs 3.38±1.27 ms) were similar in ROT- and VEH-injected rats while evaluation of PNS tone measures showed that RMSSD (3.59±1.36 ms vs 2.00±0.75 ms) and SD1 (2.55±0.96 vs 1.42±0.53 ms) were slightly but not significantly higher in ROT-injected rats albeit relative HF power (50.1±18.9 vs 55.2±20.9% (nu)) was similar in both groups. Evaluation of sympatho-vagal balance measures showed that LF/HF ratio (1.05±0.40 vs 1.52±0.58) and SD1/SD2 ratio (0.56±0.21 vs 0.46±0.17) were similar in ROT- and VEH-injected rats albeit both measures appeared to favor slightly enhanced PNS tone in ROT-injected rats. Qualitative evaluation of Poincaré plot histogram data revealed that ROT-injected rats exhibited multiple modal clusters of beat-to-beat RR interval behaviors, suggesting that alterations in HRV are likely present. While our preliminary data show some slight alterations in HRV in ROT-injected rats, additional data are needed to improve statistical power of our comparisons as well as to better capture changes in sympatho-vagal balance and identify underlying mechanisms responsible for autonomic dysfunction in PD. Thomas Hartman Center for Parkinson's Disease Research at Stony Brook University This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.