Parkinson-like early autonomic dysfunction induced by vagal application of DOPAL in rats

Abstract

Aim: To understand why autonomic failures, a common non-motor symptom of Parkinson's disease (PD), occur earlier than typical motor disorders.

Methods: Vagal application of DOPAL (3,4-dihydroxyphenylacetaldehyde) to simulate PD-like autonomic dysfunction and understand the connection between PD and cardiovascular dysfunction. Molecular and morphological approaches were employed to test the time-dependent alternation of α-synuclein aggregation and the ultrastructure changes in the heart and nodose (NG)/nucleus tractus solitarius (NTS).

Results: Blood pressure (BP) and baroreflex sensitivity of DOPAL-treated rats were significantly reduced accompanied with a time-dependent change in orthostatic BP, consistent with altered echocardiography and cardiomyocyte mitochondrial ultrastructure. Notably, time-dependent and collaborated changes in Mon-/Tri-α-synuclein were paralleled with morphological alternation in the NG and NTS.

Conclusion: These all demonstrate that early autonomic dysfunction mediated by vagal application of DOPAL highly suggests the plausible etiology of PD initiated from peripheral, rather than central site. It will provide a scientific basis for the prevention and early diagnosis of PD.

Keywords: DOPAL; Parkinson's disease; autonomic dysfunction; vagus; α-synuclein.

FIGURE 1

Changes in blood pressure and baroreflex sensitivity in rats administrated with DOPAL. (A–C) shows the systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse pressure difference, respectively, n = 6. (D, E) The representative changes in blood pressure (BP, pink traces) and heart rate (HR, blue traces) were monitored in the presence of 1, 3, and 10 μg/kg sodium nitroprusside (SNP) or phenylephrine (PE). The BRS (ΔHR/ΔMAP) was calculated before and after SNP and PE, n = 4. Data were expressed by mean ± SD. *p < 0.05 and **p < 0.01 versus sham

FIGURE 2

BP changes while changing position in rats administrated with DOPAL. (A) Schematic diagram of experimental operation. Rats were fixed on the operating table, and the heart rate and blood pressure at orthostatic or supine status were recorded in real time using femoral artery cannulation. (B–E) The representative changes in blood pressure (BP, pink traces) and heart rate (HR, blue traces) at orthostatic or supine status compared with steady state, and the differences were expressed as mean ± SD. **p < 0.01 versus sham, n = 4

FIGURE 3

Ultrasound results of DOPAL‐administered rats and representative images of transmission electron microscope. (A, B) Ultrasonic evaluation of cardiac function during DOPAL application, LVIDd: left ventricular diastolic internal diameter, LVPWd/s: left ventricular diastolic/systolic posterior wall. Data were presented as mean ± SD. *p < 0.05 versus sham. n = 5–7; (C, D) Representative images of transmission electroscope of LVAW from rats at 8 w after DOPAL administration. Scale bar: 2 μm, direct Magnification: 15,000×, the yellow arrowheads: filaments of myocardium, white arrowheads: mitochondria, and black arrowheads: autophagic vesicles

FIGURE 4

Expression of α‐Syn in LVAW and TA. (A) mRNA expression of α‐Syn in LVAW at different time points; (B–D) protein expression of α‐Syn in LVAW at different time points; (E) higher molecular weight of α‐Syn aggregation in LVAW; (F) mRNA expression of α‐Syn in TA at different time point; and (G–I) protein expression of α‐Syn in TA at different time point. Data were expressed as mean ± SD. *p < 0.05 and **p < 0.01 versus sham, n = 3–5

FIGURE 5

Representative images of transmission electron microscope. (A) The representative image of NG in rats administrated with DOPAL. (B) The representative image of NTS. Scale bar: 2 μm and 500 nm, direct Magnification: 8000× and 15,000×, the yellow arrowheads: mitochondria, white arrowheads: endoplasmic reticulum, and red arrowheads: lysosome

FIGURE 6

Expression of α‐Syn in the NG and NTS. (A) mRNA expression of α‐Syn in the NG at different time points; (B, C) protein expression of Mon‐ and Tri‐α‐Syn in the NG at 4 and 14 w; (D) mRNA expression of α‐Syn in NTS at different time point; and (E, F) protein expression of Mon‐ and Tri‐α‐Syn in the NTS at 8 and 14 w. Data were presented as mean ± SD, *p < 0.05 and **p < 0.01 versus sham, n = 3–5 from 12 to 16 rats

FIGURE 7

Expression of α‐Syn and TH in the NG. Left panel: Representative graph of immunohistochemistry (IHC) results of α‐Syn at NG in rats administrated with DOPAL. Right panel: Immunohistochemical quantitative statistics. Data were presented as mean ± SD, *p < 0.05 and **p < 0.01 versus sham, n = 20–35

FIGURE 8

Schematic diagram of DOPAL administration. Application of DOPAL on vagus causes significant accumulation of α‐Syn monomers to form toxic oligomers that could be transported to the heart‐TA and NG‐NTS by axon flow