Elsevier

Brain Research

Volume 1657, 15 February 2017, Pages 156-166
Brain Research

Research report
Cardiovascular dysfunction associated with neurodegeneration in an experimental model of Parkinson’s disease

https://doi.org/10.1016/j.brainres.2016.12.008Get rights and content

Highlights

  • Parkinson’s disease (PD) is associated with cardiovascular autonomic dysfunction.

  • Baroreflex sensitivity is reduced in 6-OHDA model of PD.

  • Number of cardiovascular brainstem neurons is reduced in 6-OHDA model of PD.

  • Physiological and anatomical changes can be related to control of blood pressure.

  • This novel result could conceivably be applied to understand human condition in PD.

Abstract

Patients with Parkinson’s disease (PD) exhibit both motor and non-motor symptoms. Among the non-motor symptoms, cardiovascular autonomic dysfunction is frequently observed. Here, we evaluated baroreflex function, vascular reactivity and neuroanatomical changes in brainstem regions involved in the neural control of circulation in the 6-hydroxydopamine (6-OHDA) model of PD. Male Wistar rats received a bilateral injection of 6-OHDA or vehicle into the striatum. After 61 days, baroreflex function and vascular reactivity were assessed. The 6-OHDA and vehicle groups showed similar increases in mean arterial pressure (MAP) in response to phenylephrine (PE). However, the bradycardia observed in the vehicle group was blunted in the 6-OHDA-treated rats. Injection of sodium nitroprusside (SNP) decreased hypotension, tachycardia and vascular relaxation in 6-OHDA-treated rats. Bilateral intrastriatal 6-OHDA led to massive degeneration of tyrosine hydroxylase (TH)-immunoreactive neurons in the substantia nigra and to reductions in the numbers of A1/C1 and A5 catecholaminergic neurons while sparing A2 neurons within the nucleus of the solitary tract (NTS). 6-OHDA-treated rats also showed decreases in Phox2b-expressing neurons in the NTS and in choline acetyltransferase (ChAT) immunoreactivity in the nucleus ambiguus. Altogether, our data suggest that this model of PD includes neuroanatomical and functional changes that lead to cardiovascular impairment.

Introduction

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders. Clinically, it is well known by its motor symptoms such as bradykinesia, rigidity, tremor and postural instability. However, while the motor symptoms of PD are considered pathological hallmarks of the disease (Fearnley and Lees, 1991), several debilitating symptoms that substantially impair patients’ quality of life are related to the non-motor aspects of PD (Wolters, 2009). Some common non-motor symptoms of PD include sleep disturbances, neuropsychiatric and cognitive deficits, sensory dysfunction, and breathing instability, as well as cardiovascular autonomic dysfunction (Bassetti, 2011, Chaudhuri et al., 2011, Dickson et al., 2009, Truong et al., 2008, Tuppy et al., 2015). There is no doubt that the motor symptoms of PD are associated with the loss of a specific group of dopaminergic neurons located in the substantia nigra (SN) and that this underlies the physiopathology of the disease; however, the specific populations of neurons responsible for various non-motor symptoms remain unclear. Orthostatic hypotension (OH), the most common cardiovascular dysfunction in PD, results from the impairment of baroreflex function and cardiac sympathetic innervations (Cai et al., 2005, Tipre and Goldstein, 2005). Baroreflex dysfunction can also be associated with neurodegeneration in important regions of the brainstem. Previous reports show that the brainstems of patients with PD show considerable loss of an important adrenergic region involved in the neural control of circulation, i.e., the C1 region (Gai et al., 1993, Guyenet et al., 2013). However, according to other studies, patients with PD and OH showed marked individual variations in the numbers of catecholaminergic neurons in the C1 region, obscuring the correlations among OH, PD and catecholaminergic neurons (Benarroch et al., 2000). Despite the controversial observations in patients with PD as described above, no previous studies have reported cardiovascular autonomic dysfunction in a rat model of PD and its relationship with neurodegeneration in specific areas of the brainstem that are responsible for the neural control of blood pressure (Kuo et al., 2010, Lu et al., 1995, Takatsu et al., 2000). Here, we selected a widely used rat model of PD that is generated by injection of 6-hydroxydopamine (6-OHDA) into the striatum. The neuroanatomical and functional assessment of cardiovascular involvement in the 6-OHDA model of PD may represent an important step for future clarification of the mechanisms underlying the appearance of cardiovascular autonomic dysfunction in PD.

Therefore, it is important to use the 6-OHDA model of PD to evaluate cardiovascular dysfunction, vascular reactivity and neuroanatomical changes in the brainstem regions involved in the neural control of circulation.

Section snippets

Animal model of Parkinson’s disease: bilateral intrastriatal injection of 6-OHDA destroyed tyrosine hydroxylase-expressing neurons of the substantia nigra

The 6-OHDA neurotoxic lesion within the nigrostriatal dopaminergic system is one of the most widely used methods to model PD in rodents (McDowell and Chesselet, 2012). In our study, 6-OHDA (24 μg/μL) was injected into the dorsal striatum of rats. The rostral-caudal extent of the lesion was determined by counting the neurons in the SN showing tyrosine hydroxylase immunoreactivity (TH-ir) in every sixth 40-μm brain section from each rat (from 5.32 to 6.04 mm caudal to bregma). Compared to

Discussion

The current study reveals cardiovascular autonomic deficits after degeneration of dopaminergic neurons in the SN. We suggest that the 6-OHDA model of PD produces a dysfunction in baroreflex sensitivity and considerable changes in neuronal cytoarchitecture in the brainstem regions involved in the regulation of circulation.

Approximately 30–40% of PD patients have orthostatic hypotension (OH) (Goldstein, 2003, Velseboer et al., 2011), a key manifestation of cardiovascular dysautonomia. One of the

Cardiovascular deficits and Parkinsonism

Our results show that the bilateral intrastriatal 6-OHDA model of PD has a significant reduction in the number of neurons in regions involved in baroreflex control, such as the NTS, NA and the catecholaminergic neurons within the A1/C1 and A5 regions. For several reasons, the decreases in the catecholaminergic neurons of the A1/C1 and A5 regions are probably not due to catecholaminergic or non-catecholaminergic neurons in different brain areas coming into contact with 6-OHDA by the diffusion of

Conclusion

Our results showed that the bilateral intrastriatal 6-OHDA model of PD led to a massive degeneration of neurons with TH-ir in the SN, and this was associated with significant decreases in Phox2b-ir in the NTS, ChAT-ir in the NA and TH-expressing neurons in the A1/C1 and A5 regions. We also observed that other brainstem regions involved in neural control of blood pressure, such as ChAT-ir in the DMV and TH-ir in A2/C2, were not affected in this model. Our conclusion is that those specific

Animals

Experiments were performed in 22 adult male Wistar rats (250–350 g), and the entire protocol lasted two months. Animals were used in accordance with the guidelines of the Animal Experimentation Ethics Committee of the Institute of Biomedical Sciences at the University of São Paulo (ICB/USP) and the NIH.

6-OHDA injection

The bilateral injection of 6-OHDA hydrochloride (6-OHDA hydrochloride, H4381, Sigma, Saint Louis, MO, USA) into the striatum was performed acutely as previously described (Tuppy et al., 2015).

Grants

This research was supported by public funding from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (grants: 14/22406-1 to ACT; 12/20398-6 to CA) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (grants: 471263/2013-3 to ACT; 471283/2012-6 to TSM) and by funds from a FAPESP fellowship (2011/21841-8 to MT; 2015/11268-0 to BF) and a CNPq fellowship (305533/2012-6 to TSM and 301651/2013-2 to ACT).

Author contributions

TSM, CA and ACT designed the experiments; BF, MT, SRP and ACT collected and analyzed data; BF, MT, TSM, CA and ACT wrote the paper. All authors approved the final version of the manuscript.

Conflict of interest statement

We declare no conflict of interest.

Acknowledgments

We gratefully acknowledge J.F. Brunet (Departement de Biologie, EcoleNormaleSuperieure, Paris, France) for providing the Phox2b antibody, J.C. Callera (Department of Basic Sciences, School of Dentistry of Araçatuba, Araçatuba, Brazil) for the stereotaxic apparatus and Fabiane C. Fernandes for expert technical assistance. We would like to also acknowledge Dr. Lisete C. Michelini for helping with the baroreflex analysis.

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    1

    B. Falquetto and M. Tuppy contributed equally to this study.

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