Research reportCardiovascular dysfunction associated with neurodegeneration in an experimental model of Parkinson’s disease
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.
References (50)
- et al.
Chemoreflex and baroreflex alterations in Parkinsonism induced by 6-OHDA in unanesthetized rats
Neurosci. Lett.
(2015) - et al.
Pontomedullary and hypothalamic distribution of Fos-like immunoreactive neurons after acute exercise in rats
Neuroscience
(2012) - et al.
Molecular pathways involved in the neurotoxicity of 6-OHDA, dopamine and MPTP: contribution to the apoptotic theory in Parkinson’s disease
Prog. Neurobiol.
(2001) - et al.
Arterial baroreflex dysfunction promotes atherosclerosis in rats
Atherosclerosis
(2005) - et al.
Parkinson’s disease: the non-motor issues
Parkinsonism Relat. Disord.
(2011) - et al.
Neuropathology of non-motor features of Parkinson disease
Parkinsonism Relat. Disord.
(2009) - et al.
Activation of P2-purinoceptors in the nucleus tractus solitarius mediate depressor responses
Neurosci. Lett.
(1994) - et al.
Chemosensory control by commissural nucleus of the solitary tract in rats
Respir. Physiol. Neurobiol.
(2011) - et al.
Changes in tyrosine hydroxylase and dopamine-beta-hydroxylase activities but not in phenylethanolamine-N-methyltransferase activity within central adrenaline neurons after 6-hydroxydopamine administration
Biochem. Pharmacol.
(1984) Dysautonomia in Parkinson’s disease: neurocardiological abnormalities
Lancet Neurol.
(2003)
Comparison of noradrenaline, dopamine and serotonin in mediating the tachycardic and thermogenic effects of methamphetamine in the ventral medial prefrontal cortex
Neuroscience
6-Hydroxydopamine lesion of the rat substantia nigra: time course and morphology of cell death
Neurodegeneration
Direct projections from the A5 catecholamine cell group to the intermediolateral cell column
Brain Res.
Nigrostriatal dopamine system mediates baroreflex sensitivity in rats
Neurosci. Lett.
Animal models of the non-motor features of Parkinson’s disease
Neurobiol. Dis.
Dopamine microinjected into brainstem of awake rats affects baseline arterial pressure but not chemoreflex responses
Auton. Neurosci.
Nitroprusside-related cyanide poisoning. Time (long past due) for urgent, effective interventions
Chest
Management of non-motor symptoms in advanced Parkinson disease
J. Neurol. Sci.
Respiratory deficits in a rat model of Parkinson’s disease
Neuroscience
Prevalence of orthostatic hypotension in Parkinson’s disease: a systematic review and meta-analysis
Parkinsonism Relat. Disord.
Non-motor extranigral signs and symptoms in Parkinson’s disease
Parkinsonism Relat. Disord.
S-Nitrosothiols: a class of nitric oxide-donor drugs
Clin. Sci. (Lond)
Purinergic receptor blockade in the retrotrapezoid nucleus attenuates the respiratory chemoreflexes in awake rats
Acta Physiol.
Nonmotor disturbances in Parkinson’s disease
Neurodegener. Dis.
Involvement of the ventrolateral medulla in parkinsonism with autonomic failure
Neurology
Cited by (0)
- 1
B. Falquetto and M. Tuppy contributed equally to this study.