Abstract
Article abstract Heart tissues of patients with PD or incidental Lewy body (LB) disease (ILBD) were examined by light and electron microscopy. LBs and α-synuclein–positive neurites were identified in the hearts from 9 of 11 patients with PD and from 7 of 7 patients with ILBD. LBs were present in both tyrosine hydroxylase-positive and -negative nerve processes, which are nerves of extrinsic sympathetic and intrinsic origin, respectively. These findings provide histologic evidence that the postganglionic sympathetic and intrinsic neurons in the heart are involved in the PD disease process.
Autonomic symptoms are a cardinal clinical feature of Parkinson’s disease (PD). Cardiovascular abnormalities are observed in patients with PD; orthostatic hypotension and an abnormal electrocardiographic R-R interval are found in 43% and 56% of patients with PD, respectively.1,2 Postmortem studies of patients with PD have shown neuronal degeneration and Lewy bodies (LBs) in brainstem pigmented nuclei, as well as in the central and peripheral autonomic nuclei.3 Myocardial imaging with 123I-metaiodobenzylguanidine (MIBG), an analog of norepinephrine, has recently been used to assess cardiac sympathetic function, and a decrease in myocardial MIBG uptake is reported to be a consistent finding in patients with PD, including those in the mild clinical stage.4-6 These findings raise the question of whether postganglionic sympathetic nerves are involved in mild or early-stage PD more frequently than previously thought.
To test the hypothesis that sympathetic denervation is present in the cardiac plexus in PD, we examined, both histologically and immunocytochemically, sympathetic ganglia and cardiac plexuses collected at autopsy examinations of patients with PD, patients with incidental LB disease (ILBD), and control patients.
Methods.
Eleven patients with PD (age, 54 to 84 years; mean, 68.0 years), 7 with ILBD (age, 56 to 87 years; mean, 72.6 years), 7 with diabetes mellitus (age, 46 to 71 years; mean, 60.0 years), 7 with recent to old myocardial infarcts (age, 54 to 79 years; mean, 67.6 years), and 25 non-PD patients (age, 55 to 85 years; mean, 67.0 years) were selected on the basis of their clinical histories and pathologic findings. The patients with PD had presented with resting tremor, rigidity, and bradykinesia, and obvious neuronal loss, with LBs in the brainstem pigmented nuclei, was detected. Disease duration for patients with PD ranged from 3 to 30 years (mean, 11.5 years). Four of the patients with PD had orthostatic hypotension and one had shown an abnormal R-R interval on electrocardiography. The patients with PD had been given l-dopa alone or l-dopa combined with a dopa agonist or anticholinergic drugs, which had been effective. Seven of the patients with PD had died of pneumonia, three had died of other causes (pulmonary embolism, acute myocardial infarct, or renal failure), and one had died suddenly of unknown causes. The patients with ILBD were free of parkinsonism and autonomic symptoms, but had LBs in the substantia nigra or locus ceruleus, or both, and mild neuron depletion.
The left ventricle and right atrium were collected from each subject, fixed with formalin for 3 to 4 weeks, and embedded in paraffin and cut into 4-μm sections. For routine histologic examination, sections were stained with hematoxylin and eosin (H-E). We also examined each subject’s stellate and thoracic sympathetic ganglia.
Paraffin-embedded, 4-μm–thick sections from the heart and sympathetic ganglia were immunolabeled with polyclonal antibodies against ubiquitin (1:500; Dako, Glostrup, Denmark), α-synuclein (1:500),7 and tyrosine hydroxylase ([TH] 1:400; Eugene Tech, Inc., Allendale, NJ). Selected H-E–stained sections of the cardiac plexus were reused for electron microscopy.
Results.
LBs were present in the sympathetic ganglia of 9 of the 11 patients with PD (figure, A). Although they occurred in both the nerve cell somata and processes, most of the LBs were found in the processes. Furthermore, many α-synuclein–immunoreactive (IR) swollen processes were present in the ganglia (see figure, B). These α-synuclein–IR processes also were positive for ubiquitin. LBs and α-synuclein–IR processes were present in the ganglia of five of seven patients with ILBD, but not in the patients with diabetes mellitus or ischemic heart disease, or in the control patients.
Figure. Sympathetic ganglia (A, B) and cardiac plexuses (C–F) of patients with PD. (A) Lewy bodies (LBs) were seen in both nerve cell somata (arrow) and processes (arrowheads). Hematoxylin and eosin (H-E) stain, bar = 20 μm. (B) α-Synuclein–immunoreactive swollen neurites. Bar = 20 μm. (C) A typical LB with a clear surrounding halo. H-E stain, bar = 10 μm. (D) Electron micrograph of a section through the LB in (C). This intraneuritic LB consisted of a core with randomly aggregated filaments and electron-dense materials together with an outer area with radially arranged filaments. Bar = 1 μm. (E) Ubiquitin-immunoreactive swollen neurites in the myocardium. Bar = 50 μm. (F) α-Synuclein–immunoreactive swollen neurites around blood vessels in the heart. Bar = 50 μm.
In cases of PD, spherical eosinophilic inclusions with clear surrounding halos were present in the interatrial groove of the ganglia, in the myocardial nerve fibers, and around the coronary arteries (see figure, C). Electron microscopy showed they were composed of filamentous structures (see figure, D). Although small clusters of ganglion cells (cardiac ganglia) were occasionally present in sections from the right atrium, no LBs were present in the neuronal cell bodies; all of the LBs found were located in neuronal cell processes.
In addition to the typical LBs, ubiquitin and α-synuclein immunocytochemistry detected abnormally swollen neurites (see figure, E and F), similar to those seen in the brainstems and sympathetic ganglia of patients with PD, and they were present occasionally in TH-IR neuronal cell processes. LBs and abnormally swollen neurites were present in the cardiac plexus in 9 of 11 patients with PD and in all 7 patients with ILBD, and there appeared to be no significant difference between the numbers of inclusions in these two disease groups. Of the 9 patients with PD who had LBs in the cardiac plexus, 7 had LBs in the sympathetic ganglia. Moreover, there was no apparent loss of TH-IR neuronal cell processes compared with the control patients. LBs or α-synuclein–IR swollen neurites were not detected in the patients with diabetes mellitus or myocardial infarcts, or in the control subjects.
Discussion.
LB formation is a marker of neuronal degeneration. Recent studies have shown that LBs, as well as ubiquitin-positive degenerating neurites (also called Lewy neurites), are strongly immunoreactive with antibodies against α-synuclein.7,8 We found typical LBs and Lewy neurites that were α-synuclein–IR in the cardiac plexus in 9 of 11 patients with PD. These findings provide strong evidence that the cardiac plexus is involved in the PD disease process.
LBs and Lewy neurites were present in the cardiac plexuses of all seven patients with ILBD. ILBD is considered to be the presymptomatic phase of PD because the topography of pigmented cell loss in the substantia nigra seen in ILBD is identical to that seen in PD, although it is less severe in the former. Recently, a reduction in uptake of MIBG, an analog of norepinephrine, has been reported to be a consistent finding in patients with PD, including those in the mild clinical stages of the disease (Stages I and II on the Hoehn-Yahr scale).4,6 These findings suggest that the cardiac plexus is involved in PD even during the early phase. Moreover, no α-synuclein–IR swollen processes were found in patients with diabetes or ischemic heart disease or in the aged non-PD patients, which suggests that α-synuclein specifically accumulates in axons in LB disease.
The heart has dual sympathetic and parasympathetic innervation.9 Postganglionic sympathetic (noradrenergic) nerves are derived from the stellate and middle cervical ganglia, and innervate both myocardial cells and coronary vessels. Preganglionic parasympathetic (adrenergic) nerves derived from the dorsal vagal nucleus form synapses with postganglionic neurons close to and within the heart (hereafter referred to as the cardiac ganglia). By contrast, most of the intrinsic neurons in human cardiac ganglia are cholinergic.9 In our study, all of the LBs in the cardiac plexus in PD and in ILBD were located in the neuronal cell processes. Some neurites with LBs were TH-IR (i.e., catecholaminergic), which indicates that they were derived from the sympathetic ganglia, the parasympathetic dorsal vagal nucleus, or both. In ILBD, however, we frequently observed LBs in the sympathetic ganglia but not in the parasympathetic dorsal vagal nucleus, which indicates that most of the LB-bearing TH-IR neuronal cell processes found in the heart are extrinsic sympathetic nerve fibers. The LB-containing processes derived from the sympathetic ganglia are catecholaminergic,10 and most of the intrinsic neurons of the heart have acetylcholine as a neurotransmitter,9 so LB-bearing TH-negative processes in the heart can be considered intrinsic in origin. The four patients with PD who had orthostatic hypotension all had LBs in the sympathetic ganglia. The current findings may account for the cardiac sympathetic abnormalities recently detected in patients with PD by myocardial MIBG imaging.4-6
Acknowledgments
Supported in part by a grant from the Research Committee for CNS Degenerative Diseases and by a Health Sciences Research Grant from the Ministry of Health and Welfare, Japan.
- Received September 1, 1998.
- Accepted January 9, 1999.
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