Differential involvement of the periaqueductal gray in multiple system atrophy

Abstract

The periaqueductal gray (PAG) consists of distinct columns that participate in the integrated control of autonomic function. We sought to determine whether the PAG is affected in multiple system atrophy (MSA), a disorder characterized by prominent autonomic failure. Brains were obtained at autopsy from 13 MSA patients (10 M, 3 F, age 61±3 years) and 13 controls (8 M, 5 F, age 67±4 years). Transverse formalin-fixed 50 μm sections were obtained throughout the PAG and immunostained for the vesicular transporter 2 (VGLUT-2), nitric oxide synthase (NOS), or α-synuclein and co-stained with thionin. Some sections were processed for myelin or astrocyte staining. Stereological quantitation was performed separately in the ventrolateral, lateral, dorsolateral, and dorsomedial columns of the PAG. In MSA cases, there was a decrease in the total estimated number of VGLUT-2 immunoreactive neurons in the ventrolateral, lateral, and dorsomedial and to a lesser extent dorsolateral PAG compared to controls (ventrolateral PAG: 16,299±1612 vs. 27,906±2480 respectively, p<0.01; lateral PAG: 11,004±1401 vs. 16,078±1140 respectively, p<0.05; and dorsomedial PAG: 8847±1052 vs. 15,412±1097 respectively, p<0.001). The number of NOS immunoreactive neurons in the dorsolateral PAG was similar to controls. In all columns, the number of non-immunolabelled Nissl-stained cells was similar between groups. There was accumulation of glial cytoplasmic inclusions in all PAG columns in MSA. Our findings indicate involvement of the PAG columns in MSA, which may contribute to autonomic disturbances in this disorder.

Figure 1

Representative 50 μm transverse hemisection at the level of the periaqueductal gray (PAG) showing the characteristics of vesicular glutamate transporter-2 (VGLUT-2) immunoreactive neurons in the ventrolateral (vl) column) (left panel), and nitric oxide synthase (NOS) immunoreactive neurons in the dorsolateral (dl) column in a 75 year-old man with no neurological history (A,C, post mortem delay 18 hrs), and in a 65 year-old woman with multiple system atrophy (B,D, post mortem delay 10 hrs). There was loss of VGLUT-2 immunoreactive neurons in the vlPAG but preservation of NOS neurons in the dlPAG in the MSA compared to the control case. Bar = 25μm.

Figure 2

Total estimated numbers of VGLUT-2 (left) and non immunoreactive Nissl stained neurons in the ventrolateral, (vl), lateral (l), dorsolateral (dl), and the dorsomedial (dm) columns of the PAG (right). In MSA cases, there was a reduction in the total estimated number of VGLUT-2 immunoreactive neurons in the ventrolateral, lateral and dorsomedial with a trend to decrease in the dorsolateral PAG. There was no significant difference between MSA and controls in the total estimated cell counts or cell density of Nissl-stained, non-VGLUT-2, non-TH, or non-NOS immunoreactive neurons in any of the PAG columns.

Figure 3

Glial cytoplasmic inclusion (GCI) distribution throughout the periaqueductal gray (PAG) in a 66 year-old man with multiple system atrophy (MSA). (Case MSA-9 in Table 1). Insert shows the approximate level of the sections.

Figure 4

A: Schematic representation of the periaqueductal gray (PAG) showing the topography ventrolateral (vl), lateral (l), dorsolateral (dl), and the dorsomedial (dm) columns and B, composite of the thirteen sections (from Figure 3) showing the distribution of glial cytoplasmic inclusions (GCIs) in one MSA case. C. Density of GCIs in the different PAG columns in all MSA cases. GCIs appeared to be more abundant in the ventrolateral than in other columns. (** p<0.01 vl vs dm, † p<0.05, vl vs dl). DRN, dorsal raphe nucleus. Bar = 20μm.

Figure 5

Representative 12 μm sections of the ventrolateral PAG stained for Luxol fast blue for myelin (A, B), and double-label immunocytochemistry for α-synuclein (FITC) and glial fibrillary acidic protein (GFAP) (Cy3). There was loss of myelin and astrocytic gliosis in the area of GCI accumulation. Bar = 25 μm.