Occurrence and regional distribution of striated muscle fibers in the rat pineal gland

Abstract

In a total of 96 rat pineals studied 31 were found to contain striated muscle fibers or their precursors. The muscle fibers were most frequently present in the stalk region and more frequently found in the left than in the right hemisphere. Size measurements revealed that the lengths of pineal muscle cell nuclei differ only slightly from those of the sphincter muscle of the iris. However, the yellowish appearance of pineal muscle cell nuclei under darkfield investigation, a phenomenon observed in all muscular tissues of mesenchymal origin and connective tissue cells, may support the hypothesis that pineal musculature is of mesenchymal rather than ectodermal origin.

Age-related Histological Findings in the Pineal Gland of Crl:CD(SD) Rats

“…Other reports dealt with only male rats except for ones without a description discerning the sexes. The histological characteristics of the striated muscle fibers in our study were similar to those in the previous reports, as the fibers appeared in the connective tissue near the stalk of the pineal glands, especially with fibrosis 9 , 12 , 15 . The immunohistochemical results in our showed positive and negative staining for desmin and myogenin, respectively, suggesting that the fibers were mature.…”

“…In our study, striated muscle fiber was a rare finding with an age-related increase like previous reports, though the incidences varied among the reports 9 , 12 , 15 . Interestingly, these fibers were only found in male rats in our study; however, there are a few reports referring to the incidence in females.…”

“…The appearances of striated muscle fibers in the pineal glands have previously been reported in some mammals, including the human, bovine, swine, bat and rat 9 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 . In our study, striated muscle fiber was a rare finding with an age-related increase like previous reports, though the incidences varied among the reports 9 , 12 , 15 .…”

“…The immunohistochemical results in our showed positive and negative staining for desmin and myogenin, respectively, suggesting that the fibers were mature. After examination of the fibers and consideration of the arguments of several other authors 12 , 13 , the origin of the fibers remains unknown.…”

Morphofunctional aspects of the mammalian pineal gland

“…Originally they were reported in the human and cow (Bargmann, 1943) but striated muscle has been also reported in the rat (Quay, 1959;Dill, 1963;Tapp and Blumfield, 1970;Krstic, 1972;Diehl, 1978a), and recently in the cotton rat (Karasek, 1983;Karasek et al, 1983d). The fibers lie primarily near the surface of the gland, and their association with blood vessels has been noted (Dill, 1963;Krstic, 1972;Diehl, 1978a). The origin and functional significance of pineal striated muscle, which seem to be embryonic in appearance and probably of mesodermal origin (Krstic, 1972;Diehl, 1978a1, are obscure.…”