The distribution of T lymphocytes, B lymphocytes, and dendritic-like cells of the anal tonsil in the laboratory shrew, Suncus murinus.

We investigated the distribution of T lymphocytes, B lymphocytes, and S-100 protein-immunoreactive dendritic-like in the anal tonsil of the laboratory shrew, Suncus murinus. In adult animals, T lymphocytes were located mainly at the periphery of the anal tonsil, especially around small blood vessels. B lymphocytes were located in the central and subepithelial region of the anal tonsil, which includes primary lymphoid follicles, and in which there are small numbers of scattered T lymphocytes. B and T lymphocytes were distributed over 72.7 and 27.3% of the tonsillar area, respectively. However, their areas of distribution were not clearly distinguished. The areas containing B lymphocytes were enriched in S-100 protein antibody-immunoreactive cells, which exhibited a dendritic shape. These S-100-positive cells appeared to be identical to the follicular dendritic cells (FDC) seen in the follicles of lymphoid organs. These results suggest that the anal tonsils constitute one of the gut-associated lymphoid tissues (GALT), and that a function of the anal tonsil includes the capture of intruding antigens that would generate protective antibody responses.

Light and electron microscopic observation of intracytoplasmic inclusion bodies in the locus coeruleus of the hamster.

The authors previously demonstrated that intracytoplasmic inclusion bodies (1-3 microm) in the mouse locus coeruleus under light and electron microscopy are characteristically stained using the Holmes modified method. We reported that one inclusion body existed in almost all neurons of the locus coeruleus. The present study examined whether similar inclusion bodies are present in the Syrian hamster (weight, about 60 g). Paraffin sections stained with the modified Holmes' method dis played numerous small inclusion bodies in the cytoplasm of cells in the locus coeruleus. Epon sections (1 microm thick) stained using toluidine blue were observed under light microscopy, and numerous small inclusion bodies were again observed. Under electron microscopy observation, inclusion bodies (<1 microm in diameter) predominantly comprised small granular materials, similar to those described by previous investigators. Although inclusion bodies were devoid of a limiting membrane, the relation ship to cytoplasmic organelles was unclear. However, free and polyribosomes were occasionally noted in close proximity to inclusion bodies. Inclusion bodies may thus be formed from ribosomes. Intracytoplasmic inclusion bodies in the hamster locus coeruleus differed in appearance compared with inclusion bodies in the mouse locus coeruleus.

Fine structure of the anal tonsilliar epithelium in the laboratory shrew (Suncus murinus).

The epithelium of the anal tonsil of the laboratory shrew was studied by scanning and transmission electron microscopy, with particular attention focused on the structure of the epithelium lining the anal tonsillar crypt. The tonsillar crypt surface is lined by two kinds of epithelia: squamous epithelium, which is located mainly at the neck of the crypt and includes keratohyalin granules in the superficial layer, and reticular epithelium, which is invaded by many immigrating cells and has several micropores immigrating cells to pass through. In addition, basal granulated cells are present in the basal layer. These results suggest that the reticular epithelium of the anal tonsil belongs to the well-developed gut-associated lymphoid tissue (GALT) in the alimentary canal. It represents a specialized and important compartment in immunological function, similarly to the palatine tonsils of other mammals, and has as yet unknown roles in digestion.

Cellular localization of endocrine cells in the adult pancreas of the house musk shrew, Suncus murinus: a comparative immunocytochemical study.

The right and left lobes of the pancreas in the house musk shrew, Suncus murinus, were found to be completely separated. A morphologic study of the pancreas in S. murinus in terms of the blood supplies and innervation of the right and left lobes was performed in our previous study. It revealed clearly different blood supply and innervation patterns in the right and left lobes, suggesting that the right lobe of the pancreas corresponded to the ventral pancreas, and the left lobe related to the dorsal pancreas. To test this perspective from the histology, in this study, we investigated the immunolocalization of the cells of Langerhans islets in the pancreas of the animal. The distribution of insulin-, glucagon-, somatostatin-, and pancreatic polypeptide (PP)-secreting cells of the right and left lobes of the pancreas was examined in 10 animals. The glucagon-immunoreactive cells were distributed in both the right and left lobes. The PP-immunoreactive cells were extremely abundant in the right lobe and distributed throughout almost all the islets of Langerhans in the right lobe. By contrast, in the left lobe, immunoreactive PP cells were absent in the islets of Langerhans, and only very few immunoreactive PP cells were scattered in the exocrine parenchyma in part of the specimens. Therefore, these findings support our previous studies, and showed that the right and left lobes of the S. murinus pancreas could be related to an embryological origin from the ventral and dorsal pancreatic primordium, respectively, and that the S. murinus pancreas is suitable as a new experimental model to study the development of the human pancreas.

Blood supply to the retina and the lens in the gerbil (Meriones unguiculatus).

The blood supply to the retina and the lens in 32 gerbils (Meriones unguiculatus) of both sexes from infancy to maturity was studied under light and stereoscopic microscopes, and a scanning electron microscope. Mercox (CL-2R; Dai Nippon Ink, Tokyo, Japan) was injected into the left ventricle of 30 animals in order to visualize the blood supply to the retina and the lens from the ophthalmic artery. The central retinal artery arises from the ophthalmic artery, passes through the papilla of the optic nerve together with the central retinal vein and penetrates the vitreous space (cavity of the eye) between the lens and the internal limiting membrane of the retina, where it divides into the central branches covering the lens and the parietal branches to supply the retina. The former passes through the hyaloid space after branching several arterioles and then covers the lens like a network from its medial and marginal sides. Different from small experimental animals, the parietal branches, just after separating from the central one, divides into the nasal, dorsal and temporal branches in the vitreous space, each of which then subdivides to distribute across the retina on the inner limiting membrane, then delineates the membrana vasculosa retinae. This basal pattern of vasculization 1 day after birth continues to death. Both the central and parietal branches of the central retinal artery correspond to the branches of the hyaloid artery in embryo and the latter is preserved in adult gerbils.

Developmental study of the anal tonsil in the laboratory shrew, Suncus murinus.

The laboratory shrew, Suncus murinus, which lacks such gut associated lymph organs as the appendix and Peyer's plates, was recently demonstrated (Kubo and Isomura, 1996) to possess a pair of anal tonsils at the end of its rectum. The present paper deals with the development of this lymphoid organ as observed by light and electron microscopy. The anal tonsil was characterized by the initial postnatal development. On neonatal Day 1, a pair of epithelial crypts formed at the dorsal boundary between the anus and the ostium urogenitoanale. On Day 2 after birth, lymphocytes began to accumulate in the subepithelial mesenchymal tissue under the crypt. From Day 3 on, the lymphocytes increased to form a lymph nodule, from which, on Day 5, some lymphocytes began to penetrate into the crypt epithelium. The crypt and the nodule were fused together between Days 6 and 8. A germinal center-like structure was observed on Day 20 after birth. Around Day 40, the invading cells comprised cellular units consisting of large and small lymphocytes and plasma cells. High endothelial venules were observed in the parafollicular area at this time. These findings indicate that the anal tonsil originates from an accumulation of lymphocytes in the mesenchymal tissue close to a particular epithelium of the crypt, presumably in response to antigens in foods; the tonsilar structure is then gradually completed by fusion of the lymphoid and epithelial elements. This paper further reports on an electron microscope finding on Day 8 where the anal tonsillar crypt epithelium was seen to contain some basal-granulated cells of the open type.