Is it or isn't it? A reexamination of the anterior orbital glands of the fat-tailed Dunnart Sminthopsis Crassicaudata (Dasyuridae: Marsupiala) and a reevaluation of definitions for the Harderian gland.

The anterior orbital glands of tetrapods, which include the Harderian and nictitans glands, can usually be differentiated either anatomically (nictitans gland is more anterior) or histochemically (Harderian gland secretes lipids). However, conflicting statements exist in the literature about the presence and identity of these glands. Two previous studies on Sminthopsis crassicaudata (Dasyuridae: Marsupiala) either failed to note any anterior ocular glands or used no histochemical analyses. This study reexamined the structure of the anterior orbital glands of S. crassicaudata. Histological, histochemical, and ultrastructural examination revealed three glandular units: two of which are located superficially in the nictitating membrane, the third lying deeper in the connective tissue. The ducts of these three glandular units all open onto the corneal aspect of the nictitating membrane. These cells contain mainly serous granules with sparse intracellular lipid droplets. The nomenclature of these structures depends upon the definition used. According to the anatomical definition, S. crassicaudata has two glands: anteriorly the nictitans and posteriorly the Harderian gland. In contrast, if the histochemical definition is used, there is only one gland, but its precise identity cannot be confirmed until the role of the lipid droplets is established. Moreover, the histochemical definition poses additional problems with respect to the mechanism of secretion, multiple secretions, and glandular plasticity. Finally, the unitary definition identifies one deeply subdivided gland with an anterior and a posterior lobe in S. crassicaudata. This last definition is broad enough to accommodate a wide level of anatomical variation in the anterior ocular glands of tetrapods.

Immunophenotyping of lymphocyte subsets in the third eyelid tissue in dogs (Canis familiaris): morphological, microvascular, and secretory aspects of this ocular adnexa.

The third eyelid is an important adnexa of the eye. The objective of this study was to evaluate (i) morphological aspects (ii) vascularization, and (iii) the immunophenotype of lymphocyte subsets in the third eyelid of dogs. Flow cytometric analysis revealed the presence of three patterns concerning the immunophenotype of the third eyelid tissue. Dogs without ocular insult or deficient tear production might belong to one of the following immunophenotype patterns: I--the number of T-cells that expressed CD3(+) CD8(+) was higher than the number of cells that expressed CD3(+)CD4(+). II--the number of cells CD3(+)C4(+) was higher than the number of cells CD3(+)CD8(+) and in this case a higher number of cells that expressed CD19 were identified. III--Proximity of values of the cells that expressed CD3(+)CD4(+) and CD3(+)CD8(+). These data might suggest that the number of lymphocyte T cells alone should not be considered a direct indicator of the presence of an immune-based inflammation. Besides, a particular population of T-cells does not indicate a particular inflammatory state. The morphological study of the third eyelid revealed a rather uncommon angioarchitecture. The artery that irrigates the eyelid crosses almost the entire length of this structure to achieve its free border, and only then, ramificates deeply towards an inner segmental level. This spatial microvascular arrangement probably results from an adaptation to the fact that the third eyelid, in the medial cantus of the eye, is inwardly compressed into a tiny space. Efficient vascularization is achieved by allowing the first ramifications of the third eyelid artery to run straight to the top. Accini secretor cells of the third eyelid show a mucin content while tubuloacinar cells are mainly serous.

Morphologic changes of the anterior corneal epithelium caused by third eyelid removal in dogs.

Morphologic changes of corneal epithelium after third eyelid removal were observed in six normal Beagle dogs. The observation was conducted on the 17th, 35th and 72nd week after the removal. Morphologic changes were observed on corneal epithelium layers at 17 and 35 weeks post excision of the third eyelid but they were limited to minor changes including abnormal intercellular adhesion and further exfoliation of superficial cells at 72 weeks. The reduced BUT and evidence of vital positive staining correspond with these morphologic changes. Therefore, these changes are thought to be important findings from a morphologic view point in identifying pathologic symptoms of the cornea using clinical evaluation methods such as BUT and vital staining method. Grossly, no clinical indication of ocular disease was indicated by slit-lamp biomicroscopic observation; however, the BUT shortage and positive finding of vital staining indicated that the corneal epithelium layers after third eyelid removal lacked the essential barrier function. Thus, it would seem appropriate to consider that such a condition of the ocular surface would worsen with excessive exposure of the ocular surface, palpebration disorders and other exogenous factors.

Histology, histochemistry and fine structure of the lacrimal and nictitans gland in the South American armadillo Chaetophractus villosus (Xenarthra, Mammalia).

The anatomical, histological, histochemical and ultrastructural characteristics of the lacrimal gland (LG) and nictitans gland (NG) of the armadillo Chaetophractus villosus were described. The histochemical and histological features of both glands in male and female adult animals were compared. The tissues were processed with conventional techniques for light and transmission electron microscopy. Fixed specimens were submitted to a battery of tests for glycans, glycosaminglycans, glycoconjugates, proteins, and lipids. The LG of the armadillo may be considered within the set of glandulae lacrimales superior in which primates, carnivores, perisodactyls and artiodactyls are included. The localization of the NG was similar to that of other mammals. Lacrimal and NG were histologically and histochemically identical. The secretory endpieces consisted of three cell types: (1) Mucous cells (MC) with different types of mucous secretory granules with neutral and sialic acid-containing glycoconjugates (GCs). (2)Seromucous cells (SMC) showing a variety of moderately electron dense secretory granules with flocculent material with carboxylated acidic, neutral, and sialic acid-containing GCs. Intercellular canaliculi with junctional complexes and basolateral intercellular spaces were frequent. (3) Serous cells (SC) with electron dense secretory granules. Histochemically, they showed the strongest reaction for proteins and neutral, weakly acid and carboxylated acidic GCs. The epithelium of the intra- and inter-lobular excretory ducts showed secretory activity, junctional complexes, and wide basolateral intercellular spaces with lateral folds. The endpieces and ducts were surrounded by myoepithelial cells. The stroma was characterized by fenestrated endothelium, unmyelinated axons, and abundant plasma cells. MC, SMC, and the duct system were richly innervated by hypolemmal nerve terminals.

The conjunctiva and nictitating membrane of the eyelids in some reptilian species: a SEM overview.

The conjunctiva and nictitating membrane of reptilian eyelids have been studied by means of SEM. The whole surface pattern of the eyelids can be subdivided into the centrally positioned A-zone near the rims and the surrounding B-zone, including the fornix conjunctivae. The A-zone is characterized by the presence of epithelial lamellae or similar arranged cellular protrusions. All conjunctival epithelial cells demonstrate protrusions of extent morphological variety. Numerous goblet-cells occur in the B-zone and progressively increase in density in the direction of the fornix conjunctivae and the epithelial cells exhibit decreasing protrusions. The lower eyelid incorporates the discus conjunctivae, a platelike formation. It consists of dense connective tissue in which the collagen fibres stretch out orthogonally in a plywood-like manner. The nictitating membrane can be considered as a conjunctival fold near the rostral angle of the eyelids. Its bulbar surface folds in a perpendicular direction.

Functional morphology of the nictitating membrane in the domestic cat.

Morphological differences between the corneal and palpebral surfaces of the nictitating membrane of the domestic cat were examined using histology, histochemistry and the scanning electron microscope. Both surfaces are covered by one or two layers of epithelial cells. The epithelium contains numerous goblet cells, particularly on the palpebral side. These cells revealed binding sites for six lectins as well as positive PAS reactivity, and alcianophilia at both pH 2.5 and pH 3.5. Numerous lymph follicles located on the corneal side make the epithelium look like lymphoepithelial tissue. Accumulations of lymphatic tissue may also be found on the palpebral side. Scanning electron micrographs showed microvilli on the epithelial surfaces. The function of the cat nictitating membrane is discussed on the basis of our findings and those of other authors. Movements of the nictitating membrane alternate between active and passive phases of gliding. The membrane as a whole effectively protects the nasal portion of the bulb from dust, dehydration and pathogens.

[The effect of sympathetic denervation on the structure, contractility and electrical activity of the smooth-muscle cells in the cat nictitating membrane]. / Vliianie simpaticheskoi denervatsii na strukturu, sokratimost' i élektricheskuiu aktivnost' gladkomyshechnykh kletok migatel'noi pereponki koshki.

The nucleus and soma of sympathetically denervated smooth muscle cells (SMCs) of the cat nictitating membrane were found to be enlarged. The number of free ribosomes was dramatically increased and a disintegration of microfilaments was found. The functional changes involved spontaneous or agonist-induced generation of APs. These findings suggest that the denervation destructed the adrenoreceptor control mechanisms of the excitable membrane's potential. The possibility of emergence of new Ca2+ channels in the denervated SMCs is discussed.

Post-ganglionic chemical sympathectomy of the cat nictitating membrane following systemic epinephrine: degeneration of nerve terminals followed by regeneration.

The present study was designed to provide further evidence that high doses of systemically administered epinephrine can result in a post-ganglionic chemical sympathectomy and to look for evidence of regeneration of nerve terminals. Three days following the systemic administration of a high dose of epinephrine a prolapse of the cat nictitating membrane was observed. Examination of the inferior smooth muscle associated with the membrane revealed ultrastructural evidence of nerve terminal destruction which was associated with a marked depletion of endogenous norepinephrine as measured with a catecholamine radioenzyme assay. Three weeks following treatment, appearance of nerve terminals and endogenous norepinephrine levels in the contralateral nictitating membrane were indistinguishable from untreated controls. High doses of epinephrine appear to result in nerve terminal degeneration, followed by regeneration, similar to that reported following 6-hydroxydopamine.