Morphology of the Harderian gland of the Gecko, Tarentola mauritanica.

The Harderian gland of the gecko, Tarentola mauritanica, was studied at the histological, histochemical, and ultrastructural levels. It is a nonlobate compound acinar gland surrounded by a thin capsule of connective tissue. Numerous connective tissue-type mast cells, ultrastructurally similar to those described in other higher vertebrates, were identified in the interstitial tissue between the acini. Pyramidal or columnar-shaped secretory glandular cells were observed in the acini. In the glandular cells, two types of structures could be distinguished on the basis of their high or low electron density. Lipid droplets were found in the cytoplasm of the Harderian gland of both sexes. Histochemical tests showed that the Harderian gland of the gecko is a seromucous gland. The secretion is essentially merocrine, although an apocrine type of secretion is sometimes observed.

TSH and thyroid hormones induce the release of secretory granules in the harderian gland of hypophysectomized frogs, (Rana esculenta): morphological observations.

The secretory activity of the harderian gland (hg) in the frog Rana esculenta is influenced by pituitary and thyroid hormones. Administration of thyroid stimulating hormone (TSH), T3 and T4 to hypophysectomized male and female frogs, affects the release of secretory granules in the lumina of glandular acini. In particular, treatment with T3 radically modified morphological parameters (height and area of acinar lumina of the glandular cells); T4 or TSH had less effect. Administration of thiouracil counteracted TSH effect, restoring the secretory content of the glandular cells. Ultrastructural observations confirmed these results. Our data suggest the existence of a thyroid-hg interaction and that thyroid hormones may be involved in the mechanism of release of mature secretory granules in the hg of the frog, Rana esculenta.

Number of mast cells in the Harderian gland of the lizard Podarcis sicula sicula (Raf): the annual cycle and its relation to environmental factors and estradiol administration.

The Harderian gland of the lizard Podarcis sicula sicula (Raf) contains connective tissue type mast cells whose numbers vary during the year showing two peaks, one in spring the other in winter. No sex differences are found throughout the year. Thermal and photoperiodic manipulations indicate that only temperature influences mast cell number (MCN) both in winter and in summer but not in spring. In animals exposed to high temperatures in February (but not in May) MCN declined, while exposure to low temperature in July had the opposite effect. Estradiol treatment of the February and April lizards increased MCN, an effect counteracted by the synthetic antiestrogen tamoxifen; in July lizards, this did not occur. In animals exposed to a high temperature in February, estradiol had no effect, as in animals exposed to low temperatures in July. These data suggest that in spring MCN seems to be more responsive to hormonal stimuli rather than external cues (temperature), while in summer MCN is more sensitive to temperature than to hormonal stimuli (estradiol). Both humoral and external factors are concluded to influence mast cell numbers in the Harderian gland of the lizard P. sicula sicula.

The harderian gland in autoimmune diabetes of the nonobese diabetic mouse.

Infiltration of the nonobese diabetic (NOD) mouse's Harderian gland (HG) was studied in 1-30-week-old animals. A mononuclear cell invasion of this gland is first seen in 8-week-old female mice (i.e., at a slightly later age than that for the onset of infiltration of pancreatic islets). Infiltrating elements are mainly located at the hilus of the gland or at one or two foci (periacinar infiltration) within the parenchyma. In the latter case, a few elements infiltrate the fibrous connective tissue surrounding the acini (one or more) without damaging them. The most severe histopathological lesion was observed in 16-week-old animals; at this time infiltration ranges from a still focal lesion to complete acinar destruction of the gland. Ultrastructural observations confirm that in several cases acinar cells are destroyed and the HG parenchyma is substituted with infiltrating elements, fibroblasts, and connective tissue. HG infiltration is comparable to the pancreatic inflammatory infiltration; the two processes are very similar, though insulitis starts slightly earlier than HG infiltration. Furthermore, as for insulitis and diabetes incidence, HG infiltration affects NOD males less than females. Moreover, immunocytochemistry has shown that T lymphocytes are the prevalent infiltrating element both in pancreatic islets and HGs. Further studies are required to understand the reasons for autoimmune destruction of this gland.

Organogenesis of the Harderian gland: a comparative survey.

Although research interest in the Harderian gland (HG) has increased during the last few years, only a small amount of information exists about its organogenesis. In mouse the HG appears in the posterior part of eye region, in the form of nonluminated tubules between the sixteenth and eighteenth days of gestation. At birth it is still not differentiated histologically. In birds the HG originates from the conjunctival epithelium at a late embryonic stage. In the English sparrow, Passer domesticus (incubation period of about 13 days), it appears between the seventh and the eighth days of incubation. In the chick embryo (incubation period of about 21 days) it originates between the eleventh and the twelfth days. Among reptiles the lizard Podarcis s. sicula has proved to be a useful model to clarify the embryological origin of the orbital glands since it possesses the anterior lacrimal gland contiguous to the HG in the medial corner of the orbit. The anlage of the orbital glands appears on about the twenty-second day of development (incubation period of about 43 days) in the form of a short tubule projecting from the conjunctival epithelium, at the time of development of the nictitating membrane. At this stage the mesenchymal cells surrounding the glandular blastema form a well-defined sac, later occupied by the orbital glands. From this stage until hatching the growth of the glandular blastema continues with the formation of acini which move posteriorly into the preformed mesenchymal sac. At the thirty-sixth day of development the more lateral acini differentiate into the HG. Only at the forty-first day do the more medial acini differentiate into the anterior lacrimal gland. At hatching the HG is fully differentiated. In anuran amphibia the primordium of the HG appears during the metamorphosis at the time of development of the nictitating membrane.

Effects of prolactin and cortisol on the Harderian gland of the terrapin, Pseudemys scripta, adapted to different salinities.

BACKGROUND: The Harderian gland (HG) of the terrapin, Pseudemys scripta, plays a prominent role in osmoregulation owing to the presence of "salt secreting cells" among the acinar cells of its glandular epithelium. Osmotic stress provokes different responses according to salinity. Seawater adaptation activates a major structural reorganization. The most striking change is shown by the type I glandular cells and "salt secreting cells." The latter increase in number and change from a unicellular form to multicellular complexes. METHODS: Terrapins were divided into eight groups for two experiments. For both experiments, one group was maintained in freshwater, whereas three groups were raised in seawater. For the first experiment, each group was administered with various doses of ovine prolactin on alternate days for 2 weeks. For the second experiment, each group received various doses of cortisol on alternate days for 2 weeks. In addition three freshwater and three seawater adapted terrapins, injected only with vehicle, were used as control for both experiments. RESULTS: Following prolactin treatment degenerative phenomena occurred in the salt cells of seawater-adapted HG, whereas inhibition of salt cell maturation was observed in freshwater-adapted HG. Although cortisol clearly maintained the number of the salt cells in seawater-adapted terrapin HG, it stimulated the salt cells in freshwater adapted terrapins. CONCLUSIONS: These data strongly support the hypothesis that osmoregulatory activity of the Harderian gland of Pseudemys scripta is under hormonal factors which seem to interplay in reply to osmotic stresses.

Molecular cloning of a novel mRNA (harderin) specifically and highly expressed in the Harderian gland of the frog, Rana esculenta.

A cDNA clone encoding a novel mRNA (harderin) has been isolated from the cDNA library of frog Rana esculenta Harderian gland. The cDNA is 875 bp long and encodes a novel protein of 218 amino acid residues. The deduced proteins reveals no significant homology to other proteins. The mRNA is a single 0.9 kb transcript detected only in the RNA of frog Harderian gland, highly expressed throughout the year. The constant and exclusive presence of harderin in the frog Harderian gland, suggests a constitutive tissue specific expression for this protein.

Cell biology of the harderian gland.

The harderian gland is an orbital gland of the majority of land vertebrates. It is the only orbital gland in anuran amphibians since the lacrimal gland develops later during phylogenesis in some reptilian species. Perhaps because it is not found in man, little interest was paid to this gland until about four decades ago. In recent years, however, the scientific community has shown new interest in analyzing the ontogenetic and morphofunctional aspects of the harderian gland, particularly in rodents, which are the preferred experimental model for physiologists and pathologists. One of the main characteristics of the gland is the extreme variety not only in its morphology, but also in its biochemical properties. This most likely reflects the versatility of functions related to different adaptations of the species considered. The complexity of the harderian gland is further shown in its control by many exogenous and endogenous factors, which vary from species to species. The information gained so far points to the following functions for the gland: (1) lubrication of the eye and nictitating membrane, (2) a site of immune response, particularly in birds, (3) a source of pheromones, (4) a source of saliva in some chelonians, (5) osmoregulation in some reptiles, (6) photoreception in rodents, (7) thermoregulation in some rodents, and (8) a source of growth factors.

The vitamin-E derivative U-83836-E in the low-dose streptozocin- treated mouse: effects on diabetes development.

Low-dose streptozocin-treated (LDS) mice were administered an inhibitor of lipid peroxidation, U-83836-E (a derivative of vitamin E), in order to observe its ability to alter the onset of diabetes. Ten or 20 mg/kg body wt. per day of U-83836-E were given to mice for 7 days and they were killed after 21 days. Results revealed that there was a significant increase in glycaemia in treated groups up to day 14 after which no further increase was noticed. Superoxide dismutase (SOD) assay showed that: (1) the LDS treatment significantly reduces SOD activity when compared with untreated controls (P < 0.005); (2) U-83836-E increases SOD levels (when compared with untreated controls); and (3) U-83836-E counteracts LDS treatment, since SOD activity is significantly higher with respect to that found in LDS-controls (P < 0.05), and SOD levels were significantly higher with respect to that found in Group 2 animals (P < 0.05), but significantly lower with respect to those found in groups 3 and 4 (P < 0.005). Moreover, malondialdehyde (MDA), the end-product of lipoperoxidation, was found at much higher levels in LDS controls than in the other groups and the lowest values were found in U-83836-E controls and in normoglycaemic animals treated with both streptozocin and U-83836-E. Morphological observations demonstrated that islet beta cells were of normal appearance in normoglycaemic animals of the treated groups. In conclusion, the in vivo inhibition of lipid peroxidation by this compound produces a limited but significant prevention of the islet beta cell destruction.

Effect of cholinergic secretagogue substances on the morphology of the harderian gland in the frog, Rana esculenta.

The present study using secretagogue substances was undertaken to investigate Harderian gland secretion in the frog, Rana esculenta. Carbamylcholine chloride and bethanechol injections caused enhancement of the secretory activity and hyperemia, while nicotine did not. Morphological examinations showed reduced cellular height and dilated alveolar lumina, containing secretory granule discharge, nuclei and cytoplasmic fragments, indicating an apocrine and holocrine secretion type. The administration of atropine prevented the enhancement of the secretion. Our data suggest that cholinergic stimulation provokes enhancement of the secretory activity on the frog HG, and this mechanism appears to be mediated by the activation of the muscarinic receptors.

Mast cell-Leydig cell relationships in the testis of the lizard Podarcis s. sicula Raf: thermal manipulation, ethane 1,2-dimethane sulphonate (EDS) and sex hormone treatment.

Mast cells of connective tissue type are scattered in the interstitial compartment of the lizard Podarcis s. sicula. Their number varies during the year, showing peaks in spring and in winter, respectively. Thermal manipulation affects mast cell number (MCN): high temperature decreased MCN in both January and May, while low temperature increased MCN only in January. Ethane dimethane sulphonate, a toxin which specifically destroys Leydig cells, induced an increase in MCN on days 3 and 7 of treatment. Oestradiol treatment provoked a strong increase in MCN that was blocked by tamoxifen. Blocking androgen receptors with cyproterone acetate resulted in an increase in MCN, while testosterone injection provoked a strong decrease. These results suggest a relationship between the presence of mature Leydig cells and mast cell proliferation and/or differentiation.

Pancreatic duct inflammatory infiltration in the nonobese diabetic (NOD) mouse.

The pancreatic duct system during the early stages of type 1 diabetes was examined in 8-wk-old female nonobese diabetic (NOD) mice. Infiltration was seen to involve the smaller ducts while the larger ducts were usually free from ductulitis. The infiltration affected ducts both close to and remote from the islets of Langerhans. In the former situation, infiltration of the islet and that of the duct were not separable. A strong positivity for both Ia and ICAM-1 molecules was observed in all infiltrated ducts, indicating that this infiltrating process is due to the same elements as are involved in the islet inflammation and that also mononuclear cells infiltrating the nonislet ducts express adhesive mechanisms. At the ultrastructural level, endocrine cells that were mainly of the 'closed' type were observed intermingled with the ductular epithelial cells and infiltrating mononuclear cells were detected either in the connective layer or among the epithelial cells of the affected ducts.

The orbital glands of the terrapin Pseudemys scripta in response to osmotic stress: a light and electron microscope study.

The histochemical and ultrastructural features of both orbital glands--the anterior lacrimal and harderian glands--were compared in the terrapin Pseudemys scripta following adaptation either to distilled water or to seawater. Seawater adaptation activated the harderian gland and caused a major structural reorganisation. Type I cells increased in number, whereas type II cells became smaller and less numerous. The most striking change was shown by the type IV cells which display the features of a salt-secreting cell. This cell type increased in number and changed from a unicellular form to multicellular complexes. Transfer from fresh water to distilled water caused a decrease in alcianophilia in type I and type III glandular cells and degenerative phenomena were often seen in type I and type IV cells. The anterior lacrimal gland showed only minor changes either in distilled or seawater adapted terrapins. Transfer to distilled water also caused degenerative phenomena in the lacrimal gland. These results establish for the first time the involvement of the harderian gland of a terrapin in osmoregulation.

Intratesticular control of spermatogenesis in the frog, Rana esculenta.

Adult intact and hypophysectomized (PDX) frogs, Rana esculenta, were treated with a gonadotropin releasing hormone agonist (GnRHA, HOE 766) and/or cyproterone acetate (CPA), the antiandrogen, in order to investigate the regulation of primary spermatogonial (I SPG) multiplication in vertebrates. Treatment with GnRHA (injections containing 900 ng administered for 12 days on alternate days) caused a significant increase of the mitotic index (MI) of I SPG in PDX animals and a further MI increase of SPG was observed when 0.66 mg CPA was given concomitantly with GnRHA. The treatment with 0.66 mg CPA in combination with GnRHA also increased secondary spermatocyte (II SPC) appearance. Moreover, number of nests containing spermatids (SPT) decreased as CPA, in combination with GnRHA, was administered in increasing doses (0.33 and 0.66 mg/injection). Intact animals treated with CPA (0.66 mg/injection) showed a time-dependent I SPG multiplication increase which reached highest values after 28 days. Secondary SPC also proliferated until day 28; meanwhile the number of nests containing SPT decreased. Neither testosterone nor R5020 (a progestin which is not converted to androgens) modified the basal and GnRHA-induced spermatogonial proliferation. These results confirm that in the frog, Rana esculenta, spermatid formation is impaired by CPA treatment and that I SPG multiplication is enhanced by a direct effect of GnRHA; moreover, we suggest that the absence of spermatids constitutes a signal promoting spermatogonial proliferation.

Harderian gland and the lacrimal gland of the lizard Podarcis s. sicula: histology, histochemistry, and ultrastructure.

Histology, histochemistry, and ultrastructure of the Harderian gland and lacrimal gland of the lizard Podarcis s. sicula were investigated. The Harderian gland, located at the medial corner of the orbit, can be divided into three zones showing different tinctorial features either with Mallory or hematoxylineosin stains. The glandular cells of the acinar medial zone secrete predominantly acidic sulphated mucosubstances. The acinar cells of the intermediate zone contain secretory granules that show a weak reaction to the histochemical tests for mucosubstances. The lateral zone has a tubulo-acinar type of structure and tests strongly for proteins, whereas Alcian-PAS staining is very weak. The lacrimal gland is smaller than the Harderian gland and lies in the region of the posterior commissure of the eyelids. it shows the same histological and histochemical characteristics of the medial zone of the Harderian gland, i.e., it is mucous secreting. At the ultrastructural level the zonation is well defined, especially when the secretory granules are examined. Granules of the mucoid type are found in the lacrimal gland and the medial zone of the Harderian gland. The secretory granules of the lateral part of the Harderian gland show a composite structure never described before. Therefore, they have been called "special secretory granules." Each of these granules is composed of three sharply separated components. It is not known whether the three components correspond to different secretions. Histochemical tests suggest that they are of the serous type. Both mucous and serous granules are secreted by the same glandular cells of the intermediate zone of the Harderian gland. The two types of granules usually occupy different cell compartments. The mechanism of secretion appears either merocrine or apocrine in both the Harderian gland and the lacrimal gland.

A sexual dimorphism of the harderian gland of the toad, Bufo viridis.

The Harderian gland of the toad, Bufo viridis, is an acinar gland located at the medial corner of the orbit. The columnar glandular cells show considerable variation in height depending upon their functional state. During July they are taller than in November and May, and filled with secretory seromucous granules. The glandular cells of the female toad, only, contain at their base numerous lipid droplets dispersed in a smooth endoplasmic reticulum. This is the first observation of sexual dimorphism in the Harderian gland of a nonmammalian vertebrate. The secretion of the gland is mainly merocrine. Although the secretion of the Harderian gland is mainly concerned with lubrication of the eyeball, the presence of lipid secretion only in the female glandular cells suggests a pheromonale function, which may influence the sexual behaviour of the male.