Cells producing insulin-like androgenic gland hormone of the giant freshwater prawn, Macrobrachium rosenbergii, proliferate following bilateral eyestalk-ablation

We found that the androgenic gland (AG) of Macrobrachium rosenbergii possesses three cell types. Type I cells are small polygonal shaped-cells (13.4 μm in diameter), stain strongly with hematoxylin-eosin (H&;E), have abundant multilayered rough endoplasmic reticulum (rER), and nuclei containing mostly heterochromatin. Type II cells are slightly larger (18.6 μm in diameter), stain lightly with H&;E, have rER with dilated cisternae, and nuclei containing mostly euchromatin. Type III cells (previously undescribed) are similar in size and shape to type I cells, but the cytoplasm is unstained and they have a high amount of smooth endoplasmic reticulum (sER) and mitochondria with tubular cristae. Bilateral eyestalk-ablation resulted in AG hypertrophy with a proliferation and predominance of type I cells as determined by bromodeoxyuridine (BrdU) assays. Expression of insulin-like androgenic gland hormone (Mr-IAG), determined by immunohistochemistry, was weak in type I cells, strong in type II cells of both the intact and eyestalk-ablated, and negative in type III cells. It was also detected in spermatogonia, nurse cells, and epithelium lining of the spermatic duct. The function of Mr-IAG in these tissues is yet to be elucidated but the distribution implies a strong role in male reproduction.     

Bilateral eyestalk ablation of the blue swimmer crab, Portunus pelagicus, produces hypertrophy of the androgenic gland and an increase of cells producing insulin-like androgenic gland hormone

The androgenic glands (AG) of male decapod crustaceans produce insulin-like androgenic gland (IAG) hormone that controls male sex differentiation, growth and behavior. Functions of the AG are inhibited by gonad-inhibiting hormone originating from X-organ-sinus gland complex in the eyestalk. The AG, and its interaction with the eyestalk, had not been studied in the blue swimmer crab, Portunus pelagicus, so we investigated the AG structure, and then changes of the AG and IAG-producing cells following eyestalk ablation. The AG of P. pelagicus is a small endrocrine organ ensheathed in a connective tissue and attached to the distal part of spermatic duct and ejaculatory bulb. The gland is composed of several lobules, each containing two major cell types. Type I cells are located near the periphery of each lobule, and distinguished as small globular cells of 5-7 μm in diameter, with nuclei containing mostly heterochromatin. Type II cells are 13-15 μm in diameter, with nuclei containing mostly euchromatin and prominent nucleoli. Both cell types were immunoreactive with anti-IAG. Following bilateral eyestalk ablation, the AG underwent hypertrophy, and at day 8 had increased approximately 3-fold in size. The percentage of type I cells had increased more than twice compared with controls, while type II cells showed a corresponding decrease.     

Immunocytochemical and immuno-electron-microscopical study of growth hormone cells in male and female rats of various ages

Summary Growth hormone (GH) secretory cells were identified by immunogold cytochemistry, and were classified on the basis of the size of secretory granules. Type I cells contained large secretory granules (250\2-350 nm in diameter). Type II cells contained the large secretory granules and small secretory granules (100\2-150 nm in diameter). Type III cells contained the small secretory granules. The percentages of each GH cell type changed with aging in male and female rats of the Wistar/Tw strain. Type I cells predominated throughout development; the proportion of type I cell was highest at 6 months of age, and decreased thereafter. The proportion of type II and type III cells decreased from 1 month to 6 months of age, but then increased at 12 and 18 months of age. The pituitary content of GH was highest at 6 months of age, and decreased thereafter. Estrogen and androgen, which are known to affect GH secretion, caused changes in the proportion of each GH cell type. The results suggest that when GH secretion is more active the proportion of type I GH cell increased, and when GH secretion is less active the proportion of type II and type III cells increased. The type III GH cell may therefore be an immature type of GH cell, and the type I cell the mature type of GH cell. Type II cells may be intermediate between type I and III cells.     

Distribution and morphology of amphibian extra-adrenal chromaffin tissue

1. The distribution and morphology of chromaffin cells in the para-aortic region and in the ganglia of the paravertebral sympathetic chain was studied with fluorescence histochemistry and electron microscopy. 2. Four types of chromaffin cell were distinguished largely on the basis of their vesicular content: Type I cells contain large, electron-dense vesicles (600-7000 A) and are comparable to noradrenaline-containing cells in the adrenal gland, Type II cells contain large, vesicles (600-7000 A) that are filled with a less electron-dense material than that in Type I cells and are comparable to adrenaline-containing cells in the adrenal gland, Type III cells contain smaller vesicles (1000-3000 A) that are incompletely filled with an electron-dense material and may represent cells that have been depleted of their catecholamines by stimulation, Type IV cells are clearly different from the other three cell types with respect to the size and appearance of the vesicles (1000-1500 A), nuclei and rough endoplasmic reticulum and may represent immature sympathetic neurons. 3. Nerve profiles, identified as cholinergic, were found in close apposition with all four cell types. No examples of a close association between processes of chromaffin cells and sympathetic neurons were found.     

Fine structure of the accessory glands of the female genital tract of the ichneumonid Pimpla turionellae (Insecta,Hymenoptera)

Summary The female accessory glands include the tubular poison gland, the paired, lemon-shaped uterus glands, and Dufour's gland, an unbranched tubular organ. They consist essentially of a single layer of epithelium cells surrounded by a basement membrane. The lumen is lined by cuticle. The proteinaceous secretion of the poison gland is released into intracellular ducts provided with microvilli, each connected to a channel lined with cuticle which leads to the central lumen of the gland. The channel is formed by special canal cells. Nerve endings are interspersed among the gland cells. The uterus gland consists of four cell types derived from a single type of precursor cell found in newly hatched wasps. Type I cells are covered by type II cells and are thus without contact to the luminal surface of the gland. They contain stacks or whorls of mitochondria and smooth cisternae in an alternating arrangement. Vesicles with a secretory product are found in cells of types II and III. Deep anastomosing infoldings of the plasmalemma, stabilized by microtubules and dense material at the branchings, are characteristic for type II cells. Most secretory vesicles are found in type III cells, the prevalent cell type which is thought to be the source of the lipoprotein secretion. Coated vesicles are present at deep infoldings of the plasmalemma. The greatly enlarged apical surface area of type IV cells and the presence of mitochondria in slender outgrowths is suggestive of an osmoregulatory function. In Dufour's gland, two cell types appear in succession, the first with a very dense cytoplasm, the second with dense inclusions and many seemingly empty vesicles of smooth endoplasmic reticulum. The secretion products, lecithin and a cholesterol ester, are thought to be formed by the second cell type. The dense inclusion might be lecithin, which reacts with osmium tetroxide. The cholesterol ester could have been washed out of the empty vesicles by the embedding procedure.     

Observations on Variations in the Male Sex Characters and Their Relation to the Androgenic Gland in the Shrimp Macrobrachium idae (Heller)

A majority of the males of the brackish water shrimp, Macrobrachium idae, show a hypertrophy in the length of the second cheliped, the length and spinuosity of the appendix masculina and the width of the vas deferens, during the breeding season. Statistical analyses of the measurements of these characters show that this hypertrophy has only very little correlation to the size of the individual, and that the above sex characters have marked variation in a population having the same body length. The hypertrophy of these structures is more linked with the extent of development of the androgenic gland. Also, in such individuals, the androgenic gland shows signs of increased secretory activity as evidenced by increase in size of the cells, vacuolisation of cytoplasm and presence of degenerative areas. It is suggested that there is a direct relation between the secretory activity of the androgenic gland and the hypertrophy of these structures i.e. there is a “cause and effect” relation between the androgenic gland and the primary and secondary sex characters.     

Histo- and cytophysiology of the lactating mammary gland of the African elephant (Loxodonta africana)

The lactating mammary gland of the African elephant (Loxodonta africana) has been studied with a panel of morphological techniques focusing on (1) the functional changes during the secretory process, (2) proliferative process [by application of proliferating cell nuclear antigen (PCNA) immunohistochemistry] and apoptotic phenomena [by use of the TUNEL technique] in the individual lobules, and (3) components of milk and milk-fat-globule membrane. In the lactating gland, the lobules are variably differentiated; within a lobule, however, the alveoli are usually similarly differentiated. The morphology of their alveoli suggests a classification of the lobules into types 1–3. Lobules of type 1 are composed of immature tubular alveoli with mitotic figures and numerous PCNA-positive nuclei; advanced type 1 alveoli contain abundant glycogen and specific secretory granules. Lobules of type 2 are further subdivided. In type 2a lobules, the epithelial cells of the alveoli form tall apical protrusions, which in part are occupied by small lipid droplets and which are pinched off in an apocrine fashion. The number of lysosomes varies considerably. Type 2b is the most common type, with striking basal membrane foldings, abundant rough endoplasmic reticulum cisterns, large Golgi apparatus, numerous mitochondria, lipid droplets, and protein vesicles with 30- to 90-nm-wide casein micelles. The lipid droplets are pinched off with minimal amounts of cytoplasm. Type 2c is composed of alveoli with a cuboidal epithelium and few signs of secretory activity. Increasing expression of peanut-agglutinin-binding sites parallels the maturation and differentiation of the glandular cells. Type 3 lobules are marked by numerous TUNEL-positive nuclei and large lipid droplets and are apparently degenerating structures. Cytokeratin (CK) 14 is usually present in the myoepithelial cells; CK 19 and CK 7 mark ductal and immature alveolar epithelia. Milk protein content varies between 2.6% and 6.3%, and casein micelles range from 35 to 90 nm in diameter. The diameter of intra-alveolar milk fat globules ranges from 5 to 25 µm and the membranes bear a filamentous surface coat composed of membrane-anchored mucins; gel-electrophoretic analysis of these mucins from different individuals demonstrates the presence of mucin MUC 1, which is expressed with considerable genetic heterogeneity.     

Immunocytochemical study of the GH cells in the anterior pituitary gland of human fetus II. Anencephalic fetus

In order to elucidate the effects of hypothalamic regulation on the morphology of GH cells, light and electron microscopic immunocytochemical examinations were carried out comparing GH cells in the anterior pituitary gland of anencephalic fetus with those of normal fetuses. Three types of GH cells were identified in the anterior pituitary gland of anencephalic fetus as well as in the normal fetus. Type-I is a small, round cell containing a few small secretory granules. Type-III is a large, polygonal cell with numerous large secretory granules. Type-II is a polygonal cell with medium-sized secretory granules. The Type-II GH cell was predominant in both anencephalic and normal fetuses. The most striking difference between anencephalic and normal fetuses was the presence of atypical forms of the Type II cell. These were polygonal cells containing secretory granules, which were either immunopositive or immunonegative to anti-human GH (anti-hGH) serum. Furthermore, two other types of GH cells were identified. The somatomammotroph (SM cell) contained GH and PRL in different granules within the same cell. Also, a different type of the GH cell was noted containing two varieties of secretory granules; one was immunolabeled only with anti-hGH and the other was not immunolabeled to either anti-hGH or anti-human PRL (anti-hPRL). From these results, we suggest that an absence of hypothalamic regulation in the anencehpalic does not seriously modify GH cell morphology but induces an altered GH storage pattern in some of the cells.     

Liver ultrastructure and a new cell type in the Japanese newt, Cynops pyrrhogaster.

The liver of the Japanese newt, Cynops pyrrhogaster, has been investigated using light, scanning, and transmission electron microscopy. Hepatic parenchyma was composed of clusters and cords or tubules of polyhedral cells separated by a sinusoidal net. Hepatocytes had spherical, euchromatic nuclei with one or more nucleoli and stacked mitochondria with sparse cristae and dense bodies. Rough endoplasmic reticula formed peribiliary stacks and diffusely scattered vesicles and tubules. Smooth endoplasmic reticula were more pronounced in glycogen-rich hepatocytes. Most hepatocytes contained peroxisomes, Golgi complexes and large numbers of fat droplets within the cytoplasm along with glycogen. Some cells were mainly glycogen-storing and contained few or no fat droplets. A special feature of the newt liver was biliary atresia. Bile canaliculi had short, stout microvilli which were entirely atretic in some canaliculi. Canaliculi were sealed off by junctional complexes including zonulae occludentes and maculae adherentes. The latter showed extraordinary wider desmosomal gaps in the vicinity of the atretic bile canaliculi. The sinusoid wall was non-distinctive and contained fenestrated endothelial cells connected to Kupffer cells by zonulae occludentes. A distinctive new cell type (OG cell) was observed in the newt liver. These cells were found individually or in small clusters in proximity with the sinusoidal surfaces. They had small nuclei, a paucity of cytoplasmic organelles, but numerous, unique, osmiophilic granules of two distinct types. Less numerous Type I granules contained homogeneous electron-dense material, and a predominant Type II granule contained circumferentially arranged subparticulation. Granules of both types were detected within the cytoplasm of endothelial cells and within sinusoids together with blood elements. The function of this secretory type cell remains obscure, though it may represent a stage of melanophore.     

Ultrastructural and cytochemical study of a mucous gland of the foot of Mytilus galloprovincialis

The ultrastructural study of the ventral pair mucous gland (VPMG) of the foot of Mytilus galloprovincialis shows the presence of two cell types (type I and II cells) characterized by the cytoarchitecture typical of mucous secreting cells and distinct for the different structure of their secretory granules. The cytochemical tests performed on semithin (1 micron) and ultrathin sections show that type I secretory granules are made up of proteinaceous nucleoids and of a microfilamentous matrix containing both carboxylated and sulphated glycosaminoglycans. Type II secretory granules are mainly formed by glycoproteins. The ultrastructural and cytochemical studies do not support the hypothesis that VPMG secretions directly contribute to the formation of byssus threads. It is more probable that such secretions provide a protective and lubricating blanket during the multistep process of secretion, moulding and extrusion of byssus threads.     

Ultrastructure of the adenohypophysis in the larval anadromous sea lamprey,Petromyzon marinus L.

The ultrastructure of the adenohypophysis (AH) in the larval anadromous sea lamprey, Petromyzon marinus L., was examined. The AH is subdivided into three regions, the pro-, meso-, and meta-AH. Cells of the nasopharyngeal stalk extend directly beneath the pro- and meso-AH to form the ventral surface of the gland. Some cells in the pro- and meso-AH are arranged into small follicles. Each region of the AH is characterized by a single granulated (secretory) cell type. Granulated cells constitute 80–90% of the pro-AH and contain secretory granules that range from 800 to 2400 Å in diameter. Only 10–20% of the cells in the meso-AH are granulated and they contain much smaller secretory granules (400 to 1250 Å diameter) than those in the pro-AH. Granulated cells constitute 80–90% of the meta-AH and contain only a few secretory granules, ranging from 1000 to 2500 Å in diameter, and many vesicles containing either a loose flocculent or dense granular material. Nongranulated (stellate) cells are found in all regions. They are characterized by their long cell processes, abundant cytoplasmic filaments, and variable electron density. The appearance of organelles in these cells suggests they are nonsecretory. They may play a role in maintaining the structural integrity of the gland and the regulation of granule release in the pro-AH. Two types of nongranulated cells make up 80–90% of the meso-AH. Type I are stellate cells, type II may be undifferentiated cells. The functional significance of the secretory cells in the larval AH is discussed.     

Three types of cutaneous glands in the skin of the salamandrid Pleurodeles waltl. A histological and ultrastructural study

Histological and ultrastructural investigations revealed three different multicellular skin gland types in the salamandrid Pleurodeles waltl. The mucous glands are small, with one layer of secretory cells surrounding a central lumen; they produce the viscous and slippery mucus film that has various functions in amphibians. The serous glands can be divided based on their histological and ultrastructural characters into the granular gland Type I (GGI) and the granular gland Type II (GGII). The first type (GGI) is moderately sized and distributed throughout the body surface, with higher concentrations in the parotoid and back regions. In contrast, the second type (GGII) is very large (for Pleurodeles) and was found only in the tail, with highest concentration in the tail dorsum. Both granular gland types contain mainly proteinaceous materials but differ in their morphological features including size, shape, cellular organization and vesicle distribution, vesicle size and vesicle shape. Both GGI and GGII are especially concentrated in body parts that are presented to an attacking predator and are hypothesized to produce repellent to poisonous substances to thwart potential aggressors. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Synapsoarchitectonics of the septum of the cat brain

In the medial and lateral septal nuclei, 4 types of axonal terminals are distinguished. Type I contains spherical vesicles and forms asymmetric synapses on small and middle stems and spines of the dendrites; type I terminals comprise 63% in the medial nucleus of the total number of axons, and in the lateral one--52%. Type II contains polymorphic vesicles and forms symmetrical synapses on the soma and large dendrites. In the medial nucleus they comprise 6%, and in the lateral one--3%. Type III contains either clear spherical (IIIa), or polymorphic (IIIb) vesicles, as well as 1-2 vesicles with a dense core. They form axodendritic, axospine and axosomatic synapses. In the medial nucleus they comprise 25% and 3%, respectively, in the lateral one--40% and 2%. Type IV contains a great number of vesicles with a dense core. These terminals in both septal nuclei comprise 3% and do not participate in formation of active contacts.     

Morphometric studies of the parotid gland of rats after bilateral gonadectomy and after gonadectomy and administration of mesterone

The influence of bilateral gonadectomy on the secretory segments of the partoid gland in male rats was investigated. The changes in the section area of cell nuclei, secretory cells, serous vesicles as well as in the mean number of cells in the vesicles were statistically analyzed. Eleven-day gonadectomy caused a statistically significant increase of the mean section area of cell nuclei, secretory vesicles and cells. Eight-day mesterone treatment in the dose of 2 mg/kg of body mass does not eliminate the changes caused by gonadectomy but results in the further increase of the mean section area of cell nuclei and secretory vesicles, as well as in the increase of cells in the vesicles.     

Histology,ultrastructure, and seasonal variations in the bulbourethral gland of the African straw-colored fruit bat Eidolon helvum

We studied the morphological characteristics and seasonal changes of the bulbourethral gland of Eidolon helvum in a typical African tropical environment. Forty-eight bulbourethral glands were examined using gross anatomical, histological, histochemical, and ultrastructural techniques during the early rainy, late rainy, and peak dry seasons. The pear-shaped bilateral bulbourethral glands were located extra-abdominally in the inguinal region. Trabeculae from the capsule divided the parenchyma into numerous lobules of tubuloalveolar glandular acini. The mucosa was covered by a simple columnar epithelium consisting up of principal secretory cells, columnar dense cells and basal cells, which were progressively pronounced during the dry season. The principal cells contained eosinophilic granules, which were PAS positive while the dense cells did not show affinity for the stains. The mean gross weights, acini diameters, and epithelial heights were greater during the rainy season than the dry season. Ultrastructural evaluation showed that the cytoplasm of the principal cells contained well-developed Golgi complexes, rough endoplasmic reticulum, mitochondria, and secretory vesicles of varying electron densities and sizes. The secretory vesicles were numerous during the early rainy season, decreased during the late rainy season and were scanty during the peak dry season. The simple columnar epithelium observed during the rainy season was replaced by an undefined stratified epithelium during the dry season, and this was associated with cellular degenerations and regenerations. In conclusion, E. helvum has a typical mammalian bulbourethral gland, with a unique cell type, the dense cell whose functions are not well-understood. The gland exhibits cyclical seasonal variation in structure and secretory activity; being active during the early rainy season (breeding season), and showing the lowest activity during the dry season (non-breeding season). Glandular epithelial cell renewal occurs during the dry season in preparation for the next breeding season.     

麦蛾柔茧蜂幼虫唾液腺的显微与超微形态观察

本文采用解剖学观察、显微摄影、透射电镜等方法对麦蛾柔茧蜂Habrobracon hebetor幼虫唾液腺的显微形态、超微结构以及发育特性进行了观察和分析。麦蛾柔茧蜂幼虫唾液腺为一对无色透明至乳白色的管状腺体,自口腔沿中肠两侧向后延伸,单侧腺体在中部先分支、后合并成一不规则环状,端部呈单盲管状。唾液腺管道长度随幼虫龄期增加而呈线性增长。对唾液腺切片进行超微结构观察,发现腺管由两类差异明显的单层细胞组成,I型细胞微绒毛层较厚,胞内除有丰富的内质网和线粒体之外,还含有大量囊泡,并观察到囊泡运输分泌颗粒的现象;II型细胞微绒毛短,胞内的内质网和线粒体数量丰富。本文研究为深入探究寄生蜂幼虫的消化生理以及寄生蜂-寄主互作机制奠定了基础。     

Subcellular distribution of secretogranins I and II in GH3 rat tumoral prolactin (PRL) cells as revealed by electron microscopic immunocytochemistry

The GH3 rat pituitary cell line which secretes prolactin (PRL) is characterized by the paucity and small size of secretory granules. We looked for the presence, in these cells and in normal PRL cells, of two acidic tyrosine-sulfated proteins which are widely distributed in dense-core secretory granules of endocrine and neuronal cells, secretogranins I and II, using immunofluorescence and electron microscope immunoperoxidase techniques. Both secretogranins were detected in secretory granules of GH3 cells and of normal cells. Moreover, with our pre-embedding approach, secretogranins were localized within some RER cisternae and within all sacules of the Golgi stacks in both PRL cell models. A few small vesicles, large dilated vacuolar or multivesicular structures, and some lysosome-like structures were also immunoreactive. Double localization of secretogranins and PRL performed on GH3 cells by immunofluorescence indicated that all cells contained secretogranins I and II, whereas only 50-70% of the cells contained PRL. Moreover, in the case of hormone treatment known to increase the number of secretory granules, most if not all mature secretory granules were immunoreactive for secretogranins, whereas in certain cells some of the granules were apparently not immunoreactive for PRL. These immunocytochemical observations show that GH3 cells, which under normal conditions form only a small number of secretory granules, produce secretogranins and package them into these granules.     

Ontogeny of the endocrine pancreas in sea bass (Dicentrarchus labrax): an ultrastructural study. II. The big and secondary islets

The big and secondary islets of sea bass larvae were characterized ultrastructurally from, 25 to 60 days after hatching. From the 25th day, big islets consisted of inner type II and III, external type I and peripheral type IV cells. From the 55th day, type V cells appeared in limited peripheral areas. Secondary islets, first found in 32-day-old larvae, were made up of inner type II and III, external type I, and peripheral either type IV and V cells (type I islets), or only type V cells (type II islets). Type I cells contained secretory granules with a fine granular, low-medium electron-dense material, whereas the secretory granules of type II cells were smaller and had a high electron-dense core with diffused limits; needle and rod-like crystalloid contents were occasionally found. Type III secretory granules posessed a homogeneous, high or medium electron-dense material with or without a clear halo. Type IV cells had secretory granules with a polygonal dense core embedded in a granular matrix and granules containing a high or medium electron-dense material. Type V cells had secretory granules with a fine granular, high or medium electron-dense content. These cell-types correlated with cells previously identified immuno-cytochemically, as regards to their distribution in the islets, and related to those characterized ultrastructurally in adult specimens. Thus, types I, II, III, IV and V correspond to D₁, B, D₂, A and PP cells, respectively. From the 32nd day onwards, endocrine cells of all the different types were found grouped, type V cells also being observed in isolation close to pancreatic ducts and/or blood vessels. Small groups consisting of type I and II cells were found in 40-day-old larvae. A mitotic centroacinar ductular cell containing some secretory granules similar to those of type I cells, was seen adjacent to a type I cell. As the larvae grew older, the endoplasmic reticulum developed, the number of free ribosomes decreased, and the number and size of the secretory granules increased. Dark type I, II, III, IV and V cells were found in the islets and cell clusters from the 55th day onwards.     

An ultrastructural investigation of the early stages of oocyte differentiation in Actinia fragacea (Cnidaria; Anthozoa)

Individuals from a population of the intertidal sea anemone Actinia fragacea (Tugwell) were collected at approximately monthly intervals over an 18 month period. Samples of gonad were removed from each anemone and examined by light and electron microscopy. During late spring and early summer, large numbers of small cells were seen in the endoderm of the female gonads, lying close to the mesoglea. For convenience, these cells were classified into three types. Type I cells are 6–9 μm in diameter, with relatively very large nuclei, which may contain synaptinemal complexes, and scant cytoplasm containing few organelles. Type II cells are larger, reaching 15 μ m in diameter, with more abundant cytoplasm containing more organelles and inclusions. The nucleus is more dense, but may also contain synaptinemal complexes. Type III cells are less common. They are similar in size to Type II cells, but their nuclei contain irregular dense chromatin masses, and the nuclear envelope is incomplete or absent. The possible significance of the various cell types is discussed. It is suggested that Type I cells are oocytes at a very early stage of differentiation and that Type II cells are rather later oocytes. The status of the Type III cells is uncertain.     

Serous gland polymorphism in the skin of<Emphasis Type="Italic"> Phyllomedusa hypochondrialis azurea</Emphasis> (Anura,Hylidae): response by different gland types to norepinephrine stimulation

Stimulation by norepinephrine in physiological concentration was used on the dorsal skin of the Argentine tree-frog Phyllomedusa hypochondrialis azurea to trigger contraction of myoepithelial cells encircling the serous glands and provoke secretory release. This hylid species possesses two kinds of serous cutaneous glands, producing secretory granules or vesicles (type Ia and Ib serous units, respectively), along with serous-derived glands which synthesise lipids and store them in complex aggregates (type II units). Structural and ultrastructural observations on myoepithelia, secretory units and gland products collected in saline after discharge, revealed consistent but different responses in the three types investigated. Type Ia glands reacted intensely to treatment, with both contractile and secretory responses, type Ib glands were only mildly affected in their myoepithelia and glands of type II were not affected at all. According to data available in the literature, these findings suggest that: (a) the dense (type Ia) granules are expelled as a phasic response through bulk (holocrine) discharge, (b) the secretory (type Ib) vesicles are released as a tonic response through a merocrine mechanism and (c) lipid (type II) aggregates are exuded as a secretory component of a complex behavioural response which tends to reduce transcutaneous water loss. Furthermore, these findings indicate that the use of pharmacological modulation of myoepithelial activity allows selective collection of skin products in species characterised by serous gland polymorphism.