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At least 145 records · Page 8Linked to original sources
PubMed2003

Placentation in garter snakes. II. Transmission EM of the chorioallantoic placenta of Thamnophis radix and T. sirtalis.

Transmission electron microscopy was used to examine the ultrastructure of the allantoplacenta of garter snakes during the last half of gestation. This placenta occupies the dorsal hemisphere of the egg and is formed through apposition of the chorioallantois to the inner lining of the uterus. The uterine epithelium consists of flattened cells with short, irregular microvilli and others that bear cilia. The lamina propria is vascularized and its capillaries lie at the base of the uterine epithelial cells. The chorionic epithelium consists of a bilayer of squamous cells that are particularly thin superficial to the allantoic capillaries. Neither the chorionic epithelium nor the uterine epithelium undergoes erosion during development. Although a thin remnant of the shell membrane intervenes between fetal and maternal tissue at mid-gestation, it undergoes fragmentation by the end of gestation. Thus, uterine and chorionic epithelial are directly apposed in some regions of the allantoplacenta, forming continuous cellular boundaries at the placental interface. During development, capillaries proliferate in both the uterine and chorioallantoic tissues. By late gestation, the interhemal diffusion distance has thinned in some areas to less than 2 microm through attenuation of the uterine and chorionic epithelia. Morphologically, the allantoplacenta is well adapted for its function in gas exchange. However, the presence of cytoplasmic vesicles, ribosomal ER, and mitochondria in the chorionic and uterine epithelial cells are consistent with the possibility of additional forms of placental exchange.

Allantois↗
PubMed2003

Placentation in garter snakes. III. Transmission EM of the omphalallantoic placenta of Thamnophis radix and T. sirtalis.

The omphalallantoic placenta is a complex organ that is unique to viviparous squamates. Using transmission EM and light microscopy, we examined this placenta in garter snakes in order to understand its structural organization and functional capabilities. The omphalallantoic placenta is formed from the uterine lining and the bilaminar omphalopleure, the latter of which is associated with the isolated yolk mass and allantois. A thin shell membrane separates the fetal and maternal tissues throughout gestation. The uterine epithelium contains cuboidal cells with large droplets or granules and appears to be secretory. Epithelium of the omphalopleure is specialized for absorption and contains cells with prominent microvilli and others with large cytoplasmic droplets or granules. The brush-border cells are rich in mitochondria and Golgi bodies and interdigitate extensively with adjacent cells, forming elaborate intercellular canaliculi. Their morphology is consistent with their proposed role in sodium-coupled water movement. During development, the isolated yolk mass becomes depleted as yolk droplets are digested by cells of the omphalopleure and allantois. However, the allantois does not fuse to or vascularize the inner face of the omphalopleure. Consequently, the distance between fetal and maternal circulatory systems remains large (about 250-300 microm), precluding efficient gas exchange and hemotrophic transfer. The morphology of the omphalallantoic placenta strongly suggests that it functions in nutrient transfer through uterine secretion and fetal absorption.

Allantois↗
PubMed2004

Variation in seasonal ultrastructure of sexual granules in the renal sexual segment of the Northern Water Snake, Nerodia sipedon sipedon.

The renal sexual segment of the kidney (RSS) can be found in many male squamate reptiles, encompassing the distal region of the nephron and, in some cases, collecting ducts. This sexually dimorphic structure exhibits varying degrees of hypertrophy and regression throughout the year. Although researchers have been aware of and have investigated this unique structure for over a century, its ultimate function remains under discussion. In many studies hypertrophy and regression of the RSS have been correlated with testicular activity and androgen secretion. As in most of the snakes studied to date, the male Northern Water Snake (Nerodia s. sipedon) does not exhibit a dramatic cycle of hypertrophy and regression, as reported in lizards. Following the initial hypertrophy at maturity, the male Northern Water Snake maintains a level of RSS hypertrophy throughout the year. Variations in the appearance and makeup of the sexual granules provide an identifiable and quantifiable seasonal pattern that can be correlated with the concentration of plasma androgens. In the Northern Water Snake, plasma androgens are elevated upon emergence and the RSS epithelial cells are filled with solid granules. As androgen levels decline during spring, sexual granule content appears to be breaking down (utilized?), becoming diffuse in appearance. By mid- to late summer androgen synthesis is at a maximum, increasing circulating androgens and stimulating the development and return of the solid granules. This study utilized electron microscopy and steroid radioimmunoassay to examine seasonal cycles of sex granules, in terms of development, maintenance, and regression, correlated with plasma androgen concentration. In addition, this investigation provides evidence of a possible secondary source of androgen secretion.

Androgens↗
PubMed2004

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). IV. Occurrence of an ampulla ductus deferentis.

The distal end of the ductus deferens of Seminatrix pygaea (Cope) differs from more proximal portions of the tube by possessing a highly fluctuated epithelium. Similar morphology has been reported in this area in one lizard and some mammals and the region has been designated in these taxa as the ampulla ductus deferentis. In this study, light and transmission electron microscopy were used to study the posterior ductus deferens in S. pygaea and compare the histology in this region to more proximal regions of the duct and to descriptions of the ampulla of other species. Seminatrix pygaea stores sperm throughout the ductus deferens during the entire year. The epithelium of the ductus deferens is not secretory, but the presence of numerous small apical vesicles indicates a role in fluid absorption. In addition to the highly folded epithelium, clusters of sperm nuclei are more intimately associated with the apical ampullary epithelium than elsewhere in the ductus deferens. No evidence of phagocytosis of sperm was found. In contrast, the ampulla of mammals and presumably the lizard Calotes versicolor is glandular and phagocytic. The common character shared by the squamates and mammals with specializations in this area is the folded epithelium, and whether this is due to shared ancestry with amniotes or is homoplastic is unresolved.

Animals↗
PubMed2005

Differentiation of snake epidermis, with emphasis on the shedding layer.

Little is known about specific proteins involved in keratinization of the epidermis of snakes. The presence of histidine-rich molecules, sulfur, keratins, loricrin, transglutaminase, and isopeptide-bonds have been studied by ultrastructural autoradiography, X-ray microanalysis, and immunohistochemistry in the epidermis of snakes. Shedding takes place along a shedding complex, which is composed of two layers, the clear and the oberhautchen layers. The remaining epidermis comprises different layers, some of which contain beta-keratins and others alpha-keratins. Weak loricrin, transglutaminase, and sometimes also iso-peptide-bond immunoreactivities are seen in some cells, lacunar cells, of the alpha-layer. Tritiated histidine is mainly incorporated in the shedding complex, especially in dense beta-keratin filaments in cells of the oberhautchen layer and to a small amount in cells of the clear layer. This suggests the presence of histidine-rich, matrix proteins among beta-keratin bundles. The latter contain sulfur and are weakly immunolabeled for beta-keratin at the beginning of differentiation of oberhautchen cells. After merging with beta cells, the dense beta-keratin filaments of oberhautchen cells become immunopositive for beta-keratin. The uptake of histidine decreases in beta cells, where little dense matrix material is present, while pale beta-keratin filaments increase. During maturation, little histidine labeling remains in electron-dense areas of the beta layer and in those of oberhautchen spinulae. Some roundish dense granules of oberhautchen cells rich in sulfur are negative to antibodies for alpha-keratin, beta-keratin, and loricrin. The granules eventually merge with beta-keratin, and probably contribute to the formation of the resistant matrix of oberhautchen cells. In conclusion, beta-keratin, histidine-rich, and sulfur-rich proteins contribute to form snake microornamentations.

Animals↗
PubMed1993

Developmental changes in cytochrome oxidase histochemistry in the main and accessory olfactory bulbs of embryonic and neonatal garter snakes (Thamnophis sirtalis spp.).

Developmental studies examining the changes in oxidative metabolic activity are useful for understanding how and if the vomeronasal and olfactory systems respond to stimulation during embryogenesis. Garter snakes are good candidates for examining the potential functionality of the vomeronasal system in utero. In adult garter snakes, the vomeronasal system mediates many behaviors. Neonatal garter snakes exhibit these same behaviors, and the vomeronasal system has been shown to mediate feeding behavior in neonates. Using cytochrome oxidase histochemistry, we examined changes in the oxidative metabolic activity of main and accessory olfactory bulbs of embryonic and neonatal garter snakes (Thamnophis sirtalis sirtalis and T. s. parietalis). Cytochrome oxidase staining is greater in the accessory olfactory bulb than in the main olfactory bulb of embryonic garter snakes. However, neonates show no differences in the staining of the accessory and main olfactory bulbs, suggesting a change in the stimulation of the main olfactory bulb after birth. This is the first report of cytochrome oxidase histochemistry in reptiles and in the vomeronasal system of embryonic vertebrates.

Aging↗
PubMed2002

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). III. Sexual segment of the male kidney.

In mature male snakes and lizards, a distal portion of the nephron is hypertrophied in relation to its appearance in females and immature males. This sexual segment of the male kidney apparently provides seminal fluid that is mixed with sperm and released into the female cloaca during copulation. In this article, we provide the first study at the ultrastructural level of seasonal variation in the sexual segment of the kidney of a squamate, the natricine snake Seminatrix pygaea. Previous workers have indicated that the sexual segment is secretory only when the testes are spermatogenically active. The sexual segment of the kidney in S. pygaea does not go through an extended period of inactivity but does show a cycle of synthesis and secretion that can be related to the spermatogenic cycle and mating activity. We show that synthesis of secretory product is initiated with the onset of spermatogenic activity in the spring and culminates with completion of spermiation in the fall. Secretion of the product, however, occurs in a premating period in March when the testes are inactive. Secretion during this premating period is probably necessary to provide time for the passage of the products down the ureter in order to mix with sperm during mating later in spring.

Animals↗
PubMed2002

Placentation in garter snakes: scanning EM of the placental membranes of Thamnophis ordinoides and T. sirtalis.

Surface topography and cross-sections of the placental membranes were examined by scanning electron microscopy in two species of Thamnophis. The chorionic epithelium of the chorioallantoic placenta consists of broad, squamous cells that lack surface specializations. The apposed uterine epithelium contains ciliated cells and larger, nonciliated cells. Neither the epithelium of the chorion nor that of the uterus is eroded; thus, underlying capillaries are not exposed to the luminal surface. In both the omphaloplacenta and the omphalallantoic placenta, epithelium of the omphalopleure consists of brush-border cells bearing prominent microvilli, interspersed with cells bearing minuscule microvilli. These surface epithelial cells are joined at their apices and their lateral surfaces are extensively sculpted by intercellular channels, presenting the appearance of an epithelium specialized for absorption. Deep to the epithelium lie the yolk spheres of the isolated yolk mass, interspersed with endodermal cells. Surface topography of the uterine epithelia of the omphaloplacenta and omphalallantoic placenta is relatively unspecialized. The acellular shell membrane separates maternal and fetal tissues in each of the three placental types. Marked differences in surface features of the chorioallantois and omphalopleure probably reflect different roles of these membranes in gas exchange and transfer of water and nutrients.

Animals↗
PubMed1997

Chemosignal transduction in the vomeronasal organ of garter snakes: Ca(2+)-dependent regulation of adenylate cyclase.

Earthworm shock secretion contains a 20-kDa vomeronasally mediated chemoattractive protein for garter snakes. Both the ligand-receptor binding and the chemoattractivity of ES20 are Ca(2+)-dependent. When ES20 binds to its G-protein-coupled receptors in the vomeronasal epithelium, the inositol 1,4,5-trisphosphate (IP3) level is increased, but the level of cAMP is reduced. Furthermore, forskolin-stimulated levels of cAMP are completely blocked by ES20-receptor binding or by Ca2+ alone and the effect of calcium ions can be nullified by EGTA. Previously, we hypothesized that the decrease in cAMP was due to activation of a Ca(2+)-dependent phosphodiesterase. In the present study, we provide evidence that the decrease in cAMP is due mainly to the regulation of adenylate cyclase (AC) activity by Ca2+ or is indirectly mediated by ES20. Results obtained with intact vomeronasal sensory epithelium suggest that the binding of ES20 to its receptors facilitates generation of IP3 which mobilizes intracellularly sequestered Ca2+, resulting in an increase of cystosolic Ca2+. A further increase in cytosolic Ca2+ occurs through Ca2+ influx from extracellular sources. Garter snake vomeronasal AC does not require calmodulin for its activity and shows a biphasic response to increasing concentrations of Ca2+; its activity is modulated both positively and negatively by this bivalent cation.

Adenylate Cyclase Toxin↗
PubMed1993

Thyroxine-induced changes in metabolic rate and cytochrome oxidase activity in Thamnophis sirtalis: effects of nutritional status.

The effects of nutritional status on thyroxine-induced changes in standard metabolic rate (SMR), and the activity of hepatic cytochrome oxidase were examined in the garter snake Thamnophis sirtalis. Twelve snakes were fed ad libitum, and 12 more were fed a maintenance diet, which was half as many fish per gram of body weight as that eaten by ad libitum snakes. Snakes in the first group gained weight during the 3-week treatment, while individual snakes in the second group either maintained their original weight or showed a slight loss (less than 10%). Within each diet treatment, half of the snakes received a 5-mg thyroxine (T4) pellet implant, and half received placebo implants. Plasma [T4] was unchanged by treatment. Plasma [T3] was elevated in T4-supplemented snakes fed ad libitum, but the difference was not statistically significant (P = 0.09). Standard metabolic rate and cytochrome oxidase activity at 25 degrees were increased significantly (34 and 24%, respectively) only in the T4-supplemented snakes on the ad libitum diet. Thus, T. sirtalis must be in a positive energy balance for thyroid hormones to have an effect on SMR or hepatic cytochrome oxidase activity.

Animals↗
PubMed1993

Pregnancy-associated factors affecting organic phosphate levels and oxygen affinity of garter snake red cells.

Pregnancy in Thamnophis elegans is associated with an increase in the nucleoside triphosphate (NTP) concentration and a concomitant decrease in the oxygen affinity of the adult red cell. Red cell NTP levels rise at about the time of ovulation and peak during mid-gestation. Since plasma progesterone levels appear to have a similar profile, we examined the influence of progesterone on this phenomena. Surgical removal of the corpora lutea (CL), primary site of progesterone release, plus fetuses abolished the pregnancy-associated effect on red cell NTP levels. Removal of the CL alone resulted in NTP levels intermediate to those of the red cells of the nonpregnant and the pregnant groups. Progesterone implants in nonpregnant females, as well as in males, caused red cell NTP concentrations to rise. These data support the hypothesis that progesterone, secreted by the CL, in the presence of the fetus, is largely responsible for the pregnancy-associated increase in the red cell NTP concentration.

Animals↗
PubMed1994

Melanin-concentrating hormone-producing neurons in reptiles.

Melanin-concentrating hormone (MCH)-like producing neurons were mapped in the brains of several reptiles using antisera (AS) prepared against salmon MCH (sMCH) and peptides derived from the rat MCH precursor (rMCH, NGE, NEI) or cross-reacting with these peptides (anti-GRF37 and anti-alpha-MSH). MCH neurons were detected in the periventricular and lateral hypothalamic nuclei. The coexpression of MCH-, GRF37- and NEI-like immunoreactivities suggests that the reptile precursor presents large sequence homologies with the rat/human precursor. MCH neurons project to many brain areas, but fibers are very scarce in the median eminence, and the neurohypophysis is devoid of immunoreactive processes. Thus the MCH produced by these neurons would not be a neurohormone as in fish. The great quantity of processes observed in the optic lobes and in the olfactive encephalic areas (particularly in the septum) is most probably related to behavioral and adaptive regulations controlled by the hypothalamus.

Animals↗
PubMed1995

Effect of various vitamin D metabolites on serum calcium and inorganic phosphate in the freshwater snake Natrix piscator.

Vitamin D3 (650 pmol and 6.50 nmol/100 g body wt), 25-hydroxyvitamin D (650 pmol and 6.50 nmol/100 g body wt), and 1,25-dihydroxyvitamin D (65 pmol and 650 pmol/100 g body wt) were administered daily to the freshwater snake Natrix piscator for 15 days. Both serum calcium and inorganic phosphate levels were increased significantly in all of the treated groups. This is the first report of hypercalcemia and hyperphosphatemia in reptiles induced by 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D.

Animals↗
PubMed1998

Characterization of bradykinin-related peptides generated in the plasma of six sarcopterygian species (African lungfish, amphiuma, coachwhip, bullsnake, gila monster, and Gray's monitor).

Incubation of heat-denatured plasma from six species occupying different evolutionary positions within the Sarcopterygian lineage [the dipnoan, Protopterus annectens (African lungfish); the urodele, Amphiuma tridactylum (three-toed amphiuma); the colubrid snakes, Pituophis melanoleucus sayi (bullsnake) and Masticophis flagellum (coachwhip); and the lizards Heloderma suspectum (Gila monster) and Varanus Grayi (Gray's monitor)] with trypsin generated bradykinin-related peptides that were detected by radioimmunoassay using an antiserum raised against mammalian bradykinin (BK). The peptides were purified by HPLC and their primary structures were established as lungfish [Tyr1,Gly2,Ala7,Pro8]BK, amphiuma [Phe1,Ile2, Leu5]BK, bullsnake and coachwhip [Val1,Thr6]BK, Gila monster [Leu2, Thr6]BK, and Gray's monitor [Thr6]BK. Monitor BK is identical to the peptide generated in turtle and alligator plasma and coachwhip/bullsnake BK shows one amino acid substitution (Ala1 --> Val) compared with the peptide generated in the plasma of the python. The data provide further evidence for the widespread occurrence of a kallikrein-kininogen system in nonmammalian vertebrates but indicate that the primary structure of BK has been poorly conserved during evolution.

Amino Acid Sequence↗