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At least 343 records · Page 19Linked to original sources
PubMed1986

Characterization of estrogen binding sites in the liver of the newt Pleurodeles waltl (Urodela:Amphibia): demonstration of a sex-linked heterogeneity.

Saturation analysis over a wide range of [3H]estradiol-17 beta concentrations (1-40 nM) in cytosols prepared from liver of the newt Pleurodeles waltl of both sexes revealed a sex-linked heterogeneity of the estradiol-17 beta binding sites. In females, one type of binding site has been identified as a classical receptor. It exhibited a high affinity for estradiol-17 beta (Kd = 9 X 10(-9) M), had a high specificity for estrogenic compounds and was stabilized by monothioglycerol. In males, in addition to the receptor found in females, a second estrogen binding component was detected, not observed in female cytosols. It exhibited a Kd of 4.8 X 10(-8) M for estradiol 17 beta, higher capacity and displayed the same highly specific estrogen binding as does the estrogen receptor. It was affected by monothioglycerol and its binding was found to be significantly increased on cytosol dilution, as well as by estrogen-treatment.

Animals↗
PubMed1983

Co-localization of vasoactive intestinal peptide (VIP) and enkephalins in chromaffin cells of the adrenal gland of amphibia. Stimulation of corticosteroid production by VIP.

Recent studies have shown that biologically active peptides and monoaminergic neurotransmitters coexist in certain neuronal cell populations. Using the immunofluorescence technique, we have examined the localization of enkephalins, vasoactive intestinal peptide (VIP) and tyrosine hydroxylase in the adrenal gland of the frog Rana ridibunda. Most chromaffin cells which stained for tyrosine hydroxylase contained VIP-like immunoreactivity, whereas methionine- (Met-) and leucine- (Leu-) enkephalin-like immunoreactivity was detected in about 40% of the cells revealed by the anti-tyrosine hydroxylase serum. No VIP- or enkephalin-like immunoreactive nerve fibres were observed. Since in the frog, the chromaffin cells are in close contact with the adrenocortical (interrenal) tissue, a possible action of VIP and opiates on corticosteroidogenesis has been investigated. At doses 10(-6) and 10(-5) M, 20-min infusions of synthetic porcine or chicken VIP elicited a significant increase in corticosterone and aldosterone production by perifused frog adrenals, in a dose-dependent manner. As compared to ACTH, VIP was several orders of magnitude less effective in stimulating corticosteroid production. Morphine, Met- and Leu-enkephalins (10(-5) M) had no effect on spontaneous secretion of corticosteroids. In addition, Met- and Leu-enkephalins (10(-5) M) did not alter the production of corticosterone induced by ACTH. THese results suggest that VIP contained in the chromaffin cells of the frog adrenal gland may exert a local action in stimulating corticosteroid production by the interrenal tissue.

Acetylcholine↗
PubMed1985

Oxygen binding in blood of Xenopus laevis (Amphibia) and evidence against Root effect.

Blood oxygen binding was examined in the amphibian, Xenopus laevis, with the particular aim of determining whether the O2 capacity is diminished when blood pH is lowered, which is known as the Root effect in blood of some fishes. Hemoglobin-bound O2 concentration, [O2Hb], was determined by the Lex-O2-Con technique, and both total hemoglobin, [Hb]tot, and Met-hemoglobin, [MetHb], contents were measured spectrophotometrically. From these measurements were calculated the oxygen capacity, O2cap, and the content of active hemoglobin, [Hb]act, i.e. the difference between [Hb]tot and [MetHb]. The main finding was the independence of the ratio of O2cap/[Hb]act on pH, when differences between samples in [Hb]tot and the presence of MetHb, which was particularly pronounced at low pH, where properly accounted for. It is concluded that the Root effect does not exist in blood of the amphibian Xenopus laevis.

Animals↗
PubMed1976

Quantitative and comparative ultrastructure of the vertebrate cornea. I. Urodele Amphibia.

The cornea of the urodele amphibian Triturus c. cristatus was studied ultrastructurally in order to provide the basis for a comparison among corneas throughout the vertebrate phylum. The cornea of this salamander consists of relatively thick epithelium and basement membrane and thin Descemet's membrane, unlike the mammalian corneas. The outermost epithelial cells contain Ruthenium Red stainable extracellular filaments and intracellular vesicles which are thought to play a role in the process of lubricating the corneal surface. Occluding junctions have been observed in the apical region of the superficial epithelial cells and are considered as barriers to the intercellular passage of material. A thin substantia propria (stroma) consists of about 40 collagenous highly organized lamellae. The thicknesses of the basement membrane, Descemet's membrane and the epithelium are believed to represent the primitive situation in the process of corneal evolution.

Animals↗
PubMed1976

Quantitative changes and ultrastructural alterations of the cornea in response to ultraviolet light. II. Effects of amphibia; elucidation of desmosomal structure and basement membrane synthesis.

The effects of far ultraviolet light irradiation upon an amphibian cornea were studied to compare the effects observed both quantitatively and ultrastructurally with data obtained after UV irradiation of mammalian corneas. The ultimate goal of this series of investigations is the elucidation of the alterations and the regeneration mechanisms, which might reflect existing morphological diversities among the species, observed in vertebrate corneas following exposure to UV light. It was found that while the epithelial cells undergo oedema after low dose exposures and are gradually damaged after high doses of UV light, 2-4 days leter a new epithelium has been formed. Intercellular permeability is increased by low dose exposure as was detected by the penetration of Ruthenium Red into the intercellular clefts. Under these conditions desmosomal structure revealed a 21-laminar configuration. The basement membrane of the amphibian, unlike that of the mammal, does not dissolve away upon exposure but shows localized disruptions which are thought to accommodate the passage of leucocytes from stroma to epithelium. That a new basement membrane is subsequently formed is evident by the existence of extracellular and intracellular secretion granules. In comparison to irradiated rabbit corneas, this stroma remains remarkably at the same thickness following a high dose exposure although a noticeable disorganization of collagen arrangement is apparent. Finally, as in the case of the rabbit corneas, a secondary degeneration of endothelium was observed 4 days after a moderate dose exposure.

Animals↗
PubMed1983

Morphological and biochemical studies on the innervation of the testis of Salamandra salamandra (L.) (Amphibia, Urodela).

The innervation of the male gonad of Salamandra salamandra was studied by fluorescence microscopy using the glyoxylic acid method, acetylcholinesterase histochemistry, electron microscopy using glutaraldehyde/osmium tetroxide and chromate/dichromate fixation, and high-performance liquid chromatography (HPLC) with electrochemical detection of biogenic amines in homogenates of the testicular tissue. Noradrenaline has been found to be the prevailing neurotransmitter in the testicular nerves; dopamine could be identified only in minor concentration. The relatively scarce noradrenergic innervation is mainly restricted to the connective tissue septa between the immature and the mature part of the testis and between the mature part and the glandular tissue. Most of the fluorescent fibers have a close connection to blood vessels. After chromate/dichromate fixation the nerve profiles contain in most cases small vesicles with electron-dense reaction products, indicating the presence of catecholamines. Varicosities are to be found near the capillaries, in the vicinity of vascular (in the wall of arterioles) and non-vascular (near the testicular surface) smooth muscle cells; no relationships were found between nerve fibers and glandular (steroid hormone-secreting) or germinal cells. Cholinergic fibers could not be identified, non-adrenergic/non-cholinergic fibers were present only in very small numbers.

Acetylcholinesterase↗
PubMed1985

Visual projections in larval Ichthyophis kohtaoensis (Amphibia: gymnophiona).

The visual projection patterns of retinal efferents were studied in larval Ichthyophis kohtaoensis by means of anterogradely transported HRP. Our results show in all larvae a projection contralateral to a thalamic terminal field, a pretectal terminal field, and a basal optic neuropil, but only a sparse innervation of the contralateral tectum. In addition, all larvae possess an uncrossed projection to a thalamic and a pretectal terminal field. The fibers are bilaterally almost confined to the medial optic tract with only a few fibers running in the marginal and basal optic tract. The ipsilateral and contralateral tracts and terminal fields seem to enlarge during larval life. Comparison with other amphibian orders reveals that larval Ichthyophis are unique in that they develop the medial optic tract and the related thalamic and pretectal terminal fields very early in larval life. In addition they possess only a very sparse tectal projection, though it is the largest projection in larval urodeles and anurans. This suggests a selective phylogenetic loss of those ganglion cells or collaterals which project mainly to the tectum in other amphibian orders and a change in the ontogenetic program leading to an earlier development of the medial optic tract in Ichthyophis as compared to urodeles and anurans.

Amphibians↗