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Results for “Necturus maculosus”

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PubMed1992

Autocrine and paracrine role of steroids during spermatogenesis: studies in Squalus acanthias and Necturus maculosus.

Due to a cystic mode of spermatogenesis and zonal testes, the spiny dogfish shark (Squalus acanthias) and salamander (Necturus maculosus) are advantageous for studying the relationship between steroidogenesis and germ cell development. Direct analysis of steroidogenic enzymes and steroid receptors in staged tissue samples, together with light and electron microscopic observation, suggests that androgens and estrogens produced by Sertoli cells or Leydig cells immediately before or after spermiation serve as intratesticular regulators of events specific to premeiotic stages of spermatogenesis. These correlative data are consistent with limited observations in mammalian testis and provide a conceptual framework for direct testing of functional interactions between spermatogenesis and steroidogenesis in future studies.

Animals↗
PubMed1993

Modulation of Cl-, K+, and nonselective cation conductances by taurine in olfactory receptor neurons of the mudpuppy Necturus maculosus.

Odors are transduced by processes that modulate the membrane conductance of olfactory receptor neurons. Olfactory neurons from the aquatic salamander, Necturus maculosus, were acutely isolated without enzymes and studied with a resistive whole-cell method to minimize loss of soluble intracellular constituents. 55 of 224 neurons responded to the test compound taurine at concentrations between 10 nM and 100 microM. Four different conductance changes were elicited by taurine: an increased Cl- conductance (33%), an increased nonselective cation conductance (15%), a decreased Cl- conductance (15%), and a decreased K+ conductance (15%); in addition, responses too small to be characterized were elicited in some neurons. In most cases, taurine appeared to modulate only a single conductance in any particular cell. Modulation of each conductance was dose dependent, and each response ran down quickly in the normal whole-cell mode, presumably due to washout of a diffusible component in the transduction pathway. Modulation of taurine-sensitive conductances caused either inhibitory or excitatory responses. A similar diversity of responses in vivo would produce a complex pattern of electrical activity that could encode the identity and characteristics of an odor.

Animals↗
PubMed1989

Cardiovascular regulation in the mudpuppy Necturus maculosus at rest and during short term exercise.

Prebranchial blood pressure (Pva), heart rate (fH) and plasma catecholamine concentration were measured in the mudpuppy Necturus maculosus at rest and during exercise. During exercise, both fH and Pva increased, as did the plasma noradrenaline concentration. There was no significant effect on Pva after injection of the adrenergic neuron blocker, bretylium, in resting animals, neither did bretylium affect the exercise-induced increase in Pva. This suggests that there is no adrenergic nervous tone on the vasculature at rest or during exercise. The alpha-adrenoceptor antagonist yohimbine had no effect on the resting Pva in the bretylium-treated animals, but it abolished the increase in Pva during exercise. This is compatible with the view of no influence on Pva by the plasma catecholamines at rest, while during exercise the increase in plasma noradrenaline concentration is responsible for the increase in Pva. Injection of atropine elevated resting fH, and reduced or abolished cardiac arrythmia, indicating an inhibitory cholinergic tone on the heart at rest, and that variations in this tone are responsible for the intrinsic variation seen in untreated animals. After the atropine treatment, there was still an increase in fH during exercise. The beta-adrenoceptor antagonist sotalol decreased fH in resting atropinized animals, and inhibited the exercise-induced tachycardia, implying that there is an additional beta-adrenoceptor-mediated adrenergic tone, affecting the heart both at rest and during exercise. The cholinergic tone decreased during exercise with a concomitant increase in adrenergic tone. Falck-Hillarp fluorescent histochemistry was used to study the presence of adrenergic nerve fibres and other catecholamine-storing cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Arachidonic acid may mediate the galanin-induced hyperpolarization in parasympathetic neurons from Necturus maculosus.

The effects of arachidonic acid (AA) and compounds that inhibit intracellular signalling pathways on membrane potential and galanin-induced hyperpolarizations were investigated in parasympathetic neurons from Necturus maculosus. Treatment for 10-90 min with 10-20 microM 4-bromophenacylbromide or 10 microM cyclosporin A caused a progressive decrease in the amplitude of galanin-induced hyperpolarizations without any change in resting membrane potential. The galanin-induced hyperpolarization was not altered following a 10-120 min treatment with the protein kinase inhibitor H-7. These results indicated that phospholipase A2 activation, but not protein kinase activation, may be required for the galanin-induced hyperpolarization. Arachidonic acid (20-100 microM) caused a concentration-dependent membrane hyperpolarization of the parasympathetic neurons and a decrease in the amplitude of the galanin-induced hyperpolarization. These data indicate that phospholipase A2-catalyzed liberation of AA may be involved in the galanin-induced membrane hyperpolarization observed in mudpuppy parasympathetic neurons.

Acetophenones↗
PubMed1982

A fine-structural study of interstitial cell changes in the testes of Necturus maculosus during a portion of the annual cycle, and possible evidence for local feedback control by seminiferous epithelium.

The developmental stages of the interstitial cells of Leydig in Necturus maculosus were studied in testes of animals obtained in November and December. As a consequence of the caudal to cranial progression of the wave of spermatogenesis, samples obtained from cranial, central, and caudal portions of these testes exhibit regional differences in the morphology of their Leydig cells. In these samples, fibroblast-like stromal cells with large, dense, elongated nuclei and thin sheets of cytoplasm surround the cranial seminiferous lobules that usually contain spermatozoa. Such stromal cells possess a small juxtanuclear Golgi apparatus, profiles of smooth and rough endoplasmic reticulum, and mitochondria with tubular and shelf-like cristae. In the central area of the testis, interstitial cells with oval nuclear profiles and a finer chromatin pattern surround degenerating seminiferous lobules. The abundant cytoplasm of these cells contains predominantly smooth endoplasmic reticulum interspersed with a few lipid droplets. These cells contain mitochondria that are packed with tubular cristae. Inthe caudal part of the testis, the Leydig cells have a round nucleus with finely dispersed chromatin. Numerous lipid droplets accumulate in the ample cytoplasm, which is filled with smooth endoplasmic reticulum. The juxtanuclear Golgi apparatus becomes enlarged; associated with it are vesicles with an electron-dense content. The cristae of the mitochondria are more numerous and have tubules of 50-nm diameter mixed with arrays of small tubules 25-30 nm in diameter. The appearance of morphologically mature interstitial cells of Leydig only adjacent to degenerated seminiferous lobules inthe caudal portion of the testis suggests the possibility of local feedback control of Leydig-cell development.

Animals↗
PubMed1985

Neuropeptides in the gastrointestinal canal of Necturus maculosus. Distribution and effects on motility.

The presence and distribution of regulatory peptides in nerves and endocrine cells of the stomach, intestine and rectum of a urodele amphibian, the mudpuppy, Necturus maculosus, was studied immunohistochemically in sections or whole-mount preparations of the gut wall. The effect of the occurring peptides on gut motility was studied in isolated strip preparations of circular and longitudinal smooth muscle from different parts of the gut. Bombesin-, neurotensin-, substance P- and VIP-like immunoreactivity was present in abundant nerve fibres in the myenteric plexus of both stomach, intestine and rectum. Single fibres or bundles were present in the circular muscle layer and in a well-developed deep muscular plexus in the intestine and rectum. Immunoreactive nerve cells were found in the myenteric plexus of the stomach, intestine (neurotensin only) and rectum. Gastrin/CCK-like immunoreactivity was observed only in a few fibres in stomach and rectum. Endocrine cells containing bombesin-, met-enkephalin-, gastrin/CCK-, neurotensin-, somatostatin- or substance P- like immunoreactivity were present in the mucosa. The effect of bombesin was an inhibition of the rhythmic activity in circular muscle preparations and in longitudinal muscle from the rectum, while longitudinal muscle from the stomach usually responded with a weak increase in tonus. Neurotensin, like-bombesin, was inhibitory on the spontaneous rhythmic activity of circular muscle throughout the gut, while the effect on longitudinal muscle was an increase in tonus. Met-enkephalin and substance P increased the tonus of all types of preparations, and often, in addition, initiated a rhythmic activity superimposed on this maintained tonus. VIP had a general inhibitory effect on the preparations, decreasing tonus and/or abolishing rhythmic activity. It is concluded that bombesin-, neurotensin-, substance P- and VIP-like peptides are present in nerves throughout the urodele gut and may have physiological functions in regulating the motility of the gut. The gastrin/CCK-like peptide present in nerves of the stomach and rectum may affect the function of these parts of the gut. The regulatory peptides present in endocrine cells may, perhaps with the exception of the somatostatin-like peptide, affect the motility humorally.

Animals↗
PubMed1998

Uptake and release of neurotransmitter candidates, [3H]serotonin, [3H]glutamate, and [3H]gamma-aminobutyric acid, in taste buds of the mudpuppy, Necturus maculosus.

Neurotransmitters in vertebrate taste buds have not yet been identified with confidence. Serotonin, glutamate, and gamma-aminobutyric acid (GABA) have been postulated, but the evidence is incomplete. We undertook an autoradiographic study of [3H]serotonin, [3H]glutamate, and [3H]GABA uptake in lingual epithelium from the amphibian, Necturus maculosus, to determine whether taste bud cells would accumulate and release these substances. Lingual epithelium containing taste buds was incubated in low concentrations (0.4-6 microM) of these tritiated transmitter candidates and the tissue was processed for light microscopic autoradiography. Merkel-like basal taste cells accumulated [3H]serotonin. When the tissue was treated with 40 mM K+ after incubating the tissue in [3H]serotonin, cells released the radiolabelled transmitter. Furthermore, depolarization (KCl)-induced release of [3H]serotonin was Ca-dependent: if Ca2+ was reduced to 0.4 mM and 20 mM Mg2+ added to the high K+ bathing solution, Merkel-like basal cells did not release [3H]serotonin. In contrast, [3H]glutamate was taken up by several cell types, including non-sensory epithelial cells, Schwann cells, and some taste bud cells. [3H]glutamate was not released by depolarizing the tissue with 40 mM K+. [3H]GABA uptake was also widespread, but did not occur in taste bud cells. [3H]GABA accumulated in non-sensory epithelial cells and Schwann cells. These data support the hypothesis that serotonin is a neurotransmitter or neuromodulator released by Merkel-like basal cells in Necturus taste buds. The data do not support (nor rule out) a neurotransmitter role for glutamate or GABA in taste buds.

Animals↗
PubMed1997

Bitter taste transduction of denatonium in the mudpuppy Necturus maculosus.

Bitter substances are a structurally diverse group of compounds that appear to act via several transduction mechanisms. The bitter-tasting denatonium ion has been proposed to act via two different G-protein-regulated pathways, one involving inositol 1,4, 5-trisphosphate and raised intracellular calcium levels, the other involving phosphodiesterase and membrane depolarization via a cyclic nucleotide-suppressible cation channel. The aim of the present study was to examine these transduction mechanisms in taste cells of the mudpuppy Necturus maculosus by calcium-imaging and whole-cell recording. Denatonium benzoate increased intracellular calcium levels and induced an outward current independently of extracellular calcium. The denatonium-induced increase in intracellular calcium was inhibited by U73122, an inhibitor of phospholipase C, and by thapsigargin, an inhibitor of calcium transport into intracellular stores. The denatonium-induced outward current was blocked by GDP-beta-S, a blocker of G-protein activation. Neither resting nor denatonium-induced intracellular calcium levels were affected by inhibition of phosphodiesterase (with IBMX) or adenylate cyclase (with SQ22536) or by raising intracellular cyclic nucleotides directly (with cell permeant analogs). Our results support the hypothesis that denatonium is transduced via a G-protein cascade involving phospholipase C, inositol 1,4,5-trisphosphate, and raised intracellular calcium levels. Our results do not support the hypothesis that denatonium is transduced via phosphodiesterase and cAMP.

1-Methyl-3-isobutylxanthine↗
PubMed1983

The differentiation of Leydig cells, steroidogenesis, and the spermatogenetic wave in the testis of Necturus maculosus.

The study of seminiferous tubule--Leydig cell interactions in relation to specific germ cell stages during the cycle of the seminiferous epithelium is extremely difficult in most mammalian species due to the continual presence of different spermatogenetic stages in the testis from the onset of puberty. The problem is also compounded by the uniform distribution of both seminiferous tubules and interstitial tissue throughout the entire testis. This difficulty can be circumvented, however, by studying certain species where there is a topographical distribution of germ cell stages within the testis. The urodele amphibian Necturus maculosus exhibits a breeding cycle during which a longitudinal wave of spermatogenesis occurs along the length of the testis, resulting in a spatial and temporal segregation of differentiating germ cells. Moreover, this topographical pattern of spermatogenesis is also reflected in the degree of development of adjacent Leydig cells. This anatomical arrangement allows distinct testicular regions to be obtained using a dissecting microscope. The isolated zones, containing germ cells and Leydig cells in various stages of development, were analyzed for 17 alpha-hydroxylase, C-17,20-lyase, and aromatase activities (key enzymes for the synthesis of androgens and estrogen), estrogen binding, and cytochrome P-450 content. Functional parameters were then correlated with the morphology of Leydig cells in the various zones observed by both light and electron microscopy. It was found that there existed a distinct correlation between the state of differentiation of the leydig cells, their steroidogenic potential, and the distribution of estrogen receptors. These results in Necturus indicate indicate in this species, at least, the steroidal microenvironment of different germ cell associations may be quite specific.

Androgens↗