Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Necturus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40Linked to original sources
PubMed1990

Paired arrangement of nonhomologous centromeres during vertebrate spermiogenesis.

Indirect immunofluorescence staining with human anti-kinetochore antibodies was used to study the position of centromeres during vertebrate spermiogenesis. Many species of Amphibia have a low chromosome number and very large spermatids and spermatozoa. The number of kinetochore dots correlates exactly with the haploid chromosome number. This implies that kinetochore duplication occurs in the interval between meiosis I and meiosis II. The nonhomologous centromeres are arranged in tandem during the entire course of spermiogenesis and in mature spermatozoa. A higher order centromere arrangement was found in spermiogenic cells of Anura and Urodela. In mammals, immunofluorescence analysis is complicated by the extreme condensation of chromatin during spermiogenesis and the high chromosome numbers. Nevertheless, centromere-centromere associations were observed in mammalian round spermatids and sporadically in testicular spermatozoa. This indicates that pair-wise association of centromeres is a universal principle of centromere arrangement at the postmeiotic stage.

Animals↗
PubMed1983

The action of peptides on the mudpuppy electroretinogram (ERG).

Two neuropeptide substances were applied to the mudpuppy retina while the electroretinogram (ERG) was recorded. A low concentration of somatostatin (10(-9)M) was found to be a potent agent in increasing the amplitudes of all the oscillatory potentials (OPs) of the ERG. There was no appreciable change of the threshold sensitivity or the stimulus response curve of the b-wave. The highest concentration tested (10(-6)M) reduced the first OP to about the same amplitude as at the start of the experiment and attenuated the later OPs. A decrease of the suprathreshold b-wave was induced by the highest concentrations (10(-7), 10(-6)M) of somatostatin. A low concentration of substance P (10(-11)M) selectively and differentially decreased the earlier OPs (O1O2). Higher concentrations (10(-10), 10(-9)M) diminished the earlier OPs further, reduced the later OPs and decreased the supra-threshold a- and b-waves. The results support previous suggestions that the OPs reflect activities in feedback circuits initiated by the amacrines and indicate that somatostatin and substance P through separate mechanisms seem to interact with the inhibitory neuronal circuits which have been suggested to give rise to the OPs. Secondly, in agreement with previous work, the OPs appear to have a different origin from the b-wave. Thirdly, two separate classes of amacrines, each with a different transmitter, seem to be associated with different physiological roles.

Animals↗
PubMed1984

Autoradiographic studies of [3H]-glycine, [3H]-GABA, and [3H]-muscimol uptake in the mudpuppy retina.

Autoradiographic studies showed selective accumulation of [3H]-glycine, [3H]-GABA, and the GABA agonist [3H]-muscimol by neurons of the mudpuppy retina. [3H]-Glycine was taken up by bipolar cells, amacrine cells, and displaced amacrine or ganglion cells. Both [3H]-GABA and [3H]-muscimol were also accumulated by bipolar cells, amacrine cells and ganglion layer cells. However, the [3H]-GABA uptake pattern differed from that of [3H]-muscimol in showing labeling of horizontal cells, an increased percentage of cells in the ganglion cell layer, and a band in the most proximal portion of the inner plexiform layer. Variations in grain density suggested the presence of multiple subpopulations of [3H]-glycine- and [3H]-GABA-labeled amacrine cells. The labeled cells may play a role in inhibitory pathways in the inner retina.

Animals↗
PubMed1986

GABA-like immunoreactivity in the vertebrate retina: a species comparison.

Rabbit antisera directed against gamma-amino butyric acid (GABA) conjugated to bovine serum albumin was used to localize neurons containing GABA-like immunoreactivity in the retinas of nine species of animals: human, cat, rabbit, rat, chicken, turtle, frog, mudpuppy and goldfish. The retinas of all species contained GABA-like labeling in several populations of amacrine cells in the inner nuclear layer, cells in the ganglion-cell layer that may include displaced amacrine cells and in fibers in the inner plexiform layer and in the optic nerve fiber layer. Labeled horizontal cells were found in cat and in all non-mammalian retinas. Labeled interplexiform cells were found in rat, rabbit, cat and human retinas. Labeled bipolar cells were restricted to frog and mudpuppy retinas. The distribution of anti-GABA is usually similar to that of anti-glutamic acid decarboxylase and neuronal [3H]GABA uptake, indicating good correspondence between these 'GABAergic' markers. However, several significant differences among these markers are discussed.

Animals↗
PubMed1984

Cardiac actions of bovine parathyroid hormone fragment (1-34) in some lower vertebrates.

Only recently have the cardiac actions of parathyroid hormone and its N-terminal (1-34) fragment (bPTH(1-34] been examined. Parathyroid hormone was found to exert a positive chronotropic effect on the heart tissue of several mammals and one amphibian in vivo and/or in vitro. The purpose of the present study was to examine in vitro the heart tissue of several lower vertebrates, particularly aquatic vertebrates, for responsiveness to bPTH(1-34) and, for comparative purposes, isoproterenol. Heart tissue (atrium or the entire heart) from all the animals studied (trout, mudpuppy, bullfrog tadpole, and adult bullfrog) responded to isoproterenol in a dose-dependent fashion with increased heart rate and contractile force. Only the atria from the adult bullfrog, however, responded in a similar manner to the administration of bPTH(1-34). In all cases propranalol (10(-6) M) was able to block both chronotropic and inotropic effects of isoproterenol but had no effect on the cardiac stimulation induced by bPTH(1-34) in the adult bullfrog atrium. The data suggests that cardiac responsiveness to bPTH(1-34) is associated with a terrestrial as opposed to an aquatic existence.

Animals↗
PubMed1990

A polarized photobleaching study of chromatin reorientation in intact nuclei.

Polarized fluorescence recovery after photobleaching (pFRAP) was used to monitor the effects that condensation, i.e. compaction and aggregation, have on the (microseconds and ms) internal dynamics of chromatin in intact nuclei. When divalent cations were present with physiological (approximately 90 mM) monovalent salt the chromatin was found to exist in a compact and aggregated state which was characterized by rotational immobilization over timescales that range from 10 microseconds to 40 milliseconds. This immobilization is attributed to suppression of internal dynamics by intermolecular interactions. When the divalent cations were removed, the compact fibers no longer aggregated and were free to reorient with a characteristic decay time of about 1.2 milliseconds. It is shown that this millisecond relaxation could represent rigid rotation of topologically independent structural domains. Dilution of the monovalent salt induced a gradual change in the structural state of the chromatin that was manifest as a dramatic increase in internal flexibility. At the lowest salt concentration studied (11 mM-monovalent salt) the chromatin reorients in fewer than ten microseconds. These changes in flexibility are continuous with salt concentration, indicating that there are no well-defined endpoints to structural transitions and that the microsecond-millisecond internal dynamics of chromatin are a sensitive measure of structure. Measurements made on nuclei from cells that are either transcriptionally quiescent or active indicate that the dynamics mirrors biological activity.

Animals↗
PubMed1992

Bethanechol-induced responses in mudpuppy parasympathetic neurons.

The effect of bethanechol on membrane potential and excitability was determined in mudpuppy parasympathetic postganglionic neurons. Bethanechol induced a large amplitude hyperpolarization, which was followed by a smaller amplitude depolarization, in 115 out of 135 cells tested. In approximately 20% of these cells, a brief depolarization preceded the hyperpolarization. During the bethanechol-induced hyperpolarization, the membrane input resistance decreased markedly, whereas the input resistance was increased during the subsequent depolarization. The hyperpolarization and depolarization were blocked by atropine and were unaffected by d-tubocurarine, thus, both appeared to be mediated by muscarinic receptors. The bethanechol-induced hyperpolarization was inhibited by the M2 muscarinic receptor antagonist AF-DX 116, whereas the bethanechol-induced depolarization was unaffected. Both a nonselective increase in membrane conductance and a decrease in membrane potassium conductance appeared to be involved in the generation of the bethanechol-induced depolarization. Evidence for the first mechanism was obtained in barium-treated cells in which bethanechol initiated a rapid onset depolarization, which was reversed at membrane potentials near 0 mV. Evidence for the second mechanism was obtained when the hyperpolarization was inhibited by AF-DX 116. In AF-DX 116-treated cells, the membrane input resistance was increased during most of the bethanechol-induced depolarization. Mudpuppy neurons initiate repetitive action potential activity in response to long depolarizing current pulses. Following application of bethanechol, with the hyperpolarization negated electrotonically, the number of action potentials produced by a depolarizing current pulse was greater than that produced prior to application of bethanechol. It is suggested that activation of muscarinic receptors on mudpuppy cardiac neurons influences multiple conductance systems and determines the excitability of these neurons.

Animals↗
PubMed1983

Intracellular chloride in retinal neurons: measurement and meaning.

Intracellular chloride activity measurements were obtained from mudpuppy retinal neurons using dual microelectrodes, one of which was made chloride-selective by filling the tip with chloride liquid ion exchange resin. In addition ionic substitution experiments were carried out in the perfused retina-eyecup preparation of the mudpuppy. A comparison of the membrane potential and calculated chloride equilibrium potential shows that retinal neurons differ in relative transmembrane chloride distribution. Ganglion cells have an ECl more negative than the resting membrane potential, whereas amacrine cells have a passive distribution of chloride. Horizontal cells have chloride distributed such that an increase in chloride conductance is depolarizing. On-bipolars have a chloride distribution similar to that of horizontal cells whereas off-bipolars show either passive distribution or some chloride accumulation. These findings are consistent with the idea that chloride ions may play a role as a depolarizing driving force for electrogenic activity of horizontal cells and on-bipolars. Results with Cl substitution experiments are consistent with this interpretation.

Animals↗
PubMed1984

Aspartate-induced dissociation of proximal from distal retinal activity in the mudpuppy.

The effects of aspartate (Asp) on the ERG and on neuronal, glial, and K+ responses were monitored continuously in the superfused mudpuppy eyecup. Asp induced a time-dependent sequence of events which may be divided into three stages: Stage 1, initially, light-evoked responses throughout the retina are depressed; Stage 2, distal responses (horizontal, bipolar, and K+ responses) return to near pre-drug amplitudes and there is a simultaneous ERG enhancement, but responses in the proximal retina remain suppressed; Stage 3, a second depression of retinal responses leads to a-wave isolation. The dissociation of distal from proximal responses observed during Stage 2 strongly supports the hypothesis that the ERG b-wave results from events arising in the distal retinal network.

Animals↗
PubMed1987

Excitatory amino acids have different effects on horizontal cells in eyecup and isolated retina.

Horizontal cells in the mudpuppy eyecup responded to continuous superfusion with L-glutamate, L-aspartate, kainate and quisqualate with a transient depolarization and reduction of the light evoked responses. However, in isolated retina preparations, in which these substances were applied to the photoreceptor side of the retina, the effects were sustained as long as the agonists were present. These results suggest that the transient action of these agonists in eyecup preparations was due to the rapid development of an intraretinal diffusion barrier, and are consistent with the hypothesis that photoreceptors release an excitatory amino acid transmitter.

Amino Acids↗
PubMed1989

APB increases apparent coupling between horizontal cells in mudpuppy retina.

2-Amino-4-phosphonobutyrate (APB), an agonist at a unique type of glutamate receptor on depolarizing bipolar cells, caused an apparent increase in coupling between horizontal cells as evidenced by a decrease in amplitude of responses to illumination of the receptive field center and an increase in responses to illumination of the peripheral part of the receptive field. APB also caused a hyperpolarization of horizontal cells in darkness and increased the amplitude of responses to full-field illumination, which cannot be explained by an increase in electrical coupling between horizontal cells. Possible mechanisms for these actions are discussed.

Aminobutyrates↗
PubMed1992

An intensity-dependent biphasic neuron in mudpuppy retina.

Intracellular recordings in dark-adapted mudpuppy retinas have revealed a type of infrequently encountered cell with unusual response properties. These cells may be a subclass of horizontal cell since they are encountered at the same depth as horizontal cells and have large receptive fields and response amplitudes. However, they differ from typical horizontal cells in that they are depolarized by low intensity illumination and hyperpolarized by higher intensity illumination at all wavelengths. Both types of responses appear to be driven mainly by 572 nm cones. Both the depolarizing and hyperpolarizing responses were unaffected by APB, indicating that they are not mediated by on-center bipolar cells.

Animals↗
PubMed1992

Pattern generator system as a versatile visual stimulator.

We have designed and implemented a Motorola 68000 microprocessor-based pattern generator system (PGS) that uses a color video display terminal (VDT) to provide light stimuli to the intact vertebrate retina. This communication is intended for those who are considering acquisition of a commercial retinal stimulator or those who are custom designing their own pattern generator system. The discussion surveys the features to be included as well as design factors which must be considered in such a device. The memory organization of the PGS allows as stimuli multiple, complex patterns consisting of one or more disks, annuli, bars or gratings to flash or modulate in intensity according to a pre-defined function. In addition, patterns can move smoothly in any direction at selectable, uniform speeds without the re-drawing of video memory. The presence of a 12-bit A/D converter internal to the PGS allows a dynamic change in stimulus position, speed or pattern based upon physiological feedback. A physically realistic image size (0.9 cm2) and resolution (20 mu/pixel) in the retinal plane are achieved with simple intervening optics. The video field rate of 60 Hz is above the flicker fusion frequency for most vertebrate animals and does not induce artifacts in cellular responses. The PGS operating in a PC-based environment meets the requirements of a versatile optical stimulator for investigations in retinal electrophysiology.

Ambystoma↗
PubMed1992

Galanin stimulates phosphatidylinositol turnover in cardiac tissue of the mudpuppy.

A galanin-like peptide has been found in the parasympathetic fibers innervating the mudpuppy myocardium and direct application of galanin produces hyperpolarization of atrial myocytes and a decrease in twitch tension. In the present study, atrial and ventricular strips were incubated with galanin and then evaluated for changes in either phosphatidylinositol turnover or cyclic nucleotide levels. Galanin caused a significant and concentration-dependent increase in phosphatidylinositol turnover in both atrial and ventricular tissue. However, galanin had no effect on cyclic AMP or cyclic GMP levels in either basal or adrenergically-stimulated preparations. These results suggest that the galanin-induced cardio-inhibition in the mudpuppy may be mediated, at least in part, by a change in phosphatidylinositol turnover.

Animals↗