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At least 1,243 records · Page 69Linked to original sources
PubMed1982

Ultrastructural analysis of the posterior hypothalamus of salamander.

The anatomical organization of the tuberal area of th posterior hypothalamus in Salamandra was investigated by the Golgi methods, SEM and TEM techniques. The ependymal cells of this area are poor in cilia and often show morphological features of actively secreting or absorbing elements. Intermingled with ependymal cells, two kinds of CSF-contacting processes are seen, arising from neurons of the periventricular grey. Their contents and morphological characteristics allow them to be divided into two groups, A and B. In the neuropil different synaptic contacts are seen. The observation of unconventional synaptic contacts possibly of axo-axonic type suggests the occurrence of local circuits on the final neurosecretory pathway.

Animals↗
PubMed1983

Scanning electron microscopic study of the microarchitecture of the lung of the giant salamander Amphiuma tridactylum.

This paper reports observations made using scanning electron microscopy (SEM) on the internal structure of the lung of Amphiuma tridactylum. This lung is highly septate at the cranial end, but the septa become gradually reduced in size and number with increasing distance caudally until the septa are reduced to ridges in the wall of the lung. However, there is no respiratory dead space as respiratory epithelium is found throughout the lung. Treatment of isolated lung segments with acetylcholine causes the septa to shorten and thicken which in turn causes the lung diameter to decrease and the alveoli to collapse. These observations are consistent with the hypothesis that the collapse of the Amphiuma lung in vivo, which is responsible for the highly efficient ventilation of the lungs, is brought about by the contraction of pulmonary smooth muscle in the septa and wall of the lung.

Animals↗
PubMed1982

The transplantation of eyes to genetically eyeless salamanders: visual projections and somatosensory interactions.

Eyes were transplanted from normal axolotls to eyeless mutants, and several anatomical and physiological observations were made on the central visual centers in these animals. Some central projections were bilateral to the optic centers of the thalamus and midbrain, some traveled ipsilaterally to the same centers, and the rest grew down the spinal cord. This is similar to what has been found in eyes transplanted to normal hosts. The type of projection made in eyeless hosts correlated with the site of nerve entry into the CNS as in control hosts. Thus, the transplanted projection did not appear to be influenced by the host's optic nerves and tracts or lack of them. In spite of the transplanted optic fibers' taking abnormal paths, they made normally organized topographic maps on the host tecta. The visual and somatosensory topographic projections to the tectum were found to be in near perfect register normally, but in eyeless mutants to which rotated eyes had been transplanted, they were not. Acetylcholinesterase activity, found in the primary optic neuropil in normal animals, was greatly diminished in eyeless mutants, yet normal mutants with grafted eyes. Finally, transplantation of an eye to an eyeless mutant corrected the abnormally dark pigmentation caused by eyelessness but only in those cases of bilateral central innervation.

Acetylcholinesterase↗
PubMed1995

Dopamine modulates GABAc receptors mediating inhibition of calcium entry into and transmitter release from bipolar cell terminals in tiger salamander retina.

Using optical recording techniques, we directly monitored pre- and postsynaptic calcium dynamics at bipolar cell terminals while inhibiting synaptic release with applied GABA and modulating inhibition with dopamine. To monitor pre-synaptic activity, individual bipolar cells in the retinal slice were filled with either fura-2 or fluo-3 through a patch electrode. Calcium entry into bipolar terminals, elicited by depolarization from -60 mV to 0 mV, was reduced to 36% of control in the presence of 200 microM bath-applied GABA. Further addition of 100 microM dopamine to the bath relieved the GABAergic inhibition and nearly doubled the calcium entry. Yet dopamine alone had no apparent direct effect upon calcium entry. The relief from GABAergic inhibition could be reproduced with SKF-38393, a dopamine D1 receptor agonist, and with forskolin, an adenylyl cyclase activator, suggesting that dopamine acts through a cAMP second-messenger pathway. To monitor transmitter release from bipolar cells, slices were loaded with fura-2AM, a membrane permeable form of the dye. Puffs of 110 mM KCl at bipolar dendrites depolarized bipolar cells and elicited calcium signals that could be monitored both at bipolar terminals and in postsynaptic cells. Consistent with the results above, GABA inhibited calcium entry at bipolar terminals and also reduced transmitter release, measured as a decrease in calcium entry in amacrine and ganglion cells. The addition of dopamine relieved this inhibition and increased transmitter release. Our results show the spatiotemporal correlation between the GABAergic inhibition of calcium entry at bipolar terminals, the resulting reduction in postsynaptic activity, and the relief of this inhibition with dopamine.

Animals↗
PubMed1995

[Mirror symmetrical and "left dominant" organization in the gastrula stage molted parabiotic larva of mountain salamander].

Gastrulae of Triturus alpestris were laterally fused (body axes in equal directions). The parabiotic larvae mostly showed an undivided body with tail, but exhibited two heads. Defects of organogenesis were frequently observed in the gut, and, to some fewer extent, in the heart. The gut mostly develops undivided, the heart in singular or (with transitions) as two organs. The number of organ-inversions and partial inversions was high (table 1). In addition a transindividual organ-symmetry (mirror-image symmetry of the "pair situs") was abundant (table 3, fig. 6) and the gut and the habenular nuclei showed a strong dominance for that phenotype. The organ inversions were more abundant in the right organ or part of the organ. These right-left-differences were statistically significant referring to the inversion tendency of the heart and the habenular nuclei (table 2). This "left-dominance" observed in the organ Anlagen investigated is discussed in regard to results published previously.

Animals↗
PubMed1995

Desensitizing glutamate receptors shape excitatory synaptic inputs to tiger salamander retinal ganglion cells.

AMPA/kainate (KA) receptors mediate a component of ganglion cell excitatory postsynaptic currents (EPSCs). We investigated whether desensitization at these receptors contribute to the shape of transient EPSCs in ON-OFF ganglion cells. Whole-cell, voltage-clamp recordings were made from ganglion cells in the retinal slice or in isolation. EPSCs were evoked by either stimulating the slice with light or puffing K+ at the outer plexiform layer (OPL). The AMPA/KA receptor-mediated component of the EPSCs was isolated by including NMDA receptor antagonists in the bath. Strychnine and picrotoxin blocked inhibitory inputs. In isolated ganglion cells, cyclothiazide (10 microM), which blocks desensitization in non-NMDA receptors, enhanced both the amplitude and the duration of currents evoked by puffs of AMPA or glutamate. EPSCs evoked by K(+)-puffs in the OPL were also enhanced by cyclothiazide (30 microM). When AMPA/KA receptors were blocked with NBQX (10 microM), no enhancement of the EPSCs by cyclothiazide was observed, indicating that cyclothiazide did not act presynaptically. Cyclothiazide also enhanced the amplitude and duration of both the ON and OFF light-evoked (L-) EPSCs recorded in ON-OFF ganglion cells. Current-voltage relationships showed the enhancement was not voltage dependent. When control and enhanced responses where normalized, it was observed that the rate of desensitization of both the ON and OFF L-EPSCs was decreased by cyclothiazide. Cyclothiazide selectively enhanced the AMPA/KA receptor-mediated component of ganglion cells EPSCs, suggesting that desensitization of AMPA/KA receptors shape transient L-EPSCs.

Ambystoma↗
PubMed1995

[The symmetrical relation of intestines, the habenular nuclei and the intestinal venous system in dorsal-doral and ventral-ventral grown parabiontic larva of mountain salamanders (Triturus alpestris)].

Embryos of the newt Triturus alpestris were fused in their dorsal regions (DD-parabionts) of their ventral regions (VV-parabionts), while the longitudinal axes were in equal direction. In these parabionts situs and symmetry of the gut, the heart, the habenular nuclei and the vitelline vein were studied. The fusion of the embryos of the DD-parabionts was performed in three developmental stages (after Harrison): phase of neurulation (14-18, N-parabionts), late phase of neurulation (19-22, E-parabionts) and tail bud stage (23-27, S-parabionts). VV-parabionts were only fused in phase of neurulation (14-18). The external development of the parabionts in most cases was normally. DD-parabionts showed a more or less pronounced deformation of their longitudinal axes. In DD-parabionts all organs developed separately in nearly all cases. In VV-parabionts a partial fusion of the heart was sometimes observed, while fusion of large part of gut occurred regularly. In DD-parabionts complete and incomplete inversions of all organs and the vitelline vein are extremely abundant in the N-parabionts, much lower in E-parabionts and nearly absent in S-parabionts. The differences are statistically of high significance. The "pair situs" symmetries of N-parabionts (DD-parabionts) show always a strong dominance of a transindividual organ- and vitellin vein-symmetry. In VV-parabionts (N-parabionts) the tendency for inversion of the asymmetric organs is statistically significant lower as in DD-parabionts. In regard to this observation there is a preference for an asymmetric "pair situs" in the heart, habenular nuclei and vitelline vein system. In "polarisied" DD-parabionts ("left" as well as "right" parabionts) the asymmetric organs as well as the vitelline vein system inversions were more often observed in the "left" parabiont compared with the "right" parabiont in N- and E-parabionts. These right-left differences partial are statistically significant (P < 0.05). The organ situs-correlation as well as the situs-correlation between vitelline vein and gut or heart, respectively, are mostly positive (concordant). The frequency of dominance of "left" organ inversions argues against a morphogenetic "left dominance" of the amphibian embryo. The determination of organ-asymmetries is irreversible only after the end of neurulation in tail-bud-stage. The results suggest the efficiency of a "symmetry-factor", which determines the organ symmetry during neurulaphase. The differences between DD- and VV-parabionts are statistically significant and point to a dorso-ventral polarity of the embryo, with a maximal morphogenetic potency in the dorsal region.

Animals↗
PubMed1994

Spike initiation and propagation in wide field transient amacrine cells of the salamander retina.

Our results suggest that the prominent spike, commonly recorded in wide field amacrine cells, is actively propagated along its processes. Current was passed through a patch pipette at the soma to elicit spike activity in the cell. The field potentials accompanying this spike activity were then measured with an extracellular electrode positioned at different sites along the cell and its processes, which had been made visible with Lucifer yellow. Different extracellular waveforms were measured at the soma, stalk, and cell processes: A monophasic negative-going extracellular voltage waveform, typically found at the site of action potential initiation, was recorded along the stalk between the soma and the radial processes. A biphasic, positive-negative waveform, typically associated with the truncated propagation of an action potential, was measured at the soma. A triphasic, positive-negative-positive extracellular waveform, typically associated with a fully propagated action potential, was recorded along the peripheral processes. The time to peak of this triphasic waveform increased with distance from the soma such that the calculated propagation velocity ranged from 0.5 to 2.5 cm/sec. The membrane regions carrying potassium, sodium, and calcium currents were examined by depolarizing the soma and eliminating different ionic currents in the cell. With only sodium present, extracellular potentials were measured at the stalk and processes, but rarely at the soma. When only potassium was present, extracellular potentials were measured at the soma and processes, but not the stalk. When only calcium channels carried the membrane current, extracellular potentials were measured only at the processes. The sites of different ligand-gated receptors were identified by puffing various transmitter substances at different positions radially along the processes and measuring their effects at the soma. In all cells tested, glutamate puffs elicited currents only when applied at processes within 200 microns of the soma. In some cells, GABA and glycine elicited currents up to 300 microns from the soma. As a control for the measurement of electrotonic spread, potassium puffs elicited depolarizations along a broader region of the processes. These results suggest that the excitatory glutamate-elicited synaptic input to these cells is confined to a narrow area of the processes near the soma. The spike then appears to be initiated at the stalk and propagated along the processes. Calcium currents at these processes suggest the presence of possible transmitter release sites. Thus, each wide field amacrine cell seems to be functionally and concentrically polarized, receiving input centrally near the soma and broadcasting its output by propagating spikes along its extensive processes.

Ambystoma↗
PubMed1994

Dopamine enhances a glutamate-gated ionic current in OFF bipolar cells of the tiger salamander retina.

The transmitter glutamate is thought to be used by all vertebrate photoreceptors to drive the second-order neurons of the retina, horizontal and bipolar neurons. Dopamine, an endogenous retinal neurotransmitter localized to amacrine and interplexiform cells, has previously been shown to enhance glutamate-gated currents in retinal horizontal cells. In the present study we demonstrate that bipolar cells, like horizontal cells, possess glutamate receptors that are modulated by dopamine. We then identify some components of the pathway through which dopamine acts. We used whole-cell patch recording to measure how bath-applied dopamine modulated the currents elicited by puffs of transmitter solutions at bipolar cell dendrites. Excitatory amino acid-gated currents were evoked by pressure ejecting 1 mM glutamate or 10 microM kainate for 40 msec through a micropipette positioned at the dendrites of bipolar cells. Bath-applied dopamine (20 microM) enhanced the response to glutamate in OFF bipolar cells in the retinal slice by 40% and in isolated OFF bipolar cells by 65%. We also explored the components of the intracellular pathway mediating this modulation. Response enhancement was blocked by the D1 receptor antagonist SCH23390, but not by the D2 receptor antagonist spiperone, suggesting that the enhancement by dopamine is mediated by a D1 receptor. GDP-beta-S, a G-protein inactivator, blocked the enhancing action of dopamine, suggesting that the D1 receptor activated a G-protein to enhance the glutamate-gated current. Both 8-(4-chlorophenylthio)adenosine, a cAMP analog, and the addition of the catalytic subunit of protein kinase A (PKA) to the recording pipette enhanced glutamate-gated currents, while H-7, a PK inactivator, and PKI20amide, a PKA-specific inhibitor, blocked the enhancing action of dopamine. These data suggest that dopamine acts at D1 receptors in the dendrites of bipolar cells to activate adenyl cyclase, which through cAMP enhances a glutamate-gated current in bipolar cell dendrites. Thus, dopamine may modulate synaptic transmission from photoreceptors to OFF bipolar cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗