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At least 829 records · Page 46Linked to original sources
PubMed1978

A light and scanning electron microscopic study of the basial papilla in the salamander, Ambystoma tigrinum.

The basilar papilla and basilar recess of Ambystoma tigrinum have been investigated by light and scanning electron microscopy. The recess is an evagination of the lagena, and is invested externally by dense periotic connective tissue, except over a thin area of one wall abutting against a periotic diverticulum communicating with the periotic sac. The surface and histological features of the non-sensory lining epithelium are described. The basilar papilla occupies both slopes of an elevation adjacent to the thin wall of the recess, and consists of 40 to 80 sensory cells interposed between sustentacular cells. The sensory cells are innervated by 30 to 40 nerve fibers exhibiting two ranges of diameter, and they are capped by typical ciliary bundles that are taller at the center of the receptor than at its periphery. Bundles in the proximal and distal halves of the papilla are polarized, respectively, toward the saccule and toward the thin wall in contact with the periotic diverticulum; this divergent pattern of polarization has not been reported previously in the basilar papilla of other vertebrates. A tectorial body overlies only the bundles in the distal half of the receptor, and is attached to both the neuroepithelium and the opposite wall of the recess. Functional considerations are discussed, and comparisons are made with conditions reported in frogs and toads. The findings suggest that the basilar papilla and recess in caudate and anuran amphibians arose from common precursors and probably function in a similar manner.

Ambystoma↗
PubMed1992

Ultrastructure and immunocytochemistry of the neuroepithelial bodies in the lung of the tiger salamander, Ambystoma tigrinum (Urodela, Amphibia).

Light and electron microscopy of the lungs of Ambystoma tigrinum (Urodela) revealed a relatively complex pattern of the neuroendocrine (NE) cells. In the apical parts of smaller septa single NE cells not associated with nerve fibres were covered and surrounded by pneumocytes. The larger septa possessed small areas of ciliated epithelium, in which the NE cells were grouped in a form of neuroepithelial bodies (NEB) consisting of 3-5 cells and covered by goblet cells. NE cells possessed a large nucleus with patches of condensed chromatin, clear cytoplasm, and membrane-bound vesicles of variable morphology and size, containing an electron dense interior surrounded by a lucent space. The size of these dense core vesicles (DCV) ranged from 70-140 nm, while rarely the larger ones exhibited a diameter of 300-600 nm. In some NEB a second type of NE cells was observed for the first time in an amphibian species: these cells communicated with the air space and exhibited on their surface microvilli and a single modified cilium with a 8 + 1 microtubule arrangement. Their cytoplasm contained two types of DCV: dense core granules with a diameter of 140-260 nm and vesicles 320-700 nm in diameter with a moderately electron dense interior. The NEB were associated with intracorpuscular, sensory nerve terminals morphologically afferent and efferent. By immunocytochemistry, the NE cells revealed the presence of serotonin, met-enkephalin, and leu-enkephalin. A paracrine and chemoreceptor role is proposed for NEB of Ambystoma tigrinum.

Ambystoma↗
PubMed1977

The development of monamine-containing neurons in the brain and spinal cord of the salamander, Ambystoma mexicanum.

The distribution of monoamine-containing neurons in the CNS of the developing and adult axolotl, Ambystoma mexicanum, has been investigated using the histochemical fluorescence technique of Falck and Hillarp combined with microspectrofluorimetry. The earliest catecholamine-containing neurons to be detected are located in the ventral ependymal zone of the spinal cord at the time of hatching (Stage 41). Between stages 43 and 46, catecholamine fluorescence can be detected in neurons in the following regions: nucleus preopticus, the hypothalamic-infundibular region, and the brain stem reticular formation. 5-HT-containing neurons are only observed in the midbrain raphe region and are first detected at stage 44. In contrast to these early monoamine fluorescing groups, catecholamine-containing neurons are not routinely detectable in the nucleus interpeduncularis until six months of age. All monoamine-containing neuronal groups detected in developing axolotls are also present in both sexes of the adult. However, the fluorescence intensity is less in monoamine-containing neurons observed in adults than in early developing subjects. All catecholamine-containing neuronal groups, with the exception of those located in the midbrain region (nucleus interpeduncularis, reticular zone) have fluorescent processes that contact the cerebrospinal fluid (CSF). The presence of CSF-contacting processes in the hypothalamic and spinal cord regions suggest that the CSF may act as a medium through which bioactive substances are transported from one brain region to another. Intense catecholamine fluorescence is observed in cells of the notochord prior to the detection of the monoamine-containing neurons in the CNS. A possible involvement of catecholamines in the inductive effects of the notochord during development is discussed.

Age Factors↗
PubMed1980

The effects of eliminating impulse activity on the development of the retinotectal projection in salamanders.

The California newt Taricha torosa manufactures tetrodotoxin, a blocker of voltage-sensitive sodium channels and therefore of action potentials.The newt's own nervous system is insensitive to this toxin. Grafting an embryonic eye to the newt from a tetrodotoxin-sensitive species, the Mexican axolotl, blocks action potentials in the retinal ganglion cells of the transplanted eye. Neuroanatomical and electrophysical techniques demonstrate that while such ganglion cells are incapable of firing impulses, they develop normally, grow axons to the host tectum, terminate in the appropriate neuropil layers, form synapses, and project to the tectum retinotopically. Furthermore, they develop these apparently normal projections even in competition with electrically active axons from a host eye.

Action Potentials↗
PubMed1980

Regions of the brain influencing the projection of developing optic tracts in the salamander.

Eye primordia from the Mexican axolotl or the California newt were transplanted into hosts of either species. These "third" eyes often developed an optic nerve that penetrated the host brain and made one of three central projections: bilateral to the dorsal thalami, tecta, and basal optic nuclei; ipsilateral to the same areas; or ipsilateral into the cord. The type of projection made by a transplanted eye seemed to depend on where its nerve first entered the brain. The optic fibers that reached the visual centers of the midbrain were organized retinotopically in the optic tectum and mediated visually-guided behavior.

Ambystoma↗