摘要:

The Apteronotidae, a family of weakly electric fish from South America (Gymnotiformes), possess a structure called the dorsal filament with an unknown function and evolutionary origin. This study compared the gross anatomy of the dorsal filament of 13 species of apteronotids and used light microscopy to examine the filaments of Adontosternarchus balaenops, Apteronotus albifrons, and Apteronotus leptorhynchus. The dorsal filament is an unsealed, thin, tapering structure attached to a mid-dorsal groove on the posterior half of the fish''s back. The interior of the filament is a gelatinous mucopolysaccharide matrix (connective tissue) containing blood vessels and a bilateral nerve in which nearly all the afferents are large (8–10 µm) and heavily myelinated. The location of the anterior origin of the filament varies from 0.48 to 0.66 of the body length, posterior to the snout, in 13 species. The filament is covered with hundreds of large-type tuberous electroreceptors and some ampullary receptors, at approximately the same density and ratio as those on the nearby back. The morphology of the large-type tuberous receptors and their afferents suggests that they are phase-coding T-units. A double layer of epithelial cells separates the ventral side of the filament from the groove in the trunk of the fish, except at the anterior origin where the interior of the filament is continuous with the body. This specialized double epithelium could provide a high resistance barrier to electrical current. This study was unable to distinguish between two hypotheses: that the dorsal filament is a modified adipose fin (as suggested previously), retained only in this family of Gymnotiformes; or that it is a uniquely derived character of the Apteronotid

ISSN:0006-8977    

DOI:10.1159/000113236

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Application of intraovarian pressure is known to trigger profound cytomorphological changes in the neurosecretory cells of nucleus preopticus in the teleost Clarias batrachus. These findings indicate the presence of stretch receptors in the ovaries, perhaps equipped with mechanosensitive channels that transduce the stretch signals to be transmitted to the brain. To test the occurrence of the mechanosensitive channels in the ovaries, we administered a range of pharmacological agents (lignocaine, quinidine, tetraethylammonium chloride, ethylenediaminetetraacetic acid and gadolinium) known to block the mechanosensitive ion channels, in the ovarian lumen prior to the administration of the intraovarian pressure. Pretreatment with the above agents inhibited the response by the nucleus preopticus neurosecretory cells to intraovarian pressure. The results suggest the occurrence of the mechanosensitive channels in the ovaries of teleostean fishes. In terms of function we speculate that the stretch sensory system and the ensuing pathway connecting the ovaries with the hypothalamus might play a role in apprising the brain of the status of ovarian maturity and in the initiation of the spawning reflex.

ISSN:0006-8977    

DOI:10.1159/000113237

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The claimed absence of efferents to the basilar papilla in frogs was reexamined in Xenopus laevis with the use of acetylcholinesterase (AChE) histochemistry. We also tested the presence of common lateral line and inner ear efferents by employing neuroanatomical tract tracing techniques. Our data show some AChE-positive fibers to the basilar papilla and all other sensory epithelia of the inner ear in larval and postmetamorphic frogs. Labeling of anterior lateral line and inner ear fibers with different fluorescing dextran amines resulted in a few double labeled efferent cells in the brainstem. Examination of the branching patterns of anterior lateral line efferents revealed collaterals to the inner ear, predominantly to the saccule and the lagena. In addition, two animals showed common efferents between the anterior lateral line and the basilar papilla. In derived anurans, such as ranids, which reportedly lack efferents to the basilar papilla, the basilar papillary afferents have a peripheral course that differs from that in salamanders and Xenopus. If such efferents are, indeed, absent, we propose that changed cues for pathway selection may have enabled only the afferents, and not the efferents, to reach the basilar papilla in derived frogs.

ISSN:0006-8977    

DOI:10.1159/000113238

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Food storing passerines have a larger hippocampus, relative to the rest of the telencephalon and/or body mass, than do non-storing species. This study looked at the relationship between relative size of. the hippocampus and degree of food storing in six species of Paridae (blue tit, Parus caeruleus, great tit, P. major, marsh tit, P. palustris, coal tit, P. ater, black-capped chickadee, P. atricapillus, and willow tit, P montanus). The degree of storing by these species varies from little or none to thousands of food items. The period over which food is stored also varies from a few hours to several months. The results showed that hippocampal volume, relative to the rest of the telencephalon, is larger in those species that store more food, store for longer, or both. In an analysis of intraspecific variation within two of the species, the food storing marsh tit and the non-storing blue tit, there was a significant positive relationship between hippocampal volume relative to body mass, and telencephalic volume relative to body mass, in the marsh tit but no relationship between these variables in the blue tit.

ISSN:0006-8977    

DOI:10.1159/000113239

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

We have shown previously that GAP-43, a growth associated protein characteristically present in growing and regenerating axons, is relatively abundant in the spinal cord of adult opossums. In the present study, we combined the orthograde transport of the fluorescent marker Fluoro-Ruby with immunofluorescence for GAP-43 to determine if any of it is present within descending spinal axons. When Fluoro-Ruby was injected into the red nucleus and midbrain tegmentum, the medial pontine or medullary reticular formation, the medullary raphe or the lateral vestibular nucleus, axons were labeled in the expected areas of the spinal cord, but in most cases none showed evidence for GAP-43. In two of the four cases with rubral injections, however, a few labeled axons within the rubrospinal tract showed GAP-43 immunofluorescence, and in one case with an injection of the gigantocellular reticular nucleus and adjacent raphe, labeled axons within lamina IX immunostained for the protein. Since serotoninergic neurons are present within the gigantocellular reticular nucleus and adjacent raphe, and axons of the same phenotype are abundant within lamina IX, we asked whether serotoninergic axons contain GAP-43. When sections of the spinal cord were immunostained for both serotonin and GAP-43, many axons within lamina IX showed evidence for both substances. Such axons appeared to contact presumptive motoneurons. In cases with Fluoro-Ruby injections of the forelimb motor cortex, labeled axons were present within the pyramidal tract, and some of them showed evidence for GAP-43.

ISSN:0006-8977    

DOI:10.1159/000113240

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The presence of seven cervical vertebrae is an almost universal mammalian trait. The posterior boundary of the cervical series is traditionally defined osteologically, but its location is also predictable using neurological markers of the brachial plexus. The existence of three living mammalian genera with osteologi-cally defined cervical counts other than seven offers the opportunity to examine the coincidence of osteological and neurological definitions of the term ''cervical''. Despite variations in rib and articular processes of cervical vertebrae, dissections of the brachial plexuses of these genera reveal that neurological and osteological markers of the cervical series define the same, nontraditional, posterior boundaries of the series. Subdivision of the predetermined cervical mesoderm into a nontraditional number of segments has not altered the relationship of the limb or its innervation to the cervical/thoracic boundary. This nontraditional subdivision appears to have evolved separately at least three times.

ISSN:0006-8977    

DOI:10.1159/000113241

出版商:S. Karger AG    

年代:1996

数据来源: Karger