摘要:

In several brains of the Florida manatee, Trichechus manatus latirostris, the architecture of caudal regions of cerebral cortex was examined in order to complete a map of cortical areas in the brain of this unique herbivore. Through observation of sections stained for Nissl substance, myelinated axons, acetylcholinesterase and cytochrome oxidase, we have identified 11 new cortical areas based on qualitative cytoarchitectural appearance and measurements of laminar thicknesses, for a total of 24 such cortical areas in manatee cerebral cortex. Some areas exhibit poorly differentiated laminae while in others there are 6 clearly demarcated layers, often with sublaminar organization. Some previously identified areas were found to extend into the region caudal to the vertically oriented lateral fissure. As in other mammalian brains, cortical areas in manatees are organized in concentric rings of allocortex, mesocortex, and isocortex. Putative functional roles have been assigned to most of the identified areas based on location, architecture, behavioral and anatomical considerations, and extrapolation from other taxa in which functional mapping has been done.

ISSN:0006-8977    

DOI:10.1159/000113381

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The structure of the olfactory epithelium in the larval, juvenile and upstream migrant stages of the sea lamprey, Petromyzon marinus, was investigated by light microscopy and by scanning and transmission electron microscopy. Ciliated olfactory receptor cells (ORC) were present in all stages. In larval specimens, the number of ORC was 20±8 ORC per 100 μm length of olfactory epithelial surface. In juveniles and in upstream migrants the ORC density dropped to 9±2 and 6±2 ORC/100 μm, respectively. Sustentacular cells were microvillar in the smallest larval stage (with a body length of 15 mm) and ciliated in larger larvae and later life stages. The morphological characteristics of the olfactory mucosa suggest that the sea lamprey's capacity for use of the olfactory system extends into the larval stage, and that there are specific changes associated with metamorphosis.

ISSN:0006-8977    

DOI:10.1159/000113382

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The spatial resolution of the visual system during growth of the cichlid fish Haplochromis argens was deduced from the cone density according to two models of possible connectivity patterns. The models include a convergency type of 5 cones per visual unit and a divergency type of 1.25 cones per visual unit. The minimum separable angle in this species was measured during ontogeny using operant conditioning in a two choice discrete trial situation. As a consequence of the moderate performances of the juveniles, the behavioural study showed a greater change of visual resolution than was predicted by the morphology. The minimum separable angle of the adult fishes was accurately predicted by the 'divergency model', which led to rejection of the other morphological model. It is argued that the high resolution as found in some other fish species by authors using the same technique may be due to imperfect calculations.

ISSN:0006-8977    

DOI:10.1159/000113383

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Infusion of cobaltous-lysine into the optic nerve of juvenile Florida garfish reveals that the preoptic area, pretectum, thalamus and the mediorostral and ventrolateral poles of the optic tectum each receive bilateral, monosynaptic input. The bilateral input to the mediorostral pole of the tectum projects via the dorsal optic tract and terminates in the rostral half of the tectum. The bilateral input to the ventrolateral tectum projects via the ventral optic tract and extends the whole length of the tectum. The incidence of direct ipsilateral input to the tectum suggests binocular vision may play a functional role in the survival of this species. In order to test this hypothesis, we examined the retinal distribution of ipsilateral retinal ganglion cells that project to the mediorostral tectum and the size and location of the binocular visual field. Cell distribution was examined by retrograde labelling with rhodamine-conjugated dextran amine delivered by microinjections into the mediorostral pole of the right optic tectum. In the ipsilateral retina, ganglion cells are distributed in a narrow temporoventral area with a mean of 0.44±0.14 x 103 cells per mm2 apposing the retinal margin. In the contralateral retina, ganglion cells are also distributed within this temporoventral region with a mean peak density of 2.33 ± 0.47 x 103 cells per mm2. Three broad classes of ipsilaterally projecting retinal ganglion cells (orthotopic cells within the ganglion cell layer, displaced cells within the inner nuclear layer, and giant cells within the ganglion and inner nuclear layers) are identified, intermingled in both the ipsilateral and contralateral retinae after retrograde labelling from the mediorostral pole of the tectum. Ophthalmoscopic mapping of the monocular and binocular visual fields reveals two small frontal wedges of binocular overlap. A dorsal wedge (12° wide) extends from approximately 7° above the horizontal axis to 10° beyond the vertical axis, and a ventral wedge (20° wide) extends approximately 10° below the horizontal axis to 15° beyond the vertical axis. The dorsal binocular visual field is subtended by the temporoventral region of the retina possessing both ipsilaterally and contralaterally projecting ganglion cells which terminate in the mediorostral pole of the optic tectum. Therefore, the partial decussation of retinal ganglion cell axons at the optic chiasm brings information from corresponding regions of the binocular visual field into register in the mediorostral pole of the optic tectum. In addition, the size of the binocular visual field matches the relative proportion of the retina containing ipsilaterally projecting ganglion cells. The ontogeny and phylogeny of ipsilateral retinofugal projections in actinopterygians is discussed in relation to the putative secondary pathways mediating binocular vision.

ISSN:0006-8977    

DOI:10.1159/000113384

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Infusion of cobaltous-lysine into the optic nerve of juvenile Florida garfish reveals that the preoptic area, pretectum, thalamus and the mediorostral and ventrolateral poles of the optic tectum each receive bilateral, monosynaptic input. The bilateral input to the mediorostral pole of the tectum projects via the dorsal optic tract and terminates in the rostral half of the tectum. The bilateral input to the ventrolateral tectum projects via the ventral optic tract and extends the whole length of the tectum. The incidence of direct ipsilateral input to the tectum suggests binocular vision may play a functional role in the survival of this species. In order to test this hypothesis, we examined the retinal distribution of ipsilateral retinal ganglion cells that project to the mediorostral tectum and the size and location of the binocular visual field. Cell distribution was examined by retrograde labelling with rhodamine-conjugated dextran amine delivered by microinjections into the mediorostral pole of the right optic tectum. In the ipsilateral retina, ganglion cells are distributed in a narrow temporoventral area with a mean of 0.44±0.14 x 103 cells per mm2 apposing the retinal margin. In the contralateral retina, ganglion cells are also distributed within this temporoventral region with a mean peak density of 2.33 ± 0.47 x 103 cells per mm2. Three broad classes of ipsilaterally projecting retinal ganglion cells (orthotopic cells within the ganglion cell layer, displaced cells within the inner nuclear layer, and giant cells within the ganglion and inner nuclear layers) are identified, intermingled in both the ipsilateral and contralateral retinae after retrograde labelling from the mediorostral pole of the tectum. Ophthalmoscopic mapping of the monocular and binocular visual fields reveals two small frontal wedges of binocular overlap. A dorsal wedge (12° wide) extends from approximately 7° above the horizontal axis to 10° beyond the vertical axis, and a ventral wedge (20° wide) extends approximately 10° below the horizontal axis to 15° beyond the vertical axis. The dorsal binocular visual field is subtended by the temporoventral region of the retina possessing both ipsilaterally and contralaterally projecting ganglion cells which terminate in the mediorostral pole of the optic tectum. Therefore, the partial decussation of retinal ganglion cell axons at the optic chiasm brings information from corresponding regions of the binocular visual field into register in the mediorostral pole of the optic tectum. In addition, the size of the binocular visual field matches the relative proportion of the retina containing ipsilaterally projecting ganglion cells. The ontogeny and phylogeny of ipsilateral retinofugal projections in actinopterygians is discussed in relation to the putative secondary pathways mediating binocular vision.

ISSN:0006-8977    

DOI:10.1159/000316247

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The size of the hippocampus has been previously shown to reflect species differences and sex differences in reliance on spatial memory to locate ecologically important resources, such as food and mates. Black-capped chickadees (Parus atricapillus) cached more food than did either Mexican chickadees (P. sclateri) or bridled titmice (P. wollweberi) in two tests of food storing, one conducted in an aviary and another in smaller home cages. Black-capped chickadees were also found to have a larger hippocampus, relative to the size of the telencephalon, than the other two species. Differences in the frequency of food storing behavior among the three species have probably produced differences in the use of hippocampus-dependent memory and spatial information processing to recover stored food, resulting in graded selection for size of the hippocampus.

ISSN:0006-8977    

DOI:10.1159/000113385

出版商:S. Karger AG    

年代:1995

数据来源: Karger