摘要:

The visual projections of the remaining eye of posthatch congenitally monophthalmic chicks were examined using wheat germ agglutinin-horseradish peroxidase. The morphology of the primary visual centres and their retinal projections contralateral to the injected eye were similar to those of normal chicks. The ipsilateral primary visual centres were smaller and less organized, yet all received retinal input. These ipsilateral retinal projections differ from those found in normal posthatch chicks [O'Leary et al.: Devl. Brain Res. 10: 93–109, 1983] in that they are more extensive and occupy some centres not previously reported to receive input. In the case of the ipsilateral isthmo-optic projection to the retina there was a substantial increase in the number of cells compared with normal chicks [O'Leary and Cowan: Devl. Brain Res. 12: 293–310, 1984]. A comparison of the extent of ipsilateral retinal afferents with that of normal chicks suggests that following loss of an eye two responses occur within the visual centres: in some centres there is a massive increase in the amount of ipsilateral terminals, whereas in others there is only a small increase. We propose that these responses are related to the intrinsic retinotopy within the visual centres. That is, highly retinotopic visual centres do not normally contain ipsilateral fibres, but following eye removal fibres from the ipsilateral eye are able to substantially innervate these regions. Presumably this effect is due to loss of the overriding influence of contralateral input, which would normally recognize and eliminate inappropriate ipsilateral fibres. In poorly retinotopic regions ipsilateral fibres are able to persist in both normal and monophthalmic chicks, as recognition cues may not be as precise as in highly retinotopic regions. Thus, the greater the retinotopic precision, the finer the cues able to recognize ipsilateral fibres.

ISSN:0006-8977    

DOI:10.1159/000118635

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The pattern of retinogeniculate connections has been examined in a range of diprotodont marsupials, including wallabies, possums, forest wombat and koala. The lateral geniculate nucleus (LGd) in most species has alternating bands of ipsilateral and contralateral retinal terminal fields, with considerable interspecific variability. The number of terminal bands of retinogeniculate input varies from eight to eleven in most species, with little binocular overlap. By contrast in one species, the feather-tailed glider, the most significant feature of LGd organisation is binocular overlap. No relationship is apparent between LGd organisation and the life-style of the animals.

ISSN:0006-8977    

DOI:10.1159/000118636

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The inner ear of the sea lamprey, Petromyzon marinus, was examined using scanning and transmission electron microscopy. Many of the nonsensory surfaces of the ear chamber are lined by numerous, noninnervated, multiciliated epithelial cells. Each multiciliated epithelial cell has 43–66 true cilia projecting from its apical surface into the lumen of the ear. Although the cilia leave the cell individually, all of the cilia from a single cell come together just above the apical cell surface and are held together by a cross-network of fibrillar material. The cell bodies of the multiciliated cells sit upon a basal lamina which overlies a collagen-filled matrix. Petromyzon has typical vertebrate sensory hair cells on the cristae of the two semicircular canals as well as on the main sensory epithelium, the macula communis. Cell bodies of the sensory hair cells are similar to hair cells of other vertebrates. However, unlike other fishes, the sensory hair cells in Petromyzon have striated organelles between the nucleus and the apical cell membrane. The hair cells are innervated by afferent and efferent nerve fibers.

ISSN:0006-8977    

DOI:10.1159/000118637

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Primary lateralis projections in silver lampreys, Ichthyomyzon unicuspis, and young adult sea lampreys, Petromyzon marinus, were examined utilizing silver impregnation of degenerating fibers and transganglionic transport of horseradish peroxidase. Anterior lateral line nerve afferents terminate throughout the neuropil of the electroreceptive dorsal nucleus and in the lateral neuropil of the mechanoreceptive medial nucleus. The superficial ophthalmic, buccal and recurrent rami of the anterior lateral line nerve all project to the ipsilateral dorsal nucleus; the recurrent ramus, supplying electroreceptors on the trunk, possesses the largest terminal field. No somatotopy was apparent in the projections to the dorsal nucleus. Primary afferents in the posterior lateral line nerve project to the medial neuropil of the ipsilateral medial nucleus, continue rostrally into the cerebellum and cross to the central neuropil of the contralateral medial nucleus. Lateralis projections in lampreys resemble those in nonteleost bony fishes and elasmobranchs; however, the contralateral projection of the posterior lateral line nerve is presently recognized only in petromyzontids.

ISSN:0006-8977    

DOI:10.1159/000118638

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The inner ears of 5 different gerbil species are compared on the basis of cochlear microphonic recordings, serial sections and computerized quantitative reconstructions of the cochleae and their specific morphological structures. The hearing range of most gerbils is below 20 kHz. Some species are extremely sensitive in the frequency range of 1–4 kHz. This special sensitivity is reflected in, among other features, the following cochlear structures and their suggested functions: (1) the rapid width increase of the basilar membrane in the basal portion of the cochlea provides additional space for the representation of lower frequencies at the expense of higher frequencies; (2) the large hyaline mass and the cells of Claudius and Hensen in the medial and apical portions of the cochlea influence the vibratory properties of the cochlear partition, and (3) the specialized structures of the cochlea may be an adaptation to the acoustical environment in arid habitats.

ISSN:0006-8977    

DOI:10.1159/000118639

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The problems of the evolution of varying brain size, the specialization of particular functional systems and overall differences in the relative complexity of brain organization are discussed in terms of alterations of regressive events in neurogenesis (cell death and axon retraction). Three scenarios for evolution, cascade reorganization, parcellation and heterochrony, are considered in light of regressive mechanisms during development.

ISSN:0006-8977    

DOI:10.1159/000118640

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The problems of the evolution of varying brain size, the specialization of particular functional systems and overall differences in the relative complexity of brain organization are discussed in terms of alterations of regressive events in neurogenesis (cell death and axon retraction). Three scenarios for evolution, cascade reorganization, parcellation and heterochrony, are considered in light of regressive mechanisms during development.

ISSN:0006-8977    

DOI:10.1159/000316017

出版商:S. Karger AG    

年代:1987

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000118641

出版商:S. Karger AG    

年代:1987

数据来源: Karger