摘要:

Data from cats, ferrets, hamsters, macaques, mice, rabbits and rats concerning the time of occurrence of 26 developmental events involved in the establishment of the retinofugal, geniculocortical, corticogeniculate and corticocollicular pathways were analysed. For each species the timing of developmental events was expressed as a proportion of the period between conception and eye opening ('caecal period’). For 6 of these events, the values for all species fell within a range of 1–5% of the caecal period, the values for 11 other events fell within a range of 6–10% of the caecal period, 4 events had ranges of 11–15% of the caecal period, and only 5 events were spread over more than 15% of the caecal period. The 26 events had an overall mean variation of about 11% of the caecal period, suggesting that the visual pathways of eutherian mammals develop according to a common 'timetable' that is related to the duration of the caecal period. One of the roles of this common timetable may be to assist the establishment of orderly interconnections between the visual centres. Relatively few data are available concerning the timing of developmental events in marsupial visual pathways. However, it is apparent that, during the first half of the caecal period, most events occur much earlier in marsupials than in eutherians, whereas during the second half of the caecal period most events occur at the same stages of the caecal period in both marsupials and eutherians. The accelerated rate of visual development during the first half of the caecal period in marsupials may be related to the precocious development that they undergo prior to their very early birth.

ISSN:0006-8977    

DOI:10.1159/000115306

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Data from cats, ferrets, hamsters, macaques, mice, rabbits and rats concerning the time of occurrence of 26 developmental events involved in the establishment of the retinofugal, geniculocortical, corticogeniculate and corticocollicular pathways were analysed. For each species the timing of developmental events was expressed as a proportion of the period between conception and eye opening ('caecal period’). For 6 of these events, the values for all species fell within a range of 1–5% of the caecal period, the values for 11 other events fell within a range of 6–10% of the caecal period, 4 events had ranges of 11–15% of the caecal period, and only 5 events were spread over more than 15% of the caecal period. The 26 events had an overall mean variation of about 11% of the caecal period, suggesting that the visual pathways of eutherian mammals develop according to a common 'timetable' that is related to the duration of the caecal period. One of the roles of this common timetable may be to assist the establishment of orderly interconnections between the visual centres. Relatively few data are available concerning the timing of developmental events in marsupial visual pathways. However, it is apparent that, during the first half of the caecal period, most events occur much earlier in marsupials than in eutherians, whereas during the second half of the caecal period most events occur at the same stages of the caecal period in both marsupials and eutherians. The accelerated rate of visual development during the first half of the caecal period in marsupials may be related to the precocious development that they undergo prior to their very early birth.

ISSN:0006-8977    

DOI:10.1159/000316082

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Bilateral ear asymmetry is found in some, but not all, species of owls. We investigated the neural basis of sound localization in symmetrical and asymmetrical species, to deduce how ear asymmetry might have evolved from the ancestral condition, by comparing the response properties of neurons in the external nucleus of the inferior colliculus (ICx) of the symmetrical burrowing owl and asymmetrical long-eared owl with previous findings in the symmetrical great horned owl and asymmetrical barn owl. In the ICx of all of these owls, the neurons had spatially restricted receptive fields, and auditory space was topographically mapped. In the symmetrical owls, ICx units were not restricted in elevation, and only azimuth was mapped in ICx. In the barn owl, the space map is two-dimensional, with elevation forming the second dimension. Receptive fields in the long-eared owl were somewhat restricted in elevation, but their tuning was not sharp enough to determine if elevation is mapped. In every species, the primary cue for azimuth was interaural time difference, although ICx units were also tuned for interaural intensity difference (IID). In the barn owl, the IIDs of sounds with frequencies between about 5 and 8 kHz vary systematically with elevation, and the IID selectivity of ICx neurons primarily encodes elevation. In the symmetrical owls, whose ICx neurons do not respond to frequencies above about 5 kHz, IID appears to be a supplementary cue for azimuth. We hypothesize that ear asymmetry can be exploited by owls that have evolved the higher-frequency hearing necessary to generate elevation cues. Thus, the IID selectivity of ICx neurons in symmetrical owls may preadapt them for asymmetry; the neural circuitry that underlies IID selectivity is already present in symmetrical owls, but because IID is not absolutely required to encode azimuth it can come to encode elevation in asymmetrical owls.

ISSN:0006-8977    

DOI:10.1159/000115307

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Bilateral ear asymmetry is found in some, but not all, species of owls. We investigated the neural basis of sound localization in symmetrical and asymmetrical species, to deduce how ear asymmetry might have evolved from the ancestral condition, by comparing the response properties of neurons in the external nucleus of the inferior colliculus (ICx) of the symmetrical burrowing owl and asymmetrical long-eared owl with previous findings in the symmetrical great horned owl and asymmetrical barn owl. In the ICx of all of these owls, the neurons had spatially restricted receptive fields, and auditory space was topographically mapped. In the symmetrical owls, ICx units were not restricted in elevation, and only azimuth was mapped in ICx. In the barn owl, the space map is two-dimensional, with elevation forming the second dimension. Receptive fields in the long-eared owl were somewhat restricted in elevation, but their tuning was not sharp enough to determine if elevation is mapped. In every species, the primary cue for azimuth was interaural time difference, although ICx units were also tuned for interaural intensity difference (IID). In the barn owl, the IIDs of sounds with frequencies between about 5 and 8 kHz vary systematically with elevation, and the IID selectivity of ICx neurons primarily encodes elevation. In the symmetrical owls, whose ICx neurons do not respond to frequencies above about 5 kHz, IID appears to be a supplementary cue for azimuth. We hypothesize that ear asymmetry can be exploited by owls that have evolved the higher-frequency hearing necessary to generate elevation cues. Thus, the IID selectivity of ICx neurons in symmetrical owls may preadapt them for asymmetry; the neural circuitry that underlies IID selectivity is already present in symmetrical owls, but because IID is not absolutely required to encode azimuth it can come to encode elevation in asymmetrical owls.

ISSN:0006-8977    

DOI:10.1159/000316083

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

In mammals, the supraspinal descending projections that influence distal limb muscles are the rubrospinal and corticospinal tracts. The former, which is found in other vertebrates, shows greater somatotopy in mammals that are 'dextrous' (e.g. monkeys) than those that are not (e.g. opossums). Similarly, the corticospinal tract, which is found only in mammals, has more extensive connections (i.e. direct corticomotoneural) in mammals that are dextrous than in mammals that are not. Descending spinal pathways have been described in 'non-dextrous’ avian species (chickens, ducks, geese and pigeons), and the purpose of this study was to determine if there are any differences in the origins of descending projections to the spinal cord in 'dextrous' or prehensile parrots (sulphur-crested cockatoo, Cacatua galerita, and eastern rosella, Platycerus eximius). True Blue or wheat germ agglutinin-horseradish peroxidase was injected into the lumbar or cervical spinal cord. The distribution of retrogradely labelled cells was similar to that previously reported for non-prehensile birds. We found no evidence of any direct spinal projections from the telencephalon (including any pathway homologous to the corticospinal tract of mammals), nor any specialized anatomical organization of the descending pathways that could account for the pedal dexterity of these species.

ISSN:0006-8977    

DOI:10.1159/000115308

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Horseradish peroxidase (HRP) was used to identify parts of the presumptive neural pathway for gill cover erection, a behavioral display pattern performed by Siamese fighting fish (Betta splendens) during aggressive interactions. Motor, motor integration and sensory areas were identified in the medulla and mesencephalon. Motor neurons of the dilator operculi muscle, the effector muscle for gill cover erection, are located in the lateral and medial parts of the caudal trigeminal motor nucleus. lontophoretic injections of HRP into the lateral trigeminal motor nucleus resulted in labeled cell bodies in two motor areas (medial part of the trigeminal motornucleus, anterior part of the motor nucleus of cranial nerve IX-X), two parts of the reticular formation (medial and inferior reticular areas), and two nuclei of the octavolateralis system (nucleus medialis, magnocellular octaval nucleus). The HRP injections in the medial part of the caudal trigeminal motor nucleus resulted in labeled cells in the lateral part of the nucleus and in the medial reticular nucleus. Discrete injections of HRP into nucleus medialis revealed a strong axonal projection that terminated in the torus semicircularis. The medial reticular area and both of the octavolateralis nuclei received projections from their contralateral counterparts. Connections between motor areas, and between parts of the reticular formation, may coordinate the performance of gill cover erection with other behavioral patterns used during aggressive display. Connections with the octavolateralis system may provide information on the strength of an opponent's tail beats via the lateral-line system, as well as vestibular information about the fish's own orientation during aggressive display. The organization of inputs to the trigeminal motor nucleus in Betta, a perciform fish, was found to differ from that reported in the common carp, a cypriniform fish. These differences may underlie the different behavioral capabilities of the two groups of fish.

ISSN:0006-8977    

DOI:10.1159/000115309

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The boundaries of the primary auditory cortex of the long-eared hedgehog, Hemiechinus auritus, were determined by single-cell recordings, myeloarchitecture and retrograde horseradish peroxidase labeling in the medial geniculate, using anesthetized animals. The auditory cortex is located on the lateral surface of the temporal cortex, medial to the rhinal fissure. Responses to pure tones revealed an orderly representation of best frequencies in the primary auditory cortex, with low frequencies represented rostrally and high frequencies caudally. A second auditory field caudal to the primary one was indicated.

ISSN:0006-8977    

DOI:10.1159/000115310

出版商:S. Karger AG    

年代:1990

数据来源: Karger