摘要:

Using a combination of anatomical and physiological techniques we have studied some of the neural connections subserving binocular vision in two species of artiodactyl ungulates (the sheep, Ovis sp., and the goat, Capra hircus). After monocular injections of tritiated proline, transsynaptic transport was observed bilaterally in layers 4 and 6 of visual cortical areas V1 and V2, but there were no sharply defined ocular dominance columns of the kind seen in cats and rhesus monkeys. In coronal sections there was a discontinuity in density of labelling between areas V1 and V2 corresponding to a point in the visuotopic map about azimuth –15° in the ipsilateral visual field. This discontinuity was most pronounced in the hemisphere ipsilateral to the injected eye. We conclude, therefore, that while the cortical representation of ipsilateral visual space can be explained by the retino-geniculo-cortical input pathway from the contralateral eye, the physiologically demonstrated cortical contribution to ipsilateral visual space from the ipsilateral eye cannot be explained in this way. This conclusion was reinforced by experiments using retrograde transport of horseradish peroxidase from the lateral geniculate nucleus (LGN) and medial interlaminar nucleus (MIN) to retinal ganglion cells in flattened whole mounts. These experiments revealed a sharp nasotemporal decussation in the ipsilateral retina, which could not thereby subserve any significant representation of the ipsilateral visual field. In contrast the contralateral nasotemporal decussation was smeared, with many labelled ganglion cells in the temporal retina which could subserve visual input from the ipsilateral hemifield. When we estimated the projection of the nasotemporal decussation line into visual space, we found that it was tilted from vertical by about 5°in each eye, in a similar way to that already reported in the cat. Neurophysiological recordings from binocular neurons in area V1 with different vertical eccentricities also showed that the vertical horopter (the midsagittal reference plane for binocular vision) would be tilted in life when the cyclotorsional position of the eyes was taken into account. Thus both anatomical and physiological methods concur in the prediction that ungulates have a tilted vertical horopter like that described for two other terrestrial species, the burrowing owl and the cat. Anatomical experiments reveal other similarities between the organisation of the ungulate''s visual pathways and that of the cat. For example, after tritiated proline injection in V1, we found visuotopic labelling in the claustrum, dorsal LGN, cortical area V2, and the superior colliculus. Horseradish peroxidase injections in V2 also revealed a direct input to that area from the MIN and dorsal LGN and also from layers 2, 3 and 5 of the splenial a

ISSN:0006-8977    

DOI:10.1159/000121306

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Using a combination of anatomical and physiological techniques we have studied some of the neural connections subserving binocular vision in two species of artiodactyl ungulates (the sheep, Ovis sp., and the goat, Capra hircus). After monocular injections of tritiated proline, transsynaptic transport was observed bilaterally in layers 4 and 6 of visual cortical areas V1 and V2, but there were no sharply defined ocular dominance columns of the kind seen in cats and rhesus monkeys. In coronal sections there was a discontinuity in density of labelling between areas V1 and V2 corresponding to a point in the visuotopic map about azimuth –15° in the ipsilateral visual field. This discontinuity was most pronounced in the hemisphere ipsilateral to the injected eye. We conclude, therefore, that while the cortical representation of ipsilateral visual space can be explained by the retino-geniculo-cortical input pathway from the contralateral eye, the physiologically demonstrated cortical contribution to ipsilateral visual space from the ipsilateral eye cannot be explained in this way. This conclusion was reinforced by experiments using retrograde transport of horseradish peroxidase from the lateral geniculate nucleus (LGN) and medial interlaminar nucleus (MIN) to retinal ganglion cells in flattened whole mounts. These experiments revealed a sharp nasotemporal decussation in the ipsilateral retina, which could not thereby subserve any significant representation of the ipsilateral visual field. In contrast the contralateral nasotemporal decussation was smeared, with many labelled ganglion cells in the temporal retina which could subserve visual input from the ipsilateral hemifield. When we estimated the projection of the nasotemporal decussation line into visual space, we found that it was tilted from vertical by about 5°in each eye, in a similar way to that already reported in the cat. Neurophysiological recordings from binocular neurons in area V1 with different vertical eccentricities also showed that the vertical horopter (the midsagittal reference plane for binocular vision) would be tilted in life when the cyclotorsional position of the eyes was taken into account. Thus both anatomical and physiological methods concur in the prediction that ungulates have a tilted vertical horopter like that described for two other terrestrial species, the burrowing owl and the cat. Anatomical experiments reveal other similarities between the organisation of the ungulate''s visual pathways and that of the cat. For example, after tritiated proline injection in V1, we found visuotopic labelling in the claustrum, dorsal LGN, cortical area V2, and the superior colliculus. Horseradish peroxidase injections in V2 also revealed a direct input to that area from the MIN and dorsal LGN and also from layers 2, 3 and 5 of the splenial a

ISSN:0006-8977    

DOI:10.1159/000121307

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

In a first experiment, dorsomedial forebrain ablated birds showed similar homeward orientation when compared to untreated controls independent of whether the birds were released from a previous training site or a site they had never been before. However, although all control birds returned to the home loft, only 2 of 28 birds with lesions homed successfully. In a subsequent experiment, both sham operated control birds and birds with lesions of the visual Wulst homed successfully when released only 800 m from and in full view of their respective home lofts. Pigeons with dorsomedial forebrain lesions, however, failed to return to their respective home lofts. The results show that (1) the avian dorsomedial forebrain plays a critical role in that step of the homing process by which a pigeon returns to its home loft once in its vicinity, and that (2) the failure to reassociate with the home loft is a likely result of deficient recognition of the home loft and/or its surrounding area. In an additional experiment, pigeons with Wulst lesions were shown to orient as controls and to successfully return to the home loft when released from two distant sites. This experiment demonstrated that the avian Wulst plays no necessary role in the homing behavior of pigeons.

ISSN:0006-8977    

DOI:10.1159/000121308

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

Labeled neurons were found in most reticular and raphe nuclei of the opossum''s medulla after horseradish peroxidase (HRP) injections into either the spinal cord or diencephalon. The labeling produced by spinal injections differed somewhat from that produced by diencephalic ones, but HRP-positive neurons were found in what appeared to be comparable areas. In order to study the intermingling of bulbospinal and bulbodiencephalic neurons more directly, we used fluorescent markers (true blue, nuclear yellow and diamidino yellow dihydrochloride) in double-labeling experiments. When injections of one dye into the spinal cord were combined with injections of another into the diencephalon, neurons labeled by one or the other marker were found to be intermingled in most reticular and raphe nuclei. The double-labeling experiments also showed that some neurons of the bulbar reticular formation and raphe project to both the spinal cord and diencephalon, presumably by axonal collaterals. The number of such neurons represents a somewhat larger proportion of those projecting to the diencephalon than to the spinal cord. It appears, however, that most neurons project either to the spinal cord or to the diencephalon and do not provide collaterals to both areas.

ISSN:0006-8977    

DOI:10.1159/000121309

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The midline ridge formation (MRF) of the trigeminal complex in 127 cartilaginous fish of 15 species was examined by scanning electron microscopy or light microscopy. Five distinct species variations of the MRF in sharks are described. The formation has not yet been observed to be present in skates and rays, but its presence in the subclass Holocephali, the sister group to the Elasmobranchii, indicates that this proposed circumventricular organ is an ancient brain characteristic of this line of vertebrates, perhaps predating the emergence of the class Chondrichthyii. The different types of MRF are compared to a current phyletic organization of the elasmobranchs and the possible functional significance of the formation is discussed briefly.

ISSN:0006-8977    

DOI:10.1159/000121310

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

In the frog, we have recorded the activity of efferent and afferent fibers in the nerve of the horizontal semicircular canal in response to somatosensory stimulation. Recordings were made extracellularly by means of glass micropipettes filled with 2 M NaCl, and somatosensory stimulation was produced either by electrical stimulation of the sciatic nerve (ipsi- or contralateral to the recording side) or by vibratory stimulation of the gastrocnemius. The discharge frequency of 43 % of the efferent fibers recorded was significantly increased by such stimulation, while the activity of the others was unaffected. The discharge rate of the afferent fibers was either significantly increased (in about 11 % of the cases when the results were pooled together) or significantly decreased (in about 22% of the cases) by stimulation of the somatosensory system. The latencies of the responses ranged from 5 to 50 ms. These results show that: (1) somatosensory input can influence the activity of the vestibular apparatus at the most peripheral level; (2) modulation of the afferent discharge is mediated by the efferent vestibular system (EVS); (3) the influence of the EVS on the vestibular afferent activity is both inhibitory and facilitatory, and (4) the responses to somatosensory stimulation are mediated by both long-latency polysynaptic and short-latency oligosynaptic pathways. The functional significance of these two pathways is discussed.

ISSN:0006-8977    

DOI:10.1159/000121311

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

The somatotopic representation of facial muscles within the facial nucleus was investigated by means of the retrograde horseradish peroxidase and cell degeneration techniques in the mouse. The nasolabial muscle is represented in the dorsolateral, lateral, and dorsal intermediate subnucleus; the mentalis muscle, in the ventral intermediate subnucleus; the platysma, in the dorsomedial part of the dorsal intermediate subnucleus and along the lateral border of the dorsomedial and ventromedial subnucleus; the orbicularis oculi and frontalis muscle, in the dorsal portions of the dorsolateral, dorsal intermediate, and dorsomedial subnucleus; the rostral and caudal auricular muscles, in the dorsomedial and ventromedial subnucleus, respectively; and the caudal belly of the digastric muscle, in the suprafacial nucleus. The present study shows that the facial muscles are represented in an orderly fashion in seven subnuclei of the facial nucleus, as in other animal species.

ISSN:0006-8977    

DOI:10.1159/000121312

出版商:S. Karger AG    

年代:1984

数据来源: Karger

摘要:

A model of cortical folding in mammals is presented. The model consists of a cube, superimposed on which are straight close-packed gyri, running the length of the cube. The cortex is represented by a thin layer of constant thickness. It proves possible, by adjusting the length, height, and width of the ''gyri'' and the thickness of the ''cortex'', to obtain a reasonable fit to the available empirical data (which extend over three to four orders of magnitude in brain weight). The model directs attention to possible features of the macroscopic organization of the mammalian brain which are novel and hitherto unremarked.

ISSN:0006-8977    

DOI:10.1159/000121313

出版商:S. Karger AG    

年代:1984

数据来源: Karger