摘要:

Intracellular recordings and horseradish peroxidase injections were performed in the pretectum and adjacent tegmentum of Salamandra salamandra, while both optic nerves were electrically stimulated. In approximately half of the recorded units spikes could be evoked but rather graded postsynaptic potentials. The latter type morphologically showed features of interneurons. From a total of 48 recorded units, nearly 60% were excited only by the contralateral optic nerve, whereas approximately 40% were binocular. For the most part (10/19) the binocular cells were excited by the contralateral and inhibited by the ipsilateral optic nerve. Fewer neurons (7/19) received excitatory inputs from both optic nerves. The latency distribution of the monocular cells shows a maximum of 20–30 ms. The same maximum exists for the contralateral inputs to the binocular cells, whereas the ipsilateral inputs to these units were nearly as frequent with latencies of 20–30 and 40–50 ms. Since neurons with the short ipsilateral latencies always had parts of their dendrites within the ipsilateral ocular projection field, a feature which was lacking in the cells with long ipsilateral latencies it is possible that the longer latencies are due to indirect ipsilateral inputs. Efferents of labelled dorsal pretectal cells reach the contralateral pretectum via the posterior commissure, the basal optic neuropil of the accessory optic system and the tegmental white substance. More ventrally located cells often reach the pretectal and the basal optic neuropil with their dendrites. Axons of this type descend to the medulla oblongata via the medial longitudinal fasciculus.

ISSN:0006-8977    

DOI:10.1159/000118716

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The projection targets of the olfactory bulb in pigeons and turtles were investigated using autoradiographic techniques. Despite the relatively smaller size of the olfactory bulbs in pigeons, the projection targets of the olfactory bulb are very similar to those in turtles. In both pigeons and turtles, the olfactory bulb projects to the entire rostrocaudal extent of a portion of the dorsolateral telencephalon (which is here recognized as the pyriform cortex in both birds and reptiles) and to portions of the medial telencephalic wall including the medial septal region. In addition, a projection to the olfactory tubercle of the ventral telencephalon is clearly present in turtles and also appears to be present in pigeons. Pigeons and turtles do differ significantly, however, in the extent of the projection to the amygdaloid region. In turtles, olfactory bulb input encompasses the entire mediolateral and rostrocaudal extent of the amygdaloid region, while in pigeons the input is restricted to a small dorsomedial portion of the amygdala termed nucleus taeniae of the archistriatum. The present results suggest that the olfactory bulb projections in birds are generally similar to those in reptiles, with the exception that secondary olfactory bulb projections to the amygdala may be much reduced in birds compared to those in reptiles. The functional significance of the reduction in olfactory input to the amygdala is presently uncertain.

ISSN:0006-8977    

DOI:10.1159/000118717

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The evolution of the brain in mammals has been accompanied by a progressive enlargement of the cerebral cortex. Allometric analysis of the volume, surface and convolutedness of this cortex shows that among mammals two major groups can be distinguished: (1) species with lissencephalic brains, where surface-volume relationships are determined by linear geometric laws, and (2) species with gyrencephalic brains, where strict geometric similarity no longer applies. Different mathematical models are required to describe the brain morphology in these groups. It has been shown, moreover, that among species with convoluted brains, marine mammals (Cetacea) form a subgroup in that the cerebrocortical surface in these animals is more folded than in terrestrial mammals of similar brain size. Thus it appears that the use of a single allometric relation in studying the effect of size increase on the geometry of the brain – irrespective of convolutedness or ecological strategy – as has been done in previous studies, is unjustified and obscures the differences in the structural organization of mammalian brains. Finally, a dimensionless index of cortical folding is proposed, which indicates that the degree of cortical folding depends not only on the volume of the brain or cortex but on cortical thickness as w

ISSN:0006-8977    

DOI:10.1159/000118718

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The evolution of the brain in mammals has been accompanied by a progressive enlargement of the cerebral cortex. Allometric analysis of the volume, surface and convolutedness of this cortex shows that among mammals two major groups can be distinguished: (1) species with lissencephalic brains, where surface-volume relationships are determined by linear geometric laws, and (2) species with gyrencephalic brains, where strict geometric similarity no longer applies. Different mathematical models are required to describe the brain morphology in these groups. It has been shown, moreover, that among species with convoluted brains, marine mammals (Cetacea) form a subgroup in that the cerebrocortical surface in these animals is more folded than in terrestrial mammals of similar brain size. Thus it appears that the use of a single allometric relation in studying the effect of size increase on the geometry of the brain – irrespective of convolutedness or ecological strategy – as has been done in previous studies, is unjustified and obscures the differences in the structural organization of mammalian brains. Finally, a dimensionless index of cortical folding is proposed, which indicates that the degree of cortical folding depends not only on the volume of the brain or cortex but on cortical thickness as well.

ISSN:0006-8977    

DOI:10.1159/000316004

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The abducens nucleus in carpet sharks is not a discrete delimited nucleus, as the dendrites of the motoneurons extend into the reticular formation and the medial longitudinal fasciculus. lnjections of horseradish peroxidase (HRP) designed to trace the inputs to these neurons are therefore difficult to confine to this system alone. Despite this problem a consistent finding from injection of HRP in the area of the abducens nucleus is the retrograde labelling of a column of cells in the contralateral octaval nuclei. The column of cells is predominantly in the ventral portion of the descending octaval nucleus, but does straddle the entrance of nerve VIII, extending into the caudal part of the ascending octaval nucleus. Labelled cells correspond in location and morphology to those cells receiving input from horizontal canal afferent fibers, confirming the trineuronal nature of the horizontal vestibulo-ocular reflex arc in elasmobranch fishes.

ISSN:0006-8977    

DOI:10.1159/000118719

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Surgical transection of the basal optic root in Rana pipiens leads to substantial increases in prey-orientation latencies for stimuli presented in the contralateral visual field. In general, the greater the reduction in retinal innervation of nBOR, the greater the postoperative increase in prey-orientation latencies. The results support Herrick's earlier suggestion that the accessory optic system may be substantially involved in early activation and temporal modulation of visuomotor behaviors mediated via mesencephalic circuits.

ISSN:0006-8977    

DOI:10.1159/000118720

出版商:S. Karger AG    

年代:1985

数据来源: Karger