Torus Longitudinalis Research Articles

Projections of the optic tectum in two teleost species.

The efferent pathways of the optic tectum have been investigated in the percomorph Eugerres and the berycomorph Holocentrus. A portion of the dorsal-dorsolateral region of the optic tectum was unilaterally resected by suction. The animals were perfused 6-30 days thereafter, and the brains were processed according to a modification (Method 7 in Ebbesson, '70) of the Fink-Heimer ('67) technique for the selective silver impregnation of degenerating axons and terminals. Three groups of fibers emerge from the lesioned region (a) a medial group, which runs towards the midline and terminates in the ipsilateral torus longitudinalis and the contralateral tectum; (b) an ascending group, which enters the dorsocaudal region of the diencephalon and terminates in pretectal cell groups, in the dorsomedial optic thalamic nucleus, and in the nucleus rotundus or prethalamicus; and (c) a descending group, which funnels down into the midbrain tegmentum. Here abundant terminals are given to dorsolateral cell groups and to the nucleus isthmi. A recurrent fascicle leaves the mainstream and ascends to terminate in scattered diencephalic cell groups, in the nucleus geniculatus posterior pars ventralis, and in the nucleus rotundus or prethalamicus. The bulk of descending fibers then forms an ipsilateral bundle, which gives terminals to the lateral reticular formation of mesencephalon and rhombencephalon, and a contralateral (i.e., the predorsal) bundle, which terminates in the medial reticular formation of mesencephalon and rhombencephalon.

Tectal efferents in the blind cave fish Astyanax hubbsi.

Suction lesions were placed in the optic tecta of 36 blind cave fish. Three main bundles of tectal efferents were observed. A large, caudally directed fascicle distributes to the ipsilateral torus semicircularis, nucleus isthmi, and lateral tegmental areas of the mesencephalon and pons via the ipsilateral tectobulbar tract. Contralaterally, this fascicle descends to pontine levels as the contralateral tectobulbar tract. A second, rostrally directed bundle exits from the tectum at two levels. A small fascicle leaves from the caudal tectum and ascends rostrally as the commissura transversa. This bundle then joins with more rostrally exiting fibers and the combined fascicles collect in the area of the medial optic tract. They remain in this position until the level of the postoptic commissure where they decussate. Subsequently, this bundle moves caudally and enters the contralateral tectum at its most rostral extreme. The third bundle of tectofugal efferents leaves the tectum medially, at the level of the lesion, and enters the tectal commissure, through which it is distributed to the ipsilateral torus longitudinalis and contralateral optic tectum.

Fine structure of the carp torus longitudinalis

AbstractFine structure of the carp torus longitudinalis was studied by electron and light microscopy and compared with the granular layer of the carp cerebellum. There are three types of cells in the torus longitudinalis, that is, small, medium‐sized and large cells. From the small cells to the medium‐sized cells, there is gradual transition in size and in the amounts of cell organelles. These cell profiles and the closely packed cell pattern in a part of the torus longitudinalis are quite similar to those in the granular layer of the cerebellum. Moreover, peculiar synaptic configurations of so‐called “synaptic glomeruli” are found both in the torus longitudinalis and in the granular layer of the cerebellum. In the torus longitudinalis, unmyelinated nerve fibers are seen to have bulbous swellings along their course, most of which contain a mitochondrion, as do they in the carp tectum opticum.It is speculated that the torus longitudinalis may be partly related to the granular layer of the cerebellum and partly to the tectum opticum.

A CONTRIBUTION TO THE STUDY OF THE TORUS LONGITUDINALIS IN SOME TELEOSTEAN BRAINS.

A CONTRIBUTION TO THE STUDY OF THE TORUS LONGITUDINALIS IN SOME TELEOSTEAN BRAINS.

Contributions to the neurobiological study on the structure and relations of the torus longitudinalis in the teleostean brains

Contributions to the neurobiological study on the structure and relations of the torus longitudinalis in the teleostean brains