The efferent projections of the fornix system have been studied in the squirrel monkey using modified silver staining techniques to delineate degP*.mating fibers and terminal boutons after inducing careful lesions of the subcallosal fornix and dorsal fornix.Subcallosal fornix projections, after supplying the medial and lateral septa1 nuclei, are traced via precommissural fibers to terminal degeneration in the nu&us of the diagonal band of Broca, nucleus accumbens, ~Y N S rectus, olfactory tubercle, medial and lateral preoptic areas, and medial hypothalamus. Degenerating precommissural subcallosal fornix fibers course with the medial forebrain bundle throughout the extent of the lateral hypothalamus, extending caudally to the medial mammillary nucleus with specific hypothalamic offsets to the tuberal region and nucleus intercalatus (''lateral cortico-hypothalamic tract"). Subcallosal postcommissural fornix fibers are traced to terminal degeneration in the bed nucleus of the stria terminalis and medial preoptic and anterior hypothalamic structures (''medial cortico-hypothalamic tract"); fornix column fibers disperse throughout the perifornical nucleus; these fibers more caudally supply nucleus intercalatus and medial mammillary nucleus. In the thalamus postcommissural fibers supply the nucleus reuniens, the paraventricular, anterior ventral, and lateral dorsal nuclei. In the mammillary nucleus a laminated radiation is described with some fibers extending caudally to the prerubral field.A "midline subcallosal stria," derived from the subcallosal fornices, distributes fibers to the subfornical organ, the dorsal part of the medial septum, the precommissural fornix and especially the medial cortico-hypothalamic tract.The dorsal fornix projection is predominantly pericallpsal to the ~Y N S rectus and parolfactory area, with only a minor callosal-penetrating contribution to pre-and postcommissural fibers.The composite projections of the hippocampal formation fornix system appear more extensive than those of the amygdala to basal forebrain, preoptic, and hypothalamic areas.A review of anatomical descriptions of fornix system projections, comprising a voluminous literature, reveals significant discrepancies. Although G. Elliot Smith concluded in 1897 that I'. . . the fornix conforms to one and the same fundamental plan in the arrangement of its fibers in all vertebrates," five years later Edinger and Wallenberg ('02) found that postmammillary fornix connections differed significantly in different strains of rabbits. Thereafter, many of the seeming discrepancies of the early studies were explained by further work which showed that there is significant interspecific variability in the distribution and extent of direct fornix fibers (Tello, '36; Simpson, '52; Cowan and Powell, '55; Valenstein and Nauta, '59).Recently further clarification of fornix system projections has been achieved using the newer technique of studying axonal transport CHARLES E. POLETTI AND GEORGE CRESWELLof radioactive amino acids (Swanson and...
In the squirrel monkey, nerve cells in certain areas of the brain are characterized by abundant granules which stain intensely with aldehyde-fuchsin but not with chromium hematoxylin.These cells fall into three main types: Type A, with a polar clumping of the granules, characterize the region surrounding the stria terminalis in the amygdala and the supratrochlear nucleus of the mid-brain. Type B, which have a heavy diffuse granulation, are found in the lateral and caudal hypothalamus and in nucleus raphes ventralis. Less heavily granulated cells classified as Type C distinguish the entire nucleus subthalamicus, and are prominent in nucleus septalis triangularis, rostral midline thalamus, and area CA2 of the rostral hippocampus. Cells of these corresponding types and distribution are not seen in the brains of cat, rat and mouse.The cerebellum and pineal body contain extracellular material which stains with aldehyde-fuchsin but not chromium hematoxylin.The granules of the nerve cells stain with PAS, Sudan black B, and oil red 0, suggesting that they have carbohydrate and lipid components.As in other species, the neurosecretory substance of the paraventricular and supraoptic nuclei is stained both by aldehyde-fuchsin and chromium hematoxylin.Material showing a positive reaction to both these stains is also found in the glia of the nucleus septalis triangularis, subfornical organ, lateral hypothalamus, and locus caeruleus. All these regions, except the lateral hypothalamus, show similarly staining material in the extracellular spaces.Of anatomical interest is the close association of the aldehyde-fuchsin positive neurons with phylogeneticdly ancient cellular structures and fiber systems of the brain. In the squirrel monkey they would seem to provide a basis for further characterization of certain nuclei and a new division of the amygdala.Thi:s study was originally undertaken in the squirrel monkey (Saimiri sciureus) to explore the possibility of finding neurosecretory material (Scharrer and Scharrer, '37; Bargmann, '49) in the amygdaloid region. The outcome was negative in so far as no cells were found which stained both with chromium hematoxylin and aldehydefuchsin. In a circumscribed part of the amygdala, however, distinctive cells were found with densely packed granules that stained intensely with aldehyde-fuchsin but were chromium hematoxylin negative. This made it of interest to explore the entire brain to learn if similar staining cells were present elsewhere. This report will describe the distribution of intra-and extracehlar aldehyde-fuchsin positive (AFP) granular material that was found, as well as the preliminary attempt to identify its chemical nature. Findings will also be given of a preliminary comparative study.AM. J. ANAT., 115: 543-558. MATERIALS AND METHODSThe squirrel monkey is a small, New World monkey with an average weight of about 700 g. Its brain is comparable in size to that of the cat. The stereotaxic brain atlas prepared by Gergen and MacLean ('62) served as an anatomical reference...
The question of anatomical connections between the visual system and the temporo-occipital limbic cortex was investigated in 24 squirrel monkeys (Saimiri sciureus) with the utilization of stains for showing fine degenerating cortical fibers. Lesions of various size were placed in the geniculo-pulvinar complex by electrocoagulation. Electrodes were usually inserted in the Horsley-Clarke frontal plane, but in two cases lesions of the lateral geniculate body were made by an extracerebral approach.With a lesion well confined to the ventrolateral part of the lateral geniculate body, heavy degeneration appeared in the inferior longitudinal fasciculus and continued into its ventromedial extension designated as band 3 in the core of the posterior hippocampal gyrus. Some degenerating fibers could be traced from band 3 into the cortex of this gyrus, as well as into adjoining cortical areas in the fusiform and lingual gyri. Sparse degeneration in the postsplenial cortex could n o t be excluded as arising from the lesion made by a n electrode in approaching the lateral geniculate body in the frontal plane. Degeneration in band 3 did not extend as far forward as the entorhinal cortex i n the anterior hippocampal gyrus. In two animals with small rostra1 lesions of the lateral geniculate body made by the extracerebral approach, some degeneration also extended into band 3, supporting other control observations that such degeneration is not dependent on the destruction of tissue made by an electrode in approaching the lateral geniculate body in the frontal plane.When a lesion involved the inferior pulvinar as well as the lateral geniculate body, heavier degeneration appeared in the posterior hippocampal, fusiform, and lingual cortex. With a large lesion of the inferior pulvinar, a band of degeneration appeared ventrolaternl to the optic radiations and was traced into these same cortical areas.The anatomical results are discussed in the light of recent microelectrode findings of photically responsive units in the cortex of posterior hippocampal gyrus and adjoining cortical areas. The combined evidence suggests a n explanation for the temporal detour made by that part o€ the optic radiations commonly referred to as Meyer's temporal loop.In preceding studies on the functional relationship of the visual system and limbic cortex it was found that photic stimulation evoked unit potentials in the posterior part of the hippocampal gyrus and adjoining fusiform cortex, the parahippocampal portion of the lingual gyrus, and the retrosplenial cortex. (CuBnod, Casey, MacLean, '65; MacLean, Yokota and Kinnard, '68) Findings with electrical stimulation of the lateral geniculate body suggested the possibility of a direct orthodromic pathway to these cortical areas (Casey, CuBnod and MacLean, '65). In view of this evidence we have placed lesions in the lateral geniculate body for the purpose of learning whether or not any fibers of the optic radiations terminate in the temporo-occipital limbic cortex. This paper will describe results obtai...
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