Diffusion-tensor neuronal fiber tractography and manganese-enhanced MR imaging of primate visual pathway in the common marmoset: preliminary results.

PURPOSE: To investigate whether diffusion-tensor tractography (DTT) of neuronal fibers is useful for delineating the configuration of the neuronal fiber trajectories in the primate visual pathway, including the well-developed optic chiasm, in comparison with tract tracing at manganese-enhanced magnetic resonance (MR) imaging. MATERIALS AND METHODS: The handling methods used for all the animals in this study were approved by the institutional committee for animal experiments. Diffusion-tensor MR imaging was performed in four healthy common marmosets, and in two of these animals, manganese-enhanced MR imaging tract tracing was performed by using a 7.0-T MR imaging unit. The visual pathways were quantitatively investigated in terms of the manganese distribution observed on the manganese-enhanced MR images. The images obtained with DTT and manganese-enhanced MR imaging tract tracing were qualitatively compared, and the features of the visual pathway were verified through fusion of the reconstructed images obtained by using these two modalities. RESULTS: DTT provided information regarding the neuroanatomic features of the marmoset visual pathway and revealed the bilateral branching patterns of the typical primate retinogeniculate pathways, although several incorrectly tracked fibers were noted. The distribution of manganese on the manganese-enhanced MR images revealed bilateral innervation of the retinal projections and depicted the layered internal structure of the lateral geniculate nuclei bilaterally, depending on the ocularity of each layer. These morphologic findings were consistent with those of previous histopathologic studies. CONCLUSION: The findings of this preliminary study raise the possibility that DTT is useful for visualizing the neuronal fiber trajectories in primate visual pathways. SUPPLEMENTAL MATERIAL: http://radiology.rsnajnls.org/cgi/content/full/249/3/855/DC1.

The middle perforated substance of the diencephalon.

The diencephalon, upper brain stem and other basal brain structures are supplied chiefly by penetrating branches of the cerebral arteries. We examined the retrochiasmatic space between the superior border of the pons and posterior edge of the optic chiasm in six randomly selected adult fresh brain specimens. Lateral or anterolateral to the mamillary bodies, two small quadrangular spaces (2.5 x 3.5 mm) were found that were limited laterally by the junction of the optic tract and crus cerebri. These spaces were pierced on each side by 1 to 5 small penetrating branches (premamillary arterial complex) of the posterior communicating artery. A single, large and obliquely oriented penetrating branch of the posterior communicating artery (the so-called premamillary, thalamotuberal or mamillothalamic artery) was found to pierce this area in all specimens. Based on our findings, the above-mentioned vessels of this perforating substance supply the floor of third ventricle, hypothalamus and ventral thalamic nuclei. Hence, special attentions should be made during surgery in this area such as third ventriculostomy for hydrocephalus.

Mash1 is required for generic and subtype differentiation of hypothalamic neuroendocrine cells.

The neuroendocrine hypothalamus regulates a number of critical biological processes and underlies a range of diseases from growth failure to obesity. Although the elucidation of hypothalamic function has progressed well, knowledge of hypothalamic development is poor. In particular, little is known about the processes underlying the neurogenesis and specification of neurons of the ventral nuclei, the arcuate and ventromedial nuclei. The proneural gene Mash1 is expressed throughout the basal retrochiasmatic neuroepithelium and loss of Mash1 results in hypoplasia of both the arcuate and ventromedial nuclei. These defects are due to a failure of neurogenesis and apoptosis, a defect that can be rescued by ectopic Ngn2 under the control of the Mash1 promoter. In addition to its role in neurogenesis, analysis of Mash1(-/-), Mash1(+/-), Mash1(KINgn2/KINgn2), and Mash1(KINgn2/+) mice demonstrates that Mash1 is specifically required for Gsh1 expression and subsequent GHRH expression, positively regulates SF1 expression, and suppresses both tyrosine hydroxylase (TH) and neuropeptide Y (NPY) expression. Although Mash1 is not required for propiomelanocortin (POMC) expression, it is required for normal development of POMC(+) neurons. These data demonstrate that Mash1 is both required for the generation of ventral neuroendocrine neurons as well as playing a central role in subtype specification of these neurons.

Characteristics of distribution and configuration of intracranial arachnoid membranes.

An understanding of the microsurgical anatomy of the arachnoid membranes and the subarachnoid cisterns is important in minimally invasive neurosurgery. But the topography of the arachnoid membranes has not been completely elucidated. The description of the distribution and the configuration of the intracranial arachnoid membranes is still a subject of controversy. In order to clarify this we examined eight Han Chinese adult human cadavers under an operating microscope. The dissections were performed with microsurgical instruments and techniques without staining of the intracranial structures nor injection of colored material into blood vessels. Twenty seven arachnoid membranes were identified. They were named according to their locations and attachment. They were divided into three groups: basal, convex and trabecular arachnoid membranes. They varied greatly in appearances and configurations. They were single-leaf structured except Liliequist's membrane, the chiasmatic membrane and the cerebellar precentral membrane. They were distributed extensively and unevenly and crisscrossed in the cranial cavity. The more complexly and intricately the blood vessels or the nerves converged or branched within the subarachnoid space, the more luxuriant and complex the arachnoid membranes and trabeculae were. The areas where the arachnoid membranes crowded most thickly in the subarachnoid space included the regions around the bifurcation of the internal carotid artery, the area around the hypothalamus, the interpeduncular cistern, the arachnoidal sheaths of the oculomotor nerve, the quadrigeminal cistern and the cisterna magna. Almost all the cranial nerves were encased by their own arachnoidal sheaths when they crossed the cisterns. The arachnoid membranes and trabeculae must be dissected or incised sharply during the operations. Thorough knowledge of the anatomy of the intracranial arachnoid membranes is valuable to take full advantage of the natural anatomic landmarks and interfaces formed by them during surgery.

Branches of the anterior cerebral artery near the anterior communicating artery complex: an anatomic study and surgical perspective.

The anatomy of the branches of the anterior cerebral artery (ACA) near the anterior communicating artery (ACoA) complex were investigated to minimize neurovascular morbidity caused by surgical procedures performed in this region. Thirty-one cadaver brains were perfused with colored silicone, fixed, and studied under the operating microscope. The recurrent artery of Heubner (RAH), orbitofrontal artery (OFA), and frontopolar artery (FPA) were identified as the branches of the ACA arising near the ACoA complex. The OFA and FPA were identified in all hemispheres. Forty-nine (64%) of a total of 77 RAHs arose from the A2 segment. The OFA always arose from the A2 segment, was consistently the smallest branch, and coursed to the gyrus rectus, olfactory tract, and olfactory bulb. The mean distance between the ACoA and the OFA was 5.96 mm. The FPA arose from the A2 segment in 95% of the specimens, and coursed to the medial subfrontal region. The mean distance between the ACoA and the FPA was 14.6 mm. The RAH, OFA, and the FPA are three branches that arise from the ACA near the ACoA complex. These vessels have similar diameters, but can be distinguished by the final destination. Distinguishing these vessels is important since the consequences of injury or occlusion of the FPA and OFA are significantly less than of the RAH.

Hypothalamic circadian organization in birds. I. Anatomy, functional morphology, and terminology of the suprachiasmatic region.

In mammals, the "master clock" controlling circadian rhythmicity is located in the hypothalamic suprachiasmatic nuclei (SCN). Until now, no comparable structure has been unambiguously described in the brain of any nonmammalian vertebrate. In birds, early anatomical and lesioning studies described a SCN located in the anterior hypothalamus, but whether birds possess a nucleus equivalent to the mammalian SCN remained controversial. By reviewing the existing literature it became evident that confusion in delineation and nomenclature of hypothalamic cell groups may be one of the major reasons that no coherent picture of the avian hypothalamus exists. In this review, we attempt to clarify certain aspects of the organization of the avian hypothalamus by summarizing anatomical and functional studies and comparing them to immunocytochemical results from our laboratory. There is no single cell group in the avian hypothalamus that combines the morphological and neurochemical features of the mammalian SCN. Instead, certain aspects of anatomy and morphology suggest that at least two anatomically distinct cell groups, the SCN and the lateral hypothalamic nucleus (LHN), bear some of the characteristics of the mammalian SCN.

Retinohypothalamic projections in the common marmoset (Callithrix jacchus): A study using cholera toxin subunit B.

Retinal projections in vertebrates reach the primary visual, accessory optic, and circadian timing structures. The central feature of the circadian timing system is the principal circadian pacemaker, the suprachiasmatic nucleus (SCN) of the hypothalamus. The direct projections from the retina to the SCN are considered the entrainment pathway of the circadian timing system. In this study, unilateral intravitreal injections of cholera toxin subunit B were used to trace the retinal projections to the marmoset hypothalamus. The retinohypothalamic tract reaches the ventral suprachiasmatic nucleus bilaterally, as anticipated from previous studies. However, labeled fibers were found in several other hypothalamic regions, such as the medial and lateral preoptic areas, supraoptic nucleus, anterior and lateral hypothalamic areas, retrochiasmatic area, and subparaventricular zone. These results reveal new aspects of retinohypothalamic projection in primates and are discussed in terms of their implications for circadian as well as noncircadian control systems.

[Topography of the hypophysis and its neighboring structures]. / Topographie der Hypophyse und der benachbarten Strukturen.

The first part of the article informs about four points: the skeletal structures of the middle cranial fossa, the basic divisions of the gland and their connections with the hypothalamus, its blood supply, and its development. The topographic part deals with the incorporation of the pituitary gland in the sella turcica, its relationship to the meninges, the subarachnoid cavity and other neighbouring structures, especially the sphenoidal sinus, the posterior ethmoidal cells as well as the chiasma opticum. With respect to the latter, the position of the fibres in the optic nerve, chiasma and optic tract and the consequences of lesions in characteristic areas are described. Finally, the variant structures of the cavernous sinus and the topography of its contents are discussed. Detailed data can be found about the course of the oculomotor nerves and the possible locations of their lesions.

Anatomical connections of the primate pretectal nucleus of the optic tract.

The pretectal nucleus of the optic tract (NOT) plays an essential role in optokinetic nystagmus, the reflexive movements of the eyes to motion of the entire visual scene. To determine how the NOT can influence structures that move the eyes, we injected it with lectin-conjugated horseradish peroxidase and characterized its afferent and efferent connections. The NOT sent its heaviest projection to the caudal half of the ipsilateral dorsal cap of Kooy in the inferior olive. The rostral dorsal cap was free of labeling. The NOT sent lighter, but consistent, projections to other visual and oculomotor-related areas including, from rostral to caudal, the ipsilateral pregeniculate nucleus, the contralateral NOT, the lateral and medial terminal nuclei of the accessory optic system bilaterally, the ipsilateral dorsolateral pontine nucleus, the ipsilateral nucleus prepositus hypoglossi, and the ipsilateral medial vestibular nucleus. The NOT received input from the contralateral NOT, the lateral terminal nuclei bilaterally, and the ipsilateral pregeniculate nucleus. Although our injections involved the pretectal olivary nucleus (PON), there was neither orthograde nor retrograde labeling in the contralateral PON. Our results indicate that the NOT can influence brainstem preoculomotor pathways both directly through the medial vestibular nucleus and nucleus prepositus hypoglossi and indirectly through both climbing and mossy fiber pathways to the cerebellar flocculus. In addition, the NOT communicates strongly with other retino-recipient zones, whose neurons are driven by either horizontal (contralateral NOT) or vertical (medial and lateral terminal nuclei) fullfield image motion.

Projections of the suprachiasmatic nuclei, subparaventricular zone and retrochiasmatic area in the golden hamster.

The patterns of projections from the hamster suprachiasmatic nucleus, retrochiasmatic area and subpraventricular hypothalamic zone were examined using anterograde tracing with the plant lectin, Phaseolus vulgaris leucoagglutinin. Suprachiasmatic nucleus efferents comprise four major fiber groups: (i) an anterior projection to the ventral lateral septum, the bed nucleus of the stria terminalis and anterior paraventricular thalmus; (ii) a periventricular hypothalamic projection extending from the preoptic region to the premammillary area; (iii) a lateral thalamic projection to the intergeniculate leaflet and ventral lateral geniculate; and (iv) a posterior projection to the posterior paraventricular thalamus, precommissural nucleus and olivary pretectal nucleus. The retrochiasmatic area showed a similar projection pattern with several major exceptions. There are projections to endopiriform cortex, fundus striati, ventral pallidum, horizontal limb of the nucleus of the diagonal band and three separate routes to the amygdala. There are also projections laterally with fibers of the supraoptic commissures, which enter the superior thalamic radiation and innervate the caudal dorsomedial thalamic nuclei. Other fibers traveling with the commissures terminate in the ventral zona incerta. The subparaventricular zone projects to most targets of the suprachiasmatic nucleus, but not to the intergeniculate leaflet. There is a substantial input to both the subparaventricular zone and retrochiasmatic area from the suprachiasmatic nucleus, but little apparent reciprocity. There is extensive overlap of suprachiasmatic nuclei and retrochiasmatic efferents, and between retrochiasmatic and known medial amygdaloid efferents. The anatomical information is discussed in the context of circadian rhythm regulation, photoperiodism and chemosensory pathways controlling male hamster reproductive behavior.

Organization of the visual system in larval lampreys: an HRP study.

The organization of the visual system of larval lampreys was studied by anterograde and retrograde transport of HRP injected into the eye. The retinofugal system has two different patterns of organization during the larval period. In small larvae (less than 60-70 mm in length) only a single contralateral tract, the axial optic tract, is differentiated. This tract projects to regions in the diencephalon, pretectum, and mesencephalic tegmentum. In larvae longer than 70-80 mm, there is an additional contralateral tract, the lateral optic tract, which extends to the whole tectal surface. In addition, ipsilateral retinal fibers are found in both small and large larvae. Initially, the ipsilateral projection is restricted to the thalamus-pretectum, but it reaches the optic tectum in late larvae. Changes in the organization of the optic tracts coincide with the formation of the late-developing retina and consequently, the origin of the optic tracts can be related to specific retinal regions. The retinopetal system is well developed in all larvae. Most retinopetal neurons are labeled contralaterally and are located in the M2-M5 nucleus of the mesencephalic tegmentum, in the caudolateral mesencephalic reticular area and adjacent ventrolateral portions of the optic tectum. Dendrites of these cells are apparent, especially those directed dorsally, which in large larvae extend to the optic tectum overlapping with the retino-tectal projection. These results indicate that in lampreys, visual projections organize mainly during the blind larval period before the metamorphosis, their development being largely independent of visual function.

Sonographic examination of the brain stem area in infants. An echographic and anatomic analysis.

For differentiation of diseases with impaired cerebrospinal fluid circulation and pathological alterations of the midbrain an exact and reproducible sonographic visualization of the brain stem area is of paramount importance. The approach through the anterior fontanelle has proved to be insufficient to accomplish this task. Therefore, we have developed 5 standard sonographic sections enabling detailed study of the brain stem. Typical sonographic views are compared with equivalent anatomical brain sections. To date, 330 infants have been examined using this method, making evaluation of brain stem, aqueduct, fourth ventricle, basilar artery and basal cisterns possible.

Retinofugal and retinopetal projections in the cichlid fish Astronotus ocellatus.

The retinofugal and retinopetal projections of the cichlid fish Astronotus ocellatus were studied by applying cobaltous-lysine to the optic nerve. Retinal axons terminate bilaterally in a preoptic-suprachiasmatic region between the base of the third ventricle and the anterior genu of the horizontal commissure and among periventricular cells along the sides of the ventricle. Other retinal axons innervate the tuberal region of the hypothalamus anterior to the infundibulum. Targets innervated in the pretectum include nucleus lateralis geniculatus and dorsal, medial, and ventral pretectal nuclei. Three other targets (nucleus opticus dorsolateralis, nucleus opticus commissurae posterior, nucleus opticus ventrolateralis) are innervated by fibers that leave the medial edge of the dorsal optic tract. Two other targets (basal optic nucleus and accessory optic nucleus) are innervated by fibers from the ventral optic tract. These retinal projections are similar to those previously reported for goldfish in an experiment that used the cobaltous-lysine method (Springer and Gaffney, J. Comp. Neurol. 203:401-424, '81). Retinotectal optic axons were found in a superficial lamina just above the stratum opticum, in the stratum opticum, in three layers of the stratum fibrosum et griseum superficiale, in a lamina just beneath the stratum fibrosum et griseum superficiale, and in the stratum album centrale just above the stratum periventriculare. This result is similar to that previously reported for goldfish; however, the spatial relationships between the various retinorecipient laminae differ for goldfish and Astronotus ocellatus. Efferents to the retina originate in two nuclei and both project contralaterally. The first is the nucleus olfactoretinalis, which is located ventrally between the olfactory lobe and telencephalon. It consists of about 400 cells, of which, approximately 200 cells project to the retina. The second retinopetal nucleus, nucleus thalamoretinalis, is a diffuse group of about 200 cells that project to the retina.

A retinohypothalamic pathway in man: light mediation of circadian rhythms.

It has been proposed that, in animals, a retinohypothalamic pathway exists which mediates the synchronization of the diurnal light-dark cycle with the central neural components regulating endogenous rhythms. There have been numerous anatomic, physiologic and behavioral investigations to substantiate this proposed connection in experimental animals. Morphologic investigation of a retinohypothalamic tract in man has awaited the development of a technique capable of axonal tracing in the human brain. The paraphenylenediamine method was applied to 7 post-mortem human brains. Degenerated axons were found in the suprachiasmatic nuclei of the hypothalamus in each of the 4 patients who had incurred prior optic nerve damage. The retinosuprachiasmatic pathway may be the anatomical substrate for the integration of retinal light information with endogenous rhythms in man.

Hypothalamo-retinal centrifugal projection in the dog.

Horseradish peroxidase (HRP)-filled neurons and their processes were consistently detected in the ventral portion of the dog hypothalamus after intraocular injection of HRP. The number of HRP-filled neurons decreased in parallel with the extent of the resection of the optic nerve. HRP-filled neurons were never detected in specimens with a complete resection of the optic nerve. These findings strongly indicate that these HRP-filled neurons in the ventral hypothalamus are the source of centrifugal fibers to the retina.

Structure and ultrastructure of the external glial layer in the hypothalamus of the hamster.

The hypothalamic subpial limitans has been studied by light and electron microscopy. It consists of a palisade of astrocytic cell bodies or their processes. Beneath the optic chiasma (white matter) the glial layer consists of flattened astrocytic cell bodies arranged in parallel to the myelinated fibres or located between the fibres, but sending their processes towards the basement membrane. Beneath the ventral hypothalamus nuclei, the astrocytic cell bodies can appear in two places: a) in contact with the basement membrane with their processes arranged in parallel to it, or b) located a certain distance from the basement membrane, sending long processes that, near the limitant zone, enlarge to form end-feet (supraoptic nuclei) or sending processes located in parallel to the basement membrane (mamillary nuclei). The astrocytic processes forming the glia limitans show gap junctions, and desmosomes. The different arrangement of the astrocytic processes and the different types of junctions suggest that the marginal glia might represent a regulatory mechanism for the diffusion between the different compartments of the brain.

The afferent connections of the suprachiasmatic nucleus of the golden hamster with emphasis on the retinohypothalamic projection.

The afferent connections of the hypothalamic suprachiasmatic nucleus (SCN) of the golden hamster were examined using horseradish peroxidase (HRP) as the retrograde tracer molecule. Unilateral iontophoretic deposition of HRP into the SCN labeled ganglion cells bilaterally in the retinae. The labeled ganglion cells all had large somata and were randomly distributed across the retina. A similar number were labeled in each retina, which contrasted with the findings from injections into the optic chiasm and lateral geniculate body. Chiasm and geniculate injections both labeled three classes of ganglion cell (small, large, and giant) predominantly in the contralateral retinae. Telencephalic afferent projections to the SCN included the ventral subicular cortex and the septum. Notable diencephalic afferents included the dorsal lamina of the internal division of the ventral lateral geniculate nucleus (vLGN); the ipsilateral input was twice that of the contralateral projection. The same region of the vLGN was also noted to be reciprocally connected to the contralateral vLGN. The thalamic paraventricular nucleus was also heavily labeled but only ipsilaterally. Of functional significance, the SCN was discovered to innervate its contralateral homologue. Other less numerous afferents in the midbrain included the dorsal and median raphe nuclei and the dorsal nucleus of the lateral lemniscus. The afferent projections to the SCN determined in this study are discussed in regard to the known physiological role of the SCN as part of the circadian clock system.

Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry: VI. Catecholamine innervation of vasopressin and oxytocin neurons in the rhesus monkey hypothalamus.

The co-localization patterns of catecholamine varicosities and peptide-specific neuronal perikarya were assessed within the supraoptic and paraventricular nuclei in the rhesus monkey, Macaca mulatta. Formaldehyde-induced histofluorescence was coupled with the unlabelled antibody technique for the demonstration of neuropeptides. Hormone-specific neurophysin staining served to identify vasopressin and oxytocin-containing neurons in these hypothalamic nuclei. Catecholamine varicosities were seen in juxtaposition to vasopressin- and oxytocin-containing perikarya and proximal dendrites. The densest catecholamine innervation patterns were seen in the ventrolateral portion of the supraoptic nucleus; the dorsomedial portion of this nucleus received a considerably less dense innervation pattern. Oxytocin neurons were clustered in this relatively catecholamine poor region, whereas the vasopressin-containing neurons were more abundantly found in the catecholamine rich region. The paraventricular nucleus presented a considerably more complex pattern, perhaps reflecting the more diverse organization of this nucleus. Nevertheless, some separation of the oxytocin neurons, in a region less densely innervated by catecholamine varicosities, was noted. These observations confirm our earlier reports, in rat hypothalamus, that the norepinephrine innervation of the hypothalamic magnocellular neurons as seen with catecholamine histofluorescence favors the vasopressin-containing neurons over those located within the same nuclei which synthesize another neurohyphysial principal, oxytocin.

The magnocellular and parvocellular paraventricular nucleus of rat: intrinsic organization.

The magnocellular and paravocellular regions of the rat hypothalamic paraventricular nucleus (PVN) were examined in several hundred brains. Converging qualitative and quantitative anatomical methods, including Golgi impregnations, Nissl stains, silver stains, and immunocytochemistry were used to study the intrinsic organization of the PVN with light, scanning, and transmission electron microscopy. A computer-assisted quantitative analysis of dendritic branching patterns was used to examine total dendritic length, center of mass, orientation of dendritic tree, and several other parameters of dendritic organization and revealed statistically significant differences between cells in the lateral and posterolateral magnocellular and medial parvocellular areas of PVN. Electron microscopy, Golgi impregnation, and neurophysin immunohistochemistry showed that dendrites of posterolateral cells were generally oriented perpendicular to the third ventricle; dendrites of cells in the lateral PVN usually projected medially from the perikaryon. Cells in the medial zone of PVN had dendritic trees which often paralleled the third ventricle. Large numbers of axons entered and left PVN ventrally near the midline and laterally in the area of the posterolateral PVN; axons generally were oriented parallel to the mean major axis of dendritic trees in these areas. Ultrastructural examination of serial thin sections showed a peculiar astroglia multiple lamellar isolation of axodendritic synaptic contacts. Intrinsic axons commonly arose from parvocellular but not from magnocellular neurons and contacted dendrites of both medial parvocellular and more lateral magnocellular neurons. Synapses were found on shafts and spines of dendrites, on perikarya and somatic appendages, and invaginated into the soma. Both dendrites axons with large neurosecretory vesicles and immunostained with neurophysin antiserum were found postsynaptic to other axons. Presynaptic neurosecretory axons were not found within the PVN. A semiquantitative analysis of catecholamine axons identified with the glyoxylic acid method and fibers immunoreactive with ACTH and Substance P antisera indicated that the parvocellular region of PVN received ggreater innervation than the lateral magnocellular area; similarly, a reater density of stained fibers was found in the medial parvocellular PVN region with Golgi impregnations and silver stains. With a stereological analysis of 1-micrometer plastic sections, the parvocellular area had a significantly greater neuropil to cell volume ration, with cells accounting for 48 +/- 9% in the lateral magnocellular zone, but only for 26 +/- 7% in the parvocellular area. A quantitative analysis of vasculature from thin sections showed that the PVN had 3.3 times more blood vessels, and 3.6 times more lumen perimeter than a control area ventrolateral to PVN; an interesting finding here was that the medial parvocellular PVN had a high degree of vascularity, not significantly different from the lateral magnocellular zone...