The vascularization of the neural stalk and the pars nervosa of the hypophysis in the toad,Bufo bufo (L.) (amphibia,anura)

The angioarchitecture of the neural stalk and the encephaloposthypophysial portal system of the hypophysis of the toad, Bufo bufo (L.), was studied using three different methods. The neural stalk is mainly supplied by branches of the arteria infundibularis superficialis which form a widemeshed vascular network. Dorsally this network continues into the plexus of the pars nervosa. The vascularization of the pars nervosa is made up of the encephalo-posthypophysial portal system. This portal system consists of a hypothalamic branch (=portion), a mesencephalic and a mesencephalicbulbar branch (=portion). The hypothalamic branch was found to drain the pars ventralis of the tuber cinereum as well as more dorsal regions of the diencephalon. The mesencephalic-bulbar trunk enters the hypothalamic branch. The resulting common stem of the encephalo-posthypophysial portal vein the curves around the retroinfundibular communicating artery, crosses its ventral side and runs caudally. The secondary capillary plexus of the pars nervosa is characterized by well defined capillary plexus of the pars nervosa is characterized by well defined capillary networks which are located at the periphery of the parenchyma of the pars nervosa, thus forming a rostral, dorsal and ventro-caudal net. The central region of the parenchyma of the pars nervosa is supplied only by main branches of the encephalo-postpophysial portal vein. The venous drainage of the pars nervosa is via the vena hypophysea transversa.     

The Vascularization of the Anuran Brain Diencephalon and Choroid Plexus: A scanning electron microscopical study of vascular corrosion casts

Albrecht, U., Lametschwandtner, A., Adam, H. 1979. The vascularization of the anuran brain. Diencephalon and choroid plexus. A scanning electron microscopical study of vascular corrosion casts. (Department of Zoology, University of Saulzburg, Austria.) — Acta zool. (Stockh.) 61(4): 203–220. The vascularization of the diencephalon (with choroid plexus of the third ventricle, epithalamus and pineal region, thalamus and hypothalamus) of the toad, Bufo bufo (L.) has been studied by means of scanning electron microscopy of vascular corrosion casts. To localize angioarchitectonic patterns of distinct diencephalic regions the authors refer to critical point dried specimens and to histological sections. In the choroid plexus a supply via one choroid artery, which arises from the posterior telencephalic artery, was found. Its strict dichotomous branching is pointed out. In generally a similar vascular pattern like that in the choroid plexus of the fourth ventricle has to be reported. Furthermore the epithalamic region with the epiphysial area was under investigation. No special angioarchitecture of the epiphysis was found. There are also no prominent vascular connections with thalamic or hypothalamic regions. The thalamic region is supplied by branches of the posterior telencephalic artery as well as by branches of the preoptic artery. Epithalamic and thalamic regions are drained via the posterior diencephalic vein. Special attention was also paid to the preoptic, the chiasmatic and the retrochiasmatic area. No special vascular connections, however, were found.     

Tectal and Related Target Areas of Spinal and Dorsal Column Nuclear Projections in Hedgehog Tenrecs

The terminal distributions of spinal and dorsal column nuclear projections to tectum, pretectum, and central gray of hedgehog tenrecs (Echinops telfairi and Setifer setosus) were investigated using anterograde axonal flow and various tracer substances. In the inferior colliculus, the densest and most extensive mesencephalic projections were found within the pericentral regions. One target area, referred to as the external portion of the inferior colliculus, was represented as a semicircle of grain patches lateral and caudal to the central nucleus. This region received somesthetic afferents from the dorsal column nuclei and from spinal segments at various levels. In contrast, after high cervical injections, the pericentral portion dorsomedial to the rostral half of the central nucleus was labeled almost exclusively. This area of labeling was distinct from the labeling in the central gray and might be best compared with the intercollicular zone in other species. The superior colliculus received projections predominantly from the high cervical cord; minor projections also arose from lumbar spinal segments and the dorsal column nuclei. The terminal field covered roughly the caudal half of the colliculus and involved the stratum griseum intermediale in a patch-like fashion. Some labeling was also found in the stratum griseum profundum and in the stratum griseum superficiale. Other than in the colliculi, weak pretectal projections were observed following dorsal column nuclear injections, while the nucleus of Darkschewitsch was labeled best following lumbosacral injections. All mesencephalic target areas were labeled consistently on the contralateral side, while their ipsilateral side was involved to a varying degree: The relatively most prominent ipsilateral labeling was seen in the central gray, being roughly similar on both sides; scarcely any labeling was noted in the ipsilateral superior colliculus. Tectal injections of retrograde tracer, in addition, revealed a considerable number of labeled neurons in a relatively cell-poor region immediately ventral to the high cervial dorsal horn. This region might correspond to the lateral cervical nucleus, an aggregation of neurons that so far has only been demonstrated in higher mammals.     

The synaptic distribution of the retinal input in the superficial layers of the guinea-pig superior colliculus

An evoked potential consisting of four postsynaptic components was recorded in the guinea-pig superior colliculus following electrical stimulation of the contralateral optic nerve. This potential was generated in response to the activation of four populations of optic nerve fibres with different conduction velocities. Current source-density analysis revealed that the two slower conducting fibre populations synapse in the upper third of the stratum griseum superficiale on dendrites whose cell bodies appear to be found in the lower part of this layer and in the stratum opticum. The two faster conducting populations synapse deeper, near the border of the stratum griseum superficiale and stratum opticum, on neurons with cell bodies that may lie towards the upper part of the stratum griseum superficiale. The locations of these postsynaptic sites correspond to the layers in which the optic nerve terminates as revealed by neuroanatomical tracing techniques. Furthermore, neurons of the shape and orientation predicted by the current source-density analysis were found in the superficial layers by using the Golgi-Cox technique.     

A crossed projection from the optic tectum to craniocervical premotor areas in the brainstem reticular formation. An anterograde and retrograde tracing study in the mallard (Anas platyrhynchos L.)

The optic tectum in birds receives visual information from the contralateral retina. This information is passed through to other brain areas via the deep layers of the optic tectum. In the present study the crossed tectobulbar pathway is described in detail. This pathway forms the connection between the optic tectum and the premotor area of craniocervical muscles in the contralateral paramedian reticular formation. It originates predominantly from neurons in the ventromedial part of stratum griseum centrale and to a lesser extent from stratum album centrale. The fibers leave the tectum as a horizontal fiber bundle, and cross the midline through the caudal radix oculomotorius and rostral nucleus oculomotorius. On the contralateral side fibers turn to ventral and descend caudally in the contralateral paramedian reticular formation to the level of the obex. Labeled terminals are found in the ipsilateral medial mesencephalic reticular formation lateral to the radix and motor nucleus of the oculomotor nerve, and in the contralateral paramedian reticular formation, along the descending tract. Neurons in the medial mesencephalic reticular formation in turn project to the paramedian reticular formation. Through the crossed tectobulbar pathway visual information can influence the activity of craniocervical muscles via reticular premotor neurons.     

Retinal projections in the catfish,Mystus vittatus (Bloch) as revealed by tracer studies with horseradish peroxidase

Summary The retinal efferents of the catfish, Mystus vittatus, were investigated with the use of the horseradish peroxidase (HRP) technique. Most retinal fibres extended contralateral to the eye that had received HRP label, while a few fascicles projected to the ipsilateral side without decussation in the optic chiasma. The contralateral fibres projected to the suprachiasmatic nucleus, the nucleus opticus dorsolateralis, the nucleus of the posterior commissure, the nucleus geniculatus lateralis, pretectal nuclear complex, and to two layers of the optic tectum, i.e., stratum fibrosum et griseum superficiale and stratum griseum centrale. The accessory optic tract arose from the inner area of the optic tract and extended ventromedially to the accessory optic nucleus. The ipsilateral fascicles projected to almost all the above mentioned nuclei, but these projections were comparatively sparse. The ipsilateral retinal projection was restricted to the rostral tectum.     

Neuronal and synaptic organization in the gravity receptor system of the statocyst of Octopus vulgaris

Summary The optic tectum of Calamoichthys calabaricus (Polypteriformes) shows a relatively complex vertical stratification, with six main layers and a varied neuronal typology. In particular, pyriform neurons in the well developed stratum griseum periventriculare and some multipolar neurons in the stratum griseum profundum represent the efferent elements of the tectum, while the optic and lemniscal inputs to the tectum converge in the plexiform sublayers of the stratum fibrosum et griseum superficiale. In the circuitry of the tectum some modulation is achieved by some of the polymorphic cells of the stratum griseum internum and by the horizontal cells of the outer layers. Notwithstanding some differences with respect to the teleost optic lobe (i.e., the absence of a torus longitudinalis; the lack of a stratum fibrosum marginale; the modest size of the stratum fibrosum profundum; the paucity of neurons in the stratum fibrosum et griseum superficiale; and the ill-defined separation of the layers of the afferent and efferent fibers), the optic tectum of Calamoichthys resembles the mesotectal type characteristic of teleosts, anurans and reptiles. It exhibits higher degree of organization than the optic tectum of the Chondrostei.     

Projections of the optic tectum and the mesencephalic nucleus of the trigeminal nerve in the tegu lizard (Tupinambis nigropunctatus)

Summary Fibers undergoing Wallerian degeneration following tectal lesions were demonstrated with the Nauta and Fink-Heimer methods and traced to their termination. Four of the five distinct fiber paths originating in the optic tectum appear related to vision, while one is related to the mesencephalic nucleus of the trigeminus. The latter component of the tectal efferents distributes fibers to 1) the main sensory nucleus of the trigeminus, 2) the motor nucleus of the trigeminus, 3) the nucleus of tractus solitarius, and 4) the intermediate gray of the cervical spinal cord.The principal ascending bundle projects to the nucleus rotundus, three components of the ventral geniculate nucleus and the nucleus ventromedialis anterior ipsilaterally, before it crosses in the supraoptic commissure and terminates in the contralateral nucleus rotundus, ventral geniculate nucleus and a hitherto unnamed region dorsal to the nucleus of the posterior accessory optic tract.Fibers leaving the tectum dorso-medially terminate in the posterodorsal nucleus ipsilaterally and the stratum griseum periventriculare of the contralateral tectum. The descending fiber paths terminate in medial reticular cell groups and the rostral spinal cord contralaterally and in the torus and the lateral reticular regions ipsilaterally. The ipsilateral fascicle also issues fibers to the magnocellular nucleus isthmi.     

Interactions between tectal radial cells in the red-eared turtle, Pseudemys scripta elegans: an analysis of tectal modules.

The optic tectum is a major subdivision of the visual system in reptiles. Previous studies have characterized the laminar pattern, the neuronal populations, and the afferent and efferent connections of the optic tectum in a variety of reptiles. However, little is known about the interactions that occur between neurons within the tectum. This study describes two kinds of interactions that occur between one major class of neurons, the radial cells, in the optic tectum of Pseudemys using Nissl, Golgi and electron microscopic preparations. Radial cells have somata which bear long, radially oriented apical dendrites from their upper poles and short, basal dendrites from their lower poles. They are divided into two populations on the basis of the distribution of their somata in the tectum. Deep radial cells have somata densely packed in the stratum griseum periventriculare. Their plasma membranes form casual appositions. Middle radial cells have somata scattered throughout the stratum griseum centrale and stratum fibrosum et griseum superficiale and do not contact each other. The apical dendrites of both populations of radial cells participate in vertically oriented, dendritic bundles. The plasma membranes of the dendrites in these bundles form casual appositions in the deeper tectal layers and chemical, dendrodenritic synapses within the stratum fibrosum et griseum superficiale. The synapses have clear, round synaptic vesicles and slightly asymmetric membrane densities. Thus, radial cells interact via both casual appositions and chemical synapses. These interactions suggest that radial cells may form a basic framework in the tectum. Because both populations of radial cells extend into the stratum fibrosum et griseum superficiale and stratum opticum, they may receive input from some of the same tectal afferent systems. Because the deep radial cells alone have somata and dendrites in the deep tectal layers, they may receive additional inputs that the middle radial cells do not. Neurons in the two populations interact via chemical dendrodentritic synapses, thereby forming vertically oriented modules in the tectum.     

Retinal projections in the chain pickerel (Esox niger Lesueur)

Summary The retinal projections inEsox niger, as determined with the aid of a modified cobalt-lysine method, are considerably more extensive in the diencephalon and pretectum than in other teleost fishes so far examined. Although most retinal axons terminate contralaterally, rare fibers can be traced to the same aggregates ipsilaterally. The retinohypothalamic projection appears larger than hitherto reported in teleosts, and the dorsomedial optic tract issues fibers to a series of cell clusters extending from the rostral thalamus to mid-torus levels. A retinal projection to a presumed ventrolateral optic nucleus (VLO) is described for the first time in a teleost. Other targets of retinal fibers include the nucleus geniculatus lateralis ipse of Meader (GLI), the pretectal nucleus (P), the cortical nucleus and a well-developed ventromedial optic nucleus (VMO). The projection to the optic tectum is principally to the stratum fibrosum et griseum superficiale (SFGS) and stratum marginale (SM), but a considerable number of axons also course through the stratum album centrale (SAC) before terminating there or piercing the stratum griseum centrale (SGC) and terminating in SFGS. Rare terminal arborizations of retinal fibers were also observed in stratum griseum centrale (SGS) and in the stratum griseum periventriculare (SGC) in restricted portions of the tectum. Because of the relatively large size of the visual structures inE. niger it is a potentially useful model for future experimental studies on the visual system.     

Distribution of glycogen phosphorylase and cytochrome oxidase in the central nervous system of the turtle Trachemys dorbigni

Glycogen phosphorylase (GP) and cytochrome oxidase (CO) activities were mapped histochemically in the brain of the turtle Trachemys dorbigni. In the telencephalon, both activities occurred in the olfactory bulb, in all cortical areas, in the dorsal ventricular ridge, striatum, primordium hippocampi and olfactory tubercle. In the diencephalon, they were identified in some areas of the hypothalamus, and in rotundus and geniculate nuclei. Both reactions were detected in the oculomotor, trochlear, mesencephalic trigeminal nuclei, the nucleus of the posterior commissure, torus semicircularis, substantia nigra and ruber and isthmic nuclei of the mesencephalon. In all layers of the optic tectum GP activity was found, but CO only labelled the stratum griseum centrale. In the medulla oblonga both enzymes appear in the reticular, raphe and vestibular nuclei, locus coeruleus and nuclei of cranial nerves. In the cerebellum, the granular and molecular layers, and the deep cerebellar nuclei were positive for both enzymes. The Purkinje cells were only reactive for CO. In the spinal cord, motor and commissural neurones exhibited a positive reaction for the two enzymes. However, CO also occurred in the marginal nucleus and in the lateral funiculus. These results may be useful as a basis for subsequent studies on turtle brain metabolism.     

Vascularization of the telencephalic choroid plexus of a ganoid fish [Acipenser ruthenus (L.)

The vascularization of the telencephalic choroid plexus of the sterlet Acipenser ruthenus, a ganoid fish, was examined by vascular corrosion casting and by light and transmission electron microscopy. The arterial supply is from the dorsal mesencephalic artery via: 1) the ventral choroidal arteries (left and right); 2) the dorsal choroidal arteries (left and right); 3) the caudal choroidal arteries (left and right); 4) the ventral arteries of the dorsal sac; and, from the olfactory arteries, via 5) the rostral choroidal arteries. The venous drainage is mainly through a single main choroidal vein that can take various courses either directly to the anterior cardinal vein or via the middle cerebral vein to the anterior cardinal vein. To a lesser extent, the plexus is drained via the lateral telencephalic veins and the ventral vein of the dorsal sac to the middle cerebral vein. By angioarchitecture and form, the plexus can be subdivided into five distinct parts: the surface network, the median folds, the large lateral folds, the small lateral folds, and the area common to the bottom of the dorsal sac and the telencephalic plexus. Diameters of terminal vessels as measured from vascular corrosion casts and from paraplast, semithin, and ultrathin sections were never less than 10 micron. It is suggested that the different areas in one plexus may have different functions with respect to secretion and absorption of cerebrospinal fluid.     

Distributions of choline acetyltransferase and acetylcholinesterase activities in layers of rat superior colliculus

Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities were assayed in samples dissected from sagittal sections through rat superior colliculus. The magnitude of ChAT activity was about half to equal that found in rat whole brain in all layers except stratum griseum intermediale, where the average activity was higher than whole brain. AChE activity was three to four times that found in rat whole brain in superficial layers and about the same as average brain in deeper layers, except in the statum griseum intermediale, where the average activity was about twice whole brain. Rostral-caudal gradients in both ChAT and AChE activities occurred in stratum griseum intermediale, with activities in the caudal region of some animals as high as four times those in the rostral. ChAT activity in samples associated with locations of patches or spots of AChE staining product in stratum griseum intermediale was significantly higher than in samples from "nonpatch" regions. Results are discussed relative to inputs into the colliculus, whose terminations may correlate in location with the distributions of the enzyme activities.     

Glutamate-like immunoreactivity in chick cerebellum and optic tectum

Glutamate was coupled via glutaraldehyde to bovine serum albumin. The conjugate was used for raising specific anti-glutamate antibodies. The purified antibody was used for immunostaining of chick cerebellum and optic tectum. Staining was intense in the molecular layer and in cell bodies of the granule cell layer. In the optic tectum a diffuse staining was detected in the superficial layers of stratum griseum fibrosum superficiale and in cell bodies especially in the layers a and e. Large cell bodies located in the stratum griseum centrale were also stained.     

Neurons with complex receptive fields in the stratum griseum centrale of the zebra finch (Taeniopygia guttata castanotis Gould) optic tectum

The electrophysiological and morphological features of visually driven neurons of the stratum griseum centrale of the zebra finch optic tectum were studied by extracellular recording and staining techniques. Stratum griseum centrale neuron responses are sustained in most cases. Receptive fields are big, up to 150 degrees of the visual field. The excitatory center (hot spot) varies in size from 1 degrees to 15 degrees. It can be mapped by small static stimuli, adapts slower than the surround, and has a shape comparable to the excitatory fields of upper-layer neurons. In contrast, the big surround shows responses only to small moving objects which elicit a typical pattern of alternating bursts and silent periods. Alternatively, the same stimuli elicit long-lasting bursts followed by strong adaption. Anatomically, stratum griseum centrale neurons are characterized by far reaching dendrites which terminate with "bottlebrush"-like endings in the upper retinorecipient layers. In addition, they are connected with retinorecipient structures by an interneuron located between layers 10 and 11. The role of the structure of inputs for the organization of the receptive fields is discussed.     

Distribution of MAP1A,MAP1B,and MAP2A&;B during layer formation in the optic tectum of developing chick embryos

The expression patterns of three microtubule-associated proteins (MAP1A, MAP1B, and MAP2A&B) were investigated in the developing optic tectum. Expression of MAP1B and middle-molecular-weight peptide of neurofilament (NF-M) was first observed in the same mesencephalic cells on day 3 of incubation, indicating that neuroblasts had been produced. At day 5, MAP1A and MAP2A&B expression appeared in the cellular layer containing the first neuroblasts that differentiate into large multipolar cells. The NF-M⁺ neurites in the striatum album centrale (SAC) and the striatum opticum (SO) were MAP1B⁺ up to day 19, but the intensity of MAP1B immunoreactivity decreased with development. All three MAPs were expressed in large multipolar neurons in the developing stratum griseum centrale from the beginning of maturation. Stratum griseum et fibrosum centrale cellular layers, containing radially arranged piriform neurons, were MAP1A^–/MAP2A&B^– on day 11 but became MAP1A⁺/MAP2A&B⁺ during later stages. These results suggest that the timing of MAP expression in neuronal maturation of large multipolar cells differs from that of piriform cells. The expression of MAPs has revealed specific cellular events in the developing optic tectum. Based on our observations, the development of the optic tectum can be divided into four periods.     

The lateral forearm flap as a modification of the lateral arm flap: vascular anatomy and clinical implications

The forearm extension of the lateral arm flap was introduced on the basis of the vascular territory of the posterior radial collateral artery extending beyond the elbow into the forearm. However, there is controversy as to whether the posterior radial collateral artery extends as a single trunk below the elbow or if it terminates more proximally with only a rich vascular plexus extending beyond the elbow. The purpose of this study was to revisit the artery's anatomy in the region of the elbow and to study its distribution in the forearm. Using latex and barium-gelatin injections of the posterior radial collateral artery in ten cadaveric upper limbs, it was observed that terminal branching of the artery occurred 4.5 cm proximal to the lateral epicondyle of the humerus. Distal to the epicondyle, the terminal branches of the posterior radial collateral artery were seen to fan out as finely arborized branches supplying the lateral forearm skin. No single, constant vascular trunk to the forearm skin could be identified. Furthermore, in its distribution toward the periphery, the terminal branches of the posterior radial collateral artery took an increasingly superficial course. Proximal to the epicondyle, the vessels lay deep within the subcutaneous fat, whereas distal to the epicondyle, they were very close to skin. These findings suggest that lateral forearm skin cannot be islanded without risk of vascular disruption and that the distally sited flap should include skin proximal to the epicondyle for safety.     

Presynaptic dendrite cells and two other classes of neurons in the superficial layers of the superior colliculus of the chimpanzee

In the superior colliculus of chimpanzee, three classes of neurons can be identified by ultrastructural criteria. They are 1) marginal cells located in the stratum zonale, 2) collicular relay cells in the stratum griseum superficiale and 3) presynaptic dendrite (PSD) cells, i.e., neurons with presynaptic specializations in soma and/or dendrites. PSD cells are the smallest neurons in the stratum griseum superficiale; they have a relatively large, deeply infolded nucleus and a small rim of cytoplasm rich in free ribosomes. PSD cells are sufficiently different from the two other classes of neurons to be reliably identified at the ultrastructural level. They closely resemble presynaptic neurons as described in the lateral geniculate nucleus of other mammalian species. Presynaptic dendrites in continuity with PSD cells are rich in organelles, especially ribosomal cluster, and establish en passage contact with other dendrites. Another type of presynaptic dendrite, poor in organelles, except for bundles of microtubules, could not be traced back to its parent neuron. Homo- or heterogeneity of PSD cells is discussed. No amxon was traced from a PSD cell.     

The role of the cardiac-pulmonary blood volume in the changes in left ventricle output during stimulation of the afferent fibers of somatic nerves

Stimulation of tibial nerve afferent fibers has revealed heterogeneous shifts of left ventricular output, as well as pulmonary artery and posterior vena cava blood flow in anesthetized cats. Uniform changes in left ventricular output and pulmonary artery blood flow were noted in the majority of cases, with venous return most often exceeding pulmonary artery blood flow. beta-adrenoreceptor blockade failed to influence changes in pulmonary artery blood flow. It is concluded that the increase in pulmonary artery blood flow depends on the rise in venous return, but not on neurogenic influence upon the right ventricle. The reduction in left ventricular output is the result of decreased right ventricular outflow due to its overload caused by pulmonary vasoconstriction.     

Die Vaskularisation der Kiemen von Myxine glutinosa L. (Cyclostomata)

The angioarchitecture of the gills in Myxine glutinosa L. was studied by scanning electron microscopy of vascular corrosion casts (methylmethacrylate). It was found that the afferent branchial artery may be connected to the sinus peribranchialis by a papilla. The sinus is connected to delicate vessels and sinuses, which are interposed between meridionally arranged radial arteries. These delicate vascular formations continue into the interior of the gill and form a plexus on both poles of the gill folds. Light and scanning electron microscopical studies on the vascular endothelium of the afferent vessels of the gill lamellae reveal rounded endothelial cells, which are characterized by a high content of granula, by long cellular processes and by bridge-formations towards neighbouring cells. Supporting columns within the vascular system of the lamellae were found to be set up by several spirally arranged cells. SEM observations reveal goblet cells and numerous superficial epithelial cells with various numbers of microvilli and microridges forming the epithelial surface of the gill folds.