bluuebunny/crossref_metadata_2025 huggingface dataset:
The vestibular complex of the american opossum, Didelphis virginiana. I. Conformation, cytoarchitectur and primary vestibular input
Authors: Henkel C. K. , Martin G. F.
Published: December 2004

Degeneration experiments reveal that the vestibular nerve of the adult opossum distributes to an extensive and diverse area of the brainstem and, as in placental mammals, the traditionally named nuclei do not receive a uniform distribution of primary afferent fibers. Nevertheless, such nuclei as well as other nearby cell groups have been considered as vestibular since they share other mutual connections. Except for subgroups. “1”, “g” and the nucleus suprvestibularis all of the vestibular subdivisions generally recognized in more specialized placentals (e.g., the cat) have been identified in the marsupial opossum.

Each of the vestibular nuclei and “extra‐nuclear” cell stations are described as to their boundaries, cytoarchitecture and dendritic domain. Whenever possible we have employed a terminology consistent with that used for the cat. In several instances we have used results from experimental degeneration material to identify nuclear boundaries and divisions which are not apparnt in routine Nissl, Golgi or silver preparations.
Projections from the amygdaloid complex to the cerebral cortex and thalamus in the rat and cat
Authors: Krettek J. E. , Price J. L.
Published: December 2004

Projections asre described from the basolateral, lateral and anterior cortical nuclei of the amygdaloid complex, and from the prepiriform cortex, to several discrete areas of the cerebral cortex in the rat and cat and to th mediodorsasl thalamic nucleus in the rat. These projections are very well‐defined in their origin, and in their area and laminar pattern of termination.

The basolateral amygdaloid nucleus can be divided into anterior and posterior divisions, based on cytoarchitectonic and connectional distinctions. In both the rat and cat the posterior division projects to the prelimbic area (area32) and the infralimbic area (area 25) on the medial surface of the hemisphere. The anterior division projects more lightly to these areas, but also sends fibers to the dorsal and posterior agrangular insular areas and the perirhinal area on the lateral surface. Furtheremore, in the cat the perirhinal area is divided into two areas(area 35 and 36) and the anterior division projects to both of these and also to a ventral part of the grangular insular area; this last area is adjacent to, but separate from the auditory insular area and the second cortical taste area. In most of these areas, the fibers from the basolateral nucleus terminate predominantly in two bands: one in the deep part of layer I and layer II, and a heavier band in layer V (in the rat) or layers V and VI (in the cat).

The lateral amygdaloid nucleus projects heavily to the perirhinal area, and also to the posterior agranular insular area. These fibers terminate predominantly in the midle layers of the cortex, although the cellular lamination in these two areas is relatively indistinct. The anterior cortical amygdaloid nucleus and the prepiriform cortex both project to th infralimbic area and the ventral agranular insular area, and the anterior cortical nucleus also projects to the posterior agranular area and the perirhinal area. In all of these areas, the fibers from these olfactory‐relasted structures terminate in the middle of layer I.

In the rat, the two divisions of the basolateral nucleus also project to the medial segment of the mediodorsasl thalamic nucleus, with the anterior division projecting mainly to the posterior part of this segment and the posterior division to the anterior part. The endopiriform nucleus, deep to the prepiriform cortex, projects to the central segment of the mediodorsasl nucleus, since little or no projection could be demonstrated from the prepiriform cortex itself. Projections to the mediodorsal nucleus have not been found in the cat.
Unmyelinated and small myelinated axons in rat ventral roots
Authors: Coggeshall Richard E. , Emery Dennis G. , Ito Haruhide , Maynard Christine W.
Published: December 2004

The present study is an analysis of the ventral roots in the rat. The smallest myelinated fibers are found in segments T1‐L2 and L6‐S1. These fibers are regarded as preganglionic efferents and the L6‐S1 outflow is more cranial than the sacral parasympathetic outflow in other animals. Large numbers of unmyelinated axons are seen in segments T1‐L2 and L6‐S1, the same segments that contain the smallest myelinated fibers. This data will be used as a baseline for determining the functional categories of the unmyelinated axons.
Retinotectal projection of the adult winter flounder (Pseudopleuronectes americanus)
Authors: Luckenbill‐Edds L. , Sharma S. C.
Published: December 2004

The winter flounder shifts the orientation of its body 900 at metamorphosis so that its left side is functionally ventral and its right side functionally dorsal. Concomitantly the left eye migrates onto the right side. The net result of these complex metamorphic changes is that the dorsoventral axes of the visual fields are perpendicular to the body rather than parallel as in most other teleosts. The developing faltfish may provide a resource for studying the formation of neural connections, for the change in orientation may necessitate some shift in connections in visumotor pathways. As a baseline for developmental studies, we have established the retinotectal projection in adult winter flounder by means of anatomical tracing techniques (autoradiography and degeneration staining) and electrophysiological mapping techniques. The histological pattern of retinal afferents to the tectum is similar to that of other teleosts; afferents are confined to the superficial white and gray zone, with a few fibers coursing in the deep white zone. Electrophysiological mapping shows that the visuotectal projection is complete over the entire extent of the tectum, symmetrical for right and left fields and patterned normally.
Descending inputs to octopus cell area of the cat cochlear nucleus: An electron microscopic study
Authors: Kane Eileen S.
Published: December 2004

Large, unilateral lesions of the superior olivary complex (SOC) were made in 18 adult cats. Terminal degeneration was studied electron microscopically in the octopus cell area (OCA) of the caudal cochlear nuclei both ipsilateral and contralateral to lesions, after 1 to 14 postoperative days. Three synaptic types (OCA types 1, 2, and 3) have been previously described upon octopus cell somas and dendrites and types 1 and 2 identified as cochlear in origin. The present study shows a new synasptic ending (OCA type 4) on small octopus cell dendrites as well as dendrodentritic contacts. Following SOC ablations, type 4 endings degenerated in the OCA ipsilateral to the lesion. In the OCA contralateral to the same lesion, however, degeneration was found in type 3 terminals ending upon more proximal octopus cell dendrites and upon somas. Ipsilateral terminal degeneration occured between two and four postoperative days, was rere by seven days, and was gone by 14 days after these lesions. However, contralateral terminal degenaration was rare until four days, was most abundant after seven days, and was still present after 14 postoperative days. The different synaptic types and time courses of degeneration in the ipsilateral versus the contralateral OCA, suggested that type 4 endings originate from an ipsilateral source, ssuch as the lesioned periolivary region, while type 3 endings originate either from the contralateral SOC or from higher contralateral nuclei. Other evidence for these sources and possible functions of these descending inputs asre briefly discussed.
The organization of the pulvinar in the grey squirrel (Sciurus carolinensis). II. Synaptic organization and comparisons with the dorsal lateral geniculate nucleus
Authors: Robson J. A. , Hall W. C.
Published: December 2004

The purpose of these experiments was to compare the synaptic organization of the subdivisions of the pulvinar defined in the preceding paper (Robson and Hall, '77) with each other and with the organization present in the dorsal lateral geniculate nucleus. The electron microscope was used to analyze normal synaptic arrangements and degenerating axonal terminals resulting from lesions. The dorsal lateral geniculate nucleus in the grey squirrel contains synaptic clusters similar to those described previously for other species. These clusters are characterized by large optic tract terminals which form multiple contacts onto large dendritic processes and other processes containing flat or pleomorphic vesicles. The geniculate lamina adjacent to the optic tract receives projections from the superior colliculus as well are from the retina. The terminals of the superior colliculus axons are small and medium sized and lie outside of the synaptic clusters. The retinal terminals are in the clusters. In the pulvinar, the rostro‐medial subdivision contains synaptic clusters which resemble those in the lateral geniculate nucleus. These clusters contain large axon terminals which make multiple contacts onto large dendrites. However, these terminals are not contributed by an ascending sensory pathway but by axons from strait cortex. The rostro‐lateral and caudal subdivisions of the pulvinar also contain synaptic clusters, but these clusters consist of a segment of a large dendrite which is ensheathed by medium‐sized terminals. Since only a few of these medium sized terminals in any one cluster degenerate after tectal lesions, and none degenerate after cortical lesions, it is suggested that the morphological arrangement of these clusters may permit the convergence of axons from several sources, some of which are unidentified, onto the same dendritic segment.
Corticocortical fiber connections of the rabbit visual cortex: A fiber degeneration study
Authors: Towns Lex C. , Giolli Roland A. , Haste David A.
Published: December 2004

Corticocortical fiber projections of the striate and occipital cortex of the rabbit, as defined by Rose ('31) have been determined by fiber degeneration methods following the production of cortical lesions within each of 24 rabbits. We have assumed that the striate and occipital cortices correspond respectively to the visual cortical areas 1 and 2 (V1 and V2) which have been demarcated electrophysiologically by Thornpson et al. ('50).

A study of the ipsilateral fiber projections of the striate and occipital cortex of the rabbit reveals three distinct sets of associational corticocortical connections.(1) Neurons located in layers I‐III of all regions of the striate cortex and the occipital cortex send fibers to terminate predominantly in layer V, but also in layers IV and VI, immediately beneath the cells of origin; however, the cells in the supragranular layers have not been found to send fibers to any other region of cerebral cortex. (2) The binocular portions of V1 and V2 appear to be interconnected ipsilaterally since cells in layers IV‐VI of the lateral striate cortex have been shown to project to all layers of a restricted, adjacent portion of the medial occipital cortex; and the cells in layers TV‐VIof medial occipital cortex send a similar, restricted projection to the adjacent lateral striate cortex. (3) Nerve cells in layers IV‐VI of the lateral striate cortex (binocular Vl) send a restricted projection to the lateral portion of the occipital cortex. (4) After all lesions of the striate and/ or occipital cortices, degenerating fibers are seen radiating away from the lesion in layer I; the origin of these degenerating fibers could not be determined.

The following observations have been made concerning the origins and terminations of commissural corticorticalfihers. (1) After ablation of most of the visual cortex of one side, commissural fibcrs are secn to terminate in all cortical layers in two narrow bands of visual cortex: one band occupies both sides of the striate‐occipital boundary; the second band is found in the lateral portion of occipital cortex. (2) More punctate lesions reveal that commissural fibers arise from layers IV‐VI of the lateral striate cortex and medial occipital cortex (binocular portions of V1 and V2 respectively) and end in hornotopic areas of the contralateral cortex.
The organization of thalamocortical relay neurons in the rat ventrobasal complex studied by the retrograde transport of horseradish peroxidase
Authors: Saporta Samuel , Kruger Lawrence
Published: December 2004

The organization of thalamocortical relay neurons in the thalamic ventrobasal complex (VB) of the rat was investigated by the use of the retrograde axonal transport of horseradish peroxidase (HRP). Injections of HRP into somatosensory cortex (SI) resulted in a distinctive gradient of neuronal and non‐neuronal HRP reaction product. Electrophysiologically characterized points of SI injected with small volumes of HRP labeled a sector of neurons in VB ipsilateral to the injection. This zone of labeled neurons consisted of a complex curvilinear array or lamina with a rostral hollow or solid expansion of densely packed HRP positive neurons which continues caudally as a less dense tapering wing. Despite this complex arrangement, an approximate pattern of somatotopy was determined indicating the direction of shifts in peripheral receptive fields moving in any axis of VB. The number of labeled neurons projecting upon a point in SI was also determined. Injections of the cortical vibrissae, face and forepaw representations labeled a greater number of neurons in VB per unit area of cortex than did injections in the hindlimb or body representations. The total number of HRP positive neurons in VB increased proportionately with areal increase of the HRP injections into overlapping cortical representations. The number of HRP positive neurons in the rostral half of the laminae increased almost linearly with the area of injection, while the number of HRP positive neurons in the caudal half of the laminae showed relatively smaller increases.
The ultrastructure of a cerebellar analogue in octopus
Authors: Woodhams P. L.
Published: December 2004

The peduncle lobe of Octopus, a centre concerned with regulating motor behaviour primarily on the basis of visual cues, though it also receives a “labyrinthine” or statocyst input, has been examined for the first time in the electron microsope. In the lower part of the lobe, the basal zone, there are large “motor” cells up to 20 μm across with a rounded, pale nucleus and a large perikaryon; there are also smaller cells, 4‐10 μm in diameter with a dark irregularly‐shaped nucleus. The latter receive synapses from afferent fibres to the lobe, and those from the principal afferent source, the ipsilateral optic lobe, have been characterised as large terminals with many small clear vesicles. Other optico‐peduncular afferents and the small‐cell fibres themselves run directly up to the second part of the lobe, the peduncle spine, which contains exclusively small granular cells about 5 μm in diameter. The fibres of these spine cells form a conspicuous and characteristic array of parallel fibres in the neuropil and they bear a striking resemblance to those of vertebrate cerebellar granule cells: serial synaptic relays are present along their length. These findings, together with earlier evidence about the effects on motor behaviour of lesions to the lobe, suggest a close functional and morphological analogy to a folium of the vertebrate cerebellum. The hypothesis is discussed that parallel fibres, with their narrow diameter and hence long conduction time, are an essential feature of fine motor control systems, and that their primary function is one of providing critical time delays in the millisecond range.
Direct and indirect preoculomotor pathways of the brainstem: An autoradiographic study of the pontine reticular formation in the cat
Authors: Graybiel Ann M.
Published: December 2004

The efferent connections of the paramedian pontine reticular formation have been studied in the cat in autoradiographic experiments designed to analyze direct and indirect preoculomotor pathways. Injections of tritium‐labelled amino acids were placed (1) near the border between the oral and caudal subdivisions of the nucleus pontis centralis, (2) in more rostral and dorsal parts of the pontine tegmentum, (3) at the pontomesencephalic border, and (4) at the pontomedullary border.

Tegmental injections of the first group were unique in labelling a direct ipsilateral pathway to the abducens nucleus and nucleus prepositus hypoglossi. More rostral injections failed to produce discrete labelling of the nuclei of the extraocular muscles but labelled nearby tegmentum and central gray substance. Caudal deposits, involving the pontomedullary reticular formation at its junction with the abducens, perihypoglossal and vestibular nuclei, labelled a decussating fiber system reaching the contralateral abducens nucleus, nucleus prepositus hypoglossi and parts of the vestibular complex. In a single additional case, an injection placed in the oculomotor complex produced heavy labelling of the abducens nuclei.

All tegmental injections labelled discrete reticulo‐reticular and other variably complex longitudinal pathways. Most injections of (a) the pontomedullary and (b) the pontomesencephalic zones elicited labelling of the pretectum including the nucleus of the optic tract. An incidental finding in the latter group was dense labelling of the pars compacta of the substantia nigra, subthalamic nucleus, and (1 case) entopeduncular nucleus; in one case of each of these groups, labelled fibers were traced to the external pallidum.

These observations suggest that, with respect to its efferent oculomotor affiliations, the paramedian pontine tegmentum may be divided into compartments whose supranuclear connections are distinct but for the most part heavily weighted toward influencing the abducens nucleus and periabducens region. Considered within the framework of behavioral and physiological studies of the so‐called pontine gaze center, and studies of pontine afferents, the findings are interpreted as suggesting a functional differentiation of these tegmental zones with respect to their influence on eye‐head coordination.
A comparison of the early development of axodendritic and axosomatic synapses upon embryonic mouse spinal motor neurons
Authors: Vaughn James E. , Sims Terry , Nakashima Mariko
Published: December 2004

The early embryonic development of axodendritic and axosomatic synapses upon motor neurons has been investigated in mouse spinal cord. This investigation had two main objectives: (a) to determine the earliest embryonic day on which recognizable synaptic contacts occur upon motor neurons, and (b) to compare the development of synaptic contacts upon the dendrites and somata of motor neurons during the early synaptogenic period. The broad goal of this investigation was to determine whether the location of early‐forming synapses upon motor neurons is consistent with the possibility that axosomatic synapses might be involved in the primary induction of motor neuronal dendrogenesis.

Embryonic day 11 (E11) was the earliest developmental time at which synaptic contacts were observed in developing mouse spinal cord. All of these synaptic contacts appeared to be located upon motor neuronal dendrites within the lateral and ventral marginal zones. The number of synaptic contacts observed on E11 was too small to be detected by the quantitative sampling procedure used in this investigation, but the procedure was sufficiently sensitive to detect synaptic contacts on embryonic day 12. Both axodendritic and axosomatic synapses were found upon E12 motor neurons, but there were about four times as many synaptic contacts per unit length of dendritic membrane as there were per equivalent length of somal membrane. Furthermore, dendritic membranes continued to exhibit a higher density of synaptic contacts on all of the remaining embryonic days (i.e., 13–16) examined in this investigation. These quantitative data and the E11 observations indicate that axosomatic synaptic contacts are not a necessary prelude to the formation of motor neuronal dendrites. Therefore, it is suggested that axosomatic synapses do not play an obligatory role in the primary induction of motor neuronal dendrogenesis.

The experimental findings of other investigators, however, have provided reasons to suspect that early‐forming axosomatic synapses may somehow facilitate dendritic development once it has been induced. This possibility is discussed in terms of our observation that early‐forming axosomatic synapses rather commonly occur at sites which may represent somal growth regions. This relationship leads us to suggest that early axosomatic synapses may facilitate dendritic development by signalling the motor somata that the formation of a synaptogenic axonal field is underway. Furthermore, we speculate that the positioning of early axosomatic contacts might be providing directive cues as to the location of the developing synaptogenic field. Thus a directive facilitation of dendritic growth is suggested as a function of early axosomatic synapses rather than one involved with the primary induction of dendrogenesis.
Time dependence of terminal degeneration in spino‐cerebellar mossy fiber rosettes in the chicken and the application of terminal degeneration in successive degeneration experiments
Authors: Vielvoye G. J. , Voogd J.
Published: December 2004

Mossy fiber rosettes in the granular layer of the cerebellar cortex were studied after sections of the lateral funculus of the spinal cord of the chicken and silver impregnation with the Fink‐Heimer ('67) method I. After a survival time of two or three days two types of degenerated rosettes were found. The first type is characterized by digitiform protrusions, the second type of rosette is spherical. Both types are covered by small argyrophilic particles which disappear when the degeneration proceeds. With longer survival times the rosettes become swollen and finally desintergrate and loss their argyrophilia. After a survival time of 30 days only debris of rosettes can be found.

These observations were used to determine the cerebellar cortical projection of mossy fibers originating from segments of the spinal cord isolated in “successive degeneration” experiments consisting of a chronic cordotomy followed by an acute cordotomy rostral to the first one.
Extraocular muscle representation in the brainstem of the carp
Authors: Luiten P. G. M. , Dijkstra‐de Vlieger H. P.
Published: December 2004

The representation of the extraocular muscles in the oculomotor nuclei in the brainstem of the carp was studied with the horseradish peroxidase technique. Some normal anatomical features of the various oculomotor nuclei are described. Following intramuscular HRP injections in the eye muscles and applying survival times of up to 25 days labeled perikarya were found in the various nuclei of the oculomotor complex. Rectus inferior, rectus internus, and obliquus inferior are represented in the ipsilateral nucleus oculomotorius, while the rectus superior was found to be innervated from the contralateral n III. The efferent cells innervating the obliquus superior are located mainly in the contralateral nucleus trochlearis and for a low percentage in the ipsilateral counterpart of the n IV. The rectus externus is represented in the rostral and caudal subnuclei of the ipsilateral nucleus abducens. These results show a remarkable resemblance with data on mammalian extraocular muscle representation, although the overlap of the various cell populations is larger in fish.
The superior colliculus control of pinna movements in the cat: Possible anatomical connections
Authors: Henkel Craig K. , Edwards Stephen B.
Published: December 2004

Possible anatomical pathways mediating superior colliculus control of pinna movements were determined in the cat using the orthograde autoradiographic tracing method and the retrograde horseradish peroxidase technique. This was done in the following manner. First, the division of the the pinna muscles with HRP and surveying the facial nucleus for retrogradely filled cells. Second, the brainstem regions that project to the facial neucleus were identified using the horseradish peroxidase method. Third, the superior colliculus projections to these areas were studied using the autoradiographic tracing method.

The results suggest that superior colliculus control of pinna movements is mediated entirely by indirect connections with the facial nucleus and that these connections occur mainly in a paralemniscal zone in the lateral midbrain. Of all the brainstem regions shown by the horseradish peroxidase experiments to project to the facial nucleus only this midbrain paralemniscal zone received a projection from the superior colliculus that was dense and overlapped precisely the region containing facial projecting neurons. Further autoradiographic tracing revealed that the facial nucleus was the primary brainstem target of this paralemniscal fibers projecting to the facial nucleus ended in the subdivision that innervates the pinna muscles. Other paralemniscal efferent terminate in the opposite paralemniscal zone. The data suggest that other connections between the superior colliculus and the facial nucleus may occur in the cuneiform nucleus of the midbrain, the region around the oculomotor complex, and the reticular formation dorsal to the superior olive.
Ultrastructural specificity of synaptic sites in nerve terminals mediating both presynaptic and postsynaptic inhibition
Authors: Smith Dean O.
Published: December 2004

The ultrastructural basis of presynaptic inhibition of the excitatory efferent axon innervating the opener muscle of the crayfish walking leg was studied using the electron microscope. The inhibitory efferent axon terminals form axoaxonal synapses onto excitor terminals in very close proximity to sites of excitatory transmitter release. There is no evidence that these synapses are located at regions of low safety factor of action potential conduction in the excitor. In the area of axoaxonal synaptic connections, the inhibitory axon also forms inhibitory neuromuscular junctions on the opener muscle. Synaptic vesicles are clustered in active zones bordered postsynaptically by extensive invaginations, or junctional folds, in the sarcolemma. These results are consistent with the hypothesis that the primary effect of presynaptic inhibition is to shunt depolarization‐secretion coupling at specific sites of transmitter release in the target cell, rather than to block impulse propagation into a more generalized population of nerve terminals distal to the axoaxonal synapse. Further physiological implications of this structural arrangement are considered.
The axonal arborizations of lateral geniculate neurons in the striate cortex of the cat
Authors: Ferster David , Levy Simon
Published: December 2004

Horseradish peroxidase (HRP) was injected into the optic radiations of adult cats. With placements close to the lateral geniculate nucleus (LGN), the enzyme diffused retrogradely along the axons of geniculocortical relay neurons, entered their cell bodies, and, after reaction with diaminobenzidine, produced a Golgi‐like staining of entire neurons. When the injections were made close to the visual cortex, the enzyme diffused anterogradely and filled complete axonal arborizations in area 17.

In the LGN, examples of type 1 and type 2 relay neurons (Guillery, '66) were reconstructed, and their axon diameters measured. The type 1 neurons (thought to correspond to Y‐cells – LeVay and Ferster, '77) possessed large diameter axons (2–3.3 μm), while the type 2 neurons (thought to be X‐cells) had medium‐sized axons (1–1.7 μm). Both types of neurons gave off axon collaterals to the perigeniculate nucleus.

In the cortex, two types of afferent supplied layer IV. One distributed to the upper part of the layer (layer IVab), extending a short distance into layer III. The parent trunks of these axons, measured in the white matter, had diameters matching those of type 1 LGN relay cells. The other type distributed to layer IVc. The diameters of these axons matched those of type 2 LGN relay cells. Most afferents of both types gave off collaterals to layer VI — there were no axons which exclusively innervated this layer.

The axons supplying layer IVab had a wide lateral spread in the cortex (up to 2 mm), and the boutons were grouped into two to five clumps, whose size and arrangement were similar to ocular dominance columns. The axons supplying layer IVc had a much more restricted arborization, usually consisting of a single clump of boutons.

LGN neurons with very fine axons (less than 1 μm) were found in laminae C1–C3. They probably corresponded to Guillery's type 4 neurons. In the cortex, fine‐diameter axons arborized in the upper half of layer I. These axons sometimes had collaterals in the lower part of layer III and in layer V.

Taken together, the arborizations of the cortical afferents observed in the present study account fully for the autoradiographic labelling pattern seen after 3H‐proline injections into the LGN (LeVay and Gilbert, '76).

The identification of type 1 and type 2 neurons as Y‐ and X‐cells is strengthened by the observed difference in their axon diameters, in agreement with the different axonal conduction velocities reported for Y‐ and X‐cells. The presence of cells with very fine axons in the deeper C laminae is consistent with the reported presence of W‐cells (which have slowly conducting axons) in these layers. We conclude that the different classes of geniculate relay neuron have different laminar projections in area 17.
Development of the diencephalon in the rat. III. Ontogeny of the specialized ventricular linings of the hypothalamic third ventricle
Authors: Altman Joseph , Bayer Shirley A.
Published: December 2004

The development of the specialized linings of the hypothalamic third ventricle was examined autoradiographically in mature rats that were labelled with 3H‐thymidine during the developmental period, and in a closely spaced series of embryonic and infant rats. We distinguished in mature rats, apart from the typical ependymal wall, three specialized linings: the convoluted ependyma, the laminated epithelium, and the tanycytic epithelium. The ventricular wall of most of the anterior hypothalamus, and of the dorsal portion of the posterior hypothalamus, is composed of ciliated ependymal cells and most of them are generated several days before birth, soon after the cessation of neurogenesis in the adjacent hypothalamic nuclei. The cells of the rostral convoluted ependyma adjacent to the paraventricular nucleus are produced at about the same time as the neighboring cells of the smooth ependyma. Its cells come from the same germinal region that we have assumed to generate the neurons of the magnocellular neurohypophysial secretory system. The structural differentiation of the convoluted ependyma starts after birth and is completed by the beginning of the second week. Many of the ependymal cells of the laminated epithelium are produced postnatally, and the production of the specialized cells that form a parallel subependymal row extends into the third week. These cells appear to arise from the same matrix that generates earlier the neurons of the dorsomedial and ventromedial hypothalamic nuclei; their structural differentiation begins during the second week. Also the cells of the tanycytic epithelium are produced mostly postnatally, predominantly during the first week. They appear to arise from the same matrix that generated earlier the neurons of the hypophysiotropic tuberomammillary and arcuate nuclei. It is postulated that these three specialized ventricular linings are specifically related to the three components of the endocrine hypothalamus with which they have shared neuroepithelial sites of origin.
Opening of tight junctions in cerebral endothelium. I. Effect of hyperosmolar mannitol infused through the internal carotid artery
Authors: Nagy Zoltan , Pappius Hanna M. , Mathieson Gordon , Hüttner Istvan
Published: December 2004

Infusion of 1.8 M mannitol solution into the internal corotid artery of Wistar rats allows horseradish peroxidase (HRP) to cross cerebral vascular endothelium via intercellular pathways. This was made evident by density gradients of HRP observed in consecutive tight junctional compartments following in vivo administration, and by the passage of colloidal lanthanum through junctional membrane appositions of glutaradehyde fixed cerebral endothelium. Three hours after mannitol infusion, small no‐capillary vascular segments were still focally permeable to HRP. Twenty‐four hours after the osmotic insult, the tracer was absent in the affected hemisphere. Water and electrolyte essays indicated absence of brain edema during the period of observation of blood‐brain barrier opening.
3H‐Estradiol, 3H‐Testosterone and 3H‐Dihydrotestosterone localization in the brain of the lizard Anolis carolinensis: An autoradiographic study
Authors: Morrell J. I. , Crews D. , Ballin A. , Morgentaler A. , Pfaff D. W.
Published: December 2004

The presence and the neuroanatomical topography of sex hormone concentrating cells in the brain of the American chameleon, Anolis carolinensis have been demonstrated by these experiments. After 3H‐estradiol administration large numbers of hormone concentrating cells were found in the amygdala, septum, medical preoptic area, anterior hypothalamic area, the ventromedial and periventricular nuclei of the hypothalamus, and anterior pituitary. In addition, labelled cells were found in the torus semicircularis, in and around the nucleus isthmus pars parvocellularis. A small number of labelled cells could also be found in the rostral pallium, motor nucleus of the fifth cranial nerve, the raphe nuclei, and the spinal cord. After 3H‐testosterone or 3H‐dihydrotestosterone administration the neuroanatomical pattern was very similar to that found after 3H‐estradiol; however, fewer labelled cells were seen after the androgens were given. Two exceptions to the similarity of pattern were in a caudal part of the pallium and in the mesencephalic tegmental area. Hormone‐concentrating cells were found after 3H‐testosterone or 3H‐dihydrotestosterone administration, while labelled cells in these two areas after 3H‐estradiol administration were extremely rare. The pattern of hormone‐concentrating cells was the same in male and female brains, for each of the hormones. The preoptic area, hypothalamus, and anterior pituitary have been demonstrated in reptiles to be involved in neuroendocrine regulation and in the control of sex behaviors.

The presence and neuroanatomical pattern of sex steroid binding cells in the brains of a wide variety of vertebrates have been documented. Large numbers of hormone‐concentrating cells were found in all of these species in the medial preoptic area, tuberal hypothalamus, specific limbic structures, the mesencephalon deep to the tectum, and the anterior pituitary. Most hormone‐concentrating cells in the brain of A carolinensis were found in these same brain regions, thus indicating a vertebrate‐wide stable core of hormone‐concentrating cells in neuroanatomically defined regions.
The cellular origin of the b‐wave in the electroretinogram— a developmental approach
Authors: Rager Günter
Published: December 2004

Retinal ganglion cells and retinotectal synapses of chick embryos can be activated by electrical stimulation at early stages of development (Rager, '76a,b), whereas light evoked responses occur only towards the end of the incubation period. Thus, photoreceptors seem to be the last cells to mature in the chain of elements necessary to enable transmission of visual information to tectal neurons. In the present study the development of light evoked activity in the retina was investigated and compared with the strutural maturation of retinal cells. This ontogenetic approach offers a solution to the problem of the cellular origin of the b‐wave called in question by recent records of the potassioretinogram (KRG).

Lamellar structures in the developing outer segments of photoreceptors can first be observed on incubation day 17. Late on the same day a corneal electroretinogram (ERG) and a visual evoked response on the optic tectum (VER) can be recorded. The response properties of the developing b‐wave and VER were tested using various stimulus parameters. From the latencies of the b‐wave and of the VER it is concluded that the b‐wave is not generated directly by the activity of neurons involved in intraretinal signal transmission. Thus it is necessary to consider secondary processes triggered by neuronal activity such as depolarization of glial cells. In the chick retina, Müller cells are virtually the only glial cells. They fulfill all structural requirements necessary to explain the current which spreads through the retina during the b‐wave. Electronmicroscopic analysis reveals that Müller cells undergo drastic changes during the early phase of b‐wave development (incubation day 18). In particular, the number of microtubules per unit volume and the surface area of Müller cell processes in the outer plexiform layer increase considerably. It is, therefore, suggested that the b‐wave originates in the depolarization of Müller cells secondary to synaptic activity in the outer plexiform layer.
Rods and cones in the mouse retina. I. Structural analysis using light and electron microscopy
Authors: Carter‐Dawson Louvenia D. , Lavail Matthew M.
Published: December 2004

Rods and cones of the C57BL/6J mouse retina have been examined by light and electron microscopy to distinguish the structural features of the two photoreceptor types. By light microscopy, cone nuclei are conspicuously different from rod nuclei in 1‐2 μm plastic sections. Cone nuclei have an irregularly shaped clump of heterochromatin that appears in single sections to be one to three clumps, whereas rod nuclei are more densely stained and have one large, central clump of heterochromatin. Cone nuclei make up approximately 3%; of the photoreceptor nuclei in both the central and peripheral retina at all ages examined up to 267 days. Cone nuclei are confined to the outer half of the outer nuclear layer, and more than 50%; of the cone nuclei lie adjacent to the outer limiting membrane. By electron microscopy, cones in the mouse retina meet virtually every morphological criterion of mammalian cones. The outer segments are conically shaped. Many, if not all of the outer segment discs are continuous with the outer plasma membrane, whereas almost all of the rod discs are not. Cone outer segments are only about half the length of the rod outer segments, and they are contacted by long, villous pigment epithelial cell processes. The cone inner segment diameter is greater than the outer segment diameter, and the accumulation of mitochondria present at the apical end of the inner segment forms a more conspicuous ellipsoid than in rods. The internal fiber or axon of the cone is larger in diameter than that of the rod, and it terminates in a large synaptic pedicle with multiple ribbon synapses, whereas the rod terminal is a smaller spherule with only a single ribbon synaptic complex.
Development of chick paravertebral sympathetic ganglia. I. Fine structure and correlative histofluorescence of catecholaminergic cells
Authors: Luckenbill‐Edds L. , van Horn C.
Published: December 2004

Paravertebral sympathetic ganglia from the lumbosacral region of a series of chick embryos have been studied with electron microscopic methods, including aldehyde‐osmium and permanganate fixatives, and correlative histofluorescence (Grillo et al., '74). Our purpose was to assess the differentiation of catecholaminergic (CA) cells during histogenesis in ovo. Examination of comparable adult ganglia as a baseline for differentiating stages confirmed that the principal sympathetic neuron (PN) is similar to those of other species in that it contains predominately small dense‐cored vesicles (SDCV) preserved only by permanganate, and does not histofluoresce following the method of Grillo et al. ('74). At embryonic day (E) 7–8, when ganglia have just formed, areas fluorescing bright yellow‐green are correlated with two types of cells: (1) Neuroblasts with vesicular nuclei and large dense‐cored vesicles (LDCV) are common. As the neuroblasts grow and differentiate, LDCV move away from perikaryal cytoplasm into developing processes. Around E13–15, SDCV appear in the neuroblasts which continue to develop until they resemble miniature adult PN in late embryos and hatchlings. (2) Granule (GR) cells with clumped chromatin and sparse cytoplasm are clustered in the ganglionic periphery at E7–8, but are rare. The GR cells increase somewhat in size and numbers by E11, but retain essentially the same characteristics as at earlier stages. Neither bright fluorescence nor GR cells appear later than stages E13–15. These results are interpreted to mean that when chick sympathetic stem cells have migrated from the primary ganglia into the paravertebral ganglia, they give rise to two separate lines of CA cells, one of which is not maintained and subsequently disappears. The results are significant as a basis for understanding how a mixed population of CA cells might arise within sympathetic ganglia in situ.
Neuronal increase in various areas of the nervous system of the guppy, Lebistes
Authors: Birse Stewart C. , Leonard Robert B. , Coggeshall Richard E.
Published: December 2004

The numbers of 1) dorsal root ganglion cells in the 2nd spinal segment, 2) ventral horn cells in the 2nd spinal segment, 3) Purkinje cells of the cerebellum, and 4) neurons in the nucleus glomerulosus were counted and correlated with age and size in the guppy, Lebistes. The findings were that the neuronal numbers in all these areas increased throughout much of the life of the animal. These data, combined with the previously demonstrated increases in retinal neurons in goldfish and sensory and spinal neurons in stingrays, suggest that neurons are added to many areas of the nervous system of fish as the animal ages and grows. In this respect, the nervous systems of fish differ from the nervous systems of other vertebrates. We offer the suggestion that the comparatively greater ability of fish to regenerate their nervous system after injury may be related in part to their ability to add neurons to various parts of the nervous system throughout life.
Regions of the brain influencing the projection of developing optic tracts in the salamander
Authors: Harris William A.
Published: December 2004

Eye primordia from the Mexican axolotl or the California newt were transplanted into hosts of either species. These “third” eyes often developed an optic nerve that penetrated the host brain and made one of three central projections: bilateral to the dorsal thalami, tecta, and basal optic nuclei; ipsilateral to the same areas; or ipsilateral into the cord. The type of projection made by a transplanted eye seemed to depend on where its nerve first entered the brain. The optic fibers that reached the visual centers of the midbrain were organized retinotopically in the optic tectum and mediated visually‐guided behavior.
Immunocytochemical localization of tyrosine hydroxylase in the human fetal nervous system
Authors: Pickel Virginia M. , Specht Linda A. , Sumal Khushdev K. , Joh Tong H. , Reis Donald J. , Hervonen Antti
Published: December 2004

The peroxidase‐antiperoxidase (PAP) technique is used to determine the cellular localization of tyrosine hydroxylase in the human fetal nervous system. Antiserum to trypsin‐treated tyrosine hydroxylase from the bovine adrenal medulla can be detected immunocytochemically in peripheral sympathetic neurons in the 8‐mm (5‐week) fetus, but can not be detected in the central nervous system until later stages of development. The cytological features and distribution of the neuronal perikarya and processes labeled for the enzyme are similar to those of the catecholaminergic neurons previously identified by histofluorescence. These findings indicate that specific neurons in the human fetus have at least one of the enzymes necessary for the biosynthesis of catecholamines and that cross‐species reactivity exists between antiserum produced to the bovine tyrosine hydroxylase and human tissues.
Development of rat Merkel cells
Authors: English Kathleen B. , Burgess Paul R. , Norman Dolores Kavka‐Van
Published: December 2004

The ultrastructure of Merkel cells and cutaneous nerves was examined in fetal, newborn, and 7‐day‐old rats. The earliest observation of cells having some, but not all, of the features of mature Merkel cells was at 16 days gestation in snout skin. These early presumptive Merkel cells resembled the neighboring keratocytes, except that they contained dense‐cored vesicles scattered in the cytoplasm. Presumptive Merkel cells were seen only in the epidermis, although a careful search was made of the dermis. Developing neurons were not observed to penetrate the epidermal basal lamina when presumptive Merkel cells were first seen. The earliest observation of identifiable nerve axons in the snout epidermis was at 17–17 1/2 days gestation. Study of the presumptive Merkel cells through successively older gestational stages showed that the cells became innervated and progressively developed the characteristics of adult Merkel cells. We suggest that Merkel cells arise from keratocyte‐like precursors in rat epidermis, at a time when skin nerves may still be several micrometers away.
Convergence of autonomic and limbic connections in the insular cortex of the rat
Authors: Saper Clifford B.
Published: December 2004

The connnections of the insular cortex in the rate were studied by using the anterograde and retrograde transport of wheat germ agglutinin‐conjugated‐horseradish peroxidase. Both anterograde and retrogrde transport were seen in the ipsilateral lateral frontal, infralimbic, piriform, and perirhinal cortical areas and in the contralateral insular cortex. In the thalaamus, both types of labeling were seen in the mediodorsal and ventroposteromedial parvocellular nuclei; primarily retrograde labeling was seen in the centromedial and paracentral nuclei. In the basal forebrain, anterograde labeling was seen in the lateralpart of the bed nucleus of the stria terminalis and in the central nucleus of the amygdala, while retrogradely labeled neurons were found in the magnocellular basal nucleus and in the lateral and basolateral amygdaloid nuclei. Both types of labeling were seen in the posterior lateral hypothalamic area; the tuberomammillary nucleus contained retrogradely labeled neurons bilaterally. In the midbrain, retrogradely labeled neurons were found in the ventral tegmental area and in the dorsal and superior central raphe nuclei. In the pons, both retrogradely and anterogradely transported label was seen bilaterally in the parabrachial nucleus, primarily in the ventromedial caudal part of the medial subnucleus. Retrogradely labeled neurons were found bilaterally in the locus coeruleus. Anterograde transport was followed into the medulla, bilaterally but more heavily in the contralateral side. Labeled axons appeared to terminate in a topographic pattern in the nucleus of the solitary tract.

These results indicate that the insular cortex of the rat is an important part of the highly interconnected central autonomic system. Furthermore, the autonomic representation in the insular cortex may be organized in a viscerotopic manner. The insular cortex also has connections with the limbic system and with the lateral frontal cortical system. Although it is not yet clear whether these connections converge upon the same neurons within the insular cortex, earlier physiological data suggest that each of the diverse systems of connections of this area receives relayed vagal inputs. The insular cortex of the rat may contain a primary cortical visceral representation, and its connections may underlie autonomic integration with behavioral and emotional events.