bluuebunny/crossref_metadata_2025 huggingface dataset:
Topological analysis of the brain stem of the crossopterygian fishLatimeria chalumnae
Authors: Kremers Jan‐Willem P. M. , Nieuwenhuys Rudolf
Published: January 2005

The ventricular sulcal pattern and the cellular structure of the brain stem of the single surviving crossopterygian speciesLatimeria chalumnaehave been studied in transversely cut Nissl, Klüver‐Barrera and Bodian staine serial sections. Five longitudinal sulci, the sulcus medianus inferior, the sulcus medianus superior, the sulcus intermedius ventralis, the sulcus limitans and the sulcus intermedius dorsalis could be delimited. The latter three of these sulci are confined to the rhombencephalon. The walls of the mesencephalon also display some longitudinal grooves, but none of these could be traced into continuity with any of the rhombencephalic sulci. Although the neuronal perikarya in many places show a diffuse arrangement, 27 cell masses could be delineated; eight of these are primary efferent nuclei, seven are primary afferent centers, seven nuclei are considered as components of the reticular formation, and the remaining five cell masses may be interpreted as “relay” nuclei.

In order to study the zonal pattern of the brain stem, this structure was subjected to a topological analysis (cf., Nieuwenhuys, 1974, and fig. 16). This analysis yielded the following results. The sulcus limitans divides the greater part of the rhombencephalon into a basal plate and an alar plate. In the basal plate the sulcus intermedius ventralis marks the boundary between an area ventralis and an area intermedioventralis. The area ventralis contains two somatic motor centers (i.e., the rostral end of the spinal motor column and the nucleus of IV) and almost the entire rhombencephalic medial reticular formation. The latter may be primarily considered as a somatic motor coordinating center. The area intermedioventralis contains the visceral motor nuclei of V, VII, IX and X. However, the basal plate also harbours a number of non‐motor centers, for example the sensory princeps nucleus of V and the inferior olive. The alar plate is subdivided by the sulcus intermedius dorsalis into an area intermediodorsalis and an area dorsalis. The area intermediolateralis is largely occupied by the common visceral sensory center of VII, IX and X; however, this area also contains a number of somatic sensory cell masses, as e.g. the nucleus descendens of V and the magnocellular vestibular nucleus. The area dorsalis is entirely occupied by two large lateral line centers. The cell masses in the isthmus region do not exhibit a clear‐cut morphological pattern. As regards the mensencephalon, the medial part of the tegmentum, which contains a primary somatic motor center (the nucleus of III) and a somatic motor coordination center (the nucleus of the f.l.m.) may be considered a direct rostral continuation of the area ventralis. The remainder of the midbrain contains a number of somatic sensory centers of primary and higher order.
Origin, course and terminations of the rubrospinal tract in the pigeon (Columba livia)
Authors: Wild J. Martin , Cabot John B. , Cohen David H. , Karten H. J.
Published: January 2005

The red nucleus and its spinal projections in the pigeon (Columba livia) have been studied using both normal and experimental material. The cytoarchitecture of the nucleus is described on the basis of Nissl‐stained sections and reveals an organization generally similar to that of mammals. The large neurons (40‐50μm) tend to be located dorsomedially and ventrolaterally at more caudal nuclear levels, while the small‐and medium‐sized neurons (15‐35μm) predominate at rostral levels. However, neurons of all sizes are present throughout the nucleus.

Following lesions of the nucleus, the course of degenerating axons stained with the Fink‐Heimer method has been traced throughout the brainstem and spinal cord. The rubrospinal tract crosses the midline, courses past the ventrocaudal aspect of the contralateral nucleus ruber, and then descends rostroventral and lateral to the nucleus tegmenti pontinus. In its caudal continuation the tract lies ventral to the brachium conjunctivum and the entering radix of the trigeminal nerve. It then assumes a ventrolateral position in the caudal brainstem before shifting to a dorsolateral position in the lateral funiculus of the spinal cord. Within the spinal grey the rubrospinal tract terminates in laminae V, VI and to a lesser extent VII.

The possibility of a topographical organization of the nucleus was investigated with injections of horseradish peroxidase into brachial, thracic and lumbar spinal cord. Regardless of the level of injection, labelled neurons of all sizes were present throughout the contralateral nucleus ruber, indicating the absence of an obvious topography.
Descending inputs to the caudal cochlear nucleus of the cat: Degeneration and autoradiographic studies
Authors: Kane Eileen S. , Conlee John W.
Published: January 2005

Descending paths from the inferior colliculus (IC) and dorsal (DNLL) and ventral (VNLL) nuclei of the lateral lemniscus and their terminations in the caudal cochlear nucleus in cats were studied both in silver degeneration material following central lesions and in autoradiographs following central injections of tritiated leucine (3H‐leu). Eight adult cats received electrolytic lesions of the IC, the IC and DNLL, or the IC, DNLL and VNLL. Control cats were subjected either to surgery alone or to a lesion in a non‐auditory nucleus. After survival periods of 1 to 16 days, all cats were killed and their brain stems prepared by modified Nauta methods. Twenty‐two other cats received injections of 3H‐leu into the dorsal IC, the ventral IC and DNLL, or the DNLL and VNLL. Their brains were prepared for LM autoradiography. After lesions of the IC, Nauta material contained moderate degeneration of fine fibers that coursed predominantly in the lateral lemniscus, and partially decussated in the caudal trapezoid body to enter the cochlear nuclei of both sides. Sparse, mainly peridendritic degeneration of fine fibers occurred in the PVCN, while moderate, peridendritic and perisomatic degeneration occurred in the deep and innermost fusiform cell layers of the dorsal cochlear nucleus (DCN). Lesions of both the ventral IC and the DNLL showed additional bilateral degeneration of medium‐caliber axons in the descending tracts as well as preterminal degeneration of these larger axons sparsely distributed in the deep layers of the DCN. The density of medium‐caliber axonal degeneration (particularly in the deep DCN) increased when lesions also included the VNLL. After 3H‐leu injections into the tectum and/or upper pons, autoradiographs confirmed the presence of sparse bilateral inputs from both the IC and from the DNLL and VNLL to ventral cochlear nucleus neurons, including some octopus cell dendrites. The autoradiographic studies also clearly revealed a predominant input to the outer layer of the DCN from the dorsal IC, a predominant input to the middle layer from the ventral IC, and a predominant input to the deeper DCN from the lateral lemniscal nuclei. Limited evidence of a topographic, perhaps tonotopic, order within the descending connections was best seen in Nauta material. The differences shown here in fiber types, trajectories, and target sites from the IC, the DNLL, and the VNLL are discussed in terms of possible functional differences among the descending influences on neurons of the caudal cochlear nucleus.
The development of vibrissae representation in subcortical trigeminal centers of the neonatal rat
Authors: Belford Gary R. , Killackey Herbert P.
Published: January 2005

In every station of the trigeminal system of the young rat, the segmented activity of the mitochondrial enzyme succinic dehydrogenase (SDH) clearly delineates the representation of the mystacial vibrissae. In the trigeminal complex of the medulla, three parallel representations can be seen, two in the spinal trigeminal nucleus and one in the principal trigeminal nucleus. In the next station, the ventrobasal complex of the thalamus, a single representation occurs. Likewise, layer IV of somatosensory cortex contains one representation of the vibrissae. Further, neonatal damage to the mystacial vibrissae results in anomalies within each representation.

The present study delineates both the normal development of subcortical trigeminal stations and the aberrant organization seen after vibrissae removal. The results of a similar study on somatosensory cortex (Killackey and Belford, '79) and the present data allow the comparison of the development of each of the five vibrissae representations in the trigeminal system.

In the brainstem, each of the three trigeminal complex representations are present at birth, although the pattern becomes more distinct over the first several days of life. Interestingly, vibrissae removal at birth induces an aberrant pattern that is distinct by postnatal Day 3. Although details are not equally discernible in each representation, the abnormalities appear to be similar. The SDH segmentation in the ventrobasal complex develops during postnatal Days 1 through 4. At Day 1, portions of the matrix of high density SDH activity break up into bands. Clusters can be discerned within these bands on Day 2. By Day 4 the pattern is sharply delineated. Vibrissae removal at birth results in anomalies that are a part of the initial development of segmentation, not a later reorganization.

Comparison of the present data with that of our previous studies indicates that there is a sequential development of the central somatosensory structures related to the vibrissae, beginning with the most peripheral station. Further, there are many similarities in the development of each station. There are also differences which are particularly important in comparing the trigeminal nuclei with the later stations. The unique features in the abnormal development of the trigeminal nuclei are likely due to their direct connections with the periphery.
Development of the diencephalon in the rat. VI. Re‐evaluation of the embryonic development of the thalamus on the basis of thymidine‐radiographic datings
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

The development of the thalamus was examined in normal and X‐irradiated embryos from day 13 (E13) to the day before birth (E22). The differentiating, radioresistant neurons of the lateral habenular nucleus, derived from a portion of the superior neuroepithelial lobule (SL1), were settling by day E15 and by this time the habenulopeduncular tract was forming. The neurons of the reticular nucleus, derived from the middle neuroepithelial lobe, began to settle on day E15 but a massive migration was still evident on day E16. Adjacent to the reticular nucleus the internal capsule appeared on day E16; this fiber bundle seemed to be continuous with fibers embedded in the first transitory zone of cells issuing from the dorsal neuroepithelial lobe. Because of the immaturity of the neocortex at this time, it was postulated that thalamocortical fibers of the dorsal thalamus are the earliest components of the internal capsule. By day E17 all the sensory relay nuclei of the thalamus were recognizable and it was assumed that the second transitory zone issuing from the receding dorsal neuroepithelial lobe contained the neurons of the later forming intralaminar nuclei. Suggestive evidence was obtained that the late arising neurons of the medial thalamus (the anterior nuclei, the mediodorsal nucleus, and some or all of the midline nuclei) originate in a portion of the superior neuroepithelial lobule designated as SL2.

Our present and previous studies showed that the major divisions of the hypothalamus and thalamus are derived embryonically from distinguishable parts of the third ventricle neuroepithelium. This implies that the third ventricle neuroepithelium has a “mosaic” organization and suggests that the fate of hypothalamic and thalamic neurons may be determined to some extent while their precursors are still proliferating.
Patterns of connections from the striate cortex to cortical visual areas in superior temporal sulcus of macaque and middle temporal gyrus of owl monkey
Authors: Montero Vicente M.
Published: January 2005

Double label‐emulsion autoradiography has been used in rhesus monkeys to study cortico‐cortical connections, arising from two separate sites of the striate cortex, and going in the same hemisphere into the cortex in the medial part of the posterior (or ventral) bank of the superior temporal sulcus (area STS). The projections from a single cortical locus are segregated into several patches of labeled terminals in layers III–IV, which from bands in consecutive sections. Fields of distribution of these bands from two sites of area 17 may completely overlap, when they arise from neighboring regions, or may partially overlap, when they arise from more separated regions. The latter show a retinotopical order in these connections and, consequently, of area STS itself: central visual field is lateral and ventral in STS to peripheral visual field, and upper visual field is ventral and medial to lower visual field. Connections from area 17 to area MT in owl monkey were analyzed in a comparative study. Results show that these connections are also highly segregated into bands, and that those arising in separate, but neighboring regions of 17, may greatly overlap in MT. The retinotopy of these connections was not studied, however. The similar divergent distribution of area 17 connections to STS and MT, and the similarity of the topography of STS connections and of the known retinotopy of area MT, are considered as elements of homologies between these areas. Functional implications of these divergent patterns of connections to these motion‐sensitive areas (Zeki, '74), are considered.
Representation of the body surface in somatic koniocortex in the prosimian Galago
Authors: Sur Mriganka , Nelson R. J. , Kaas J. H.
Published: January 2005

Microelectrode mapping methods were used to determine the organization of somatosensory cortex in galagos, a prosimian primate. A systematic representation of the controlateral body surface was found within somatic koniocortex with an organization comparable to that of Area 3b of parietal cortex of monkeys (S‐I proper) and primary somatosensory cortex (S‐I) of other mammals. Limited studies of the response properties of single neurons within the representation revealed further similarities with the 3b field of monkeys. We conclude that somatic koniocortex of galagos and Area 3b of monkeys are homologous, and suggest the term S‐I proper for the representation in both prosimians and monkeys. Differences in the details of S‐I proper in galagos and monkeys suggest a more primitive organization in galagos.
Noradrenergic innervation of the adult rat hippocampal formation
Authors: Loy Rebekah , Koziell David A. , Lindsey James D. , Moore Robert Y.
Published: January 2005

The noradrenaline (NA)‐containing innervation of the hippocampal formation arises exclusively in the brainstem nucleus locus coeruleus. The projection is 75–90% ipsilateral, originating predominantly in the large, multipolar cells of the compact component of the nucleus. The axons course into the hippocampal formation by three pathways. Ammon's horn receives its NA innervation principally through the ventral amygdaloid bundle‐ansa peduncularis, with smaller contributions from the fornix and ipsilateral fasciculus cinguli. The innervation of the area dentata is to a larger extentbilateral, with the greatest contribution arising from the ipsilateral fasciculus cinguli and approximately equal proportions of fibers traveling via the contralateral cingulum, fornix, and the ventral path. In general, the endogenous content of NA is greater in the area dentata than in Ammon's horn, and in both structures is greater in the temporal than in the septal ends. The pattern of NA innervation is similar at all septotemporal levels, however. The densest plexuses of preterminal and terminal elements appear in the infragranular hilus of the area dentata, stratum lucidum of CA3, and in the molecular layer of the subiculum. Fluorescent varicosities often appear in perisomatic clusters, or, closely apposed to dendrites of granule and pyramidal cells.
Normal and abnormal uncrossed retinotectal pathways in rats: An HRP study in adults
Authors: Lund R. D. , Land P. W. , Boles J.
Published: January 2005

Horseradish peroxidase was injected into the superior colliculus of normal pigmented and albino rats and rats which had been unilaterally enuleated at birth, in order to identify the retinal ganglion cells which contribute normal and abnormal uncrossed retinotectal axons. The results show that while in pigmented rats, the normal uncrossed pathway derives solely from the lower temporal retina and distributes to the anterior and medial parts of the colliculus, occasional cells throughout the retina of albino rats contribute to the uncrossed pathway and the terminal distribution is broader in the tectum. These findings are confirmed with orthograde pathway tracing methods.

After neonatal unilateral eye enucleation, many more ganglion cells in the remaining eye of both pigmented and albino rats project ipsilaterally. It is notable from both HRP studies and from further degenration experiments that cells in part of the lower temporal retina do not restrict their distribution to a mirror togographic position in the ipsilateral tectum but send axons across all but the posterolateral part of the colliculus.

No single class of ganglion cell (defined by soma diameter) appears responsible for the expanded ipsilateral projection, although more large cells from the lower temporal retina are involved. These may be the result of enlargement of cells with expanded terminal fields rather than necessarily indicating a preferential contribution from one retinal ganglion cell class.
Early postnatal development of the monkey neostriatum: A Golgi and ultrastructural study
Authors: Difiglia Marian , Pasik Pedro , Pasik Tauba
Published: January 2005

Paired specimens of the neostriatum were taken from monkeys at zero (newborn), one, two, four, eight, and 16 weeks of age, and prepared for Golgi impregnations and electron microscopy. Light microscopy shows that in the first postnatal week, the structure contains the five neuronal types and four categories of afferent axons described in the adult, as well as some cells too undifferentiated to classify. Most neurons exhibit immature dendritic features, including local enlargements, terminal growth cones with filopodia, and filiform processes. In spiny type I cells, various levels of maturity may coexist in regions of a single dendrite, in different dendrites of the same neuron, and among individual cells. Spine density increases progressively with age, but the relative distribution of spine types remains about the same. Spiny type II neurons show some decline in spine density, and generally mature sooner than spiny type I cells. The long axons of spiny neurons have varicosities which disappear at about eight weeks. In younger animals (newborn and one week), the dendrites of aspiny neurons (types I, II, and III) may have a “spiny” appearance, exhibiting many spine‐like and filiform processes. Concurrently, the short axons vary in degree of arborization from very immature to well developed.

Electron microscopy corroborates the developmental features recognized in the Golgi material: dendritic and axonal growth cones, filopodia and varicosities, as well as various stages of maturation in somata and dendrites. Degenerating elements, mostly of an axonal nature, are seen up to eight weeks. The synapses which reach maturity at birth are of the asymmetric axospinous type, in which the axonal profile contains small round vesicles, and of the symmetric axodendritic class, with the presynaptic elements having pleomorphic vesicles. Some synapses are slower to mature and appear at one to eight postnatal weeks. These include those made by profiles with pleomorphic vesicles, forming either symmetric contacts with somata and axon initial segments, or asymmetric contacts with spines. The same applies to the asymmetric axodendritic synapses made by elements containing small round vesicles. Finally, profiles containing large round or flat vesicles are the latest to participate in mature synapses formation.

Findings indicate that a considerable degree of qualitative and quantitative change takes place in the monkey neostriatal neuropil during early postnatal development, especially in the first eight‐week period.
Somatotopic organization of the embryonic chick trigeminal ganglion
Authors: Noden Drew M.
Published: January 2005

Horseradish peroxidase (HRP) has been injected into periocular, upper beak, or lower jaw tissues of chick embryos aged 6–8 days of incubation. Subsequent mapping of the distribution of labeled neurons in the trigeminal ganglion indicates that the somatotopic organization of neurons is essentially identical to that found after hatching.

At these stages most labeled cells are in the distal parts of the bilobed ganglion. There is no indication that any of these neurons, most but not all of which are derived from epidermal placodes, establish any erroneus projections. Most of the proximo‐central or core neurons, which are of neural crest origin, are immature at these stages. On the eighth day of development, by which time the embryo is responsive to tactile stimulation of the beak, few of these core cells have established projections to more distal (rostral) periocular or upper beak areas or to the lower jaw. In contrast, injection of HRP above the eye results in labeling of many of the core neurons. This suggests that there is an asymmetry in the time of neurite outgrowth from core neurons that is correlated with their peripheral projections but not with their time of terminal mitosis.

Following injection of HRP into temporal periocular tissues, most of the core cells in the maxillo‐mandibular lobe contain peroxidase. This is probably due to uptake by growth cones emerging along the maxillary ramus.

Examination of contralateral trigeminal ganglia indicates that the transmedian projections of these sensory fibers form later in development. Branches of the mandibular motor nerve extend throughout the lower jaw and presumptive jaw‐closing muscle anlagen, as evidenced by incorporation of HRP into motoneurons of the trigeminal nucleus.
An experimental study of the ventral striatum of the golden hamster. II. Neuronal connections of the olfactory tubercle
Authors: Newman Richard , Winans Sarah Schilling
Published: January 2005

As part of an experimental study of the ventral striatum, the horseradish peroxidase (HRP) method was used to examine the afferent and efferent neuronal connections of the olfactory tubercle. Following iontophoretic applications or hydraulic injections of HRP in the tubercle, neurons labeled by retrograde transport of HRP were observed ipsilaterally in the telencephalon in the main olfactory bulb, the medial, lateral, ventral, and posterior divisions of the anterior olfactory nucleus, and in the orbital, ventral, and posterior agranular insular, primary olfactory, perirhinal, and entorhinal cortices. Labeled cells were also present in the basolateral, basomedial, anterior cortical, and posterolateral cortical amygdaloid nuclei, and bilaterally in the nucleus of the lateral olfactory tract. In the diencephalon, ipsilateral HRP‐containing neurons were observed in the midline nuclei paraventricularis, parataenialis, and reuniens, and in the parafascicular intralaminar nucleus. Retrograde labeling was present in the ipsilateral brainstem in cells of the ventral tegmental area, substantia nigra, and dorsal raphe. Many of the above projections to the tubercle were found to be topographically organized.

Anterograde axonal transport of HRP from the olfactory tubercle labeled terminal fields ipsilaterally in all parts of the anterior olfactory nucleus, in the ventral pallidum, and in the substantia nigra, pars reticulata. Contralaterally, terminal fields were present in the dorsal and lateral divisions of the anterior olfactory nucleus.

The projections to the tubercle from the orbital, ventral, and posterior agranular insular, and perirhinal neocortices, intralaminar thalamus, and dopamine‐containing areas of the ventral mesencephalon are analogous to the connections of the caudatoputamen, as are the efferents from the tubercle to the ventral globus pallidus and substantia nigra. These connections substantiate the recent suggestion that the olfactory tubercle is a striatal structure, and provide support for the ventral striatal concept.

In the present study of the olfactory tubercle, and in the first study in this series on the nucleus accumbens, the ventral striatum was found to receive projections from a number of limbic system structures, including the main olfactory bulb, anterior olfactory nucleus, amygdala, hippocampus, and subiculum, and the entorhinal and primary olfactory cortices. These findings suggest that the ventral striatum is concerned with integrating limbic information into the striatal system.
Pattern of myelination and distribution of neuroglial cells along the developing optic system of the rat and rabbit
Authors: Skoff Robert P. , Toland Denise , Nast Edward
Published: January 2005

In order to gather information about the factors influencing myelination and neuroglial cell formation in the central nervous system, the development of myelin and neuroglia was investigated along the length of the optic nerve and tract of rats and rabbits. The results of this study revealed complex developmental patterns for both of these processes. Furthermore, the pattern of myelination for the rat is different from that of the rabbit. Myelination of the rat optic pathway exhibits a general rostro‐caudal gradient extending from the eye to the lateral geniculate nucleus, whereas a more homogeneous pattern is present in the rabbit. Myelination along the nerves of both species shows many sharp peaks and trough, especially in the region of the optic canal. Formation of myelin begins at several different sites along the nerve, with the first fibers appearing on both sides of the optic canal. Another small site of myelination develops just in front of the optic chiasm. Myelination of the entire length of an individual axon is not homogeneous but instead it begins at several discrete sites. The number of glial cells along the nerve and tract also fluctuates sharply but their pattern does not precisely parallel that of myelination. A better correlation is obtained by comparing the distribution of axons being myelinated with that of oligodendroglial cells. The complex patterns and the species differences observed in this study indicate that myelination and neuroglial cell development must be regulated by both neuronal and local factors. The data presented here together with other available information suggest that the vascularization of the nerve and the direct effects of hormones upon glial cells are possible factors that contribute to the local variability.
Development of sensory innervation in dentin
Authors: Byers Margaret R.
Published: January 2005

We have labeled dental nerves of 3‐week‐ to 1‐year‐old rats by axonal transport of radioactive protein in order to detect nerves in developing dentin by autoradiography. We found that, in addition to nerve growth, two processes determine adult dentinal nerve location: (1) enclosure of nerves within circumpulpal dentinal tubules during the last few weeks of dentinogenesis, beginning at the tip of the pulp horn and spreading to include most coronal dentin; and (2) gradual loss of the nerves near the tip of the cusp because of dentinal attrition and replacement by noninnervated, reparative dentin. Several days before a molar erupts, nerves at the tip of the cusp have already begun to be enclosed by dentin; 2–3 weeks later, when dentinogenesis at the cusp tip slows down, most of the innervation for that region has been established, nerves extend up to 160 μ into dentin, and the molar has reached the has reached the stage of functional occlusion. Soon after initial occlusion, the process of dentinal attrition and replacement by noninnervated reparative dentin begins; however, simulataneous dentinogenesis in more apical regions produces new innervated dentin. We studied nerve position in relation to dentin growth lines and found that there is a long‐term association of nerve endings with specific sites in the dentinal tubules. The similarities between the development of dentinal innervation in rat molars and in human permanent teeth are discussed; it is found that as teeth mature and become more sensitive to painful stimuli, the density of dentinal nerves increases.
Studies on the somatotopy of the trigeminal system in the mallard, anas platyrhynchos L. II. Morphology of the principal sensory nucleus
Authors: Dubbeldam Jacob L.
Published: January 2005

The projections from the ophthalmic, maxillary, and mandibular parts of the trigeminal ganglion upon the principal sensory trigeminal nucleus (PrV) in the mallard have been studied with the Fink‐Heimer I method. PrV is a large nucleus subdivided in cell groups by layers of fibers. The orientation of the dendritic arborizations differs in the different parts of the nucleus. A dorsocaudal cell group sIX is an exclusive glossopharyngeal terminal field. A second, caudo‐ventral projection area of NIX also receives trigeminal afferents. A small n. supratrigeminalis lies medial to PrV in the pathway of the mesencephalic trigeminal root. This nucleus seems to be part of the proprioceptive trigeminal system. The rostralmost part of PrV receives opthalmic projections, the caudalmost part receives mandibular projections, the maxillary area being intermediate. Taking the stereotaxic plane of the mallard atlas (weers, '71) into account, it can be concluded that the situation is essentially not different from that in the pigeon and from the situation described for mammals.
Distribution and light microscopic features of granule cells in the cochlear nuclei of cat, rat, and mouse
Authors: Mugnaini Enrico , Warr W. Bruce , Osen Kirsten Kjelsberg
Published: January 2005

In the present study the cytology and the topography of the cochlear granule cell domain (a comprehensive term introduced here for all granule cell‐containing regions of the cochlear nuclear complex) have been studied light microscopically in Nissl, Bielschowsky, and Golgi‐Del Rio‐Hortega material of cats, rats, and mice; in Golgi rapid material of 0–14‐day‐old kittens; and in sections of 6‐week‐old kittens following HRP injections in the superficial dorsal cochlear nucleus (DCN). The domain has been parcellated in seven subdivisions which, in spite of some species' differences, are easily identifiable in all of the included animals. The cochlear granule cells are considered as a particular class of neuron, which is slightly different from, but nevertheless principally similar to the cerebellar granule cells in both shape and mode of neuronal connections. The digitiform terminals of the cochlear granule cells differentiate after the first two weeks of extrauterine life. In several respects these cells show larger variation among species than do the cerebellar granules, the similarity between the two classes of granule cells being most conspicuous in the rodent. The silver, Golgi rapid, and HRP material suggest that all, or at least the majority, of the granule cell axons project to the molecular layer of the DCN, forming parallel fibers similar to those of the cerebellar cortex. Also, the cochlear parallel fibers traverse the spiny apical dendrites of principal neurons (the pyramidal cells) and the smoother dendrites of molecular layer stellate cells.
An ultrastructural study of the normal synaptic organization of the optic tectum and the degenerating tectal afferents from retina, telencephalon, and contralateral tectum in a teleost, holocentrus rufus
Authors: Ito Hironobu , Butler Albert B. , Ebbesson Sven O. E.
Published: January 2005

The ultrastructure of the optic tectum in the squirrel fish, Holocentrus rufus, has been studied and the normal synaptic organization is described. Synaptic terminals were classified into eight types (S1‐S6, F1, F2) by their morphology and synaptic relations. The distribution pattern for each type of terminal was determined by counting the relative number of terminals in each layer. Most S1 terminals are localized in Stratum marginale (SM), whereas S2 terminals are most common in Stratum fibrosum et griseum superficiale (SFGS). S3, S4, S5, F1, and F2 terminals are limited mainly to SFGS and Stratum griseum centrale (SGC). S6 terminals are most frequently seen in SGC and Stratum griseum periventriculare (SPV).

In order to determine the origins of the various types of synaptic terminals in the optic tectum, the telencephalon, eye, and optic tectum were removed unilaterally and areas of resultant degeneration examined. Electron microscopic observations show that nearly all S2 terminals in SFGS of the contralateral optic tectum degenerate after eye enucleation, whereas some S4 terminals in SFGS and SGC exhibit degernerative changes after removal of the ipsilateral telencephalon. Unilateral ablation of the optic tectum was associated with degenerative changes in occasional S5 terminals within SGC of contralateral optic tectum. All experiments resulted in some increased electron density of S3 and F terminals, some of which were identified as F2 terminals. The possible origins of S1 and S6 terminals, which were not altered in the present experiments, are discussed.
Representation pattern in the second somatic sensory area of the monkey cerebral cortex
Authors: Friedman D. P. , Jones E. G. , Burton H.
Published: January 2005

The body representation in the second somatic sensory area of macaques has been studied by tracing with anatomical techniques the projections from defined parts of the body representation in the first somatic sensory area (SI) to their terminal regions within the lateral sulcus. The second somatic sensory area (SII), as identified in terms of cytoarchitecture and its connection with the thalamic ventrobasal complex, is the only region of the lateral sulcus to receive a projection from SI. The nearby retroinsular area and area 7b receive a projection from area 5.

Within SII the face and head representations lie anteriorly, occupying the dorsalmost part of the insula and portions of the fronto‐parietal operculum. The digits, hand, and arm are represented posterior to the face and may take up the mediolateral extent of the parietal operculum in the region immediately in front of the posterior pole of the insula. The trunk representation is lateral to the arm representation, i.e., deep within the superior circular sulcus and on the dorsal insula. The hindlimb appears behind the trunk also occupying the superior circular sulcus in addition to the deepest 2–3 mm of the upper bank of lateral sulcus immediately posterior to the insula.

Areas 3b, 1, and 2 each project to SII, and their projections appear to converge within the representation of a given body part.

Injections of anterogradely transported tracers in SI label vertically oriented columnar arrays of terminal ramifications in SII, resembling those previously described for other cortico‐cortical projections within the sensory‐motor region. In experiments which combined anterograde and retrograde labeling, cells projecting from SII to SI formed columns exactly coinciding with the columns of anterogradely labeled axons terminating in SII. The cells of origin of cortico‐cortical projections emanating from SII formed two distinct laminar populations, one in the supragranular layers and the second mainly in layer VI. There is evidence for fiber terminations within layer VI mainly underlying the column formed by the terminal ramifications in layers I through IV.
Organization of somatosensory receptive fields in cortical areas 7b, retroinsula, postauditory and granular insula of M. fascicularis
Authors: Robinson C. J. , Burton H.
Published: January 2005

The boundaries of the second somatic sensory cortex (SII) in primates are difficult to define physiologically because cutaneous stimulation activates several regions around SII that do not receive projections from the ventroposterior nucleus of the thalamus. These cortical regions, which include portions of area 7b, the retroinsular (Ri) and postauditory fields (PA), and the granular insula (Ig) are largely buried within the lateral sulcus and most lie posterior to the caudal end of the insula. The differences in somatic activity in these various cortical fields in the unanesthetized cynomolgus monkey became apparent only after the properties of many neighboring neurons could be compared. Receptive fields for area 7b and Ig neurons were generally large (> 10cm2), with bilateral, moderately defined boundaries; some neurons in area 7b had receptive fields with labile borders as a function of wakefulness. In contrast, receptive fields for Ri neurons were generally < 10cm2 and contralateral, with stable, well‐defined boundaries.

Taken as an ensemble, the neurons in areas neighboring SII exhibited a very crude topography; but at the level of an individual neuron and its neighbor, there was never a pattern of gradual transition in peripheral receptive field locations between one unit and the next, like that seen in SII. In area 7b, this crude map was organized mediolaterally across the inferior parietal lobule and into the upper bank of the lateral sulcus, with the head represented medially and the lower trunk and hindlimb laterally. In Ri‐PA, an anteroposterior organization was noted along the fundus of the lateral sulcus with the head represented anterior to the lower trunk and hindlimb. No organization was apparent in Ig. Additional sensitivity to visual stimuli was noted in the more medial aspects of area 7b that were located on the exposed inferior parietal lobule. Sensitivity to auditory stimuli was principally found in PA and occasionally in Ri. The results, especially from area 7b, are discussed with respect to previous notions about the organization of SII.
Somatic submodality distribution within the second somatosensory (SII), 7b, retroinsular, postauditory, and granular insular cortical areas of M. fascicularis
Authors: Robinson C. J. , Burton H.
Published: January 2005

Somatic response properties were determined for over 1,300 neurons isolated within and near the lateral sulci of unanesthetized and unparalyzed cynomolgus monkeys. Somatic stimuli unequivocally activated the majority of units studied in SII (93%) and in cortical fields surrounding SII: area 7b (65%), the retroinsular field (74%), and the granular insula (76%).

No activation other than somatic was seen for SII neurons, and noxious somatic stimulation was rarely required. The SII units almost always responded in a rapidly adapting manner to hair or skin stimulation, but not both; however, the submodality distribution seen in SII varied as a function of peripheral receptor locations. Two small zones within SII contained neurons that responded only if the animal actively interacted with the stimulus.

In contrast, one‐half of the sample of neurons from area 7b unequivocally responded only to somatic stimulation. Although many neurons in the lateral parts of area 7b were vigorously activated by innocuous tactile stimulation, others demonstrated little association with an identifiable somatic submodality, had sluggish responses, required complex, noxious, visual or other non‐somatic stimuli for activation, and had labile response properties and receptive fields. Indeed, the responses of some area 7b neurons suggested a possible relationship with the animal's attention towards or anticipation of a noxious or a novel somatic stimulus. Neurons within the retroinsular cortex (Ri), which receives projections from the posterior nucleus (PO), primarily responded to light tactile stimulation of rapidly adapting skin receptors; less than 3% responded to moderate or high threshold mechanical stimulation. The sensitivity to tactile stimulation in Ri closely resembled the responses of SII neurons. Neurons in the granular insula (Ig) often responded to gentle hair deflection within receptive fields covering large areas of the body. Ig and area 7b were the principle loci within the lateral sulcus that contained neurons responding to noxious stimulation.

Owing to the great similarity in the somatic response properties within these areas in the awake and unparalyzed animal, the designation of cortical areas could only be made after correlating the recording sites with connectional and cytoarchitectonic analyses in the same animal. Consequently, previous physiological studies may have attributed to SII some of the response characteristics of neurons in neighboring areas.
Segmental localization of sensory cells that innervate the bladder
Authors: Applebaum Arnold E. , Vance W. Hugh , Coggeshall Richard E.
Published: January 2005

The present study labels the neuronal cell bodies that give rise to afferent fibers that innervate the bladder of cat and rat. The method used was the retrograde transport of horseradish peroxidase (HRP) from its injection site in the bladder to cells in the various dorsal root ganglia. In the rat, the labelled cells are located in the L1–L2 and L6–S1 dorsal root ganglia. In the cat, the labelled cells are located in the L2–L5 and S1–S4 dorsal root ganglia. This confirms older clinical findings, and for the first time directly demonstrates the afferent cell bodies for the bladder. The bladder afferents are small ganglion cells in both rat and cat, and because there is a correlation between the size of axon and the cell body from which it originates, we conclude that the great majority of bladder afferents are small myelinated or unmyelinated axons. In addition, by restricting the HRP to one side of the bladder, we were able to show that some afferent cell bodies send their distal processes across the midline. These results will be useful in considerations of the neural control of bladder function.
Development of spiny and aspiny neurons in the caudate nucleus of the dog during the first postnatal month
Authors: Tanaka Duke
Published: January 2005

The adult and developmental morphology of spiny and aspiny neurons in the dog caudate nucleus was examined using the Golgi‐Kopsch technique. In the adult, three types each of spiny and aspiny neurons were identified based upon dendritic morphology and cell soma size. They corresponded in large part to those neurons described previously in the caudate nuclei of the rat, cat, and monkey. At birth, dendrites of spiny neurons possessed varicosities, filopodia, and thick proximal dendritic stumps—all characteristic of immaturity. Maturation of these processes involved the thinning of proximal dendrites, lengthening of dendritic shafts, and growth of dendritic spines. Although most of the dendritic maturation occurred during the first postnatal month, spine densities and dendritic lengths of spiny I neurons at 30 days were still less than those seen in the adult. Aspiny I neurons were also immature at birth but lacked the filopodia and thicker proximal dendrites that characterized immature spiny neurons. Aspiny dendritic development involved primarily the lengthening of dendritic processes; by 30 days the aspiny I neurons were indistinguishable from those seen in the adult. These results suggest that dendritic development of spiny I neurons may extend well past the end of the first postnatal month and that studies investigating functional development in the caudate nucleus should consider the relatively extended time period required for maturation of these primary synaptic sites.
Innervation of embryonic rat cerebral cortex by catecholamine‐containing fibers
Authors: Schlumpf Margret , Shoemaker William J. , Bloom Floyd E.
Published: January 2005

Catecholamine‐containing neuronal processes penetrate to the outer superficial layers of the developing neocortex via the lateral neocortex anlage by embryonic day (ED) 16, only 48 hours after the final cell division of the catecholamine neurons in the mesencephalon and pons‐medulla. Sagittal sections were taken from a series of perfused embryos at precise time‐intervals after insemination. The corpus striatum receives a large catecholamine input and serves as a reference for tracing the very fine varicose processes that course through the caudate nucleus to innervate the more rostral structures of the developing neocortex cerebri. The input fibers to the neocortex arrive via three to four small fiber bundles, entering chiefly at the ventro‐rostral aspect. The bundles then bifurcate into the deep and superficial layers of the cortex. Between ED16 to ED21 the innervation progresses in ventral to dorsal and rostral to caudal directions. Embryonically, fluorescent fibers are observed in the outermost superficial layer and in the intermediate zone, below the cortical plate; only rarely are they seen crossing the cortical plate. The demonstration of monoaminergic neuronal fibers reaching neocortical structures by ED16 adds further weight to the speculation that they may play a role in induction and differentiation, and suggests that post‐natal experimental manipulations using ascending‐bundle lesions will have been performed at least five days after the arrival of catecholamine fibers at their cortical destinations.
Neuroanatomy of the visual afferents in the horseshoe crab (Limulus polyphemus)
Authors: Chamberlain Steven C. , Barlow Robert B.
Published: January 2005

The central nervous system of Limulus consists of a circumesophageal ring of fused ganglia and a paired ventral nerve cord. The anterior portion, the protocerebrum, receives sensory inputs including visual information. Three optic nerves, one each from the lateral eye, median ocellus, and ventral eye enter each side of the protocerebrum. The central connections of each optic nerve were determined by staining cut nerve trunks with cobalt chloride.

The lateral optic nerve innervates the lamina, medulla, optic tract, ventral central body, and ocellar ganglion. The branching patterns of single axons, probably those of eccentric cells in the lateral eye retina, were observed. Single, large‐diameter axons in the lateral optic nerve ramify at seven loci including sites in each of the structures innervated by the lateral optic nerve as a whole.

The median optic nerve innervates the ocellar ganglion, central body, optic tract, and medulla. Three types of branching patterns were observed for single, large‐diameter fibers in the median optic nerve. One type bypasses the ocellar ganglion and innervates the central body. A second type passes through the ocellar ganglion and optic tract without branching and innervates the posterior medulla. A third type innervates the ocellar ganglion, ventral central body, optic tract, and medulla.

The ventral optic nerve is composed of large‐diameter axons of ventral photoreceptors. Each axon enters the ganglion cell layer of the medulla and branches over a planar area less than 150 μm in diameter.

We also observed that axons from mechanoreceptors on the anterior carapace innervate the posterior neuropil of the medulla, and that about 5% of the neurons in the medullar ganglion cell layer send axons to the ipsilateral circumesophageal connective.