bluuebunny/crossref_metadata_2025 huggingface dataset:
Mormyromast electroreceptor organs and their afferent fibers in mormyrid fish: I. Morphology
Authors: Bell C. C. , Zakon H. , Finger T. E.
Published: January 2005

Mormyromast electroreceptor organs are the most numerous type of electroreceptor organs in mormyrid electric fish and provide the sensory information necessary for active electrolocation. Mormyromast organs and their primary afferent fibers have not been studied very extensively. Both morphological and physiological questions remain to be answered before the neural basis of active electrolocation in mormyrids can be understood. This paper examines four different aspects of the morphology of mormyromast organs and afferent fibers: (1) Mormyromast organs in the skin. The innervation patterns for the two types of separately innervated sensory cells in the mormyromast organ are described on the basis of silver‐stained whole mounts of skin. The number of sensory cells per mormyromast organ increases linearly with fish growth for both types of sensory cells. (2) Relation between peripheral sensory cell innervated and central zone of termination for mormyromast afferent fibers. The afferent fibers arising from the two types of sensory cell in the mormyromast organ project to separate zones of the electrosensory lateral line lobe, as shown by using retrograde labeling with horseradish peroxidase. (3) Central trajectories and terminal arbors of mormyromast afferent fibers. These aspects of mormyromast fibers are described by using intracellular staining of individual fibers as well as whole nerve staining of an electrosensory nerve. (4) Fine structure of mormyromast afferent terminals in the electrosensory lateral line lobe. Afferent fibers make various synaptic contacts, including contacts of a mixed type, gap junction‐chemical, onto a restricted class of granule cells. The fine structure is described based on electron microscopy of horseradish‐peroxidase‐labeled fibers.

The results provide an anatomical base for current physiological studies on mormyromast afferent fibers.
Visual area MT in the Cebus monkey: Location, visuotopic organization, and variability
Authors: Fiorani Mario , Gattass Ricardo , Rosa Marcello G. P. , Sousa Aglai P. B.
Published: January 2005

The representation of the visual field in the dorsal portion of the superior temporal sulcus (ST) was studied by multiunit recordings in eight Cebus apella, anesthetized with N2O and immobilized with pancuronium bromide, in repeated recording sessions. On the basis of visuotopic organization, myeloarchitecture, and receptive field size, area MT was distinguished from its neighboring areas.

MT is an oval area of about 70 mm2 located mainly in the posterior bank of the superior temporal sulcus. It contains a visuotopically organized representation of at least the binocular visual field. The representation of the vertical meridian forms the dorsolateral, lateral, and ventrolateral borders of MT and that of the horizontal meridian runs across the posterior bank of ST. The fovea is represented at the lateralmost portion of MT, while the retinal periphery is represented medially.

The representation of the central visual field is magnified relative to that of the periphery in MT. The cortical magnification factor in MT decreases with increasing eccentricity following a negative power function. Receptive field size increases with increasing eccentricity. A method to evaluate the scatter of receptive field position in multiunit recordings based on the inverse of the magnification factor is described. In MT, multiunit receptive field scatter increases with increasing eccentricity.

As shown by the Heidenhain‐Woelcke method, MT is coextensive with two myeloarchitectonically distinct zones: one heavily myelinated, located in the posterior bank of ST, and another, less myelinated, located at the junction of the posterior bank with the anterior bank of ST.

At least three additional visual zones surround MT: DZ, MST, and FST. The areas of the dorsal portion of the superior temporal sulcus in the diurnal New World monkey Cebus are comparable to those described for the diurnal Old World monkey, Macaca. This observation suggests that these areas are ancestral characters of the simian lineage and that the differences observed in the owl monkey may be secondary adaptations to a nocturnal ecological niche.
Brainstem facial‐motor pathways from two distinct groups of stapedius motoneurons in the cat
Authors: Guinan John J. , Joseph Michael P. , Norris Barbara E.
Published: January 2005

To determine the brainstem origins and axonal routes of stapedius motoneurons, we labeled motoneurons by injecting cat stapedius muscles with horseradish peroxidase. Some injections were made in normal cats and some in cats in which the middle segment of the internal facial genu had been cut. By tracing labeled axons and by comparing the locations of labeled cell bodies in normal and lesioned cats, we divided stapedius motoneurons into two groups: “perifacial” and “accessory.” Perifacial stapedius motoneurons have cell bodies located around the motor nucleus of the facial nerve and axons which follow the classical course of facial motor axons through the internal genu of the facial nerve. Accessory stapedius motoneurons have cell bodies near the descending facial motor root and axons which ascend to the rostral tip of the internal facial genu, abruptly reverse direction, and then join the descending facial motor root. The sharply hooked course of axons of accessory stapedius motoneurons is similar to the course of axons from other accessory nuclei of cranial nerves V‐VII. Our present results, with those of McCue and Guinan (J. Neurophysiol. 60:1160–1180, '88), demonstrate that cats have two groups of stapedius motoneurons which can be separated anatomically by the locations of their cell bodies or by the courses of their axons, and which, on the average, have different response properties.
Enkephalin‐immunoreactive neuronal projections from the medulla oblongata to the intermediolateral cell column: Relationship to substance P–immunoreactive neurons
Authors: Sasek Cathrine A. , Helke Cinda J.
Published: January 2005

The present study investigated the ventral medullary distribution of enkephalin‐immunoreactive neurons that project to the intermediolateral cell column and the relationship of these neurons to substance P–immunoreactive neurons. Neurons that projected to the intermediolateral cell column were identified by the presence of rhodamine‐labeled microspheres within the neuronal cell body after an injection of the microspheres into the intermediolateral cell column of the third thoracic spinal cord segment. Enkephalin‐ and substance P‐immunoreactivities were identified by dual‐color immunohistochemistry. Enkephalin‐immunoreactive neurons that projected to the intermediolateral cell column were present in the raphe magnus, the nucleus reticularis magnocellularis pars alpha, the paragigantocellular reticular nucleus, and the parapyramidal region. These neurons were present throughout the rostrocaudal extent of each of these nuclei. However, in the raphe magnus the greatest number was present at more rostral levels of the nucleus. The morphology and distribution of enkephalin‐immunoreactive neurons that projected to the intermediolateral cell column were similar to those of enkephalin‐immunoreactive neurons that were not observed to contain rhodamine‐labeled microspheres. Substance P– and enkephalin‐immunoreactive neurons that projected to the intermediolateral cell column were present in similar distributions in each of the nuclei studied, except the raphe magnus. The raphe magnus contained more enkephalin‐ than substance P–immunoreactive neurons at rostral levels and more substance P‐immunoreactive neurons than enkephalin‐immunoreactive neurons at caudal levels. Coexistence of substance P‐ and enkephalin‐immunoreactivities in ventral medullary neurons that projected to the intermediolateral cell column was rarely seen. These studies support the hypothesis that ventral medullary enkephalinergic neurons project to the intermediolateral cell column where they could act to modulate preganglionic sympathetic activity.
Modulation of disk margin structure during renewal of cone outer segments in the vertebrate retina
Authors: Corless Joseph M. , Worniałło Ewa , Fetter Richard D.
Published: January 2005

In the process of disk renewal in retinal cone outer segments (COSs), apical displacement of disks must be coupled to systematic reductions in disk area and perimeter in order to retain overall conical geometry. We have quantified these changes in disk area and perimeter segment lengths by morphometric analyses of cross sections of fully formed disks taken from basal to apical ends of COSs. Specifically excluded from these analyses are data arising from partial or incomplete disks within the COS, which do not conform to the conical geometry and which constitute a minor fraction of the COS disk population. Thus, our results address the long‐range pattern of structural changes affecting the major population of disks along the length of the COS. Our data indicate that decreases in total disk margin length associated with apical displacement of fully formed disks are due to decreases in the length of the margin opposite the cilium, i.e., the open margin segment. In contrast, the average length of the closed margin segment remains constant or increases slightly in the apical direction.

The open margins of frog COS disks have recently been shown to possess a distinctive lattice of membrane‐associated components (Fetter and Corless: Invest. Ophthalmol. Vis. Sci. 28:646–657, '87). We have also examined COSs by the freeze‐fracture, deep‐etch technique for evidence of a mechanism whereby measured changes in open margin length may be accommodated while maintaining the overall organization of the open margin segments. In regions of membrane continuity between open margins and the COS plasma membrane, we have observed elevated ridges on the plasma membrane that (1) tend to lie parallel to the open margin segments, (2) have a similar axial spacing, (3) occasionally demonstrate interconnecting filaments similar to those of the open margin lattice, and (4) appear to have a particulate substructure. The mechanism proposed for reducing open margin length involves tangential displacement of the lateral edges of the open margin lattice to the adjacent plasma membrane. These shifted lattice domains initially give rise to the plasmalemmal ridges, which subsequently disassemble, and whose components become redistributed in the COS plasma membrane. These structural features of COS open margins suggest several revisions of our earlier model of disk morphogenesis (Corless and Fetter: J. Comp. Neurol. 257:24–38, '87), which was based on the margin structure of ROS disks alone.

Eckmiller (J. Cell Biol. 105:2267–2277, '87) has recently proposed that partial disks observed within the COS represent sites of new disk formation. We evaluate the consequences of partial disk geometries for local remodelling of the open margin lattice and briefly outline an alternative interpretation of the partial COS disks that is fully consistent with available morphological data.
Photoreceptor topography of the retina in the adult pigtail macaque (Macaca nemestrina)
Authors: Packer Orin , Hendrickson Anita E. , Curcio Christine A.
Published: January 2005

In spite of the crucial role retinal photoreceptors play in mapping optical images into a pattern of neural excitation, there are no complete studies of photoreceptor topography in any primate retina. We have measured the spatial density and inner segment areas of cones and rods across the whole mounted retinas of three adult pigtail macaques (Macaca nemestrina) and constructed maps of photoreceptor density and inner segment diameter.

These retinas contain an average of 3.1 million cones (2.8–3.3 million), with an average peak foveal cone density of 210,000 cones/mm2 (190,000–260,000 cones/mm2). Cone density falls steeply with increasing eccentricity, to 100,000 cones/mm2 at 200 μm from the fovea, and to 50,000 cones/mm2 at 750 μm. Imposed on this gradient is a “streak” of higher cone density along the horizontal meridian. At equivalent eccentricities, cone density is higher in nasal and inferior retina. Cone inner segments increase in diameter from 2.3 μm at the foveal center to 11 μm in far temporal retina and 10 μm in far nasal retina.

These retinas contain an average of 60.1 million rods (44.9–75.3 million). Rod density is zero within 20 μm of the foveal center, increases to the crest of a “rod ring” at the eccentricity of the optic disk, and then declines. Central rod topography is asymmetric, with higher densities in superior retina. Density along the crest of the rod ring peaks in superior retina at 177,000 rods/mm2, dips as low as 120,000 rods/mm2 along the horizontal meridian, and increases to about 150,000 rods/mm2 in inferior retina. Far peripheral rod topography is relatively symmetric around the fovea. Rod inner segment diameter ranged from 1.5 μm in the fovea to 4 μm at the temporal edge and 3.4 μm at the nasal edge of the retina. At eccentricities exceeding 6 mm, rod inner segment diameter was greater temporally than nasally.

Cone inner segments cover 85–90% of the central fovea, with extrareceptor space accounting for the remainder. Cone coverage declines with increasing eccentricity to 20% at the temporal edge and 35% at the nasal edge of the retina. In contrast, rod coverage increases from zero at the foveal center to a maximum of 65% in temporal retina and 50% in nasal retina.

The photoreceptor topography of the pigtail macaque is qualitatively similar to that of other macaques and to humans. Photoreceptor topography is formed by a complex interaction between regional changes in cone and rod density and inner segment diameter.
Terminal arbors of single ON‐center and OFF‐center X and Y retinal ganglion cell axons within the ferret's lateral geniculate nucleus
Authors: Roe Anna W. , Garraghty Preston E. , Sur Mriganka
Published: January 2005

The lateral geniculate nucleus of the ferret contains not only eye‐specific layers, but a further subdivision of layers A and A1 into inner and outer sublaminae that contain, respectively, ON‐center and OFF‐center cells (Stryker and Zahs, '83). To study how the arbors of single retinal ganglion cell axons correlate with these cellular divisions, we have examined the morphology of physiologically classified retinal axons in the ferret's lateral geniculate nucleus.

As in cats, we could classify retinal axons as X or Y on the basis of a number of physiological criteria. X and Y axons have distinct patterns of termination in the lateral geniculate nucleus. Contralateral X axons innervate lamina A and ipsilateral axons lamina A1. X axons are further segregated in these laminae so that ON‐center axons terminate in the inner sublamina, and OFF‐center axons in the outer sublamina. We did not observe any branches of X axons innervating the medial interlaminar nucleus or the midbrain. Y axons have much larger terminal arbors and exhibit greater variation in their terminations. Generally, within layers A and A1, ON‐center Y axons innervate the inner sublamina and OFF‐center Y axons innervate the outer sublamina. However, they often innervate both sublaminae, and occasionally have a few boutons in the inappropriate lamina as well. Y axons also terminate in the dorsal C laminae, the interlaminar zones, and the medial interlaminar nucleus; branches of these axons course toward the midbrain, presumably to innervate the superior colliculus. Thus, whereas the Y pathway in the ferret is one of high divergence, the X pathway appears to be the substrate for segregated ON and OFF channels through the lateral geniculate nucleus.
Primate spinothalamic pathways: I. A quantitative study of the cells of origin of the spinothalamic pathway
Authors: Apkarian A. Vania , Hodge Charles J.
Published: January 2005

In six monkeys spinothalamic (STT) cells were retrogradely labeled by injecting 2% wheat germ agglutinin–conjugated horseradish peroxidase into the somatosensory thalamus. Following a 5‐day survival period, the animals were perfused and the tissue was removed and processed with the tetramethyl benzidine technique. In all animals there were HRP‐labeled STT cells in all segments of the spinal cord. In one old world monkey, the injection included most of the thalamus and resulted in 18,235 estimated total number of STT cells. Of this total, 35% were located in the upper cervical segments (C1–C3), 18% were located in C4–C8, 19% were in the thoracic spinal cord with most found in T1–T3; 6% were in L1–L3, 13% were in L4–L7, and 7% were in the coccygeal segments. Of the total labeled STT cells, 17% were found in the spinal cord ipsilateral to the thalamic injection; 53% of these cells were located in C1–C3 primarily in lamina VIII. The percentage of label found in the contralateral lower cervical region laminae I–III (43–50%), IV–VI (33–48%), and VII–X (8–17%) was similar among three animals with similar thalamic injections.

The distributions of the shapes of the labeled STT cells were similar for each lamina between the lower cervical and lower lumbar regions. The mean diameter of the labeled STT cells varied with spinal cord segment and lamina. The lamina I STT cells were the smallest. In the cervical spinal cord, lamina VIII STT cells had the largest diameters, while in the lumbar region laminae IV–VI had the largest STT cells.
Development of location‐specific hair cell stereocilia in denervated embryonic ears
Authors: Corwin Jeffrey T. , Cotanche Douglas A.
Published: January 2005

The developmental mechanisms that allow physiological coding of acoustic pitch have remained unexplained. Cochlear hair cells that have different structures respond to different sound frequencies and synapse with neurons that project to different locations in the brain. How do these hair cells develop appropriate structures, and how are the connections between specific hair cells and the neurons that code for their pitch sensitivities matched? We have investigated one aspect of this by denervating embryonic chicken ears, before the time of hair cell production, and then transplanting them to the aneural chorioallantoic membrane of host embryos where they have continued to develop. We report that vestibular and auditory hair cell phenotypes differentiate appropriately and that correct gradients of hair cell structural phenotypes, as expressed in stereocilia bundles, develop in the cochleae of these denervated ears. Therefore, the normal development of gradients in hair cell stereocilia properties must be controlled by location‐specific cues originating in the ear itself. Neuronally directed modification of target cell phenotypes is not required for the quite specific phenotype development represented by the stereocilia bundles of individual hair cells and the connectional matching in the numerous distinct peripheral information lines of the auditory system.
Prenatal development of GABA‐ergic neurons in the neocortex of the rat
Authors: van Eden C. G. , Mrzljak L. , Voorn P. , Uylings H. B. M.
Published: January 2005

The present study shows that in the prenatal rat neocortex the GABA immunoreactive neurons are not limited to the marginal, subplate, and intermediate zones, but are also found in all fetal zones of the cerebral anlage. The first GABA‐ergic cells are observed on embryonic day 14 in the plexiform primordium. On embryonic day 15, a second population of GABA‐ergic cells is observed in the intermediate zone. Beginning on day 16 of gestation and continuing throughout gestation, GABA‐ergic neurons are observed in the marginal zone, the subplate zone, the cortical plate, and the ventricular and subventricular zones. Furthermore, while the number of GABA‐ergic cells in the cortical plate increases, GABA‐ergic neurons in the intermediate zone and subventricular zone decrease in number after embryonic day 19.
Regional differences in the distribution of muscarinic cholinergic receptors in the macaque cerebral cortex
Authors: Lidow Michael S. , Gallager Dorothy W. , Rakic Pasko , Goldman‐Rakic Patricia S.
Published: January 2005

The in vitro autoradiographic technique was used to characterize the density and laminar distribution of muscarinic cholinergic receptors in 12 cytoarchitectonic areas in the frontal, parietal, and occipital lobes of the rhesus monkey. The entire population of muscarinic receptors was labeled with [3H]quinuclidinyl‐benzilate; the M1 receptor subtype was labeled with [3H]pirenzepine; and the density of the M2 receptor subtype was estimated by subtracting the density of M1 receptors from the total population. The overall density of M1 and M2 receptor subtypes was similar throughout the cerebral cortex. However, their laminar distribution varied regionally. In cortical regions of the parietal and occipital lobes and in the primary motor cortex of the frontal lobe, both M1 and M2 receptor subtypes were concentrated in the supragranular layers. By contrast, in prefrontal cortical areas, the combined population of M1 and M2 receptors was evenly distributed across the cortical layers, though M1 receptors were most dense and M2 receptors least dense in layer IV. The difference in the distribution of cholinergic receptors in the prefrontal cortex compared to other neocortical areas reveals a degree of chemoarchitectural specificity of this region with respect to cholinergic markers that has escaped immunohistochemical and other anatomical and functional techniques.
Regeneration of the neurohemal terminals for identified cerebral neurosecretory cells in an insect
Authors: Agui Noriaki , Westbrook Anne L. , McQueen Chapman T. , Flanagan Thomas R. , Bollenbacher Walter E.
Published: January 2005

The axons of specific neurosecretory cells, L‐NSC III, in the brain of the tobacco hornworm, Manduca sexta, were transected during larval‐pupal development to study the effects of this type of lesion on these peptidergic neurons and to begin to identify factors that may regulate their regeneration and growth. The two somata of these bilaterally paired neurons produce the prothoracicotropic hormone and are located in the pars intercerebralis. Their axons exit from the contralateral brain lobe via a retrocerebral nerve and pass through the corpus cardiacum before terminating at the glandular corpus allatum. At the corpus allatum, the L‐NSC III axons arborize to form the terminal neurohemal organ for prothoracicotropic hormone release. The retrocerebral nerve was severed either in vitro followed by brain transplantation or in situ; in either protocol, the distal axon segments and corpus allatum were removed. The ability of the injured L‐NSC III axons to regenerate was assessed immunocytologically by using a monoclonal antibody against the prothoracicotropic hormone. In both treatments, the proximal axon stumps exhibited regenerative growth as early as 1 day after axotomy, and, by the third day, neurites had extended. By the fifth day, the regenerating axons had branched to form terminal varicosities similar to those of a normal neurohemal organ. The regenerated neurohemal structure appeared to be functional, because larvae that had been bilaterally axotomized were able to metamorphose to pupae, a process requiring temporally precise periods of prothoracicotropic hormone release. In addition to the regeneration of the terminal axon structures, several other responses to axotomy and retrocerebral organ excision occurred. These included an apparent accumulation of prothoracicotropic hormone in the axons and regenerating neurohemal‐like structures, sprouting of ectopic neurites from the axotomized somata, and a change in shape of the cell bodies from spherical to ovoid.
Glucose‐6‐phosphate dehydrogenase activity in the olfactory system of the young rat: An enzyme histochemical study using computerized image analysis
Authors: Coopersmith Robert , Leon Michael
Published: January 2005

An understanding of olfactory system glucose metabolism is necessary for the interpretation of radiolabeled 2‐deoxyglucose studies of odor processing since the relationship between glucose uptake and neural activity is based on assumptions regarding cellular glucose utilization. As part of an ongoing study examining divergent pathways of glucose metabolism in the olfactory system, the relative activity of glucose‐6‐phosphate dehydrogenase, the rate‐limiting enzyme of the hexose monophosphate shunt, was examined among cells of the rat olfactory bulb and anterior olfactory nucleus, by using enzyme histochemistry on fresh frozen tissue. Optical density measurements of formazan reaction product in stained tissue were quantified by computerized image analysis. To aid in the identification of histochemically stained neurons, alternate sections were Nissl‐stained. The highest olfactory bulb dehydrogenase levels were found in the olfactory nerve and glomerular layers. Individual mitral and tufted cells also showed high dehydrogenase activity. In most stained neurons, formazan reaction product filled the cytoplasm and sometimes extended into the proximal part of dendrites and axons. The external plexiform and granule cell layers had low enzyme activity. High activity also was seen in pyramidal cells of pars dorsalis and pars lateralis of the anterior olfactory nucleus, one of the first, and most rostral of the olfactory bulb projection sites. High glucose‐6‐phosphate dehydrogenase activity in the olfactory system indicates that a significant amount of glucose can be channeled through the hexose monophosphate shunt in these neurons, with a concomitant production of NADPH. This may reflect high activity of cellular detoxification enzymes that rely on NADPH for reducing power. Such detoxification processes may be engaged in response to the potential entry and transsynaptic movement of airborne chemicals into the brain via the olfactory system.
Distribution of uncrossed axons along the course of the optic nerve and chiasm of rodents
Authors: Baker G. E. , Jeffery Glen
Published: January 2005

The distribution of the ipsilaterally projecting population of retinofugal axons has been analyzed following injections of horseradish peroxidase (HRP) into the optic tract of adult hamsters and rats to determine whether the topographical segregation of the cells of origin seen in the retina is maintained by their axons throughout the course of the optic nerve and chiasm.

Axons are limited to a roughly appropriate topographic location within the intraorbital course of the nerve but this organization changes at levels progressively closer to the optic chiasm. Immediately rostral to the chiasm labelled profiles are found dispersed across most of the cross‐sectional area of the nerve. This dispersal is maintained within the region of the optic chiasm where a complex rearrangement of ipsilaterally projecting axons takes place.

The results show that axons are not retinotopically organized along the entire length of the optic nerve. The order of axons changes along the course of the nerve and in the optic chiasm. The change seen within the intracranial course may indicate a chronotopic re‐sorting of axons prior to the optic tract where the organization of axons has previously been interpretted as a map of time of axon arrival.
Interrelationship of the distribution of neuropeptides and tyrosine hydroxylase immunoreactivity in the human substantia nigra
Authors: Haber S. N. , Groenewegen H. J.
Published: January 2005

The relationship in the human substantia nigra of peptidergic fibers with intrinsic dopaminergic neurons was studied in adjacent coronal sections of the mesencephalon immunohistochemically stained for enkephalin (ENK), substance P (SP), and tyrosine (TH) hydroxylase immunoreactivity. TH‐positive elements are present in the substantia nigra in at least two different arrangements: (1) a dorsal tier of rather loosely arranged neurons, which is continuous medially with the ventral tegmental area and laterally with the retrorubral area, (2) a ventral tier of more closely packed neurons, clusters of which frequently form finger‐like extensions deep into the pars reticulata. This ventral region contains TH‐positive dendrites extending ventrally into the pars reticulata.

The distribution of ENK is mainly restricted to the medial half of the ventral aspect of the substantia nigra, while SP occupies its entire rostral‐caudal and medial‐lateral extents. Peptide‐positive fibers vary in density from dense to light. There is very little overlap between the dorsal tier of the TH‐positive neurons and the ENK or SP staining. The dorsal part of the peptide‐immunoreactive area extensively overlaps with the TH‐positive neurons of the ventral tier of cells. The ventral part of the peptide‐positive area overlaps with the pars reticulata of the substantia nigra in which the TH‐positive dendrites extend.

The overlap between the neuropeptide fibers and the TH‐positive cells of the ventral tier is not complete, with cells found both within and outside peptide‐positive fiber networks. Three patterns of overlap emerge. In dorsal regions elongated cell clusters lie partially within and partially outside the dense peptide‐positive fiber networks. In the ventral regions TH‐positive cells are either completely embedded within peptide fibers or clusters of cells are present in peptide‐free zones.

These data suggest that specific peptidergic pathways differentially innervate the substantia nigra. TH cells which lie within or outside these fibers may reflect functionally different subsystems in the striatonigral pathways in the human.
Fate of descending interneurons in the metamorphosing brain of an insect, the beetle Tenebrio molitor L
Authors: Breidbach Olaf
Published: January 2005

The fate of descending brain‐thoracic neurons in the metamorphosing supraoesophageal ganglion of the mealworm beetle, Tenebrio molitor, is described. Comparison of the descending neurons of the larval, various pupal, and adult stages outlines a high degree of topological invariance in the structure of descending interneurons; i.e., the basic organization of the imaginal set of descending neurons is anticipated by the structure of the larval neurons. Single descending neurons of analogous clusters of larval and imaginal neurons outline a virtual identical structural organization in both the larval and imaginal brain.

There is a quantitative increase from approximately 70 to approximately 120 brain‐thoracic interneurons during metamorphosis. This increase does not cause complex transformations in the structural organization of the descending interneurons. Experiments with the DNA‐inhibitor hydroxyurea prove that the described topological invariant structure of the set of descending neurons is based on the persistence of individually descending neurons. There is evidence that the whole set of larval interneurons persists throughout the beetles' metamorphosis.

The essential characteristics of the later imaginal set of descending neurons are qualitatively and quantitatively established within the first 10% of pupation. Structural invariance of the set of descending neurons is discussed with regard to the significance of cellular interaction for the mechanisms of metamorphic reorganization of nervous tissue.
Comparative immunocytochemical study of the catecholaminergic and peptidergic afferent innervation to the dorsal vagal complex in rat and guinea pig
Authors: Siaud P. , Denoroy L. , Assenmacher I. , Alonso G.
Published: January 2005

Light and electron microscopic immunocytochemistry was used to study the fine structural organization of the catecholaminergic and hypothalamic peptidergic innervation of the dorsal vagal complex of the medulla oblongata in the rat and guinea pig, the latter of which is known to lack central adrenergic neurons. In the rat, adrenergic fibers immunoreactive to phenylethanolamine‐N‐methyltransferase were concentrated in the dorsal motor nucleus of the vagus, where they established frequent symmetric synapses with dendrites and perikarya. On the other hand, the density of both oxytocin‐ and corticotropin‐immunoreactive fibers appeared far lower in this nucleus than in the dorsal regions of the nucleus of the tractus solitarius, where they formed asymmetric synapses with small dendrites. In tissue treated for the dual labeling of two neuronal antigens, oxytocin‐ or corticotropin‐reactive fibers were in close contact with adrenergic neurons in this dorsal medullary region. In the guinea pig, unlike the rat, the dorsal motor nucleus of the vagus contained large amounts of oxytocin‐ and corticotropin‐reactive fibers, which formed many symmetric synapses with perikarya and dendrites. Taken together, these data suggest that the control of vagal preganglionic neurons by hypothalamic peptidergic neurons involves a bisynaptic neuronal pathway including adrenergic medullary neurons in the rat, whereas it is direct in the guinea pig, which lacks this adrenergic relay.
Ascending unmyelinated primary afferent fibers in the dorsal funiculus
Authors: Patterson J. T. , Head P. A. , McNeill D. L. , Chung K. , Coggeshall R. E.
Published: January 2005

The primary purpose of the present study is to obtain evidence as to the destination of the recently discovered unmyelinated primary afferent fibers in the mammalian dorsal funiculus. To do this rat dorsal roots were transected unilaterally from segments T8 or T9 caudally, and the numbers of axons were determined in the C3 fasciculus gracilis in normal animals and from both sides of the rhizotomied animals. In addition, C3 fasciculus gracilis counts were done in animals that had complete T6 or T10 spinal transections. The data indicate that there is an 80% loss of unmyelinated axons ipsilaterally and a 60% loss contralaterally in the fasciculus gracilis of the rhizotomied animals. These findings are interpreted as indicating that a significant fraction of the unmyelinated fibers in the fasciculus gracilis ascend, presumably to the nucleus gracilis in the brain stem, and also that a significant number of these fibers branch. We also provide evidence for contralateral myelinated primary afferent fiber projection in the fasciculus gracilis and show that the myelinated primary afferent fibers seem to be a more diverse population than the unmyelinated primary afferent fibers in the C3 fasciculus gracilis.
Cytoarchitecture of the tectum mesencephali in salamanders: A golgi and HRP study
Authors: Roth Gerhard , Naujoks‐Manteuffel Christiane , Grunwald Wolfgang
Published: January 2005

The tectum mesencephali of salamanders shows a morphology that has long been considered primitive when compared with that of frogs. The alternative hypothesis is that the salamander brain is secondarily simplified. In order to test these two hypotheses, the cytoarchitecture of the tectum and the projections of tectal neurons were studied in 11 species of salamanders. Application of the Golgi method reveals three major morphological types. Type 1 has a very wide dendritic arborization mostly confined to the deep fiber layers, and somata are always located within the most superficial part of the periventricular gray matter. Type 2 possesses a wide to medium‐size dendritic arborization. In subtype 2a the somata are located in the uppermost part of the gray, and dendrites always reach the uppermost layer of retinal afferents; in subtype 2b the somata are found in deeper parts of the gray, and dendrites arborize in the deeper layers of retinal afferents; and in subtype 2c the somata are also located in deeper parts, but the wide dendritic arborization is confined to deep fiber layers. Type 3 shows the narrowest dendritic arbors that always reach the upper two tectal fiber layers. The somata are found at any depth of the gray matter.

HRP experiments reveal a correlation between morphological differences and the projections of tectal neurons. Type 1‐ and type 2c‐like cells constitute the uncrossed tecto‐bulbo‐spinal tract, whereas type 1‐ and type 2a‐like cells and migrated large spindle‐shaped cells (Salamandra) constitute the crossed tecto‐bulbo‐spinal tract. Type 3‐like neurons project to thalamic, pretectal and isthmc termination sites.

The HRP experiments also demonstrate the existence of two classes of mesencephalic trigeminal cells.

A comparison shows that salamanders and frogs possess very similar functional and morphological types of tectal cells. However, tectal cells of salamanders show a “juvenile” morphology, and the number of migrated cells is about 10 times higher in frogs compared to salamanders. Both phenomena are seen as the result of secondary simplification of brain structures in the context of paedomorphosis.
Variation and symmetry in the lumbar and thoracic dorsal root ganglion cell populations of newly metamorphosed xenopus laevis
Authors: Sperry David G.
Published: January 2005

The size of the lumbar and thoracic dorsal root ganglion cell populations in normally developing newly metamorphosed Xenopus laevis were measured in order to determine whether these neuron populations have the same characteristics as the hindlimb motoneuron population; i. e., large individual as well as sibling group differences, striking bilateral symmetry, and a rough correspondence between neuron number and body size that suggests some peripheral control of cell number during normal development (Sperry, J. Comp. Neurol. 264:250‐267). Among animals from three sibling groups, the total numbers of thoracic and lumbar ganglion cells are highly variable and symmetrical, although symmetry is not uniformly present at the level of individual ganglion pairs. Significant sibling group differences in neuron number are also present. Metamorphic body size and cell number in the thoracic but not in the lumbar ganglia are significantly correlated. The motoneurons innervating the hindlimbs were also counted and measured in the same animals. While variable as well as symmetrical, motoneuron number and metamorphic body size are correlated in only two of the three sibling groups. Interestingly, the numbers of motoneurons and lumbar ganglion cells, two populations of neurons whose sizes one might predict would be significantly correlated in normally developing animals, are not correlated. The relationship between these observations and currently held views concerning how neuron numbers might be controlled during normal development is discussed.
Müller cells in adult rabbit retinae: Morphology, distribution and implications for function and development
Authors: Robinson Stephen R. , Dreher Zofia
Published: January 2005

We describe the morphology and distribution of Müller cells in wholemounts of rabbit retinae labelled with either monoclonal antibodies (anti‐Vimentin, 3H3, 4D6, and 4H11), or intracellular horseradish peroxidase. Several new features of Müller cell organization are noted. First, Müller cells appear to compose a single morphological class and their morphology varies systematically with retinal thickness. Second, in contrast to other retinal glia, Müller cells have a neuronlike distribution, with a peak density of 10,700–15,000 cells per 2 at the visual streak and a minimum density of 4,400–6,000 per mm2 at both the superior and inferior retinal edges. There are 4.2 ± 0.5 × 106 Müller cells per retina. Third, unlike in other species, rabbit Müller cells do not contact blood vessels, suggesting that they do not participate in the transfer of metabolites or in the blood:retinal barrier. Fourth, each Müller cell has a vitread endfoot about 20–40 μm in diameter composed of numerous fimbriae. The fimbriae from a single Müller cell generally contact several axon fascicles in the nerve fibre layer, and at each point along its length each fascicle is enclosed by the overlapping fimbriae from several Müller cells. Fifth, in the inner and outer plexiform layers, numerous filamentous branchlets extend 20 μm or more from the radial trunk, interweaving with branchlets from nearby Müller cells to form dense and continuous strata. In the ganglion cell layer and outer nuclear layer, Müller cell processes completely wrap neuronal somata, whereas in the inner nuclear layer they partially wrap somata. We discuss the functional and developmental implications of these observations.
Morphological organization of thalamocortical relay cells in the dorsal lateral geniculate nucleus of the north american opossum
Authors: Condo George J. , Wilson Paul D.
Published: January 2005

The morphology of relay cells in the dorsal lateral geniculate nucleus of the North American opossum was studied by using both Golgi‐Cox material and cells stained from retrograde transport of horseradish peroxidase. In general, soma sizes were largest in the part of the nucleus representing the central retina and decreased from the middle third of the nucleus to the anterior to posterior poles. Relay cells labeled with horseradish peroxidase were found to constitute approximately 90% of the dorsal lateral geniculate nucleus cells and have larger soma diameters than most unlabeled cells. From morphometric analysis of several structural characteristics, three classes of relay cells were identified in both Golgi‐Cox and horseradish peroxidase material. Type 1 cells, the predominant class, exhibited radially arranged primary dendritic fields, symmetrically organized relative to projection lines. Type 2 cells had relatively few primary dendrites, and complex dendritic fields that were oriented parallel to projection lines. Least numerous were Type 3 cells, which were characterized by relatively sparse dendritic fields oriented perpendicular to projection lines. An additional class of neuron, Type 4 cells, with small somata and sparse dendritic branching, was found only in Golgi‐Cox material. Cells with Type 4 dendritic morphology were not found with retrograde horse‐radish peroxidase labeling and may represent interneurons. The classification of morphologically characterized cells in the opossum dorsal lateral geniculate nucleus was evaluated quantitatively with multivariate discriminant analysis. The classes are compared to physiologically identified Y‐, X‐, and W‐like relay cells in the opossum and to relay cell classes in other species.
Central projections of C4–C8 dorsal root ganglia in the rat studied by anterograde transport of WGA‐HRP
Authors: Arvidsson J. , Pfaller K.
Published: January 2005

Injections of WGA‐HRP were made in the rat C4–C8 dorsal root ganglia (DRGs) individually to study the central projections and their relations to each other. The main dorsal horn projections from these DRGs to the dorsal horn lamina II extended for about two segments rostrally and caudally to the injected DRG, whereas the projections to laminae I, III, and IV were less restricted rostrocaudally. Comparisons of the dorsal horn projections from the DRGs investigated indicated a tendency for a somatotopic organization, which was most prominent in lamina II. Labeled central branches from the C4–8 DRGs could be traced in the dorsal column as far caudally as 12‐17 segments caudal to the level of entrance. Most of these fibers appeared to end in the medial dorsal horn base, including the column of Clarke. Labeling of primary afferents in the ventral horn generally extended for at least 3‐4 segments rostral and caudal to the level of the injected DRG. Projections to the central cervical nucleus were most prominent from the C4 DRG and gradually became less prominent from the more caudal DRGs. Heavy projections to the cuneate nucleus (Cun) originated from the C7 and C8 DRG, whereas those from the C4–C6 DRGs were less extensive. The Cun projections from the different DRGs appeared to overlap, and the same was true for the projections to the external cuneate nucleus. Projections to the gracile nucleus, the vestibular nuclear complex, including nucleus X, and to trigeminal sensory nuclei were seen from all DRGs investigated.
Comparative neuroanatomy of the histaminergic system in the brain of the frog xenopus laevis
Authors: Airaksinen Matti S. , Panula Pertti
Published: January 2005

The distribution of the histaminergic neuronal system in the brain of the clawed frog Xenopus laevis was mapped with an antiserum against carbodiimide‐fixed histamine and compared to that in mammals. The histamine‐immunoreactive cell bodies were located in a small area of the posterolateral hypothalamus, close to the dorsal infundibular nucleus, which contains catecolaminergic and serotonergic neurons. This area may be homologous to the tuberomammillary nucleus in mammals. A thick process extended from each cell between the ependymal cell layer and terminated in the ventricle lumen. The number of histaminergic cell bodies in adult Xenopus brain was relatively low, as compared with the mammalian brain. Preliminary analysis of adjacent sections stained with antisera against GABA or serotonin indicated that the histamine cells were not immunoreactive for these.

The pathways and distribution of histaminergic fibers in Xenopus brain showed many similarities to mammals. The densest fiber networks were present in the medial basal forebrain, particularly in the medial amygdala and septum. A distinct cluster of fibers was concentrated around the cell bodies of nucleus accumbens. In most pallial areas, the density was moderate to low. In the primordial piriform cortex and the striatum, very few fibers were seen. In diencephalon, highest fiber densities were found in the anterior and ventral thalamus and posterior and lateral hypothalamus. In hindbrain, the density was highest in the medullary central gray, as in some mammals.

The results suggest that the general pattern of the histaminergic system in vertebrate brain is conserved from amphibians to mammals.
Postnatal gliogenesis in the nerve fiber layer of the rabbit retina: An autoradiographic study
Authors: Schnitzer Jutta
Published: January 2005

Cell proliferation was studied in the retina of rabbits at various postnatal stages. Autoradiography was performed with animals that received a single injection of 3H‐thymidine and were sacrificed 1 hour later. This short survival time allowed the determination of the position of a cell undergoing DNA synthesis at that moment.

Between birth and day 6, cells engaged in DNA synthesis were seen in the inner nuclear layer (INL) of the entire retina. Cytogenesis ceases in this layer after the first postnatal week. Few labeled cells were detectable in the INL at day 9; these were found close to the ora serrata. Thus neurogenesis, which is known to occur in this layer of the retina, ceases by that time.

In the nerve fiber layer (NFL), labeled cells were found at all ages between birth and day 27, which was the oldest stage examined in this study. By using horizontal sections through the NFL of entire retinae, it was observed that almost all labeled cells were confined to the medullary ray region, which is the neuroglia (astrocyte and oligodendrocyte)‐ bearing part of the NFL. Microglial cells, the only cellular elements present in the NFL outside the medullary ray region, were rarely labeled, and thus do not play a major role in gliogenesis occurring in the NFL. In addition to neuroglia, some endothelial cells were labeled after day 9. It is concluded that gliogenesis taking place in the NFL persists after the cessation of neurogenesis, suggesting that both processes occur independently.