bluuebunny/crossref_metadata_2025 huggingface dataset:
The organization of trigeminotectal and trigeminothalamic neurons in rodents: A double‐labeling study with fluorescent dyes
Authors: Bruce Laura L. , McHaffie John G. , Stein Barry E.
Published: January 2005

Retrogradely transported fluorescent dyes (fast blue and diamidinodihydrochloride yellow) were used to compare the distributions of trigeminofugal neurons that project to the superior colliculus and/or the thalamus in three rodent species. The objective was to determine what the projection and collateralization patterns of these trigeminofugal pathways are and whether they are similar among different species. In each anesthetized animal, one dye was injected into the superior colliculus and the other into the topographically congruent area of the thalamus. Counts of the numbers of yellow, blue, and double‐labeled neurons were made throughout the trigeminal complex: principalis, pars oralis, pars interpolaris, and pars caudalis.

Trigeminothalamic projections were similar in each of the rodent species studied. The densest concentration of retrogradely labeled neurons was in principalis, with substantially fewer neurons in pars interpolaris, and fewer still in pars oralis and pars caudalis. These neurons were generally small and tended to have round or fusiform somata. A common pattern was also noted among the three species for trigeminotectal neurons. Most trigeminotectal projections originated from neurons in pars interpolaris, somewhat fewer from pars oralis, and the fewest from principalis and pars caudalis. These neurons tended to be the largest in each subdivision and were often multipolar.

Following paired injections of the tracers, double‐labeled neurons were scattered throughout the sensory trigeminal complex and had morphologies characteristic of single‐labeled trigeminotectal neurons. Although comparatively few double‐labeled neurons were observed in any species, most of those seen were restricted to the ventrolateral portion of pars interpolaris, a position that corresponds to the representation of the vibrissae. These data indicate that, regardless of the rodent species, the vast majority of labeled trigeminal neurons project either to the superior colliculus or the thalamus, but not to both targets. This might be expected on the basis of the very different behavioral roles these structures play. On the other hand, a sub‐population of trigeminal neurons exists (mainly in pars interpolaris) that does project to both the superior colliculus and the thalamus, perhaps because both structures require some of the same somatosensory information to perform their behavioral functions.
Neuropeptide neuronal efferents from the bed nucleus of the stria terminalis and central amygdaloid nucleus to the dorsal vagal complex in the rat
Authors: Gray Thackery S. , Magnuson Debra J.
Published: January 2005

The lateral bed nucleus of the stria terminalis (BSTL) and central nucleus of the amygdala (Ce) are amygdaloid nuclei that have similar affer‐ent and efferent connections within the brain. Previous studies have demonstrated that both regions send axonal projections to the dorsal vagal complex (dorsal motor nucleus and nucleus tractus solitarii). The present study used the combined retrograde fluorescence‐immunofluorescence method to examine whether cells contributing to this pathway contained any of the following neuropeptides: corticotropin‐releasing factor, neurotensin, somatostatin, substance P, enkephalin, or galanin. The inputs to the dorsal vagal complex originated mainly from ventral BSTL and medial Ce, although a significant number of neurons within the dorsal BSTL and lateral Ce also contributed. Corticotropin‐releasing factor, neurotensin, and somatostatin neurons mainly located within the dorsal BSTL and the lateral Ce contained retrograde tracer after injections into the vagal complex. Substance P neurons in the ventral BSTL and medial Ce provide a sparse input to the dorsal vagal complex. Enkephalin and galanin neurons within the BSTL and Ce did not appear to project to the dorsal vagal complex. Corticotropin‐releasing factor and neurotensin neurons within the lateral hypothalamus also project to the dorsal vagal complex. Approximately 22% of the Ce and 15% of the BSTL retrogradely labeled neurons were peptide immunoreactive. Thus, it is concluded the Ce and BSTL are sources of a significant peptidergic pathway to the dorsal vagal complex. However, it is also apparent that the majority of putative transmitter types within the amygdaloid vagal projection still are unknown. The results suggest that the dorsal and ventral BSTL and the lateral and medial Ce, respectively, are homologous zones with regard to chemoarchitecture and connections. The data is discussed considering the possible function of peptides within descending amygdaloid pathways to the brainstem.
Developing neuronal populations of the cat retinal ganglion cell layer
Authors: Wong R. O. L. , Hughes A.
Published: January 2005

An improved flat‐mount procedure demonstrates that the developing ganglion cell layer of the cat retina contains two morphologically distinct populations of presumed neurons at all ages between embryonic day 36 (E36) and adulthood. One population resembles the adult “classical neurons” composing the ganglion cells and bar‐cells of Hughes, while the remaining cells, which are smaller and possess much less Nissl substance, presumably correspond to precursors of the adult microneurons.

Although the total neuron population of the retinal ganglion cell layer remains quite constant at all studied ages, its component subpopulations alter significantly during prenatal development; some 50% of classical neurons disappear before birth and the microneuron population doubles during the same period. An obvious centroperipheral gradient exists for classical neurons by stage E47, but the microneuron density gradient only becomes apparent at birth. A 2:1 centroperipheral ratio for the total neuron population is also apparent at E47. Centroperipheral neuronal density gradients continue to increase during postnatal growth.

Loss of classical neurons during prenatal life as a result of cell death or transformation into microneurons, has been postulated as a mechanism for determining neuron density gradients. Cell death does occur in the ganglion cell population but it is not yet established whether microneurons of the ganglion cell layer originate from ganglion cell transformation or migrate as a differentiated class from the ventricular layer. However, it can be concluded that not all microneurons originate from ganglion cell transformation, because the total loss of classical neurons is less than the increase in microneuron numbers during development.

The population magnitudes of both neuronal classes in the ganglion cell layer stabilise after birth. However, it is during the postnatal period that the adult cruciate density topography is achieved by both populations. It is concluded that differential areal growth is the prime mechanism for postnatal cell redistribution.
Spatiotemporal gradients of kainate‐sensitivity in the developing chicken retina
Authors: Catsicas Stefano , Clarke Peter G. H.
Published: January 2005

We have studied the age‐dependence of the effects of kainate (KA) on the chick retina as a prelude to the accompanying paper on the effects of target‐removal on the isthmo‐optic nucleus. KA was injected into the eyes of chick embryos and chicks at different ages, and the retinas were fixed a few hours or several days later. The former group of retinas was scanned for pyknotic cells. The earliest age at which KA caused pyknosis was embryonic day 10 (E10), when pyknotic cells appeared in a ventrotemporal patch in the amacrine sublayer near the fundus. Over the next two days the sensitive region expanded tangentially, reaching the periphery first temporally, then nasally. Only after E12 did the KA cause pyknotic cells to occur also in the bipolar sublayer, where the sensitivity spread in the same spatiotemporal sequence as the initial wave, but two days later.

Cell loss was examined in embryos that survived a week or more after the KA injection. Substantial cell depletion was found in both the inner nuclear and ganglion cell layers, but only when the injection had been made after E12. With progressively later injections, the depleted zone expanded in the same spatiotemporal sequence as described above, until at E15 the injections caused depletion throughout the entire extent of the retina. The reasons for the lack of cell depletion after KA injections made before E12 are discussed. Cell counts in the ganglion cell layer and studies of anterograde transport of intravitreally injected peroxidase along the retinofugal fibers showed that about half the ganglion cells (including the displaced ganglion cells) pass through a period of vulnerability to the KA injections, to which they subsequently become insensitive.
Immunocytochemical localization of γ‐aminobutyric acid in the hypoglossal nucleus of the macaque monkey, Macaca fuscata: A light and electron microscopic study
Authors: Takasu N. , Nakatani T. , Akikuni T. , Kimura H.
Published: January 2005

The hypoglossal nucleus of the macaque monkey Macaca fuscata was investigated with light and electron microscopic immunocytochemistry with an antibody directed against γ‐aminobutyric acid (GABA). At the light microscopic level, GABA immunoreactivity was present in small neurons, punctate structures, and thin, fiberlike structures. These GABA‐positive elements were distributed throughout the hypoglossal nucleus at rostrocaudal levels. There was no immunoreactivity in the hypoglossal motoneurons. The GABA‐positive small neurons, were fusiform or ovoid (15 × 9 μm) and extended a few proximal dendrites from both poles. At the ultrastructural level, there small neurons were characterized by a markedly invaginated nucleus and a scanty cytoplasm in which cisternae of rough endoplasmic reticulum were not organized into extensive lamellar arrays as seen in the motorneurons. The GABA‐positive punctate structures at the light microscopic level were identified as vesicle‐containing axon boutons at the electron microscopic level. These GABA‐positive axon terminals made synaptic contacts mainly with the dendrites of the motoneurons and infrequently with the somata. The majority of them made symmetric synapses and they contained pleomorphic synaptic vesicles. However, a small number of GABA‐positive terminals (7%) formed asymmetric synapses with the dendrites of motoneurons, and these contacts exhibited postsynaptic dense bars or Taxi bodies lying beneath the postsynaptic membranes. There were no GABA‐positive boutons that contacted the cell bodies of the small neurons. Although GABA‐positive myelinated and unmyelinated axons were seen as thin, fiberlike structures, these myelinated and unmyelinated axons rarely gave rise to boutons on the motoneurons.

The present study suggests that GABAergic inhibition in the monkey hypoglossal nucleus occurs mainly on the dendrites of the motoneurons and to some extent on the somata.
Evidence for the existence of a lateral cervical nucleus in mice, guinea pigs, and rabbits
Authors: Giesler Glenn J. , Miller Lisa R. , Madsen Anne M. , Katter James T.
Published: January 2005

The lateral cervical nucleus of carnivores is large and is thought to play a prominent role in somatosensory processing. In contrast, early studies indicated that rats, mice, guinea pigs, and rabbits did not have a lateral cervical nucleus. However, we reported the existence of a lateral cervical nucleus in rats as a result of studies using retrograde transport techniques. In the present study, similar techniques were used to examine the possibility that early studies also overlooked the lateral cervical nucleus in mice, guinea pigs, and rabbits. In each of these species, a retrograde tracer was injected into the thalamus. These injections labeled a small number of neurons contralaterally in the dorsal part of the lateral funiculi of rostral cervical segments. Mice had the greatest number of neurons projecting from the lateral cervical nucleus to the thalamus, and rabbits had the fewest.
Spinocerebellar projections from the cervical enlargement in the cat, as studied by anterograde transport of wheat germ agglutinin–horseradish peroxidase
Authors: Matsushita Matsuo , Ikeda Michiko
Published: January 2005

The projection fields of spinocerebellar tracts arising from the cervical enlargement were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) in the cat.

Following injections of WGA‐HRP into the C5–C8 or T1 segments, labeled terminals were seen in lobule I to sublobule Vf of the anterior lobe, and lobule VI, sublobule VIIb, lobules VIII and IX, the simple lobule, crus II, and the paramedian lobule of the posterior lobe. In the sagittal plane of sublobules Ib–Vf and sublobules VIf and VId, the labeled terminals were distributed mainly in the superficial two thirds of the apicobasal extent. The labeled terminals in the anterior lobe accounted for about 70% of the total labeled terminals; the great majority were in lobule IV (17–20%) and lobule V (40%). The labeled terminals in the posterior lobe accounted for 30% of the total labeled terminals; the majority were in sublobules VIf (11–15%) and VId (6%). In the mediolateral extent, more than 50% of the total labeled terminals in each lobule were concentrated within 1.0 mm from the midline (the vermis) and 70–80% within 2.0 mm from the midline (the vermis and the medial part of the intermediate regions). A smaller number were also present in the intermediate region. Cases with lateral cordotomies revealed that the projections were bilateral but predominantly ipsilateral to the cells of origin and that the quantity of the ipsilateral projection was 66.5–75% of the total in each of sublobules IVb, Va, and VIf, The projection to the paramedian lobule was also predominantly ipsilateral.

Projection fields in the horizontal plane were reconstructed from a series of transverse sections through each lobule. In sublobules Va–VIf labeled terminals were distributed in three areas; area 1 located within 0.25 mm from the midline in zone Al of Voogd; area 2 located between 0.5 and 0.75 mm lateral to the midline in zones Al and A2; and area 3, which appeared to be located between 0.75 and 1.5 mm lateral to the midline in zones A2‐B. These areas extended longitudinally in the apical two thirds of the lobules.

From the present and previous retrograde HRP studies it was suggested that the neuronal groups in the cervical enlargement (the medial lamina VI group and the central lamina VII group) project to lobules I–V of the anterior lobe and lobule VI, sublobule VIIb, and lobule VIII of the posterior lobe. They have strong projections to caudal lobules of the anterior lobe (lobules III–Va) and lobules facing the primary fissure (sublobules Vd–Vf and sublobules VIf and VId).
VIP‐ and CCK‐like‐immunoreactive neurons in the hedgehog (Erinaceus europaeus) and Sheep (Ovis aries) brain
Authors: Antonopoulos J. , Papadopoulos G. C. , Karamanlidis A. N. , Parnavelas J. G. , Dinopoulos A. , Michaloudi H.
Published: January 2005

The distribution pattern and the morphology of vasoactive intestinal polypeptide (VIP)‐ and cholecystokinin (CCK)‐like‐immunoreactive neurons were studied in the brain of the hedgehog and the sheep by means of the peroxidase‐antiperoxidase immunocytochemical method. A total of 34 hedgehogs and 26 sheep of both sexes were used. Fourteen hedgehogs and 13 sheep received an intracerebroventricular injection of colchicine that enhanced the immunostaining and revealed “new” immunoreactive cell bodies. VIP‐immunoreactive bipolar and multipolar neurons were observed in both species in the cerebral cortex, hippocampal formation, amygdaloid complex, hypothalamus, and central gray substance of the midbrain. CCK‐immunoreactive bipolar, bitufted, and multipolar neurons displayed a broader distribution in both mammals than VIP neurons and were found in the cerebral cortex, the hippocampal formation, the amygdaloid complex, the hypothalamus, the mesencephalon, and the pons.

In the cortex, in both the hedgehog and the sheep, VIP neurons were located in all layers but were concentrated in layers II and III, with the majority being typical bipolar. CCK neurons were more numerous in the superficial layers (I‐III) but were found in the deep layers as well. They were bipolar, bitufted, or multipolar in morphology. From these neurons a small percentage, which were located almost exclusively in layers II and III of the visual cortex, exhibited also VIP immunoreactivity. Perikarya of such double‐labeled cells were ovoid or round in shape with one or two main processes emanating from each pole of the cell body and oriented perpendicularly to the pia. The coexistence of the two peptides within individual neurons of the cortex has not been reported in other species and its physiological significance is discussed in relation to the GABAergic neurons of the cortex.
Role of the target in directing the outgrowth of retinal axons: Transplants reveal surface‐related and surface‐Independent cues
Authors: Hankin Mark H. , Lund Raymond D.
Published: January 2005

In the present investigation we have examined whether retinal axons can be directed to the superior colliculus via an alternate route when they do not have access to their normal substrates along the optic tract. To address this issue we transplanted embryonic mouse retinae into the mid‐brain parenchyma and to various positions around the outer surface of the midbrain of newborn rats and then examined the development of projections from the transplanted tissue. The projections from cortical grafts placed in the midbrain were studied to determine whether axons from different classes of neurons respond to the same cues for outgrowth.

When retinae were placed within the midbrain close to the cerebral aqueduct, axons projected dorsally to the superficial layers of the superior colliculus. Directed outgrowth was seen from the earliest time a projection could be detected and was independent of whether the superior colliculus still received host optic afferents. In contrast, the major projection from similarly placed cortical transplants was directed toward the ventral part of the midbrain. Deafferentation of midbrain corticorecipient areas did not affect the projection patterns from either type of graft. Projections from retinae placed more ventrally in the midbrain tegmentum could not be detected. However, retinae placed on the surface of the midbrain, even as far ventral as the cerebral peduncle at the level of the inferior colliculus, always had a projection to the superior colliculus that ran along the brain‐stem surface.

These observations, suggest that the superior colliculus exerts a positive influence on the growth of optic axons to the midbrain. However, while target cues appear to be able to support retinal axon growth through the midbrain parenchyma, their range appears to be limited, and at distances beyond the extent of their influence, optic fiber outgrowth occurs only over the surface of the brain. It is suggested, therefore, that there are both local surface‐related and target‐derived surface‐independent cues that guide optic axons to the tectum in developing mammals.
Factors guiding optic fibers in developing Xenopus retina
Authors: Bork Tracie , Schabtach Eric , Grant Philip
Published: January 2005

We have characterized, by electron microscopy, the growth of pioneering axons from the retina into the visual pathway during early development of Xenopus laevis. The subsequent development of following fibers from the growing retinal margin as they accumulated in the ganglion cell fiber layer (GCFL) of the retina was also studied.

Extracellular channels bordered by neuroepithelial cells appear in the developing retina in a dorsal to ventral gradient before any pioneering axons are seen. Pioneering axons are subsequently observed in these channels, usually surrounded by neuroepithelial cell processes. Ruthenium red treatment of embryonic retinas reveals extracellular matrix (ECM) within these retinal channels, while extracellular spaces in the proximal optic stalk, just beyond the optic disc, lack this material. ECM is also seen in optic tectum wherever ingrowing retinal and nonretinal axons are found. The channels and the ECM contained within them may provide guidance cues for pioneering retinal axons. The early association of pioneering retinal axons with neuroepithelial cell processes (putative glia) appears to be important in further development of the GCFL.

The so‐called following fibers of ganglion cells, arising later in development, fasciculate with pioneer axons in extracellular spaces and form fiber bundles of the GCFL on top of the layer of glial cell endfeet. It is not clear whether pioneering axons, glial cell surfaces, or both serve as guidance cues for following fiber migration.
Anatomical demonstration of ocular segregation in the retinogeniculocortical pathway of the new world capuchin monkey (Cebus apella)
Authors: Hess Douglas T. , Edwards Michael A.
Published: January 2005

We describe the architecture of the dorsal lateral geniculate nucleus and primary visual cortex (striate cortex; area 17) of the New World capuchin monkey (Cebus apella) on the basis of the distribution of cell bodies and cytochrome oxidase histochemistry. Changes in staining for cytochrome oxidase following unilateral enucleation served to indicate the organization of the representation of the two eyes in the retinogeniculocortical pathway.

The number and disposition of eye‐specific layers within the lateral geniculate nucleus of Cebus are consistent with the common plan of geniculate organization in anthropoid primates, and the radial organization of area 17 fits the pattern common to New World squirrel and Old World macaque monkeys, including the presence of cytochrome‐oxidase‐rich zones in supragranular and deeper cortical layers (Horton: Philos. Trans. R. Soc. Lond. [Biol.]304: 199–253, '84).

Our principal finding is that cytochrome oxidase histochemistry following unilateral eye removal unequivocally reveals ocular dominance columns in the striate cortex of Cebus. As in the macaque (Hubel: Nature 292: 762–764, '82), ocular dominance columns extend through the thickness of cortex and blobs are centered on columns, but the array of columns viewed tangentially is less orderly or more mosaic than in the macaque, and there is apparently significant overlap between columns.

The presence of well‐defined ocular dominance columns in Cebus, as in Ateles (Florence, Conley, and Casagrande: J. Comp. Neurol. 243: 234–248, '86) but not in other New World monkeys examined previously, emphasizes the phylogenetic lability of binocular segregation in the primate visual cortex. In addition, the present results indicate significant differences with respect to the tangential organization of the ocular dominance domain between primate species in which ocular dominance columns are present.
Antibodies against retinal photoreceptor‐specific proteins reveal axonal projections from the photosensory pineal organ in teleosts
Authors: Ekström Peter , Foster Russell G. , Korf Horst‐W. , Schalken John J.
Published: January 2005

With the aid of specific antisera to the retinal proteins S‐antigen and α‐transducin and to the rhodopsin apoprotein opsin, we have labeled various cell populations in the pineal organ, parapineal organ, habenular nucleus, and subcommissural organ in two teleost species: the rainbow trout and the European minnow. Although these proteins are associated with photoreceptor functions, not only photoreceptor cells but also the majority of parenchymal cells in the pineal organ were immunoreactive. Immunoreactive cells with dendrite‐ and axonlike processes were observed also in the parapineal organ and the habenular nucleus. Furthermore, S‐antigen‐immunoreactive, long, axonal processes were observed in the pineal organ and could be traced from the pineal organ to the habenular nucleus and to the pretectal area. In the light of recent HRP electron microscopical and immunocytochemical studies we propose (1) that not only the classical pineal photoreceptor cells of poikilothermic vertebrates but also other types of CSF‐contacting neurons may be the phylogenetic ancestors of mammalian pinealocytes, and (2) a close interrelationship between the pineal organ and the limbic system, effectuated by the direct projections from pineal photoreceptors/CSF‐contacting neurons/pinealocytes to the habenular nucleus, and by displaced “pinealocytelike” elements scattered in the habenular nucleus.
Plantar motoneuron columns in the rat
Authors: Crockett David P. , Harris Suzan L. , Egger M. David
Published: January 2005

In the rat, the numbers and locations of motoneurons innervating the short plantar muscles of the hindlimb (supplied by the medial and lateral plantar nerves, as well as a branch of the sural nerve) were determined by using both horseradish peroxidase (HRP) and fluorochromes as retrograde labels.

Topographical organization within the plantar motor nucleus was examined by exposing individually the cut ends (encapsulated in low melting‐point paraffin) of medial plantar, lateral plantar, and sural nerves to HRP. In addition, double‐labeling experiments were conducted in which the medial plantar nerve was labeled with one fluorochrome (either true blue or diamidino yellow) and the lateral plantar nerve with another.

The plantar motor pool is located in the extreme dorsolateral portion of the ventral horn, usually concentrated in the fifth lumbar (L5) spinal segment. Labeled motoneurons extended caudally into the sixth lumbar (L6) segment and rostrally into portions of the fourth lumbar (L4) segment. Motoneurons of the medial plantar, lateral plantar, and sural nerve have overlapping territories. Sural motoneurons (about 70 cells per side) are generally confined to L5, medial plantar motoneurons (about 180 cells per side) tend to be concentrated in caudal L5 and rostral L6, whereas the lateral plantar motoneurons (about 310 cells per side) extend throughout the entire length of the plantar motor pool.

The distribution of motoneuronal cell size is unimodal (mean cross‐sectional area = 610 ± 150 μm2). Cell bodies of plantar motoneurons tend to have similar geometries in all three major planes of sectioning.

In all, the combined plantar plus sural nerve population amounts to about 560 motoneurons on each side of the spinal cord. On the basis of these data, and those published by others, the innervation of the small muscles of the foot accounts for about 25% of the motor axons carried by the entire sciatic nerve.
Morphology, number, and distribution of putative GABA‐ergic neurons in the basilar pontine gray of the monkey
Authors: Their Peter , Koehler Walther
Published: January 2005

We used an antibody raised against the inhibitory transmitter gamma‐aminobutyric acid (GABA) in the basilar pontine gray (bpg) of the monkey. Somata, dendrites, and a plexus of probably axonal fibers exhibited GABA‐like immunoreactivity. Labeled neurons were small with oval, triangular, or circular soma shape. They gave rise to 2 to 4 dendrites with little branching. No axons were seen issuing from the soma. Occasionally, appendages consisting of spheroidal bodies positioned at the distal end of tenuous stalks and (in 1 cell) axonlike processes were observed to originate from dendrites. According to their morphology, we suggest that these putative GABA‐ergic neurons may correspond to the type II neurons observed in Golgi material.

The average number of putative GABA‐ergic cells in 40–μm sections was about 30/mm2. When compared with Nissl‐stained sections, these amounted to about 5% of all cells. There was no substantial variation in average density in different parts of the bpg. However, labeled cells tended to lie in clusters, perhaps related to the well‐established input‐output compartments of the bpg.

The demonstration of a significant population of putative inhibitory neurons challenges the traditional view of the bpg, which suggests that this brainstem cell group functions as a simple relay exchanging signals between cortex and cerebellum.
Evidence for coexistence of GABA and dopamine in neurons of the rat olfactory bulb
Authors: Gall Christine M. , Hendry Stewart H. C. , Seroogy Kim B. , Jones Edward G. , Haycock John W.
Published: January 2005

Immunoreactivities for γ‐aminobutyric acid (GABA) and the dopaminesynthesizing enzyme tyrosine hydroxylase (TH) wore localized ultrastructurally and colocalized at the light microscopic level in neurons of the rat main olfactory bulb. By means of a simultaneous indirect immunofluorescence technique, GABA and TH immunoreactivities were found to coexist in a large number of neurons in the glomerular and external plexiform layers. Virtually all the TH‐immunoreactive periglomerular neurons also contained GABA immunoreactivity (GABA‐I) while there was an additional number of GABA‐immunoreactive periglomerular cells (27%) which did not contain TH immunoreactivity (TH‐I). In contrast, the numerous tufted‐type neurons in the glomerular and superficial external plexiform layers which contained TH‐I did not contain GABA‐I. In the external plexiform layer (EPL), 41% of the immunoreactive neurons contained GABA‐I alone, 24% contained TH‐I alone, and 35% contained both. EPL neurons containing GABA‐I only or both GABA‐I and TH‐I never exhibited tufted cell morphological characteristics and were generally of the short‐axon type. Electron microscopic examination of GABA‐I and TH‐I elements in the glomerular layer detected morphologically similar periglomerular perikarya and intraglomerular processes immunoreactive for each substance and other neurons and processes of the same type containing neither GABA‐I or TH‐I. These data indicate that the classical neurotransmitters GABA and dopamine coexist in large numbers of neurons in the rat main olfactory bulb including characteristic periglomerular cells and certain other local‐circuit neuronal types.
Enkephalin fibers in autonomic nuclear regions: Intraspinal vs. supraspinal origin
Authors: Romagnano Maryann A. , Braiman Jonathan , Loomis Mario , Hamill Robert W.
Published: January 2005

The present studies in the rat employ spinal transactions and hemisections, dorsal and/or ventral rhizotomies to determine whether enkephalin fibers in spinal sympathetic and parasympathetic nuclei are of supraspinal, intraspinal, or peripheral origin. Our results suggest enkephalin fibers in thoracolumbar sympathetic nuclei are of both supraspinal and intraspinal origin, whereas the enkephalin innervation of the sacral parasympathetic nucleus is primarily intraspinal in origin. Furthermore, the majority of descending enkephalin systems selectivity project to the intermediolateralis, pars principalis and pars funicularis, and the dorsal commissural sympathetic nuclei, whereas intraspinal enkephalin pathways appear to exist primarily in the intercalatus spinalis and intercalatus spinalis, pars paraependymalis sympathetic nuclei. These new observations suggest that specific patterns exist for supraspinal and intraspinal enkephalin pathways.
Ontogeny of peptide‐ and amine‐containing neurones in motor, sensory, and autonomic regions of rat and human spinal cord, dorsal root ganglia, and rat skin
Authors: Marti E. , Gibson S. J. , Polak J. M. , Facer P. , Springall D. R. , van Aswegen G. , Aitchison M. , Koltzenburg M.
Published: January 2005

The developmental patterns of neurofilament triplet proteins, peptide and amine immunoreactivities were compared in motor (ventral spinal cord), sensory (dorsal spinal cord, dorsal root ganglia, epidermis), and autonomic (intermediolateral cell columns, dermis) regions in the rat and human. In the rat, neurofilament triplet proteins first appeared in motoneurones (embryonic day 13). In the youngest human fetuses studied (6 weeks), immunoreactivity was present throughout the spinal cord. Peptides and amines occurred later. Calcitonin gene‐related peptide, galanin, somatostatin, neuropeptide Y and its C‐flanking peptide (CPON) were the first to appear localized to motoneurones (embryonic days 15–17 rat, fetal weeks 6–14 human). Numbers of immunoreactive motoneurones decreased toward birth, but immunoreactive fibers increased in the ventral horn with enkephalin, thyrotrophin‐releasing hormone, and the monoaminergic markers 5‐hydroxytryptamine and tyrosine hydroxylase (all presumably of supraspinal origin) the last to appear perinatally. In the dorsal horn, particularly in the rat, a transient expression of substance P‐, somatostatin‐, and neuropeptide Y/CPON‐immunoreactive cells was detected (embryonic days 15–17). A pronounced increase of calcitonin gene‐related peptide‐, galanin‐, somatostatin‐and substance P‐ immunoreactive fibers was found perinatally in both species. This coincided with an increased detection of cells in the dorsal root ganglia containing these peptides and the earliest appearance of calcitonin gene‐related peptide‐, somatostatin‐, and substance P‐immunoreactive fibers in the rat epidermis. Few antigens were localized to the intermediolateral cell columns before embryonic day 20 (rat), fetal week 20 (human), with thyrotrophin‐releasing hormone‐, 5‐hydroxytryptamine‐, tyrosine hydroxylase‐, and vasoactive intestinal polypeptide‐immunoreactive nerves appearing perinatally. In the rat dermis, tyrosine hydroxylase‐immunoreactive fibers (sympathetic fibers) and fibers immunoreactive for neuropeptide Y/CPON and vasoactive intestinal polypeptide were detected from postnatal day 1. In conclusion, (1) peptide and amine immunoreactivity develops in motor before sensory or autonomic regions, (2) many pep tide‐containing cells are transient in fetal life, and (3) central terminals of dorsal root ganglion cells express peptides before terminals in the skin.
Correlations between structure, topographic arrangement, and spectral sensitivity of sound‐sensitive interneurons in crickets
Authors: Atkins Gordon , Pollack Gerald S.
Published: January 2005

The morphology of nine prothoracic, sound‐activated, interganglionic interneurons in Teleogryllus oceanicus is described. Only two of the neurons can, on anatomical grounds, receive input directly from auditory receptors. The morphology of many of the cells suggests that they may provide output to motor areas. The nine cells can be divided into two groups on the basis of their spectral sensitivity: high‐frequency neurons and low‐frequency neurons. Correlations were found between morphology and spectral sensitivity. High‐frequency neurons have a ventromedial soma, dorsally positioned neuropile processes, and an axon in the lateral half of the promesothoracic connective. In contrast, low‐frequency neurons have a dorsal and/or laterally positioned soma, neuropile processes in the ventral portion of the prothoracic ganglion, and an axon projecting in the medial half of the connective. These findings reveal the existence of a crude tonotopic organization of central neurons. In addition, they provide hints as to the type of output and the targets of these neurons.
Retina of the tadpole and frog: Delayed dendritic development in a subpopulation of ganglion cells coincident with metamorphosis
Authors: Frank Bennett D. , Hollyfield Joe G.
Published: January 2005

In this study, the morphology of tadpole retinal ganglion cells was compared to that of frogs to determine if changes in dendritic structure occur during metamorphosis. Ganglion cells were analyzed in the tadpole and frog after backfilling with horseradish peroxidase. Representative ganglion cells are present in the tadpole retina, which directly correspond to each of the 7 cell classes found in the frog. However, cells in 3 of these classes (1, 3, and 7) exist in morphologically immature states in retinas from tadpole stages St. XIV‐XIX. New dendritic branches appear and the dendritic arbors of these ganglion cells expand during metamorphosis. We propose that the increased dendritic arborization may be followed by new synaptic contacts onto these cells, which contributes to the emergence of new physiological receptive field properties in the frog.
Rod bipolar array in the cat retina: Pattern of input from rods and GABA‐accumulating amacrine cells
Authors: Freed Michael A. , Smith Robert G. , Sterling Peter
Published: January 2005

The potential and actual connections between rod and rod bipolar arrays in the area centralis of the cat retina were studied by electron microscopy of serial ultrathin sections. In the region studied there were about 378,000 rods/mm2 and 36,000–47,000 rod bipolars/mm2. The tangential spread of rod bipolar dendrites was 11.2 μm in diameter, and the “coverage factor” for the rod bipolar cell was 3.5–4.6. We estimate that about 37 rods potentially converge on a rod bipolar cell and that one rod potentially diverges to about four rod bipolar cells. The actual connections, however, are less than this by about half: 16–20 rods actually converge on a bipolar cell and one rod actually diverges to slightly less than two rod bipolar cells. The degree of convergence appears to reflect a compromise between the need to signal graded stimulus intensities (requiring wide convergence) and the need to maintain a good signal/noise ratio (requiring narrow convergence).

Amacrine varicosities that provide reciprocal contact at the rod bipolar dyad were studied in serial electron microscopic autoradiograms following intraocular administration of 3H‐GABA or 3H‐glycine. More that 90% of the reciprocal amacrine processes accumulated GABA in a specific fashion. This information, in conjunction with Nelson's recordings from the rod bipolar and amacrine cells postsynaptic at the dyad (Nelson et al: Invest. Ophthalmol 15:9 46–953, '76; Kolb and Nelson: Vision Res. 23:301–312, '83), suggests that feedback at the rod bipolar output might be positive.
Ultrastructural organization of normal and transplanted rat fascia dentata: I. A qualitative analysis of intracerebral and intraocular grafts
Authors: Sørensen Torben , Zimmer Jens
Published: January 2005

Few studies have dealt with the general ultrastructure and synaptic organization of grafted brain tissue. This study was therefore performed to extend current light microscopic observations on intracerebral and intraocular grafts of hippocampal tissue to the ultrastructural level. Blocks of tissue containing the hippocampus and fascia dentata from day 21 embryonic rats were grafted into the brain of developing and adult rats and to the anterior eye chamber of adult rats. After 100 or 200 days of survival the recipient rat brains or eyes were processed for electron microscopy. Tissue containing the graft dentate molecular layer and adjacent granule cell layer was selected for ultrastructural analysis, together with a few samples of the hilus and CA3. Normal dentate tissue was analyzed as control.

At the light microscopic level most intracerebral and intraocular grafts displayed an organotypic organization with clearly recognizable cell and neuropil layers. Under the electron microscope the grafted granule cells had normal‐appearing dendrites bearing the normal types of spines and forming the normal types of synapses. This was the case even in the absence of the normal major extrinsic afferents like the perforant path. The graft dentate granule cells formed axons and terminals with characteristics of the normal mossy fiber system in the hilus and CA3, in addition to aberrant supragranular mossy fiber terminals known from light microscopic studies of dentate transplants. Abnormal structures included a few dendritic growth cones and an increased occurrence of polyribosomes in spines. Their occurrence indicates ongoing dendritic plasticity even 100 days after transplantation. There was also an increased density of glial elements, particularly in the intraocular grafts. In some of these grafts the granule cells displayed immature traits in terms of nuclear indentations. Dentate interneurons of the basket cell type were present in both the intracerebral and the intraocular grafts.

We conclude that grafted dentate granule cells, in different surroundings and without the normal, major perforant path input, can develop a basically normal cellular morphology, which includes the normal ultrastructural characteristics of the dendrites with spines and synapses, and the mossy fibers and its terminals.
Ultrastructural organization of normal and transplanted rat fascia dentata: II. A quantitative analysis of the synaptic organization of intracerebral and intraocular grafts
Authors: Sørensen Torben , Zimmer Jens
Published: January 2005

As part of an ultrastructural analysis of the normal rat fascia dentata and intracerebral and intraocular dentate transplants the synapses in the dentate molecular layer were quantified. Hippocampal and dentate tissue from 21‐day‐old rat embryos were grafted into the brain of developing and adult rats and to the anterior eye chamber of adult rats. After 100 or 200 days of survival the recipient rat brains and the recipient eyes were processed for electron microscopy, and the graft dentate molecular layer with the adjacent granule cell layer selected for ultrastructural analysis. Tissue from the dentate molecular layer of normal adult rats served as control. The dentate synapses were classified as asymmetric (Gray's type 1) or symmetric (Gray's type 2), and according to the postsynaptic element (cell body, dendritic shaft, dendritic spine). The spine synapses were further classified into simple and complex types according to the spine‐terminal configuration. Also, the length of synaptic contacts of the individual synaptic types was measured in some grafts, just as the percentage of the cross sectional area of the neuropil covered by blood vessels.

The results showed that the synaptic density, expressed as number per unit area of neuropil, to a large extent was the same within the different parts of the normal dentate molecular layer. Compared with this the synaptic density was reduced with 16.4% in dentate molecular layer of the intracerebral graft, primarily because of a 17.6% reduction of simple synapses on dendritic spines and almost halving of the symmetric synapses on dendritic shafts. The synaptic density was independent of the age of the recipient, the intracerebral location of the graft, and the survival time. Although the synaptic length of some of the individual synaptic types increased, this did not compensate for the loss of synapses. In the intraocular grafts the synaptic density was lower than in the intracerebral grafts.

Despite the reduced synaptic density, which mainly involved two synaptic types, we conclude that grafted dentate granule cells can develop a remarkably normal, ultrastructural synaptic organization even in the absence of major afferent inputs. This outcome must accordingly be achieved by reorganization of the available intrinsic afferents.
Raphe nucleus of the pons containing omnipause neurons of the oculomotor system in the monkey, and Its homologue in man
Authors: Büttner‐Ennever J. A. , Cohen B. , Pause M. , Fries W.
Published: January 2005

Omnipause neurons take part in the generation of saccadic eye movements. They lie around the midline in the caudal pontine reticulur formation, in an area usually ascribed to the nucleus raphe pontis (rp). In this study of the monkey (Macaca fascicularis and M. mulatta), we describe four series of experiments aimed at establishing that omnipause neurons lie within a distinctive cytoarchitectonic entity, which we call the nucleus raphe interpositus (rip): (1) cytoarchitectural study, (2) recording‐lesion experiments to establish in which cell group omnipause neurons lie, (3) cytochrome oxidase distribution in the omnipause region and neighboring structures, and (4) neuroanatomical tracing experiments to demonstrate afferents to the omnipause region.

In the detailed cytoarchitectural study of the midline structures in the caudal pons and rostral medulla, a distinctive group of neurons (rip) adjoining the ventrocaudal border of rp and dorsal to the nucleus raphe magnus (rm) is described. The striking features of rip are the uniformly arranged, narrow row of the cells either side of the midline, and the extensive horizontally oriented dendritic trees of its neurons. The abducens rootlets (NVI) pass through the reticular formation at the same rostrocaudal level as rip and form a reliable landmark for its location. Cytochrome‐oxidase‐stained sections demonstrated additional differences between rip and adjacent cell groups: in rip the neurons and their extensive dendrites stained strongly, but not the surrounding neuropile, whereas in rp both the neurons and the neuropile stained darkly, so that individual neurons were difficult to see.

Unlike rp, rip coincides with the location of omnipause neurons, and lesions marking the sites of individual omnipause units lay within its boundaries. Tritiated leucine was injected into superior colliculus (sc), which is known to have monosynaptic connections with omnipause neurons. Labelled axons and patterns of silver grains taken to indicate the presence of terminal branching were found in and around rip, but no significant labelling was seen in rp or rm. It is concluded that the omnipause neurons lie within the rip in the monkey.

These functional and morphological differences between rip and the adjacent raphe nuclei are used to justify its characterization as an independent cell group in the monkey.

In order to relate these findings to man, cytochrome oxidase experiments were carried out to the human brainstem, and the pattern of staining at the level of the abducens rootlets was correlated with the cytoarchitecture. Similar results to those in the monkey were found, and a group of cells is outlined which we suggest is the homologue of rip in man.
Species differences in hippocampal commissural connections: Studies in rat, guinea pig, rabbit, and cat
Authors: van Groen Thomas , Wyss Michael
Published: January 2005

The tritiated amino acid autoradiographic method was employed to characterize the patterns of commissural projections originating in the hippocampus of the rat, guinea pig, rabbit, and cat. The results demonstrate that significant differences between species are present despite the overall similarity of the projections. In the rat and cat the commissural connections are widely distributed along the septotemporal axis of the hippocampus, but in the guinea pig and rabbit they are less widely distributed along this axis. Second, within the hippocampus proper the radial distribution of the commissural projection is species specific. In the rat, CA3 commissural projections are present in both the strata oriens and radiatum, but the densest projection is to the stratum oriens. In the guinea pig the radial distribution of this projection is similar to that observed in the rat, but in the rabbit the projection is almost entirely confined to the stratum oriens. In contrast, in the cat the CA3 commissural projection is very dense to the stratum radiatum and sparse to stratum oriens. An analysis of the relative density of label in the molecular layer of the fascia dentata suggests that the density of the commissural projection from CA4 is much greater in the rat and cat than in the guinea pig or rabbit. These results indicate that care must be exercised in the generalization of connectional data between species. The results also suggest a possible explanation for differences observed in the electrophysiology of these connections between species.