bluuebunny/crossref_metadata_2025 huggingface dataset:
An autoradiographic examination of corticocortical and subcortical projections of the mediodorsal‐projection (prefrontal) cortex in the rat
Authors: Beckstead Robert M.
Published: January 2005

The efferent connections of the cortex projected upon by the mediodorsal thalamic nucleus (MD‐projection cortex) have been re‐examined autoradiographically in the rat following the microelectrophoretic injection of 3H‐proline‐leucine into different parts of the medial and sulcal MD‐projection cortex. Contrary to previous negative findings, the present experiments revealed a system of extensive corticocortical projections and indicated that different areas of the MD‐projection cortex have distinctive patterns in both their corticocortical and subcortical projections. Thus, cell of Brodmann's area 32 send axons to the retrosplenial cortex, area 29d, the peri‐ and entorhinal cortices, and the presubiculum. Both supragenual and more posterior regions of area 24 project to the retrosplenial cortex and area 29d, but only the posterior portion projects additionally to the entorhinal area and presubiculum. The cortical targets of axons from the sulcal MD‐projection cortex are mainly the anterior part of the piriform cortex and, for the posterolateral part of the sulcal cortex (insular area), the retrosplenial area, lateral entorhinal area, and presubiculum. While the medial and sulcal divisions of the MD‐projection cortex project upon one another, the medial‐to‐sulcal projection is in general denser than its reciprocal.

Earlier findings of projections to subcortical structures affiliated with the limbic system such as midline thalamic nuclei, hypothalamus, and paramedian mesencephalic tegmentum are confirmed, and appear to originate primarily in area 32 and the insular part of the sulcal cortex. The corticothalamic projection to MD in general terms reciprocates the organization seen in the thalamocortical projection from the various subnuclei within MD. Previously undocumented projections are demonstrated mainly from area 32 of the medial cortex and the insular part of the sulcal cortex to the lateral and basal amygdaloid nuclei, the medial part of the lateral septal nucleus, the nucleus accumbens, and the deep layers of the olfactory tubercle; the medial part of the lateral habenular nucleus receives a projection from areas 32 and 24. Projections to the pretectal area and superior colliculus appear to originate from all parts of the medial MD‐projection cortex, but are markedly denser when the posterior part of area 24 is injected. The distribution of this corticotectal projection shows a highly characteristic configuration in which areas of high grain concentration surround areas of lower grain concentration.
An autoradiographic examination of the central distribution of the trigeminal, facial, glossopharyngeal, and vagal nerves in the monkey
Authors: Beckstead Robert M. , Norgren Ralph
Published: January 2005

The central distributions of primary afferent axons in cranial nerves V, VII, IX, and X have been re‐examined autoradiographically after 3H‐proline injections into their peripheral ganglia. Fiber‐labeling after subtotal injections of the trigeminal ganglion, besides confirming earlier classical descriptions, suggests that trigeminal fibers of the ophthalmic and mandibular (but not maxillary) branches enter the ventrolateral part of the nucleus of the solitary tract (NST). Injection of VII's geniculate ganglion labels fibers which both ascend and descend upon reaching NST. The ascending fibers distribute in a compact and circumscribed zone immediately dorsal to the spinal V nucleus as far rostral as the caudal pole of the principal trigeminal nucleus. The descending fibers distribute to the lateral NST rostral to the level at which X joins the solitary tract. For a short distance caudal to this level, sparse label is confined to a small part of lateral NST ventral to the solitary tract, which corresponds to the zone receiving direct trigeminal afferents. Fiber‐labeling after injections of the ganglia of nerves IX and X suggest the following. Although, upon reaching NST, a few fibers of either IX or X ascend as far rostrally as had those of VII, both have a much larger descending component which distributes to more caudal levels of NST. Most of IX's axons appear to end in the lateral NST; only a few travel as far as the obex. Fibers of X, on the other hand, are abundant in the medial and commissural parts of NST. Moreover, only X appears to have a crossed projection in the commissural nucleus and caudal portion of the contralateral NST. A few fibers of vagal origin also appear to enter the area postrema. Whereas fibers of X appear to constitute the solitary tract, few if any fibers of VII or IX travel within that fascicle. A significant descending components of labeled fibers appears in the spinal V tract when the superior ganglion of either IX or X is injected. These fibers distribute mainly in the pars caudalis of the spinal V nucleus and, to a lesser degree, the cuneate nucleus.
Abnormal retino‐geniculate and geniculo‐cortical pathways in several genetically distinct color phases of the mink (Mustela vison)
Authors: Guillery R. W. , Oberdorfer M. D. , Murphy E. H.
Published: January 2005

Several genetically distinct color phases of mink, which all show an abnormal reduction of pigment in the retinal pigment epithelium and which also show abnormalities of the retinofugal pathways, have been studied. Autoradiographic methods have been used to demonstrate the retino‐geniculate pathways, and retrograde degeneration or the retrograde transport of horseradish peroxidase has been used for the geniculo‐cortical pathways.

The retino‐geniculate abnormality is mild in some of the color phases and extremely severe in others, but within any one color phase the variability is relatively low. Although the severity of the abnormality varies between color phases, a rather specific pattern of abnormal geniculate innervation is recognizable for mink in general and this is distinct from that found in Siamese cats. In the abnormal mink the size of geniculate lamina A1 is reduced and there is an abnormal crossed input going to the intermediate sectors of this reduced layer. Layer C1 also receives an abnormal crossed input, but this is more variable than that going to A1 and there appears to be little correspondence, retinotopically, between the normal inputs to layers A1 and C1. In some of the abnormal mink there are interruptions within the cytoarchitectonically definable layer A1, and opposite these gaps reduplications of layer A are commonly seen, as though there is an intrinsic geniculate mechanism for generating the characteristic multilaminar geniculate structure. However, there are also numerous examples of fusions between layers receiving afferents from the same eye, and these demonstrate that the development of geniculate lamination must also be under the influence of the retinal inputs.

The geniculo‐cortical pathway shows a normal topography in most of the mink. Abnormal geniculo‐cortical projections, comparable to the “Boston” pattern of Siamese cats are extremely rare, and their occurrence could not be correlated with the severity of the retino‐geniculate abnormality or with the laminar pattern in the lateral geniculate nucleus. We suggest that the development of one or the other pattern of geniculo‐cortical projection may depend upon the relative timing of the two mechanisms that produce the geniculate lamination.
Neuronal populations of the human periaqueductal gray, nucleus lateralis
Authors: Laemle Lois K.
Published: January 2005

The present communication is part of a study designed to explore the neuronal populations and the organization of the periaqueductal gray matter (PAG). The data presented here deals exclusively with the nucleus lateralis (PAGL) and is based upon Golgi studies of 14 human brainstems. In this investigation 400 cells were measured and classified. Axonal origin, axonal and dendritic ramifications, and spine population were studied. The data demonstrate that morphologically the PAGL is comprised of a heterogeneous population of small and medium sized neurons consisting of three major cell types: vertical cells, stellate cells, and horizontal cells. Observations of axonal pathways and dendritic ramifications describes an anatomical substrate for direct communication between the PAGL and the superior colliculus, which includes a system of axonal projections from the PAGL into the superior colliculus. The cells of origin of this pathway have been identified as being primarily vertical and stellate cells. It is anticipated that these data will provide the groundwork for further detailed study of PAGL neurons and for identifying specific neuronal populations with their functional roles.
Topographic organization of the projections of the retina to the pretectal region in the rat
Authors: Scalia Frank , Arango Victoria
Published: January 2005

The pattern of projection of the retina to the pretectal region and its retinotopic organization were investigated in the rat by autoradiographic and silver impregnation techniques for axonal pathways. The endings of retinal axons form three terminal fields in the pretectum in: 1, olivary pretectal nucleus (PO), bilaterally; 2, posterior pretectal nucleus (PP), bilaterally; and 3, nucleus of the optic tract (NTO), contralaterally. The following retinotopic pattern was observed in rats surviving peripheral retinal lesions and injections of 3H‐proline in the same eye, when the positions occupied by terminal degeneration in Fink‐Heimer stained sections were matched with the corresponding areas deficient in radiolable in adjacent autoradiographic sections showing the surviving parts of the terminal fields. The nasal periphery of the retina maps along the adjoining edges of PO and PP, both of which extend obliquely, in a posterolateral direction, through the entire extent of the pretectum. Both nuclei map the line of representation of the anterior midline (in the temporal retina) along their opposite edges (anterolaterally, in PO; posteromedially, in PP). This mirror‐image symmetry is completed by the representation of the ventral peripheral retina separately in the rostral poles and the dorsal peripheral retina separately in the caudal poles of both nuclei. The map in NTO is vertically oriented, with the temporal retina, dorsally, the nasal retina, ventrally, the ventral retina, rostrally, and the dorsal retina caudally represented. The binocular area of the terminal field in PO is subdivided by a terminal‐free zone into two parts that may process separately events in the central and lateral visual field.
Ruffed cell: A new type of neuron with a distinctive initial unmyelinated portion of the axon in the olfactory bulb of the goldfish (Carassius auratus). I. Golgi impregnation and serial thin sectioning studies
Authors: Kosaka Toshio , Hama Kiyoshi
Published: January 2005

A new type of neuron was recognized in the olfactory bulb of the goldfish (Carassius auratus) by means of light and high voltage electron microscopy of Golgi‐impregnated material, combined Golgi‐electron microscopy, and electron microscopy of serial thin sections.

The neuron is located in the layer between the olfactory nerve layer and the anterior olfactory nucleus. It has a spherical cell body, about 10–20 μm in diameter, and several dendrites which form a spherical dendritic field, about 70–100 μm in diameter, in the vicinity of the cell body.

The most remarkable structural feature of this neuron is that its initial unmyelinated portion of the axon (IP) has elaborate protrusions with many synapses. The IP can be divided into three parts, parts 1, 2 and 3, based on its structural features.

Part 1 is the initial part of the IP, about 20–40 μm in length. Many elaborate protrusions arise from the shaft and intermingle with one another to constitute a spherical field, about 20–40 μm in diameter, around the shaft. Part 2 is the middle part of the IP, about 10–20 μm in length. There are several collaterallike protrusions, which are scattered along the shaft and extend laterally about 5–15 μm. Part 3 is the last part of the IP, and is cylindrical without protrusions. The length of part 3 varies from 20 to more than 100 μm. The axon acquires a myelin sheath at a distance of 70–250 μm from its origin.

Protrusions make synaptic contacts mainly with granule cell dendrites. Some of them are of the reciprocal type. Protrusions are presynaptic in asymmetrical synapses, and postsynaptic in symmetrical synapses with granule cell dendrites. The shaft of the IP also has synapses similar to those on protrusions.

The neuron described is a new type of neuron in the vertebrate central nervous system. We propose for it the name “ruffed cell”.
Efferent connections of the habenular nuclei in the rat
Authors: Herkenham Miles , Nauta Walle J. H.
Published: January 2005

The efferent connections of the medial (MHb) and lateral (LHb) habenular nuclei in the rat were demonstrated autoradiographically following small injections of tritiated amino acids localized within various parts of the habenular complex. Comparison of individual cases led to the following conclusions.

MHb efferents form the core portion of the fasciculus retroflexus and pass to the interpeduncular nucleus (IP) in which they terminate in a topographic pattern that reflects 90° rotations such that dorsal MHb projects to lateral IP, medial MHb to ventral, and lateral MHb to dorsal IP. Most MHb fibers cross in the interpeduncular nucleus in the “figure 8” pattern described by Cajal, and terminate throughout the width of IP with only moderate preference for the ipsilateral side. However, the most dorsal part of MHb projects almost exclusively to the most lateral IP zone in a cluster pattern that is particularly dense on the ipsilateral side. The MHb appears to have no other significant projections, but very sparse MHb fibers may pass to the supracommissural septum and to the median raphe nucleus.

Except for some fibers passing ventrally into the mediodorsal nucleus, all of the LHb efferents enter the fasciculus retroflexus and compose the mantle portion of the bundle. No LHb projections follow the stria medullaris. In the ventral tegmental area LHb efferents become organized into groups that disperse in several directions: (a) Rostrally directed fibers follow the medial forebrain bundle to the lateral, posterior and dorsomedial hypothalamic nuclei, ventromedial thalamic nucleus, lateral preoptic area, substantia innominata and ventrolateral septum. (b) Fibers turning laterally distribute to the substantia nigra, pars compacta (SNC); a small number continue through SNC to adjacent tegmentum. (c) The largest contingent of LHb efferents passes dorsocaudally into paramedian midbrain regions including median and dorsal raphe nuclei, and to adjacent tegmental reticular formation. Sparse additional LHb projections pass to the pretectal area, superior colliculus, nucleus reticularis tegmenti pontis, parabrachial nuclei and locus coeruleus. No LHb projections appear to involve the interpeduncular nucleus. All of these connections are in varying degree bilateral, with decussations in the supramammillary region, ventral tegmental area and median raphe nucleus.

On the basis of differential afferent and efferent connections, the LHb can be divided into a medial(M‐LHb) and a lateral (L‐LHb) portion. The M‐LHb, receiving most of its afferents from limbic regions and only few from globus pallidus, projects mainly to the raphe nuclei, while L‐LHb, afferented mainly by globus pallidus and in lesser degree by the limbic forebrain, projects predominantly to a large region of reticular formation alongside the median raphe nucleus. Both M‐LHb and L‐LHb, however, project to SNC. The reported data are discussed in correlation with recent histochemical findings.
The cytoarchitecture of the interfascicular nucleus and ventral tegmental area of tsai in the rat
Authors: Phillipson O. T.
Published: January 2005

The cytoarchitecture of the ventral tegmental area of Tsai (VTA) has been studied in detail in the rat with the aid of both conventional techniques and glyoxylic acid‐fluorescence histochemistry. Three main dopamine containing cells groups can be distinguished: nucleus paranigralis, nucleus parabrachialis pigmentosus lies dorsally, and nucleus paranigralis ventrally in the VTA, while nucleus linearis continues posteriorly and medially from VTA and extends dorsally in the midline up towards the dorsal raphe nucleus. Fluorescent neurons in these three groups correspond to the A10 group. In addition to these previously described findings, the present study shows evidence for a further small but cytoarchitecturally distinct dopaminergic group called the interfascicular nucleus. This lies anterorly and ventrally in the ventral tegmentum in the midline, dorsal to the rostral portion of the interpeduncular nucleus and interpeduncular fossa.

The significance of these cytoarchitectural findings in discussed in relation to the known connections of the region.
The GABA Neurons and their axon terminals in rat corpus striatum as demonstrated by GAD immunocytochemistry
Authors: Ribak C. E. , Vaughn J. E. , Roberts E.
Published: January 2005

Glutamic acid decarboxylase (GAD, EC 4.1.1.15), the enzyme which catalyzes the α‐decarboxylation of L‐glutamate to form the neurotransmitter γ‐aminobutyric acid (GABA), was localized immunocytochemically in neurons of rat neostriatum, pallidum and entopeduncular nucleus. A large amount of GAD‐positive reaction product was observed in both the pallidum and entopeduncular nucleus in light microscopic preparations and was localized ultrastructurally to axon terminals that surrounded dendrites and large somata. In the neostriatum the relative numbers of GAD‐positive axon terminals per unit area were substantially less than in the pallidum. GAD‐positive terminals predominantly formed symmetric synapses with somata, dendrites and spines, but a small number of them formed asymmetric synapses with either dendrites or spines. The presence of GAD within these terminals is consistent with results of other investigations which have indicated that the striatopallidal and striatoentopeduncular pathways as well as neostriatal local circuit neurons and/or collaterals from neostriatal projection neurons, use GABA as a neurotransmitter.

GAD‐positive reaction product was also localized within the somata and dendrites of neostriatal and pallidal neurons in colchicine‐injected preparations. The GAD‐positive somata in the pallidum were medium‐sized neurons and since such cells project to the substantia nigra, our results are in agreement with those from other studies which demonstrate a GABAergic, pallidonigral pathway. In the neostriatum, GAD‐positive somata were identified light microscopically as medium‐sized neurons with either round or fusiform shapes. Electron microscopic examinations also showed GAD‐positive reaction product within the perikaryal and dendritic cytoplasm of these neurons, as well as in dendritic spines. These findings are in accord with the results of studies which have indicated that medium‐sized, spinous neurons of the neostriatum give rise to a GABAergic, striatonigral pathway. The significance of GAD localization within these neostriatal neurons is discussed in relation to recent findings which show that substance P is contained within this same class of striatonigral projection neuron.
Differentiation of photoreceptors and horizontal cells in the embryonic mouse retina: An electron microscopic, serial section analysis
Authors: Hinds James W. , Hinds Patricia L.
Published: January 2005

The early differentiation of photoreceptors and horizontal cells in the mouse retina has been studied with serial thin sections and reconstructions in embryos on the fifteenth and seventeenth days of gestation (E15 and E17). The following developmental sequences have been inferred. At E15 photoreceptors develop from ventricular cells when a long vitreal process fails to develop following mitosis, and the end of the ventricular process forms a bulbous enlargement (the future inner segment) which contains a pair of centrioles and a cilium and extends into the optic ventricle. This future inner segment is considerably larger at E17, but otherwise the photoreceptors resemble those seen at E15. At E15 horizontal cells develop from ventricular cells when a long vitreal process fails to develop following mitosis, and the end of the ventricular process detaches from the junctional complex at the ventricular surface. By E17 future horizontal cells are located in the middle of the ventricular layer (neuroblastic layer) and have developed from bipolar shaped cells into cells with multiple branching processes, predominantly radially arranged but rarely with a more tangential orientation. These relatively advanced cells at E17 resemble closely the earliest stage of horizontal cell formation described previously in silver studies by Cajal.

A scheme is proposed which explains the initial differentiation of several of the major cell types in the retina in terms of two key features: whether or not the cell remains attached to the junctional complex and whether or not a vitreal process grows into the ganglion cell layer. By independent variations in these two features, four classes of cells are produced that, by virtue of their differing environments, differentiate into four cell types: ganglion (and amacrine) cells, horizontal cells, photoreceptors, and Müller cells.
Efferent connections of the brainstem trigeminal complex with the facial nucleus of the rat
Authors: Erzurumlu Reha S. , Killackey Herbert P.
Published: January 2005

The sensory surface of the face of the rat is topographically represented in the brainstem trigeminal complex (Nord, '67), and in parallel with this the underlying facial musculature is also represented in a topographic fashion in the facial nucleus (Papez, '27; Martin and Lodge, '77; Watson and Sakai, '78). It has been recently reported that in the young rat three distinct representations of the vibrissae are present in the sensory portion of the brainstem trigeminal complex (Belford and Killackey, '79). Within this perspective, the specific connectivity between the brainstem trigeminal complex and the facial nucleus was investigated in adult rats by the Fink‐Heimer technique.

The two major sensory nuclei of the brainstem trigeminal complex, the spinal trigeminal nucleus and the principal sensory nucleus, differ in their projection patterns to the facial nucleus. While the principal sensory nucleus sends sparse projections to the ipsilateral lateral and dorsal subdivisions of the facial nucleus, the spinal trigeminal nucleus sends differential projections to various subdivisions of the facial nucleus depending on their origin with respect to three cytoarchitectonically different subnuclei that compose the spinal trigeminal nucleus. It is concluded that the magnocellular portion of subnucleus caudalis projects rather heavily to the ipsilateral lateral subdivision of the facial nucleus, while the projections from the subnucleus interpolaris are sparser and distributed more widely to parts of the lateral, dorsal and intermediate subdivisions of the facial nucleus ipsilaterally. In contrast to ipsilateral facial projections from the rest of the brainstem trigeminal complex, the projections from the subnucleus oralis of the spinal trigeminal nucleus are bilateral and confined to the intermediate subdivision of the facial nucleus. However, ipsilateral projections of the subnucleus oralis are denser than the very sparse contralateral projections.

In addition to the facial projections from the brainstem trigeminal complex, projections from the upper portions of the cervical cord to the medial subdivision of the facial nucleus were observed. These projections are bilateral, and those fibers destined for the contralateral medial subdivision cross over below the level of the pyramidal decussation.
Cells of origin of long descending propriospinal fibers connecting the spinal enlargements in cat and monkey determined by horseradish peroxidase and electrophysiological techniques
Authors: Skinner Robert D. , Coulter Joe Dan , Adams Robert J. , Remmel Ronald S.
Published: January 2005

The cells of origin of the long descending propriospinal tract (LDPT) in the cervical enlargement were studied in cat and monkey by using the retrograde transport of horseradish peroxidase (HRP). Their distribution was confirmed electrophysiologically in cat by recording their antidromic action potentials.

In cats and monkeys unilateral injections of HRP were made into the gray matter of the lumbosacral enlargement, but there was some spread to the contralateral side. In cats labeled somas were found in greatest numbers in lamina VIII and medial lamina VII, bilaterally. Labeled cells also were found bilaterally in laminae I, IV–VI, and X, but few were in IV and VI. Those in lamina V were usually in the lateral part of the lamina near the reticulated region. The cross‐sectional areas of 20 neurons from each of laminae I and V–VIII were measured. Cells in lamina I were smallest and the largest were in VII and VIII.

In cats with the spinal cord hemisected between the injection site and the cervical enlargement containing the somas, the bilaterality of the LDPT neurons in laminae VII and VIII was confirmed anatomically and physiologically. Contralaterally projecting neurons in laminae VIII and medial VII constituted a majority of LDPT cells in those laminae. The LDPT neurons in the dorsal horn appeared to project mainly ipsilaterally, but the number of labeled dorsal horn cells in these preparations was small.

The distribution of antidromically localized cells of the LDPT was found to be in good agreement with the anatomical results. Their conduction velocity was 59 ± 22 m/s (mean ± s. d., n = 245). Histograms of the conduction velocity by laminae are given.

In monkey the distribution of labeled somas was similar to that in the cat, except that the concentration of labeled somas in the ventral horn was more medially and dorsally located. Labeled somas were found bilaterally in laminae I, IV – VIII, and X, but more appeared to be ipsilateral to the side of the injection, especially in the dorsal horn. The bilaterality of the LDPT in the monkey was not tested with hemisections of the spinal cord.

Neurons of the LDPT are ideally situated for conveying sensory information from the forelimb for eliciting reflexes in the hindlimb, as has been observed after stimulating afferents in the forelimb, and for coordinating, in general, motor functions between the two pairs of limbs.
A technique for estimating total spine numbers on golgi‐impregnated dendrites
Authors: Feldman Martin L. , Peters Alan
Published: January 2005

The functional significance of dendritic spines and their morphological sensitivity to a wide spectrum of experimental manipulations and pathological states have led to a number of studies in which counts of dendritic spine number have been carried out. These studies have, for the most part, involved the enumeration of only those spines which protrude from the opaque shafts of Golgi‐impregnated dendrites into the clear zones flanking the dendrite. Such counts, limited to only those spines which are visible, underrepresent the true total number of spines borne by the dendrites. The magnitude of underrepresentation correlates positively with dendritic shaft diameter and negatively with spine length. This seriously restricts the usefulness of comparisons of spine density between dendrites, or even between segments of the same dendrite.

In the present report, a geometrically based method is presented whereby total dendritic spine numbers can be estimated with reasonable accuracy, taking into account factors such as dendrite diameter and spine length. The technique entails the following principal steps: a determination, for a given length of dendrite over which spines are to be enumerated, of the volume of the flanking zones in which spines are visible and can be counted; a determination of the volume of the entire zone which encircles the dendritic shaft and which contains all spines, both visible and not visible; and a proportional extrapolation from the number of visible spines to obtain an estimate of the true total spine number. Tests of the predictive accuracy of the technique using dendrites of known total spine number suggest that estimates which deviate from true total spine numbers by less than 10% can be achieved.
Nuclei in which functionally identified spinothalamic tract neurons terminate
Authors: Applebaum A. E. , Leonard R. B. , Kenshalo D. R. , Martin R. F. , Willis W. D.
Published: January 2005

The approximate level of termination of the axons of individual, functionally characterized spinothalamic tract neurons within the monkey thalamus was mapped by antidromic activation using a monopolar electrode which was moved in a systematic grid of tracks through the thalamus. The course of individual axons could be followed through several thalamic levels, and in a few cases branches to both the VPL nucleus and to the intralaminar nuclei were demonstrated. Most of the axons studied, however, projected just to the VPLc or VPLo nuclei. The spinothalamic tract cells that projected to the VPLc nucleus included representatives of all known functional categories: low threshold, wide dynamic range, high threshold and “deep”. It is speculated that these different classes of spinothalamic projections could make contributions to such sensory modalities as touch, proprioception and pain.
Anatomy and ultrastructure of the axons and terminals of neurons R3‐R14 in Aplysia
Authors: Price Christopher H. , McAdoo David J.
Published: January 2005

Using light and electron microscopy and autoradiography, we have traced the axons of neurons R3‐R14 in the parietovisceral ganglion (PVG) of Aplysia to terminal fields associated with vascular tissue. The axons are identified by their large size (15‐30 μm diameter), extensive glial infolding, characteristic dense core vesicles (DCV; ∼180 nm diameter), and specific, rapid uptake of 3H‐glycine. Each neuron in this homogeneous group sends an axon via the branchial nerve to the pericardial region surrounding the junction of the efferent gill vein and the heart. R14 also sends axons to major arteries near the PVG. The R3‐R14 axons branch extensively; we estimate that there are at least several hundred per cell. Branches along axons in the branchial nerve exit the nerve, subdivide, and end blindly in the sheath which is bathed by hemolymph. Similar blind endings from R3‐R14 occur in the sheath of the PVG (Coggeshall, '67). Axonal branches in the pericardial region and the special R14 axons in the arterial walls from both varicose endings near and terminals in contact with vascular smooth muscle. All R3‐R14 endings are free of glia, packed with DCV, show occasional omega‐shaped profiles and rapidly take up 3H‐glycine. R3‐R14 manufacture specific low molecular weight peptides (Gainer and Wollberg, '74), and both the cell bodies (Iliffe et al., '77) and the terminals contain unusually high concentrations of glycine. The presence of peptides as putative neurohormones and sheath endings (neurohormonal release areas) are consistent with R3‐R14 being neurosecretory (Coggeshall et al., '66). While glycine could not be a circulating hormone due to its high circulating levels (Iliffe et al., '77), glycine could act as a local chemical messenger between R3‐R14 and smooth muscle. The terminal morphology of R3‐R14 is consistent with these neurons having both synaptic‐type and neurosecretory‐type functions.
Early development and migration of the trigeminal motor nucleus in the chick embryo
Authors: Heaton Marieta B. , Moody Sally A.
Published: January 2005

The development of the trigeminal motor nucleus in the chick embryo was studied using autoradiographic, cell staining, fiber staining, and axonal transport techniques. It was found that this nucleus arises very early in neurogenesis, with the first cells produced at 48 hours of incubation (stage 12), peak cell production at 50–56 hours (stage 15), and neuroblast proliferation completed by 72 hours (stage 18). As has been described in mammalian embryos, the primordial trigeminal cells move from the ventricular layer to accumulate as part of the common medial column, and later migrate in a ventrolateral direction to form the definitive lateral motor nucleus. The first identifiable component of the trigeminal system is the semilunar ganglion, which flanks the neural tube at stage 12, and sends afferents into the metencephalon by stage 13. By stage 12–13, the medial column cells are first apparent, and at stage 14, a few of these medial column cells have moved to begin formation of a lateral nucleus. At this time, a thin motor root can be seen exiting the brainstem. During subsequent stages, migratory traffic from medial to lateral regions increases, with cells frequently moving in association with fiber processes in the marginal zone. These fibers are presumed to emanate from secondary sensory, reticular, and medial column neuroblasts. By day 5, the medial column is greatly depleted and by day 6–7, the definitive lateral motor nucleus is formed. Beginning at 5 days, the dorsal motor nucleus can be detected, with cells from the lateral nucleus appearing to stream in a dorsomedial direction for its formation. Injections of horseradish peroxidase (HRP) into the mandibular process of the first visceral arch resulted in retrograde labeling of lateral nucleus cells as early as 3.5 days of incubation. In addition, migrating cells, intermediate between medial column and lateral nucleus, were similarly labeled. These observations indicate that processes of the lateral nucleus cells and those of migrating cells are well into their peripheral field at this age, but we cannot conclude that neuromuscular affiliations have been established, due to the possibility of HRP diffusion and growth cone uptake.
Neuronal transport of acid hydrolases and peroxidase within the lysosomal system of organelles: Involvement of agranular reticulum‐like cisterns
Authors: Broadwell Richard D. , Oliver Constance , Brightman Milton W.
Published: January 2005

Neurosecretory neurons of the hyperosmotically stressed hypothalamo‐neurohypophysial system have been a useful model with which to demonstrate interrelationships among perikaryal lysosomes, agranular reticulum‐like cisterns, endocytotic vacuoles, and the axoplasmic transport of acid hydrolases and horseradish peroxidase. Supraoptic neurons from normal mice and mice given 2% salt water to drink for 5–8 days have been studied using enzyme cytochemical techniques for peroxidase and lysosomal acid hydrolases. Peroxidase‐labeling of these neurons was accomplished by intravenous injection or cerebral ventriculocisternal perfusion of the protein as previously reported (Broadwell and Brightman, '79).

Compared to normal controls, supraoptic cell bodies from hyperosmotically stimulated mice contained elevated concentrations of peroxidase‐labeled dense bodies demonstrated to be secondary lysosomes and acid hydrolase‐positive and peroxidase‐positive cisterns either attached or unattached to secondary lysosomes. These cisterns were smooth‐surfaced and 400–1,000 A wide. Their morphology was similar to that of the agranular reticulum. Some of the cisterns contained both peroxidase and acid hydrolase activities. The cisterns probably represent an elongated form of lysosome and, therefore, are not elements of the agranular reticulum per se. By virtue of their direct connections with perikaryal secondary lysosomes, these cisterns may provide the route by which acid hydrolases and exogenous macromolecules can leave perikaryal secondary lysosomes for anterograde flow down the axon. Very few smooth‐surfaced cisterns were involved in the retrograde transport of peroxidase within pituitary stalk axons from normal and salt‐treated mice injected intravenously with peroxidase. Peroxidase undergoing retrograde transport was predominantly in endocytotic structures such as vacuoles and cupshaped organelles, which deliver this exogenous macromolecule directly to secondary lysosomes for degradation in the cell body.

These observations extend our previously reported findings in the axon to the cell body and suggest that agranular reticulum‐like cisterns in the perikaryon, like those in the axon, may be part of the lysosomal system rather than associated with the agranular reticulum. A diagram summarizing the lysosomal system of organelles and proposed transport of acid hydrolases and peroxidase in neurosecretory neurons specifically and in neurons in general is provided.
Cytoarchitectonic organization of the human auditory cortex
Authors: Galaburda Albert , Sanides Friedrich
Published: January 2005

A new cytoarchitectonic study of the human auditory cortex was undertaken in the light of recent knowledge concerning the architecture, fiber connectivity, and physiology of this region in the monkey. The survey of three normative human brains (six hemispheres) processed in whole‐brain serial sections disclosed a cytoarchitectonic organization of the cortical auditory region similar to that in the macaque. Unlike the monkey, auditory‐related cortex was found in parietal operculum and inferior parietal lobule. Similarities in cortical architectonics between human and monkey brains may provide a rationale for the application of knowledge concerning animal physiology and connectivity to man.
Cytoarchitecture of the optic tectum of the squirrelfish, Holocentrus
Authors: Schroeder Dolores M. , Vanegas Horacio , Ebbesson Sven O. E.
Published: January 2005

The Holocentrus has large eyes and a well‐developed optic tectum. Nissl and fibers stains and various Golgi techniques show that the optic tectum of Holocentrus has six strata which can be subdivided into 14 alternative cell and fiber layers, some of which have additional organization. The stratum marginale (SM) is especially impressive in this fish and contains dendrites of pyramidal neurons, marginal fibers from torus longitudinalis, and axon‐like processes (the SM ascending axons) from cell located in the stratum griseum centrale (SGC). Stratum opticum (SO) and stratum fibrosum et griseum superficiale (SFGS) have many small neurons with limited dendritic fields. The large, so‐called pyramidal cell of SFGS has an extensive dendritic tree in SM and descending dendrites and axon to SGC. The latter has a variety of neurons with large dendritic fields in various layers of the tectum; the most distinctive, however, is the large fusiform neuron with its shepherd's crook axon. This stratum also has a dense layer of neuropil, the internal plexiform layer. Stratum album centrale (SAC) is primarily a fibrous layer, and stratum periventriculare (SPV) is a dense cellular area with the upper portion containing neuronal types also found in SGC and different from the typical neurons found in SPV. The latter have a major ascending branch with various dendritic patterns, and often do not have an identifiable axon; however, some of these cells have extensive branches throughout SFGS with an axon‐like appearace. Some general conclusions were made about the functional significance of the various tectal layers and cell types.
Origins of crossed and uncrossed retinal projections in pigmented and albino mice
Authors: Dräger Ursula C. , Olsen John F.
Published: January 2005

The extent of the binocular cortical field in albino mice, as revealed by recording from single cells, was almost normal; although the input from the ipsilateral eye was weaker than normal, most cells were driven from both eyes. By backfilling retinal ganglion cells from one optic tract with horseradish peroxidase we examined the origins of the retinofugal projections. Filled cells ipsilateral to the injected tract were concentrated in a crescent‐shaped area bordering the inferior temporal retina. In black mice this area constituted 20% of the total retinal area, in albinos 17%. In black mice we counted nearly 1,000 labeled cell in the ipsilateral retina, or 2.6% of all cells filled in both eyes. Albinos had about one‐third fewer filled cells ipsilaterally than black mice. Four percent of all ipsilaterally filled cells in black mice and 8% in albinnos were scattered outside of the crescent region. The density of ipsilaterally projecting cells was uniform throughout the crescent region in black mice, but decreased toward the central retina in albinos.

In retinas contralateral to the injection up to 39,000 cells were filled—about two‐thirds of the cells in the ganglion‐cell layer whose cytoplasm contained conspicuous Nissl substance. Depending on classification of unfilled cells as ganglion cells or interneurons, we estimated a total 48,000 to 65,000 ganglion cells to exist in the retina.

The size distribution of ipsilateraly projecting ganglion cells was similar in albinos and normals. Ipsilaterally projecting ganglion cells were on average 1.8–3 times larger in volume than contralaterally projecting ones in both types of mice.

Displaced ganglion cells were relatively more common in ipsilateral retinofugal projections: 21% of all ipsilateral ganglion cells were displaced versus less than 1% of all the contralateral ganglion cells in black mice. In albinos only 13% of the ganglion cells in the ipsilateral retina were displaced. The overall reduction in ipsilaterally projecting cells in albinos was reflected twice as much in displaced ganglion cells as in normally placed ones.
Topology of ascending brainstem projections to nucleus parabrachialis in the cat
Authors: King Gary W.
Published: January 2005

The afferent projections to nucleus parabrachialis (NPB) and nearby pontine areas from the lower brainstem were studied in cats using retrograde horseradish peroxidase (HRP) and anterograde autoradiographic tracing techniques. Two groups of medullary neurons send major projections to NPB and the Kölliker‐Fuse nucleus (KF): (1) the solitary complex, especially the medial nucleus of the solitary tract (SM), nearby smaller cells of the dorsal motor nucleus of the vagus (DMV) and the commissural nucleus; and (2) the lateral tegmental field (FTL), or parvocellular reticular formation. Autoradiographic tracing from these areas demonstrated terminal fields in NPB/KF and emphasized a ventrolateral route to NPB from both sources, with axons ascending between the facial nerve and superior olive and passing rostral to the trigeminal nuclei. Minor projections to NPB/KF originate in the ventrolateral nucleus of the solitary tract, area subpostrema, the alaminar spinal trigeminal nucleus, the gigantocellular and magnocellular tegmental fields, and an area dorsal to the ipsilateral inferior olive.

Topographical features of the major projections were studied by correlating the locus of overlap of injection sites with the locations of HRP‐positive cells. Medial areas of SM/DMV project mostly to medial parts of NPB, while lateral areas near the solitary tract project to lateral parts of NPB and KF. Crossing projections from SM/DMV favor dorsolateral NPB and KF. FTL neurons in dorsomedial areas project more to medial NPB, and ventrolateral areas project to lateral NPB/KF.

Using a new coordinate system to locate and normalize the positions of FTL neurons, data from many brains were collated. FTL cells projecting to NPB/KF were found to be on discrete longitudinal sheets, running radially with respect to the fourth ventricle. This substructure and related evidence suggest a preferred pattern for neuroanatomical connections and information processing in the lateral reticular areas of the brainstem, and help in understanding the topography of the projections to NPB/KF.
Spinocerebellar projections to the vermis of the posterior lobe and the paramedian lobule in the cat, as studied by retrograde transport of horseradish peroxidase
Authors: Matsushita Matsuo , Ikeda Michiko
Published: January 2005

Spinal neurons projecting to the posterior lobe of the cerebellum were identified with the retrograde horseradish peroxidase technique in the cat. In four cases with the injections, which were preceded by hemisections at cervical or thoracic levels, it was determined whether in the spinal cord the identified neurons give rise to crossed ascending axons or uncrossed ascending ones.

The main groups of neurons projecting to sublobule VIIIB were located in the central cervical nucleus (with crossed ascending axons), Clarke's column (with uncrossed ascending axons), and the medial part of lamina VII of L6 to the caudal segments (with crossed ascending axons). Additional labeled neurons were found in the medial part of lamina VI between C2 and T1 and of L5 and L6 (with uncrossed ascending axons), and in the ventral as well as dorsal horns of the sacral‐caudal segments (with crossed ascending axons). On the other hand, neurons projecting to sublobule C (the copular part) of the paramedian lobule, which appeared always ipsilaterally to the side of the injections, were located in lamina V of C8 to L4 (with uncrossed ascending axons). Marginal neurons of Clarke's column (with uncrossed ascending axons) and spinal border cells (with crossed ascending axons that recross in the cerebellum) projected specifically to this part. At L1 and L2 or L2 and L3 labeled large and medium‐sized neurons were also found within Clarke's column.

The present study suggests that there are segregated projections of spinal neurons to the cortex of the cerebellar posterior lobe.
Auditory cortico‐cortical connections in the owl monkey
Authors: Fitzpatrick Kathleen A. , Imig Thomas J.
Published: January 2005

Two tonotopically organized cortical fields, the primary (A1) and rostral (R) fields, comprise a core of auditory cortex in the owl monkey. Injections of tritiated proline were made into each of these fields to determine their projections to the auditory fields in the ipsilateral and contralateral hemispheres using autoradiographic methods. Neurons in R project to the rostromedial (RM) and primary fields in both hemispheres, and to the posterolateral (PL) and anterolateral (AL) fields in the ipsilateral hemisphere. In addition, the rostral fields in the two hemispheres are connected. Neurons in the primary field project to RM and R in both hemispheres and to AL, PL, and the caudomedial (CM) field in the ipsilateral hemisphere. The primary fields in the two hemispheres are connected. Single injections into A1 and R often result in labelingof two or more columns of tissue in the ipsilateral and contralateral target fields. Cortico‐cortical axon terminations are concentrated in layer IV of fields AL and RM and in upper layer III and layer IV of R and CM. In A1, axon terminals of neurons whose cell bodies lie in A1 in the opposite hemisphere are concentrated in upper layer III and layer IV; axon terminals of neurons located in field R of the same hemispheres are concentrated in layers I and II. Layer IV of PL contains the greatest concentration of cortico‐cortical axon terminals; the supragranular layers contain a somewhat lower concentration. Neurons in R project contralaterally in the anterior commissure while A1 neurons send their axons contralaterally in the corpus callosum.