bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptic fine structure and the termination of corticospinal fibers in the lateral basal region of the cat spinal cord
Authors: Hanaway Joseph , Smith Jeanne M.
Published: January 2005

The lateral basal region (LBR) of the spinal cord gray matter (Rexed's laminae IV‐VII) by physiologic and anatomic criteria is the major terminal zone for the corticospinal (CS) tract in the cat. The neurons in this area are medium‐sized with abundant spines on their dendrites. Axon terminals on the dendrites and somata of these neurons form synapses easily classified as asymmetric with spheroid vesicles and symmetric with flattened vesicles. There are rare exceptions to this. In a systematic count of terminals, 82% have spheroid and 18% flattened vesicles. The majority of all terminals are on dendrites (84.9%) and a minority on somata (14.1%). Less than 1% are axoaxonic.

Degeneration of the corticospinal tract was produced by transecting one hemisphere of our experimental cats. Its termination in the lower cervical cord was studied for 17 hours to 7 days after surgery. Vesicle depletion and clumping and dense polymembranous inclusions were the most common forms of degeneration. Filamentous proliferation in the terminals was also prominent; dark degeneration, however, was infrequent. The percent of degenerating CS terminals in the LBR was the following: 17 hours – 2.2%, 36 hours – 4.19%, 2 days – 10.3%, 3 days – 8.4%, 4 days – 6.9%, 7 days – 10.25%; 84.8% of degenerating CS terminals were axodendritic and 15.2% axosomatic.
The time of origin of the mesencephalic trigeminal neurons in Xenopus
Authors: Lewis Simon , Straznicky Charles
Published: January 2005

Time of orgin of the mesencephalic trigeminal cells (MTC) in Xenopus has been studied with 3H‐thymidine autoradiography. The first MTC's were formed at stage 20, and they continued to arise up to stage 58. The mitotic rate of MTC's was found to be ten per cent at any time from stages 20–50, with a slow decrease thereafter. MTC's in the tectum were distributed in a spatiotemporal manner. Cells generated earliest were located in the rostral pole of the tectum and were followed in caudomedial sequence by cells formed later. The generation times of MTC and the neurons of the sensory trigeminal ganglion (TGC) were strikingly dissimilar, indicating that they probably do not represent a common cell lineage, that is, the former may not arise from the mesencephalic neural crest. It is proposed that the majority of MTC's generated from stage 30 onward, derive through proliferative activity of precursor cells in the di‐mesencephalic junction and in the tectal neuroepithelium.
Afferent influences on the development of the brain stem auditory nuclei of the chicken: Otocyst ablation
Authors: Parks Thomas N.
Published: January 2005

The effects of embryonic deafferentation on the morphological development of the avian cochlear nuclei, n. angularis (NA) and n. magnocellularis (NM), were investigated. The right otocyst was surgically removed from chick embryos at 55 to 60 hours of incubation and the subsequent development of total volume, neuron number, and neuron cross‐sectional area were studied with quantitative methods in animals sacrificed at 2‐day intervals between embryonic days 9 and 19 and at 28 days posthatching. The development of NA and NM is severely affected by otocyst ablation. Between embryonic days 9 and 19, a large group of NA neurons in the medioventral portion of the nucleus on the perated side moves to an ectopic ventromedial position, while the remainder of this nucleus stays in its normal dorsolateral position. Beginning about day 13 of incubation, the normal increase in the volume of NA and the size of its neurons becomes progressively retarded and 40% of its neurons are lost. The growth of NM is also retarded after day 11 of incubation and the growth of mean neuron size is retarded after day 15. There is a 30% loss of neurons in NM which begins after embronic day 11.

The results indecate the primary cochlear fibers make a critical contribution to the growth and maintenance of their target neurons. The absence of this facilitative influence following otocyst ablation becomes apparent just at the time synapses would normally be formed between the promary auditory afferents and the brain stem auditory neurons. The abnormal movement of neurons in nucleus angularis to an ectopic position after otocyst ablation suggests that primary auditory afferents may serve to stabilize the position of their target cells within the developing brain.
Histofluorescence and ultrastructural evidence for catecholamine‐containing sensory neurons bordering the interventricular foramen of the toad brain
Authors: McKenna Olivia C. , Gorski Victoria A.
Published: January 2005

A population of catecholamine‐containing cells that borders the interventricular foramen of the toad brain has been studied by both fluorescence histochemical and electron microscopic methods. The perikaryon of these cells, which lies immediately subjacent to the ependyma, sends a fluorescent apical process between the ependymal cells to border on the ventricular surface and a basal process displaying fluorescent varicosities into the underlying neuropil. A few cells possess a broad lateral extension which runs parallel to the ventricular surface. Histochemical and pharmacological specificity tests indicate that the cells contain catecholamines, including epinephrine. The most distinctive ultrastructural feature of the subependymal cells' cytoplasm is large numbers of dense cored vesicles that vary in diameter from 500 A to 2,400 A; these are found in the perikarya, apical and basal processes, and lateral extensions. In addition, bundles of filaments ($100 A in diameter) are seen lying adjacent to the nucleus, and numerous axosomatic synapses are found along the surface of the cell bodies. The luminal surface of the apical processes is covered by microvilli and extends a short distance into the ventricular lumen. The basal processes are narrow in diameter, measuring 0.5‐1.1 $m, and contain some filaments, microtubules and dense cored vesicles, but no clusters of ribosomes and no granular endoplasmic reticulum. The characteristics of these subependymal cells, i.e., apical processes which contact the cerebrospinal fluid and basal processes which resemble axons, suggest that the cells may be sensory neurons, and as such, they may respond to the changing composition or pressure of the cerebrospinal fluid and relay this information via their axons to other neurons. The results of this study contribute further evidence that the cerebrospinal fluid provides a means of chemical communication within the brain.
Synaptic Contacts of the Horizontal Cells in the Retina of the Marine Teleost, Callionymus Iyra L.
Authors: van Haesendonck E. , Missotten L.
Published: January 2005

The horizontal cell system in the retina of the fish Callionymus Iyra L. was investigated light microscopically and electron microscopically. One type of rod horizontal cells, which are only found in the mixed ventral part, exclusively contacts spherules with lateral endknobs in the triads. Three types of cone horizontal cells occur. The first type, c‐H1, contacts pedicles of pale and dark double cones and single cones. The processes always have a lateral position in the triads. This type has a constant contact pattern with the photoreceptor cells. The second type, c‐H2, selectively contacts pedicles of pale double cones and the endbuds occupy a central position in the triads. In the single cone pedicles in the dendritic field of the c‐H2 horizontal cell, the endbuds never seem to reach the triads. The third type, c‐H3, only sends processes to pedicles of single cones where the endbuds occupy a central position in the triads. The synaptic connections of the horizontal cells of Callionymus differ from those observed in Nannacara anomala and Carassius auratus. The difference from the results obtained from Carassius is such that the information transfer model proposed for Carassius cannot apply to Callionymus.
The organization of feline entopeduncular nucleus projections: Anatomical studies
Authors: Larsen Kenneth D. , McBride Russell L.
Published: January 2005

The organization of entopeduncular nucleus (EPN) projections was studied in cats using autoradiographic and horseradish peroxidase (HRP) techniques. In autoradiographic studies, EPN axons were found to terminate in a J‐shaped region in the dorsal and medial part of the ventral anterior nucleus (VA) and the rostral portion of the adjacent ventral lateral nucleus (VL). EPN axons also terminated in the rostral portion of the centrum medianum (CM), the ventrolateral portion of the lateral habenular nucleus (LHB), and the pedunculopontine nucleus (PP). The VA included the largest terminal field although the LHB had the greatest density of terminals. Regardless of the region of EPN into which amino acids were injected, the terminal fields were the same: there was no localization within the EPN of the cells projecting to one region. HRP‐containing cells were distributed throughout the EPN following injections into the VA, LHB, or PP, although many more cells were labeled following injections into either VA or LHB than PP. EPN cells containing HRP following injections into either VA or LHB were not morphologically different from those not containing HRP in the same respective animals. Following HRP injections into stria medullaris, only cells in the rostral part of the EPN were labeled, providing evidence that rostrally and caudally located EPN neurons have different paths to LHB. Although there may be a rostrocaudal organization of pathways to LHB, individual regions of the nucleus project to the same areas.
Retinofugal projections of nonecholocating (Pteropus giganteus) and echolocating (Myotis lucifugus) bats
Authors: Cotter John R. , Pierson Pentney Roberta J.
Published: January 2005

The projections and terminations of retinofugal pathways were studied in nonecholocating (Pteropus giganteus) and echolocating (Myotis lucifugus) bats by two methods, that of anterograde axonal degeneration following unilateral enucleation and anterograde axoplasmic transport of isotope following unilateral intraocular injection of tritiated proline.

In Pteropus giganteus crossed and uncorssed projections terminated in several brainstem areas and the nuclei of the accessory optic system. Bilateral projections to the hypothalamus ended in the suprachiasmatic nuclei (SCN). In the ventral thalamus the projection terminated bilaterally in internal (VLGi) and external (VLGe) divisions of the ventral lateral geniculate (VLG) nuclei, although the projection to VLGi was greater than that to the other subdivision of VLG. Three lateral laminae of the dorsal lateral geniculate (DLG) nucleus and a medial division were each involved in contralateral and ipsilateral projections of the retina to the dorsal thalamus. Partially segregated and partially overlapping patterns from the two eyes and concealed lamination were identified in the lateral three laminae at some levels. In addition, the projection to the dorsal thalamus involved the contralateral lateral posterior nucleus. In the pretectum the projection terminated bilaterally in the nuclei of the optic tract (NOT), pretectal olivary nuclei (PON), anterior pretectal nuclei (APN) and posterior pretectal nuclei (PPN). The pattern of termination in the superior colliculus was such that contralateral and ipsilateral projections ended in different tiers in the superficial gray (SG) layer, those on the contralateral side being largely confined to the upper and lower tiers and those of the ipsilateral side being confined to a middle tier. Projections to contralateral medial, lateral, and dorsal accessory optic nuclei traversed the accessory optic tract.

In Myotis lucifugus crossed projections terminated in the SCN, VLG, DLG, pretectum and superior colliculus. The projection to the VLGe was greater than that to VLGi. In the DLG, retinal fibers terminated in two major subdivisions. The stratification of retinal terminals observed in Pteropus was not present in Myotis> Pretectal terminations were confined to two restricted areas which were tentatively identified as the NOT and the PON. In the contralateral superior colliculus the projection terminated in two tiers in the SG. A small uncrossed component of the projection was limited in its termination to the ipsilateral SCN, DLG and VLG. The accessory optic system did not appear to be present in Myotis.

These results indicate that there are basic differences in the overall projection of the retina upon the brainstem of echolocating and nonecholocating bats.
Primary afferent fibers in the tract of Lissauer in the rat
Authors: Chung Kyungsoon , Langford Lauren A. , Applebaum Arnold E. , Coggeshall Richard E.
Published: January 2005

More than two‐thirds of the axons in the tract of Lissauer at mid‐thoracic and lumbosacral levels of the rat spinal cord are primary afferent fibers. The proportions of primary afferents in the tract are approximately the same at the two spinal levels. A slightly higher percentage of the unmyelinated, as opposed to the myelinated, fibers are primary afferents. There is a somewhat greater percentage of primary afferent axons in medial parts of the tract in mid‐thoracic levels, but all areas of the tract that were examined contain a majority of primary afferent fibers. The primary afferent axons appear to travel less than a segment in the tract at mid‐thoracic levels but for several segments in the tract at lumbo‐sacral levels. These data indicate that the tract of Lissauer is predominately a primary afferent fiber system in these segments of the rat.
Electron microscopic studies of serially sectioned cat spinal α‐motoneurons. II. A method for the description of architecture and synaptology of the cell body and proximal dendritic segments
Authors: Conradi S. , Kellerth J‐O. , Berthold C‐H.
Published: January 2005

The paper presents a method for ultrastructural analysis and description of neuronal architecture and synaptology of cat spinal α‐motoneurons from complete series of consecutive ultrathin sections through the cell body and proximal parts of the dendrites. The method implies that sections are selected for analysis only at certain constant intervals in the series. The occurrence of boutons of different morphological types on the neuronal surface was expressed by their percentage covering of the neuronal membrane. The neuronal surface was divided into a number of compartments and the synaptic covering was calculated separately for each compartment. An interval of 6 μm between the sections was used for these calculations, and the obtained values for synaptic covering were found not to differ significantly from those obtained in controls at 3 μm intervals. The number and location of individual large boutons (C‐ and M‐types) were studied at 3 μm section intervals, and the escape of boutons connected to this procedure was estimated from control observations at 1 μm intervals. It is concluded that detailed information on neuronal synaptology can be obtained with this method, which will be used in three subsequent studies on functionally identified and intracellularly stained cat α‐motoneurons.
An autoradiographic study of the subcortical projections of the rabbit striate cortex in the adult and during postnatal development
Authors: Holländer H. , Tietze J. , Distel H.
Published: January 2005

The subcortical projections of the rabbit striate cortex were studied by autoradiography. Small injections of 3H‐leucine were placed into the striate cortex of 15 rabbit pups aged between one day and one month and six adult rabbits (strain Chbb:Ch). Terminal fields of projection occurred only ipsilateral to the injection, and these were found in the caudate nucleus (CN), the claustrum (Cla), the thalamic reticular nucleus (TRN), the dorsal (LGNd) and the ventral (LGNv) lateral geniculate nuclei, the pulvinar (Pul), the ventrolateral (Vl) the posterior (Po) thalamic nuclei, the anterior (APN) and posterior (PPN) pretectal nuclei, the nucleus of the optic tract (NOT), the superior colliculus (SC) and the basal pontine nuclei (PN). Cla was innervated via the superficial corticocortical and CN via the corticocaudate pathways. The remaining projections were innervated via the subcortical pathway which comprised three bundles: The deep bundle (to TRN, LGNd, Pul and Po), the superficial bundle (to LGNv, APN, PPN, NOT, and SC), and the peduncular bundle (to PN). The projection to SC showed remarkable changes of its terminal pattern during the first and second postnatal weeks. These changes were characterized by a strong reduction of the horizontal extension of the terminal labelling and an increasing concentration on the stratum griseum superficiale. Similar changes were not observed in the other projections.
Aging in the rat olfactory bulb: Quantitative changes in mitral cell organelles and somato‐dendritic synapses
Authors: Hinds James W. , McNelly Nancy A.
Published: January 2005

Quantitative measurements of the major organelles in the mitral cell perikaryon as well as numbers of mitral somato‐dendritic synapses, have been made on electron micrographs from rats aged 3 to 30 months. The volume fraction of the cisternae of rough endoplasmic reticulum (RER) is constant throughout the period studied. Hence the amount of RER per cell reflects changes in perikaryal size. Thus there is a 3‐fold increase of volume of cisternae of RER per mitral cell from 3 to 27 months and a halving from 27 to 30 months. A similar pattern is seen for the volume of mitochondria per cell. The volumes of dense bodies and cisternae of the Golgi complex per cell show a different pattern, that of a linear increase throughout the period, with no suggestion of a decrease from 27 to 30 months. An interesting finding is that the volume fraction of ground substance (perikaryal cytoplasm exclusive of the measured organelles) shows a remarkably constant value from 3 to 27 months and then a highly significant decrease from 27 to 30 months. This decrease, restricted to the period from 27 to 30 months, suggests a fundamental breakdown in cellular homeostasis in the oldest animals.

Numbers of somato‐dendritic, mitral‐to‐granule synaptic junctions per mitral cell and per olfactory bulb show a significant increase from 3 to 24 and 27 months, respectively, and then a suggestive decrease from 24 and 27 to 30 months. This finding indicates that new synapse formation is possible in normal adult rats, perhaps even in quite old rats.
The cochlear nuclei of some turtles
Authors: Miller Malcolm R. , Kasahara Michiko
Published: January 2005

Histological sections of the brains of eight species of turtles representing six different families were studied in order to delineate the cochlear nuclei. In addition, the posterior eighth cranial nerve root and its ganglion were sectioned in 15 specimens of Kinosternon leucostomum, and the distribution of the degenerated nerve fibers and terminals was determined. Two primary and one probably secondary nuclei were demonstrated by the terminal degeneration pattern of the cochlear fibers.

A spherical nucleus angularis and an elongated nucleus magnocellularis together form a column of primary cochlear nuclei in the dorsal alar lamina of the medulla. Heavy terminal degeneration is seen associated with these cells following transection of the posterior eighth nerve and ganglion. Nucleus magnocellularis is probably homologous with the nucleus magnocellularis medialis of lizards and crocodiles, and has been described in turtles as nucleus dorsalis magnocellularis by previous authors.

A probably secondary cochlear nucleus, nucleus laminaris, lies just ventral to the nucleus magnocellularis. It is associated with the nucleus magnocellularis throughout its length but is shorter. Nucleus laminaris remains free of terminal degeneration after destruction of the posterior eighth nerve and ganglion.

The cochlear nuclei of other turtle species were very similar to those of Kinosternon leucostomum.
Distribution of primary afferent fibers within the sacrococcygeal dorsal horn: An autoradiographic study
Authors: Réthelyi M. , Trevino D. L. , Perl E. R.
Published: January 2005

The spinal segmental distribution and intersegmental course of primary afferent fibers were studied by injecting (by pressure or iontophoresis) tritiated amino acids (L‐proline or L‐leucine) into spinal ganglia of coccygeal and sacral segments and autoradiographically analyzing histological sections of the spinal cord, particularly those regions lying dorsal to the central canal. The results from eight cats and three monkeys are described.

A heavy projection of primary afferent fibers to the marginal zone (lamina I), the substantia gelatinosa Rolandi (lamina II), and throughout the nucleus proprius (laminae III‐IV) was demonstrated. The projections to these three areas appeared to be substantially independent. Primary afferent fibers were found to course rostrally and caudally within the marginal zone, in the midline dorsal to the central canal, in Lissauer's tract, and in the dorsal columns. A crossed projection passed by way of the dorsal commissure to the contralateral marginal zone and to a region ventrolateral to the contralateral nucleus proprius.

There was a distinct medial‐to‐lateral shift in the termination of primary afferent fibers in the substantia gelatinosa and in the dorsal protion of the nucleus proprius. The most medial distribution occurred immediately caudal to the entry zone of the primary afferent fibers, and the most lateral at the cephalad end of the segment immediately rostral to the entry level. Small (iontophoretic) injections revealed circumscribed fields of termination, approximately 40 μm 70 μm (dorsoventrally) by 400 μm or more (rostrocaudally) in the substantia gelatinosa.
Thalamic relay nuclei for cerebellar and certain related fiber systems in the cat
Authors: Hendry S. H. C. , Jones E. G. , Graham J.
Published: January 2005

Anterograde labeling techniques were used to define the terminal distributions in the thalamus of afferents arising in the deep cerebellar nuclei, entopeduncular nucleus and substantia nigra. Anterograde and retrograde labeling methods were then used to determine the extent of the cortical projections of the cerebellar relay nuclei. The cerebellar projection to the contralateral ventral nuclei of the thalamus terminates in a zone which is separate from that receiving pallido‐ and nigrothalamic fibers. None of the zones of termination of these fiber systems corresponds to commonly recognized cytoarchitectonic divisions. Instead, they include parts of the ventroanterior (VA), ventrolateral (VL) and principal ventromedial (VMp) nuclei.

Some cells within the zone of termination of cerebellar afferents project to parietal cortex (areas 5 and 7). A further, distinct group of cells in this zone projects to motor cortex (area 4). But projections to area 4 also arise from small groups of cells: (a) in the zone receiving nigro‐ and pallidothalamic fibers; (b) in the part of VL, distinct from the cerebellar terminal zone, in which spinothalamic fibers terminate.

Cerebellar, nigral, and entopeduncular fibers also terminate in the intralaminar nuclei. These projections are far greater in extent than those arising in the spinal cord. Some parts of the intralaminar nuclei are dominated by a particular afferent system, while others show substantial overlap of the terminal zone of several afferent systems.
An HRP and autoradiographic study of the projection from the cerebellar cortex to the nucleus interpositus anterior and nucleus interpositus posterior of the cat
Authors: Bishop G. A. , McCrea R. A. , Lighthall J. W. , Kitai S. T.
Published: January 2005

The recently developed anatomical techniques of retrograde transport of the enzyme horseradish peroxidase (HRP), anterograde transport of tritiated amino acid, and intracellular injections of HRP were used to study the organization of the corticonuclear projection to the nucleus interpositus anterior (NIA) and the nucleus interpositus posterior (NIP) of the cat.

Injections of HRP into the NIA and the NIP revealed that the major areas of the cortex which provided afferents to these two nuclei were the intermediate cortex of the anterior lobe (IAL) and the paramedian lobule (PML). There were, however, significant differences in the distribution of Purkinje (Pk) cells which projected to each nucleus. The NIA received afferents from all areas of the IAL while the NIP projection area was restricted to a band located at the medialmost aspect of the lobe. All areas of the PML, in particular the intermediate folia, projected to the NIP, while the Pk cells which sent axons to the NIA were restricted to the rostral and caudal folia of this lobule. The projection from each area was somatotopically organized.

The axons of intracellularly stained Pk cells were followed to their termination in the NIA and NIP confirming the results obtained with the two extracellular techniques. An attempt was made to examine the organization of the corticonuclear projection at the single cell level in the PML. Pk cells located in the same sagittal plane appeared to terminate in the same area of the same nucleus while Pk cells located not more than 500 μm medial or lateral to each other terminated in different nuclei.

Basically, the organization of the corticonuclear projection from the IAL is longitudinally organized while the PML has a much more complex arrangement in which the Pk cells projecting to the NIA and NIP are interspersed.
Efferent projections of the dorsal ventricular ridge and the striatum in the Tegu lizard, Tupinambis nigropunctatus
Authors: Voneida Theodore J. , Sligar Catherine M.
Published: January 2005

A H3 proline‐leucine mixture was injected into the dorsal ventricular ridge (DVR) and striatum of the Tegu lizard in order to determine their efferent projections. The brains were processed according to standard radioautographic technique, and counterstained with cresyl violet. DVR projections were generally restricted to the telencephalon, while striatal projections were limited to diencephalic and mesencephalic structures. Thus the anterior DVR projects ipsilaterally to nuclei sphericus and lateralis amygdalae, striatum (ipsilateral and contralateral) ventromedial nucleus of the hypothalamus, nucleus accumbens, anterior olfactory nucleus, nucleus of the lateral olfactory tract and lateral pallium. Posterior DVR projections enter ipsilateral anterior olfactory nucleus, lateral and interstitial amygdalar nuclei, olfactory tubercle and bulb, nucleus of the lateral olfactory tract and a zone surrounding the ventromedial hypothalamic nucleus. Labeled axons from striatal injections pass caudally in the lateral forebrain bundle to enter (via dorsal peduncle) nuclei dorsomedialis, medialis posterior, entopeduncularis anterior, and a zone surrounding nucleus rotundus. Others join the ventral peduncle of LFB and enter ventromedial nucleus (thalami), while the remaining fibers continue caudally in the ventral peduncle to the mesencephalic prerubral field, central gray, substantia nigra, nucleus intercollicularis, reticular formation and pretectal nucleus posterodorsalis. These results are discussed in relation to the changing notions regarding terminology, classification and functions of dorsal ventricular ridge and striatum.
An anatomical reinvestigation of the termination of the spinothalamic tract in the monkey
Authors: Boivie Jörgen
Published: January 2005

The projections of the spinothalamic tract in the macaque monkey have been reinvestigated using the Wiitanen modification of the Fink‐Heimer technique. In agreement with previous studies in the monkey (Mehler, Bowsher, Kerr) it was found that the spinothalamic tract ascends outside the medial lemniscus, enters the thalamus just dorsal to this structure, and terminates in the posterior, intralaminar and ventral regions, as well as in the zona incerta.

The posteromedial nucleus (POm) receives a dense spinothalamic projection medially and ventromedially; elsewhere in the POm the projection is more scattered. The fibers to the intralaminar region terminate in the nucleus centralis laterials (CL) with a distinct pattern of the distribution. The nucleus centralis medialis (CeM) has a minute projection. There was no evidence for somatotopic organization in the projections to the POm or to the intralaminar region.

The distribution of the terminal degeneration in the ventral nuclear region was more complex. Although present in the whole nucleus ventralis posterolateralis (VPL), the degeneration was unevenly distributed and also extended beyond the VPL. So‐called clusters of dense degeneration lay in the outskirts of the forelimb and hindlimb representation areas, namely at its ventral, ventrolateral, dorsolateral, and medial borders. Centrally the degeneration was scattered. Thus, most of the VPL receives only a sparse spinothalamic projection, but a small portion contains dense networks of terminal spinal fibers. A somatotopic pattern was evident, for after low thoracic lesions most of the medial VPL lacked degeneration.

Spinothalamic fibers pass beyond the VPL to terminate in a zone of transition (nucleus ventralis intermedius or V.im of Hassler, '59; Mehler, '71) between the rostral pole of the VPL and the nucleus ventralis lateralis (VL). This zone also reportedly receives cerebellar and vestibular afferent fibers.

Observations suggesting that the evolution of the spinothalamic tract and the spino‐cervico‐thalamic pathway in carnivores and primates may be linked are discussed. The spinothalamic clusters in the monkey's VPL appear to be homologous to much of the cervicothalamic tract projection to the VPL in the cat.
An electronmicroscopic analysis of the optic nerve in the golden hamster
Authors: Rhoades Robert W. , Hsu Linda , Parfett Gail
Published: January 2005

The electronmicroscopic examination of sections taken from the hamster's optic nerve 5 mm behind the globe indicated that the nerve contains 110,165 ± 4,177 (p < 0.05) fibres of which 96.4% are myelinated. The fibre diameter distribution is unimodal with a peak at 1.2 μm and axon diameters ranging from 0.20 μm to 3.93 μm. Fibres of all sizes are distributed uniformly throughout the cross section of the nerve. The thickness of the myelin sheath surrounding a given axon is highly (0.80) correlated with axonal diameter and the degree of myelination for a fibre of a given size is nearly constant throughout the nerve's cross section. In nerve sections taken just posterior to the globe most (64%) of the fibres counted are unmyelinated and the percentage of unmyelinated axons is highest near the peripheral boundary of the nerve. The process of myelination is essentially complete in sections taken 3.5 mm behind the eye. These differences in the myelination of the proximal and distal nerve most probably account for the discrepancy between the results reported here and those provided by a previous study (Tiao and Blakemore, '76) concerned with the structure of the optic nerve in this species.
Membrane specializations and cytoplasmic channels of Schwann cells in mammalian peripheral nerve as seen in freeze‐fracture replicas
Authors: Kruger L. , Stolinski C. , Martin B. G. H. , Gross M. B.
Published: January 2005

Mammalian Schwann cells in rat, rabbit and human fetal nerves were studied using several cryoprotective agents for electron microscopic study of freeze‐fracture replicas. The findings in fixed and unfixed tissue reveal surface plasmalemma caveolar specializations and the outer layer membrane junctional complexes found in non‐mammalian species. The plasmalemma also reveals a complex arrangement of contours outlining cytoplasmic channel networks distinct from the long‐recognized Schmidt‐Lanterman incisures and paranodal cytoplasmic loops. A specialized interconnected channel system in the outer “loose” myelin layer displays relatively uniform dimensions comparable in diameter to nodal microvilli, paranodal loops and some incisures. An adaxonal tubular channel system constituting the “axon‐Schwann network” is found in the internodal region in addition to other variants of the adaxonal Schwann plasmalemma. The several forms of sequestration of Schwann cell cytoplasm presumably underlie the specialized needs of cytoplasmic continuity in a dynamic functional entity in which large domains of cytoplasm have been displaced by the formation of compact myelin.
A Golgi study of the class V cell in the visual thalamus of the cat
Authors: Updyke B. V.
Published: January 2005

Golgi methods were used to study class V cells within the cat visual thalamus. Counterstaining was combined with Golgi staining to assess the distribution of dendrites relative to cytoarchitectural boundaries. Class V cells were encountered within all laminae of the lateral geniculate nucleus, the medial interlaminar nucleus, and the lateral posterior complex. The cells possess medium‐sized perikarya and smooth and varicose or moniliform dendrites. Dendritic appendages are sparse and occur as single or serial swellings on thin processes. Many class V cells exhibit large, sparse dendritic arbors which span laminar or nuclear borders; dendrites were seen to lie within and to cross the interlaminar zones of the lateral geniculate nucleus, and extend beyond this nucleus into the perigeniculate nucleus and medial interlaminar nucleus. Class V cells of the lateral posterior complex send dendrites into the external medullary lamina. Indirect evidence favors the interpretation that the class V cells are thalamo‐cortical relay cells.
Thalamic projections to area 17 in a prosimian primate, Microcebus murinus
Authors: Cooper H. M. , Kennedy H. , Magnin M. , Vital‐Durand F.
Published: January 2005

Electrophysiological recording of single neurons was used to describe the representation of visual space in area 17, and the technique of retrograde transport of horseradish peroxidase (HRP) was applied to relate these results to projections from the thalamus in the prosimian primate Microcebus murinus. The visuotopic organization of area 17 was found to resemble that of other primates. On the dorsal surface, the border of area 17 corresponds to the representation of the vertical meridian. Proceeding medially across the surface the location of receptive fields descends along the vertical meridian, while moving caudally receptive fields progress temporally. Most of the dorsolateral surface is devoted to central vision and corresponds to a well developed area centralis. Following HRP injections in striate cortex, columns of labeled cells were found in the dorsal lateral geniculate (dLGN) extending orthogonally across all six layers. These columns run in a general ventrodorsal and caudorostral direction, parallel to a line connecting the cellular discontinuities corresponding to the optic disc. These discontinuities are present in magnocellular layer 1 and parvocellualr layers 5 and 6, thus receiving from the nasal retina of the contralateral eye. The representation of the vertical meridian is situated in the ventromedial portion of the dLGN, and the monocular field is represented in the dorsal extremity. Anterior dLGN projects to the calcarine fissure (lower field). and posterior dLGN projects to the ventral surface of the cortex (upper field). Exptrgeniculate input to area 17 was found to originate from the pulvinar. HRP labeled cells were located in two distinct divisions of this nucleus, the cytoarchitecture of which is described. In addition, projections to occipital cortex were found to arise form the intralaminar nuclei.
A cerebello‐pulvino‐cortical and a retino‐pulvino‐cortical pathways in the cat as revealed by the use of the anterograde and retrograde transport of horseradish peroxidase
Authors: Itoh Kazuo , Mizuno Noboru , Sugimoto Tetsuo , Nomura Sakashi , Nakamura Yasuhisa , Konishi Akira
Published: January 2005

A cerebello‐pulvino‐cortical and a retino‐pulvino‐cortical pathways were revealed in the cat by means of the horseradish peroxidase (HRP) method. The sites of termination of the cerebellofugal and retinofugal fibers in the pulvinar nucleus (Pul) were visualized by the use of the anterograde transport of HRP. The cerebello‐pulvinar fibers were found to arise mainly from the parvicellular region of the lateral cerebellar nucleus and to terminate contralaterally in a narrow area at the extreme dorsolateral edge of the Pul at the level of the stereotaxic frontal plane A‐7.0. The area of terminal ramification of the retino‐pulvinar fibers was seen as a thin sheet lying at the extreme lateral edge of the Pul through most of the rostrocaudal extent of the Pul, bilaterally with contralateral predominance. The cerebellorecipient area in the Pul did not seem to overlap with the retinorecipient Pul area; the former appeared to be contiguous ventrolaterally to the latter. The cerebellorecipient and retinorecipient Pul areas were also observed to be connected reciprocally with the cerebral cortical areas; the former was connected with the most posterior part of the area 20, and the latter with the area 19.
Connections of the tectum of the rattlesnake crotalus viridis: An HRP study
Authors: Gruberg Edward R. , Kicliter Earl , Newman Eric A. , Kass Leonard , Hartline Peter H.
Published: January 2005

We have studied the connections of the tectum of the rattlesnake by tectal application of horseradish peroxidase. The tectum receives bilateral input from nucleus lentiformis mesencephali, posterolateral tegmental nuclei, anterior tegmental nuclei and periventricular nuclei; ipsilateral input from nucleus geniculatus pretectalis, and lateral geniculate nucleus pars dorsalis; and contralateral input from dorso‐lateral posterior tegmental nucleus and the previously undescribed nucleus reticularis caloris (RC). RC is located on the ventro‐lateral surface of the medulla and consists of large cells 25–45 μm in diameter. Efferent projections from the tectum can be traced to the ipsilateral nucleus lentiformis mesencephali, the ipsilateral lateral geniculate region, anterior tegmental region and a wide bilateral area of the neuropil of the ventral tegmentum and ventral medulla. We have not found any direct tectal projections from the sensory trigeminal nuclei including the nucleus of the lateral descending trigeminal tract (LTTD). We suggest that in the rattlesnake, RC is the intermediate link connecting LTTD to the tectum.
A quantitiative study of the occurrence and distribution of cytoplasmic laminated bodies in the lateral geniculate nucleus of the normal adult cat
Authors: Schmidt Marie Luise , Hirsch Helmut V. B.
Published: January 2005

The proportion of neurons containing cytoplasmic laminated bodies (CLB) in the dorsal lateral geniculate nucleus (dLGN) of normal cats was determined by using a new method which permitted examination of large areas of this nucleus. Near the medial border of the dLGN (projection of the area centralis) in the A‐laminae 30–60% of the neurons contain CLBs. Within the same region in lamina B only 10–30% of the nerve cells contain CLBs. In the monocular segment (MS) of lamina A 27–48% of the nerve cells contain CLBs. In the medial interlaminar nucleus (MIN) 25% of the neurons contain CLBs; these cells were distributed throughout the medio‐lateral extent of the MIN. CLBs were also observed in neurons of the perigeniculate nucleus (PN) and in nerve cells embedded in the fiber sheet separating the dLGN from the pulvinar complex. The distribution of cells containing CLBs is extremely variable in all portions of the dLGN studied.

The data presented in this paper indicate that CLB‐containing cells in the dLGN may not be X‐cells, as has been suggested by LeVay and Ferster ('77) because: (1) the distribution of neurons containing CLBs in lamina A does not match the distribution of X‐cells recorded in this lamina; (2) some nerve cells in the MIN contain CLBs but very few X‐cells have been found in this region.
Postnatal differentiation of the rat trochlear nerve
Authors: Kerns James M.
Published: January 2005

A morphometric analysis of postnatal differentiation in the rat trochlear nerve was studied by light and electron microscopy as an initial basis for understanding motor unit heterogeneity in the extraocular muscles (EOM). A total of 35 animals were examined 7–90 days postnatal (dpn). The mean number of fibers increased from 222 at 7 dpn to 274 in the adult and the size distribution became bimodal at 21 dpn. In the adult 17% of the myelinated fibers had a mean diameter of 2.5 μm and 83% were 7.3 μm. The estimated number of unmyelinated axons decreased from about 40% at 7 dpn to 20% at 14 dpn and 16% in the adult. The myelinated fiber diameter was more highly correlated with age and body weight than was fiber number. Certain organelles characteristic of active membrane growth were present in the Schwann cell cytoplasm at the paranode region. Redundant loops were prominent at 10 dpn, when many axons were still in Schwann cell bundles. During the third postnatal week a number of alterations were noted which may reflect a loss of polyneuronal innervation. These included thicker myelin sheaths and ultrastructural evidence of axonal degeneration. Branching of myelinated fibers was limited to the intramuscular portions of the nerve at 18 dpn. The g‐ratio of the largest fibers at selected ages was nearly constant at .71 and was correlated with fiber diameter (r = 0.40), except at 14 dpn. The periodicity of the myelin sheath had either an inverse or constant relationship to the number of lamellae. The significance of the results is discussed in relation to postnatal development, the size principle and heterogeneity in the EOM motor units.
Organization of the ascending striatal afferents in monkeys
Authors: Szabo Janos
Published: January 2005

Horseradish peroxidase was injected in various parts of the caudate nucleus and the putamen of monkeys to ascertain the relative locations of striatal projecting cells in the mesencephalon. The nigrostriatal component, as expected, is the greatest but numerous cells of the mesencephalic raphe system also project to the striatum. The projections from the pars compacta are organized in a topographical manner in all principal planes. The rostral two thirds of the substantia nigra are related to the head of the caudate nucleus. Nigral neurons projecting to the putamen are more posteriorly located and display an anteroposterior topography. The medial two thirds of the pars compacta send efferents to the head of the caudate nucleus from ventromedial to laterodorsal regions, reflecting a mediolateral topographical relationship. An inverse relationship exists dorsoventrally between nigra and caudate so that ventral compacta cells project to dorsal caudate and the dorsally situated neurons project to ventral‐ventro‐medial caudate regions. The dorsal and lateral parts of the putamen are more intimately related to the lateral and posterior nigra; by contrast, the ventral and ventromedial putamen receives more afferents from medial and central regions of the substantia nigra. A large group of cells in the tegmentum dorsal and medial to the medial lemniscus shows continuity with the pars compacta, and has similar connections with the striatum. This cell group should be included with the pars compacta. Significant overlap exists between the projection fields in all planes, making the nigrostriatal topographical organization seem less than precise. This apparent lack of point‐to‐point reciprocity may be due to the considerable size difference between the striatum and the substantia nigra. The raphe nuclei project to the greater part of the striatum but more significantly to its ventral and medial regions. The paranigral cell group sends its efferents mainly to the ventral striatum.
Ascending projections from the lateral descending and common sensory trigeminal nuclei in python
Authors: Molenaar G. J. , Fizaan‐Oostveen J. L. F. P.
Published: January 2005

The primary sensory trigeminal system of Python is characterized by the presence of an additional nucleus which is involved in processing data obtained by infrared sensors. This so‐called lateral descending nucleus (LTTD) is strictly separated from the nuclei of the common sensory trigeminal system. The present study was undertaken in order to establish the relation between the two sensory trigeminal systems and higher brainstem structures. Further we studied whether the projections of these two systems remain separated at higher brainstem levels

It is shown that the organization of particularly the thalamus is characterized by the presence of specific projection areas of each of the two trigeminal systems: (a) the ability of infrared perception is reflected particularly in the presence of an unique thalamic nucleus: the nucleus pararotundus and probably also in the enlargement of nucleus rotundus; and (b) distinct subnuclei in the thalamic ventral nuclear complex are related to the various nuclei of the common sensory trigeminal system

The main ascending projection of LTTD runs via a distinct tract to the central gray layer (SGC) of the contralateral tectum mesencephali and the nucleus pararotundus (PR). Rostrally, numerous fibres decussate again via the tectal commissure and terminate ipsilaterally in the rostral part of SGC and in PR

The ascending projections of the common sensory trigeminal nuclei resemble those of mammals by gaining thalamic nuclei (ventral nuclear complex). No projections to the tectum nor to the striatum (like in birds) were observed

The two sensory trigeminal systems remain separately organised, in their projections as well as in their structure. No major connection between the two trigeminal systems is present.
Ontogeny of the retina and optic nerve in Xenopus laevis. I. Stages in the early development of the retina
Authors: Grant Philip , Rubin Eric , Cima Charles
Published: January 2005

A staging series for retinal histogenesis is described for Xenopus laevis. It is based on scanning EM studies of intact eyes and serial section analysis of silver‐stained preparations. Retinal development is arbitrarily divided into twelve stages (I–XII) based on distinct morphological and histological changes. In general, four different phases of retinal development can be identified: an embryonic phase of rapid histogenesis (Nieuwkoop‐Faber stages 21–39) and onset of visual function; a second or functional phase completed by stage 52 is a period of growth, synaptogenesis, and the organization of visual function; a third phase ending at metamorphic climax (NF57) when mature function is achieved and binocular vision begins; and a final mature phase at the end of metamorphosis, when rod and cones are adult size and the visuotectal projection extends over the entire tectum. Ten of the twelve developmental stages are assigned to the first phase since this is the period of intense morphogenesis and differentiation.