bluuebunny/crossref_metadata_2025 huggingface dataset:
The organization of centrifugal projections from the anterior olfactory nucleus, ventral hippocampal rudiment, and piriform cortex to the main olfactory bulb in the hamster: An autoradiographic study
Authors: Davis Barry J. , Macrides Foteos
Published: May 2005

The centrifugal projections from the various subdivisions of the anterior olfactory nucleus (AON) can be categorized into four groups based on the organization of terminal fields in the main olfactory bulb (MOB). Pars lateralis and dorsalis have bilaterally asymmetric laminar projections to the MOB. The ipsilateral projections terminate primarily in the superficial half of the granule cell layer and in the deep third of the glomerular layer, whereas the contralateral projections terminate primarily in the superficial half of the granule cell layer and do not extend into the glomerular layer. Pars ventralis and posterior have bilaterally symmetric laminar projections with heavy terminations both in the superficial half of the granule cell layer and in the deep third of the glomerular layer. Pars medialis sends predominantly ipsilateral projections to the deep half of the granule cell layer. Pars externa has predominantly contralateral projections with a very narrow terminal field immediately deep to the internal plexiform layer. The projections to the MOB from the ventral hippocampal rudiment (HR) and the piriform cortex (PC) are exclusively ipsilateral. The projections from the ventral HR terminate primarily in the deep half of the granule cell layer. The projections from the PC also terminate predominantly in the granule cell layer, but there is a progressive shifting of terminal fields from the superficial half of this layer toward deeper regions for centrifugal axons arising from progressively more caudal levels of the PC. The laminar termination patterns of cortical afferents to the ipsilateral MOB thus are correlated with the mediolateral axis of the olfactory peduncle and the rostrocaudal axis of the piriform cortex.

The centrifugal axons from these various sources enter directly into the granule cell layer of the caudal MOB or pass through the internal plexiform layer of the accessory olfactory bulb to reach the middle and anterior part of the MOB. We have termed these two routes the final common bulbar pathway. The centrifugal axons from the laterally situated sources join the anterior and bulbar limbs of the anterior commissure before entering the final common bulbar pathway. In contrast, the centrifugal axons from pars medialis and the ventral HR travel diffusely in the cellular layer of the ipsilateral olfactory peduncle. A small component of the centrifugal projections from the PC travels in association with the lateral olfactory tract.
Maturation of rat visual cortex. II. A combined Golgi‐electron microscope study of pyramidal neurons
Authors: Miller Michael , Peters Alan
Published: May 2005

Tissue removed from 3, 6, 9, 12, 15, and 21‐day‐old rats has been prepared for correlative light and electron microscopy to examine the maturation of cell bodies, dendrites, and axons of pyramidal neurons in layer V of rat visual cortex. As the size of the cell body increases steadily during the first 3 postnatal weeks there is an equivalent growth in nuclear volume. By day 15, there are infoldings in the nuclear envelope which may be induced by eye opening on day 14. Nucleoli increase in size until day 9, after which they appear to condense. Within the perikarya, the most conspicuous change is the amount and organization of the rough endoplasmic reticulum. Symmetric axosomatic synapses are evident by day 6. The ultrastructure of dendrites does not change substantially with age. Dendrites form synapses with symmetric densities as early as day 3 and asymmetric ones by day 9. It seems that dendritic spines begin as low, broad protrusions having symmetric junctions with smaller diameter axonal processes. With time they become taller stumps, before acquiring their mature lollipop shape and participating in asymmetric synapses with axonal varicosities. Other dendritic appendages, filopodia, and growth cones are transient structures, being conspicuous only between days 3 and 12. “Terminal” growth cones are essential for extension of dendritic processes, whereas “en passant” growth cones and filopodia seem important for dendritic branching. Boutons of mature pyramidal cell axons form asymmetric synapses with dendritic shafts and spines, but the developing synapses formed by these axons have more symmetric junctions. The maturation of pyramidal cell features progresses in concert with such extrinsic determinants as afferent input and is probably influenced by the competency of synaptic connections.
Bilateral serotonergic projections to the dorsal hippocampus of the rat: Simultaneous localization of 3H‐5HT and HRP after retrograde transport
Authors: Azmitia Efrain C.
Published: May 2005

Horseradish peroxidase (HRP, Sigma VI, 30–70 nl of a 10–15% solution in saline) or 3H‐5HT (30 Ci/mmole, 2.5 × 10−3 M containing 3.3 × 10−3 M norepinephrine in saline, 50–100 nl) was injected unilaterally into the dorsal hippocampus in separate groups of rats.

HRP‐labeled cells were seen in the hippocampus, medial septal nucleus, nucleus of the diagonal band, supramammilary nucleus, median raphe nucleus, interfascicular portion of the dorsal raphe nucleus, and the locus coeruleus. In contrast, 3H‐5HT‐labeled cells were largely restricted to the raphe nuclei. In this nucleus an equal number of ipsilateral and bilateral cells were found. Occasionally, these labeled cells stretched across the midline (bridge pattern).

In another series, the 3H‐5HT and HRP were injected into the same hippocampus either as a mixture or sequentially. This resulted in double labeling of the median and dorsal raphe neurons. A final group of rats received injections of 3H‐5HT and HRP into opposing hippocampi. Double‐labeled cells accounted for 10% of the neurons labeled. In addition, closely paired neurons composed of an HRP‐and 3H‐5HT‐containing cell were found. In summary, the serotonergic fibers may play a key role in harmonizing the electrical activity of the hippocampi by use of bilateral projections, paired neurons with differential projections, and bridging neurons stretching across the midline but with unilateral projections.
Myelination kinetics of spiral ganglion cells in kitten
Authors: Romand R. , Romand M.‐R.
Published: May 2005

A study of the regions of myelination of spiral ganglion cell bodies at birth in the kitten revealed that the first signs of myelination occurred before birth. A quantitative analysis of myelinated versus unmyelinated cells, and the distribution of myelin lamellae of the ganglion cell sheath reflect the kinetics of the later stages of cochlear maturation. The onset of the final maturation process begins in the basal region of the first turn, which is 20% of the length of the spiral lamina measured from the basal extremity of the cochlea. This maturation proceeds in an orderly manner from the lower half of the first turn to the apex, but also develops to a smaller degree toward the hook region. Results are compared with previous findings.
Further observations on the cerebellar projections from the pontine nuclei and the nucleus reticularis tegmenti pontis in the rhesus monkey
Authors: Brodal Per
Published: May 2005

The projections from the pontine nuclei and the nucleus reticularis tegmenti pontis (N.r.t.) onto the flocculus, uvula, and the paramedian lobule were studied with retrograde transport of horseradish peroxidase in the rhesus monkey. The main findings are as follows:

There is a conspicuous tendency for labeled cells to occur in numerous discrete clusters in the pontine nuclei after injections of these parts of the cerebellum.

There appears to be very limited overlap between pontine cell groups projecting to the flocculus, the uvula, and the paramedian lobule, respectively.

The flocculus appears to receive a substantial projection from the pontine nuclei. The projection is almost totally crossed (3% ipsilateral), and arises mainly laterally in the rostral half of the pons, but in addition from a minor group dorsomedially. The flocculus receives a bilateral projection (slight contralateral preponderance) from medial and dorsomedial parts of the NRT. The number of labeled cells in the NRT was 13% of the number in the pontine nuclei.

The uvula is amply supplied from the pontine nuclei. The projection takes origin throughout the rostrocaudal extent of the pons, from one medial and one dorsolateral region. Labeled cells are found in greatest number dorsolaterally in the rostral half of the pons. In the caudal N.r.t., one medial and one lateral cell group were labeled after injection of the uvula. The number of labeled cells in the N.r.t. was only 4% of the number in the pontine nuclei.

Findings with regard to the paramedian lobule confirm and extend earlier observations in the monkey (Brodal, '79, '80).

The present results are discussed in relation to HRP studies of the pontocerebellar projection in lower animals. Several possible species differences are noted—for example, with regard to projections to the flocculus. There is some evidence that the pontocerebellar projection is more precisely organized in the monkey than in lower animals.
Localization and morphology of cat extraocular muscle afferent neurones identified by retrograde transport of horseradish peroxidase
Authors: Porter John D. , Spencer Robert F.
Published: May 2005

Afferent neurones that provide proprioceptive innervation of extraocular muscles of the cat have been identified by means of retrograde axonal transport of horseradish peroxidase (HRP). Discrete injections of HRP into the medial rectus, lateral rectus, or retractor bulbi muscles labeled pseudounipolar neurones that were localized exclusively to the ipsilateral semilunar ganglion. The distribution of labeled neurones within the ganglion was consistent with its somatotopic organization with the majority found within the ophthalmic subdivision. Cell counts indicating approximately 90 labeled neurones per horizontal rectus muscle correlated well with earlier quantitative observations regarding the percentage of afferent fibers in oculomotor nerves and the number of proprioceptive terminals in the extraocular muscles. Neither the trigeminal mesencephalic nucleus nor the contralateral semilunar ganglion contained labeled neurones following injections of HRP into extraocular muscles.

Consistent with other studies of spinal and cranial ganglia the contingent of pseudounipolar neurones present in the cat semilunar ganglion included both light and dark cell types. Light and electron microscope analysis of HRP‐labeled neurones in combination with acetylcholinesterase (AChE) histochemistry revealed that only one of the two neuronal types, the light cell, subserves extraocular muscle proprioception. Our data support the hypothesis that ganglion neurone type and, more specifically, soma diameter, are important determinants of functional status.
Ontogeny of somatostatin‐containing neuron system of the rat: Immunohistochemical analysis. II. Forebrain and diencephalon
Authors: Shiosaka Sadao , Takatsuki Kenichi , Sakanaka Masahiro , Inagaki Shinobu , Takagi Hiroshi , Senba Emiko , Kawai Yuriko , Iida Hisashi , Minagawa Hideo , Hara Yoshinobu , Matsuzaki Takashi , Tohyama Masaya
Published: May 2005

The ontogeny of the somatostatin (SRIF) neuron system in the forebrain and diencephalon of the rat was investigated by means of the indirect immunofluorescence method.

SRIF‐positive cells first appear in the primordium of the hypothalamus surrounding the fasciculus mammillothalamicus of the fetus at gestational day 14 (10–12‐mm embryo). At gestational days 16–17 (14–17‐mm embryo), SRIF‐positive cells appear in the developing piriform cortex and entopeduncular nucleus. The fetus at gestational days 18–19 (17–26‐mm embryos) showed a remarkable increase in the number of SRIF‐positive cells and numerous groups of such cells are detectable in various forebrain and diencephalic areas such as the hypothalamic periventricular zone, zona incerta, area lateral to the commissura posterior (ACP), area between the optic tract and capsula interna, pars retrolenticularis (AOR), n. caudatus putamen, hippocampus, somatic sensory cortex, and n. accumbens, etc. At gestational day 20, SRIF‐positive cells newly appear in the septum, olfactory bulb, diagonal band of Broca, claustrum, lateral preoptic area, and lateral habenular nucleus. The majority of SRIF‐positive structures found in the forebrain and diencephalon increase in number during the perinatal stage (between gestational day 21 and postnatal day 2) and more or less maintain their immunoreactivity even in adult rats. However, SRIF‐positive cells located in the AOR, ACP, and lateral septal area, etc., begin to decrease in number during the perinatal stage and no or only a few SRIF‐containing cells are identified in these areas of infant and adult rats.
The thalamic connectivity of the primary motor cortex (MI) in the raccoon
Authors: Sakai Sharleen T.
Published: May 2005

The purpose of this study was to determine the pattern of thalamic projections of the primary motor cortex (MI) in the raccoon, a carnivore species noted for neural specialization of sensorimotor function.

Following electrophysiological identification of circumscribed regions of MI, injections of horseradish peroxidase (HRP) or HRP combined with tritiated amino acids were made in 15 animals. Labeled thalamic cells were found predominantly in the ventral lateral nucleus (VL). For a given cortical injection site within MI, labeled neurons in VL formed a crescent‐shaped band which extended in a dorsoventral direction when viewed in coronal sections. These bands were topographically organized. Following an injection of the MI hindlimb area in the medial part of the posterior cruciate gyrus, both retrogradely labeled neurons and anterograde label formed a thin band at the lateral edge of VL while an injection of the MI face area in the lateral part of the anterior cruciate gyrus resulted in both anterograde and retrograde label in medial VL and the principal division of the ventromedial nucleus (VMp). An injection of the MI forepaw area localized to the rostral and central part of the posterior cruciate gyrus resulted in a band of labeled neurons occupying the dorsal extent of VL and continuing into the ventrolateral aspect of the ventral anterior nucleus (VA). In contrast, an injection of the MI forepaw area which was localized to the caudal extent of the posterior cruciate gyrus resulted in a wide and diffuse band of labeled neurons and anterograde label in the ventral portion of VL. All injections of MI produced cell labeling in the paracentral nucleus (PC) and the central lateral nucleus (CL) of the intralaminar group.

These results demonstrate that VL is the primary thalamic dependency of MI in the raccoon. Labeled cells were not observed in the ventrobasal complex. The MI pattern of thalamic connectivity observed in the present study suggests that while differences exist in the regional specialization of sensorimotor structures among species, there appears to be little variation in the overall organization of thalamocortical relations.
Membrane specializations in the outer plexiform layer of the turtle retina
Authors: Schaeffer Susan F. , Raviola Elio , Heuser John E.
Published: May 2005

The internal organization of the plasma membrane at specialized contacts in the outer plexiform layer of the turtle, Pseudemys scripta elegans, was analyzed with the aid of the freeze‐fracturing technique. In the invaginating synapse of cone pedicles the plasma membrane of the photoreceptor ending contains an aggregate of P‐face particles, images of synaptic vesicle exocytosis, and rows of forming coated vesicles which are arranged in sequence from apex to base of the synaptic ridge. Thus, freeze‐fracturing provides positive evidence that the synaptic ridge represents the active zone at the surface of the photoreceptor endings. Horizontal cell processes of dyads and triads have an aggregate of P‐face particles opposite the apex of the ridge, but lack images of vesicle exocytosis. Deep‐etching and rotaryshadowing demonstrate that an array of minute protrusions decorates the true outer surface of the horizontal cell membrane at the site of the intramembrane particle aggregate. The membrane of the invaginating bipolar dendrite is unspecialized. At basal junctions, the cone pedicle membrane has a sparse complement of P‐face particles, but images of vesicle exocytosis are absent. The adjoining bipolar membrane is characterized by a prominent aggregate of E‐face particles, often arranged in an orthogonal lattice. The freeze‐fracture profile therefore suggests the existence of (1) a sign‐conserving cone‐to‐horizontal cell synapse; (2) a sign‐inverting synapse between cones and invaginating bipolar dendrites; and (3) a sign‐conserving synapse between cones and bipolar dendrites at basal junctions. No freezefracture evidence was found for a horizontal‐to‐cone or horizontal‐to‐bipolar cell synapse within the synaptic invaginations.
Organization of the hand area in the primary somatic sensory cortex (SmI) of the prosimian primate, Nycticebus coucang
Authors: Carlson Mary , Fitzpatrick Kathleen A.
Published: May 2005

The topography of low‐threshold (LT) cutaneous input from the hand to SmI cortex of the prosimian primate Nycticebus coucang was mapped in detail by means of threshold receptive field techniques. The area of cortex responding to LT stimulation of the hand can be divided into three distinct subdivisions on the basis of physiological as well as cytoarchitectonic criteria. The rostral subdivision in the hand area (G1) responds to stimulation of the glabrous surface of the digits and hand. Within this field cells located rostrally have receptive fields located on the glabrous digit tips, while caudally located cells respond to stimulation of the proximal glabrous palm. Receptive fields in G1 are small in size and have low thresholds. G1 is coextensive with an area of cortex having the cytoarchitectonic features of koniocortex. The caudal region of the LT hand area consists of two subdivisions. Laterally, cells in this caudal region (H) respond to stimulation of the dorsal hairy digits and hand. Receptive fields on the dorsal hairy digits are found rostrally in this subdivision, while receptive fields on the dorsal hand and wrist are encountered caudally. Thus, the hand is projected serially across G1 and H. Within H, thresholds are similar to those in G1, but receptive fields are much larger in H than in G1. A second glabrous hand area (G2), is found in the medial part of the caudal region of the LT hand area. In G2 receptive fields on the glabrous ulnar digits are encountered rostrally, while more caudally cells respond to stimulation of the radial digits. Few glabrous palm fields were found in G2. Receptive field sizes and thresholds in G2 are quite similar to those in G1. Subdivisions H and G2 have the cytoarchitectonic characteristics of parakoniocortex. Although H and G2 are not distinguishable from one another, they can be easily separated from the more rostral koniocortex which contains the first glabrous hand area (G1). Thus, the SmI hand area of Nycticebus is unique among those of the other prosimian, Galago, thus far mapped in that two separate somatotopic projection patterns of the glabrous hand are present within the LT area. In this respect, Nycticebus more closely resembles simian species in which multiple LT hand areas are present in SmI in all forms which have been mapped. This is not to suggest that G2 in Nycticebus is either homologous to, or a precursor of, those multiple cutaneous areas reported for Old and New World simian species. Rather we suggest that the second glabrous projection in Nycticebus, and that of simian species, may have been achieved by the displacement of the dorsal hand projection occupying the architectonically distinct caudal SmI field in earlier prosimian species.
Cell death in the mammalian visual system during normal development: I. Retinal ganglion cells
Authors: Sengelaub D. R. , Finlay B. L.
Published: May 2005

Degenerating cells may be observed with light microscopy in the hamster retinal ganglion cell layer during early postnatal development. On the first postnatal day, degenerating cell profiles were found at a rate of 2.7 per 1,000 live cells. This rate increased to a peak of 14.7 degenerating cells per 1,000 live on postnatal day 5 and then slowed to 4.2 per 1,000 live by postnatal day 10. These rates of cell death correspond to a 49% reduction in cell number in the ganglion cell layer. Examination of the spatial pattern of cell death revealed that although on visual inspection degenerating cells appear to occur in clumps, statistical analyses demonstrated a random distribution within retinal areas. Across the retina, cell death rates were higher in peripheral retina than in central retina. The timing and pattern observed correspond well with that of cell degeneration observed in the superficial layers of the superior colliculus, the major target of the retinal projection.
Organization of HRP‐labeled trigeminal mandibular, primary afferent neurons in the rat
Authors: Jacquin Mark F. , Semba Kazue , Egger M. David , Rhoades Robert W.
Published: May 2005

Horseradish peroxidase (HRP) applied to the transected mandibular division of the trigeminal (V) ganglion was transported anterogradely to pri‐mary afferent terminal zones in the dorsal and dorsomedial trigeminal brain‐stem nuclear complex (TBNC). Primary V afferents of ganglionic origin were also visible in the ipsilateral cerebellar cortex (crus I and II, paraflocculus) and the dentate, cuneate, solitary, supratrigeminal, and dorsal motor vagal nuclei, parvicellular reticular formation, area postrema and C1–C6 dorsal horn, laminae I–V. Contralateral subnucleus caudalis and C1–C2 dorsal horn were also innervated by primary afferents which crossed in the spinal gray to terminate medially, primarily in laminae I, II, and V. Almost all of these projections were also labeled in various combinations when HRP was applied to individual sensory branches of the mandibular nerve: lingual, infe‐rior alveolar, mylohyoid, and auriculotemporal. Transganglionic transport of HRP in the latter four cases revealed strong evidence for mtradivisional somatotopy among the four branches in both the ganglion and TBNC. Cell bodies innervating posterior and/or lateral portions of the head and face (i.e., auriculotemporal and mylohyoid) were found with greater frequency in dor‐sal mandibular ganglion regions, while somata supplying more rostral oral‐perioral regions (i.e., lingual and inferior alveolar) were predominant ventrally. Components of the mandibular projection to the TBNC were organized topographically in at least some portion of all of its three dimen‐sions. Subnuclear preferences were not clear‐cut; all four nerves innervated at least some portion of principalis, oralis, interpolaris, and caudalis, save for mylohyoid, which did not project to caudalis. Lingual fibers were most prominent in principalis and oralis, occupied medial portions of the mandib‐ular projection to the TBNC, and descended only to rostral caudalis, most notably laminae I‐III. Inferior alveolar afferents were ubiquitous in the mandibular component of the TBNC and C1–C2, save for its far lateral bor‐der. Mylohyoid terminals were sparse, most prominent in interpolaris, and occupied only dorsolateral TBNC regions and laminae III and IV of C1–C3. The auriculotemporal innervation of the mandibular TBNC was heaviest in interpolaris and was restricted to mostly ventrolateral regions. Its primary focus, however, was laminae III and IV of C1–C4. The clinical implications of this topographical organization are discussed, particularly with respect to the rostrocaudal intradivisional lamination in caudalis and the cervical dorsal horn.
The embryonic development of the cortical plate in reptiles: A comparative study in Emys orbicularis and Lacerta agilis
Authors: Goffinet A. M.
Published: May 2005

From the earliest stage of its ontogenesis, the mammalian cerebral cor‐tex displays a remarkable cytoarchitectonic organization, with its neurons oriented radially within the cortical plate (CP).

It is not known whether this radial organization of cortical neurons is characteristic of every cerebral cortex or whether it reflects a progressive phylogenetic acquisition. In order to study this question, the embryonic de‐velopment of the cortex has been examined in reptiles, where it is the most primitive. Two species, Emys orbicularis and Lacerta agilis, representative of the two principal reptilian orders (chelonians and squamates), have been studied with histological methods, Golgi impregnation, and electron micros‐copy. Very similar patterns of cell proliferation, migration, maturation, and synaptogenesis have been observed. However, important species differences are present in the cellular organization of the cortical plate. Whereas in Emys the structure of the cortical plate is rudimentary, in Lacerta it appears well developed and quite reminiscent of its mammalian counterpart. Prelimi‐nary comparisons with embryological preparations of Sphenodon and Croco‐dilus niloticus show that the organization of the cortical plate displays significant variations among the different reptilian groups.

The present results suggest that the radial organization of cortical neu‐rons is not an all or nothing phenomenon but has been acquired indepen‐dently and is thus acase of homoplasy, probably due to convergence (North‐cutt, 1981). Several possible implications of these findings are discussed and a working hypothesis based on the role of radial glial cells in the formation of cytoarchitectonic patterns (Rakic, 1980) is presented.
Collaterals of spinothalamic cells in the rat
Authors: Kevetter Gold Aanne , Willis William D.
Published: May 2005

Spinothalamic (STT) cells were investigated in the rat to determine the distribution of subpopulations with terminals in both the lateral and medial thalamus, the thalamus bilaterally, or the thalamus and the medullary retic‐ular formation. Two or more retrogradely transported substances (fluores‐cent dyes, and/or horseradish peroxidase) were injected in each animal. Three combinations of injections were most commonly used: (1) injections of the medullary reticular formation and thalamus, (2) separate injections into each side of the thalamus, and (3) separate injections into the medial and lat‐eral thalamus. The distribution of single labeled cells after each injection was compared with previously published results for rats. The distribution of cells which contained both tracers, double‐labeled (DL) cells, was the focus of this study. An average of 15% of STT cells and 8% of spinoreticular cells projected to both the reticular formation and thalamus. However, only a small component of STT cells (less than 2%) projected bilaterally into the thalamus. Most DL cells were found in upper cervical segments. The laminar distributions of all three groups of DL neurons were similar. These cells were most often located in the reticulated part of lamina V and the intermediate zone, lamina VII. STT cells that had terminals in both the medial and lateral thalamus and STT cells with collaterals in the reticular formation were con‐centrated on the side contralateral to their terminals. These DL neurons pro‐vide an anatomical substrate for noxious stimuli to activate the reticular for‐mation and thalamus and/or specific sensory and intralaminar thalamus simultaneously.
Dendritic distribution of splenius motoneurons in the cat: Comparison of motoneurons innervating different regions of the muscle
Authors: Keirstead S. A. , Rose P. K.
Published: May 2005

The distribution and dendritic organization of splenius motoneurons innervating extrafusal muscle fibers in different regions of the muscle were examined by electrophysiological and intracellular HRP staining techniques. Motoneurons innervating the regions of the splenius muscle supplied by the C2, C3, and C4 peripheral nerves were arranged in three nonoverlapping sub‐nuclei. Reconstructions of the dendritic trees of splenius motoneurons in these three subnuclei showed that there were no major differences in their dendritic distributions. Instead, the dendritic distribution followed a single pattern which was composed of five major dendritic projections. These included a dorsolateral projection to the lateral part of lamina VIII, a lateral projection into the spinal accessory nucleus and beyond the gray‐white border, ventral and ventrolateral dendrites in the lateral half of the ventromedial nucleus and the surrounding white matter, medial dendrites which projected both dorsally and ventrally, and finally a conspicuous collection of dendrites which projected rostrally and caudally from the cell body.

These results indicate that the dendritic distributions of splenius motoneurons are not related to the segmental position of the motoneuron or the zone of the muscle innervated by the motoneuron. However, a comparison of the dendritic distribution of splenius motoneurons to the dendritic distribution of biventer cervicis‐complexus motoneurons indicated that there are major differences in the form of their dendritic trees even though dendrites from both sets of motoneurons share the same territory. As a consequence, although these motoneurons may receive the same connections, the effect of these connections on the excitability of the motoneurons may differ.
Distribution of dendrites of mitral, displaced mitral, tufted, and granule cells in the rabbit olfactory bulb
Authors: Mori Kensaku , Kishi Kiyoshi , Ojima Hisayuki
Published: May 2005

To determine the dendritic fields, mitral, displaced mitral, middle tufted, and granule cells in the rabbit olfactory bulb were stained by intracellular injection of HRP. The secondary dendrites of mitral cells were distributed mostly in the inner half of the external plexiform layer (EPL). Those of displaced mitral cells extended mainly into the middle and superficial sublayers in the EPL. The secondary dendrites of middle tufted cells weredistributed mostly in the superficial portion of the EPL.

Mitral cells extended their secondary dendrites in virtually all directions within a plane tangential to the mitral cell layer (MCL) and thus had a disklike projection field with a radius of about 850 μm. Displaced mitral cells had similar dendritic projection fields in the tangential plane but with somewhat distorted shapes. The secondary dendrites of middle tuftedcells had a tendency to extend in particular directions.

From the projection pattern of the gemmules on the peripheral processes, granule cells were classified into three types. Type I granule cells had gemmules both in the superficial and in the deep sublayers of the EPL. The peripheral processes of Type II granule cells were confined to the deep half of the EPL. The gemmules of Type III granule cells were distributed in the superficial half of the EPL.

The differing dendritic ramification among mitral, displaced mitral, and middle tufted cells suggests the separation of the dendrodendritic synaptic interactions with granule cells in different sublayers in the EPL. It also suggests a functional separation of the sublayers of the EPL.
Postnatal changes in retinal ganglion cell and optic axon populations in the pigmented rat
Authors: Perry V. H. , Henderson Z. , Linden R.
Published: May 2005

The number of ganglion cells in the retina of the postnatal rat has been examined. We estimated both the number of axons in the optic nerve and the number of cells which can be retrogradely labelled with horseradish peroxidase from injections into the brain. In the retina of the newborn rat there are at least twice as many ganglion cells as in the adult rat. By retrograde labelling of the ganglion cells and following transection of their axons 24‐48 hrs later we can find no evidence that ganglion cells withdraw their axon without degeneration of the parent cell body. We have found that the excess ganglion cells are lost over the first ten postnatal days and during this period we observe pyknotic nuclei in the ganglion cell layer. From our estimates of the total number of neurones in the ganglion cell layer and the number of ganglion cells found at different ages we conclude that themigration of amacrine cells into the ganglion cell layer occurs in the first five postnatal days.
Transient cholinesterase staining in the mediodorsal nucleus of the thalamus and its connections in the developing human and monkey brain
Authors: Kostovic Ivica , Goldman‐Rakic Patricia S.
Published: May 2005

The histochemical and morphological maturation of the mediodorsal nucleus (MD) and its connections were compared in human and rhesus monkey using acetylthiocholine iodide and Nissl methods. Histochemical analysis in fetuses, neonates, and adults of both primate species revealed that MD passes through three major stages of cholinesterase (ChE) reactivity. In Stage I (up to about 16 fetal weeks in man; 9 fetal weeks in monkey), ChE staining gradually increases in the MD nucleus and is intense in axons directed toward the frontal lobe through the internal and external capsules. In Stage II (about 16‐28 fetal weeks in man; about 9‐14 weeks in monkey), ChE staining in MD reaches peak intensity so that reaction product in the neurons and neuropil blackens the entire nucleus in both species. In favorable planes of section, ChE‐positive fibers appear to connect MD and the basal forebrain both of which stain intensely. ChE‐positive fibers can also be traced from the lateral margins of MD to the subplate zone beneath the developing frontal cortical plate where they continue to accumulate before later invading the cortex with heaviest concentration in presumptive layers 3 and 5. In Stage III (after 28 weeks of gestation to 6 postnatal months in man; from about 14 fetal weeks until 2 postnatal months in monkey), except for scattered positive cells, ChE staining gradually disappears in MD and the formerly dense laminar pattern in the cortex begins to lighten. The dramatic but transient increase in ChE staining in MD during fetal development as well as the sequentially related changes in its projections indicate that this early appearing enzyme may play a role in the development of the frontal lobe by influencing the differentiation of thalamoprefrontal connections.
Structure of the piriform cortex of the opossum. III. Ultrastructural characterization of synaptic terminals of association and olfactory bulb afferent fibers
Authors: Haberly Lewis , Behan Mary
Published: May 2005

Terminals of olfactory bulb afferent (OB) and association (ASSN) fiberswithin the piriform cortex were characterized ultrastructurally. Identification was by electron microscopic (EM) autoradiography following injections of tritiated amino acids into the olfactory bulb and anterior piriform cortex. The results show that terminals of both fiber systems contain round vesicles and make asymmetrical synaptic contacts predominantly onto dendriticspines. Profiles with pleomorphic vesicles do not appear to be labeled from either site. Since there is strong evidence that both fiber systems generate excitatory postsynaptic potentials (EPSPs) in pyramidal cells, these results provide additional examples in the mammalian CNS of terminals with round vesicles and asymmetrical contacts that mediate an excitatory effect.

Percentage density analysis and quantitative study of a large number of heavily labeled terminals revealed that while OB and ASSN terminals are similar in terms of vesicle shape and contact type, they differ in many morphological details including pre‐and postsynaptic profile size, the packing density and distribution of synaptic vesicles, synaptic contact shape, and the presence of overlying neuroglial lamellae. However, large variations in appearance of different terminals of the same type are also present so that a small percentage of OB and ASSN terminals are indistinguishable morphologically in the absence of label.

An important finding of the quantitative analysis is that spines contacted by lateral olfactory tract (LOT) terminals appear to be of two types based on a bimodal distribution in size and differences in morphology, while spines contacted by ASSN terminals appear to be of a single type. Comparison of these data with results from Golgi analysis indicates that ASSN terminals predominantly contact pyramidal cell spines while OB terminals contact both pyramidal and semilunar cell spines.

Quantitative analysis of synaptic vesicles revealed that histograms of vesicle size for OB and ASSN terminals are virtually identical in shape, but peaks are slightly displaced (ASSN vesicles are 5% larger; significant with P < .002).

An analysis of the laminar distribution of OB and ASSN synaptic terminals revealed that while moat OB terminals are segregated in layer Ia and most ASSN terminals in layer Ib, occasional OB terminals are observed up to approximately 50 μm deep to the Ia‐Ib boundary and occasional ASSN terminals up to approximately 50 μm superficial to this boundary.
Developmental alterations in sensory neuroanatomy of the Caenorhabditis elegans dauer larva
Authors: Albert Patrice S. , Riddle Donald L.
Published: May 2005

The anterior sensory ultrastructure of the C. elegans dauer larva was examined in several specimens and compared with that of the second‐stage (L2) larva, which immediately precedes the dauer stage. In some instances comparisons were made with L3, postdauer L4, and adult stages. Whereas sensory structures in different nondauer stages closely resemble each other, the dauer larva differs in certain chemosensory and mechanosensory organs, including the inner labial sensilla, amphids, and deirids. The relative positions of the afferent tips of the two types of inner labial neurons are reversed in the dauer stage compared to the L2 and postdauer L4 stages. Inner labial neuron 1 rather than neuron 2 is more anterior in each of the six sensilla, and neuron 1 has an enlarged tip. The neuron 2 cilia are only one‐third as long as those in the L2. Amphidial neurons c., d, g, and i and the amphidial sheath cell are altered in shape or position in the dauer stage. Neurons g and i are displaced posteriorly within the dauer amphidial channel. Neuron d has significantly more microvillar projections than do the d cells in L2, L3, or postdauer L4 larvae. Winglike processes of dauer neuron cform a 200°–240° are in transverse section, including extensive overlap of the two cells. The arc in an L2 seldom spans more than 100°, and overlap does not occur. While L2 larvae possess two separate bilateral amphidial sheath cells, the left and right sheath cells are often continuous in the dauer larva. Deirid sensory dendrites exhibit a dauer‐specific structure and orientation. The tip of each neuron is attached to the body wall cuticle by a substructure not observed in L2 or postdauer L4 stages, and the neurons are oriented parallel to the longitudinal axis of the dauer larva. The deirid sensory terminals are oriented perpendicular to the cuticle in other stages. Reversible alterations in neural structure are discussed in the context of dauer‐specific behavior.
The development and postnatal organization of primary afferent projections to the rat thoracic spinal cord
Authors: Smith Carolyn L.
Published: May 2005

Primary afferent projections to the thoracic spinal cord in fetal and postnatal rats were labelled by applying horseradish peroxidase (HRP) to the central stumps of cut peripheral nerves. Diaminobenzidine (DAB) and tetramethyl benzidine (TMB) histochemical processing procedures were used to reveal the HRP reaction product.

In postnatal rats, individual muscle nerves were labelled to reveal the organization of muscle afferent projections to the motor nuclei. The terminals of muscle afferents were distributed widely across the dendritic arbors of motoneurons supplying the same muscles. No spatial segregation of the terminations of different populations of muscle afferents was discernable.

Afferents supplying different regions of the skin were labelled by applying HRP to the dorsal and ventral primary rami of the spinal nerves. Afferents in the dorsal rami projected to lateral portions of both the ipsilateral and contralateral dorsal horns while afferents in the ventral rami projected to the medial portions of both dorsal horns. The projections of the dorsal rami were shifted caudally relative to those of the ventral rami. This relationship reflects the fact that the regions of skin innervated by the dorsal rami are displaced caudally relative to those innervated by the corresponding ventral rami.

In fetuses, dorsal rami were labelled alone or in combination with ventral rami. These experiments disclosed the time course of development of the projections to different laminae of the spinal gray matter and revealed that afferents in the two primary rami project to appropriate regions in the ipsilateral and contralateral dorsal horns from the very outset.
Computer‐assisted analyses of barrel neuron axons and their putative synaptic contacts
Authors: Harris Roger M. , Woolsey Thomas A.
Published: May 2005

The “barrels” in layer IVof rodent SmI neocortex receive inputs from individual whiskers on the contralateral face. Previous analyses of neuronal morphology in mouse and rat barrel cortex, as revealed by Golgi impregnations, have focused on the dendritic patterns of the stellate cells. The cells can be classified into two groups: Class I cells with spiny dendrites and Class i I cells with smooth, beaded dendrites. These classes can be subdivided further according to somal position and spatial distribution of dendrites with respect to barrel cytoarchitectonic boundaries. In the present study the axons of these cells were examined and the locations of close appositions to dendrites of other impregnated neurons were mapped. All data are taken from Golgi‐Cox preparations, cut parallel to layer IV at 140 μm, counter‐stained with Nissl to reveal the barrels, and measured with a computer‐microscope. Axons which had extensive branching within the section (present on 10% of all impregnated cells) were chosen for measurement.

The analysis of the axons revealed: (1) Class I axons are thin and directed to the white matter with recurrent collaterals in the barrels, while Class II axons are thick, frequently beaded, and directed toward the pia before cascading down into the barrels; (2) in layer IV, the axons of both cell classes tend to be as restricted to a barrel as the dendrites of the same cell are (i.e., most axons are confined to one barrel); (3) within layer IV, the Class II cell axons have a total length about three times that of Class I cell axons, and about four times as many branch points.

The analysis of the appositions of these axons to impregnated dendrites of other cells revealed: (1) A maj ority of “contacts” tended to be made by terminal branches of the axonal trees. (2) For the Class I neurons, a greater number of appositions occur near the distal ends of complete dendritic segments. As measured from the “contacted” cell soma, appositions are more or less uniformly distributed along dendritic trees. (3) No striking patterns are found, such as an obvious propensity for axons of one cell type to prefer or avoid another cell type.

These results show that the axons of barrel cells of each class are as consistent and distinctive as their dendritic trees. Specifically, the cells in each class can be distinguished by their axonal patterns on purely numerical bases. The new computer programs which were developed to systematically search for sites of apposition between axons and dendrites ‐a necessary prerequisite for the existence of synaptic contacts‐greatly facilitated the collection of these data: The data may be of value for defining “probable” sites of interaction between particular cell types. In particular, these light microscopic observations of the distribution of appositions along dendritic segments are similar in some ways to White and Rock's ('80, '81) electron microscopic mapping of synapses on single‐barrel neurons.
Invariance and sex‐specific variations of the glomerular organization in the antennal lobes of a moth,Mamestra brassicae, and a butterfly,Pieris brassicae
Authors: Rospars Jean Pierre
Published: May 2005

The glomerular organization of the antennal lobes was analyzed in the mothMamestra brassicaeand comparatively in the butterflyPieris brassicae.The invariance of the lobes in number, position, and size of the glomeruli was verified quantitatively in the moth for all the glomeruli in individuals of the same sex (67 in males, 68 in females) and for 56 sex‐invariant glomeruli which can be identified in all individuals whatever their sex. In the butterfly, the positional variability is greater than in the moth and hinders identification. The most conspicuous sex‐variant glomeruli are two adjoining macro‐glomeruli in the male moth which have homologs of very small size in the female. No such dimorph ism was observed inPieris, a species in which males are attracted to female by visual stimuli and not by a sex pheromone as inMamestra.There are other sex‐variant glomeruli inMamestra: four varying in location, three subdivided in the female, two found only in the male, and three found only in the female. Consequently, differing olfactory sensitivity related to species and sex could correlate with detectable modifications in the glomerular organization. A hypothesis on the function of glomeruli is discussed in which most of the glomeruli are viewed as “olfactory general‐ists” giving rise collectively to proposed “across‐glomeruli patterns”.
Subcortical projections to the occipital and parietal lobes of the chimpanzee brain
Authors: Tigges Johannes , Walker Lary C. , Tigges Margarete
Published: May 2005

The subcortical sources of aff erents to occipital andparietal cortex were studied in two chimpanzees with the aid of retrogradely transported horseradish peroxidase (HRP). In chimpanzee 1, HRP was inj ected into right cortical areas 17 and 18; chimpanzee 2 received HRP into right areas 17, 18, 19, and 39. The following subcortical structures were found to project to area 17 and/or area 18: locus coerulcus, dorsalraphe nucleus, nucleus annularis, nucleus centralis superior, pontine reticular formation, mesencephalic reticular formation, dorsal hypothalamus, lateral hypothalamus, nucleus basalis of Meynert, nucleus of the diagonal band of Broca, claustrum, nucleus basalis lateralis amygdalae, lateral geniculate nucleus, inferiorpulvinar.lateralpul‐vinar, nucleus limitans, medial magnocellularpartof the nucleus ventralis anterior, nucleus paraccnlralis, and nucleus centralis medialis thalami. Some of these structures may also project to area 19 and/or area 39. The following thalamic nuclei were found to project to area 19 and/or area 39 but not to areas 17 and 18: nucleus lateralis posterior, nucleus centralis lateralis, nucleus medialis dorsalis, nucleus ventralis lateralis, nucleus ventralis anterior, nucleus lateralis dorsalis, and nucleus anterior ventralis. In several instances, the Hftp‐labeledcells traversed specific nuclear borders, extending uninterruptedly fromone classically definednucleus into another. Thesere‐sults in the chimpanzee largely confirm data from a number of other mammalian taxa on the subcortical sources of afferents to the posterior cortex. Because of the close biological relationship between chimpanzee and man, we feel confident that such projections are also features of the human brain.
Columnar aggregation of prefrorital and anterior cingulate cortical cells projecting to the thalamic mediodorsal nucleus in the monkey
Authors: Arikuni Tomio , Sakai Masaki , Kubota Kisou
Published: May 2005

The columnar arrangement, of the prefrontal and anterior cingulate cortex cells that project to the thalamic mediodorsal (MD) nucleus in rhesus and Formosan monkeys was studied by injecting horseradish peroxidase into the MD nucleus. Labelled cells appeared ipsilaterally in layers V and VI in the dorsolateral, medial, and orbital prefrontal cortex, and in layer VI in the anterior cingulate cortex. Labelled cells were aligned in the radially oriented cords of neurons and grouped into clusters, 25‐200 μm wide, thus forming columns. Radial cellular cords with no labelled cells were interspersed between the labelled radial cords.