bluuebunny/crossref_metadata_2025 huggingface dataset:
Afferent projections to the deep mesencephalic nucleus in the rat
Authors: Veazey Randolph B. , Severin Charles M.
Published: May 2005

Afferent projections to the deep mesencephalic nucleus (DMN) of the rat were demonstrated with axonal transport techniques. Potential sources for projections to the DMN were first identified by injecting the nucleus with HRP and examining the cervical spinal cord, brain stem, and cortex for retrogradely labeled neurons. Areas consistently labeled were then injected with a tritiated radioisotope, the tissue processed for autoradiography, and the DMN examined for anterograde labeling. Afferent projections to the medial and/or lateral parts of the DMN were found to originate from a number of spinal, bulbar, and cortical centers.

Rostral brain centers projecting to both medial and lateral parts of the DMN include the ipsilateral motor and somatosensory cortex, the entopeduncular nucleus, and zona incerta. At the level of the midbrain, the ipsilateral substantia nigra and contralateral DMN likewise project to the DMN. Furthermore, the ipsilateral superior colliculus projects to the DMN, involving mainly the lateral part of the nucleus.

Afferents from caudal centers include bilateral projections from the sensory nuclei of the trigeminal complex and the nucleus medulla oblongata centralis, as well as from the contralateral dentate nucleus. The projections from the trigeminal complex and nucleus medullae oblongatae centralis terminate in the intermediate and medial parts of the DMN, whereas projections from the contralateral dentate nucleus terminate mainly in its lateral part.

In general, the afferent connections of the DMN arise from diverse areas of the brain. Although most of these projections distribute throughout the entire extent of the DMN, some of them project mainly to either medial or lateral parts of the nucleus, thus suggesting that the organization of the DMN is comparable, at least in part, to that of the reticular formation of the pons and medulla, a region in which hodological differences between medial and lateral subdivisions are known to exist.
Three‐dimensional structure of the mammalian suprachiasmatic nuclei: A comparative study of five species
Authors: Lydic Ralph , Albers H. Elliott , Tepper Beverly , Moore‐Ede Martin C.
Published: May 2005

The suprachiasmatic nuclei from five mammalian species (rat, hamster, cat, rhesus, and squirrel monkey) were reconstructed in three‐dimensions by use of computer graphics and conventional histological techniques. The gross nuclear structures of the suprachiasmatic nuclei have complex threedimensional geometries in every plane of orientation, and between the five species there are marked differences in the three‐dimensional morphology of the suprachiasmatic nuclei. These dimensionally accurate reconstructions are discussed in relation to previous data suggesting morphological and/or functional specialization within specific regions of the suprachiasmatic nuclei.
Cell death in the mammalian visual system during normal development: II. Superior colliculus
Authors: Finlay B. L. , Berg A. T. , Sengelaub D. R.
Published: May 2005

Degenerating cells may be observed with light microscopy in the hamster superior colliculus during early postnatal development. In the superficial gray layer and stratum opticum, 1.8 degenerating cells for each 1,000 live cells could be seen on the first postnatal day. This rate increased to 5.6 degenerating cells per 1,000 live cells by postnatal day 5, and declined to 2.6 per 1,000 live cells by postnatal day 8. The rate of cell degeneration was consistently elevated at the medial, lateral, and caudal margins of the superficial gray layer relative to the center. In the intermediate and deep gray layers, the rate of cell death was consistently higher, starting at three degenerating cells per 1,000 on the first postnatal day, increasing to 15 per 1,000 on postnatal day 5, and declining to 4.7 per 1,000 by postnatal day 8. In contrast to the superficial gray layer, the number of degenerating cells in the central versus peripheral segments of the intermediate and deep gray layers was quite similar.

Although the rate of observable degeneration is low, the likely rapid clearance of degenerating cell debris indicates a substantial loss of cells from the midbrain tectum in early development. The time course of observable degeneration, the amount, and the distribution of degenerating cells are quite similar in the tectum, and its major innervating structure, the retina.
The localization of vasotocin and neurophysin neurons in the diencephalon of the pigeon, Columba livia
Authors: Berk Mitchell L. , Reaves Troy A. , Hayward James N. , Finkelstein Judith A.
Published: May 2005

Vasotocin (VT)‐ and neurophysin (NP)‐synthesizing neurons were demonstrated by immunocytochemistry in the diencephalon of the pigeon, Columba livia. Three diencephalic regions contain VT‐NP cells: (1) periventricular preoptic area and hypothalamus, including nucleus periventricularis magnocellularis (PVM); (2) lateral preoptic area and hypothalamus; and (3) dorsal diencephalon. The immunoreactive cells in each of these three regions were divided into groups based on cytology and topography. No differences were found in the location of VT and NP cell groups.

The periventricular region contains three continuous cell groups (P1–P3) extending from the posteroventral preoptic area to the anterodorsal hypothalamus and PVM. The lateral region has two cell groups composed of medium‐ to large‐sized cells associated with the quintofrontal tract (L1) or with the optic tract (L2), while a third group (L3) lies between these two cell groups. Two accessory cell groups reside in the dorsolateral hypothalamus; L4 contains scattered cells of varied size, whereas L5 has small‐ to medium‐sized cells clumped together. The dorsal diencephalic cell groups are found in the following locations: (1) lateral and dorsal to the lateral forebrain bundle (DD1); (2) in the area ventral to the dorsomedial anterior thalamic nucleus and dorsolateral to PVM (DD2); and (3) at the dorsolateral border of nucleus rotundus (DD3).

To avoid potentially inaccurate mammalian homologies, the cell group nomenclature denotes topographic position. Nevertheless, the presence of VT‐NP cells in PVM and projections to the brainstem and spinal cord suggest a homology between PVM and some of the parvocellular subnuclei of the mammalian paraventricular nucleus.
Overall distribution of substance P‐containing nerves in the wall of the cerebral arteries of the guinea pig and its origins
Authors: Yamamoto Kazumi , Matsuyama Tomohiro , Shiosaka Sadao , Inagaki Shinobu , Senba Emiko , Shimizu Yoshiki , Ishimoto Ichiro , Hayakawa Tōru , Matsumoto Masayasu , Tohyama Masaya
Published: May 2005

The overall distribution of substance P‐like immunoreactivity (SPI) in the wall of the cerebral arteries and their origins were investigated in the guinea pig by using whole‐mounts.

Two types of SPI fibers were seen: one forming dense fiber bands and lo‐cated among the periadventitial nerves, and the other forming a meshwork. The SPI fibers located in the periadventitial nerves often leave these nerves to form a meshwork of SPI fibers of varying density according to the diame‐ter or location of the blood vessels.

The present study suggests that: (1) SPI fibers located on the circle of Willis and its branches originate from SPI cells in the trigeminal ganglion; (2) SPI fiber's of the rostral one‐third of the basilar artery originate partly from trigeminal SPI cells; and (3) SPI fibers in the caudal two‐thirds of the basilar artery originate exclusively from other SPI cells, apart from the tri‐geminal ganglion.
The indusium griseum and anterior hippocampal continuation in the rat
Authors: Wyss J. M. , Sripanidkulchai K.
Published: May 2005

The morphology and connections of the indusium griseum (IG) and anterior hippocampal continuation (AHC) suggest that this cortex contains analogues to several portions of the hippocampal formation. Whereas the outer neuronal layer of this cortex is made up of cells which are similar in structure to the neurons of the granule cell layer of the dentate gyrus, the three successively deeper layers contain morphological analogues to the neurons of the dentate hilus, Ammon's horn, and the subiculum, respectively. The neurons within each of these four layers of the AHC and IG have afferent and efferent connections which are quite similar to the connections of their hippocampal counterparts. Thus, the granule cells of the IG and AHC receive laminar inputs from the entorhinal cortex, the IG‐AHC itself, and the supramammillary region. Each of these three classes of inputs ends at successively more proximal positions on the dendritic tree of these granule cells. Other inputs to this region include those from the septal nuclei and the olfactory bulb. The deeper layers of the IG and AHC receive several inputs, including those from the thalamic and septal nuclei and the entorhinal cortex. The efferent cell bodies of the IG and AHC are segregated in such a way that the granule cells appear to give rise to only short connections, while the hilar cells project to the granule cells, the intermediate pyramidal neurons project to other portions of the IG and AHC and to the olfactory bulb, and the deep pyramidal neurons project to the diencephalon. These results demonstrate that the IG‐AHC is a continuation of the hippocampal formation.
Organization of the projections of a circumventricular organ: The area postrema in the rat
Authors: van der Kooy Derek , Koda Leonard Y.
Published: May 2005

The projections of the rat area postrema were analysed using antero‐grade and retrograde axonal transport techniques. Discrete injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) into the area postrema produced anterograde labeling in specific medullary and pontine nuclei. In the medulla, anterograde labeling was present in the internal solitary zone and dorsal division of the medial solitary nucleus, both of which also contained a small number of retrogradely labeled perikarya. Prominent projections to the dorsal motor nucleus of the vagus were seen only if the WGA‐HRP injections in the area postrema invaded dorsal solitary nuclei. In the pons, anterograde labeling was present in the parabrachial nuclei, the dorsolateral Legmen tal nucleus, and the pericentral division of the dorsal tegmental nucleus. By far the major pontine projection was to the dorsolateral region of the middle one‐third of the rostrocaudal extent of the parabrachial nuclei. Retrograde fluorescent tracing studies indicated that most area postrema neurons take part in this parabrachial projection. The area postrema projection to the parabrachial nuclei was bilaterally distributed, whereas that from the dorsal solitary nuclei was primarily ipsi‐lateral. The external solitary zone, immediately subadjacent to the area postrema, neither received area postrema projections nor participated in the projections to the parabrachial nuclei. Fluorescent retrograde double labeling studies confirmed the bilateral nature of the area postrema projection to the parabrachial nuclei. In addition, because no doubly labeled neurons were observed it appears that individual area postrema neurons project to either side but not both sides of the dorsal pons. Thus, numerous neuronal pathways exist for the transfer of blood‐borne information (that cannot cross the blood‐brain barrier) from the area postrema to other brain regions.
Organization of eighth nerve afferent projections from individual endorgans of the inner ear in the teleost, Astronotus ocellatus
Authors: Meredith Gloria E. , Butler Ann B.
Published: May 2005

Eighth nerve fibers from the saccule, utricle, lagena, and the anterior, horizontal, and posterior semicircular canals of a cichlid fish were traced to the octavolateralis region of the brainstem using HRP and degeneration methods. The anterior, magnocellular, descending, and posterior nuclei of the octavus column receive inputs from all endorgans, whereas the tangential nucleus receives projections only from the utricle and semicircular canals. The most rostral projection from each endorgan is found in the eminen‐tia granularis of the vestibulolateral lobe of the cerebellum. Sparse terminals are found in the medial reticular formation from the utricle and semicircular canals, and utricular and saccular rami terminate in the vicinity of the lateral dendrite of the Mauthner cell.

Utricular and semicircular canal projections consistently overlap centrally as do saccular and lagenar inputs. Afferent fibers from all endorgans end within relatively distinct regions throughout the octavus column of nuclei. Saccular and lagenar inputs lie dorsal to the semicircular canal terminations. Utricular endings are complex, however, in that they overlap dorsally with saccular and lagenar terminals and ventrally with the semicircular canal inputs. Cerebellar inputs are found only in the eminentia granularis of the vestibulolateral lobe, and the densest terminals are from the utricle and the Semicircuhr canals; the sparsest are from the saccule.

Previous studies in fish have indicated that generally the utricle and semicircular canals are concerned with the maintenance of static and dynamic equilibrium whereas the saccule and lagena are concerned with auditory reception. There is recent evidence, however, for multiple functions within individual endorgans. Our anatomical findings suggest that in Astronotus each otolithic endorgan carries more than one modality; that the semicircular canals are concerned solely with an equilibrium function; and that acoustic information is processed dorsally and vestibular information ventrally along the octavus column of nuclei. No single nucleus appears to be solely auditory in function and only the tangential nucleus, situated ventrally in the octavus column, appears to be solely vestibular.
Fine structure and organization of the infrared receptor relays: Lateral descending nucleus of V in Boidae and nucleus reticularis caloris in the rattlesnake
Authors: Meszler Richard M.
Published: May 2005

The morphology of the lateral descending nucleus of V (LTTD) in three species of Boidae and nucleus reticularis caloris (RC) of the rattlesnake have been studied with the light and electron microscope. First‐ and second‐order relays in the infrared receptor pathway to the tectum are contained within LTTD in the Boidae, whereas in the rattlesnakes the secondary relay to tec‐tipetal neurons is in nucleus RC. The lateral descending nucleus in the boids contains small and large neurons. The larger cells project to the optic tectum and morphologically are quite similar to those of nucleus RC.

It has been determined at the ultrastructural level that LTTD of the three species of boids studied have very similar morphology and organization. A marginal neuropil, located near the lateral descending tract, consists of terminals of thin unmyelinated axons in synaptic contact with thin den‐drites. Deeper within the nucleus primary afferent terminals containing clear spherical vesicles form synaptic clusters with dendrites and are post‐synaptic to other axon terminals containing pleomorphic vesicles. The large, tectipetal neurons are postsynaptic to two morphological types of synapses, one with clear spherical vesicles, asymmetric membranes, and subsynaptic web and the other with flattened vesicles and symmetrical membranes. Similar synapses are also present on the cells of nucleus RC in the rattlesnake.

There is a close similarity in function, structure, and synaptic organization between the LTTD of boids and the LTTD plus nucleus RC of pit vipers, suggesting similar or identical evolutionary origin.
Columnar organization of corticocortical projections in squirrel and rhesus monkeys: Similarity of column width in species differing in cortical volume
Authors: Bugbee Nellie M. , Goldman‐Rakic Patricia S.
Published: May 2005

To compare the size and pattern of the terminal distribution of cortico‐cortical projections in two primate species with brains of different size, triti‐ated amino acids were injected into the prefrontal cortex of New World squirrel monkeys (Saimiri sciureus) and Old World rhesus monkeys (Macaca mulatta), and their brains were processed for light microscopic autoradiog‐raphy. In both species, prefrontal efferents are directed to a number of cortical targets in the same and opposite hemispheres, where in coronal sections, they generally terminate as radially oriented columns. In the rhesus monkey, the median width of the columns in transverse sections is 685 μ. In squirrel monkey, corresponding columns have a median width of 555 μ. Considering that the volume of the neocortex in rhesus monkey is approximately 4.5 × larger than that of squirrel monkey, the dimensions of cortical columns in the two species are surprisingly similar. This finding suggests that phylogenetic expansion in cortical surface area is accompanied by an increase in the number, rather than the width, of afferent fiber columns. The increase in number of modular units may be relevant to the increasing computational and information processing capacity of the cerebral cortex in the course of evolution.
Structural basis of orientation sensitivity of cat retinal ganglion cells
Authors: Leventhal Audie G. , Schall Jeffrey D.
Published: May 2005

We investigated the structural basis of the physiological orientation sensitivity of retinal ganglion cells (Levick and Thibos, '82). The dendritic fields of 840 retinal ganglion cells labeled by injections of horseradish peroxidase into the dorsal lateral geniculate nucleus (LGNd) or optic tracts of normal cats, Siamese cats, and cat deprived of patterned visual experience from birth by monocular lid‐suture (MD) were studied. Mathematical techniques designed to analyze direction were used to find the dendritic field orientation of each cell. Statistical techniques designed for angular data were used to determine the relationship between dendritic field orientation and angular position on the retina (polar angle). Our results indicate that 88% of retinal ganglion cells have oriented dendritic fields and that dendritic field orientation is related systematically to retinal position. In all regions of retina more than 0.5 mm from the area centralis the dendritic fields of retinal ganglion cells are oriented radially, i.e., like the spokes of a wheel having the area centralis at its hub. This relationship was present in all animals and cell types studied and was strongest for cells located close to the horizontal meridian (visual streak) of the retina. Retinal ganglion cells appear to be sensitive to stimulus orientation because they have oriented dendritic fields.
Neuronal composition and development in lamina 4C of monkey striate cortex
Authors: Mates Sharon L. , Lund Jennifer S.
Published: May 2005

Lamina 4C (Lund, '73) of the monkey, Macaca nemestrina, visual striate cortex occupies a key position as a principal recipient zone of axons from the lateral geniculate nucleus (LGN). Synaptic maturation in lamina 4C is of particular interest since it involves a competitive interaction between thalamic axons for postsynaptic territory: an interaction which is strongly influenced by afferent activity (Hubel et al., '77). As an initial step toward understanding the normal process of synapse maturation in 4C, this study examines Golgi material to define the adult neuron populations of subdivisions 4Cα (receiving afferents from magnocellular LGN) and 4Cβ (receiving afferents from parvocellular LGN). Three groups of spine‐bearing neurons are described‐one relatively confined to either α or β subdivision, the other two bridging the depth of 4C; four groups of smooth dendritic neurons interact with the spine‐bearing population. Electron microscopy of normal and Golgi‐impregnated tissue is used to define key features of synapse populations on these neurons. From embryonic day 159 through adulthood the smooth and spiny neurons occur in the same constant proportions in the neuropil (5% smooth, 95 % spiny). Changes in the distribution of synapses on the spiny neurons are analyzed qualitatively; type 1 axon terminals (asymmetric apposition ‐round vesicles) shift from dendritic shafts to spine tips during maturation. Each spine is found to bear a type 1 contact at all ages; these results allow us to conclude that the figures of Boothe et al. ('79) on changes in spine populations during maturation can now be interpreted as changes in type 1 synapse populations. It is shown that type 2 synapses (symmetric appositions ‐pieomorphic vesicles) arise from axons of the smooth dendritic neurons. These synapses are found to increase in number on the spiny cell somata in early postnatal development, and this is followed by a decrease in number to the adult level.
Spine formation and maturation of type 1 synapses on spiny stellate neurons in primate visual cortex
Authors: Mates Sharon L. , Lund Jennifer S.
Published: May 2005

This study continues an investigation (Mates and Lund, '83a) of neuronal development in lamina 4C of macaque monkey striate visual cortex. The maturational history of the type 1 synaptic contacts on spine‐bearing stellate neurons, which comprise 95% of the neurons of the lamina, is described. It is shown that type 1 contacts are initially found on the dendritic shafts; these contacts appear to be carried out on spine outgrowths. This leads to the adult condition where type 1 contacts are found only on the spine tips. A similar phenomenon has been reported for pyramidal neurons of the rat (reported during the course of this study by Miller and Peters, '81). In later maturation the spine and its type 1 contact may be lost; profiles found in the neuropil illustrate a process of shrinkage and detachment of both the type 1 axon terminals and postsynaptic dendritic spines in normal maturation. These findings provide an explanation for the marked increase and decrease in spine populations observed to occur on these neurons during normal maturation in an earlier study by Boothe et al. ('79).
The nucleus praeeminentialis: A Golgi study of a feedback center in the electrosensory system of gymnotid fish
Authors: Sas Emilia , Maler Leonard
Published: May 2005

The cytoarchitecture of the dorsal nucleus praeeminentialis in two families of weakly electric fish (Eigenmannia viriscens and Apteronotus albifrons) was examined in both Nissl and Golgi material, and an attempt was made to correlate this information with our data from HRP studies on the afferent and efferent connections of this nucleus.

The n. praeeminentialis is an isthmic structure located dorsolateral to the lateral lemniscus and anterior to the eminentia granularis‐a subdivision of the archicerebellum of fish. The n. praeeminentialis can be divided into a large dorsal portion concerned with electroreception and a small ventral portion involved with the lateral line mechanoreception. The dorsal n. praeeminentialis consists of three parts: a pars medialis, a large pars principals (p.P.) and a narrow pars lateralis. The p.P. presents three zones: a dorsal, a central, and a ventral zone, which are reciprocally and topographically connected with the zones of the electroreceptive lateral line lobe (ELLL), medial ELLL with ventral zone, central ELLL with central zone, and lateral ELLL with dorsal zone. Several types of projection cells are present in the n. praeeminentialis: (a) neurons that show preferential orientation of their long dendrites in relation to the afferent fiber systems, (b) cells with wide dendritic fields radiating in all directions, and (c) cells with small polarized dendritic fields toward the incoming ELLL afferents.

Interneurons are also identified, showing different axonal ramification patterns.

The afferent and efferent fiber systems linking the n. praeeminentialis to ELLL, lobus caudalis (L.C.), and torus semicircularis (T.S.d.) point to the important position of this nucleus in the feedback loop of the electrosensory pathway. The complex processing within this nucleus is reminiscent of the feedback loops in the auditory system.
Central projections of the octavolateralis nerves of the clearnose skate, Raja eglanteria
Authors: Koester David M.
Published: May 2005

The central projections of first‐order lateral line and octavus nerve afferents of the clearnose skate, Raja eglanteria, were, determined by nerve degeneration and horseradish peroxidase techniques. The octavolateralis area of the medulla, which receives these afferents, is organized into dorsal, intermediate, and ventral longitudinal columns of cells and neuropil. Fibers that innervate the electroreceptive sense organs enter the dorsal longitudinal column via the dorsal root of the anterior lateral line nerve and terminate within the dorsal nucleus. Mechanoreceptive fibers from neuromasts of the head and trunk are carried by the ventral root of the anterior lateral line nerve and posterior lateral line nerve, respectively. Both nerves enter the intermediate longitudinal column and terminate throughout the rostrocaudal extent of the intermediate nucleus. Fibers of the ventral root of the anterior lateral line nerve are confined to the medial portion of the intermediate nucleus and posterior lateral line nerve fibers to the lateral portion. In addition, ascending mechanoreceptive fibers from both head and trunk neuromasts project to the vestibulolateral lobe of the cerebellum.

Octavus nerve afferents enter the medulla and terminate primarily within the four octaval nuclei that comprise the ventral longitudinal column. Rostrocaudally, these nuclei are the anterior, magnocellular, descending, and posterior octaval nuclei. A few ascending axons continue beyond the anterior octaval nucleus and course to the vestibulolateral lobe of the cerebellum. Some descending axons emanate from the descending octaval nucleus and course to the reticular formation and intermediate nucleus.

Therefore, electroreceptive lateral line, mechanoreceptive lateral line, and octavus nerve afferents project ipsilaterally and terminate predominantly within separate medullary nuclei. The significance of octavus nerve projections to the intermediate nucleus and overlap of mechanoreceptive and octavus afferents within the vestibulolateral lobe of the cerebellum cannot be determined until it is known which fibers of the inner ear sense organs project to these areas.

Retrograde transport of horseradish peroxidase results in the labeling of large multipolar cells, both ipsilaterally and contralaterally, within a column of gray that lies dorsolateral to the reticular formation. These cells are interpreted as the cells of origin of the efferent components of the anterior and posterior lateral line nerves.
The properties of neurones recorded in the superficial dorsal horn of the rat spinal cord
Authors: Woolf Clifford J. , Fitzgerald Maria
Published: May 2005

The physiological properties of neurones in the superficial laminae of the dorsal horn of the fourth and fifth lumbar segments of the rat spinal cord have been investigated in decerebrate spinal animals. Both extracellular recordings with platinum‐plated tungsten microelectrodes (n = 72) and intracellular recordings with glass microelectrodes (N = 79) were made. Attempts were made to fill cells intracellularly with horseradish peroxidase or Lucifer Yellow. Thirty‐seven percent of the intracellularly injected neurones were recovered after histological processing and their cell bodies found to be in lamina 1 or 2 and in the dorsal white matter overlying lamina 1. The dendritic spread of the stained neurones was maximal in the rostrocaudal plane with a restricted mediolateral spread. The physiological properties of the extracellularly recorded units, the intracellularly unidentified units, and the intracellularly stained units were the same. The neurones were characterized by low background activity and all had excitatory receptive fields on the lower limb. Some neurones responded only to low‐threshold mechanical stimulation of the skin or only to noxious skin stimulation but the majority of units (58%) were wide‐dynamic‐range cells responding to both types of stimuli. Receptive field classification was made questionable, however, by the existence of cells (9%) that exhibited a spontaneous shift in the size of their receptive fields and in the type of stimulus that elicited a response. The neurones in the superficial dorsal horn commonly showed a marked inhibition to repeated cutaneous stimuli (27%) or a prolonged afterdischarge followed a single stimulus (20%). Afferent input from the sural nerve was found to be from A and C fibres in both extra‐ and intracellular recordings. Aδ‐ and C‐mediated excitations were most common although convergent inputs from Ab̃‐fibres occurred in 40% of units.

No correlation was found between cell structure or distribution of dendritic fields and physiological properties in our small sample of intracellularly stained cells. The morphology of the cells was highly diverse, as were the different receptive fields. There was, however, some correlation between the location of cell bodies and their responses. Neurones responding only to low‐threshold stimuli were distributed either in the dorsal white matter or in inner lamina 2. Wide‐dynamic‐range cells were distributed throughout the superficial dorsal horn. These results suggest that neurones of different shapes and positions may subserve the same function and, conversely, that neurones of the same shape and position may subserve different functions.
The distributions of photoreceptors and ganglion cells in the California ground squirrel, Spermophilus beecheyi
Authors: Long Kenneth O. , Fisher Steven K.
Published: May 2005

The topographical distributions of photoreceptors and ganglion cells of the California ground squirrel (Spermophilus beecheyi) were quantified in a light microscopic study. The central retina contains broad, horizontal streaks of high photoreceptor density (40–44,000/mm2) and high ganglion cell density (20–24,000/mm2). The isodensity contours of both cell types are elliptical and oriented along the nasal‐temporal axis. There are roughtly fivefold decreases in both photoreceptor and ganglion cell densities with increasing eccentricity, the lowest densities being found in the superior retina. Large transitions in cell density and retinal thickness occur across the linear optic nerve head. Rod frequency increases with increasing eccentricity, from 5 to 7% in the central retina to 15 to 20% in the periphery. Roughly 10% of the cones possess wide, dark‐staining ellipsoids. These cones are uniformly distributed across the retina which suggests that they may belong to a separate cone class, possibly blue‐sensitive cones. The ganglion cell soma size distribution is unimodal, with the majority of somata being 25–50 μm2. Large ganglion cells (somata > 100 μm2) are rare in the central retina, but their frequency increases with increasing eccentricity. No evidence for separate size classes of ganglion cells was found. The gradual decrement of photoreceptor density across the ground squirrel retina suggests that there are only relatively small changes in acuity across much of the animal's visual space compared with species possessing either a narrow visual streak or fovea or area centralis.
A comparison of the normal and regenerated retinotectal pathways of goldfish
Authors: Stuermer Claudia A. O. , Easter Stephen S.
Published: May 2005

This is a light and electron microscopic study of the retinotectal pathway: intact and after regeneration of the optic nerve. The spatiotemporal pattern of axonal outgrowth and termination was studied with the methods of proline autoradiography, horseradish peroxidase (HRP) labeling, and fiber degeneration.

The spatial order of optic fibers in the normal and regenerated pathways was assessed by labeling small groups intraretinally with HRP and then tracing them to the tectum. The labeled fibers occupied a greater fraction of the cross section of the regenerated than the normal optic tract. At the brachial bifurcation, roughly 20% of the regenerated fibers chose the incorrect brachium vs. less than 1% of the normals. In tectum, the regenerated optic fibers reestablished fascicles in stratum opticum, but they were less orderly than in the normals. The retinal origins of the fibers in the fascicles were established by labeling individual fascicles with HRP and then, following retrograde transport, finding labeled ganglion cells in whole‐mounted retinas. Labeled cells were more widely scattered over the previously axotomized retinas than over the normal ones. A similar result was obtained when HRP was applied in the tectal synaptic layer. All of these results indicate that the pathway of the regenerated optic fibers is less well ordered than the intact pathway.

Both autoradiography and HRP showed that the regenerating optic fibers invaded the tectum from the rostral end, and advanced from rostral to caudal and from peripheral to central tectum, along a front roughly perpendicular to the tectal fascicles. Synapses of retinal origin were noted electron microscopically in the tectum at the same sites where autoradiography indicated that the fibers had arrived. No retinal terminals were seen where grain densities were at background levels. Fiber ingrowth and synaptogenesis apparently occurred simultaneously. The synapses were initially smaller and sparser than in normals, but were in the normal tectal strata and contacted the same classes of post synaptic elements as in normals.
Morphometry of intracellularly labeled neurons of the auditory nerve: Correlations with functional properties
Authors: Liberman M. Charles , Oliver Mary E.
Published: May 2005

Single auditory‐nerve fibers were injected with horseradish peroxidase after their tuning properties, characteristic frequencies, and spontaneous discharge rates were measured. From these functional properties virtually all other aspects of auditory‐nerve response can be predicted. Labeled fibers were reconstructed from the point of peripheral termination on cochlear hair cells to the point at which they enter the cochlear nucleus. Several morphological properties were measured at the light‐microscopic level, including axonal diameter, axonal length, internodal distances, cell‐body area, and cell‐body shape. All of these parameters were correlated, though some weakly, with characteristic frequency. However, only axonal diameter was correlated with spontaneous discharge rate.
Glycine uptake by lamprey spinal neurons demonstrated by light microscopic autoradiography
Authors: Sheridan Philip H. , Youngs Laurie J. , Krieger Neil R. , Selzer Michael E.
Published: May 2005

We have mapped the neuronal uptake of 3H‐glycine in the spinal cords of large larval sea lampreys: Petromyzon marinus. Spinal cords were incubated in 10−6 M 3H‐glycine for 15 minutes. They were rinsed in lamprey solution, fixed in phosphate‐buffered 2% glutaraldehyde, and washed in phosphate buffer. They were then sectioned with a cryostat at 16‐m thickness or dehydrated, embedded in Epon, and sectioned at 1–4 μm. Sections were coated with a photographic emulsion and maintained at 4°C for 1–7 days.

By sectioning horizontally, it was possible to obtain complete serial reconstructions of up to 1.5‐mm lengths of cord in 100–150 sections. The outlines of labelled cells were traced with a Nikon drawing attachment. For one Epon‐embedded spinal cord sectioned at 4 μm, tracings were superimposed to form complete maps for 0.6–1.5‐mm lengths in three representative regions of cord: rostral (gill region), caudal (dorsal fin region), and midsection. The labelled neurons were small (5–10‐μm diameter) cells distributed throughout the central gray columns. They numbered 22 cells per hemisegment in the rostral region, 33 in the midsection, and 43 in the caudal region. None of the previously identified cell types were labelled, including lateral interneurons, edge cells, giant interneurons, dorsal cells, and Müller and Mauthner axons.
Interhemispheric connections of the visual cortex in the grey squirrel (Sciurus carolinensis)
Authors: Gould Harry J.
Published: May 2005

The total pattern of visual callosal connections was studied in the grey squirrel by using the Fink‐Heimer technique for axonal and terminal degeneration and the autoradiographic and horseradish peroxidase techniques for axonal transport. The pattern of terminations was correlated with architectonic landmarks.

The results show that callosal terminations are distributed in a complex fashion within the visual cortical areas. The major terminations form a band in area 17 along its border with area 18. This band is contiguous rostrally with the callosal terminations in area L that extend caudomedially onto the medial wall of the hemisphere. Caudally the band in area 17 wraps around the ventral aspect of the occipital pole and ends medially at the level of the hippocampus. This band exhibits a distinct periodicity in the density of terminations. The callosal terminations in area 18 are usually found along the lateral and medial borders and are concentrated in discrete patches. The pattern in area 19 exhibits two or three primary patches and only loosely corresponds to the borders of the area. Few callosal terminations are found in area 19p and the posterior temporal area, Tp, while the intermediate temporal area, Ti, receives an extensive input.

The laminar distribution of callosal terminations is different in each area studied. Characteristically, area 18 has dense terminations in layers III, II, and the inner one‐half of layer I, with less dense terminations in layers V and VI, and sparse terminations in layer IV. Area 17 has a similar pattern in the supragranular and infragranular layers but also has dense terminations in layer IV. The patterns in area 19 are intermediate between these extremes but are more similar to those in area 17.

The cells that give rise to the callosal projections were found primarily in layers III and V and occasionally in layers II, IV, and VI. The distribution of the callosal efferent neurons is more extensive than the areas of terminations.

The distribution of callosal terminations suggests that the organization of visual cortical areas in the grey squirrel is more complex than had been previously recognized. This finding is discussed with reference to the general organization of the mammalian visual cortical areas, and a need for more extensive analyses of visual cortical areas in the grey squirrel, particularly with respect to extrastriate visual areas, is indicated.
Organization of the efferent projections of the nucleus accumbens to pallidal, hypothalamic, and mesencephalic structures: A tracing and immunohistochemical study in the cat
Authors: Groenewegen Henk J. , Russchen Fokje T.
Published: May 2005

The efferent connections of the nucleus accumbens in the cat were studied with the aid of anterograde and retrograde tracing techniques. The description of the topography of these projections to pallidal, hypothalamic, and mesencephalic areas is preceded by a redefinition of the borders of the pallidal regions in the cat, using immunohistochemical criteria. In agreement with previous studies in rat and monkey substance‐P‐like and enkephalinlike immunoreactivity in the pallidum of the cat appears to be present in so‐called “woolly fibers.” Substance‐P‐ and enkephalin‐positive woolly fibers are differentially distributed in the internal and external segments of the globus pallidus, as traditionally defined, but are both present in the rostral part of the substantia innominata, here called the “ventral pallidum.” Woolly fibers are also found in a number of other basal telencephalic structures and in the rostral part of the lateral hypothalamic area.

Fibers from the medial part of the nucleus accumbens distribute to the ventral pallidum and to the just‐mentioned area in the rostral part of the lateral hypothalamus, which most probably represents part of the internal segment of the globus pallidus. The medial nucleus accumbens projects in addition to the lateral septum, the bed nucleus of the stria terminalis, the medial preoptic and hypothalamic areas, the ventral tegmental area, the retrorubral nucleus, the central superior nucleus, the nucleus tegmenti pedunculopontinus, and the central gray. The lateral part of the nucleus accumbens projects to the ventral pallidum, the subcommissural part of the globus pallidus, the entopeduncular nucleus, the substantia nigra, and the retrorubral nucleus.
Distribution of enkephalin in human fetus and infant spinal cord: An immunofluorescence study
Authors: Charnay Yves , Paulin Christian , Dray Fernand , Dubois Paul‐Marie
Published: May 2005

The distribution of enkephalin‐like immunoreactivity in the human fetus and infant spinal cord have been studied by indirect immunofluorescence. Enkephalin‐like immunoreactive fibers were detectable in the lateral funiculus of fetal spinal cord as early as 10 weeks. At the other fetal ages examined, ranging from 12 to 28 weeks, and in infant, enkephalinlike immunoreactivity was found widely distributed throughout the whole spinal cord. In fetus spinal cord several enkephalin‐like immunoreactive cells were sometimes seen scattered in the intermediate gray region. Most of the labeling was, however, represented by thin, varicose, immunofluorescent fibers mainly localized in the intermediate gray regions, in the ventral horn and in the superficial dorsal horn layers where they progressively increased in number. Further, the white matter exhibited enkephalin‐like immunoreactive fibers particularly in the lateral funiculus where a dense punctiform immunofluorescence could be seen. On the whole, similar patterns were also visible in infant spinal cord. Thus, the superficial layers of the dorsal horn and the intermediolateral and reticular nuclei areas displayed dense plexuses of immunoreactive fibers. In contrast, the white matter showed only little labeling. In addition, no immunoreactivity was found in fetus and infant dorsal root ganglia. Our results emphasize the wide distribution of the enkephalin‐like immunoreactivity in the fetus as in the infant spinal cord and further suggest its first appearance early in fetal life, possibly at the embryonic stage.
Contralateral, midline, and commissural motoneurons of neck muscles: A retrograde HRP study in the cat
Authors: Abrahams V. C. , Keane J.
Published: May 2005

Retrograde transport of HRP has been used to examine the distribution of motoneurons supplying the dorsal neck muscles biventer cervicis, and complexus in the cat. Retrogradely filled cells were present in the expected sites in lamina IX of the ventral horn, but were not confined to that area. Retrogradely labelled cells were also found more dorsally in the ventral horn and in the white matter medial to the ventral horn. Other filled cells were found in the commissural nuclei and in laminae VII and VIII contralateral to the nerve being dipped. Cells in the ipsilateral lamina IX ranged in size from 15 to 70 μm. Cells lying outside this region were smaller with the majority having mean equivalent diameters, of 40 μm or less.
Ultrastructural localization of immunoreactive neurotensin in the monkey superficial dorsal horn
Authors: Difiglia Marian , Aronin Neil , Leeman Susan E.
Published: May 2005

Neurotensin, a tridecapeptide, has been proposed to have a role in sensory systems, especially those mediating pain. The light microscopic and ultrastructural localization of neurotensin immunoreactivity in neurons of the monkey spinal cord was studied with the aim of examining their synaptic interactions. At the light microscopic level, neurotensin‐containing cells were located in laminae II and III and immunoreactive axons and terminals were found in laminae I, II, and III. Neurotensin‐positive axons were mostly thin and unmyelinated and their boutons contained both clear and large granular vesicles. Boutons varied considerably in size (1–3μm) and in their relative content of large granular vesicles, which appeared occasionally in presynaptic locations. In lamina I neurotensin‐immunoreactive terminals formed synapses with cell bodies which varied both in size and subcellular features. Some large dendrites in lamina I were contacted by numerous neurotensin‐positive axons and also unlabeled terminals. In lamina II boutons with neurotensin immunoreactivity formed synapses mostly with small unlabeled dendrites some of which contained vesicles.

The present results together with recent anatomical and physiological findings suggest that spinal cord neurons which contain neurotensin synapse with cells in the superficial dorsal horn that receive either input from primary afferents conveying nociceptive information or form part of the spinothalamic tract, or both. The diversity observed both in the morphology of neurotensin‐positive terminals and in their synaptic patterns may indicate that they arise from more than one type of dorsal horn cell.
Colonization of the developing murine enteric nervous system and subsequent phenotypic expression by the precursors of peptidergic neurons
Authors: Rothman T. P. , Nilaver G. , Gershon M. D.
Published: May 2005

The development of peptidergic neurons was analyzed in the murine bowel. Neurons, detected immunocytochemically with antisera to substance P (SP) and vasoactive intestinal polypeptide (VIP), respectively, were selected for study. Explantation of the primordial bowel with subsequent growth in organotypic tissue culture served as an assay for the presence of neuronal precursor cells within the developing gut. One objective of the study was to determine whether the neural crest population that initially colonizes the mammalian bowel contains the precursors of peptidergic neurons as well as those of neurons that contain small molecule neurotransmitters, or whether peptidergic neurons are derived from a later migration of émigrés to the gut. A second objective was to compare the timing of peptidergic phenotypic expression with that of the small molecule neurotransmitters, acetylcholine (ACh) and serotonin (5‐HT). The precursors of peptidergic neurons were found to have colonized the bowel prior to the appearance of recognizable neurons of any type. The immunocytochemical detection of SP and VIP in vivo lagged behind the appearance of cholinergic and serotonergic markers by at least 2 days in the foregut and by greater than 3 days in the hindgut. Peptidergic neurons showed a proximodistal pattern of phenotypic expression. These observations support the hypothesis that the murine bowel is colonized by a single wave of precursor cells that contains the primordia of peptidergic neurons as well as neurons that use small molecule neurotransmitters. Data are consistent with the earlier expression of the small molecule phenotype. The proximodistal sequence of phenotypic expression in the absence of a similar sequence in precursor colonization supports an interaction between the precursors of enteric neurons and the microenvironment of the gut that modulates neuronal phenotypic expression.