bluuebunny/crossref_metadata_2025 huggingface dataset:
Propriospinal fibers in the rat
Authors: Chung Kyungsoon , Coggeshall Richard E.
Published: January 2005

Segments of rat spinal cord were isolated by transecting in two places and sectioning all dorsal roots between the transections. Following this procedure, the areas of the gray and white matter are decreased by approximately 50% compared to normal. We feel, for reasons elaborated in the discussion, that the white matter of the isolated segments contains almost exclusively propriospinal axons. If this is accepted, then the axonal counts in this paper provide estimates of the numbers of propriospinal axons in rat spinal cord. In the isolated segments, the lateral funiculi contain 21,000 myelinated and 31,000 unmyelinated axons and the ventral funiculi 10,500 myelinated and 1,500 unmyelinated axons. The number of these fibers is approximately 33% of the number in unoperated spinal cords. Thus approximately one‐third of the axons in rat sacral lateral and ventral funiculi are propriospinal, a lower figure than would have been predicted from classical work. The ratio of myelinated to unmyelinated fibers is higher for proprio‐spinal fibers than for the other axons in these funiculi. Thus the propriospi‐nal axons, as a group, are slightly larger than the other axons in these funic‐uli. This is against currently accepted thinking which generally regards the propriospinal fibers as the finest in the white matter of the cord. Finally, the quantification of propriospinal systems in these funiculi allows more precision in our thinking about the organization of the spinal cord.
Topographic analysis of the innervation of the rat neocortex and hippocampus by the basal forebrain cholinergic system
Authors: McKinney Michael , Coyle Joseph T. , Hedreen John C.
Published: January 2005

The basal forebrain‐cortex connections of the rat were topographically mapped by retrograde tracer methods; and their contribution to the cholin‐ergic innervation of the cortex was assessed by excitotoxin lesions placed in the rostral and caudal aspects of the complex. Discrete injections of tracer into frontal cortex labeled the prominent multipolar acetylcholinesterase (AchE)‐positive cells of the ventromedial globus pallidus. Injections of tracer into the parietal cortex labeled cells in the ventral globus pallidus, the underlying substantia innominata, and the lateral hypothalamus. Separate injections of Fast Blue and Nuclear Yellow in the frontal and in the parietal cortex resulted in double‐labeled cells in the ventral globus pallidus, which indicates that at least some of these cells may possess collateralizing axons. The cingulate cortex is innervated predominantly by neurons in the nucleus of the horizontal limb of the diagonal band. The occipital cortex was also shown to receive a projection primarily from the nucleus of the horizontal limb of the diagonal band. The hippocampal formation is innervated primarily by cells located in the vertical limb of the diagonal band and in the medial septum. Consistent with the results of the retrograde tracing studies, excito‐toxin lesions affecting the diagonal band and medial septum decreased cho‐line acetyltransferase (CAT) activity up to 40% in the occipital cortex and by 64% in the hippocampus, but did not affect CAT activity in the rostral neo‐cortex. In contrast, ibotenate lesions of the caudal ventral globus pallidus and substantia innominata caused decreases in CAT activity in the frontal cortex of up to 65% without affecting enzyme activity in the hippocampal formation. The results of the present study provide details on the topographic organization of the cortical projections originating in the basal fore‐brain complex and indicate that these neurons are the predominant source of cortical cholinergic innervation.
The afferent and efferent connections of the feline nucleus tegmenti pedunculopontinus, pars compacta
Authors: Edley Sandra Moon , Graybiel Ann M.
Published: January 2005

The fiber connections of the nucleus tegmenti pedunculopontinus, pars compacta (TPc) were studied by means of the anterograde autoradiographic and retrograde horseradish peroxidase tracer methods. The limits of TPc, which is not a cytoarchitecturally distinct cell group in the cat, were estimated on the basis of autoradiographic experiments in which we plotted the distribution of afferent connections from the entopeduncular nucleus, motor cortex, substantia nigra, and subthalamic nucleus. We concluded that in the cat, TPc can most readily be identified by the terminal distribution of fibers originating in the substantia nigra. Deposits of radiolabel in the motor‐pre‐motor cortex, the entopeduncular nucleus, and subthalamic nucleus weakly labeled the same tegmental region. Parallel horseradish peroxidase experiments suggested that neurons near the entopeduncular nucleus, especially in the lateral hypothalamus and subthalamus, contribute to the pallido‐TPc pathway; that entopeduncular neurons projecting to TPc are most numerous in the ventral part of the nucleus; and that of the neocortical motor fields, both areas 4 and 6 project to TPc.

An autoradiographic study of the efferent connections of TPc showed that the major connections were directed toward more rostral structures. Small deposits of labeled amino acids centered in TPc invariably elicited bilateral labeling of the pars compacta of the substantia nigra and the subthalamic nucleus, the densest label being on the ipsilateral side. Other structures variably or more sparsely labeled were: the posterior and lateral hypothalamus; centre median complex; an intermediate part of the lateral thalamic nucleus; central gray substance; nucleus parabrachialis pigmentosus (retro‐rubral nucleus); the raphe nuclei linearis intermedius, dorsalis, and magnus; nucleus reticularis tegmenti pontis; the pontine and medullary reticular for‐mation including the nuclei pontis oralis and caudalis; and the nucleus reticularis gigantocellularis, especially its ventral supraolivary part. These observations demonstrate that TPc shares some connections with a wider tegmental region, but that, in addition, TPc is characterized by a set of afferent and efferent connections that differentiate it from the surrounding teg‐mentum and affiliate it with the basal ganglia. By comparison with findings in the monkey and rat, these experiments further suggest that the connections of TPc may vary across mammalian species. The location and fiber connections of TPc indicate that it is probably distinct from the physiologically defined mesencephalic locomotor region, but suggest the hypothesis that TPc, as a part of an extrapyramidal tegmental loop‐circuit, may be involved in the production of simple resting tremors.
Efferent projections of the cat oculomotor reticular omnipause neuron region: An autoradiographic study
Authors: Langer Thomas P. , Kaneko Chris R.S.
Published: January 2005

Omnipause neurons (OPNs) are midline pontine neurons that are thought to be instrumental in the generation of saccadic eye movements. Inhibition of the tonically active OPNs is postulated to disinhibit the burst neurons that cause the saccadic discharge in motoneurons, leading to a sac‐cade. To test whether the anatomical connections of OPNs are consistent with this scheme, we studied the efferent projections of the OPN region by using the technique of anterograde transport of tritiated amino acids.

Injections into the OPN region yield a distinct pattern of labeled tracts and terminal fields that is different from the patterns following control injections in the surrounding reticular formation. Caudally, there are terminal fields over the paramedian reticular formation, the caudal part of the medial accessory nucleus of the inferior olivary complex, the nucleus prepositus hypoglossi, and the nucleus reticularis paragigantocellularis dorsalis caudal and ventromedial to the abducens nuclei. Rostrally, terminal label is distributed over parts of the nuclei reticularis pontis caudalis and oralis, the nucleus raphe pontis, the nucleus reticularis tegmenti pontis, the mesencephalic reticular nucleus, the central gray, and the nucleus of the H‐field.

Thus, there are direct projections from the OPN region to all areas known to contain burst neurons. In addition, OPNs also apparently have in‐direct access to the spinal cord and cerebellum. Many of the latter connec‐tions parallel the efferent projections of the superior colliculus.
The nucleus tractus solitarii of the cat: A comparison of Golgi impregnated neurons with methionine‐enkephalin‐ and substance P‐immunoreactive neurons
Authors: Maley Bruce , Mullett Terrence , Elde Robert
Published: January 2005

Golgi‐impregnated and methionine‐enkephalin (ME)‐ and substance P (SP)‐immunoreactive neurons were studied throughout the feline nucleus tractus solitarii. The majority of Golgi‐impregnated neurons in the NTS range in size from 5 to 18 μm. A noticeable exception is the large (15–30 μm) neurons of the ventrolateral subdivision. The Golgi‐impregnated neurons possess dendritic trees which remain within the nucleus and even at times within the particular subdivisions. Golgi‐impregnated neurons had a variety of spine forms: pedunculated, sessile, filiform, and complex. A number of neurons exhibited axons originating from the cell and they could be followed for distances up to 100 μm.

ME‐ and SP‐immunoreactive neurons were found in commissural, medial, lateral, and parvocellular subdivisions while ME‐immunoreactive neurons were situated additionally in the intermediate and ventrolateral subdivisions. Both types of immunostained neurons were similar in size (6–20 μm) and shape of dendritic arbor. One population of ME‐immunoreactive neurons resembled the large ventrolateral neurons of the Golgi impregnations. Neither type of immunostained neuron possessed the extensive dendritic arbor, numbers of spines, or axons of the Golgi–impregnated neurons. The presence of ME‐ and SP‐immunoreactive neurons in regions which are associated with autonornic regulation suggests that these two peptides are involved in this process.
Afferent and efferent components of the hypoglossal nerve in the grass frog, Rana pipiens
Authors: Stuesse Sherry L. , Cruce William L.R. , Powell Katina S.
Published: January 2005

In amphibians, the spinomedullary region of the central nervous system is compressed rostrocaudally because of the absence of a neck. In Ranid frogs, the hypoglossal nerve emerges as the ventral ramus of the second spinal nerve. The first spinal nerve, though present in tadpoles, is absent as a separate nerve in adults. To investigate the central nervous system components of the hypoglossal nerve in Rana pipiens, we soaked identified, transected branches of this nerve in horseradish peroxidase, a retrograde and antercgrade tracer. We found that the hypoglossal nerve in these frogs originates from two efferent nuclei located in the caudal medulla, a medial and a lateral one. Afferent fibers, primarily from the tongue, are also found in the hypoglossal nerve and travel in the dorsolateral funiculus of the spinal cord, descending to thoracic levels of the cord. Efferents to intrinsic tongue muscles and the genioglossus muscle originate in the medial medullary nucleus. Efferents to the sternohyoid muscle, which travel through the hypoglossal nerve, originate in the lateral medullary nucleus. Since in mammals the sternohyoid muscle is innervated by the first spinal nerve, we have obtained experimental evidence that the hypoglossal nerve in Rana pipiens contains components of this spinal nerve.
Postnatal maturation of neurons in the cat's lateral geniculate nucleus
Authors: Mason Carol Ann
Published: January 2005

The maturation of dendrites in the cat's dorsal lateral geniculate nucleus was studied in Golgi Kopsch preparations of kittens from 3 days to 8 weeks postnatal. During the first postnatal week, more than a month after their birthdate, cells are immature and lack dendrites, bearing only multiple somatic processes or a few short thick extensions. Cells enter an active phase of dendritic extension during the second postnatal week. Growth cone‐like structures and filopodia occur at the ends of dendrites and also at dendritic branch points. Assignment to general cell classes based on dendritic disposition is possible only after this period, and characteristic grapelike appendages are obvious after the third week. Mature cells in the lateral geniculate nucleus are not considered spiny, yet spines and hairs are ubiquitous on most cells once dendrites elongate and remain numerous on peripheral dendrites even after the soma and proximal dendrites become smooth, by 4–6 weeks. The decline of spine levels continues after this period.

All cells go through a similar but nonsynchronous sequence of maturation. Large cells may mature first, but no correlation was noted between rate of maturation and laminar location or retinal representation. In the second and thirdpostnatal weeks, although the terminal arbors of retinal axonspre‐synaptic to geniculate cells have already attained their final topography and laminar placement, the shape and synaptic relations of axon terminal swellings remain immature (Mason, 1982a,b) through the most active phase of dendritic outgrowth. After 3 weeks, both retinal axons and target geniculate cell dendrites finalize the shapes of characteristic appendages and synaptic relations in tandem. Potential interactions between immature axon terminal arbors and dendrite‐bare geniculate cells during dendrite outgrowth and subsequent remodeling of structural details are discussed.
Space‐Mapped auditory projections from the inferior colliculus to the optic tectum in the barn owl (Tyto alba)
Authors: Knudsen Eric I. , Knudsen Phyllis F.
Published: January 2005

The optic tectum of the owl contains a topographic representation of auditory space. We have investigated the source of this space‐mapped auditory activity by using retrograde tracing with horseradish peroxidase. The major source of auditory input to the optic tectum is the ipsilateral external nucleus of the inferior colliculus (ICX), which is known to contain a map of auditory space also. Additional minor projections originate in the superficial nucleus of the inferior colliculus and the nucleus isthmi parvocellularis. There is no apparent projection to the optic tectum from the contralateral ICX or any other brainstem auditory nucleus. The projection from the ICX to the optic tectum is point‐to‐point: rostral ICX projects to rostral tectum, caudal ICX to caudal tectum, dorsal ICX to dorsomedial tectum, and ventral ICX to ventral tectum. Thus, the space‐mapped organization that exists in the ICX is passed on by topographic projections to the optic tectum.
Distribution and morphology of corticospinal tract neurons in reeler mouse cortex by the retrograde HRP method
Authors: Terashima Toshio , Inoue Yoshiro , Inoue Kaoru , Mikoshiba Katsuhiko , Tsukada Yasuzo
Published: January 2005

Reeler, a recessive mutation in mice., causes cytoarchitectqnic abnormalities to the cerebral and cerebellar cortices. In normal controls corticospinal (CS) tract neurons retrogradely labelled after HRP injection into the lumbar cord were situated only in layer V (the inner pyramidal layer). In the reeler, by contrast, the labelled CS neurons were scattered diffusely throughout all levels of the corresponding cortical area. In addition to the malpositioning of the somata, the labelled CS neurons in the cortex of the reeler could be divided into two major classes according to their dendritic pattern: typical pyramidal neurons and atypical ones. The typical pyramidal neuron had an apical dendrite projecting from the superior pole of the soma and ascending toward the pia mater and several basal and basolateral dendrites projecting from the inferior pole of the soma. The atypical neurons consisted of six types: (l)inverted, (2)tumbled, (3)bipolar, (4) V‐shaped, (5) hook‐shaped, and (6) superficial polymorphic. The typical pyramidal neurons in the reeler tended to be situated relatively deep in the cortex and the atypical neurons tended to lie relatively superficially in the cortex. The axons of both the typical pyramidal neurons and the atypical ones in the reeler usually extended from the lower surface of the soma or one of the descending dendrites as in the normal control.
The comparative effects of early‐life undernutrition and subsequent differential environments on the dendritic branching of pyramidal cells in rat visual cortex
Authors: Davies Christine A. , Katz Hillary B.
Published: January 2005

Male rats were either undernourished or fed normally from birth to day 21, after which time food was made freely available. At 1 month of age littermate pairs from both nutritional groups were housed in either enriched or impoverished conditions for 30 days and then killed for brain measurements. Significant deficits due to undernutrition were observed in the weight and size of the cerebrum, but not in the thickness or area of the visual cortex. Although there were large differences of between 21 and 39% in the number of higher‐order basal dendrites of layers II and III pyramidal cells, and of about 19% in the distal ring intersections, none except the fourth‐order branches and intersections at 100 μm from the cell body approached statistical significance. Changes in cerebral weight and size also occurred as aresult of differential housing, with theenrichedratsshowingincreased values relative to their impoverished littermates. In contrast to the nutritional treatment, differential housing significantly affected cortical thickness and area, as well as basal dendritic branching of the pyramidal cells. Enriched rats had relative increases of 26% in the number of fifth‐order branches and 45–80% in the number of distal ring intersections.
Maturation and recycling of trigeminal motoneurons in anuran larvae
Authors: Barnes Maryann D. , Alley Keith E.
Published: January 2005

Development of the trigeminal motor system was analyzed in Rana pipiens larvae and adults. The aim of this investigation was to determine the postmetamorphic fate of the primary motoneurons that innervate the larval jaw muscles. Specifically, we wanted to ascertain whether these neurons were deleted in conjunction with their muscular targets during metamorphosis or reused to innervate the adult jaw muscles. Cell counts and horseradish peroxidase tracer were used to distinguish between these two possibilities.

The number of trigeminal motoneurons was relatively constant in premetamorphic and prometamorphic larvae. A small reduction in the cellular complement of the motor nucleus occurred during metamorphic climax, but the majority (≈︁ 90%) of the primary motoneurons were retained from the larval to the adult nervous system. The cell loss may represent motoneurons that innervated specific larval muscles that have no adult successors and thus the entire myoneural unit degenerates. Retrograde tracers indicated that all trigeminal motoneurcns extended axons into the jaw muscles of both premetamorphic larvae and adult frogs. These observations provide further support for the recycling of the trigeminal motoneurons.
Corticotectal terminals in the superior colliculus of the rabbit: A light‐ and electron microscopic analysis using horseradish peroxidase (HRP)‐tetramethylbenzidine (TMB)
Authors: Holländer Horstmar , Schönitzer Klaus
Published: January 2005

The projection from the striate cortex to the superior colliculus was studied light‐ and electron microscopically by means of anterogradely transported horseradish peroxidase and tetramethylbenzidine histochemistry.

Labeled boutons were found in the stratum zonale (SZ) and in the stratum griseum superficiale (SGS), not in stratum opticum (SO). There are two maxima of frequency of labeled boutons, one in middle SGS at about 500 μm depth, and a smaller one in upper SGS at about 200 μm depth. Such a bimodal distribution of corticotectal terminals has not been described in any species before. Labeled myelinated axons were found in SGS and SO with a maximal frequency in middle SGS at about 400 μm depth. The myelinated axons in SZ, which are commonly considered to be of corticalorigin, were not labeled.

The labeled cortical terminals contained numerous round synaptic vesicles and predominantly dark mitochondria. They formed usually asymmetrical synapses and contacted dendrites, some of which contained synaptic vesicles. Occasionally, labeled boutons were observed which definitely did not belong to the type that is generally considered to be of cortical origin.
Corticopontine remodelling after cortical and/or cerebellar lesions in newborn rats
Authors: Castro Anthony J. , Mihailoff Gregory A.
Published: January 2005

The distribution of corticopontine projections was studied, primarily with the Fink‐Heimer technique, in adult rats which at 2‐3 days of age had sustained unilateral sensorimotor (SMC) or occipital (OC) cortical lesions and in animals that had received neonatal hemicerebellar (HCb) lesions singly or in combination with the neonatal SMC or OC lesions.

Neonatal left SMC or left HCb lesions induced an anomalous increase in crossed sensorimotor corticopontine (SMP) projections originating from the right SMC. This increase appeared more dense after cortical lesions as compared to cerebellar lesions and appeared more dense in those animals receiving the combined SMC plus HCb lesions. No alterations in the distribution of SMP fibers were observed after neonatal OC lesions nor were any alterations of occipital corticopontine (OP) fibers observed in any of the neonatal lesion groups.

The remodelling of right SMP projections after neonatal left SMC lesions demonstrates an interaction between corresponding pathways originating from opposite sides of the brain and which occurs in response to the partial removal of afferents to pontine gray neurons as a result of the SMC lesions. In contrast, the absence of SMP plasticity after OC lesions, and vice versa, demonstrates the absence of plasticity between pathways which differ anatomically and functiondly.

The substantial neuronal loss which occurs within the right PG after neonatal left HCb lesions is believed to influence the increase in crossed SMP fibers coursing from the right hemisphere to the larger left PG. No increase in crossed OP fibers from the right hemosphere was observed in these animals. The increase in crossed SMP fibers after neonatal SMC lesions combined with neonatal HCb lesions is more dense than found in the single lesion groups. These findings suggest that separate mechanisms of plasticity might be operational for each lesion and that these mechanisms may be additive.
The inferior olive of a prosimian primate, Galago senegalensis. II. Olivocerebellar projections to the vestibulocerebellum
Authors: Whitworth R. H. , Haines D. E. , Patrick G. W.
Published: January 2005

Olivocerebellar projections to the vestibulocerebellum of Galago senegalensis, a prosimian primate, were studied by using a horseradish peroxidase (HRP) method. Following implants of HRP into the flocculus, labeled cells are found in subgroup d of contralateral medial accessory olive (MAO), while labeled somata are present throughout subgroups c and d after injections of HRP into the nodulus and adjacent parts of the uvula. Labeled cells are also located throughout the dorsomedial cell column (DMCC) and a small contingent of HRP‐filled cells are seen in dorsomedial areas of the ventrallamellae of the principal olivary nucleus (PO) after HRP placements in nodu‐ lus and uvula. Subsequent to injections of paraflocculus, labeled cells are found in subgroup a of MAO, in the lateral bend of PO, and in its ventral lamella (VLPO).

Collectively these data indicate a topographically organized projection of olivocerebellar fibers to the flocculonodular lobe and adjacent areas of paraflocculus and uvula. The paraflocculus receives input from subgroup a of MAO, the lateral bend of PO, and VLPO. Subgroup d of MA0 projects to the flocculus and nodulus with a relatively minor contribution to uvula. Neurons in subgroups c and DMCC of MA0 project to specific portions of nodulus and adjacent uvula. These data are in general agreement with those from other species. In contrast to earlier reports, however, this study describes a projection from VLPO to lateral areas of the contralateral nodulus and uvula. A zonal organization of olivocerebellar terminations in the nodulus and ventral portions of uvula is suggested. A medial zone is subdivided into medial and lateral parts which receive projections from subgroups c and d of MAO, and from cells in DMCC, respectively. A more lateral area receives axons from cells in VLPO.
An electron microscopic study of primary afferent terminals from slowly adapting type I receptors in the cat
Authors: Semba K. , Masarachia P. , Malamed S. , Jacquin M. , Harris S. , Yang G. , Egger M. D.
Published: January 2005

Primary afferent fibers transmitting impulses from slowly adapting (SA) Type I receptors in the glabrous skin of the hind paw of the cat were injected intraaxonally in the spinal cord with horseradish peroxidase (HRP).

At the light microscopic level, terminal arborizations were observed in the medial dorsal horn extending up to 6 mm rostrocaudally in and near the seventh lumbar segment. Boutonlike swellings labelled with HRP were distributed in clusters in Rexed's laminae III‐VI. There was a tendency for the most dorsal clusters from an individual fiber to be located rostrally and for the most ventral clusters to be located caudally.

At the electron microscopic level, a combination of morphometric analysis and serial reconstruction revealed the following: (1) All the boutons labelled with HRP contained predominantly clear, round synaptic vesicles, 40–50 nm in diameter. (2) Labelled boutons (n = 75) had cross‐sectional longest dimensions of 1.72 ± 0.53 μm (Mean ± S.D.), perimeters of 4.95 ± 1.52 μn, and areas of 1.18 ± 0.59 μm2. Their shapes in section varied from rounded to elongated forms. (3) The sizes of labelled boutons decreased significantly and linearly with depth from lamina IV to VI. The shapes of the bouton cross sections also became rounder with depth in the dorsal horn. (4) About 72% of synaptic contacts associated with HRP‐filled boutons were with dendritic spines and shafts; most of these synapses were of the asymmetric type. (5) The remainder (28%) of the appositions were synapselike contacts between labelled boutons and unlabelled structures containing flattened or pleomorphic vesicles, and occasional dense‐cored vesicles. (6) We observed no unequivocal axosomatic contacts made by labelled boutons. (7) The lengths of synaptic appositions with dendritic spines (0.46 ± 0.20 μm) or with dendritic shafts (0.51 ± 0.18 μm) were significantly greater than the synapselike contacts with vesicle‐containing unlabelled structures (0.29 ± 0.09 μm). (8) Complex neuropilar organization was occasionally seen with labelled boutons as central elements, although simpler organizations were much more common.

In summary, HRP‐labelled fibers ended predominantly in boutons containing clear, round vesicles forming axospinous and axodendritic synapses. This is consistent with physiological observations of postsynaptic excitation of dorsal horn cells by the primary afferent fibers from SA Type I receptors in the glabrous skin.
An autoradiographic study of the postnatal development of sensorimotor and visual components of the corticopontine system
Authors: Mihailoff Gregory A. , Adams Catherine E. , Woodward Donald J.
Published: January 2005

Standard autoradiographic tracing methods which employed intracortical injections of 3H‐leucine were used to describe the time course of development in those components of the corticopontine system which originate in sensorimotor (SM) or visual (VIS) cortices. These studies were performed using male or female pigmented rats ranging in age from 1 to 24 days (birth = day 0). Labeled axons could easily be recognized within the cerebral peduncle at the level of the basilar pons on postnatal day 1 following either an SM or a VIS cortical injection. Labeling over the basilar pontine neuropil suggestive of axonal ingrowth could also be seen on day 1 following SM injections but not until day 3 in cases with VIS injections. During the latter part of the first postnatal week, both SM and VIS axon terminal fields were established in the pontine neuropil in locations generally similar to those described in the adult. However, at this time they occupied a larger area and appeared more diffusely organized than in the adult. Subsequently during the second postnatal week, both SM and VIS projection fields gradually became more focused and circumscribed until by day 16 in the case of the SM system, and day 18 for the VIS projection, an adultlike configuration was attained. At no time during development was there any evidence of a more substantial contralateral projection than that described for the adult. Correlation of these events with previous Golgi observations and ongoing electron microscopic studies of pontine synaptogenesis suggest that the focusing or constriction of corticopontine axon terminal fields might be the result of a selective degeneration process in which the presynaptic (corticopontine axon) and postsynaptic (basilar pontine neurons) elements both play an active role. Furthermore, the absence of a stage in development characterized by an increase in the density of the contralateral component of the projection confirms the interpretation of earlier studies which suggested that the aberrant contralateral corticopontine projections observed following neonatal cortical lesions were the result of sprouting from the intact corticopontine system and not due to failure of retraction in one component of a system which in fact distributes bilaterally for a time during development.
Substance P and catecholaminergic expression in neurons of the hamster main olfactory bulb
Authors: Kream Richard M. , Davis Barry J. , Kawano Teruaki , Margolis Frank L. , Macrides Foteos
Published: January 2005

A coordinated series of immunohistochemical and biochemical analyses have been conducted in the hamster to examine the dependence of substance P and tyrosine hydroxylase (TH) expression by second‐order olfactory neurons, and the level of dopamine in the main olfactory bulb (MOB), on the integrity of carnosine‐ and olfactory marker protein (OMP)‐containing primary afferent neurons. Substance P‐like immunoreactivity (SPLI) is localized in external tufted cells and centrifugal afferents of the MOB; TH immunoreactivity has a wider distribution, in external tufted, middle tufted, periglomerular, and deep short‐axon cells as well as in centrifugal afferents. To characterize the SPLI, this material was isolated by guanidine‐HCl extraction and passage over a C18 SEP‐PAK. The SPLI coelutes on HPLC with authentic substance P and, following oxidation, coelutes with substance P sulfoxide. It is sensitive to α‐chymotrypsin and is resistant to trypsin. Thus, the SPLI in the MOB behaves as authentic substance P. Intranasal irrigation with 0.17 M ZnSO4 results in peripheral deafferentation of the MOB for up to 8 months as evidenced by a persistent loss of OMP immunoreactivity and shrinkage of the olfactory nerve layer and glomeruli. By these criteria, the vomeronasal inputs to the accessory olfactory bulb are not destroyed and the spared vomeronasal receptor neurons do not innervate the vacated peripheral projection field in the MOB. The loss of peripheral inputs to the MOB is accompanied by marked and parallel reductions in the incidences of SPLI‐ and TH‐positive second‐order neurons despite an increase in the density of neuronal somata in the glomerular layer. Biochemical quantifications following peripheral deafferentation also demonstrate significant decreases of both substance P and dopamine, together with the expected decrease of carnosine. In contrast, the SPLI and the TH and serotoninlike immunoreactivities in centrifugal afferents as well as the TH immunoreactivity in deep interneurons do not appear to be reduced, and the MOB content of norepinephrine in centrifugal afferents is unaffected. These results collectively indicate that the loss of inputs from the primary olfactory receptor neurons can reduce the levels of at least two different, putatively neuroactive compounds (substance P and dopamine) in at least three classes of second‐order neurons (external tufted, middle tufted, and periglomerular cells). The control of central neuron phenotype by the peripheral olfactory neurons thus appears to be a phenomenon of broad influence. It may play a role in processing chemosensory information as well as offering a system in which to study neuronal plasticity.
The central nucleus of the inferior colliculus in the cat
Authors: Oliver Douglas L. , Morest D. Kent
Published: January 2005

The central nucleus of the inferior colliculus in the cat is distinguished by its unique neuropil. In Golgi‐impregnated material, it is composed primarily of neurons with disc‐shaped dendritic fields arranged into parallel arrays, or laminae, complemented by the laminar afferent axons from the lateral lemniscus. Large, medium‐large, medium, and small varieties of disc‐shaped cells are distinguished on the basis of the size of the dendritic field and cell body size, dendritic diameter, and dendritic appendages. A second major class of neurons in the central nucleus are the stellate cells with dichotomously branched, spherical‐shaped dendritic trees. Simple, complex, and small stellate cells can be distinguished by their size and by the complexity of the dendritic and axonal branching. Laminar afferent axons are recognized by the nests of collateral side branches and the grapelike clusters of terminal boutons – thick, thin, and intermediate‐sized varieties are apparent. Other axon types include local collaterals of central nucleus neurons, some of which are distinguished by their frequent and complex collaterals.

In the central nucleus, the configuration of the fibrodendritic laminae, the presence of subdivisions, and the banding of afferent axons suggest levels of organization which are superimposed on the synaptic arrangements of the individual cell and axon types. The laminar pattern, as studied in serial Golgi‐impregnated sections, differs from previous reports. The central nucleus contains subdivisions which can be distinguished by their laminar pattern, different proportions of cell types, and the packing density of the cell bodies and axonal plexus.

The patterns of degeneration observed in Nauta‐stained material after lesions of caudal auditory pathways show that thick and fine afferent fibers form dense bands of degeneration separated by sparse, fine‐fiber degeneration. The bands are thicker than individual laminae but smaller than the subdivisions.

The intrinsic organization of the neurons and axons, combined with the laminar organization, subdivisions, and banding patterns, each may contribute different aspects to the processing of auditory information in the central nucleus.
α‐Bungarotoxin binding to the myotome and choline acetyltransferase activity in the rabbit embryo
Authors: Grubič Zoran , Tennyson Virginia M. , Chang Hai Won , Kremzner Leon T. , Penn Audrey S.
Published: January 2005

We have previously found incomplete sarcomeres and acetylcholinesterase activity in the myoblasts of the myotome of the rabbit at day 13 of gestation. We now report that an acetylcholine (Ach)‐synthesizing enzyme and the nicotinic receptor are present at this stage as well. A study of the myotome using [125I]α‐bungarotoxin shows that the mononucleated myoblasts have α‐bungarotoxin binding sites before they migrate away to form multinucleated myotubes. Choline acetyltransferase activity and/or a different ACh‐synthesizing enzyme are found at early stages of development, even before the spinal nerve has formed. An ACh‐synthesizing enzyme is present in the notochord, a neural tube‐dorsal root ganglion preparation, as well as in rows of myotomes separated from the latter preparation. Assays of isolated myotomes with very little adherent mesenchyme indicate that the enzyme is located either within the myotome or in its immediate vicinity. Cholinergic components, therefore, are associated with the mononucleated myoblasts of the myotome before they fuse to form myotubes and before they receive their permanent innervation.
The distribution of Timm's stain in the nonsulphide‐perfused human hippocampal formation
Authors: Cassell M. D. , Brown M. W.
Published: January 2005

A detailed description is given of the distribution of Timm's staining in the human hippocampal formation. In sections cut transverse to the long axis of the hippocampal formation the same pattern of staining is seen throughout almost all of the structure, i.e., through all the main body except the most caudal region and, following the medial bend made by the long axis, through most of the pes hippocampi. The staining typically filled almost the whole of the hilus of the dentate gyrus and the whole depth of the adjacent stratum pyramidale and stratum lucidum of subfield CA3. Rostrally, staining was traced into the tip of the uncus. Caudally, staining was traced to the inferior surface of the splenium at the apex of the caudal taper of the hippocampus. No staining was found in the gyrus fasciolaris, indusium griseum, or anterior hippocampal rudiment. Except in the medial part of the pes hippocampi, the Timm's staining did not reach the proximal border of the subfield CA1. In some sections of the main body of the hippocampus a narrow, infragranular stain‐free zone was observed in the hilus. In the dentate gyrus of three older subjects, but not in those of three younger subjects, supragranular staining was found. It is argued that the Timm's staining described in this study is specific to the hippocampal mossy fibres. The distribution of the staining is discussed in relation to the boundaries of subfields CA3 and CA2 as delineated by other authors.
Cerebellar targets of visual pontine cells in the cat
Authors: Robinson Farrel R. , Cohen Janet L. , May Jack , Sestokas Anthony K. , Glickstein Mitchell
Published: January 2005

The cerebellum receives visual mossy fiber input from the cerebral cortex via visual cells in the pons. We identified the regions of cat cerebellum that receive cerebral visual input by injecting orthograde tracers among physiologically identified visual pontine cells. Cerebellar labeling following these injections indicates that the contralateral paraflocculus and the rostral folium of the uvula (vermal lobule IX) receive the heaviest projection from cortically activated pontine visual cells. Lighter visual input reaches much of the rest of the contralateral posterior lobe. A second experiment combined, in the same animal, orthograde tracing of the visual corticopontine pathway with retrograde tracing of the pontocerebellar projection. The results of this experiment confirm that the paraflocculus and uvula receive more cortical visual input than do other regions of the cerebellum. This experiment also shows that uvula‐projecting and paraflocculus‐projecting cells occupy different parts of the ventromedial pons. Uvula‐projecting cells cluster immediately adjacent to the ventral and medial borders of the pyramidal tract and near the midline. Paraflocculus‐projecting cells lie ventral and medial to the pyramidal tract but displaced from its border. There are few paraflocculus‐projecting cells near the midline.
A diffuse αMSH‐immunoreactive projection to the hippocampus and spinal cord from individual neurons in the lateral hypothalamic area and zona incerta
Authors: Köhler Christer , Haglund Lena , Swanson Larry W.
Published: January 2005

The course, distribution, and possible neurotransmitter specificity of a projection from the lateral hypothalamic area (LHA) and zona incerta to the hippocampal formation (dentate gyrus, Ammon's horn, subicular region, and entorhinal area) and spinal cord were examined anatomically in the adult rat. First, small injections of the fluorescent tracer fast blue were made into either the septal part of the dentate gyrus and Ammon's horn or the entorhinal area, and the distribution of retrogradely labeled cells was plotted. In each experiment many cells were labeled in the LHA and zona incerta, and little evidence for a topographically organized projection to different parts of the hippocampal formation was found. Second, a combined retrograde transport‐immunofluorescence method was used to show that some 95% of the fast blue‐labeled neurons in the LHA and zona incerta were also stained with an antiserum to the opiate peptide α‐melanocyte‐stimulating hormone (αMSH), but not an antiserum to adrenocorticotropin (ACTH)1–24. It was also found that small numbers of retrogradely labeled neurons were stained with antisera to somatostatin 14 and 28, dynorphin (1–17), and angiotensin II. Third, the distribution of αMSH‐immunoreactive fibers was plotted, and they were found to form a diffusely organized plexus throughout all of the subfields of the hippocampal formation. These fibers were virtually eliminated after transections of the fimbria and the region between the entorhinal area and the caudal amygdala. Fourth, the course of fibers from the LHA and zona incerta was examined with the anterogradely transported lectin Phaseolus Vulgaris Leucoagglutinin (PHAL). Such fibers reach the hippocampal formation by a dorsal route through the septal region and fimbria, and by a ventral route through the amygdala. And fifth, double retrograde transport and immunohistochemical methods were used to show that at least some αMSH‐stained neurons in the LHA and zona incerta give rise to collaterals that innervate both the hippocampal formation and the spinal cord. αMSH‐stained fibers in the spinal cord also form a widely scattered plexus with no obvious circumscribed terminal fields. It is suggested that the diffusely organized projection from the LHA to the cerebral cortex and spinal cord may play a role in the general arousal associated with a variety of motivated behaviors.
Topography of primary visual centres in the brain of the chick, Gallus gallus
Authors: Ehrlich David , Mark Richard
Published: January 2005

In a previous paper (Ehrlich and Mark,'83b) the primary visual centres of the chick were described. In this paper patterns of retinotopy are examined by means of silver degeneration and autoradiographic techniques following discrete laser lesions of the retina.

Well‐defined and complete retinotopic maps are found in each of the following visual centres: tectum, lateral anterior thalamus, lateroventral geniculate nucleus, superficial synencephalic nucleus, ectomammillary nucleus, and tectal grey. In the dorsolateral anterior thalamus, pars lateralis, and external nucleus there is some evidence of a retinotopic innervation, yet not as well defined as those nuclei mentioned previously.

Retinotopic maps were not observed in other retinorecipient regions. These include the ventrolateral thalamus, dorsolateral anterior thalamus, magnocellular part and rostrolateral part, pretectal optic area, and diffuse pretectal nucleus.

Within the lateroventral geniculate, lateral anterior thalamus, superficial synencephalic nuclei, and the tectal grey, the ventral to dorsal retinal axis is mapped along the rostrocaudal axis, the reverse of the orientation seen in the tectum, which may have implications for explanations of how retinotopic maps are formed.

The poor retinotopy in dorsolateral anterior thalamus, lateral part, is discussed with respect to the view that it may be the avian homologue of the mammalian lateral geniculate nucleus.
Postnatal differentiation of rat optic nerve fibers: Electron microscopic observations on the development of nodes of Ranvier and axoglial relations
Authors: Hildebrand C. , Waxman S. G.
Published: January 2005

The postnatal differentiation of rat optic nerve fibres was examined by transmission electron microscopy. The results show that many early developing axons contain clusters of vesiculotubular profiles prior to Myelination. At places vesicular elements appear to fuse with the axolemma, and, in addition, some axons exhibit deep axolemmal invaginations and axoplasmic lamellated bodies. It is suggested that these feature might reflect axolemmal remodeling, possibly involving axoglial signalling and/or functional differentiation of the axolemma. The size distribution of unmyelinated optic nerve axons changes little during development. Ensheathment of larger axons commences 6 days postnatally. The subsequent formation of compact sheaths are a few microns long and separated by long bare axon segments. In optic nerves from 10–12‐day‐old rat pups, a few sheaths consisting of about five layers border primitive asymmetric nodes with a patchy axolemmal undercoating. Extensions from one of the terminating sheaths are often associated with undercoated patches of axolemma. Relatively differentiated nodes of Ranvier first appear 14–16 days after birth. The continued nodal maturation involves establishment of a regular nodal geometry, increasing distinctness of the axolemmal undercoating, and formation of perinodal astrocytic processes embedded in an extracellular node gap substance. The results are compared with available data on the conduction properties of rat optic nerve fibres during development.
Development and degeneration of retina in rds mutant mice: Electron microscopy
Authors: Jansen H. G. , Sanyal S.
Published: January 2005

In the retina of mice homozygous for the retinal degeneration slow (rds) gene, receptor outer segments failed to develop and typical disc structures were never observed. However, cilia surrounded by a plasma membrane were regularly present. At the time when outer segments grew in the normal retina, the optic ventricle in the mutant showed an accumulation of membrane‐bound vesicles of varying size and density. The vesicles declined in frequency at later stages of degeneration. After initial growth, the inner segments in the mutant retina remained stunted but maintained their morphological differentiation, including the ciliary structures. Their number declined with loss of visual cells.

In the mutant retina development of synapses, between the receptor cells and the processes of the horizontal cells and the bipolar cell dendrites, followed in normal sequence. Formation of spherule terminals of the rods, with one triad synapse, and of pedicle terminals of the cones, with multiple triad synapses, was recorded in the same way as in the normal retina. With loss of visual cells in the mutant retina, some of the profiles of the surviving spherule terminals showed an increased occurrence of two, three, or more synaptic sites. This growth resulted from enlargement and branching of the ribbons and sprouting from the postsynaptic elements. Similar changes were not observed in the pedicle terminals.

The pigment epithelial cells in the mutant mice appeared initially normal, but phagolysosomal structures were absent. However, various inclusion bodies appeared within the pigment epithelial cells following degenerative changes in the retina. In some places, the basal infoldings deepened their furrows while thinning the cytoplasmic part of the epithelium.

Failure to form the outer segments and the subsequent lysis of the visual cells appear to be the primary effects of the rds gene, whereas the synaptic growth in the sperule terminals and the changes in the pigment epithelium appear to be consequential to those defects.
The development of photoreceptors in the zebrafish, Brachydanio rerio. I. Structure
Authors: Branchek Theresa , Bremiller Ruth
Published: January 2005

Morphological development of photoreceptors in the central retina of the zebrafish, Brachydanio rerio, was studied by using light and electron microscopic techniques. Outer segments (OS) first appeared at 2.5 days postfertilization (d2.5). On d3, synaptic elaborations were seen. By d8, two OS types were present and were identified as cones. The first indication of rod formation was also evidenced at this time, when vitreally positioned nuclei were observed and rodlike cells were infrequently detected in electron micrographs. At d12, the full complement of zebrafish photoreceptors, rods and four cone types, was identified. From this time on cells grew until adult dimensions were reached at d24. These structural observations are consistent with results of functional studies which utilized physiological and behavioral techniques.