bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional role of efferents to the avian retina. I. Analysis of retinal ganglion cell receptive fields
Authors: Pearlman Alan L. , Hughes Charles P.
Published: January 2005

Receptive fields of retinal ganglion cells were analyzed during extracellular microelectrode recordings in the optic tract of the lightly anesthetized pigeon. Four major types of receptive field can be distinguished among the 359 fibers studied. Twenty‐five percent of the receptive fields are relatively simple, responding at on and at off to stationary spots of light in the central region. All of the receptive fields have inhibitory surrounds of varying strength that do not produce a response when illuminated alone, but antagonize responses from the central region. Motion sensitive units comprise 15% of the recorded population; they are similar to the on‐off center type except that responses to stationary stimuli are absent or very weak while responses to moving stimuli are vigorous. Directionally selective units also have the basic features of on‐off, inhibitory surround cells, but respond to moving stimuli well from the preferred direction and not at all from the null direction. Directional cells have a broad range of null directions; in about one‐third of the units the range becomes broader when the stimulus involves both center and surround of the receptive field, thus enhancing directional selectivity. Directionally selective units are common, comprising 38% of the units studied. Cells unresponsive to stimuli moving from anterior in the visual field are much more common than other types, while cells unresponsive to stimuli from posterior in the field are rare. A few units (11 %) respond only at on or at off to stationary stimuli in their receptive field centers; they also have antagonistic but unresponsive receptive field surrounds. The area of the visual field sampled is uniform in regard to the relative numbers of the four major receptive field types.
Afferents to the cerebellar lateral nucleus. Evidence from retrograde transport of horseradish peroxidase after pressure injections through micropipettes
Authors: Eller Theodore , Chan‐Palay Victoria
Published: January 2005

HRP was injected by pressure from glass capillary micropipettes unilaterally into the lateral nucleus of rat so as to encompass the entire nucleus, but without spread into the interpositus nuclei. The cells of origin of the afferents to the lateral nucleus were studied after retrograde transport of the HRP. The reticulotegmental nucleus of the pons was labelled bilaterally and is the major source of crossed and uncrossed reticular inputs. The pontine nuclei also provide extensive crossed and uncrossed afferents. The inferior olive gives a large crossed olivo‐lateral nucleus projection and a minor uncrossed input. The trigeminal nuclear complex — the nucleus of the spinal tract and the mesencephalic, principal sensory, and motor nuclei — all provide uncrossed afferents. The rostral portion of the lateral reticular nucleus gives a small crossed and uncrossed projection while the perihypoglossal nuclei and the dorsal parabrachial body give crossed afferents to the lateral nucleus. The norepinephrine afferent system from the locus coeruleus is represented by one or two heavily labelled cells and the serotonin raphe systems come from at least five raphe subgroups, the dorsal, superior centralis, pontis, obscurus and magnus nuclei. No evidence was found for commissural fibers between ipsilateral or contralateral cerebellar nuclei, or afferent axons, from the spinocerebellar nuclei and the paramedian reticular nucleus. The significance of these sources of afferent inputs to the lateral cerebellar nucleus is discussed. The question is raised of the direct relationship between size of terminal axonal arborization and the quantity of HRP granules present in a cell after retrograde transport. The limitations of the HRP method for detecting subtle local differences in the distribution of afferents within the heterogeneous groups of neurons in the lateral nucleus are discussed.
Convergent thalamic and mesencephalic projections to the anterior medial cortex in the rat
Authors: Beckstead Robert M.
Published: January 2005

Small microelectrophoretic deposits of horseradish‐peroxidase (HRP) were placed at various loci within the gray matter of the rat's anterior medial cortex. A comparison of the patterns of retrograde cell‐labeling charted in 26 such cases confirmed earlier findings in fiber‐degeneration studies according to which the respective thalamocortical projections of the mediodorsal (MD) and anteromedial nucleus (AM) overlap each other over a wide region of the anterior medial cortex. This region of thalamocortical convergence, extending from pregenual levels caudalward as far as the anterior border of the retrosplenial cortex, corresponds almost exactly to the cortical region from which locally deposited HRP was found to be transported so as to label cells in one or both of two mesencephalic cell groups: the ventral tegmental area (AVT) dorsal and lateral to the interpeduncular nucleus, and the medial one‐quarter of the pars compacta of the substantia nigra (SNC). The reported findings suggest that the corticipetal projections of AVT and SNC are organized so that AVT projects largely to the area infraradiata of the pregenual cortex which receives its major thalamocortical projection from MD, whereas SNC‐efferents are distributed to the area infraradiata of the supracallosal cortex which receives most of its thalamocortical afferents from AM; the two mesencephalocortical projections do, however, appear to overlap each other in a region of the medial cortex immediately posterior to the level of the genu corporis callosi. HRP injected into the medial cortex of five rats pre‐treated with 6‐hydroxydopamine, a drug that produces chemical lesions of catecholamine neurons, failed to label any cells in AVT and SNC but did label numerous cells in MD and AM. This finding suggests that the ventral tegmental cells projecting to the anterior medial cortex are exclusively dopamine neurons.
Differentiation of Purkinje cells and their relationship to other components of developing cerebellar cortex in man
Authors: Zecevic Nada , Rakic Pasko
Published: January 2005

The differentiation of Purkinje cells and their relationship to other components of the developing cerebellar cortex were analyzed by the Golgimpregnation method and by electron microscopy in human specimens of various pre‐ and postnatal ages. The three stages of Purkinje cell maturation that have been previously recognized in other species are also evident in man: the first stage occupies primarily the fourth fetal month (12–16 weeks); the second stage lasts through the fifth, sixth and seventh fetal months (16–28 weeks); the third stage extends throughout the remaining period of intrauterine life and the first postnatal year and continues at a slow rate thereafter. During the first stage, Purkinje cells are distributed in a layer, several rows deep. Their bipolar somas are relatively smooth and have only a few processes at the apical and basal cell poles. In the 3‐month period of the second stage, Purkinje cells become gradully organized into a single row. Their somas become invested with additional randomly oriented dendritic processes and numerous somatic spines (pseudopodia). The first morphologically well‐defined synapses appear on the Purkinje cell somatic spines and on their immature dendritic shafts at the beginning of the second stage and become more prominent during the period from 18 to 24 weeks. In the third stage, the dendritic arbor becomes flattened in the plane transverse to the folium and somatic spines disappear. Spines appear on the secondary and tertiary dendrites between the twenty‐fourth and twenty‐eighth fetal weeks and continue to increase in number during the entire third stage as new dendritic branches develop. These observations indicate that cellular maturation and synaptogenesis in the primate cerebellum differ from these events in non‐primate species, with respect to time of birth, in the relative duration of each phase and in the total time necessary for neuronal differentiation. The protracted time of differentiation and the slow growth of Purkinje cell dendrites in man may be due to the numerically complex relationships existing between granule and Purkinje cells. It is probably not simply a reflection of the larger size of human Purkinje cells and their dendrites.
Midbrain, diencephalic and cortical relationships of the basal nucleus of meynert and associated structures in primates
Authors: Jones E. G. , Burton H. , Saper C. B. , Swanson L. W.
Published: January 2005

The structure and connectivity of the basal nucleus of Meynert, the substantia innominata in which it lies, and certain related areas have been examined in New World and Old World Monkeys, using retrograde and anterograde axonal transport methods.

Experiments using the retrograde, horseradish peroxidase method confirm the observations of Kievet and Kuypers ('75) that the basal nucleus and substantia innominata project directly, heavily and with a somewhat crude topography upon the neocortex.

Experiments involving the anterograde, autoradiographic method show that the basal nucleus and substantia innominata form part of a complex pathway that links them together with the lateral hypothalamus, certain parts of the amygdala and the peripeduncular nucleus of the midbrain. The peripeduncular nucleus is often regarded as a part of the central auditory pathway; it gives rise to a fiber bundle of considerable size that ascends on the dorsal surface of the ipsilateral optic tract and terminates ultimately in the lateral hypothalamic area of both sides. As well as distributing fibers to the basal nucleus, substantia innominata and lateral hypothalamus, this pathway provides a heavy projection to a cytoarchitectonically distinct posterior part of the lateral nucleus of the amygdala, the medial and intercalated nuclei of the amygdala and a less dense projection to the bed nucleus of the stria terminalis.

Certain parts of the hypothalamus and possibly the preoptic areas give rise to a complementary descending pathway that distributes fibers to the ipsilateral basal nucleus, substantia innominata and amygdala, and ends in the peripeduncular nuclei of both sides. Decussating fibers in both the ascending and descending pathways cross in the ventral supraoptic commissure.

It is concluded that the basal nucleus should include most of the aggregated and unaggregated large cells that lie in the substantia innominata and which in places intrude upon the preoptic regions and the nucleus of the diagonal band of Broca. Together, these may form a complex that receives inputs from a variety of brainstem sources, and projects widely and diffusely upon all cortical structures of the telencephalon.
Regional specialization in the golden hamster's retina
Authors: Y‐C Tiao , Blakemore Colin
Published: January 2005

Ganglion cells were counted and measured in whole mounts of the hamster's retina, stained with methylene blue. Their density varies between about 1,000/mm2 at the edge of the retina to about 5–6,000/mm2 in a broad area centralis centred about 1.9 mm (39 deg) directly temporal to the optic disk. Maps of cell density show a long horizontal extension of the dense area in the nasal direction. The sizes of ganglion cell somata fall into two main groups—small cells (5–11 μm diameter) and large cells (>11 μm), the latter including a small proportion of giant cells (>17 μm). All three classes of cells are maximal in density in the area centralis, although the small cells are relatively more numerous there. The total number of cells is about 114,000 with about 63,000 small cells and about 51,000 large. The optic nerve contains about 69,000 unmyelinated axons and about 50,000 myelinated axons, suggesting that the latter are the fibres of the larger ganglion cells. It is likely that the projections of the centres of the areae centrales of the two eyes are normally divergent in space; they are therefore not on “corresponding retinal points.”
Synapse formation in the mouse olfactory bulb Quantitative studies
Authors: Hinds James W. , Hinds Patricia L.
Published: January 2005

A quantitative study of synapse formation in the mouse olfactory bulb has been carried out using serial sections. Volumetric synaptic density as well as absolute number of synapses per olfactory bulb for eight distinct synaptic types have been determined at 15 different ages, from the beginning of synapse formation at embryonic day 14 (E14) to postnatal day 44 (P44). Synapses are first found in appreciable numbers at E15 when both axo‐dendritic and a few dendrodendritic synapses occur in the presumptive glomerular layer. Initial synapse formation correlates closely with the reorientation of mitral cells from a primitive tangential to a defintive radial direction. Synapse formation by mitral cell dendrites occurs after mitral cell axons have grown into the future olfactory cortical areas, either simultaneous with or before synapse formation by these axons.

Virtually all synaptic types detected in adults have been found on the day of birth, consistent with the idea that olfaction is an important sensory modality for newborn mice. Volumetric density of a given synaptic type generally increases 50–100 times during development while the absolute number increases about 1,000 times. Synapses in glomeruli develop more precociously than those in the external plexiform and internal granular layers, which correlates well with the time of origin and differentiation of the principal postsynaptic elements of these two divisions (mitral cells and internal granule cells) Correlation of the time of synapse formation of various synaptic types with their putative excitatory or inhibitory role determined in adult studies suggests that excitatory synapses generally form somewhat earlier, although throughout nearly all of synaptic development, both excitatory and inhibitory synapses are present.

Reciprocal dendro‐dendritic synapses in the external plexiform layer appear to have a special mode of formation. It is suggested that a granule‐to‐mitral dendro‐dendritic synapse only forms next to an already existing mitral‐to‐granule synapse on the same gemmule.
Efferents from medial basal forebrain and hypothalamus in the rat. I. An autoradiographic study of the medial preoptic area
Authors: Conrad Lily C. A. , Pfaff Donald W.
Published: January 2005

Efferent projections from the medial and periventricular preoptic area, bed nucleus of the stria terminalis and nuclei of the diagonal band were traced using tritiated amino acid autoradiography in albino rats.

Medial and periventricular preoptic area efferents were not restricted to shortaxon projections. Ascending projections from the medial preoptic area (mPOA) were traced through the diagonal band into the septum. Descending mPOA axons coursed in the medial parts of the medial forebrain bundle. Projections to most hypothalamic nuclei, including the arcuate nucleus and median eminence, were observed. In the midbrain, mPOA efferents were distributed in the central grey, raphe nuclei, ventral tegmental area and reticular formation. Projections from the mPOA were also observed to the amygdala through the stria terminalis, to the lateral habenula through the stria medullaris, and to the periventricular thalamus.

Axons of the most medial and periventricular preoptic area (pvPOA) neurons had a distribution similar to more lateral mPOA neurons but their longest‐axoned projections were weaker. The pvPOA did not send axons through the stria medullaris but did project more heavily than the more lateral mPOA to the arcuate nucleus and median eminence.

Projections from the bed nucleus of the stria terminalis (nST) were in most respects similar to those from the medial preoptic area, with the major addition of a projection to the accessory olfactory bulb.

The nuclei of the diagonal band of Broca (nDBB) gave a different pattern of projections than mPOA or nST, projecting, for instance, to the medial septum and hippocampus. Descending nDBB efferents ran in the ventral portion of the medial forebrain bundle. Among hypothalamic cell groups, only the medial mammillary nuclei received nDBB projections. nDBB efferents also distributed in the medial and lateral habenular nuclei and the mediodorsal thalamic nucleus.
Development of neurons in the visual cortex (area 17) of the monkey (Macaca nemestrina): A Golgi study from fetal day 127 to postnatal maturity
Authors: Lund J. S. , Boothe R. G. , Lund R. D.
Published: January 2005

The morphological maturation of several varieties of neurons of cortical area 17 have been followed in Golgi Rapid preparations from Macaque monkeys ranging in age from fetal day 127 to maturity. A developmental sequence common to all varieties of neuron is described. Maturation occurs at the same rate at all cortical depths and appears to relate to the size of the neuron rather than to factors such as generation time, arrival at a final laminar position or cell type. The characteristic laminar patterns of cell type distribution and the specific axonal and dendritic arborisations seen in the adult are generated in the earliest stages of growth and do not occur as the result of elimination from a wider, less precise, distribution. During the period from birth to postnatal week 8 a marked increase in the numbers of dendritic spines is seen in all varieties of neuron including those which will be spine‐free in the adult. Following this period an equally marked reduction in spine numbers occurs, initially rapid but continuing at a slower rate even nine months postnatally. Possible relationships between these postnatal dendritic spine changes and the extreme sensitivity of the system to visual input during the early postnatal weeks are discussed.
Preparation of antisera to neurofilament protein from chicken brain and human sciatic nerve
Authors: Dahl Doris , Bignami Amico
Published: January 2005

Antigens isolated by hydroxyapatite chromatography from human sciatic nerve (SN1 protein) and from 8 M urea extracts of chicken brain were selectively localized by immunofluorescence to neurofibrils in rat and chicken CNS. Absorption of the antisera with SN1 protein, chicken antigen or GFA protein abolished the staining. Antisera raised against antigen isolated with the same procedure from buffer extracts of chicken brain stained both neurofibrils and glial fibrils by immunofluroescence. Neurofibrillary staining was selectively abolished by absorption of the antisera with SN1 protein. Antisera prepared against axonal preparations isolated from bovine white matter only stained astroglia and were thus undistinguishable from anti‐GFA sera in this respect. The data suggested that the protein subunits of neurofilament and glial filaments, although difficult to separate in brain extracts by standard biochemical procedures and by subcellular fractionation in bovine white matter, still retain immunological specificity. In addition, the immunological cross reactivity between human and chicken antigens suggested that neurofilaments, as other constituents of the cytoskeleton such as microtubules and actin microfilaments, show a high degree of evolutionary stability.
The thalamic afferents to the inferior parietal lobule of the rhesus monkey
Authors: Kasdon David L. , Jacobson Stanley
Published: January 2005

The inferior parietal lobule (IPL) of the monkey is the homologous region to the supramarginal and angular gyri in man, subserving language and related cortical functions. We have examined specific zones of the IPL by injecting eight monkeys with retrogradely transported HRP, and located the positive cells in the thalamic sections with the assistance of an X‐Y plotter and reference to the atlas of Olszewski ('52). Projections to the IPL were found in the following thalamic nuclei: Anterior (Anterior Medial, Anterior Ventral); Lateral (Ventral Anterior, Ventral Anterior magnocellularis, Ventral Lateral caudalis, Pulvinar oralis, medialis, lateralis and inferior, Lateral Posterior and Lateral Dorsal); Medial (Medialis Dorsalis densocellularis, parvocellularis, and multiformis); Midline and Intralaminar (Centralis densocellularis, Centralis lateralis, Centralis inferior, Centralis superior lateralis, Subfascicularis parvocellularis, Paracentralis and Parafascicularis); and Posterior (Limitans, Suprageniculatus and Geniculatus Medialis magnocellularis).

A major projection to the superior portion of the IPL was from the anterior nuclei and Paracentralis of the intralaminar group. Ventralis Lateralis and oral Pulvinar projected primarily to the anterior‐inferior portion of the IPL, whereas Lateral Posterior projected most strongly to the anterior and superior portion. The major projection of the lateral Pulvinar was to the mid‐superior portion of the IPL and to area 19. The projections of the inferior Fulvinar were heaviest to area 19, but there was some overlap in the mid‐superior portion of the IPL with the medial and lateral Pulvinar. The major projection from the posterior thalamic nuclear complex was to the mid‐IPL.

The heterogeneous input from the thalamus to the IPL was not anticipated on the basis of prior anterograde or retrograde degeneration studies, and suggests that classical subdivisions of specific and associational thalamic nuclei should be revised with the axonal transport methods of study.
The effects of denervation and stimulation upon synaptic ultrastructure
Authors: Rutledge L. T.
Published: January 2005

Quantitative studies of synaptic ultrastructure were made in the upper layers of cat cerebral cortex. Tissues were from intact cortex and from long‐term (chronic) undercut cortex with or without electrical stimulation. The synaptic effects of chronic electrical stimulation of denervated cortex are most readily understood as growth and remodeling of synaptic elements. Associated with chronic stimulation were increases in: symmetric membrane contacts; areas of round and flat vesicle containing terminals; dendritic shaft contacts; and synaptic contact lengths. Even without stimulation there were indications of synaptic plasticity in denervated cortex; compared with intact cortex, synapses having symmetric membrane contacts showed an increase in bouton area and an increase in synaptic contacts on dendritic shafts. These data are consistent with the observations of others in which axonal terminal growth occurred after deafferentation. But it appears that chronic electrical stimulation in the adult nervous system promotes significantly more plasticity than occurs without stimulation. In a functional sense stimulation in the present experiments produced effective inhibition which did not occur with denervation alone. Thus the plasticity observed with stimulation had both structural and functional components.
The organization of olivo‐cerebellar projections in the opossum, Didelphis Virginiane, as revealed by the retrograde transport of horseradish peroxidase
Authors: Linauts M. , Martin G. F.
Published: January 2005

The retrograde transport of horseradish peroxidase was utilized to map olivo‐cerebellar projections in the Virginia opossum. The spinal cerebellum (anterior lobe, paramedian lobule and pyramis) receive input from several separate regions in the dorsal accessory nucleus, the medial accessory nucleus and portions of the principal nucleus. Evidence is present for a topographical organization whereby specific regions of the olive project to restricted longitudinal zones. The visual‐auditory region of the posterior vermis receives input from small areas within the caudal part of the medial accessory nucleus. From a distinctly separate region of the caudal part of the medial accesssory nucleus (as well as the principle nucleus), axons project to the uvula. The vestibulo‐cerebellum is the recipient of axons from the cap of Kooy and from two spatially separate regions of the medial accessory nucleus. The cerebellar hemisphere(Crus I and II, lobus simplex) is the target of axons from the different nuclei are targeted upon separate zones. The paraflocculus was found to receive an input from the rostral part of the medial accessory nucleus and from the principal nucleus.

The present relsults suggest that a distinct olivary region may project to several widely separate areas of the cerebellum, and that one cerebellar region may revieve input from several areas of the olive. The organization of the olivocerebellar projection is highly complex, but when considered in light of known inputs to the olive, certain patterns emerge.
Distribution of catecholamine‐containing cell bodies in the rabbit central nervous system
Authors: Blessing W. W. , Chalmers J. P. , Howe P. R. C.
Published: January 2005

A recently developed fluorescence histochemical technique, which both fixes the brain in situ and converts catecholamines to fluorescent derivatives, has been utilised to study the distribution of catecholamine‐conataining cell bodies in the central nervous system of the rabbit, a species particularly suited to cardiovascular investigation.

Catecholamine‐conataining cells are widely distributed through the brain stem but are absent from the spinal cord, the cerbellum and the telencephalon. In the medulla the cells form separate ventrolateral and dorsomedial groups, while pontine cells form a continuous gruop, comprising cells of the locus coeruleus, the subcoeruleus and the ventrolateral pontine area. Fluorescent cella are widely distributed in the midbrain including an extensive group in the substantia nigra and a smaller dorsal group in the central gray matter just ventral to the aqueduct. Nearly all fluorescent forebrain cells are found in the hypothalamus, in the arcuate nucleus and in the more caudal reigons of the dorsal hypothalamus.

Although the general arragement of the catecholamine‐containing cells is similar to that of the rat there are some readily appreciated differences. Ventrolateral medullary cells are more tightly grouped in the rabbit and dorsomedial medullary cells extend forther rostrally, some being found within the dorsal motor nucleus of the vagus. Locus coeruleus cells are more loosely arranged in the rabbit and the subcoeruleus group is more extensive. Midbrain cells are closely comparable but the caudal thalamic group described in the rat is less extensive in the rabbit.
Efferent projections of the subthalamic nucleus: An autoradiographic study in monkey and cat
Authors: Nauta Haring J. W. , Cole Monroe
Published: January 2005

The efferent projections of the subthalamic nucleus were studied with the autoradiographic tracing technique in Rhesus monkey and cat. From the data it appears that the major efferent projections of the nucleus are to the pallidal complex and the substantia nigra. In both monkey and cat, the projection to the pallidal complex is truly massive and is directed at both pallidal segments. The projection field includes an infracommissural part of the pallidal complex bordering on the substantia innominata. In the monkey the termination in the pallidal complex is organized in several characteristic bands oriented parallel to the medullary laminae. The subthalamo‐pallidal projection in monkey further appears to be topographically organized. The projections to the substantia nigra is prominent in both cat and monkey though not as massive as that to the pallidal complex. The distribution of termination in the substantia nigra favors the more ventral strata near the cerebral peduncle. In the monkey the terminal distribution appears to avoid regions of the substantia nigra containing pigmented neurons and it is suggested that the subthalamonigral pathway may prefer non‐dopaminergic neurons. In addition to the above major projections, sparse projections were noted to the thalamic nuclei ventralis lateralis and ventralis anterior, to the putamen, and to the mesencephalic nucleus tegmenti pedunculopontinus, pars compacta. The findings are discussed.
Organization and development of the brain stem auditory nuclei of the chicken: Primary afferent projections
Authors: Parks Thomas N. , Rubel Edwin W.
Published: January 2005

The pattern of primary auditory projections to the brain stem of young chickens was investigated using terminal degeneration methods and orthograde transport of horseradish peroxidase (HRP) or tritiated amino acid. Of particular interest was the question of whether nucleus laminaris (NL) receives primary afferents. A study of silver‐stained degeneration patterns in nucleus magnocellularis (NM) and NL at three intervals following unilateral interruption of the cochlear nerve revealed that by 48 hours after the lesion, degenerating terminals were found only in the ipsilateral nucleus angularis (NA), NM and lagenar projection areas but not in NL. Five‐ and eight‐day survival times, however, also revealed degeneration bilaterally in NL. The appearance of terminal degeneration in NL at the longer survival times is attributed to the previously‐reported severe and rapid transneuronal degeneration of neurons in NM following deafferentation and not to the presence of cochlear nerve terminals in NL. Injection of HRP or tritiated proline into the basilar papilla produced patterns of labeling similar to that seen in the 2‐day degeneration material; HRP reaction product or autoradiographic label were seen only in the ipsilateral NA and NM and in the ipsilateral projection areas of the macula lagena but not in either NL. The patterns of primary auditory projections revealed by the three methods were quite similar to each other and to that previously reported for the pigeon and confirm the conclusion that the laminar nucleus of chickens does not receive primary afferents.
Properties of the enteric nervous system: Limitation of access of intravascular macromolecules to the myenteric plexus and muscularis externa
Authors: Gershon Michael D. , Bursztajn Sherry
Published: January 2005

The possible presence of a blood‐myenteric plexus barrier similar to the blood‐ nerve and blood‐brain barriers was investigated. The myenteric plexus was found to be an enclosed tubular structure incompletely surrounded by a sheath of supporting cell processes. Capillaries do not enter the plexus. The capillaries which supply the myenteric layer differ in structure from capillaries of other layers of the gut and are non‐fenestrated. Tracers, Evans blue labeled albumin or horseradish peroxidase, readily leak out of fenestrated capillaries, but do not readily escape from myenteric capillaries. These capillaries have impermeable junctions that prevent the passage of tracer between endothelial cells. A slow leakage of macromolecules is probably accounted for by transport through endothelial cells within plasmalemmal vesicles. A backup system of phagocytic cells removes this material and prevents the tracers leaking from the vasculature from reaching detectable concentrations in the extracellular space. Neither tracer was ever found in the myenteric plexus. Therefore, there is a blood‐myenteric plexus barrier to macromolecules that resembles the bloodthymic barrier and may be functionally analogous to the blood‐brain barrier.
The localization of the motor neurons innervating the extraocular muscles in the oculomotor nuclei of the cat and rabbit, using horseradish peroxidase
Authors: Akagi Yoshio
Published: January 2005

The localization of the motor neurons innervating the extraocular muscles in the oculomotor nuclei of adult cats and rabbits was investigated by means of retrograde labelling with horseradish peroxidase (HRP).

The groups consisting of the motor neurons innervating an individual muscle lay in the nucleus as elongated columns extending in a longitudinal direction. The position of each group in the transverse section varied according to the rostro‐caudal level of the nucleus. In the cat and rabbit, entire contralateral innervation of the superior rectus and entire ipsilateral innervation of three muscles of the inferior rectus, medial rectus and inferior oblique were similarly observed. However, the arrangement of individual motor groups differed considerably in both animals except for the group innervating the inferior rectus which was generally found in the ventral position running through the rostral two‐thirds of the oculomotor nucleus.

In the case of cats, the central caudal nucleus bilaterally innervated the levator palpebrae superioris. The motor neurons innervating this muscle in the rabbit (which lacks the central caudal nucleus) formed a rostro‐caudal club‐shaped column close to the group innervating the superior rectus.

The aberrant cellular mass in the adjoining medial longitudinal fasciculus which belongs to the medial rectus appears to play an important role in the eye movement, because it commonly appears in various animals.
A comparison of projections of entopeduncular neurons to the thalamus, the Midbrain and the habenula in the cat
Authors: Filion Michel , Harnois Carmen
Published: January 2005

Anatomical studies have demonstrated that the output of the striopallidal system is distributed to two areas of the thalamus: the ventrolateral‐vertroanterior and the centromedian nuclei. The two areas are involved in different ways in the control of somatic motor activity. Pallidal efferents are also distributed to a still obscure tegmental area in the midbrain, the pedunculopontine nucleus, and to the lateral habenular nucleus, a structure of the limbic system. The present study compares the projections of entopeduncular neurons to the four sites in cats. The comparison is based on an estimation of the number of entopeduncular neurons sending fibers to each site and branching to more than one site. The four projection sites were stimulated electrically in anesthetized cats and the number of entopeduncular neurons excited antidromically were counted.

At least 68% of entopeduncular neurons were excited antidromically by stimulation of the ventrolateral nucleus, an equal number were excited antidromically by stimulation of the nucleus centromedian and slightly fewer but still more than 50% by stimulation of the pedunculopontine nucleus. The three sites gave rise to antidromic responses of the same entopeduncular neuron in at least 33% of the cases. Only 25% of entopeduncular neurons responded antidromically to stimulation of the lateral habenular nucleus exclusively (one‐third) or not (two‐thirds). Some neurons recorded incidentally in the globus pallidus responded antidromically to the stimulation sites. Neurons were also recorded in the preoptico‐hypothalamic area and 67% responded antidromically exclusively to the stimulation of the lateral habenular nucleus.
Differential projections of cat medullary raphe neurons demonstrated by retrograde labelling following spinal cord lesions
Authors: Martin R. F. , Jordan L. M. , Willis W. D.
Published: January 2005

Neurons of the medullary raphe nuclei in cats were retrogradely labelled following injection of horseradish peroxidase (HRP) into the L6 spinal cord segment. Brainstems were cut in sagittal section to facilitate examination of the rostral‐caudal extend of raphe neurons projecting to the spinal cord. Large numbers of HRP‐labelled neurons were found in nucleus raphe magnus, nucleus raphe pallidus, and nucleus raphe obscurus (as well as a few neurons in nucleus raphe pontis). Dorsal or ventral hemisections at the T12‐L1 level restricted HRP retrograde transport to those pathways within the intact portion of spinal cord, allowing a determination of the part of the cord through which raphe neurons project to the lumbar enlargement. Neurons of nucleus raphe magus were found to project primarily in dorsolateral fasciculus. A significant number of neurons of nucleus reticularis gigantocellularis also project in dorsolateral fasciculus. Nucleus raphe obscurus neurons were found to project primarily in ventral funiculus, while nucleus raphe pallidus neurons project in the ventrolateral fasciculi and ventral funiculus. The serotonergic (5HT) fibers described by Dahlström and Fuxe ('65) to terminate in the dorsal horn, intermediolateral cell column, and ventral horn are likely to coincide with the raphe‐spinal projections documented in this work.
Anatomical and physiological properties of ipsilaterally projecting spinothalamic neurons in the second cervical segment of the cat's spinal cord
Authors: Carstens Earl , Trevino Daniel L.
Published: January 2005

Anatomical and electrophysiological methods were used to investigate the projections and response properties of neurons in the second cervical (C2) spinal segment of the cat giving origin to a previously undescribed projection to the ipsilateral thalamus.

The method of retrograde axonal transport of horseradish peroxidase (HRP) was used to identify neurons in C2 giving rise to thalamic projections. Following large (3.0 μl) thalamic HRP injections, a large numbers of labeled neurons was observed in lateral laminae VII–VIII of C2 ipsilateral to the injections. They occurred as small clusters of cells along the longitudinal axis of C2. Labeled neurons were also observed contralaterally in the lateral cervical nucleus, dorsal horn (especially medial lamina VI), and loosely distributed in the ventral horn. The ipsilaterally projecting neurons were also labeled following small (0.2–0.5 μl) HRP injections restricted to individual spinothalamic terminal zones (intralaminar nuclei, ventrobasal complex‐nucleus ventralis lateralis border zone, medial division of the posterior nuclei), indicating that as a group they project widely throughout the thalamus.

Single unit recording methods were used to obtain complementary information on the functional properties of these neurons. The antidromic stimulation method was applied to identify units in C2 projecting to the ipsilateral thalamus in anesthetized, paralyzed cats. Three categories of ipsilaterally projecting C2 units were identified: (i) units not driven by any type of natural stimulation; (2) units having large cutaneous receptive fields (RFs) and wide dynamic response ranges (“widefield”), and (3) units with smaller RFs and varied properties (“other”).

Widefield units with bilaterally symmetrical and asymmetrical RFs were observed. Co‐stimulation of different portions of an excitatory RF produced summation of the unit response. Inhibitory RF components were identified in one third of the widefield units. Unit recordings after spinal tract lesions revealed that the afferent input passed via the ipsilateral lateral and/or ventral funiculi. Widefield unit responses to somatosensory stimuli could be inhibited by dorsal column conditioning stimulation. Several “other” units resembled widefield units, while a second group had small RFs restricted to the C2 dermatome.

Possible functional roles of the projecting C2 neurons in somatosensory and non‐specific systems are discussed.
A histochemical study on the innervation of cerebral blood vessels in the bullfrog
Authors: Tagawa Takasuke , Andō Kōichi , Wasano Takeo , Iijima Tadahiko
Published: January 2005

Specific histochemical techniques for the demonstration of catecholamine and acetylcholinesterase have been used to study the distribution of adrenergic and cholinergic nerves on the cerebral blood vessels of bullfrog, Rana catesbeiana.

The adrenergic nerve meshworks on the cerebral arteries of bullfrog were less dense, had a more elongate appearance along the arterial axis as compared with those of mammals and were rather similar to those of snakes. The nerve plex‐uses on the cerebral carotid artery and its main branches were somewhat denser than those on the basilar artery.

The most characteristic feature of innervation in the bullfrog cerebral vessels was that no acetylcholinesterase‐positive fibres were observed on the extraparenchymal arteries, whereas, in all higher vertebrates investigated so far, the cerebral arteries have been found to be dually innervated although differences in the density of innervation of the two nerves may exist. This suggests that the peripheral adrenergic innervation on the cerebral blood vessels appeared earlier than the cholinergic one in the evolution of vertebrates.

On the other hand, both adrenergic and acetylcholinesterase‐positive fibres were observed in close contact with parenchymal arterioles and capillaries suggesting the possible existence of a dual central innervation. This feature, however, was by no means common. Thus, the central neurons have a significant influence on the cerebral circulation in the bullfrog is somewhat equivocal.

Most of the pial and the parenchymal small vessels and the parenchymal capillaries exhibited a heavy acetylcholinesterase activity on the vascular walls. Although the significance of the enzyme is obscure as yet, this has to be considered in relation to the regulatory mechanism of the cerebral circulation.
Quantitative analysis of nerve fibre densities in the cochlea of the house mouse (Mus musculus)
Authors: Ehret Günter
Published: January 2005

Transverse sections of the cochlear nerve, silver‐stained surface preparations of the cochlea, and silver‐ and osmium‐stained tangential sections of the cochlea of the house mouse were made to determine the number and density of nerve fibres entering the organ of Corti and their distribution to inner and outer hair cells along the cochlear spiral. A number of 12,578 ± 819 fibres was counted within the cochlear nerve, which is almost equal to the total number of 12,350 ± 810 fibres entering the organ of Corti. The 12,350 fibres divide into 9,780 (≙ 79%) fibres running to the inner hair cells, 703 (≙ 6%) basilar (afferent) fibres and 1,867 (≙ 15%) upper tunnel radial (efferent) fibres innervating the outer hair cells. About 93% of all afferent fibres are connected to the inner hair cells, and only 7% innervate outer hair cells. The density of fibres running to the inner hair cells varies considerably and has a significant (p < 0.01) absolute and relative maximum 3.7 mm and 2.9 mm from the apex respectively (total length: 6.84 mm) and decreases toward apex and base. The density of afferent fibres running to the outer hair cells shows a slow increase up to 2 mm from the apex, and remains on a constant low level (5.5 fibres per 40 μm) down to the base. The density of efferent fibres running to the outer hair cells increases linearly up to about 2 mm from the apex, remains rather constant (10 fibres per 40 μm) from 2 mm to 4 mm, and then decreases toward the base. Generally, the outer hair cells show a convergent innervation pattern, the inner hair cells a divergent one. The significance of the present measurements is discussed in relation to respective results from other mammals and in relation to auditory thresholds.
The posterior lateral line lobe of certain gymnotoid fish: Quantitative light microscopy
Authors: Maler Leonard
Published: January 2005

The posterior lateral line lobe of the wave species of gymnotoid fish was investigated with the Golgi technique. The posterior lobe has a laminar structure and contains II cell types differentially distributed in the various laminae (fig. 13). The major laminae, from ventral to dorsal are the deep fiber layer, containing multipolar neurons; the deep neuropil layer, containing ovoid neurons and a sub‐lamina of spherical cells; the granule cell lamina, containing two types of granule cell; the plexiform laminae; the polymorphic cell lamina, containing basilar pyramids, non‐basilar pyramids, giant fusiform cells, and polymorphic cells; the stratum fibrosum; the molecular lamina, containing neurons of the ventral molecule layer and stellate cells.

The spherical cells are regularly distributed in their sub‐lamina and appear to receive one type of primary afferent input. Another type of primary afferent input ends in the deep neuropil and granule layers, in proximity to the basilar dendrites of the granule cells and of the basilar pyramids. The basilar pyramidal cell spatially alternates with the non‐basilar pyramidal cell, so that the basilar dendritic trees of nearest‐neighbour basilar pyramids show almost no overlap.

Descending input to the posterior lobe ends in the molecular layer, in proximity to apical dendrites of both pyramidal cells, giant fusiform cells, polymorphic cells, and one type of granule cell. There are three afferent fiber systems in the molecular layer, one running transversely, one longitudinally, and one vertically. Local circuitry in the posterior lobe is precisely organized and involves projections of granule cells onto overlying pyramidal cells. The polymorphic cell may also be involved in the intrinsic circuits of the posterior lobe.
Patterns of cell proliferation in the retina of the clawed frog during development
Authors: Beach D. H. , Jacobson Marcus
Published: January 2005

Quantitative assays of the spatial pattern of cell production in the developing retina of Xenopus have been made using 3H‐thymidine labelling and colcemid blockade of mitosis. Reconstructions were made from serial sections showing the position of every mitotic figure in the retina. After stage 54 the number of mitotic figures decreases at the dorsal margin of the retina and increases at the ventral margin. The ventral:dorsal ratio of mitoses reaches 10:1 by metamorphosis. Density of mitotic figures is maximum at the point of entry of the ophthalmic vessels at the ventral margin. In spite of asymmetrical production of retinal cells the cell density remains constant throughout the retina, probably as a result of displacement of retinal cells dorsally to compensate for the relatively greater proliferation ventrally. It is also proposed that the asymmetrical retinal growth serves to maintain the relationship between each point in visual space and corresponding points in the two retinae as the eyes are displaced dorsally on the head during metamorphosis.
The generation of neurons involved in an early reflex pathway of embryonic mouse spinal cord
Authors: Sims Terry J. , Vaughn James E.
Published: January 2005

The generation of lateral motor neurons (LMNs), interneurons and dorsal root ganglion (DRG) neurons of the cervical mouse spinal cord has been investigated by [3H]thymidine autoradiographic techniques. This investigation has two main objectives: (a) to determine on which embryonic days these three neuronal populations are born, and (b) to investigate the possibility that the neurons comprising early reflex circuits might be formed by a retrograde temporal sequencing of generation. LMNs are the first neurons generated in the cervical spinal cord. They arise between E8.8 and E11.5, and approximately 90% of these cells are born within a 36‐hour period between E9 and E10.5. The earliest time of origin for interneurons is on E9.5, and those cells which are generated between E9.5 and E10.5 cluster in two distinct regions of the adult spinal cord. One of these regions is the lateral portions of laminae IV through VI; this appears to be the location of many ipsilateral association neurons. DRG neurons begin to arise on E9.5 and their generation is completed by E14. There is a trend within the DRG population for large neurons to be born before small neurons. Those cells with diameters of 40 μm or greater reach their generation peak on E10.5, while those smaller than 40 μm arise in the greatest numbers on E12.

The findings of other investigations have provided evidence for a retrograde sequence of synaptic closure in the formation of the early disynaptic forelimb reflex pathway. The temporal difference in synapse formation in the terminal fields of DRG and association neurons is discussed in terms of our observation that both of these populations appear to have similar generation times. We suggest that factors responsible for the delayed synaptic closure of DRG afferents include the greater distances and the degree of collateralization which these afferents must undergo in order to establish their terminal fields. Finally, we discuss the possibility that the temporal sequence of neuronal generation and factors involved with the growth of neurites combine to produce a retrograde sequence of synaptic closure in the early disynaptic forelimb reflex pathway of mouse spinal cord.