bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptic reorganization in the motor trigeminal nucleus of the rat following neonatal 6‐hydroxydopamine, treatment
Authors: Hemmendinger Lisa M. , Moore Robert Y.
Published: January 2005

The synaptic organization of the motor trigeminal nucleus in adult rats treated neonatally with 6‐hydroxydopamine (6‐OHDA) was investigated quantitatively and compared with control nuclei. No statistically significant change was detected in the distribution of axon terminals in the neuropil, and the total number of axosomatic contacts per unit length of membrane was identical in the control and 6‐OHDA‐treated groups. However, 6‐OHDA treatment causes a significant redistribution of the four morphologically distinct bouton populations forming axosomatic contacts with trigeminal motoneurons. Terminals containing lucent axoplasm and spherical synaptic vesicles have been identified as norepinephrine neuron terminals (Card et al.: J. Comp. Neurol. 250:469‐484, '86). These and terminals with lucent axoplasm and pleomorphic vesicles are increased in number whereas terminals with dense axoplasm and either spherical or pleomorphic synaptic vesicles are decreased in number in the 6‐OHDA‐treated brains compared to controls.

These results confirm that the norepinephrine hyperinnervation observed in histofluorescence preparations following neonatal 6‐OHDA treatment reflects an increase in absolute numbers of norepinephrine terminals. The finding that the total number of axosomatic contacts per unit length of membrane remains constant while the proportions of individual afferent classes vary may indicate that the trigeminal motoneuron plays a major role in determining the overall density but not necessarily the individual specificity of its axosomatic innervation.

The motor trigeminal nucleus is a useful model system in which to investigate both the response of norepinephrine fibers to neonatal 6‐OHDA treatment and the respective roles of a target neuron and its afferents in the regulation of appropriate quantitative innervation patterns in the central nervous system.
Thalamic inputs to visual areas 1 and 2 in the rabbit
Authors: Weyand Theodore G. , Swadlow Harvey A.
Published: January 2005

Thalamic projections to two cortical representations of the visual field, visual areas 1 and 2 (V1, V2), in the rabbit were studied by using the retrograde transport of horseradish peroxidase (HRP). Physiological guidance was employed to inject small amounts of HRP into topographically defined regions of V1 or V2. Injections restricted to V1 revealed a dense projection from the dorsal lateral geniculate nucleus as well as projections from the pulvinar, the posterior thalamic nucleus, and the ventral lateral nucleus. Injections restricted to V2 revealed projections from the pulvinar, the ventral lateral nucleus, and the posterior thalamic nucleus, but only a slight projection from the dorsal lateral geniculate nucleus. V2, but not V1, receives an input from neurons within the fiber plexus between the dorsal lateral geniculate nucleus and the pulvinar. Finally, the neurons in the lateral geniculate nucleus that project to V2 have larger somata on average than those that project to V1 (x + 18.25 μm vs. 14.04 μm, P <.001).
Myeloarchitecture of the cerebellum of the chicken (Gallus domesticus): An atlas of the compartmental subdivision of the cerebellar white matter
Authors: Feirabend H. K. P. , Voogd J.
Published: January 2005

A myeloarchitectonic atlas of the longitudinal (or mediolateral) subdivision of the cerebellum of the chicken (white Leghorn) was prepared from serial Häggqvist or toluidine‐blue‐stained sections of five animals. This myeloarchitectonic subdivision is based on the alternate occurrence of large fiber accumulations (LFAs) and small fiber areas (SFAs) in the cerebellar white matter and allows the distinction of a number of parasagittal fiber compartments, each of which consists of a medial LFA and a lateral SFA.

The compartmental subdivision of the cerebellar white matter in mammals and birds derives its importance from the fact that essentially it corresponds to the organization of the afferent and efferent connections of the cerebellar cortex. The simple structure of the avian cerebellum makes it ideally suited for a complete description of its compartmental subdivision and may serve as a natural system of coordinates in future anatomical and physiological studies.

The number of fiber compartments that can be counted in the chicken cerebellum on either side of the midline varies from six (in the narrowest folium I) to nine (in the widest folia IX and X) and is approximately the same as in mammals, in which a maximum of eight or ten compartments can be recognized. On the basis of the organization of its myeloarchitecture and the otherwise relatively scarce data on the organization of the connecitons of its cortex, it can, therefore, be postulated that the avian cerebellum is the homologue of the entire mammalian cerebellum. In addition, the present knowledge of the connections of the cerebellar cortex in birds indicates that the avian compartments 1—3 may correspond to the mammalian compartments A1, A2, and A3 (or X), whereas the avian compartment 4 or 5 (or both) may represent the mammalian B compartment. Lack of further anatomical data so far precludes conclusions on a possible homology between the avian compartments 6–9 and the mammalian C and D compartments.
Development of reticulospinal neurons of the zebrafish. I. Time of origin
Authors: Mendelson Bruce
Published: January 2005

The times of origin (birthdays) of identifiable types of reticulospinal (RS) neurons of the zebrafish (Brachydanio rerio) were determined in order to learn if differences in neuronal characteristics among cell types correlate with differences in their times of origin. The RS neurons are located in the midbrain and hindbrain and cell types can be identified by differences in their cell body sizes and positions, axonal projections, and dendritic arborizations (Metcalfe et al., J. Comp. Neurol. 251: 147–159, 1986). In this study, the birthdays of RS cells were determined by combining 3H‐thymidine autoradiography with horseradish peroxidase histochemistry.

The RS neurons that were examined were generated between 7 and 28 h after fertilization. Each cell type had a specific time of origin. Dorsally located neurons were always generated earlier than ventral neurons present at the same axial level. Often, but not always, larger and more lateral neurons were born earlier than smaller and more medial ones. There was no overall rostrocaudal gradient of neuronal generation and no overall correlation between time of origin and axonal pathway. However, the times at which RS neurons are generated may be important with respect to the establishment of their characteristic dorsoventral positions in the brain.
Collateralization of descending pathways from the brainstem to the spinal cord in a lizard, Varanus exanthematicus
Authors: Wolters J. G. , De Boer‐Van Huizen R. , Donkelaar H. J. Ten , Leenen L.
Published: January 2005

With the multiple fluorescent retrograde tracer technique, the collateralization in the spinal cord of descending supraspinal pathways was studied in a lizad, Varanus exanthematicus. Fast Blue (FB) gels were implanted unilaterally in the spinal gray matter of the cervical enlargement and Nuclear Yellow (NY) gels were implanted ipsilaterally in two series of experiments in all spinal funiculi of the lumbar enlargement or in midthoracic spinal segments, respectively. All brainstem nuclei known to project to the spinal cord in reptiles were found to give rise to branching axons that may influence widely separate levels of the spinal cord. The number of double‐labeled FB‐NY cells varied in these brainstem nuclei from none to half the number of neurons projecting to the cervical enlargement. Highly collateralizing projections (expressed as the percentage of double‐labeled neurons, DL) were found to arise from the nucleus raphes inferior, the contralateral nucleus reticularis superior pars lateralis, the contralateral nuclei vestibulares ventromedialis and descendens, and the ipsilateral nucleus reticularis inferior pars ventralis. A lower percentage of DL neurons was noted for the contralateral nucleus ruber and bilaterally for the nucleus reticularis medius and nucleus reticularis inferior. Extensive brainstem projections directed to cervical and high thoracic spinal levels originate from the area lateralis hypothalami, the nucleus of the fasciculus longitudinalis medialis, the contralateral nucleus cerebellaris medialis, and from the nucleus tractus solitarii. Projections preferentially directed to midthoracic or lower levels of the spinal cord were found to arise from the ipsilateral locus coeruleus, the contralateral nucleus reticularis superior pars lateralis, the nucleus reticularis inferior pars ventralis, the nucleus reticularis inferior, and the nucleus raphes inferior. In contrast to findings in mammals, in Varanus exanthematicus the red nucleus, the nucleus vestibularis ventrolateralis, and certain parts of the reticular formation did not display a clearcut somatotopic organization.

In general two different patterns of collateralization can grossly be discerned: (1) a gradual decrease of spinal coaterals caudalward, which can be interpreted as a certain specificity of such projections; and (2) a constant number of collateral nerve fibers throughout the spinal cord that can be interpreted as either a nonspecific or, in contrast, a highly specific system, focussed exclusively on the cervical and lumbar enlargements.
Regional specialization in synaptic input and output in an identified local nonspiking interneuron of the crayfish revealed by light and electron microscopy
Authors: Kondoh Y. , Hisada M.
Published: January 2005

Lateral inhibition of several mechanosensory interneurons in the crayfish terminal ganglion is mediated by a pair of identified local nonspiking interneurons called local directionally selective (LDS) interneurons. The ultrastructure and synaptic distribution of these interneurons were investigated by using intracellular labeling with horseradish peroxidase for electron microscopy.

The LDS interneuron has bilateral, asymmetric arborizations. They are connected by a thick transverse neurite on which no synapses are made. The neurites on the side ipsilateral to the cell body are smooth and receive almost entirely input synapses. On the other hand, the contralateral neurites have prominent numerous swellings or varicosities from which many short fine spines arise, with intermingled input and output synapses. Both synapses, however, are not always associated with varicosities and spines. Presynaptic neurites of the LDS interneuron contain only round agranular synaptic vesicles in the vicinity of synaptic specializations. These morphological findings correlate well with the physiology of this interneuron: it is functionally polarized to receive input on one side (ipsilateral to the cell body) of the ganglion and convey it to the other side.
3H‐nicotine and 125I‐alpha‐bungarotoxin‐labeled nicotinic receptors in the interpeduncular nucleus of rats. I. Subnuclear distribution
Authors: Hamill Geoffrey S. , Clarke Paul B. S. , Pert Agu , Jacobowitz David M.
Published: January 2005

The distribution of nicotinic receptors within the interpeduncular nucleus (IPN) was determined in male rats following in vitro labeling with the cholinergic ligands 3H‐nicotine and 125I‐alpha‐bungarotoxin (BTX). Autoradiographic images of two rostrocaudal levels of IPN were analyzed by computer‐assisted densitometry and the optical density contributed by displaceable labeling was determined in the rostral, central, intermediate, and lateral subnuclei.

3H‐nicotine labeling density within the four subnuclei differs significantly at both levels of IPN. The greatest density of labeling is localized in the rostral subnucleus, followed in order of diminishing density by the central, intermediate, and lateral subnuclei. Labeling within the rostral subnucleus is prominently localized within its central zone. In the central subnucleus, a dense concentration of binding sites is apparent in the middle region, adjacent to less dense vertically oriented columns; 3H‐nicotine binding sites in the lateral subnuclei appear to be most concentrated medially, adjacent to the intermediate subnuclei.

125I‐BTX labeling density within the four subnuclei also differs significantly at both levels of IPN. The greatest density of labeling is found in the rostral subnucleus, followed in order of decreasing density by the lateral, central, and intermediate subnuclei. The ovoid regions of the rostral subnucleus contain dense 125I‐BTX labeling. In the lateral subnuclei, 125I‐BTX binding appears to be predominantly along the lateral margins of the subnucleus.

The present data indicate that the IPN contains two distinct populations of putative cholinergic nicotinic receptors identified, respectively, by 3H‐nicotine and 125I‐BTX labeling. Each population of labeled receptors is uniquely localized in patterns that suggest differences in density within and across subnuclei.
Development of anomalous retinal projections to nonvisual thalamic nuclei in syrian hamsters: A quantitative study
Authors: Frost Douglas O.
Published: January 2005

When two of the principal targets of retinofugal axons, the superior colliculus and dorsal nucleus of the lateral geniculate body, are ablated in newborn hamsters and the somatosensory (ventrobasal) or auditory (medial geniculate) thalamic nuclei are partially deafferented, the optic axons form permanent, abnormal connections in the latter nuclei. The lateral posterior nucleus of the operated hamsters also receives an anomalously large retinal projection. Here, we report on the results of a quantitative study that was undertaken in order to elucidate how these abnormal connections are formed.

In normal, newborn hamsters, there is a transient retinal projection to the ventrobasal nucleus that disappears 3‐‐4 days postnatally. Our quantitative data show that postoperatively, the volume of the retino‐ventrobasal projection increases proportionately more than the volume of the ventrobasal nucleus so that the retino‐ventrobasal projection in operated adult hamsters is due both to the stabilization of the normally transient projection and to a reactive sprouting that increases the size of the projection. The retino‐medial geniculate projection arises de novo by reactive sprouting of optic tract fibers that normally pass over and through the nucleus; in unoperated hamsters, terminating projections are never seen at any age. The quantitative data also show that the anomalously large retino‐lateral posterior projection is due almost entirely to the reactive sprouting of the normal projection and/or normal fibers of passage that are already present on the day of birth, although it is possible that a minor component can be attributed to the stabilization of a small population of normally transient retino‐lateral posterior axons.

The present results demonstrate that the transient retino‐ventrobasal axons in normal, newborn hamsters are capable of making permanent connections with ventrobasal neurons. This finding raises the important question of the cellular mechanisms that determine whether immature neuronal connections are stabilized or eliminated. The results also suggest that during both normal and abnormal development, the choice of a target by growing axons may depend upon the axons being in proximity to a potential terminal site just at the time when that site is capable of receiving afferents.
Grafted septal neurons form cholinergic synaptic connections in the dentate gyrus of behaviorally impaired aged rats
Authors: Clarke D. J. , Gage F. H. , Nilsson O. G. , Björklund A.
Published: January 2005

A group of aged, behaviorally impaired rats received suspension grafts of fetal septal‐diagonal band tissue into the otherwise intact hippocampal formation. Three months after grafting, behaviorally recovered rats were studied by immunocytochemistry by using monoclonal antibodies to choling acetyltransferase (ChAT) and electron microscopy. The innervation of the host dentate gyrus by graft‐derived ChAT‐positive fibres was unmasked by acute removal of the intrinsic septal cholinergic innervation by fimbriafornix transection 5‐‐7 days before perfusion. The pattern of termination and ultrastructural connectivity were compared with previous results obtained from both young nonoperated control animals and a group of young rats with intrahippocampal septal grafts that had been subjected to denervation of the intrinsic cholinergic input at the time of transplantation.

Graft‐derived, ChAT‐immunoreactive terminals formed abundant synaptic speciliazations with neuronal elements in the host dentate gyrus. The predominant postsynaptic target (about 65% of all boutons) was dendritic shafts, whereas about 20% of the boutons contacted dendritic spines. Very few synapses onto neuronal perikarya were found in the grafted aged rats. In some of these cases, however, it was possible to identify the target as dentate granule cells. This situation is very similar to that seen in young control rats but significantly different than the distribution observed in the denervated young grafted group, where axosomatic contacts predominated.

The results indicate that the graft‐induced behavioral improvement seen in the aged rats may depend on the formation of functional cholinergic graft connections with neuronal elements in the host hippocampal formation.
Morphological alterations in subcortical vibrissal relays following vibrissal follicle destruction at birth in the mouse
Authors: Hámori J. , Savy C. , Madarász M. , Somogyi J. , Takács J. , Verley R. , Farkas‐Bargeton E.
Published: January 2005

Morphological modifications of two subcortical vibrissal relays were analyzed, following destruction of vibrissal follicles in newborn mice. The volume of the nucleus interpolaris (NI) of the trigeminal nuclear complex in the brainstem decreased by 33%, while the number of its neuronal perikarya decreased only moderately. Vibrissal deafferentation caused no shrinkage of the ventrobasal complex (VB). In the damaged medial vibrissal part of VB (VBm), however, neuronal density was higher than normal, indicating the prevention or retardation of physiologically programmed cell death in the afferentation deprived thalamic somatosensory relay station. It is suggested that the difference in neuron density produced by deafferentation is related to the states of maturation at birth of the two subcortical vibrissal relays.

Following vibrissal deafferentation the basic organization of the synaptic neuropil appeared to be similar to the control. Quantitative electron microscopic (EM) analysis revealed, however, an increased number of axon terminals with ovoid synaptic vesicles in both deafferented relay stations. The increased density of gamma‐aminobutyric acid (GABA)‐immunostained boutons observed in the VBm following vibrissal deprivation suggested a compensatory increase most probably of the inhibitory axon endings.

Quantitative EM analysis also provided evidence that many or most of the specific afferent terminals in the damaged VBm were not identical with but were substitutes for the original “vibrissal” specific afferents. Forty percent of all “specific” afferents were shown to be modified corticothalamic terminals. The modification and the resemblence of some cortical endings to specific afferents demonstrated the morphogenetic plasticity of synaptogenesis in these terminals during development as well as the importance and inductive potential of the postsynaptic target in the differentiation of presynaptic axon terminals.
Stages in the structural differentiation of retinal ganglion cells
Authors: Maslim Juliani , Webster Maree , Stone Jonathan
Published: January 2005

Using a cultured wholemount technique we have studied the morphological differentiation of ganglion cells in the retina of the rat and cat, during normal development. In both species the differentiation of ganglion cells begins in embryonic life, before embryonic day (E) 17 in the rat and E36 in the cat.

It is useful to describe the morphological differentiation of ganglion cells as occurring in three stages. In the first stage, each germinal cell becoming a ganglion cell extends an axon into the fibre layer of the retina and towards the optic disc, and the soma of the cell moves towards the ganglion cell layer. As the soma approaches the ganglion cell layer, the processes that attach its poles to the inner and outer surfaces of the retina are withdrawn.

When the soma reaches the ganglion cell layer, a stage of active dendritic growth begins, which lasts until shortly before birth in the cat and until several days after birth in the rat. The cell extends stem dendrites that branch profusely and are commonly tipped by growth cones. The major morphological classes of ganglion cell become distinct in the latter part of stage 2, as do the centroperipheral gradients in ganglion cell size apparent in the cat.

During the third stage, the dendritic trees of ganglion cells no longer branch or extend by means of active growth cones. Very considerable growth of all parameters of the cell (soma size, dendrite calibre and length, axon calibre) occurs nevertheless, presumably by interstitial addition of membrane throughout the cell.
Map of retinal position onto the cross section of the optic pathway of goldfish
Authors: Bernhardt R. , Easter S. S.
Published: January 2005

The position of a retinal cell is defined by the two polar coordinates: r, the distance from the optic disc, and θ the angular (or clock‐face) position. Axons of similar θ value were labeled by the punctate application of horseradish peroxidase (HRP) to optic axons in the retina, and axons of similar r‐value were labeled by the application of this same marker to a tectal fascicle. Labeled axons were traced in serial transverse sections of the optic pathway from the retina to the tectum to learn the map of the retinal surface onto the cross section of the pathway. Retinas were flat‐mounted and treated for HRP to show the retinal origins of the labeled axons.

Axons of similar r were clustered together, and the fraction of the pathway's cross‐sectional area occupied by the cluster was about the same as the fraction of the retinal area occupied by the group of labeled somata. Axons of similar θ were also clustered, but the fraction of the cross‐sectional area they occupied was larger than the fraction of retinal area occupied by their somata. The geometry of the clusters of labeled axons depended on the proximodistal location in the pathway. Near the retina both were stripshaped, but the location and orientation of the strip varied. Both an r‐strip and a θ‐strip were labeled in some pathways by dual applications of HRP; the two strips were mutually orthogonal at all levels.

Each of r and θ mapped onto a separate axis. The axons from most peripheral retina (largest r) were everywhere adjacent to the pia, and axons of progressively more central retina (smaller r) were progressively more separated from the pia (except in the nerve, where the secondary fasciculation complicates the geometry by wrapping old axons in new pia). The map of the circular variable, θ onto a line, required a discontinuity, the location of which differed, depending on the proximodistal level. From the retina to the chiasm, the discontinuity was at the ventral retinal radius (i.e., the right retinal clock‐face positions were ordered 6‐9‐12‐3‐6 o'clock across the line); just central to the chiasm, the fibers reordered to put the discontinuity at the nasal radius (clock‐face positions ordered 3‐6‐9‐12‐3); at the brachial bifurcation, the 3‐6‐9 half turned dorsally, the 9‐12‐3 half, ventrally.

The results are discussed in the context of the growth of the pathway and compared with similar organizational plans in the optic pathways of other vertebrates.
Organization of corticogeniculate projections in the turtle, pseudemys scripta
Authors: Ulinski Philip S.
Published: January 2005

The efferent pathways from the visual cortex to the dorsal lateral geniculate complex of turtles have been studied by using the orthograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP in the lateral thalamus retrogradely label neurons throughout the visual cortex. The majority of labeled neurons have somata in layer 2 of the lateral part of dorsal cortex (D2); a minority have somata in layer 3. Labeled neurons in layer 2 tend to have vertically oriented, fusiform somata and dendrites that ascend into layer 1. Labeled neurons in layer 3 have fusiform somata and dendrites, both oriented horizontally. Injections of HRP in visual cortex orthogradely label corticofugal axons. Those projecting to the lateral geniculate complex course laterally from the visual cortex, pass through the striatum (occasionally bearing varicosities), and enter the diencephalon in the ventral peduncle of the lateral forebrain bundle. Individual axons leave the ventral peduncle and run dorsally in the transverse plane, entering the dorsal lateral geniculate complex from its ventral edge. They continue dorsally, principally in the cell plate of the geniculate complex, where they bear varicosities.
Ontogeny of the area centralis in the cat
Authors: Robinson Stephen R.
Published: January 2005

Previous studies have shown that after embryonic day 50 (E50) the kitten retina undergoes a relatively rapid period of maturation that begins at the area centralis and spreads toward the retinal periphery. The mechanism controlling this pattern is unknown. One possibility is that the area centralis is the most developmentally advanced region of retina from the earliest stages of eyecup formation. The present study tests this hypothesis.

Retinae from ten kittens aged between E21 and E54 were sectioned horizontally at 10 μm and stained with haematoxylin and eosin. During the earliest stages of development in other vertebrate species, the oldest part of the retina is at the posterior pole of the eyecup, just dorsal to the optic fissure. At E21 in the kitten retina, this site appeared to be developmentally advanced by several criteria. A developmentally advanced region (DAR) was recognized at each subsequent age. It gradually became displaced temporally toward the site of the area centralis in the adult. Developmental events beginning here include the formation of cell‐free channels at the vitreal margin; the appearance of the first ganglion cells and their axons; the formation of continuous inner and outer plexiform layers; the differentiation of cells in the ganglion cell, inner, and outer nuclear layers; and the cessation of cytogenesis at the outer limiting membrane. By E54 the DAR could be recognized as the area centralis by the criteria used in the adult.

Between E25 and E37 cell density in the ganglion cell layer is higher in the DAR than at other retinal eccentricities. During the E40s cell density becomes uniform across the retina because more cells migrate into the ganglion cell layer in peripheral retina than in the DAR. Several observations suggest that cells added to the ganglion cell layer from E37 onward are not ganglion cells.

The proportion of retinal area occupied by the DAR decreases geometrically between E21 and E54, indicating that this region grows at a slower rate than the rest of the retina. It is suggested that this differential growth combined with differential cell addition may be the principal mechanism responsible for generating centroperipheral cell gradients in the retina.
Fate of uncrossed retinal projections following early or late prenatal monocular enucleation in the mouse
Authors: Godement Pierre , Salaün Josselyne , Métin Christine
Published: January 2005

In mammals binocular vision is made possible by the existence in the temporal retina of ipsilaterally projecting ganglion cells (IGCs) (with axons that do not cross the brain midline and join optic fibers from the opposite eye). To learn whether early interactions between fibers of each eye play a role in generating a mixed ipsi + contralateral projection pattern, we studied with horseradish peroxidase the origin of uncrossed retinal projections in mice that developed after one eye was destroyed at very early embryonic ages. One eye was removed on embryonic day 16 (E16; when optic fibers have grown past the chiasm bilaterally, but very few have grown into the visual centers) or on E13 or E12 (when few or no optic fibers have passed the presumptive chiasm region).

Normal adult mice have a mean of 946 IGCs (range: 784–1,073) within the temporal sector of the retina, and less than 25 in the rest of the retina. In adult mice enucleated at E16, an average of 1,354 (1,215–1,484) IGCs are present within a clearly demarcated temporal sector of the remaining retina and 265 (152–312) are present throughout the rest of the retina. In both the temporal and nasal retina the excess IGCs in these mice have, generally, very small somas. In some of these mice the most peripheral part of the temporal sector contains fewer IGCs. In E12 or E13 enucleates, IGCs are also generally located in a narrow (often narrower than normal) region along the temporo‐inferior retinal border, but their number is less than in normal or E16‐enucleated mice: E13 enucleates have a mean of 639 cells (range: 361–875) in the temporal sector and 109 (8–275) in the rest of the retina. Following enucleation of one mouse at E12, the respective values are 349 and 31 cells. The reduction in numbers of IGCs in these mice is especially pronounced for ganglion cells with small cell bodies.

These findings suggest that the development of uncrossed projections in mice depends on selective guidance mechanisms of axons from temporal retina through the chiasm. These may consist of interactions of optic axons with guidance cues distributed in the presumptive chiasm (possibly at early stages) and also of fiber‐fiber guidance mechanisms, in particular between fibers from each eye.
Fine structural studies of growth‐hormone‐releasing‐factor (GRF)‐immunoreactive neurons and their synaptic connections in the guinea pig arcuate nucleus
Authors: Beauvillain J. C. , Tramu G. , Mazzuca M.
Published: January 2005

The fine structure of neurons containing human growth‐hormone‐releasing factor (hGRF) immunoreactivity located in the arcuate nucleus of the guinea pig was studied by means of the preembedding immunohistochemical technique.

The perikaryon of labeled neurons was fusiform or ovoid; the nucleus was regular in shape and contained a prominent nucleolus. The main ultrastructural features of the hGRF‐immunoreactive neurons were (1) the presence of numerous labeled secretory granules (100–120 nm in diameter) and (2) the abundance and the enlargement, of the organelles involved in the synthesis of the peptides: a well‐developed rough endoplasmic reticulum and a conspicuous Golgi apparatus. Synaptic inputs were observed on immunoreactive perikarya but, above all, on the labeled dendrites. The unstained presynaptic nerve endings most often contained only small clear vesicles and formed symmetrical contacts. In rare cases, the presynaptic terminals exhibited both small clear and large dense vesicles and constituted asymmetrical contacts. Immunoreactive nerve endings were also observed in this area: the synaptic boutons contained large, stained vesicles and small, unlabeled, clear vesicles. These axon terminals made synaptic contacts with unstained dendritic processes; the contacts were symmetrical.

The results indicate that hGRF‐immunoreactive neurons of the guinea pig arcuate nucleus present morphological features of neuroendocrine cells. Moreover, the presence of hGRF‐labeled nerve endings in the arcuate nucleus itself suggests that a substance related to hGRF might be a neuromodulator, at least in this area.
Transient expression of adenosine deaminase in facial and hypoglossal motoneurons of the rat during development
Authors: Senba E. , Daddona P. E. , Nagy J. I.
Published: January 2005

Immunohistochemical and retrograde tracing techniques were employed to demonstrate a changing pattern of adenosine deaminase (ADA) immunoreactivity in cranial motoneurons during their ontogenesis in the rat. Immunostaining for ADA was observed only in motoneurons of hypoglossal and facial motor nuclei and only at certain stages during development. Moreover, ADA immunoreactivity was restricted to subpopulations of motoneurons within each nucleus. In the hypoglossal nucleus ADA‐immunostained neurons were seen only in the dorsal subnucleus, where they appeared at about 15 days of gestation, reached maximal staining intensity early after birth, and disappeared by the 25th postnatal day. In the facial motor nucleus, immunoreactive neurons were detected only in the intermediate subnucleus, where ADA immunostaining was first detected at 18 days of gestation and was maximal during the first few postnatal days, and in the lateral subnucleus, where immunostaining appeared perinatally. In both facial motor subnuclei, ADA immunoreactivity was no longer detectable by the 15th postnatal day. Retrograde tracing with WGA‐HRP or fluorescent dye injected into various muscles of the face or tongue in young animals indicated that ADA‐immunoreactive motoneurons in the hypoglossal and facial motor nuclei innervate retractor muscles of the tongue and perioral or nasal muscles, respectively. In view of the critical role of these muscles in suckling and sniffing behavior, it is suggested that metabolic pathways associated with ADA may be involved in the early maturation of the motoneurons projecting to these muscles. Alternatively, the transient presence of ADA in these neurons may reflect a developmental period during which purine nucleosides and/or nucleotides may serve as neuromodulators at their peripheral terminations.
Ultrastructure of the caudal portion of the fourth ventricular roof in the mouse
Authors: Oda Yoshio , Nakanishi Isao
Published: January 2005

A scanning and transmission electron microscopic study was done of the caudal portion of the fourth ventricular roof in the adult mouse. The caudal portion of the fourth ventricular roof was divided into two parts: choroid plexus and nonchoroid plexus roof. The plexus epithelial cells had numerous microvilli and were connected with each other with a tight junction, gap junction, or zonula adherens. The nonchoroid plexus roof was a thin neuroglial membrane with a continuous basement membrane, which we designated as “the membranous roof.” The membranous roof was mostly composed of a single layer of paving ependymal cells supported by discontinuous pial cells. The ependymal cells were characterized by their squamous cell configuration, various numbers of microvilli and cilia, and a continuous basement membrane. They were connected with each other by gap junctions or zonulae adherentes, but they lacked tight junctions. Neither a cytoplasmic pore nor a wide intercellular cleft was identified. Neuronal and glial cell processes were occasionally observed. The aperture that is supposed to exist in the caudal, median portion of the fourth ventricular roof of the adult mammalian brains, called the foramen of Magendie in the human brain, was not found. Our observations suggest that the membranous roof itself would permit passage of the cerebrospinal fluid containing macromolecules via the interependymal cell clefts, implying that the foramen of Magendie would not be an anatomical aperture but a functional channel for the outflow of the cerebrospinal fluid.
Development of the spinal nerves in the lamprey: II. Outflows from the spinal cord
Authors: Nakao T. , Ishizawa A.
Published: January 2005

During a series of studies on the development of spinal nerves in the tail of larval lampreys (13 mm, 26 days), Lampetra japonica, we observed outflows of cytoplasmic processes (cytoplasmic outflow) or whole cell bodies (cellular outflow) from the neural tube or from the cord. Three types were distinguished according to their site of exit from the surface of the neuraxis.

The dorsal outflow (DO) is the cellular outflow seen on the midsagittal surface of the dorsal wall of the caudalmost region of the neural tube, just rostral or caudal to the opening in the dorsal tube wall. It is hypothesized that the cells from the dorsal neural tube become polymorphous cells scattered in the extramedullar space.

The dorsolateral outflow (DLO) is the cytoplasmic outflow emerging from the dorsolateral aspect of the spinal cord at the intermyotome level. DLO fibers are non‐myelinated fibers arising from the dorsolateral tract (DLT) and, after piercing the basal lamina and the glia limitans, run in the myosepta laterally to spread along the deep surface of the dermis. DLO fibers terminate in two different ways: those of one group pierce the dermis and the basal lamina to end as intraepidermal free endings that contain aggregates of clear vesicles, and those of the other group form varicosities that lie within depressions on the lateral cell surface of myotomes. DLO fibers in the extramedullary space characteristically lack any sheaths, including the basal lamina.

The ventrolateral outflow (VLO) represents primitive ventral roots consisting of both the cytoplasmic and the cellular outflows: the former shows the axonal outgrowth from primitive somatomotor neurons, and the latter is represented by elongated cells derived from the glia limitans, extending along the axonal processes to form the Schwann cell sheath around the proximal portion of the ventral root axons. The basal lamina covering the cord does not extend along the VLO fibers. The developing ventral root contains axons at different stages of differentiation. Some axons end on the medial surface of the myotome at the midsegmental level to form neuromuscular junctions. However, axonal processes of primitive motoneurons form close contacts with muscle cells by means of small cytoplasmic projections that contain no synaptic vesicles and lack the basal lamina interposed between them.

The proposed sequence of development, based on stages in caudal to rostral sections, is the DO, the DLO, and then the VLO. We observed no DLO or DLO fibers on the surface of the spinal cord and subunits of the myotome in 21‐mm larval lampreys: the typical DLO and DLO fibers have disappeared by this developmental stage.
Specific neurotrophic interactions between cortical and subcortical visual structures in developing rat: in vitro studies
Authors: Repka Ann , Cunningham Timothy J.
Published: January 2005

We investigated the influence of different subcortical structures on the survival of specific populations of occipital cortex neurons developing in vitro. Explants of embryonic day 14–15 (E14–15) rat cortex were cultured for 5 days with explants of either diencephalon or optic tectum or another occipital cortex explant. Stereological analysis of the explants revealed that after 5 days in vitro (5 DIV) all the cortical explants contained equal proportions of healthy neurons, glia, neuropil, and degenerating profiles, regardless of the culturing conditions. In order to determine if different neuronal populations survived preferentially in the cortical explants as a result of the presence of potential target or afferent structures, we used HRP filling and 3H‐thymidine labeling techniques. Specific differences in the morphology of the cells and their time of origin are found in the cortical explants. In the cortical explants cocultured with diencephalon (Cx+D) the cortical cells that survive tend to be round with small cross‐sectional areas and have few neurites. These cells are generated late in the culturing period. The surviving cortical neurons in the cortex plus tectum (Cx + T) cultures are larger‐many with a pyramidal‐shaped soma and several neurites. These cells are generated earlier in vitro. The cortex cultured with other cortex (Cx+Cx) gives values intermediate to the Cx+D and Cx+T cultures. The results of these experiments suggest that there are diffusible trophic factors that arise from subcortical structures that selectively support the survival of neuron populations in the developing neocortex.
Cortical and peripheral effects on single neurons of the lateral reticular nucleus in the monkey
Authors: Marini Gabriella , Wiesendanger Mario
Published: January 2005

The aim of this study was to extend the anatomical study of the cortico‐reticular organization in the monkey by means of microelectrophysiological techniques. Considering the relatively modest projection (see companion paper, Wiesendanger and Wiesendanger, '87), it was surprising to see that over 70% of the investigated LRN neurons were influenced from at least one cortical stimulation site. Many neurons responded, however, with long latencies suggesting an indirect transmission line. In line with the anatomical tracing study, most short‐latency responses were obtained from the motor cortex. Postcentral cortex and the SMA were, in general, less effective sites for evoking responses in the LRN. LRN neurons with similar cortical inputs tended to be clustered together suggesting that the corticoreticular projection is discretely organized with an “intermingled somatotopy.” The majority of the 87 tested LRN neurons were not reactive to any peripheral stimulus (33%) or responded only to nociceptive peripheral stimulation (31%). Very large receptive fields were seen in 8% of the units. However, a significant proportion of LRN neurons (10%) had restricted receptive fields and reacted to gentle cutaneous stimuli, and others (17%) responded to discrete passive rotations of one or more joints. There was often a somatotopical correspondence between the peripheral and the cortical inputs. It is concluded that the LRN in monkeys is under the influence of the motor cortex, which, however, may be exerted to a major extent via indirect pathways. The electrophysiological data suggest a discrete rather than a diffuse relationship with the LRN.
Localization of motoneurons innervating individual abdominal muscles of the cat
Authors: Miller Alan D.
Published: January 2005

The motor pools of the individual abdominal muscles of the cat were localized in studies by using either intramuscular injections of horseradish peroxidase (HRP) to retrogradely label abdominal motoneurons or electrical microstimulation of the ventral horn at different segmental levels to produce localized twitches of the abdominal muscles. The segmental distribution of each motor pool was as follows: rectus abdominis, T4–L3; external oblique, T6–L3; transverse abdominis, T9–L3; and internal oblique, T13–L3. The differences in the rostral extents of the individual motor pools reflect the greater rostral extents of the different muscles (rectus abdominis > external oblique > transverse abdominis > internal oblique). Labeled motoneurons were also found at other segmental levels; however, it was concluded that this labeling occurred because of spread of HRP from the injected muscle since localized abdominal muscle twitches could not be produced by electrical stimulation in these regions. In addition, control experiments showed that HRP can spread from the injected muscle and identified the sources of some of this spurious labeling. Motoneurons labeled after injections into the four abdominal muscles overlapped extensively on transverse sections of the spinal cord; however, rectus abdominis motoneurons were located more medially than the others from about T11 to L3. Soma diameters ranged between 12 and 41 μm (average 24–26 μm per cat). In summary, this study has provided a systematic description of the innervation of the individual abdominal muscles of the cat.
Synaptic reorganization in the dorsal lateral geniculate nucleus following damage to visual cortex in newborn or adult cats
Authors: Kalil Ronald E. , Behan Mary
Published: January 2005

We have studied the effects of making large lesions of visual cortex on the synaptic organization of the dorsal lateral geniculate nucleus (LGN) in the cat. Visual cortex was removed at birth in one group of cats and during adulthood in a second group. Following survival periods of 6 months to 2 years, the organization of synapses made by afferents from the retina in the LGN was investigated quantitatively with the electron microscope. In single thin sections we determined the percentage of retinal axon terminals that made synapses in the LGN, the average number of synapses made by each retinal axon terminal, and the identity of each postsynaptic process. These measurements were made separately for retinogeniculate connections in the A and C laminae of the LGN. For comparison, similar sets of measurements were made in adult cats that had been reared normally.

When single thin sections from the A or C laminae of the LGN in normal cats are examined, about 60% of the axon terminals from the retina are seen to make at least one synaptic contact. These contacts can be with dendrites or F profiles or both. On average, each retinogeniculate terminal makes approximately 1.4 synapses in the plane of a single section and contacts dendrites three times as often as F profiles.

In the A laminae of the LGN in cats that received a visual cortex lesion at birth or in adulthood, the percentage of retinal terminals that make synapses is the same as in normal cats. Similarly, the average number of synaptic contacts made by each retinogeniculate terminal is not changed by a lesion of visual cortex. In contrast, the number of contacts made with dendrites is reduced markedly, by about 29% after a lesion at birth and 53% after a lesion as an adult. However, these reductions are offset by compensatory increases in the number of contacts made with F profiles, and thus the mean number of contacts made by each retinogeniculate terminal is stabilized at a normal value. In the C laminae of the LGN, retinogeniculate terminals also reapportion their synaptic contacts. In cats with a lesion during adulthood, the redistribution of synapses is compensatory, as in the A laminae. When a lesion is made at birth, however, the number of new retinal contacts made with F profiles exceeds the number of dendritic contacts that are lost. As a result, each retinogeniculate terminal makes about 26% more synapses, in total, than normal.

These results demonstrate that retinogeniculate terminals reorganize their synaptic affiliations in response to the retrograde degeneration of lateral geniculate neurons produced by a lesion of visual cortex. In general, this reorganization preserves the normal number of synaptic contacts made by individual retinogeniculate terminals. It is of special interest that this mechanism for synaptic plasticity appears to operate as effectively in the adult brain as it does in the newborn.