bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ontogeny of the area centralis in the cat
Authors: Robinson Stephen R. 
Published: January 2005

AbstractPrevious 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

AbstractIn 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

AbstractThe 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

AbstractImmunohistochemical 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

AbstractA 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

AbstractDuring 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

AbstractWe 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

AbstractThe 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

AbstractThe 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

AbstractWe 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.
Distribution of tyrosine‐hydroxylase (TH)‐immunoreactive neurons in the diencephalon of the pigeon (Columba livia domestica)
Authors: Kiss József Zoltán , Péaczely Péter 
Published: January 2005

AbstractThe distribution of tyrosine‐hydroxylase (TH)immunoreactive cell bodies and fibers in the diencephalon has been investigated with immunohistological techniques in the pigeon. The results suggest that TH is present in a number of morphologically distinct neuronal systems. Preoptic and hypothalamic TH neurons were subdivided into a medial periventricular and a lateral group. The medial group starts with a rostral collection of small cells in the preoptic region. A significantly larger collection of TH neurons occupies the paraventricular nucleus (PVN)(stratum cellulare internum) and mainly consists of large multipolar cells. Further caudally, the main concentration of cells is in the hypothalamic posteromedial and the periventricular regions of the tuberoinfundibular (arcuate) nucleus. No TH neuron was found in the ventral and lateral parts of the tuberoinfundibular region, suggesting that the prominent tuberoinfundibular dopaminergic system described in mammals is absent in the pigeon. This is further substantiated by the relative scarcity of TH immunoreactive fibers and varicosities in the neurohemal zone of the median eminence (ME). The caudalmost components of the medial group appear to be continuous with the large population of TH neurons distributed in the midline of the mesencephalon. Tyrosine‐hydroxylase‐immunopositive cells have not been found in the paraventricular organ. The lateral group consists of TH neurons loosely arranged in the lateral hypothalamus, including regions of the supraoptic nucleus and hypothalamic posterolateral nucleus. Tyrosine‐hydroxylase containing neurons vary widely in size, shape, and dendritic arborization in each diencephalic region. However, it is possible to distinguish two main cell types. Small bipolar neurons with two simple arborizing dendrites were concentrated in the medial periventricular system. The second type of cell is large, multipolar with four to five branching dendrites. This latter cell type occurs mainly in the lateral system and in the PVN. Major fiber bundles containing TH immunoreactivity were identified in the lateral and periventricular hypothalamus. The paraventricular organ and the organum vasculosum laminae terminalis contained the densest arborization of fibers and varicosities. In the ME, dense innervation was found in the subependymal layer. Dense arborizations of TH positive fibers and varicosities were located in the septal nuclei and the paleostriatum augmentation.