bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell types and synaptic organization of the medullary electromotor nucleus in a constant frequency weakly electric fish, Sternarchus albifrons
Authors: Tokunaga Akira , Akert Konrad , Sandri Clara , Bennett Michael V. L. 
Published: January 2005

AbstractThe medullary electromotor nucleus (EMN) of Sternarchus albifrons was studied at the light and electron microscopic levels. The EMN consists of a dense meshwork of myelinated axons and glial elements with interposed large neurons; it is provided with an abundant supply of capillaries. Two types of essentially adendritic nerve cells were distinguished on the basis of size: giant neurons (approx. 70 μm in diameter) and large neurons (approx. 30 μm in diameter). Their population ratio is 1:4. Only giant cells are labelled following the injection of retrograde tracer into the spinal cord; they are therefore identified with the so‐called “relay cells” of other gymnotids. Tracer experiments further suggest that the descending axons of these relay cells give off collateral branches throughout the elongated spinal electromotor nucleus. In contrast, the large cells remain unlabelled and therefore lack spinal projections; they most likely correspond to “pacemaker cells”.The perikaryal surface, including axon hillock and proximal part of initial segment of both types of EMN cells, is contacted by clusters of synaptic terminals and astrocytic processes. Two main varieties of synaptic terminals occur: (1) large endings and (2) ordinary end feet with standard size (S‐type) and variable size (Sv‐type) clear, spherical vesicles. The junction between large endings and EMN cells is characterized by the combination of gap junctions and surrounding intermediate junctions whose freeze‐fracture characteristics were morphometrically analyzed. The large endings were formed by nodes of Ranvier as well as by fiber terminations, and synchronization within the EMN may be achieved by presynaptic fibers. Some of the contacts occur directly on the initial segment, which could allow activity to bypass the soma.It is concluded that the electromotor system of Sternarchus is comprised of a rapid conduction pathway where medullary pacemaker and relay cells as well as spinal electromotor neurons are coupled by synapses with gap junctions. In contrast to the spinal electromotor neurons, the medullary EMN cells receive synapses with morphological characteristics of chemical transmission, and the S‐type and Sv‐type terminals may possibly correspond to Gray's Type I and Type II synapses, respectively. These synapses may be involved in modulation of the electric organ discharge frequency.
Patterns of responses of cortical cells to binaural stimulation
Authors: Kitzes Leonard M. , Wrege Kathy S. , Cassady J. Michael 
Published: January 2005

AbstractThe relationship between stimulus intensity and response latency implies that the relative time of arrival of input to binaurally sensitive locican vary over a range significantly longer than the interaural delays resulting from the travel time of sound between the ears. To investigate the effect of such potentially long inter‐arrival time intervals, responses of binaurally sensitive neurons in auditory cortex of cats were examined over relatively long interaural delays. Two kinds of interaural delay functions were observed. One kind involved a sharp transition to a reduced response rate over a narrow range of interaural delays, while the other involved a gradual reduction of response rate over a relatively prolonged range of interaural delays. The amount of suppression was found to be a sensitive function of both interaural delay and the relative intensity of the stimuli delivered to the two ears. The pattern of suppression across a binaural response was stationary with respect to the excitatory contralateral stimulus over wide ranges of interaural delay. In addition, certain characteristics of a group of cells generally responsive only to binaural stimulation are described. A model is proposed which accounts for the observed stationarity of the response suppression.
The cochlear nuclei of snakes
Authors: Miller Malcolm R. 
Published: January 2005

AbstractThe cochlear nuclei of three burrowing snakes (Xenopeltis unicolor, Cylindrophis rufus, and Eryx johni) and three non‐burrowing snakes (Epicrates cenchris, Natrix sipedon, and Pituophis catenifer) were studied. The posterior branch of the statoacoustic nerve and its posterior ganglion were destroyed and the degenerated nerve fibers and terminals traced to primary cochlear nuclei in 13 specimens of Pituophis catenifer.All these snake species possess three primary and one secondary cochlear nuclei. The primary cochlear nuclei consist of a small nucleus angularis located at the cerebello‐medullary junction and a fairly large nucleus magnocellularis forming a dorsal cap over the cephalic end of the alar eminence. Nucleus magnocellularis may be subdivided into a medially placed group of rounder cells, nucleus magnocellularis medialis, and a laterally placed group of more ovate and paler‐staining cells, nucleus magnocellularis lateralis. A small but well‐defined secondary nucleus which showed no degenerated nerve terminals after nerve root section, nucleus laminaris, underlies the cephalic part of both nucleus magnocellularis medialis and nucleus magnocellularis lateralis.Larger and better‐developed cochlear nuclei were found in burrowing species than in non‐burrowing species of snakes. Of the three burrowing species studied, Xenopeltis showed the greatest development of cochlear nuclei; Eryx cochlear nuclei were not quite as large but were better differentiated than in Xenopeltis; and Cylindrophis cochlear nuclei were fairly large but not as well developed nor as well differentiated as in either Xenopeltis or Eryx. The cochlear nuclei of the three non‐burrowing snakes, Epicrates, Natrix, and Pituophis, Were not as large nor as well developed as those of the burrowing snakes.There is some, but not complete, correlation between cochlear development and papilla basilaris length and number of hair cells. Thus, Xenopeltis and Eryx, with well‐developed cochlear nuclei, have relatively long papillae basilares; but the boid, Epicrates, with less well‐developed cochlear nuclei, has a fairly well‐developed papilla basilaris. Cylindrophis, a burrowing species, shows only a moderate degree of cochlear nuclei, have relatively long papillae basilares; but the boid, Epicrates, with less well‐developed cochlear nuclei, has a fairly well‐developed papilla basilaris. Cylindrophis, a burrowing species, shows only a moderate degree of cochlear nuclei and papilla basilaris development. The non‐burrowers, Natrix and Pituophis, have both small cochlear nuclei and relatively short papillae basilares.
Denervation study of synapses of organ of corti of old world monkeys
Authors: Bodian David , Gucer Gunduz 
Published: January 2005

AbstractFine structural characteristics of synapses in the spiral organ of Corti were examined, with reference to differences between inner and outer haircell systems, and to location of neurons of origin of efferent axons. Surgical interruption of crossed olivocochlear bundle, of vestibular nerve, of facial nerve, and excision of superior cervical ganglia were used to determine the pathways of efferent axons. Interruption of the vestibular nerve near the brainstem results in degeneration of all efferent terminals on outer hair cells. Mid‐line lesions at, and caudal to, the facial colliculus result in degeneration of about half of these efferent terminals. Efferent synaptic bulbs to the inner hair‐cell system are small, of the order of one micron, and form type 2 junctions with afferent dendrites. They tend to have more large dense‐core vesicles (about 80 nm) than the large efferent terminals of the outer hair‐cell system, and appear to be the terminals of axons in the habenula perforata, which exhibit varicosities laden with large dense core vesicles. The varicosities are unaffected by excision of the superior cervical ganglia. So far as our material can reveal, it appears that the varicosities in the habenula perforata do not survive vestibular root interruption, nor do the efferent processes in the internal spiral bundle or at the base of inner hair cells. Most interestingly, the afferent processes of the inner hair‐cell system, as identified for example by their relation to pre‐synaptic bodies in the inner hair cells, are subject to a trans‐synaptic reaction after severance of the vestibular root. They undergo a dramatic cytological transformation, characterized by increase of volume, engorgement with microtubules, microfilaments, microvesicles of various sizes, and clusters of lysosomes. Thus, both the efferent and afferent terminals of the inner hair‐cell system show marked cytological differences from the corresponding terminals of the outer hair cell system.
Regional variation in the representation of the visual field in the visual cortex of the siamese cat
Authors: Cooper Michael Lee , Blasdel Gary G. 
Published: January 2005

AbstractIn Siamese cats, many ganglion cell fibers from the temporal retina misproject to the contralateral hemisphere; as a result, each lateral geniculate nucleus contains an abnormally large representation of the ipsilateral visual field. The manner in which the visual cortex processes this aberrant visual information has been examined in several previous studies. In some Siamese cats, the region of the 17/18 border was found to contain an extensive, systematic map of the ipsilateral field, while in other animals no such map was found, and the 17/18 border appeared to represent the zero meridian of azimuth (as in normal cats). These results have led to the suggestion that there are two distinct types of Siamese cat (“Boston” and “Midwestern”) which can be distinguished on the basis of cortical topography and the anatomical organization of the geniculocortical pathway.In the present study, we have recorded from four Siamese cats in order to examine the visual field map in the region of the 17/18 border; in each cat we recorded at anterior coronal levels corresponding to the representation of the lower visual field, and also at more posterior levels near the horizontal meridian representation. In all of the animals we found that the anterior penetrations (corresponding to mean receptive field elevations inferior to −7°) yielded 15–20° of ipsilateral field representation at the 17/18 border; however, the posterior, horizontal meridian penetrations (with mean elevations from +1° to −4°) showed excursions of only about 5° into the ipsilateral field. This large difference in the representation of azimuth was not due to rotation of the eyes during our recording sessions.The finding of appreciable differences in the amount of ipsilateral field represented at different anterior‐posterior levels of the same animal might lead to the suggestion that there are not two distinct populations (or types) of Siamese cat with regard to the cortical map of the ipsilateral field. Rather, we raise the possibility that Siamese cats form one population in which there is a continuous variation in the extent of ipsilateral field represented in the cortex.
Location and morphology of parasympathetic preganglionic neurons in the sacral spinal cord of the cat revealed by retrograde axonal transport of horseradish peroxidase
Authors: Nadelhaft I. , Degroat W. C. , Morgan C. 
Published: January 2005

AbstractThe distribution and morphology of preganglionic neurons in the sacral parasympathetic nucleus (SPN) of the cat have been studied with the horseradish peroxidase (HRP) tracing technique. HRP applied to the cut pelvic nerve was identified in cells located ipsilaterally, primarily in the intermediate gray matter. They formed a column approximately 10 mm long, usually contained within two, but occasionally three, sacral segments. S2 contained a majority of cells. In transverse sections the SPN had the appearance of an inverted “L.” Cells were medium‐sized, oval or spindle‐shaped, and transversely oriented. They were distributed among two major components and one minor one: (1) dorsal band (34%) located mainly in lamina V beneath the dorsal horn (cells and dendrites horizontally oriented), (2) lateral band (64%) along the lateral edge of the gray matter in laminae VII through V (cells oriented dorsoventrally with dendrites extending within the nucleus and into the dorsolateral funiculus), and (3) a small group (2%) of cells at the rostral end of the SPN in lamina VII in the middle of the ventral horn. These data coupled with the results of other investigations indicate that the SPN has a viscerotopic organization wherein the colon is innervated primarily by cells in the dorsal band and the urinary bladder is innervated primarily by cells in the lateral band.
Ontogeny of the sexually dimorphic nucleus of the preoptic area
Authors: Jacobson Carol D. , Shryne James E. , Shapiro Fred , Gorski Roger A. 
Published: January 2005

AbstractAn area of increased cell density in the medial preoptic area of the adult rat brain which is markedly larger in volume in the male has been named the Sexually Dimorphic Nucleus of the Preoptic Area (SDN‐POA). It has been further shown that the presence of the testes or exogenous androgen during the first week of postnatal life significantly increases the volume of the SDN‐POA in the brain of the adult. The present study was conducted to describe the time course of the prenatal and postnatal development of the SDN‐POA in the intact male and female rat. Sprague‐Dawley females were housed with males on proestrus. The presence of sperm in the vaginal smear on estrus was used to define day 1 of gestation. Male and female prenatal and postnatal pups were sacrificed and perfused with 10% neutral formalin on days 20, 21, 22, 23, 24, 25, 26, 27, 28, 30, and 32 postfertilization. Following histological sectioning at 60 m̈m and staining with thionin, three investigators independently drew the boundaries of the SDN‐POA on successive sections, using a microprojector at a magnification of 43.5. A fourth investigator averaged the three drawings; from this average, the nuclear volume was determined with a calibrated planimeter. All drawings and measurements were performed without knowledge of age or sex since the brains were coded according to a random number generator. The volume of the SDN‐POA was found to be significantly larger in males than in females on days 23, and 25 through 32. Moreover, the volume of the SDN‐POA increased significantly with age in the male, but there was no change in SDN‐POA volume in the female. In order to test the specificity of the sexual dimorphism of the SDN‐POA, five different linear measurements were taken of brain size. There was a significant increase in these parameters in both sexes with increasing age; however, there was no significant sex difference found. Thus, the sex difference in volume of the SDN‐POA cannot be accounted for by sex differences or age‐related changes in brain size per se. These data suggest that the development of the SDN‐POA (as measured by volume) is itself sexually dimorphic. There are dramatic increases in the male, but not in the female, during a time‐period which is known to be critical for sexual differentiation of the brain.
The Purkinje neuron: II. Electron microscopic analysis of the mature Purkinje neuron in organotypic culture
Authors: Aggerwal A. S. , Hendelman W. J. 
Published: January 2005

AbstractPurkinje neurons of organotypic cultures were investigated electron microscopically following their analysis with the Golgi technique. The purpose of this study was to critically examine the issue of synaptic specificity in CNS cultures. The unique finding was the synaptic cluster, a terminal which engulfs many Purkinje spines. In the neuropil and on the major dendrites, this synaptic arrangement was interpreted to be a hypertrophic parallel fiber, representing a type of synaptic modulation. The terminals on the somatic spines are also in the form of clusters; some or all of these spines were thought to have developed to form synapses with the climbing fiber. In the absence of this afferent, the parallel fiber—a competing system—takes over the site. This represents a form of synaptic plasticity in these cultures. The inhibitory synaptic relationships were maintained on the soma and dendrites, but it was found that the basket synapses did not quantitatively encase the soma as is seen in the intact animal. Mossy‐type terminals were found occasionally synapsing with Purkinje dendritic spines, as has been seen in agranular cerebellum in animals. These mossy terminals are presently thought to originate from the deep cerebellar nuclei within these cultures. Synaptic errors were rarely encountered. It is concluded that this preparation develops in accordance with established neurobiological principles, that the Purkinje neuron reaches a mature state in culture, and that this model has a sound anatomical basis for further experimental work.
Postnatal development of glycinergic neurons in the rabbit retina
Authors: Kong Yun‐Cheung , Fung Sek‐Chung , Lam Dominic Man‐Kit 
Published: January 2005

AbstractCertain neurons in the adult rabbit retina posses a high‐affinity uptake mechanism for glycine and release it in response to elevated K+ concentrations in the medium. Although the evidence is not yet complete, these properties, together with pharmacological studies, suggest that the glycine‐accumulating neurons may be a subpopulation of amacrine cells and may use glycine as a neurotransmitter. In the present study, we have used the uptake and K+‐stimulated release of glycine as physiological probes to follow the emergence and maturation of putative glycinergic neurons during postnatal development of the rabbit retina. We show that certain neurons in the newborn retina already possess a specific high‐affinity mechanism for glycine uptake. The positions and density of these cells in the developing retina suggest that they will become glycineaccumulating neurons of the adult retina. Thus, similar to our earlier study on the development of GABA‐ergic neurons in this retina, the commitment by certain retinal neurons to be glycinergic, if indeed these cells use glycine as the transmitter, is made prenatally. These putative glycinergic neurons are, however, probably immature at birth, because they do not release the accumulated glycine in response to high K+ concentrations in the medium. In fact, there is practically no K+‐ stimulated release of preloaded glycine from the retina until about 7 days after birth, after which the release increases drastically to about 65% of the adult level on day 10 and 80% on day 12. Assuming that this release originates synaptically, our finding suggests that the putative glycinergic neurons may be functionally mature by 10–12 days after birth. Additionally, our results show that during development of the rabbit retina, the mechanism for high‐affinity glycine uptake emerges and matures much earlier than the mechanism for K+‐stimulated glycine release.
The effects of neonatal 6‐hydroxydopamine treatment on morphological plasticity in the dentate gyrus of the rat following entorhinal lesions
Authors: Amaral David G. , Avendaño Carlos , Maxwell Cowan W. 
Published: January 2005

AbstractLesions of the entorhinal cortex, which is the major source of afferents to the outer two thirds of the molecular layer of the dentate gyrus, induce an expansion of the commissural projection, which is normally restricted to the inner third, and an intensification of acetylcholinesterase staining in the outer portion of the layer; these changes are thought to be due to the sprouting of the commissural fibers and certain cholinergic afferents to the dentate gyrus, respectively. We have studied these sequelae of entorhinal lesions in young adult rats which had been treated with 6‐hydroxydopamine (6‐OHDA) as neonates, in order to determine whether in the absence of its normal noradrenergic input, morphological plasticity in the dentate gyrus would be altered either in magnitude or extent. In animals treated with 6‐OHDA, the levels of noradrenaline in the hippocampal formation were reduced by 93%. Despite this, there was clear evidence for an expansion of the commissural projection following entorhinal lesions, as judged both autoradioraphically and in Timm‐stained material. Similarly, the intensification of acteylcholinesterase staining in the outer part of the molecular layer appeared as marked as after comparable lesions in untreated animals. From these observations it would appear that in the dentate gyrus, at least, morphological plasticity does not require the presence of an intact noradrenergic innervation.
Afferent connections to the amygdaloid complex of the rat and cat: II. Afferents from the hypothalamus and the basal telencephalon
Authors: Ottersen Ole P. 
Published: January 2005

AbstractThe projections from the basal telencephalon and hypothalamus to each nucleus of the amygdaloid complex of the rat, and to the central amygdala of the cat, were investigated by the use of retrograde transport of horseradish peroxidase (HRP). The enzyme was injected stereotaxically by microiontophoresis, using three different approaches.The ventral pallidum (Heimer, '78) and ventral part of the globus pallidus were found to project to the lateral and basolateral nuclei of the amygdala. The substantia innominata projects diffusely to the entire amygdaloid complex, except to the lateral nucleus and the caudal part of the medial nucleus. The anterior amygdaloid area shows a similar projection field, the only difference being that this structure does not project to any parts of the medial nucleus. The dorsal subdivision of the nucleus of the lateral olfactory tract sends fibers to the ipsilateral as well as the contralateral basolateral nucleus, and possibly to the ipsilateral basomedial and cortical amygdala. The ventral subdivision of the nucleus of the lateral olfactory tract was massively labeled after an injection in the ipsilateral central nucleus, but this injection affected the commissural component of the stria terminalis. The nucleus of the horizontal limb of the diagonal band of Broca connects with the medial, central, and anterior cortical nuclei, whereas the bed nucleus of stria terminalis and medial preoptic area are related to the medial nucleus predominantly. The lateral preoptic area is only weakly labeled after intra‐amygdaloid HRP injections.The hypothalamo‐amygdaloid projections terminate preponderantly in the medial part of the amygdaloid complex. Thus, axons from neurons in the area dorsal and medial to the paraventricular nucleus of the hypothalamus distribute to the medial nucleus and intra‐amygdaloid part of the bed nucleus of stria terminalis. Most of the amygdalopetal fibers from the ventromedial, ventral premammillary, and arcuate nuclei of the hypothalamus end in the medial nucleus, but some extend into the central nucleus. A few fibers from the ventromedial nucleus of the hypothalamus reach the basolateral nucleus. The lateral hypothalamic area projects heavily to the central nucleus, and more sparsely to the medial and basolateral nuclei. The dorsal hypothalamic area and supramammillary nucleus show restricted projections to the central and basolateral nuclei, respectively. There are only a modest number of crossed hypothalamo‐amygdaloid fibers. Most of these originate in the ventromedial nucleus of the hypothalamus and terminate in the contralateral medial nucleus.The projections from the basal telencephalon and hypothalamus to the central nucleus of the amygdala of the cat are similar to the corresponding projections in the rat.