bluuebunny/crossref_metadata_2025 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

The 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

The 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

The 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

Fine 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

In 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

The 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

An 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

Purkinje 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

Certain 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

Lesions 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

The 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.
The organization of projections from the olfactory bulb to the piriform cortex and olfactory tubercle in the rat
Authors: Scott John W. , McBride Russell L. , Schneider Stephen P.
Published: January 2005

The organization of the projection of olfactory bulb output cells was studied in the rat by injection of horseradish peroxidase (HRP) into the piriform cortex or olfactory tubercle. We made single HRP injections into small cuts in the fiber layer of the projection areas in order to enhance uptake by axons and to confine the region of HRP uptake. Following most of these injections, HRP‐labeled axons could be traced in discrete fascicles through the fiber layer of the cortex or tubercle. These observations indicate that axons innervating the piriform cortex do not emit many long collaterals after they leave the lateral olfactory bulb, but there were regions of greater density of labeled that differed in the various brains. The differences among the distributions of labeled mitral and tufted cells were analyzed statistically in 39 brains to test whether they varied systematically with injection site. In these analyses, the olfactory bulb was divided into 30 standard regions, and the labeled cells in each regions were counted.

The distributions of labeled cells were similar for brains where injections were made into similar regions of the piriform cortex. The variations in density of labeled cells of the dorsal and anterior regions of the olfactory bulb were most strongly correlated with the positions of cortical injections. In contrast, the posterior medial regions of the bulb were heavily labeled after almost all injections. The ventral portions of the olfactory bulb were most heavily labeled after injections into the olfactory tubercle.
Physilogy and morphology of substantia gelatinosa neurons intracellularly stained with horserdish peroxidase
Authors: Bennett Gary J. , Abdelmoumene Mohammed , Hayashi Haruhide , Dubner Ronald
Published: January 2005

Neurons in Rexed's layer II were physiologically characterized with natural and electrical stimuli applied to their cutaneous receptive field. The neurons were then intracellularly stained with horseradish peroxidase. Three general patterns of physiological responses were found Nociceptive specific neurons did not respond to gentle mechanical stimulation. Most responded exclusively to tissue‐damaging stimuli. Some also responded to moderately heavy pressure, but these responded to noxious stimuli with an increased discharge frequency. Wide dynamic range neurons responded to both gentle mechanical stimulation and to tissue‐damaging stimulation. Low‐threshold mechanoreceptive neurons responded only to gentle mechanical stimulation. Some of the low‐threshold mechanoreceptive neurons were innervated by primary afferents with unmyelinated axons. Excepting those low‐threshold mechanoreceptive neurons with input form unmyelinated afferents, the patterns of primary afferent innervation of layer II neurons were similar to the patterns innervation that gave been found for neurons in layers I and IV‐V.

All nut 2 of the 22 neurons that we found were recognized as being of two general morphological types. Stalked cells had their perikarya situated along the superficial border of layer II. Most of their dendrites traveled ventrally while spreading out rostrocaudally. This gave their dendritic arbors a fan‐like shape. Stalked cell axons arborized largely in layer I. Islet cell perikarya were found throughout layer II. Most of their dendrites traveled rostrocaudally. Their dendritic arbors were shaped like cylinders with their long axes parallel to the long axis of the spinal cord. Islet cell axons arborized in the immediate vicinity of their dendtritic territories, within layer II.

Stalked cells and those islet cells whose dendritic arbors were largely contained within the superficial one‐third of layer II (layer IIa) were either nociceptive specific or wide dynamic range neurons. The islet cells whose dendritic arbors were largely within the deeper two‐thirds of layer II (layer IIb) were all low‐threshold mechanoreceptive neurons. These observations suggest that layers IIa and IIb have different functional roles and that stalked cells and islet cells are separate and distinct components of the neural circuitry of the superficial dorsal horn.
Development of the brain stem in the rat. IV. Thymidine‐radiographic study of the time of orgin of neurons in the pontine region
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Groups of pregnant rats ware injected with two successive daily doses of 3H‐thymidine form gestational day 12 and 13 (E12 + 13) until the day before parturition (E21 + 22) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labeled) on specific embryonic days was determined quantitatively in 14 nuclei of the pontine region. Peak production time of neurons of the trigeminal mesencephalic nucleus was on day E11 or earlier, with a small proportion generated on day E12. Peak production time of the trigeminal motor neurons was on day E12, with a small proportion produced earlier. Neurons of the principal sensory nucleus were generated between days E13 and E16, with a peak on day E14; the late‐produced neurons tended to belong to a class of intermediate and large cells. The bulk of the neurons of the supratrigeminal and infratrigeminal nuclei arose on day E15 and E16.

Neurons of the locus coeruleus are produced mostly on day E12, with about 20% of the cells arising on day E13. The bulk of the neurons of the dorsal tegmental nucleus (Gudden's) are produced between days E13 and E15, whereas most of the neurons of the deep (ventral) tegmental nucleus are produced on day E15. A dorsal‐to‐caudal gradient was also obtained between the dorsal and vental nuclei of the lateral lemniscus, the neurons of the former being generated between days E12 and E15; the latter, between days E13 and E17. The neurons of both the pars lateralis and the pars medialis of the parabrachial nucleus were produced simultaneously between days E13 and E15, with a peak on day E13. the heterogeneous collection of neurons of the pontine paramedial reticular formation was produced from day E11 (or earlier) until day E15. Finally, the neurons of the raphe pontis parvicellularis were generated at an even rate between days E13 and E15, whereas the bulk of the neurons of the raphe pontis magnocellularis were produced on days E15 and E16.

On the basis of datings obtained for 9 subdivisions of the entire brain stem trigeminal complex, hypotheses were offered of the cytogenetic components of the system. The sequence of neuron production in the dorsal and deep tegmental nuclei was related to their connections with divisions of the mammillary and habenular nuclei on a “first come‐first serve” basis.
Projections of the cerebellar and dorsal column nuclei upon the thalamus of the rhesus monkey
Authors: Kalil Katherine
Published: January 2005

Projections from the cerebellar and dorsal column nuclei to the midbrain and thalamus of the rhesus monkey were traced with anterograde autoradiographic techniques, or, in a few cases, with the Fink‐Heimer method.

The cerebellar nuclei give rise to a massive projection to the contralateral midbrain and thalamus via the ascending limb of the superior cerebellar peduncle. Cerebellar efferent fibers terminate contralaterally in both divisions of the red nucleus, and bilaterally in the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the oculomotor nucleus, and the central gray.

All the deep cerebellar nuclei project upon a broad area of the contralateral ventral thalamus as well as certain intralaminar nuclei. Corresponding ipsilateral thalamic terminations are sparse. The topograpic organization of cerebellothalamic fibers does not correspond to individual cerebellar nuclei or to cytoarchitectonic divisions of the ventral thalamic nuclei. Rather there are longitudinally oriented strips of terminal labeling which extend through all divisions of the ventral lateral nucleus, i.e., the VLps, the VLc, the VLo, as well as nucleus X, the oral division of the ventral posterolateral nucleus (VPLo), the central lateral nucleus (CL), and the most caudal region of the ventral anterior nucleus (VA). The topography of the cerebellothalamic fibers is arranged in a mediolateral pattern with fibers originating from anterior zones of the dentate and interpositus ending most laterally and those from posterior dentate and interpositus terminating most medially. The fastigial contribution is relatively sparse.

The longitudinal strips of terminal labeling in the ventral thalamic nuclei are made up of still smaller terminal units consisting of disk‐like aggregates of silver grains separated from one another by grain‐free spaces.

The dorsal column nuclei terminate primarily in the contralateral caudal division of the VPL (VPLc) and never extend rostrally into VPLo.

These results demonstrate a segregation of cerebellar and dorsal columnar inputs to motor and sensory regions of the thalamus, respectively. Since these regions are separate and discrete in their cortical associations as well (Kalil, 1976), it seems unlikely that fast afferent pathways relaying to motor cortex (Lemon and Porter, 1976) could arise from the dorsal column nuclei.
Cortical and spinal somatosensory input to the superior colliculus in the golden hamster: An anatomical and electrophysiological study
Authors: Rhoades Robert W.
Published: January 2005

The horseradish peroxidase technique was used to identify the sources of somatosensory afferent fibers to the hamster's superior colliculus. These experiments demonstrated that the tectum receives axons from pyramidal cells in layer V of the ipsilateral sensorimotor cortex, contralateral lamina IV of all levels of the spinal cord, the contralateral dorsal column nuclei, lateral cervical nucleus, internal basilar nucleus, and nucleus of the spinal trigeminal tract.

Electrical stimulation of the spinal cord coupled with extracellular single unit recordings concentrated, for the most part, in the posterior portion of the tectum revealed that such stimuli activated approximately 40% of the cells tested. Almost of these units were isolated ventral to the stratum opticum and 86% were responsive only to somatosensory stimulation. Analysis of the latencies of collicular responses obtained with two point spinal stimulation in intact hamsters and in animals subjected to somatosensory cortical and/or spinal damage indicated that the initial impulse elicited from most collicular cells was mediated by a polysynaptic pathways(s) which probably synapses in the dorsal column, lateral cervical, and/or internal basilar nuclei.

Damage to the dorsal spinal cord and/or somatosensory cortex altered neither the incidence nor the response characteristics of spinally driven collicular neurons. This indicated that most somatosensory collicular cells also received input from the spinotectal fibers which travel in the ventrolateral quadrant.

Electrical stimulation of somatosensory cortex activated about 20% of the cells tested in the ipsilateral superior colliculus. If cortical and spinal stimulation were delivered with an interstimulus interval ranging between 50 and 80 msec the response of the tectal neuron to the latter stimulus was suppressed in most cases. This was true regardless of the order of the stimulus pairing. Concurrent somato‐sensory cortical shocks also suppressed responses to tactile stimuli for 21% of the cells tested.
Supplementary and precentral motor cortex: Contrast in responsiveness to peripheral input in the hindlimb area of the unanesthetized monkey
Authors: Wise S. P. , Tanji J.
Published: January 2005

Single‐unit recording and intracortical microstimulation techniques have been employed in unanesthetized monkeys in order to ascertain the relative responsiveness of the supplementary motor cortex (MII) and the precentral motor cortex (MI) to a controlled peripheral stimulus. The hindlimb representation was explored to facilitate comparison of MI and MII sensitivity in the same animal. Two main findings have emerged: (i) Many fewer neurons in MII respond to the peripheral stimulus and those that do have much weaker responses than neurons in MI. (ii) The hindlimb representation of MII and the tail representation of MI appear to be considerably further rostral than depicted in the classical maps. The latter finding serves to resolve a discrepancy between the classical physiological and cytoarchitectonic maps for this region of cortex.
The emergence, localization, and maturation of neurotransmitter systems during development of the retina in Xenopus laevis. III. Dopamine
Authors: Sarthy P. Vijay , Rayborn Mary E. , Hollyfield Joe G. , Lam Dominic M. K.
Published: January 2005

The uptake, synthesis, and release of dopamine was studied in retinas of Xenopus laevi. In the tadpole and adult retina, 3H‐dopamine is accumulated by cells located in the inner nuclear layer. Retinas preloaded with 3H‐dopamine release this compound in response to high K+ concentrations in the medium. This release is probably Ca++‐dependent as it is inhibited by Co++ in the medium. Adult retinas are also capable of synthesizing 3H‐dopamine from 3H‐tyrosine. The appearance and maturation of these dopaminergic properties were followed during retinal development. Our data indicate that synthesis of dopamine can first be detected as early as stage 35/36 whereas uptake of dopamine first occurs at stage 43. K+‐stimulated release of preloaded 3H‐dopamine from putative dopaminergic neurons is, however, not evident until stage 46. These results show that similar to the development of GABA‐ergic and glycinergic properties, the uptake, synthesis, and release mechanisms for dopamine emerge at different stages during retinal differentiation in Xenopus Laevis.
Morphology of the giant interneurons and cercal nerve projections of the American cockroach
Authors: Daley Darryl L. , Vardi Noga , Appignani Barbara , Camhi Jeffrey M.
Published: January 2005

We have investigated the morphology of the giant interneurons (GIs) and the main sensory projections to these interneurons in the American cockroach. These neurons are thought to mediate the animal's escape behavior. We describe here the dendritic branching pattern of each of the 14 GIs (7 bilateral pairs) in the terminal ganglion, the pattern of projection of the cercal sensory nerve, and the overlap of the cercal projections with the dendrites of the GIs. Visualization of the GIs and cercal nerve projection was accomplished by single cell injection and axonal backfilling with cobalt. Comparisons of the same identified GI in different animals show the position of the soma and the locations and orientations of the major processes are characteristic for each GI. The axons of the cercal nerve project to a well‐defined ipsilateral region of the terminal ganglion. After entering the terminal ganglion, the cercal afferents split into lateral and medial tracts. The projections of the lateral cercal tract overlap extensively with the dendritic fields of the GIs. In contrast, the medial tract does not overlap the dendritic fields of the GIs in the posterior portion of the ganglion and shows only a small degree of overlap in the anterior portion. Correlations between physiological properties of the GIs and cercal afferents are discussed in relation to our anatomical findings.
Localization of neurons in the rat spinal cord which project to the superior cervical ganglion
Authors: Rando T. A. , Bowers C. W. , Zigmond R. E.
Published: January 2005

Horseradish peroxidase (HRP) was used to determine the location in the spinal cord of neurons projecting to the superior cervical ganglion of the rat. HRP was applied to the proximal cut end of the cervical sympathetic trunk, close to its entry into the superior cervical ganglion. After survival times of 3, 6, or 9 days, the animals were sacrificed and their spinal cords were processed to visualize HRP using diaminobenzidine, benzidine dihydrochloride, or tetramethylbenzidine. Labeled neurons were found only ipsilateral to the site of HRP application and were restricted to spinal segments C8‐T5. Ninety percent of these neurons were located in segments T1‐T3. Similar numbers of labeled neurons were found at survival times of 3 and 6 days and the mean number ± S.E.M. for 11 experiments at these two survival times was 1575 ± 89. Nine days after application of HRP the mean number of labeled cells and the density of label per cell were reduced. Labeled neurons were found in four regions of the spinal cord: the intermediolateral nucleus (75%), the lateral funiculus (23%), the central autonomic area (1%), and the intercalated region (1%). The cells of the intermediolateral nucleus did not form a continuous column along the rostrocaudal axis of the spinal cord, but instead were often found in clusters, several clusters being present per spinal segment.
Studies on the somatotopy of the trigeminal system in the mallard, Anas platyrhynchos L. IV. Tactile representation in the nucleus basalis
Authors: Berkhoudt Herman , Dubbeldam Jacob L. , Zeilstra Schelte
Published: January 2005

This electrophysiological study complements neuroanatomical work from our department on the somatotopy of the trigeminal system of the mallard. Peripheral areas of mechanoreceptors in bills and tongue were mapped in the telencephalic nucleus basalis, a second‐order relay nucleus in the ascending trigeminal pathway. The multi‐unit responses recorded under Equithesin anaesthesia did not show spontaneous activity and all animals adapted rapidly after mechanical stimulation. They showed well‐circumscribed receptive fields whose peripheral position did not change when the electrode was lowered in the vertical stereotaxic plane, but changed immediately when its position was changed in the horizontal XZ‐plane. The somatotopic picture presented here corresponds in many details to that obtained with combined neuroanatomical techniques (Dubbeldam et al., '81). In the discussion the structural point‐to‐point relationship between the peripheral mechanoreceptive areas and the nucleus basalis is tentatively changed to a division into areas related to the functional units involved in the subsequent sensory events during feeding. The somatotopy provides a basis for future chronic experiments to investigate this postulated role of the various areas in the nucleus basalis.
The structure of the mediodorsal cerebral cortex in the lizard Agama agama: A Golgi study
Authors: Wouterlood F. G.
Published: January 2005

A Golgi analysis was made of the cell types present in the mediodorsal cerebral cortex of the lizard Agama agama. Mediodorsal cortex can be divided into two areas, small‐celled mediodorsal cortex (sMDC) and large‐celled mediodorsal cortex (lMDC). Both sMDC and lMDC are four‐layered cortices: superficial plexiform layer, cellular layer, deep plexiform layer and fiber layer, lMDC partially overlaps dorsal cortex (medial superposition). Using characteristics of the dendrites and criteria of location, dendritic field shape and soma size, two classes of neurons can be distinguished in sMDC. The first class consists of two types of solitary cells present in the superficial and deep plexiform layers and in the fiber layer. The second class consists of six types of pyramidal‐like candelabra cells, composing the cellular layer.

In lMDC solitary cells are also present in the superficial and deep plexiform layers and in the fiber layer. Large pyramidal cells of one type lie in the cellular layer. In addition, neurons of the dorsal cortex and of the ventral cell plate of Unger lie in the medial superposition area of lMDC. Throughout the entire mediodorsal cortex, protoplasmic and fibrous astrocytes and ependymal tanycytes are found.
Ultrastructure and acetylcholinesterase content of neurones forming connections between the striatum and substantia nigra of rat
Authors: Henderson Zaineb
Published: January 2005

Neurones in the striatum and substantia nigra (zona compacta) of the rat were divided into several classes according to differences in morphological appearance and ultrastructural localization of acetylcholinesterase (AChE). To determine which of the neurone types form connections between the substantia nigra and striatum, the ultrastructural localization of AChE was combined with retrograde axonal transport of horseradish peroxidase (HRP). The products of the histochemical reactions for HRP and AChE are localized in separate intracellular compartments and so identification of the efferent cell types was possible.

In the striatum there are two morphological classes of AChE‐containing neurone and two or three varieties of cell which do not stain for the enzyme. Only one neurone type projects to the substantia nigra and this is a cell with no AChE which makes up 96% of the total neurone population. In the substantia nigra there are two types of neurone with AChE: a cell with rather variable amounts of AChE which projects to the striatum, and another rarer type, possibly an interneurone.
Ultrastructural changes in olfactory receptor neurons following olfactory nerve section
Authors: Simmons Peter A. , Rafols Jose A. , Getchell Thomas V.
Published: January 2005

Unilateral olfactory nerve section was performed in the salamander, Ambystoma tigrinum. An ultrastructural study was performed to investigate the changes occuring during degeneration and replacement of the mature olfactory receptor neurons. Experimental and contralateral control tissues were examined following postoperative survival periods ranging from 12 hours to 90 days. Normal bipolar receptor neurons have a fusiform cell body containing a thin rim of cytoplasm and an ovoid nucleus with a characteristic “checkerboard” chromatin pattern. A single apical dendrite projects to the surface of the epithelium, where numerous cilia extend from its apex into the overlying mucus. A single, unmyelinated, unbranching axon originates at the basal pole of the cell. After nerve section, retrograde degeneration of the mature neurons occurs. Early degenerative changes include pronounced condensation of the nuclear chromatin, increased number of nuclear membrane infoldings, and dilation of the space between the membranes of the nuclear envelope. At a later stage, the cytoplasm of the cell increases in volume and its organelle systems break down, resulting in accumulation of various forms of cell inclusions. Subsequently, proliferation of cells in the basal region of the epithelium occurs. Between 3 week and 2 months following nerve section, these cells differentiate into mature neurons. By 3 months, neurons within the epithelium have resumed their normal ultrastructure. Correlation of the time course of the ultrastructural changes with previously reported neurophysiological studies indicates that neuronal activity of the epithelium is dependent upon the presence of fully differentiated olfactory neurons.
Ascending auditory afferents to the nuclei of the lateral leminscus
Authors: Glendenning K. K. , Brusno‐Bechtold J. K. , Thompson G. C. , Masterton R. B.
Published: January 2005

Afferents from the hindbrain auditory system to the nuclei of the lateral lemniscus were analyzed by the use of orthograde and retrograde axontracing techniques. Three divisions of the nuclei of the lateral lemniscus, a dorsal, an intermediate, and a ventral division are discussed. The dorsal nucleus of the lateral lemniscus is a recipient of afferents from cells located mainly in the superior olivary complex and the contralateral dorsal nucleus of the lateral lemniscus. It receives direct afferents from only a few cells in the cochlear nuclei. In sharp contrast, the ventral nucleus of the lateral lemniscus is the recipient of afferents from many cells in the contralateral ventral cochlear nucleus and from only a few cells in the superior olivary complex. Further, it receives no afferents from cells in the contralateral nuclei of the lateral lemniscus. The intermediate nucleus of the lateral lemniscus receives afferents from some cells in the cochlear nucleus and the superior olivary complex. It is unique among the three nuclei of the lateral lemniscus in that it receives a substantial projection from the medial nucleus of the trapezoid body.