bluuebunny/crossref_metadata_2025 huggingface dataset:
Small lateral suprasylvian cortex lesions produce visual neglect and decreased visual activity in the superior colliculus
Authors: Hardy Stephen C. , Stein Barry E.
Published: May 2005

Previous experiments in cats have shown that complete contralateral visual neglect is produced by removing all known visual cortex on one side of the brain, which can then be reversed by damaging the opposite superior colliculus. Presumably, descending facilitatory influences from the visual cortex to the ipsilateral superior colliculus are counterbalanced by intercollicular inhibition (Sprague: Science 153:1544‐1546, ′66). However, not all of visual cortex or all of the superior colliculus needs to be involved in this circuit. It is the deep rather than the superficial laminae of the superior colliculus that are primarily involved in visual attentive and orientation behaviors, and these laminae are largely independent of primary visual cortex. However, they do depend on corticotectal influences from a comparatively small extraprimary visual area of the posterior region of the lateral suprasylvian cortex (PSSC—Ogasawara et al: J. Neurophysiol. 52:1226‐1245, ′84). The present experiments demonstrate that lesions only a few millimeters in diameter in this corticotectal zone of the PSSC can produce profound visual neglect. While damage to this area has little, if any, effect on superficial laminae visual activity, it produces a dramatic decrease in the visual activity of the deep laminae. These cats with PSSC lesions fail to orient to a visual stimulus that is introduced suddenly into the contralateral visual field, yet they respond on nearly 100% of the trials to this same stimulus when it is presented in the ipsilateral visual field. The lesion‐induced visual neglect produced by PSSC lesions is long‐lasting but can be abruptly ameliorated by a midbrain lesion that primarily involves, or undercuts, the deep laminae of the contralateral superior colliculus. Thus, (1) visual neglect can be produced by depriving the deep laminae of the superior colliculus of visual inputs from the cortex, even when the principal visual cortical regions (17, 18, and 19) and their target structures are intact, and (2) visually guided behavior can be restored by eliminating afferents originating in, or passing through, the deep laminae of the contralateral superior colliculus.
Identification of the blue‐sensitive cones in the mammalian retina by anti‐visual pigment antibody
Authors: Szél Á. , Diamanstein T. , Röhlich P.
Published: May 2005

Monoclonal antibodies to visual pigments produced in our laboratory were applied to analyze the distribution of color‐specific photoreceptor cells in the retina (photoreceptor mosaic). We demonstrated in two ways that the monoclonal antibody OS‐2 specifically recognized the blue‐sensitive cone cells in the mammalian retina. First, rabbit photoreceptors damaged selectively by intense blue light were recognized by OS‐2 antibody. Second, OS‐2‐positive cones in the ground squirrel were those with thick inner segments, which is known to be characteristic of the blue‐sensitive cones. In addition, the OS‐2‐positive cones in monkeys have a distribution and pattern characteristic of blue‐sensitive cones in that species. In several other species (human, rabbit, cow, and pig), the OS‐2‐positive cones represent an appropriate minority of the population of photoreceptor cells.

The visual pigment recognized by the OS‐2 antibody had a relative molecular weight of 36,000, as shown by immunoblotting of 3 mammalian species. All other cones were recognized by another monoclonal antibody, COS‐1, which is regarded as specific to middle‐to‐long‐wavelength‐sensitive photoreceptors.
Forebrain connections of the gustatory system in ictalurid catfishes
Authors: Kanwal Jagmeet S. , Finger Thomas E. , Caprio John
Published: May 2005

Horseradish peroxidase tracing and extracellular electrophysiological recording techniques were employed to delineate prosencephalic connections of the gustatory system in ictalurid catfishes. The isthmic secondary gustatory nucleus projects rostrally to several areas of the ventral diencephalon including the nucleus lobobulbaris and the nucleus lateralis thalami. Injections of HRP in the vicinity of the nucleus lobobulbaris reveal an ascending projection to the telencephalon terminating in the area dorsalis pars medialis (Dm) and the medial region of area dorsalis pars centralis (Dc). Conversely, injections of HRP into the gustatory region of area dorsalis pars medialis label small neurons in the nucleus lobobulbaris. Gustatory neurons in the telencephalon send descending projections via the medial and lateral forebrain bundles to several nuclei in the anterior and ventroposterior diencephalon. The nucleus lateralis thalami, a diencephalic nucleus, receives ascending gustatory projections from the secondary gustatory nucleus but does not project to the telencephalon. Neurons in both the nucleus lateralis thalami and the telencephalic gustatory target exhibit multiple extraoral and oral receptive fields and complex responses to chemical (taste) and tactile stimulation.
Relationship between cortical lamination and texture sensitivity in complex neurones of the striate cortex in cats
Authors: Edelstyn N. M. J. , Hammond P.
Published: May 2005

The present study provides detailed anatomical evidence that the strongly texture‐sensitive complex neurones of the cat's striate cortex constitute a discrete subset of all complex neurones, and lie in two bands, deep in lamina III and in lamina V.

Physiological properties of simple and complex striate cortical neurones were characterized extracellularly in lightly anaesthetized cats by use of micropipettes filled with 12% Fast Green FCF dye in 2.0 M sodium chloride. Complex neurones were further subdivided on the basis of their length‐summating properties for an optimally oriented bar into “standard,” “special,” or “intermediate” categories and on the basis of their tuning and degree of sensitivity to motion of random texture.

Extracellular dye marks were made at strategic locations along each microelectrode track, especially at the site of recording from strongly texture‐sensitive complex neurones. Tracks were reconstructed with the aid of the histologically recovered dye marks in sections counterstained with cresyl violet to reveal cortical lamination.

The results confirm and refine the inference made by Hammond and MacKay (Exp. Brain Res. 22:427–430, '75; Exp. Brain Res. 30:275–296, '77) and the gross observations from 2‐deoxyglucose uptake studies by Wagner, Hoffmann, and Zwerger (Brain Res. 224:31–43, '81) concerning the laminar distribution of texture‐sensitive complex neurones in the cat's striate cortex.
Projections of the nucleus of the tractus solitarius in the pigeon (Columba livia)
Authors: Arends J. J. A. , Wild J. M. , Zeigler H. Philip
Published: May 2005

With the aid of autoradiographic and histochemical (WGA‐HRP) tracing techniques, the projections of the nucleus of the nucleus of the tractus solitarius (nTS) in the pigeon have been delineated and related to the viscerotopic organization of the nucleus. As in mammals, nTS projects to both brainstem and forebrain structures. At medullary levels, projections were seen to nTS itself, to the dorsal motor nucleus of the vagus and to the subjacent and more ventral reticular formation. There is a substantial projection to the parabrachial nuclear complex with terminations in all its subnuclei and minor projections to locus coeruleus and several mesencephalic areas, including the ventral area of Tsai, the nucleus of the ascending brachium conjunctivum, and the compact portion of the tegmental pedunculopontine nucleus. At diencephalic levels, projections to the hypothalamus (magnocellular periventricular nucleus, stratum cellulare internum and externum) and dorsal thalamus were seen. Terminal fields within the basal telencephalon included the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, and the nucleus accumbens.

The organization of nTS projections in pigeons is correlated with the pattern of inputs to specific nTS subnuclei. Lateral tier subnuclei receiving cardiovascular and pulmonary inputs project upon the ventrolateral reticular formation and the ventrolateral parabrachial complex. Medial tier subnuclei receiving gustatory and gastrointestinal inputs project upon dorsal and medial parabrachial nuclei. Transparabrachial projections arise from nTS subnuclei receiving little or no primary input from the viscera.
Lumbar lateral motor column development in triploid Xenopus laevis
Authors: Sperry David G.
Published: May 2005

The effects of increasing ploidy on the development of the lumbar lateral motor column (L‐LMC) in Xenopus laevis were investigated in order to determine how early events contribute to producing the significant difference in the average number of motoneurons present in diploid and triploid animals after cell death (Sperry: J. Comp. Neurol. 277:499–508, '88). From naturally occurring diploid and experimentally produced triploid siblings at two stages prior to significant amounts of neuronal cell death, at one stage during the peak period of cell death, and at one stage after cell death, the L‐LMC motoneurons were counted and nuclear cross‐sectional areas were measured. At stages before and after cell death, the average nuclear crosssectional areas of motoneurons and of other cells that were also measured were greater in the triploids, while the average number of motoneurons and motoneuron density (the mean number of cells per section) were less. Average body size and average motor column length in diploid and triploid animals were equal at each of the stages. The general characteristics of L‐LMC development that have been widely noted in diploids, an increase in cell size accompanied by a decrease in cell number, were also observed in the triploid animals. However, not only were these general features present in the triploids, but the increase in average motoneuron size and the decrease in average motoneuron number in diploids and triploids were roughly equal when scaled to the general differences in nuclear size or to the difference in the average number of motoneurons present prior to cell death. There was no evidence that the triploid condition affected the magnitude of the cell death process.

Overall, the findings suggest that the processes underlying L‐LMC development in experimentally produced triploids may not be different from those in naturally occurring diploids. The smaller average numbers of motoneurons after cell death in the triploids may be related to some feature of the triploid condition that affects the number of motoneurons present before cell death rather than to a feature of the triploid animals, such as peripheral size, that is thought to affect the motoneuron cell death process itself. The relationship of these findings to the general issue of how the size of the L‐LMC motoneuron population in triploids, as well as in diploids, might be regulated is discussed.
Localization of enkephalinergic neurons in the dorsolateral pontine tegmentum projecting to the spinal cord of the cat
Authors: Reddy V. Krishna , Fung Simon J. , Zhuo Huang , Barnes Charles D.
Published: May 2005

The dorsolateral pontine tegmentum of the cat is known to contain enkephalinergic neurons, with most of the enkephalin co‐contained in the catecholaminergic neurons; however, enkephalinergic cells projecting to the spinal cord have not been identified. This study employs retrograde transport of horseradish peroxidase in combination with methionine‐enkephalin or tyrosine hydroxylase immunocytochemistry to 1 determine the locations of pontospinal enkephalinergic neurons and 2 compare these with the locations of pontospinal catecholaminergic neurons.

Pontospinal enkephalinergic neurons were observed in the nuclei locus coeruleus and subcoeruleus and the Kölliker‐Fuse nucleus. A high concentration of these neurons was evident in the Kölliker‐Fuse nucleus when compared to the nuclei locus coeruleus and subcoeruleus (P<.01). Both the enkephalinergic and catecholaminergic neurons projecting to the spinal cord were located in the same general areas of the dorsolateral pontine tegmentum and there was no significant difference in the mean diameters of these two neuronal types (P>.05). Quantitative data concerning the pontospinal enkephalinergic neurons correlated well with previous data an pontospinal catecholaminergic neurons (Reddy et al., Brain Res. 491:144–149, '89). A majority of the descending neurons from the dorsolateral pontine tegmentum contain enkephalin (72–80%) and catecholamine (80–87%). The observations suggest that enkephalin is contained in many of the pontospinal catecholaminergic neurons.
Synaptic morphometry and synapse‐to‐neuron ratios in the superior colliculus of albino rats
Authors: Albers F. J. , Meek J. , Hafmans T. G. M.
Published: May 2005

The superior colliculus of mammals is generally divided into seven layers on the basis of the distribution of myelinated fibers, which are densely packed in layers III, V, and VII but sparse in the other layers. The laminar distribution of afferents and efferents allows, in addition, for the distinction of a superficial visual zone (layers I‐III) and a deeper multimodal and premotor zone (layers IV‐VII). Collicular neurons, however, do not show a lamination pattern, but are rather homogeneously distributed with only gradual transitions (Albers et al.: J. Comp. Neurol. 274:357‐370, '88).

The present study analyses whether the distribution of collicular synapses is correlated with the laminar organization of collicular axons or rather with the more homogeneous distribution of collicular neurons. For this purpose, the size and density of synaptic terminals and contacts as well as synapse‐to‐neuror ratios were determined in all collicular layers of albino rats by means of quantitative analysis of electron microscopic pictures.

The size of presynaptic terminals and contacts does not differ significantly between individual collicular layers. On average, presynaptic terminal diameter is 1,079 nm, and synaptic contact size 338 nm, while 23% of all contacts are of the symmetrical type with pleiomorphic vesicles. The average numerical synaptic density is 422 million per mm3. This value is significantly higher in layers I and II (on average 670 million per mm3) than in layers III–VII (on average 370 million per mm3). The synapse‐to‐neuron (S/N) ratios calculated show that collicular neurons have on average 6,120 synaptic contacts on their receptive surface. The S/N ratio is lowest in layer III (4,330), while this ratio is highest in layers I and VII (i.e., 8,970 and 8,560 respectively). Layer II has a significantly higher S/N ratio than layer III (i.e., 8,060 and 4,330, respectively).

Our results show that the size of synaptic terminals and contacts is not correlated with the different connectivity patterns of the distinct collicular layers. However, the density of synapses as well as the synapse‐to‐neuron ratios show a certain degree of laminar differentiation. In particular the superficial visual zone appears to be inhomogeneous in this respect, since layers I and II have a significantly higher density of synapses and higher S/N ratios than layer III. The deeper collicular zone is more homogeneously organized with synaptic densities similar to that of layer III and gradually increasing synapse‐to‐neuron ratios from layer IV to layer VII.
Local intra‐ and interlaminar connections in mouse barrel cortex
Authors: Bernardo Kerry L. , McCasland James S. , Woolsey Thomas A. , Strominger Robert N.
Published: May 2005

Focal injections of horseradish peroxidase (HRP) in dimethylsulfoxide (DMSO) were targeted into mouse somatosensory cortex, in vitro, with a template. Injections were made at different depths and in different locations in the whisker‐barrel‐defined somatosensory map in order to determine quantitative connectivity patterns within and between barrel‐defined cortical columns. Cortices were sectioned in a plane parallel to the pia at 75 βm. Data were collected directly from microscope slides by computer.

Data are presented as: (1) Plots of computer‐mapped HRP reaction product density in neurons and cell locations for each section in relation to barrel boundaries; (2) histograms of label in cortical layers related to individual barrel‐defined columns; (3) polar plots of relative amounts of label within individual barrel columns in sections through each barrel column; (4) vectors which represent HRP reaction product density as a function of direction and distance from the injection site; (5) statistical analysis of the shape of the label distribution pattern in the plane of the cortex as a function of injection site depth; and (6) probability of labeling of any other barrel column given a labeled barrel column.

The principal findings are: (1) The pattern of label distribution, after an injection directly above or directly below an individual barrel, is hour‐glass shaped with the waist of the hour‐glass in layer IV. (2) Connections within barrel cortex are asymmetrical. Barrel‐related columns within a row are more strongly interconnected than those in different rows. (3) Connections of the small barrels associated with whiskers on the upper lip are strongest with other small barrels, but strong connections also exist between these small barrels and the larger barrels. (4) The pattern of intracortical connections in SII is not asymmetrical; interlaminar connections in SII are fundamentally different from those in barrel cortex. (5) Quantitative intracortical projection patterns are highly consistent with functional data on intracortical processing of whisker information. As such, the quantitative data clearly indicate the spatial extent and relative magnitude of populations of neurons involved in intracortical processing of sensory information.

The spatial arrangements of these intracortical connections, in conjunction with known developmental events, make it highly likely that the distribution of intracortical axons in mouse barrel cortex is sculpted in part by experience.
Morphology of antennal motoneurons in the brains of two crickets, gryllus bimaculatus and gryllus campestris
Authors: Honegger Hans‐Willi , Allgäuer Cölestin , Klepsch Ulrike , Welker Jutta
Published: May 2005

The morphology of the antennal muscles of two cricket species, Gryllus campestris and G. bimaculatus, and their innervation are described. The motoneurons innervating the five tentorio‐scapal muscles M4 and M5 and the two scapo‐pedicellar muscles M6 and M7 were stained with cobalt chloride introduced via the cut axonal endings in the muscle. The seven antennal muscles are innervated by a total of 17 excitatory motoneurons and one common inhibitory neuron. These neurons branch in the dorsal neuropil of the deuto‐and tritocerebrum. No difference in the morphology of the motoneurons between the two species was evident. Two dorsal‐unpaired‐medial (DUM) neurons located in the suboesophageal ganglion also innervate the antennal muscles. Intracellular recordings of some motoneurons combined with Lucifer Yellow injections corroborated the motoneuron morphology obtained by cobalt backfilling from the muscles. The recordings showed that the motoneurons are either of the fast or the slow type.
Capsaicin‐induced neuronal degeneration in the brain and retina of preweanling rats
Authors: Ritter Sue , Dinh Thu T.
Published: May 2005

Capsaicin is a neurotoxin known for its ability to cause degeneration of small unmyelinated primary sensory neurons in both spinal and cranial nerves. Although lower motor neurons do not degenerate following capsaicin treatment, the extent to which capsaicin may damage neurons in the brain has not been thoroughly evaluated. This study examines the effects of systemic capsaicin (50–150 mg/kg) on the central nervous system of 10‐day‐old rats. Rat pups were injected with capsaicin or the injection vehicle and sacrificed 6 hours–10 days later. Brains, spinal cords, and retinas ware stained with cupric silver to label degenerating neurons. As previously reported for capsiaicin‐treated rats, degenerating nerve terminals were present in areas receiving primary afferent input: the spinal cord dorsal horn, spinal trigeminal nucleus, nucleus of the solitary tract, and area postrema. However, degenerating terminals were also present in areas not known to receive primary sensory innervation: the inferior olivary nucleus, sphenoid nucleus, medial and olivary pretectal nuclei, interpeduncular nucleus, interfascicular nucleus, caudal linear, dorsal, median, and paramedian raphe nuclei, supramammillary area, lateral habenula, ventrolateral geniculate nucleus, ventral reuniens nucleus, ventromedial hypothalamic nucleus, lateral hypothalamic and preoptic areas, suprachiasmatic nucleus, septohypothalamic nucleus, bed nucleus of the stria terminalis, lateral septal nucleus, accumbens shell, olfactory bulb, and retina. Some areas where capsaicin caused degeneration in rat pups do not appear to be capsaicin‐sensitive in adult rats. Results indicate that (1) capsaicin's neurotoxicity is not limited to primary sensory neurons and (2) developmental factors may alter the capsaicin sensitivity of some neuronal projections within the brain.
Cell death of corticospinal neurons is induced by axotomy before but not after innervation of spinal targets
Authors: Merline Michael , Kalil Katherine
Published: May 2005

The response of corticospinal neurons to axotomy at postnatal ages from 5 days to adulthood was studied in the golden hamster (Mesocricetus auratus). Corticospinal neurons were retrogradely labeled with flourescent rhodamine latex beads injected into the cervical or lumbar spinal cord. A unilateral lesion of the medullary pyramidal tract was made 1–2 days later and the brains fixed 1–30 days after axotomy. Comparisons of labeled axotomized corticospinal neurons with labeled normal corticospinal neurons in the contralateral cortex showed that axotomy at 14 days or later caused cell shrinkage but not cell death. Axotomy prior to 14 days caused cell death of corticospinal neurons. More neurons died the earlier the lesion was made, culminating in virtual complete cell death of corticospinal neurons following axotomy at 5 days. Axotomy at a given age did not affect all corticospinal neurons uniformly. Lumbar projection neurons underwent cell death ranging from slight to complete following axotomy at 13 and 9 days, respectively. Cervical projection neurons, in contrast, survived axotomy after a lesion at 9 days but underwent complete cell death if the lesion occurred at 5 days. Since corticospinal axons innervate the cervical cord from postnatal days 4–8 and the lumbar cord from 10–14 days (Reh and Kalil, '81; J. Comp. Neurol. 200:55–67), the ability of corticospinal neurons to survive axotomy appears to be temporally well correlated with their innervation of spinal targets. These neurons die if their axons are cut prior to target innervation but are able to survive if axotomy occurs after their axons innervate spinal targets. The results show that plasticity in the corticospinal pathway documented in previous reports cannot take the form of regrowth of severed axons, since early lesions cause extensive corticospinal cell death. Aberrant corticospinal pathways resulting from early lesions must therefore arise from undamaged axons. Additional retrograde labeling experiments showed that the opposite cortex responded to contralateral pyramidotomy by sprouting into denervated areas of the spinal cord. Thus another source of plasticity after early pyramidal tract lesions is sprouting from corticospinal axons arising from the intact cortex.
Sublaminar organization within layer VI of the striate cortex in Galago
Authors: Conley Michael , Raczkowski Denis
Published: May 2005

In this study we examined the organization of projections from the striate cortex to the dorsal lateral geniculate (GL) and pulvinar (PUL) nuclei in the prosimian Galago by using retrograde transport methods. Injections of wheat germ agglutinin‐conjugated horseradish peroxidase (WGA‐HRP) into the PUL labeled two bands of cells in the striate cortex: the first consisted of large pyramidal cells in the upper half of layer V; the second consisted of small and medium‐size pyramidal cells located in the deepest part of layer VI. The location of cells within layer VI coincided with a clear cytoarchitectonic sublayer, VIb, which contains fewer and paler staining cells than VIa. Injections of WGA‐HRP involving all layers of the GL produced an uninterrupted band of pyramidal cells distributed throughout layer VI (a and b), including the region labeled after injections into the PUL. Thus as a first approximation, layer VI can be divided into an upper tier (VIa) that projects only to the GL and a lower tier (VIb) that projects to both the GL and PUL. Injections of WGA‐HRP that were restricted to one or a few GL layers revealed a further refinement of the subdivisions within layer VI. Injections into the parvicellular and intercalated (or koniocellular) layers of the GL labeled neurons predominantly in the upper half of layer VIa, whereas injections restricted to the magnocellular layers labeled neurons in the lower half of layer VIa and in layer VIb. In order to determine whether individual neurons in layer VIb send axon collaterals to both the GL and PUL, we injected WGA‐HRP into one nucleus and fluorescent rhodamine latex beads into the other. In three experiments, we found only one double‐labeled cell. In sum, the results provide evidence that layer VI is divided into at least three sublayers: upper VIa, which projects to the intercalated and parvicellular GL layers; lower VIa, which projects to the magnocellular GL layers; and VIb, which sends separate projections to the magnocellular layers of the GL and to the PUL. The segregation observed is sufficiently discrete to propose the existence of multiple, descending pathways from layer VI of the striate cortex that complement those ascending from the GL and PUL.
Central projections from the skin of the hand in squirrel monkeys
Authors: Florence S. L. , Wall J. T. , Kaas J. H.
Published: May 2005

Central termination patterns of afferents from the hands of squirrel monkeys were studied after subdermal injections of wheat germ agglutinin conjugated with horseradish peroxidase (WGA‐HRP) or cholera toxin subunit B conjugated to HRP (BHRP). WGA‐HRP more effectively labeled axons terminating in the superficial dorsal horn of the spinal cord, while BHRP more effectively labeled axons terminating in the deeper layers. Injections of both tracers, when restricted to parts of glabrous digits, palm, or dorsal hand, revealed somatotopic patterns in the spinal cord and pars rotunda of the cuneate nucleus that were, in some respects, similar and, in other respects, quite different from those previously reported for macaque monkeys (Florence et al., J. Comp. Neurol. 286:48–70, 1989). As in macaques, injections in digits 1–5 produced a rostrocaudal sequence of foci of terminations in the cervical spinal cord. However, inputs from the palm were located medial to those from the digits, whereas the palm is represented lateral to the digits in macaque monkeys. Since inputs from the palm are also medial in the dorsal horn in cats (Nyberg and Blomqvist, J. Comp. Neurol. 242:28–39, 1985), the condition in squirrel monkeys may be similar to the generalized state. In the cuneate nucleus, single injections in the hand produced dense label in the pars rotunda, and sparse label in the rostral and caudal poles. As in macaque monkeys, inputs from specific parts of the hand related to rostrocaudal clusters of cells that are cytochrome oxidase dense. The representation of the digits differed from macaques in that the digits were represented dorsal to the palm, rather that ventral to the palm as in macaques. Again, comparisons with cats suggest that squirrel monkeys have the more generalized pattern. Finally, inputs from the hairy, dorsal surfaces of the digits terminated on the same clusters as the inputs from the glabrous, ventral surfaces, apparently overlapping somewhat. The proximity of these terminations from dorsal and ventral surfaces of the digits may be related to observations that cortical representations of the glabrous surfaces of digits become responsive to dorsal surfaces of the same digits when inputs from glabrous skin are chronically deactivated (e.g., Merzenich et al., Neuroscience 3:33–55, 1983).
Topographic organization of the cochlear spiral ganglion demonstrated by restricted lesions of the anteroventral cochlear nucleus
Authors: Leake Patricia A. , Snyder Russell L. , Merzenich Michael M.
Published: May 2005

The morphological organization of the central projections of the cat cochlear spiral ganglion into the cochlear nucleus has been investigated by creating restricted lesions in the anteroventral cochlear nucleus (AVCN) in order to ablate selectively either the lateral or the medial aspect of isofrequency projection laminae. Such lesions induced highly selective retrograde degeneration of spiral ganglion cells. Ablation of the lateral part of the AVCN resulted in degeneration of cells within the scala tympani portion of the ganglion, whereas medial lesions within the AVCN induced degeneration of the scala vestibuli portion of the ganglion. Since most, if not all, of the primary afferent axons of the cochlear nerve bifurcate into ascending and descending branches as they enter the brainstem, it is noteworthy that selective damage to the ascending branch in the AVCN was sufficient to induce retrograde degeneration of the spiral ganglion cell somata. The peripheral and central axons also degenerated, and the losses of both the radial nerve fibers in the osseous spiral lamina and the central axons passing into the modiolus displayed selective topographies that paralleled the cell loss within the spiral ganglion.

The results of this study support our previous hypothesis, based upon earlier horseradish peroxidase labeling experiments, that there is a topographic organization to the projection of the spiral ganglion within the isofrequency laminae that is orthogonal to the frequency representation within the ventral cochlear nuclei (VCN). That is, in addition to the spiral frequency organization of the ganglion, represented by the dorsal‐to‐ventral frequency map in the VCN, there is also an orderly and sequential distribution of inputs from the vertical (scala tympani‐to‐scala vestibuli) dimension of the spiral ganglion across the lateral‐to‐medial axis of the VCN. The interaction of these two topographic representations, distributed across the three dimensions of the VCN, must partly define the selective and/or integrative neuronal response properties at this first level of central nervous system processing of auditory signals within the cochlear nuclei.
Development and distribution of noradrenergic and cholinergic neurons and their trophic phenotypes in the avian ceruleus complex and midbrain tegmentum
Authors: von Bartheld Christopher S. , Bothwell Mark
Published: May 2005

We investigated the development of noradrenergic and cholinergic neurons in the ceruleus complex and mesencephalic tegmentum in embryonic and posthatch chickens and compared the distribution of transmitter phenotypes with the expression of nerve growth factor receptor (NGFR) mRNA and fibroblast growth factor receptor (FGFR) mRNA. Noradrenergic and cholinergic neurons were visualized by using antibodies against dopamine‐beta‐hydroxylase (DBH) and choline acetyltransferase (ChAT), respectively. Expression of receptors for trophic factors was determined by using in situ hybridization techniques.

Noradrenergic neurons concentrate in caudal parts of the locus ceruleus and nucleus subceruleus. Cholinergic ceruleus neurons are abundant in the nucleus mesencephalicus profundus, pars ventralis (MPv) as well as in the nucleus subceruleus and locus ceruleus. This cholinergic population resembles the cholinergic pontomesencephalotegmental complex of mammals. Both DBH and ChAT label is evident at and after six days of incubation (E6). The distribution and numbers of immunolabeled neurons are similar in the embryonic and posthatch chick. Initially, many tegmental and ceruleus neurons express substantial levels of NGFR mRNA (E7–E9). After E9, expression of NGFR mRNA decreases in most of these neurons, except for a distinct subpopulation of neurons in caudal parts of the ceruleus complex with increased levels of NGFR transcripts. These NGFR‐positive neurons coincide in number and distribution with the noradrenergic subpopulation of the ceruleus complex (800‐‐900 neurons). Expression of FGFR mRNA was first detected in ceruleus neurons at E13. Neurons with FGFR transcripts have the same number and distribution as the neurons with the cholinergic phenotype (2,000–‐2,300 neurons).

Transmitter heterogeneity in the ceruleus complex is reflected by a heterogeneity of receptors for trophic factors, with NGFR expressed in the noradrenergic subpopulation, and FGFR expressed in the cholinergic subpopulation. These findings provide evidence for new chemoarchitectonic subdivisions of the avian ceruleus complex. The data showing onset of ChAT expression prior to the onset of FGFR expression argue against a role of FGFR in the determination of the cholinergic transmitter phenotype. Expression of NGFR in the noradrenergic ceruleus subpopulation reveals remarkable species differences as compared to mammals.
Calcitonin gene‐related peptide in nucleus ambiguus motoneurons in rat: Viscerotopic organization
Authors: Lee Bong Hee , Lynn Richard B. , Lee Heung‐Shik , Miselis Richard R. , Altschulers Steven M.
Published: May 2005

Calcitonin gene‐related peptide has been reported in the rat nucleus ambiguus. This nucleus comprises a dorsal division that is the source of special visceral efferents innervating the striated muscle of the upper alimentary tract and a ventral division supplying general visceral efferents primarily to the heart. The distribution of caldtonin gene‐related peptide immunoreactive neurons in the two divisions was determined by using a combination of immunocytochemical techniques and fluorescent retrograde tracing. In 22 rats, injections of Fluoro‐Gold were made into either the supranodosal vagus nerve, palatopharynx, larynx, esophagus, or heart. Following colchicine injection, medullary sections were processed immunocytochemically for calcitonin gene‐related peptide.

Injection of Fluoro‐Gold into the supranodosal vagus resulted in prominent labeling of neurons in the dorsal and ventral divisions of the nucleus ambiguus. The majority of fluorescent labeled neurons in the dorsal division were found to be immunoreactive for calcitonin gene‐related peptide, while those labeled neurons in the ventral division were unreactive for the peptide. With esophageal, and palatopharyngeal and cricothyroid injections, many fluorescent labeled neurons that were immunoreactive for calcitonin gene‐related peptide were found respectively in the compact and semicompact formations of the dorsal division. In contrast, injections of the heart resulted in fluorescent labeled neurons, which were unreactive for calcitonin gene‐related peptide, localized to the external formation.

The results demonstrate that calcitonin gene‐related peptide immunoreactive neurons are localized entirely to the dorsal division of the nucleus ambiguus and that all striated muscular areas of the alimentary tract are innervated by calcitonin gene‐related peptide containing motoneurons. The localization of calcitonin gene‐related peptide to vagal motoneurons also known to contain acetylcholine and the increase in acetylcholine receptor synthesis caused by this peptide suggest that calcitonin gene‐related peptide acts as a cotransmitter with acetylcholine in special visceral efferent vagal motoneurons.
Olfactory bulb organization and development in Monodelphis domestica (grey short‐tailed opossum)
Authors: Brunjes Peter C. , Jazaeri Amir , Sutherland Mark J.
Published: May 2005

The olfactory bulbs of adult and developing Monodelphis domestica were examined with a number of techniques. Golgi, Nissl, and Timm stains as well as acetylcholinesterase histochemistry revealed a high degree of order within the adult bulb. All major cell classes characteristic of most mammalian species were observed. Tufted cells appeared to be restricted to the superficial portion of the external plexiform layer. Developing Monodelphis pups were examined with Nissl‐stained semithin sections and with immunocytochemistry for tyrosine hydroxylase, microtubule‐associated protein 2, vimentin, and glial fibrillary acidic protein. Newborn pups are extremely immature, with few postmitotic cells present in the forebrain. Considerable maturation occurs over the first four postnatal weeks, and by postnatal day 30, the bulb assumes an adult‐like organization. The extreme immaturity of the bulb at birth, coupled with its strict organization, suggest that Monodelphis is a particularly appropriate species for experimental examinations of olfactory system development.
Glutamate‐immunoreactive terminals synapse on primate spinothalamic tract cells
Authors: Westlund Karin N. , Carlton Susan M. , Zhang Dongxian , Willis William D.
Published: May 2005

Glutamate has been shown to excite spinothalamic tract (STT) neurons and has been localized to primary afferent neurons, spinal cord projection neurons, and interneurons in the spinal cord dorsal horn. The likelihood that glutamate‐immunoreactive (GLU‐IR) terminals directly innervate STT neurons was investigated. For these studies three lamina IV or V STT cells in the lumbar spinal cords of three monkeys (Macaca fascicularis) were identified electrophysiologically and characterized. Two were identified as high threshold neurons and one as a wide dynamic range neuron. Following intracellular injection of the cells with HRP and reaction to give the cells a Golgi‐like appearance, the tissues were processed for electron microscopy. Postembedding immunogold methods with antibodies specific for glutamate were used to identify GLU‐IR terminals apposing the somata and dendrites of the STT neurons, including dendrites that extended into laminae IV and III. The GLU‐IR terminals were numerous and constituted a mean of 46% of the population counted that appose the STT soma and 50% of the profiles apposing the dendrites. Fifty‐four percent of the somatic and 50% of the dendritic surface length was contacted by GLU‐IR terminals. Most terminals contained round clear vesicles and some contained a variable number of large dense core vesicles. For one of the three cells examined it was determined that 45% of the terminals apposing the soma were GLU‐IR and 30% of the terminals were gamma aminobutyric acid‐immunoreactive (GABA‐IR). In an additional monkey, a lamina I cell retrogradely labeled from the ventral posterolateral nucleus of the thalamus was found to be ensheathed in glial processes. Of the 9 terminals observed apposing the retrogradely filled STT neuron in one plane of section, 2 were GLU‐IR and 3 were GABA‐IR. The data suggest that a large percentage of the profiles adjacent to STT neurons in intermediate laminae of the spinal cord contain glutamate and many synapse directly with STT neurons.
Nuclear clefting in dorsal root ganglion neurons: A response to whole body vibration
Authors: McLain Robert F. , Weinstein James N.
Published: May 2005

Normal adult rabbits were studied in a whole body vibration model which simulates the type of environmental exposure associated with vibration‐induced low back pain. This model has previously been shown to induce changes in pain‐related neuropeptides in the dorsal root ganglion. Following two weeks of daily exposure to whole body vibration, dorsal root ganglia were excised from control and vibrated rabbits and prepared for ultrastructural evaluation. Of over 1,200 cells sampled, 190 appropriately sectioned cells were analyzed: 32 from immobilized controls, 44 from normal controls, and 114 from vibrated animals. Analysis of nuclear contours revealed more prevalent and more extensive clefting of the nuclear membrane in vibrated cells. The membrane lining these clefts was traversed by numerous pores; density of these pores was 46% greater than in adjacent nonclefted segments (p <.001). Number of clefts per nucleus was increased by 39% in vibrated animals. Cleft area represented 1.19% of nuclear area in vibrated cells compared to 0.74% in controls (p <.001). Numerous mitochondria and free ribosomes and abundant rough endoplasmic reticulum were located within the cleft spaces of vibrated cells. Pores in the cleft membrane appeared normal, supporting the conclusion that the clefts are structural alterations rather than fixation or sectioning artifacts.

Changes in dorsal root ganglion neuropeptides seen in previous studies of vibrated animals may result from increased or redirected cellular synthesis. Ultrastructural changes seen in these vibrated dorsal root ganglion neurons are consistent with such an alteration in metabolism and could reflect increased synthesis of pain‐related neuropeptides. © 1992 Wiley‐Liss, Inc.
Spatial representation of frequency‐modulated signals in the tonotopically organized auditory cortex analogue of the chick
Authors: Heil Peter , Scheich Henning
Published: May 2005

For auditory communication, many birds, including domestic chicks, use a variety of frequency‐modulated (FM) sounds. As a first approach to the spatial representation of such sounds in the central auditory system, we have analyzed 2‐deoxyglucose (2DG) patterns that were produced by FM stimuli in the tonotopic map of the auditory forebrain area (field L/hyperstriatum ventrale complex) of domestic chicks. Linear FM signals, varying in the depth and range of modulation, and in the direction and rate of the frequency change, were tested. Also included were signals designed to mimic species‐specific FM calls. All FM stimuli activated those regions of the map in which frequencies contained in the stimulus spectra were tonotopically represented. However, frequency and amplitude of the FM spectra were not faithfully reproduced by activation of the complete corresponding tonotopic space. FM signals that differed only in the direction of modulation, and therefore had identical long‐term spectra, induced maximum 2DG activation at different locations of the tonotopic gradient. FM signals that differed in the rate of change of frequency produced maxima of 2DG uptake at different positions along an isofrequency dimension of the map. These results suggest that the direction of modulation may be represented in a complex fashion along the tonotopic axis of the structure, whereas the rate of change of frequency may be represented along an isofrequency dimension. None of the experiments provided evidence of FM‐selective regions within the auditory forebrain complex. However, numerous telencephalic areas, in addition to the primary auditory area, were strongly activated in chicks stimulated with artificial “species‐specific” FM signals. These areas could be involved in the processing of biologically relevant stimuli, requiring attention, recognition, and interpretation of the signals. © 1992 Wiley‐Liss, Inc.
Lucifer yellow, retrograde tracers, and fractal analysis characterise adult ferret retinal ganglion cells
Authors: Wingate Richard J. T. , Fitzgibbon Tom , Thompson Ian D.
Published: May 2005

The dendritic morphology of retinal ganglion cells in the ferret was studied by the intracellular injection of lucifer yellow in fixed tissue. Ganglion cells were identified by the retrograde transport of red or green fluorescent microspheres that had been injected into different target nuclei, usually the lateral geniculate nucleus or superior colliculus. This approach allows the comparison of dendritic morphologies of ganglion cells in the same retina with different central projections and also identifies cells with branching axons. The digitised images of dendritic arbors were analysed quantitatively by a variety of measures. Dendritic complexity was assessed by calculating the fractal dimension of each arbor. The ferret has distinct alpha, beta, and gamma morphological classes of cells similar to those found in the cat. The gamma cell class was morphologically diverse and could be subdivided into “sparse,” “loose,” and “tight” groups, reflecting increasing dendritic complexity. Whereas the beta cell projection was limited to the lateral geniculate nucleus alone, alpha and gamma cells could project to either or both nuclei. Retinal ganglion cells labelled from the pretectal nuclei formed a morphologically distinct class of retinal ganglion cells. The ipsilateral projection lacked alpha cells and the most complex, “tight” gamma cells. However, ipsilaterally projecting “loose” gamma cells overlapped alpha cells in both soma and dendritic dimensions. Different morphological classes of retinal ganglion cells hence show characteristic axon behaviour both in their decussation at the chiasm and in which targets they innervate. Fractal measures were used to contrast variation within and between these identified classes. © 1992 Wiley‐Liss, Inc.
Long distance directed axonal growth from human dopaminergic mesencephalic neuroblasts implanted along the nigrostriatal pathway in 6‐hydroxydopamine lesioned adult rats
Authors: Wictorin K. , Brundin P. , Sauer H. , Lindvall O. , Björklund A.
Published: May 2005

Dissociated ventral mesencephalon of 6 to 8‐week‐old human embryos were implanted by stereotaxic injection at different sites along the nigrostriatal pathway in adult rats, previously subjected to a 6‐hydroxydopamine lesion of the intrinsic mesotelencephalic dopamine pathways. The recipients were immunosuppressed by daily injections of cyclosporin A to prevent rejection. At 13–20 weeks after transplantation, the implanted human neurons and their associated fiber outgrowths were visualized with a species‐specific antibody recognizing human, but not rat, intermediary neurofilaments (HNF). From implants placed in the host rostral mesencephalic region, HNF‐positive axonal projections were, seen to extend in large numbers rostrally along the medial forebrain bundle and the internal capsule, and ramify within the caudate putamen, the ventral striatum and the amygdaloid nuclei (a distance of about 5–6 mm), and more sparsely in the frontal cortex and the olfactory bulb (a distance of about 10 mm). From implants placed in the internal capsule, abundant HNF‐positive axons extended in the rostral, but not caudal, direction along the myelinated fiber bundles into the caudate putamen and the ventral striatum. Tyrosine hydroxylase (TH) immunohistochemistry revealed that the vast majority of the rostrally projecting HNF‐positive axons were also TH‐positive, and that the graft‐derived axons gave rise to dense TH‐positive terminal networks, above all in large areas of the previously denervated caudate putamen. From control implants of cortical neuroblasts, axonal projections were seen along the medial forebrain bundle and the internal capsule, but the axons were TH‐negative and showed only sparse projections to the striatal areas. Instead, dense projections were seen, e.g., in the frontal cortex.

The results demonstrate a remarkable ability of human mesencephalic neuroblasts to extend axons along the trajectories of the nigrostriatal and mesolimbocortical pathways to reach and innervate the principal striatal and limbic target areas in the forebrain. This shows that the basic requirements for the formation of long axonal pathways may be present in the adult mammalian central nervous system (CNS) at least for certain types of projection neurons. Furthermore, it implies that the developing human neuroblasts can escape the inhibitory features known to be present along myelinated growth trajectories in the adult mammalian brain. In addition, the present approach may offer new possibilities for functional neural grafting in the rat Parkinson model, since transplanted nigral neurons placed in their natural position within the rostral mesencephalon could provide an anatomically and functionally more integrated system than the standard model with ectopically placed intrastriatal nigral grafts. © 1992 Wiley‐Liss, Inc.