bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of the dendritic tree of wild‐type cerebellar Purkinje cells in lurcher chimeric mice
Authors: Caddy Keith W. T. , Herrup Karl
Published: January 2005

Naturally occurring mutations are valuable tools for the study of neural development, especially when used in conjunction with the techniques of chimeric mouse production. In this study we examine the response of Purkinje cell dendrites to the altered developmental environment found in the lurcher ↔ wild‐type chimera. Lurcher (+/Lc) is an autosomal dominant gene that causes the cell‐autonomous degeneration of all Purkinje cells of +/Lc genotype. Thus, in +/Lc → +/+ chimeras, only wild‐type Purkinje cells survive to maturity. The number of these survivors can vary from less than 10,000 to greater than 100,000, Previous work has shown that the final ratio of presynaptic granule cells to postsynaptic Purkinje cells is increased in lurcher chimeras. On average, therefore, one might expect that each remaining Purkinje cell would experience an increased supply of afferents, and our hypothesis was that dendritic growth and/or sprouting might occur as a result. This proved incorrect and, indeed, the Purkinje cells in the lurcher chimeras show changes of a predominantly atrophic nature. Unusual morphologies are found, including variable branching density, failure of the distal dendrite to reach the pial surface, loss of isoplanarity, and the frequent appearance of large caliber, primary or secondary dendritic branches ending abruptly in “stub ends.” Quantitative analysis of Golgi‐Cox impregnated material reveals that in lurcher chimeras the Purkinje cell dendritic arbor is reduced by more than 60% compared to wild‐type animals. We present possible explanations for this finding and consider several potential implications.
Vestibule‐ocular projections in the 11‐day chicken embryo: Pathway specificity
Authors: Pétursdóttir Gudrun
Published: January 2005

The organization of vestibulo‐ocular projections and their spatial relationship to vestibulo‐spinal projections were ascertained in the 11‐day chicken embryo through retrograde tracing experiments. An in vitro preparation of the brainstem facilitated precisely localized application of tracers. Unilateral labelling of the ascending medial longitudinal fascicle (MLF), just caudal to the trochlear nucleus, labelled coherent groups of vestibular neurons that had an asymmetrical distribution on the two sides of the brainstem. Axons originating from either side followed one of four trajectories, and the groups of neurons could therefore be identified on the basis of their position and their projection pathway. Labelling each side of the MLF with a different tracer showed that although neurons projecting in the ipsi‐ and contralateral MLF were intermingled in some areas, individual neurons projected on one side only.

Labelling the ascending MLF and the high cervical spinal cord with different tracers showed that vestibulo‐ocular neurons had a wider rostro‐caudal distribution than vestibulospinal neurons. Some vestibulospinal and vestibulo‐ocular groups were spatially segregated, others were intermingled. Very few (in most preparations no) neurons were found to project to both targets.

Together with our previous study on vestibulospinal projections in the 11‐day chicken embryo (Glover and Pétursdóttir, J. Comp. Neurol. 270: 25–38, '88) the results show that vestibular neurons in different regions project in characteristic subsets of the available pathways.
Interplexiform cells of the goldfish retina
Authors: Kalloniatis Michael , Marc Robert E.
Published: January 2005

Dopaminergic and glycinergic interplexiform cells (IPCs) in the goldfish retina were impregnated by using two new Golgi protocols. The two cell types have markedly different morphological characteristics: Dopaminergic IPCs have primary dendrites that descend into and stratify in the inner plexiform layer, where they give rise to processes that project to the outer plexiform layer. Conversely, glycinergic IPCs have primary dendrites that ascend to the outer plexiform layer and from this dendritic arbor, many processes then project into the inner plexiform layer. The apparent coverage of dopaminergic IPCs is almost four times that of glycinergic IPCs. Even so, the coverage of each glycinergic IPC in the outer plexiform layer allows it to provide an accurate copy of the S‐space to the inner plexiform layer. Considering the known GABAergic and glycinergic synaptologies in the inner plexiform layer, the glycinergic IPC must form a major element in the retinal circuitry of the goldfish.
Paraventricular organ of the lungfish Protopterus dolloi: Morphology and projections of CSF‐contacting neurons
Authors: von Bartheld Christopher S. , Meyer Dietrich L.
Published: January 2005

The morphology and projections of neurons in the paraventricular organ (PVO) were studied by means of silver impregnation after intraocular application of cobaltous lysine in the lungfish Protopterus dolloi. Cobalt‐labeled neurons were found exclusively in the PVO in the dorsal and infundibular hypothalamus. These bipolar neurons possess one CSF‐contacting process that protrudes into the ventricular lumen with a club‐shape ending and a thick, ramifying process directed into the hypothalamic neuropil; the ependymofugal processes form intra‐ and extrahypothalamic projections. Impregnated fibers from paraventricular neurons cross in infundibular and hypothalamic commissures, the commissure of the posterior tuberculum, the postoptic, the habenular, and the anterior commissures. Projections to the infundibulum and the median eminence are relatively sparse; no fibers are labeled in the pituitary gland. Ascending projections to the forebrain are extensive. Major targets include the dorsal hypothalamus, the periventricular preoptic nuclei, the habenula, the subhabenular region, the anterodorsal thalamus, and the medial telencephalic hemisphere (septum). Most ascending fibers follow the medial forebrain bundle; others course in the fasciculus retroflexus and terminate in rostral parts of the ipsilateral habenula. Descending fibers run caudally along the ventral floor of the brainstem. They terminate in the neuropil of the mesencephalic tegmentum, ventral tectum, isthmic region, ventral portions of the reticular formation throughout the rhombencephalon, and extend into the spinal cord.

Intraocular application of cobaltous lyaine results in selective impregnation of neurons in the PVO and their ascending and descending projections, presumably via uptake of tracer from vascular circulation. These projections do not represent retinofugal or retinopetal projections. We provide conclusive evidence for the existence of a PVO in Protopterus. On the basis of PVO location and acetylcholinesterase histochemistry, we propose subdivisions of the infundibular hypothalamus corresponding to those in amphibians. Ascending PVO projections appear to be particularly well developed in lungfish compared with other species and may be related to specialized endocrine mechanisms in this group of vertebrates.
Developmental history of the transient subplate zone in the visual and somatosensory cortex of the macaque monkey and human brain
Authors: Kostovic Ivica , Rakic Pasko
Published: January 2005

The cytological organization and the timetable of emergence and dissolution of the transient subplate zone subjacent to the developing visual and somatosensory cortex were studied in a series of human and monkey fetal brains. Cerebral walls processed with Nissl, Golgi, electron‐microscopic, and histochemical methods show that this zone consists of migratory and postmigratory neurons, growth cones, loosely arranged axons, dendrites, synapses, and glial cells. In both species the subplate zone becomes visible at the beginning of the mid‐third of gestation as a cell‐poor/fiber‐rich layer situated between the intermediate zone and the developing cortical plate. The subplate zone appears earlier in the somatosensory than in the visual area and reaches maximal width at the beginning of the last third of gestation in both regions. At the peak of its size the ratio between the width of the subplate zone and cortical plate in the somatosensory cortex is 2:1 in monkey and 4:1 in man while in the occipital lobe these structures have about equal width in both species. The dissolution of the subplate zone begins during the last third of gestation with degeneration of some subplate neurons and the relocation of fiber terminals into the cortex. The subplate zone disappears faster in the visual than in the somatosensory area.

The present results together with our previous findings support the hypothesis that the subplate zone may serve as a “waiting” compartment for transient cellular interactions and a substrate for competition, segregation, and growth of afferents originated sequentially from the brain stem, basal forebrain, thalamus, and from the ipsi‐ and contralateral cerebral hemisphere. After a variable and partially overlapping time period, these fibers enter the cortical plate while the subplate zone disappears leaving only a vestige of cells scattered throughout the subcortical white matter. A comparison between species indicates that the size and duration of the subplate zone increases during mammalian evolution and culminates in human fetuses concomitantly with an enlargement of cortico‐cortical fiber systems. The regional difference in the size, pattern, and resolution of the subplate zone correlates also with the pattern of cerebral convolutions. Our findings indicate that, contrary to prevailing notions, the subplate may not be a vestige of the phylogenetically old network but a transient embryonic structure that expanded during evolution to subserve the increasing number of its connections.
Explanation for the labeling of cervical motoneurons in young rats following the introduction of horseradish peroxidase into the calf
Authors: Haase Peter
Published: January 2005

This study was carried out to determine whether cervical motoneurons, labeled following the introduction of horseradish peroxidase into the rat hind leg, belong to the cutaneous trunci motoneuron pool. The cutaneous trunci is a superficial muscle that extends from the axilla, over the flank, and into the thigh. Its nerve supply is derived from the brachial plexus.

In experimental animals, horseradish peroxidase was either injected directly into the right gastrocnemius muscles, or applied to gelfoam and implanted over the calf muscles in the right leg of 5‐, 10‐, 15‐day‐old and adult rats. In control animals the cutaneous trunci was denervated prior to the administration of horseradish peroxidase.

Labeled cervical motoneurons were present in the 5‐, 10‐, and 15‐day‐old but not the adult experimental groups and were located within the predetermined confines of the cutaneous trunci motoneuron pool. No labeling of cervical motoneurons was observed in any of the control groups in which the cutaneous trunci muscle was denervated.

The most likely explanation for the labeling of cervical motoneurons in young rats was the local diffusion of horseradish peroxidase from the calf to the thigh, where it entered the cutaneous trunci muscle and was taken up by some of its motoneurons. The absence of such labeling in adult rats was probably due to the presence of connective tissue barriers to diffusion and to the greater distance between the site of horseradish peroxidase application and the cutaneous trunci muscle, which prevented the tracer from reaching the cutaneous trunci muscle and labeling its motoneurons.
Thalamic midline cell populations projecting to the nucleus accumbens, amygdala, and hippocampus in the rat
Authors: Su Hong‐Sen , Bentivoglio Marina
Published: January 2005

The organization of the thalamic midline efferents to the amygdaloid complex, hippocampal formation, and nucleus accumbens was investigated in the rat by means of multiple retrograde fluorescent tracing. The present findings indicate that these connections derive from separate cell populations of the thalamic midline, with a low degree of divergent collateralization upon more than one of the targets examined.

The neural populations projecting to the amygdala, hippocampus, or accumbens are highly intermingled throughout the thalamic midline, but display some topographical prevalence. Midline thalamo‐hippocampal cells are concentrated in the nucleus reuniens; thalamo‐accumbens neurons prevail in the ventral portion of the paraventricular nucleus, and in the central medial nucleus. Thalamo‐amygdaloid cells display a topographical prevalence in the rostral third of the thalamic midline and are concentrated in the dorsal part of the paraventricular nucleus and in the medial part of the nucleus reuniens. Both dorsally in the paraventricular nucleus and ventrally in the nucleus reuniens, thalamo‐amygdaloid cells are located closer to the ependymal lining than the neurons projecting to the hippocampus or nucleus accumbens. Further, thalamo‐amygdaloid cells, especially in the paraventricular nucleus, extend their dendritic processes in the vicinity of the ependymal lining, where they arborize profusely. These features indicate a close topographical relationship of neurons projecting to the amygdala with ependymal cells.

The fairly discrete origin of midline outputs to the amygdala, hippocampus, and accumbens indicates that the flow of information is conveyed through separate channels from the thalamic midline to limbic and limbic‐related targets. Together with the literature on the limbic afferents to the thalamus, these findings emphasize the relationships between the thalamus and the limbic system subserved by parallel input‐output routes. However, because of the overlap of the projection cell populations, the thalamic midline may represent a locus of interaction among neurons connected with different parts of the limbic system.

The functional implications of these findings are discussed in relation to the “nonspecific” thalamic system, as well as to the circuits involved in memory formation‐Key words: thalamus, limbic system, basal ganglia, parallel channels, memory processing.
Amygdaloid projections to the frontal cortex and the striatum in the rat
Authors: Kita H. , Kitai S. T.
Published: January 2005

Projections from the basolateral nucleus of the amygdala (BLA) to the frontal cortex and the striatum were studied by using Phaseolus vulgaris‐leucoagglutinin (PHA‐L) anterograde tracing technique in the rat.

PHA‐L injections into the rostral part of the BLA resulted in a dense labeling of fibers with boutons in the dorsal bank of the rhinal fissure and in the lateral and the medial agranular cortex. PHA‐L injections into the caudal part of the BLA produced a dense labeling of fibers in the medial surface of the frontal cortex. In most of the cortical regions, labeled fibers were predominantly distributed in two bands: one in the deep part of layers I and II and the other, heavier band, in layers V and VI.

PHA‐L injections into the rostral BLA resulted in a dense labeling of fibers with boutons in the olfactory tubercle, the rostral and caudolateral portion of the nucleus accumbens, and a large region of the caudate–putamen. The labeled area of the caudate–putamen included the rostroventral area, the central area, and the area caudal to the anterior commissure and dorsal and lateral to the globus pallidus. PHA‐L injections into the caudal BLA produced fiber labeling in the most rostromedial area of the caudate–putamen facing the lateral ventricle, the medial portion of the nucleus accumbens, and the lateral septum. In the rostroventral striatum, PHA‐L‐labeled fibers selectively innervated the matrix compartment that contains abundant somatostatin‐immunoreactive fibers. Compartmental segregation was less clear in the caudo‐dorsolateral caudate–putamen and in the nucleus accumbens. Electron microscopy revealed that PHA‐L‐labeled boutons in the striatum contained abundant, small, round vesicles. These boutons formed asymmetrical synapses with dendritic spines of striatal neurons.
Requirement for olfactory axons in the induction and stabilization of olfactory glomeruli in an insect
Authors: Tolbert Leslie P. , Sirianni Peter A.
Published: January 2005

The role of antennal sensory axons in the induction and stabilization of olfactory glomeruli has been explored in the moth Manduca sexta. First, we asked the question: how many axons are necessary to induce glomerulus formation within the first‐order olfactory neuropil of the brain? Axons from as few as 10 of the normal 70–80 repeating antennal segments were sufficient to induce glomeruli. However, there was a dose dependence in the number of glomeruli that developed in partially innervated lobes. When only 11 segments of the antenna were allowed to provide innervation to the lobe, only 37 of the normal 59 ± 2 glomeruli developed; over 20 segments were necessary to induce the normal number of glomeruli. In a second set of experiments, we asked: for how long must antennal axons be present to stabilize newly formed glomeruli? We found that antennal axons must be intact for at least 2 to 4 stages (roughly equivalent to 2 to 4 days) for glomeruli to be stable even if the axons are subsequently severed. This finding, taken in the light of other recent findings in our laboratory, suggests that the formation of synapses may be a crucial element in the stabilization of glomerular structure. All together, the results of the present study indicate that induction and stabilization of glomeruli are separable events with different underlying cellular bases.
Demonstration of discrete place‐defined columns—segregates—in the cat SI
Authors: Favorov Oleg V. , Diamond Mathew E.
Published: January 2005

The SI forelimb area of cats was examined with receptive field (RF) mapping techniques. Arrays of closely spaced, near‐radial microelectrode penetrations were inserted into the crown of postsigmoid gyrus of ketamine anesthetized subjects and minimal RFs were obtained at several depths. The minimal RF was defined as the skin site providing the strongest input to each recorded cluster of neurons. Data analysis showed that all studied cortical territories contained groups of discrete cortical columns, 300–400 μm in diameter. The columns were regarded as topographic entities because no change in minimal RF location could be observed within their boundaries. The boundaries of columns were sharp and could be unequivocally distinguished because the minimal RFs sampled on opposite sides of a boundary occupied displaced, nonoverlapping positions.

Pair‐wise comparison of single neuron maximal RFs (defined as the entire skin area providing input to the recorded neuron) further clarified the nature of the SI place‐defined columns: (1) no systematic differences in maximal RF position could be demonstrated for different parts of the same column (even though the maximal RFs in most columns varied extensively in size and skin areas covered), and (2) at the boundary between neighboring columns maximal RFs shifted en masse to center on a new skin locus. These minimal and maximal RF observations strongly support our recent proposal that body surface is represented in SI by a honeycomblike mosaic of discrete place‐defined cortical columns, segregates.
Morphology of sympathetic preganglionic neurons in the neonatal rat spinal cord: An intracellular horseradish peroxidase study
Authors: Forehand Cynthia J.
Published: January 2005

Understanding the central neural control of autonomic functions requires a knowledge of the morphology of the preganglionic neurons, for the location of the dendritic arborizations of these neurons will indicate which central pathways may have access to them. In the present study, individual sympathetic preganglionic neurons in the neonatal rat spinal cord have been examined by the intracellular injection of horseradish peroxidase (HRP) in an in vitro preparation. Seventeen HRP‐labeled preganglionic neurons in thoracic segments T1–T3 were examined in detail; of these, 12 somata were located in the intermediolateral cell column (IML), one in the lateral funiculus (LF), two in the intercalated nucleus (IC), and two at the border between IML and IC.

All of the neurons had extensive dendritic arborizations arising from an average of six primary dendrites; the average total dendritic length for these cells was 2,343 μm. The morphology of preganglionic neurons differed depending on the location of their cell bodies. Preganglionic neurons located in the IML were essentially two‐dimensional: the cells had some dendrites that coursed rostrocaudally for 300–500 μm within the IML and others that coursed mediolaterally, extending to the lateral surface of the cord and close to the central canal. Axons of these cells coursed ventrally from the cell body and exited from the spinal cord at the first ventral root caudal to the cell body. No intraspinal axon branches were observed. In contrast, preganglionic neurons with somata outside the IML had dendritic arborizations that radiated away from the cell body in three dimensions, extending into the IML, LF, and the dorsal and ventral horns of the spinal cord while traversing a rostrocaudal distance of about 400 μm. Two of these cells had axons that branched within the spinal gray.

These results indicate that the dendrites of neonatal rat sympathetic preganglionic neurons extend outside the IML, where they may be contacted by inputs that do not terminate within IML. Moreover, the different dendritic arborizations of preganglionic neurons in different preganglionic nuclei may mean that the connectivity of preganglionic neurons varies according to cell body location. Finally, the intraspinal axon collaterals on some preganglionic neurons provide an anatomical substrate for local circuit interactions.
Distribution and projection pattern of motoneurons that innervate hindlimb muscles in the quail
Authors: Tyrrell Sophia , Schroeter Sally , Coulter Lynn , Tosney Kathryn W.
Published: January 2005

We characterized the motoneuron pool positions and projection patterns in the embryonic quail hindlimb and compared them to those in the chick to determine the degree of similarity and to form a baseline for future chimeric experiments. We find that the most similar parameters of pool position correlate with the major axonal pathway choices. First, the medial‐lateral pool position, which is highly conserved among birds and mammals, is identical in the quail and chick and correlates with the dorsal‐ventral pathway choice, the first and least plastic of the choices within the limb. Second, although quail pools were known to be compressed into seven rather than eight segments, we show that the map of pools is compressed about a central point (segment three) that preserves the spatial relationships between anterior pools and the crural plexus, and between posterior pools and the sciatic plexus. Access to guidance cues that are restricted to each plexus region is thus maintained between species. Third, pool position along the anterior‐posterior axis is the least similar parameter between species. In fact, the entire lumbosacral motor complex may shift by ± half a segment in individual quail. Despite the consequent differences in segmental projections, the specific projection pattern within each quail hindlimb is identical to that in the chick. There is no need to preserve the exact segmental pattern either phylogenetically or during development, because motoneurons accommodate to modest variations in their position along the anterior‐posterior axis by sorting out at the limb base. The contrast between variable segmental and constant limb projections also demonstrates that neither the specification nor the precise projection of motoneurons is dependent upon the specification or development of somites.
Response of the monkey cholinergic septohippocampal system to fornix transection: A histochemical and cytochemical analysis
Authors: Kordower Jeffrey H. , Fiandaca Massimo S.
Published: January 2005

Transection of the fimbria‐fornix pathway is a paradigm that has been richly exploited in rats to assess the structural and functional correlates of cognitive behavior, neural grafting, and growth factor administration. Principally, the degeneration of cholinergic neurons within the septal/diagonal band region has received detailed attention following this manipulation. In contrast, no studies have examined the response of the cholinergic septal/diagonal neurons following axotomy in nonhuman primates. This study examined the neuronal and glial responses within the septal region to selective fornix transection (without cingulate gyrus ablation) in four Cebus apella monkeys. One month following unilateral transection of the fornix by means of an open microsurgical approach, a comprehensive loss of acetylcholinesterase [AChE]‐containing fibers was observed throughout the hippocampal formation and dentate gyrus ipsilateral to the lesion. Decreases in AChE fiber densities were also observed within the entorhinal cortex ipsilateral to the lesion. No such changes in AChE‐fiber density were consistently observed within the subicular region. The decrease in hippocampal AChE‐positive fibers was paralleled by a 49.5% reduction in cholinergic medial septal neurons as revealed by Nissl stains and immunohistochemical staining for the receptor for nerve growth factor, a marker of cholinergic basal forebrain neurons in primates. In contrast, no significant changes in the number of neurons within the vertical limb of the diagonal band were noted. Following the transection, a relatively intense reactive gliosis was observed within the dorsal half of the septal region ipsilateral to the transection and within the overlying transected corpus callosum. These data provide the foundation in nonhuman primates on which novel therapeutic factors can be evaluated in paradigms relevant to the study of Alzheimer's disease.
Topographic disorganization of the optic tracts following long‐term optic nerve regeneration: A quantitative image analysis study
Authors: Springer Alan D. , Morel Kimberly D. , Wilson Bryan R.
Published: January 2005

Experiments were designed to find the degree to which regenerated optic axons occupied their previous locations in the optic tracts. Following optic nerve crush and regeneration, either the dorsal, Ventral, Peripheral, Temporal, or nasal part of the retina was ablated. The axons of the remaining retinal ganglion cells (RGCs) were labeled with cobalt. Density of the regenerated dorsal and ventral axons in the dorsal vs. ventral optic tracts was determined digitally. In addition, we determined the density of temporal and nasal axons in the temporal vs. nasal compartments of each optic tract and the density of central axons in the central vs. peripheral compartments of both optic tracts.

Regenerated axons were not distributed randomly in the optic tracts. Instead, they were slightly but significantly biased toward growing through the tract or compartment that they had occupied previously. Still, the pathway specificity exhibited by the regenerated axons was closer to random than it was to the pathway specificity seen in normal animals. Dorsal, ventral, and central RGC axons were significantly better localized to their correct tract or compartment than were temporal or nasal RGC axons. Also, over time, dorsal and ventral axons tended to disappear from incorrectly chosen optic tracts. The slight bias toward choosing the appropriate optic tract or optic tract compartment may be enough to account for the topographic specificity of the regenerated retinotectal projection. Near‐randomness of the axonal positions in the tracts argues against the presence of any specific guidance cues in the optic tracts of adult animals. Axonal density was highest in the correct compartment and diminished progressively with increasing distance into the incorrect compartment. Such a gradient of axonal density suggests that regenerating axons “drift” away from their previous positions in the optic pathways.
Expression of surface glycoproteins early in leech neural development
Authors: McGlade‐McCulloh Ellen , Muller Kenneth J. , Zipser Birgit
Published: January 2005

Cell migration and axon growth during neural development rely upon cell‐cell and cell‐matrix interactions mediated by surface glycoproteins. The surface glycoprotein recognized on leech neurons by monoclonal antibody Lan3‐2 has previously been implicated in the process of axon fasciculation during regeneration in adults. In adult leeches, Lan3‐2 binds to a carbohydrate epitope of a 130 kD protein. The present study demonstrates that in embryos the antibody binds to the same carbohydrate epitope of glycoproteins with molecular weights of 130 kD and higher. As a first step in evaluating a possible role of the Lan3‐2 glycoprotein or the cells that express it during neural development, we determined its distribution in the developing nervous system of the leech Hirudo medicinalis. In embryos, Lan3‐2 epitope is expressed on fasciculated sensory afferents and it appears on the cell bodies before neurite outgrowth. The sensory fibers appear rostrally by embryonic day 10, less than halfway through development. Earlier, by 7 days of development at 20°C, Lan3‐2 binds to previously undocumented cell types: (1) cells appearing along the embryonic midline and (2) a cluster of cells located at the rostral edge of the germinal plate. These cells only transiently express this antigen and are present at critical left‐right and rostrocaudal boundaries during a period of cell proliferation, movement, and migration that produces the nervous system. Thus the Lan3‐2 surface glycoprotein or the cells expressing it are candidates for involvement in axon fasciculation, cell migration, and directed axonal growth.
Areal and laminar organization of corticocortical projections in the rat somatosensory cortex
Authors: Koralek Katherine‐Ann , Olavarria Jaime , Kellackey Herbert P.
Published: January 2005

The present study examines patterns of connectivity between the primary somatosensory cortex of the rat (SI) and surrounding cortical areas also implicated in the processing of somatosensory information. The impetus for the study was the recent reports of major differences in the organization of cortex lateral and caudal to the SI in two other rodent species; the mouse (Carvell and Simons, '86: Somatosens. Res. 3:213–237; '87: J. Comp. Neurol. 265:409–427) and the grey squirrel (Krubitzer et al., '86: J. Comp. Neurol 250: 403–430). Corticocortical connections between the somatosensory areas of the rat parietal cortex were examined by using the combined retrograde and anterograde transport of horseradish peroxidase as well as the retrograde transport of fluorescent tracers. Tracer injections were made into different locations within SI and dysgranular cortex as well as into more lateral regions of parietal cortex, The tangential patterns of distribution both of callosal connections and of cytochrome oxidase activity together provided points of reference in determining the relation between injection sites and the resultant patterns of label.

The results indicate that two distinct somatosensory areas, SI and the dysgranular cortex, are interconnected with a further lateral somatosensory area referred to as the second somatosensory area (SII). These projections are organized in a topographic fashion, which we interpret as evidence for a single representation of the body surface in SII. The three somatosensory areas each exhibit unique laminar patterns of ipsilateral corticocortical projection neurons and terminations. In SI, projection neurons are found mainly in layers II, III, and Va, and terminations are largely restricted to the infragranular layers. In the dysgranular cortex, projection neurons and terminations are found in all layers except layer I in which only terminal label is detectable and layer Vb in which notably fewer neurons are labelled. In SII, projection neurons and terminations are found in all layers except layer I and are particularly dense in lower layer III and layer IV. Further, whereas the laminar and areal distributions of ipsilateral and contralateral corticocortical projections largely overlap in both SI and the dysgranular cortex, in SII they tend to be areally segregated. Neurons projecting bilaterally to both ipsilateral and contralateral somatosensory cortex were equally rare in all three somatosensory areas.

These results are discussed in relation to the organization of SII in other rodent species, and it is concluded that in the rat, like the mouse, cortex lateral and caudal to SI contains a single representation of the body surface.
Postnatal development of crossed and uncrossed corticorubral projections in kitten: A PHA‐L study
Authors: Higashi Shuji , Yamazaki Masahiro , Murakami Fujio
Published: January 2005

Morphological changes in individual corticorubral fibers and the pattern of crossed and uncrossed corticorubral projections were studied during the postnatal development of cats in order to understand cellular mechanisms for restriction of corticorubral projections with development. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA‐L) was injected into restricted areas of the pericruciate cortex in kittens and PHA‐L‐labeled axons in the red nucleus were examined at postnatal days (PND) 7–73.

In accordance with our previous study (Murakami and Higashi, Brain Res. 1988; 447:98–108), a crossed corticorubral projection was observed in addition to the uncrossed one in every experimental animal. During the early period of development (PND 7–8), swellings of irregular shape were observed along the entire course of the axons and they were often interconnected with extremely fine axonal segments. These axons bifurcated only infrequently and often ended as growth cones. These features were common to both uncrossed and crossed corticorubral axons. At later stages of development (PND 28 or later), the total number of swellings decreased and axonal swellings with smooth contours became dominant.

A quantitative examination of axonal branches indicated that axons on the ipsilateral side branch occurred more frequently at later stages of development. However, there was no substantial change in branching frequency for the crossed corticorubral fibers during development. In parallel with morphological changes in individual axons, the crossed projection that was initially relatively abundant was reduced during development, Since a PHA‐L injection can be confined to a small region of cortex, topographic projections can easily be detected. At PND 7–8 there was no well‐defined topographic order in the ipsilateral corticorubral projection. Adult‐like topography was first discernible at PND 13.

These observations suggest that the unilateral uncrossed corticorubral projection in the adult cat is achieved at least in part by the formation of axonal arbors in the uncrossed projection. This was accompanied by the failure of crossed fibers to form complex arbors. It is possible that a similar mechanism also operates in the formation of topographic maps.
DARPP‐32, a phosphoprotein enriched in dopaminoceptive neurons bearing dopamine D1 receptors: DIstribution in the cerebral cortex of the newborn and adult rhesus monkey
Authors: Berger Brigitte , Febvret Aude , Greengard Paul , Goldman‐Rakic Patricia S.
Published: January 2005

DARPP‐32, a dopamine (DA) and cAMP‐regulated phosphoprotein, is associated with dopaminoceptive neurons bearing D‐1 receptors in the basal ganglia. The present study addressed the distribution of DARPP‐32 in the primate cerebral cortex and its putative association with D‐1 receptor laden cells in this structure. DARPP‐32‐like immunoreactive (LIR) neurons were examined in the cerebral cortex of 3‐day‐old (P3), 6‐week‐old (P42), and adult rhesus monkeys. In the younger cases, a large number of DARPP‐32 positive neurons, with the morphological characteristics of pyramidal cells, were observed throughout the cortex, in layers V–VI, and to a lesser extent in layer II and uppermost layer III. In the parietal, insular, temporal, and occipital cortices, DARPP‐32 positive neurons were arranged in a monolayer in layer Va. They were often clustered in small groups with a bundling of their dendrites. In the primary motor cortex, Betz cells were among the labeled population. In the association and somatosensory areas, the basal dendrites of DARPP‐32 positive neurons and the prominent tufting of their apical dendrites in layer I contributed to an essential bilaminar pattern resembling the distribution reported for DA afferents and D‐1 receptors in these areas. The prominence and widespread distribution of DARPP‐32 positive neurons in layer V may be a specialization of primate cortex since such cells are found only in restricted locations in rodents. The literature on the connections of the cerebral cortex suggests that a large number of the DARPP‐32 positive neurons in layer VI and perhaps even in layer Va may be corticothalamic neurons. An important developmental observation was the presence of DARPP‐32‐LIR neurons in the white matter. They were prominent in the neonates but could not be seen in the adult. Their location as well as their type and shape were reminiscent of interstitial neurons. In the adult monkeys, the distribution of DARPP‐32‐LIR neurons was more circumscribed: they were numerous in the ventral temporal gyrus and in areas related to the limbic system: caudal orbitofrontal cortex, insula, temporal pole, entorhinal, and anterior cingulate cortex. Weak labeling was detected in layer Va of the superior temporal and parietal cortex, in some prefrontal areas (10,13, and medial 9), and in the premotor and supplementary motor cortex; in adults, unlike neonates, few DARPP‐32‐LIR neurons were present in the dorsolateral prefrontal cortex, the primary motor or the primary visual or prestriate cortices. These findings demonstrate important developmental changes between birth and adulthood in the expression of DARPP‐32 and point to a possible role for this molecule and/or D‐1 receptors during postnatal development of the primate cerebral cortex.
Projections to the pontine nuclei from choline acetyltransferase‐like immunoreactive neurons in the brainstem of the cat
Authors: Aas Jan‐Erik , Brodal Per , Baughman Robert W. , Storm‐Mathisen Jon
Published: January 2005

By use of retrograde transport of horseradish peroxidase‐wheat germ agglutinin (HRP‐WGA) in combination with monoclonal antibodies against choline acetyltransferase (ChAT), we show that putative cholinergic inputs to the feline pontine nuclei originate from cells in the dorsolateral pontine tegmentum. These cells form a loosely arranged continuum that nevertheless may be subdivided into two groups on the basis of differences in cell morphology. One group consists of double‐labeled cells in the periventricular gray substance medial to, and partly merging with, the nucleus locus coeruleus. The other group consists of double‐labeled cells surrounding the brachium conjunctivum. In two cats with tracer injections in the pontine nuclei, 81% and 84%, respectively, of the retrogradely labeled cells in the dorsolateral pontine tegmentum are ChAT‐like immunoreactive (ChAT‐LI). In the same experiments, many ChAT‐LI cells, but no retrogradely labeled cells, are seen in the basal telencephalon.

The pontine nuclei contain a plexus of thin ChAT‐LI fibers with varicosities resembling en passant as well as terminal boutons. These ChAT‐LI fibers appear to branch extensively and cover all parts of the pontine nuclei.

Following injections of rhodamine‐B‐isothiocyanate (RITC) in the thalamus and Fluoro‐Gold in the pontine nuclei and surrounding regions in the same animal, all retrogradely labeled cells in the dorsolateral pontine tegmentum are labeled with both tracers, whereas most cells in the paramedian pontine reticular formation are labeled either with RITC or Fluoro‐Gold. Thus it appears that all cells in the dorsolateral pontine tegmentum that project to the pontine nuclei also project to the thalamus.

In analogy with findings by others in the dorsal lateral geniculate nucleus, we suggest that the putative cholinergic projections to the pontine nuclei may serve to modulate transmission of cerebellar afferent information in accordance with the behavioural state of the animal.
Development of connections to and from the visual cortex in the wallaby (Macropus eugenii)
Authors: Sheng X.‐M. , Marotte L. R. , Mark R. F.
Published: January 2005

The time course of the development of connections between the visual cortex and the main subcortical visual structures, as well as intrahemispheric and interhemispheric connections, has been studied in the marsupial wallaby (Macropus eugenii) to compare its development with that of placental mammals. Pouch young are born prior to retinal innervation of the primary visual centers and spend a protracted period of development in the pouch, making them ideal for visual, developmental studies. Horseradish peroxidase conjugated to wheatgerm agglutinin was injected into either the presumptive visual cortex or the superior colliculus in young of varying ages.

Thalamocortical projections from the dorsal lateral geniculate and lateral posterior nuclei reach the presumptive visual cortex between 12 and 15 days after birth. Descending cortical connections form later. Corticogeniculate axons are first detected in the geniculate and lateral posterior nucleus at 48 days after birth, while corticocollicular axons first reach the superior colliculus at 71 days and, by 81 days, have innervated the superficial layers.

Intrahemispheric and interhemispheric connections form even later. By 99 days intrahemispheric axons from area 17 have accumulated in visual association areas but are yet to invade layers III and IV, their major termination zones in adult, while axons projecting back to area 17 have also reached their target area. At this time interhemispheric axons from area 17 have begun to accumulate in the opposite visual cortex, although they have not invaded the cortical layers. By 111 days cortical cells projecting to the opposite visual cortex are first labelled. These have a more widespread distribution in area 17 at 111 and 122 days compared to the adult, where they are confined to the 17/18 border.

The results show that the marsupial wallaby has a timetable of similar sequence, but different relative timing, in. the formation of cortical connections compared to that of placental mammals. In the first half of the period between conception and eye opening, the timing in the wallaby precedes considerably that in placental mammals. Ascending connections from the thalamus develop relatively earlier in the wallaby but descending collicular connections are delayed until the same relative time that they appear in placental mammals.
Expression of the prodynorphin gene in the developing and adult cerebral cortex of the rat: An in situ hybridization study
Authors: Alvarez‐Bolado Gonzalo , Fairén Alfonso , Douglass James , Naranjo José Ramón
Published: January 2005

A population of cortical neurons contains the opioid peptide dynorphin; the laminar distribution of these neurons in the adult cerebral cortex and their patterns of development are not well known. We have utilized in situ hybridization techniques to localize prodynorphin mRNA‐containing neurons. Rats aged from embryonic day (E) 15 through postnatal day (P) 90 were used. Prenatal animals did not show any labeling in the cerebral cortex. By P4, prodynorphin was expressed in a small number of cortical neurons for the first time. The autoradiographic signal was restricted to perikarya. In the frontoparietal cortex, labeled neurons first appeared in layer V and the upper part of layer VI. Subsequently, from P11 onward, the band expanded in an “inside‐out” sequence to include layers IV through II. In the posterior cingulate cortex and in the insular and perirhinal cortices, prodinorphin mRNA containing‐neurons were located preferentially in layer V. In all cortical areas analyzed, a progressive increase in the packing density of neurons expressing prodynorphin mRNA was observed until P14; it decreased slightly thereafter.
Collateral sprouting of the central terminals of cutaneous primary afferent neurons in the rat spinal cord: Pattern, morphology, and influence of targets
Authors: Fitzgerald Maria , Woolf Clifford J. , Shortland Peter
Published: January 2005

The capacity of the central terminals of primary afferents to sprout into denervated areas of neonatal spinal cord and the morphology of any novel terminals has been investigated. In rats which had undergone sciatic nerve section on the day of birth, 12 of 18 physiologically characterized intact saphenous hair follicle afferents (HFAs) were labelled intra‐axonally with horseradish peroxidase (HRP) were shown to sprout up to 2,000 m̈m into the deafferented sciatic terminal field. The morphology of these sprouts depended on which area of the sciatic nerve territory was invaded by the afferent sprouts. Six HFAs sprouted into areas normally innervated by glabrous skin afferents and the morphology of the collateral sprouts in this region resembled that of rapidly adapting (RA) afferents. The other six saphenous HFAs had sprouted into sciatic “hairy” skin areas and the morphology of these sprouts, although abnormal, was flame shaped.

In rats whose sural, saphenous, and superficial peroneal nerves were cut at birth, 4 of 7 single HRP labelled RA afferents had central terminals that had sprouted into regions of cord normally devoted to “hairy” input. These showed clear signs of HFA morphology despite their peripheral receptive fields remaining in the glabrous skin.

The results show collateral sprouting of single cutaneous sensory afferent axons into adjacent inappropriate central target regions following neonatal deafferentation. Such plasticity may provide some compensation following neonatal injury. The morphology of the sprouted terminals is appropriate to the new target area rather than to its functional class and is also independent of the peripheral receptive field location providing an example of central rather than peripheral control over afferent growth patterns.
Times of origin of brachial sensory neurons are not correlated with neuronal phenotype
Authors: Mendelson Bruce , Frank Eric
Published: January 2005

The times of origin (birthdays) of sensory and motor neurons that innervate the triceps brachii muscles of the bullfrog (Rana catesbeiana) were determined to learn whether neurons innervating a specific target are generated at a particular developmental time. 3H‐thymidine (3H‐TdR) was made available continuously throughout a specific developmental period. All neurons that innervated the triceps muscle in juvenile frogs (identified by filling cells retrogradely with HRP) were generated prior to metamorphosis. Triceps motoneurons were all postmitotic by early limb bud stage V. Triceps sensory neurons were generated over a protracted period of larval development, from stage V through early pre‐metamorphic stage XV. Most large triceps sensory neurons were generated before the majority of the small cells. However, there was considerable overlap in the times of origin of the two populations; both large and small cells were generated at all stages of sensory neurogenesis. There was thus no strict relationship between sensory soma size and birthdate. Late‐generated sensory neurons tended to be located in clusters within ganglia, whereas HRP‐filled triceps neurons were not. These 3H‐labeled clusters may represent clones of neurons which would indicate that late stage neuroblasts give rise to neurons that supply different peripheral targets. The time course of triceps neuronal generation paralleled that of all other brachial sensory neurons implying that the time of last cell division does not in itself determine either the target a neuron will innervate or the sensory modality to which it will respond.