bluuebunny/crossref_metadata_2025 huggingface dataset:
The structure of locust nonspiking interneurones in relation to the anatomy of their segmental ganglion
Authors: Watkins B. L. , Burrows M. , Siegler M. V. S.
Published: May 2005

The morphology of eight nonspiking local interneurones in the metathoracic ganglion of the locust is described in relation to known tracts, commissures, regions of neuropile, and identified motor neurones. They are compared with the spiking local interneurones in the same ganglion. Each nonspiking local interneurone was injected intracellularly with cobalt, following characterization of its physiological effects on identified leg motor neurones. The shapes of the nonspiking interneurones are diverse, although all have processes restricted to one ganglion and lack an axon. Their cell bodies are distributed in the ventral and dorsal cortex of the ganglion. Interneurones with cell bodies in similar places have similar basic structures, with primary neurites in the same commissure or tract, and major branches in the same tracts. The fine branches of all the interneurones have the same texture throughout, and occur in the same lateral region of neuropile, dorsal to the prominent neurite of the fast extensor tibiae motor neurone. Some interneurones have branches that extend both to the midline and to the dorsal boundary of the neuropile, but none have branches in the ventral, medial neuropile. This distribution of branches corresponds with two known features of the physiology of these interneurones: (1) they make what appear physiologically to be direct connections with motor neurones, and have branches in the same region of the neuropile as the motor neurones. (2) They do not appear to receive direct inputs from hair afferents, and they have no branches in the ventral neuropile to which these afferents project.
Origin of interhemispheric fibers in acallosal opossum (with a comparison to callosal origins in rat)
Authors: Granger Ellen Moreland , Masterton R. Bruce , Glendenning Karen K.
Published: May 2005

The neocortical origins of the anterior commissure in the acallosal, marsupial opossum were studied with the horseradish peroxidase (HRP) method. Following complete surgical transection of the anterior commissure, HRP was applied directly to the cut fiber tips. This procedure resulted in very large numbers of vividly labeled cells within the neocortex. The labeled cells were plotted and counted for comparison among cytoarchitectonic areas and among cortical layers. For comparative purposes, the neocortical origins of the corpus callosum are studied with the same procedure in the rat.

No cytoarchitectonic area was entirely devoid of labeled cells in either species. The concentration of labeled cells throughout the entire neocortex averaged 25.2 cells/0.05 mm3 in opossum and 31.2 cells/0.05 mm3 in rat. The concentrations of labeled cells were correlated for the eight cytoarchitectonic areas common to the two species, though they were different enough in number to be statistically reliable. The distribution of labeled cells both among and within cytoarchitectonic areas was often more homogeneous in opossum than in rat.

Although cortical layer 1 had no labeled cells in either species, the distribution of labeled cells across the remaining cortical layers differed sharply between the two species. In opossum, layer 3 had the most labeled cells (averaging 55% of the total number) while layer 5 had considerably less (averaging 12%). In rat, layer 5 had as many labeled cells as layer 3–both layers averaging 43% of the total number of labeled cells.

In both species, striate cortex deviated markedly from other cytoarchitectonic areas. Although both species had very few labeled cells in striate cortex, those that were labeled were invariably supragranular in opossum and infragranular in rat.

The similarities and dissimilarities in the topographic distribution of the origins of the two types of interhemispheric fiber systems seem to parallel the degree of cortical (and thalamic) differentiation in the two animals. However, the differences in laminar distribution are much greater and in particular, the small contribution of layer 5 in opossum as opposed to rat may well be functionally significant.
Synaptic connections of intracellularly filled clutch cells: A type of small basket cell in the visual cortex of the cat
Authors: Kisvárday Z. F. , Martin K. A. C. , Whitteridge D. , Somogyi P.
Published: May 2005

Light and electron microscopic quantitative analysis was carried out on a type of neuron intracellularly filled with horseradish peroxidase. Two cells were studied in area 17, one of which was injected intra‐axonally, and its soma was not recovered. One cell was studied in area 18. The two somata were on the border of layers IVa/b; they were radially elongated and received synapses from numerous large boutons with round synaptic vesicles. The dendrites were smooth and remained largely in layer IV.

The cells can be recognised on the basis of their axonal arbor, which was restricted to layer IV (90–95% of boutons) with minor projections to layers III, V, and VI. Many of the large, bulbous boutons contacted neuronal somata, short collaterals often forming “claw”‐like configurations around cells. The name “clutch cell” is suggested to delineate this type of neuron from other aspiny multipolar cells. Computer‐assisted reconstruction of the axon showed that in layer IV the axons occupied a rectangular area about 300 × 500 μm, elongated anteroposteriorly in area 17 and mediolaterally in area 18. The distributions of synaptic boutons and postsynaptic cells were patchy within this area. A total of 321 boutons were serially sectioned in area 17. The boutons formed type II synaptic contacts. The postsynaptic targets were somata (20–30%), dendritic shafts (35–50%), spines (30%), and rarely axon initial segments. Most of the postsynaptic somata tested were not immunoreactive for GABA and their fine structural features suggest that they are spiny stellate, star pyramidal, and pyramidal neurons. The characteristics of most of the postsynaptic dendrites and spines also suggest that they belong to these spiny neurons. A few of the postsynaptic dendrites and somata exhibited characteristics of cells with smooth dendrites and these somata were immunoreactive for GABA.

It is suggested that clutch cells are inhibitory interneurons exerting their effect mainly on layer IV spiny neurons in an area localised perhaps to a single ocular dominance column. The specific laminar location of the axons of clutch cell also suggests that they may be associated with the afferent terminals of lateral geniculate nucleus cells, and could thus be responsible for generating some of the selective properties of neurons of the first stage of cortical processing.
The optokinetic nystagmus and ocular pigmentation of hypopigmented mouse mutants
Authors: Mangini Nancy J. , Vanable Joseph W. , Williams Marilyn A. , Pinto Lawrence H.
Published: May 2005

We tested the optokinetic nystagmus (OKN) reflex of various hypopigmented mutant mice and ultrastructurally examined the pigmentation of various ocular structures in these mutants.

Using electron microscopy we examined the pigmentation of the choroid and retinal pigment epithelium (RPE) and measured the numerical density, volume density, and distribution of RPE melanosomes of mice with the following phenotypes: (1) wild type, (2) mutants that have abnormal or no OKN in response to horizontally moving, full‐field stimulation, and (3) other mutants that have normal OKN but reduced choroidal pigmentation. We also measured the OKN of all these mice in response to horizontally moving stimuli that were restricted to the nasal or to the temporal retina.

We found that in the mutants with normal OKN the numerical density of melanosomes in the RPE was within the range found for wild type, while the numerical density was reduced for the mutants with abnormal OKN. For one mutant with normal RPE pigmentation and normal OKN, the choroidal pigmentation was nearly absent. For the genotypes with abnormal OKN the volume density of the RPE melanosomes and percent apical melanosomes were sometimes greater and sometimes less than normal.

The OKN patterns of these mice fell into the following categories: (1) wild type; (2) field‐restriction dependent OKN with small following movements but no OKN in response to full‐field stimulation, normal OKN in response to stimulation of the nasal retina, and OKN of reversed direction in response to stimulation of the temporal retina; (3) oblique with slow oblique following movements and reduced numbers of OKNs with oblique quick phases in response to horizontally moving, full‐field stimulation, nearly normal OKN in response to stimulation of the nasal retina, and OKN of reversed direction in response to stimulation of the temporal retina. The horizontal component of the oblique response to full‐field stimulation was in the same direction for the two eyes, but the vertical component was in the opposite direction. (4) Slow, small amplitude, with no or very small following movements in response to full‐field stimulation, following movements in response to stimulation of the nasal retina and reversed “following” movements in response to stimulation of the temporal retina but few or no quick phases of the OKN for any stimulus condition.

These results show that a variety of abnormalities of the OKN occur for hypopigmentation mutants of the mouse. Moreover, abnormality of the OKN is associated with a reduction of the numerical density of melanosomes in the RPE, but not with either a reduction of the volume of melanin in the RPE or hypopigmentation of the choroid.
Cytoarchitectonic development of the prefrontal cortex in the rat
Authors: van Eden C. G. , Uylings H. B. M.
Published: May 2005

This paper gives an account of the cytoarchitectonic characteristics that make it possible to delineate, from as early as day 6, different subareas of the prefrontal cortex of the rat. Three phases can be distinguished during postnatal development. The first phase (from day 1 until day 18) is dominated by differentiation of the neurons within the cortical plate and by the formation of the cortical layers. At day 1, regional differences are observed in the cytoarchitecture of the cortical plate which correspond to the future subareas of the prefrontal cortex. The formation of layer IV occurs in the dorsolateral cortex around day 6, and from this age the agranular prefrontal cortex is well demarcated from the other parts of the frontal cortex. Between day 6 and day 10, the cortical plate has disappeared and all cortical layers can be recognized in the prefrontal cortex. Differentiation of the cells within the cortical layers changes the cytoarchitectonic character of the layers through day 18. During the second phase (from day 18 until day 30) little change occurs in the cytoarchitectonic characteristics of the prefrontal subareas. During the third phase (from day 30 until day 90) the delineation of the cortical layers becomes less clear in Nissl‐stained sections, and the individual cytoarchitectonic variance increases. On the basis of cytoarchitectonic criteria it can be concluded that the orbital prefrontal cortex develops earlier than does the medial prefrontal cortex.
Funicular trajectories of brainstem neurons projecting to the lumbar spinal cord in the monkey (Macaca fascicularis): A retrograde labeling study
Authors: Carlton S. M. , Chung J. M. , Leonard R. B. , Willis W. D.
Published: May 2005

Brainstem nuclei projecting to the lumbar spinal cord in the monkey were identified by using horseradish peroxidase and the fluorescent dye granular blue. These retrogradely transported tracers were used in fluid and/or gel forms to determine the funicular trajectories of the brainstem‐spinal projections. The major descending components of the dorsal funiculus arose from the n. gracilis, n. cuneatus, and the n. of the solitary tract. Major components of the dorsolateral funiculus (DLF) came from the raphe complex, medullary and pontine reticular formation, locus coeruleus, Edinger‐Westphal n., and red n. Other nuclei giving rise to minor contributions to the DLF included n. gracilis, n. cuneatus, n. of the solitary tract, medial and spinal vestibular n., subcoeruleus, periaqueductal gray, interstitial n. of Cajal, n. of Darkschewitsch, and the anteromedian n. The major components of ventral cord paths (ventrolateral and ventral funiculi) arose from the raphe complex, the medullary and pontine reticular formation, lateral and spinal vestibular n., and the coerulean complex. Minor contributions to the ventral paths descended from the dorsal motor n. of X, n. of the solitary tract, medial vestibular n., paralemniscal reticular formation, dorsal parabrachial n., n. cuneiformis, periaqueductal gray, Kölliker‐Fuse n., and red n. The possible functional implications of the funicularr distribution of these descending pathways are discussed from the perspective of descending inhibition and pain modulation.
Dendritic plasticity in the early postnatal feline retina: Quantitative characteristics and sensitive period
Authors: Eysel U. T. , Peichl L. , Wáussle H.
Published: May 2005

Retinal lesions were made in kittens between 3 and 60 days postnatal age and in adult cats. After postlesion survival times ranging from 4 to 11 months the dendritic morphology of retinal ganglion cells was revealed by retrograde labeling with horseradish peroxidase or with neurofibrillar staining techniques. After retinal lesions on the third postnatal day changes of dendritic morphology were observed in retinal ganglion cells adjacent to regions of retrograde degeneration. Originating from eccentrically positioned somata the dendritic fields extended into the regions that were free of neighboring cells. The dendrites oriented toward the ganglion‐cell‐free region were elongated and thicker than normal. The density of dendrites per unit area was increased in this part of the dendritic trees. Lesions on the 20th, 38th, and 56th postnatal days elicited increasingly weaker changes of dendritic morphology. The sensitive period for the type of dendritic plasticity described ends between 40 and 60 days postnatally.
Innervation of cat visual areas 17 and 18 by physiologically identified X‐ and Y‐ type thalamic afferents. II. Identification of postsynaptic targets by GABA immunocytochemistry and Golgi impregnation
Authors: Freund T. F. , Martin K. A. C. , Somogyi P. , Whitteridge D.
Published: May 2005

The precise location of physiologically identified specific afferent input on the different types of cell in the visual cortex and the identification of the neurotransmitters of these cells are essential to a better understanding of the first stage of cortical processing. A combination of anatomical, neurochemical, and physiological methods was used to identify the cortical neurones that receive synaptic input from X‐ and Y‐type afferents, which are thought to originate from cells of the lateral geniculate nucleus. One method relied on chance contacts made between single physiologically characterised axons, which had been injected with horseradish peroxidase (HRP), and the processes of cells impregnated by the Golgi method. These experiments revealed that both X and Y axons formed synapses on the dendrites of spiny stellate cells in layer 4. Y axons in both areas 17 and 18 established multiple synaptic contacts on basal dendrites of layer 3 pyramidal cells. One X axon contacted the apical dendrite of a layer 5 pyramidal cell and one Y axon contacted the dendrite of a large cell with smooth dendrites in layer 3. The maximum number of synapses made between one axon and a single postsynaptic cell was eight, although in most cases it was only one. It was concluded that one axon only provides a small fraction of the geniculate afferent input to an individual cell.

A second method revealed that the somata in layer 4 in synaptic contact with the HRP‐filled axon terminals were GABA‐immunoreactive, and therefore might be involved in inhibitory processes. From light microscopic data it was found that somata receiving contacts from X axons in area 17 were significantly smaller (average diameter 15μm) than those contacted by the Y axons in areas 17 and 18 (average diameter 24 μm). Somatic contacts were extremely rare in layer 6. These data show that the X and Y afferents may activate separate subsets of inhibitory neurones.
Topographical organization of the cortical afferent connections of the prefrontal cortex in the cat
Authors: Cavada Carmen , Reinoso‐Suárez Fernando
Published: May 2005

The topographical distribution of the cortical afferent connections of the prefrontal cortex (PFC) in adult cats was studied by using the retrograde axonal transport of horseradish peroxidase technique. Small single injections of the enzyme were made in different locations of the PFC, and the areal location and density of the subsequent neuronal labeling in neocortex and allocortex were evaluated in each case. The comparison of the results obtained in the various cases revealed that (1) four prefrontal sectors (rostral, dorsolateral, ventral, and dorsomedial) can be distinguished, each exhibiting a particular pattern of cortical afferents. (2) All PFC sectors receive projections from the ipsilateral insular (agranular and granular subdivisions) and limbic (infralimbic, prelimbic, anterior limbic, cingular, and retrosplenial areas) cortices. These cortices provide the most abundant cortical projections to the PFC, and their various subdivisions have different preferential targets within the PFC. (3) The premotor cortex and the following neocortical sensory association areas project differentially upon the various ipsilateral PFC sectors: the portion of the somatosensory area SIV in the upper bank of the anterior ectosylvian sulcus, the visual area in the lower bank of the same sulcus, the auditory area AII, the temporal area, the perirhinal cortex, the posterior suprasylvian area, area 20, the posterior ectosylvian area, the suprasylvian fringe, the lateral suprasylvian area (anterolateral and posterolateral subdivisions), area 5, and area 7. (4) The olfactory peduncle, the prepiriform cortex, the cortico‐amygdaloid transition area, the entorhinal cortex, the subiculum (ventral, posteroventral, and posterodorsal sectors), the caudomedial band off the hippocampal formation and the postsubiculum are the allocortical sources of afferents to the PFC. (5) The dorsolateral PFC sector is the target of the largest insular, limbic, and neocortical sensory association projections. The dorsomedial and rostral sectors receive notably less abundant cortical afferents than the dorsolateral sector. Those to the dorsomedial sector arise from the same areas that project to the dorsolateral sector and are more abundant to the dorsal part, where the medial frontal eye field cortex is located. The rostral sector receives projections principally from all other PFC sectors, and from the limbic and insular cortices. The projections from the allocortex reach preferentially the ventral PFC sector. (6) Intraprefrontal connections are most abundant within each PFC sector. Commissural interprefrontal connections are largest from the site homotopic to the HRP injection. Contralateral heterotopic areas also project to the PFC.

The present findings are compared to the patterns of distribution of cortical afferents in the PFC reported in macaque monkeys and similarities and differences are considered.
A quantitative study of the relative contribution of different retinal sectors to the innervation of various thalamic and pretectal nuclei in goldfish
Authors: Springer Alan D. , Mednick Adam S.
Published: May 2005

The contribution of retinal ganglion cells situated in different retinal quadrants to the innervation of eight nontectal, retinorecipient targets was examined in goldfish. In some fish, cobaltous‐lysine was used to selectively fill severed intraretinal ganglion cell axons and the number of filled axons within each nucleus was determined. In other fish, either the dorsal or ventral or nasal or temporal retina was ablated and the remaining axons from the intact retina were filled with cobalt. The density of the cobalt‐filled axons within the retinorecipient targets was quantified with a microdensitometer. All of the eight targets received different degrees of innervation when the contributions from dorsal and ventral retina were compared. The suprachiasmatic nucleus received axons from ventral, but not from dorsal, retinal ganglion cells (RGCs), while the nucleus opticus dorsolateralis, nucleus opticus commissurae posterior, and nucleus opticus pretectalis dorsalis received more axons from ventral than from dorsal RGCs. The tuberal region, nucleus corticalis, and the accessory optic nucleus received axons from dorsal, but not from ventral, RGCs. The nucleus opticus pretectalis ventralis received more axons from dorsal then from ventral RGCs. Only one target, nucleus corticalis, appeared to receive more axons from nasal than from temporal RGCs. In general, those nuclei that were closest to the dorsal optic tract were innervated exclusively or predominantly by ventral RGC axons, whereas those nuclei that were closest to the ventral optic tract were innervated exclusively or predominantly by dorsal RGC axons. These data indicate that in this particular vertebrate, the dorsal and ventral retinal regions are not homogeneous with respect to their projections to nontectal nuclei. The possible role that the nontectal nuclei play in determining the course of optic axons is discussed.
Pattern of rat olfactory bulb mitral and tufted cell connections to the anterior olfactory nucleus pars externa
Authors: Scott John W. , Ranier Elizabeth C. , Pemberton Janice L. , Orona Edward , Mouradian Laurie E.
Published: May 2005

The pattern of output of mitral and tufted cells of the rat olfactory bulb (OB) to layer Ia overlying the pars externa (pE) of the anterior olfactory nucleus (AON) has been studied in the rat by iontophoresis of horseradish peroxidase and Phaseolus vulgaris‐leucoagglutinin. These agents labeled mitral and tufted cells and at least the proximal portion of their axons. In most cases we observed small branches from axons of the lateral olfactory tract that appear to terminate in the region of the pE AON, while the main axon could often be traced for considerable distances past these branches. These branches are assumed to terminate in the pE AON because they could not be traced to other terminal regions, because they ramify in layer Ia, and because they usually show small swellings characteristic of axons in terminal regions. Although each ramification could be extensive, we found that the positions of these small branches were related to the positions of the injections within the OB. Dorsal medial injections labeled dorsal branches. Ventral medial injections labeled ventral branches. Injections on the lateral face of the OB labeled intermediate branches. The centers of the regions within which branches were labeled were strongly correlated with the positions of the injection around the circumference. Comparison of the anterior‐posterior axis of the OB produced no such strong correlation. Reconstructions of axons showed that terminal branches arise from both mitral and tufted cells, although at least some mitral cells are shown not to have such branches in the pE AON.

Studies of the patterns of dendrites and terminals in the pE AON indicate that this region has the same pattern of layer Ia and Ib terminals seen in other olfactory cortical regions. The pE AON cell layer is intercalated just below the boundary between layers Ia and Ib. Since dendrites of the underlying pars lateralis of the AON (pL AON) penetrate into layer Ia over much of the pE AON, it is necessary to remember that at least part of the pL AON may also receive topographically organized inputs.
The primate mediodorsal (MD) nucleus and its projection to the frontal lobe
Authors: Goldman‐Rakic Patricia S. , Porrino Linda J.
Published: May 2005

The frontal lobe projections of the mediodorsal (MD) nucleus of the thalamus were examined in rhesus monkey by transport of retrograde markers injected into one of nine cytoarchitectonic regions (Walker's areas 6, 8A, 9, 10, 11, 12, 13, 46, and Brodmann's area 4) located in the rostral third of the cerebrum. Each area of prefrontal, premotor, or motor cortex injected was found to receive a topographically unique thalamic input from clusters of cells in specific subdivisions within MD. All of the prefrontal areas examined also receive topographically organized inputs from other thalamic nuclei including, most prominently, the ventral anterior (VA) and medial pulvinar nuclei. Conversely, and in agreement with previous findings, MD projects to areas of the frontal lobe beyond the traditional borders of prefrontal cortex, such as the anterior cingulate and supplementary motor cortex. The topography of thalamocortical neurons revealed in coronal sections through VA, MD, and pulvinar is circumferential. In the medial part of MD, for example, thalamocortical neurons shift from a dorsal to a ventral position for cortical targets lying medial to lateral along the ventral surface of the lobe; neurons in the lateral MD move from a ventral to a dorsal position, for cortical areas situated lateral to medial on the convexity of the hemisphere. The aggregate evidence for topographic specificity is supported further by experiments in which different fluorescent dyes were placed in multiple areas of the frontal lobe in each of three cases. The results show that very few, if any, thalamic neurons project to more than one area of cortex. The widespread cortical targets of MD neurons together with evidence for multiple thalamic inputs to prefrontal areas support a revision of the classical hodological definition of prefrontal cortex as the exclusive cortical recipient of MD projections. Rather, the prefrontal cortex is defined by multiple specific relationships with the thalamus.
Neuronal classes and their relation to functional and laminar organization of the lateral geniculate nucleus: A Golgi study of the prosimian primate, Galago crassicaudatus
Authors: Conley Michael , Birecree Elizabeth , Casagrande V. A.
Published: May 2005

The neuronal organization of the lateral geniculate nucleus of the prosimian primate, Galago crassicaudatus, was studied in Golgi‐Kopsch‐impregnated material. On the basis of cytoarchitecture, electrophysiology, and connections the nucleus is divisible into three pairs of layers—one magnocellular, one parvocellular, and one koniocellular—each part of a separate retinogeniculate and geniculostriate pathway (Itoh et al., '82; Norton and Casagrande, '82).

In Macaca and Saimiri, which have equally distinct geniculate subdivisions, it has been reported that, outside of cell size, no one morphological attribute differentiates magnocellular from parvocellular neurons (Campo‐Ortega et al., '68; Wong‐Riley, '72; Saini and Garey, '81; Wilson and Hendrickson, '81). Results presented here are not inconsistent with this conclusion. However, when the results are analyzed from the standpoint of the collective traits that distinguish the cell groups that make up the layers, clear morphological differences are evident.

Using this approach we find the following differences between presumed projection neurons and interneurons in each pair of layers. The projection neurons of the magnocellular layers, as a group, exhibit large cell bodies with radially arranged dendrites which often extend beyond laminar borders. The magnocellular interneurons are larger than their counterparts in the other layers and, like the magnocellular projection neurons, exhibit radially arranged dendrites. The former, however, also share characteristics in common with other interneurons such as relatively small somata, few proximal dendrites, and complex distal dendritic appendages. In contrast, the projection neurons and interneurons of the parvocellular layers have smaller somata and more restricted dendritic spreads than their counterparts in the magnocellular layers. Dendritic arbors of parvocellular neurons are typically oriented perpendicular to laminar borders and remain confined to their layer of origin. The koniocellular neurons represent a more diverse population but collectively are distinct in that the dendrites of almost all neurons in these layers run parallel to the layers.

The fact that presumed interneurons and projection neurons in a single layer share a number of related dendritic features suggests that both groups together are responsible for the structural and, hence, functional architecture of a layer. We conclude that when the organization of the lateral geniculate nucleus is considered from the standpoint of layers and not individual cell types, the functional differences between layers indicated bydifferential connections, histochemistry, and electrophysiology can be related to distinct morphological differences singular to magnocellular, parvocellular, and koniocellular divisions.
Laminar organization of geniculocortical projections in Galago senegalensis and Aotus trivirgatus
Authors: Diamond I. T. , Conley M. , Itoh K. , Fitzpatrick D.
Published: May 2005

The projections of the lateral geniculate nucleus to striate cortex were traced by anterograde and retrograde transport of WGA‐HRP in two primates, Galago and Aotus. The goal was to determine the laminar organization of the terminals of individual layers of the lateral geniculate nucleus. The results show that in both species the magnocellular layers project to cortical layer IVα, the parvicellular layers project to IVβ, and the intercalated geniculate layers (which term includes layers 4 and 5 in Galago) project to layers III and I. The distribution of terminals in layer III is periodic, which is to say, there are regularly spaced regions of terminals separated by regions devoid of terminals. When the two species are compared to Saimiri, it is clear that the basic organization of the three pathways relaying in the lateral geniculate nucleus is common to all three primates. At the same time, there are some significant species differences. The total pattern of projections in Galago is compressed in comparison to that in the monkey, and this compression seems to be related to the poorer differentiation of cortical layers in the prosimian. For example, layer IIIC is distinct only in the two monkeys and at the same time it is spared from geniculate terminations. Both Galago and Aotus differ from Saimiri in that they lack a projection from the parvicellular geniculate layers to the layer IIIB. These species comparisons are relevant to the questions of the functional significance of the three pathways and the evolution of the primate striate cortex.
The ultrastructure of enkephalin‐immunoreactive neurons in the interpeduncular nucleus of the rat
Authors: Mahalik Thomas J. , Finger Thomas E.
Published: May 2005

The interpeduncular nucleus of the rat is a complex structure, displaying diverse immunocytochemical and ultrastructural features. This nucleus contains opiate receptors, enkephalin‐positive cell bodies and enkephalin‐positive fibers. The ultrastructure of rat interpeduncular enkephalinergic neurons has not been described, nor has the role that these neurons play in the internal organization of the interpeduncular nucleus been established. The purpose of the present study was to describe the ultrastructure of enkephalinlike‐immunoreactive (ELI) cells with particular emphasis on the subnuclear organization of their dendritic and terminal fields.

Enkephalinlike‐immunoreactive (ELI) cell bodies are present in the rostral and apical subnuclei of the interpeduncular nucleus (IPN), but are absent from the other subnuclei of the IPN. The rostral subnucleus also contains immunoreactive dendrites that are postsynaptic to nonreactive terminal boutons. Numerous ELI axon terminals were observed in the central and intermediate subnuclei. The results of our study suggest that enkephalinergic interneurons link the rostral IPN with more caudal regions of this nucleus.
Glutamic acid decarboxylase and somatostatin immunoreactivities in rat visual cortex
Authors: Lin Chia‐Sheng , Lu S. M. , Schmechel D. E.
Published: May 2005

Antibodies to glutamic acid decarboxylase (GAD) and somatostatin (SS) were used to determine the laminar distribution and morphology of GAD‐and SS‐immunoreactive neurons and terminals in rat visual cortex. The present study demonstrates that GAD‐immunoreactive neurons constitute several morphologically distinct subclasses of neurons in rat visual cortex. These subclasses of neurons can be distinguished by differences in soma size, soma shape, dendritic branching patterns, axonal arborizations, and location in the neuropil.

GAD‐immunoreactive neurons are found throughout all layers of visual cortex. They have nonpyramidal morphology and constitute roughly 15% of the total neuronal population. The laminar pattern of GAD‐immunoreactive puncta is uneven, with a prominent band of terminals in layer IV. Numerous large GAD‐positive puncta surround the somata and proximal dendrites of pyramidal cells in layers II, III, and V.

SS‐immunoreactive neurons constitute a less numerous and more restricted population of nonpyramidal neurons. Their somata are located mainly in layers II, III, V, and VI. Very few, if any, SS‐immunoreactive neurons are found in layers I and IV. SS‐immunoreactive terminals are arranged along vertical and diagonal collateral branches that have a beaded appearance.

Finally, many neurons in the supra‐ and infragranular layers and in the white matter are immunoreactive to both glutamic acid decarboxylase and somatostatin. This coexistence of immunoreactivity to both GAD and SS may characterize a broad subclass of cortical nonpyramidal neurons.
Axonal growth cones in the developing amphibian spinal cord
Authors: Nordlander Ruth H.
Published: May 2005

Axonal growth cones in the spinal cord of embryonic and larval Xenopus (stages 24–48) were filled with the anatomical tracer horseradish peroxidase (HRP). Growth cones of lateral and ventral marginal zones, including those of descending spinal and supraspinal pathways, were labeled by application of tracer to the caudal medulla or to one of several levels of the spinal cord. Central axons of sensory neurons were filled via their peripheral processes. Growth cone configuration varied widely but fell into five general categories: complex with both filopodia and veils, filopodia only, lamellipodia only, clavate, and fusiform. Several general patterns emerged from the distribution of these various configurations. Growth cones of younger animals generally were more complex than those of older ones. Growth cones closer to the leading edge of descending fiber bundles were more elaborate than those that followed. Growth cones of the dorsolateral fascicle, which carries ascending central processes of Rohon‐Beard and sensory ganglion neurons, were very simple and followed a straight course rostrally, whereas those of descending axons of the lateral fiber areas were more complex and sometimes spread over almost the entire lateral marginal zone. Growth cones of Rohon‐Beard central ascending axons were fusiform or clavate, while those of sensory ganglion axons showed several fine filopodia at their tips. Growth cones of both types of sensory axons change configuration as they approached the hindbrain, becoming more complex. This study demonstrates that the configurations of growth cones belonging to the same axonal pathway vary with age and with position along their routes, and that growth cones of different neuron classes exhibit characteristic ranges of morphological variation.
Synapse formation in the olfactory cortex by regenerating optic axons: Ultrastructural evidence for polyspecific chemoaffinity
Authors: Scalia Frank
Published: May 2005

The optic nerve was severed at its entry into the optic chiasma and implanted into the striatal region of the ipsilateral cerebral hemisphere in adult frogs (Rana pipiens). Regenerating retinal ganglion cell axons, observed by the autoradiographic tracing method and by horseradish peroxidase (HRP) fiber filling, grew anteriorly along the olfactory tracts and posteriorly along the ipsilateral lateral forebrain bundle and stria medullaris. Many of the regenerating axons ultimately joined the ipsilateral optic tract. The optic axons formed terminal plexuses in the olfactory cortex, lateral geniculate complex, pretectum, tectum, and basal optical nucleus but not in the amygdala or other cerebral territories not postsynaptic to the olfactory bulb, nor in the cell groups associated with the lateral forebrain bundle or stria medullaris. Optic axon terminals labeled with HRP were observed by electron microscopy in the ipsilateral olfactory cortex and in the normal projection areas of the optic nerve, although they were misplaced to the ipsilateral side. They contained clear, spherical synaptic vesicles and pale mitochondria and made Gray type I, asymmetric contacts on dendrites. The retinal projection to the olfactory cortex was formed early in regeneration and was maintained to some degree for periods up to 39 weeks. It was absent in a specimen surviving 50 weeks. Retinal innervation appeared earlier in the lateral geniculate complex and pretectum than in the tectum.

These observations suggest that regenerating retinal ganglion cell axons have an affinity for neurons in the olfactory cortex, as well as for the neurons in the optic pathway to which they are normally postsynaptic. Unless the apparent selectivity of the aberrant projection is regulated by principles other than those that bring about the reinnervation of the normal optic centers, the data further suggest that the nature of the molecular mechanisms conveying synaptic specificity must be broad enough to permit the formation of limited sets of alternative synaptic connections. The ability to innervate selectively targets other than those normally specified is termed, here, polyspecificity. Since polyspecificity refers to the the affinity of retinal ganglion axons, as a class, for target, structures considered as unit aggregates, it is conceptually different from the graded affinity of ganglion cells in different regions of the retina for target neurons in different regions of the tectum. Hierarchically interactive mechanisms capable of regulating the expression of affinity molecules during development are discussed as a means for restricting the formation or stabilization of nonstandard connection hypothetically made possible by polyspecificity.
Morphology and synaptic connections of crossed corticostriatal neurons in the rat
Authors: Wilson Charles J.
Published: May 2005

The neurons of origin of the bilateral corticostriatal projection arising from the medial agranular cortical field in rats were identified by antidromic activation from contralateral neostriatal stimulation. The same cells were tested for antidromic activation from the contralateral neocortex and for orthodromic responses to stimulation of neocortex of the contralateral hemisphere or ipsilateral rostral thalamus. The neurons were then stained by intracellular injection of horseradish peroxidase. The laminar distribution of these neurons was compared to that of cortical cells stained retrogradely after injection of wheat germ agglutinin/HRP in the ipsilateral or contralateral neostriatum. The morphological features of physiologically identified corticostriatal neurons, their laminar organization, and their responses to stimulation were examined and compared with crossed corticocortical and brainstem‐projecting cells.

Crossed corticostriatal cells of the medial agranular cortical field were medium‐sized pyramidal neurons found in the superficial part of layer V and in the deep part of layer III. Their basilar dendritic fields and initial intracortical axon collateral arborizations were coextensive with the layer defined by the distribution of corticostriatal neurons. The apical dendrites were thin and sparsely branched but consistently reached layer I, where they made a small arborization. These morphological features were shared by cortical neurons projecting to contralateral neocortex but not responding antidromically to stimulation of contralateral neostriatum, but they were not shared by brainstem‐projecting cortical cells.

Orthodromic responses to contralateral cortical stimulation consisted of brief excitatory postsynaptic potentials that were followed by powerful and longer‐lasting inhibitory postsynaptic potentials. Corticostriatal cells also exhibited small excitatory postsynaptic potentials in response to thalamic stimulation.

Many crossed corticostriatal neurons were also commissural corticocortical neurons. The results of reciprocal collision tests showed that this was due to the existence of two separate axonal branches, one projecting to contralateral neocortex and one to contralateral neostriatum. Intracellular staining of these neurons revealed ipsilateral axonal projections to the neostriatum and cortex.
Visual and auditory association areas of the cat's posterior ectosylvian gyrus: Thalamic afferents
Authors: Bowman E. M. , Olson C. R.
Published: May 2005

The feline posterior ectosylvian gyrus contains a broad band of association cortex that is bounded anteriorly by tonotopic auditory areas and posteriorly by retinotopic visual areas. To characterize the possible functions of this cortex and to throw light on its pattern of internal divisions, we have carried out an analysis of its thalamic afferents. Deposits of differentiable retrograde tracers were placed at 17 cortical sites in nine cats. The deposit sites spanned the crown of the posterior ectosylvian gyrus and adjacent cortex in the suprasylvian sulcus. We compiled counts of retrogradely labeled neurons in 12 thalamic nuclei delineated by use of Nissl and acetylcholinesterase stains. We then employed a statistical clustering algorithm to identify groups of injections that gave rise to similar patterns of thalamic labeling.

The results suggest that the posterior ectosylvian gyrus contains 3 fundamentally different cortical districts that have the form of parallel vertical bands. Very anterior cortex, overlapping previously identified tonotopic auditory areas (AI, P and VP) receives a dense projection from the laminated division of the medial geniculate body (MGl). An intermediate strip, to which we refer as the auditory belt, is innervated by axons from nontonotopic divisions of the medial geniculate body (MGds, MGvl, MGm, and MGd), from the lateral division of the posterior group (Pol), and from the posterior suprageniculate nucleus (SGp). A posterior strip, to which we refer as EPp, receives strong projections from the LM‐SG complex (LM‐SGa and LMp), and lighter projections from the intralaminar and lateroposterior (LPm and LPl) nuclei. On grounds of thalamic connectivity, EPp is not obviously distinguishable from adjacent retinotopic visual areas (PLLS, DLS, and VLS), and may be regarded as forming, together with these areas, a connectionally homogeneous visual belt.
Cholinergic projections from the midbrain reticular formation and the parabigeminal nucleus to the lateral geniculate nucleus in the tree shrew
Authors: Fitzpatrick D. , Conley M. , Luppino G. , Matelli M. , Diamond I. T.
Published: May 2005

The distribution and sources of putative cholinergic fibers within the lateral geniculate nucleus (GL) of the tree shrew have been examined by using the immunocytochemical localization of choline acetyltransferase (ChAT). ChAT‐immunoreactive fibers are found throughout the thalamus but are particularly abundant in the GL as compared to other principal sensory thalamic nuclei (medial geniculate nucleus, ventral posterior nucleus). Individual ChAT‐immunoreactive fibers are extremely fine in caliber and display numerous small swellings along their lengths. Within the GL, ChAT‐immunoreactive fibers are more numerous in the layers than in the interlaminar zones and, in most cases, the greatest density is found in layers 4 and 5. Two sources for the ChAT‐immunoreactive fibers in the GL have been identified–the parabigeminal nucleus (Pbg) and the pedunculopontine tegmental nucleus (PPT)–and the contribution that each makes to the distribution of ChAT‐immunoreactive fibers in GL was determined by combining immunocytochemical, axonal transport, and lesion methods. The projection from the Pbg is strictly contralateral, travels via the optic tract, and terminates in layers 1, 3, 5, and 6 as well as the interlaminar zones on either side of layer 5. The projection from PPT is bilateral (ipsilateral dominant) and terminates throughout the GL as well as in other thalamic nuclei. Lesions of the Pbg eliminate the ChAT‐immunoreactive fibers normally found in the optic tract but have no obvious effect on the density of ChAT‐immunoreactive fibers in the contralateral GL. In contrast, lesions of PPT produce a conspicuous decrease in the number of ChAT‐immunoreactive fibers in the GL and in other thalamic nuclei on the side of the lesion but have no obvious effect on the number of ChAT‐immunoreactive fibers in the optic tract. These results suggest that there are two sources of cholinergic projections to the GL in the tree shrew which are likely to play different roles in modulating the transmission of visual activity to the cortex. The Pbg is recognized as a part of the visual system by virtue of its reciprocal connections with the superficial layers of the superior colliculus, while the PPT is a part of the midbrain reticular formation and is thought to play a non‐modality‐specific role in modulating the activity of neurons throughout the thalamus and in other regions of the brainstem.
Localization of tyrosine‐hydroxylase‐like‐immunoreactive amacrine cells in the larval tiger salamander retina
Authors: Watt Carl B. , Yang Shu‐Zhen , Lam Dominic M. K. , Wu Samuel M.
Published: May 2005

Immunocytochemistry was used to localize the populations of tyrosinehydroxylase‐like (TH)‐immunoreactive cells in the tiger salamander retina. Ninety percent of these cells possessed somas that were situated in the innermost cell row of the inner nuclear layer and were classified as amacrine cells. Ten percent of TH‐immunoreactive somas were located in the ganglion cell layer and were tentatively designated as those of displaced amacrine cells. The processes of TH‐immunoreactive cells ramified most heavily in sublayer 1 of the inner plexiform layer, while a relatively small number of TH‐labelled processes distributed in sublayers 3 and 5. Less than 1% of TH‐immunoreactive cells in the amacrine cell layer exhibited a short process of somal origin that extended distally toward the outer plexiform layer. However, these processes did not cross the whole of the inner nuclear layer, and no immunolabelling was observed in the outer plexiform layer.

An examination of retinal whole‐mounts revealed that TH‐immunoreactive amacrine and displaced amacrine cells were distributed throughout the center and periphery of the retina. The density of TH‐immunolabelled amacrine cells was calculated to be 49 ± 13 (mean ± standard error) cells per mm2. The vast majority of TH‐immunoreactive amacrine and displaced amacrine cells exhibited a stellate appearance and gave rise to three or more primary dendrites. A few TH‐amacrine and displaced amacrine cells possessed two primary dendrites that emerged from opposite sides of their somas. The processes of TH‐immunoreactive cells were generally poorly branched and varicose with terminal branches sometimes appearing thin and beaded. Because some TH‐immunolabelled processes were very long, there was considerable overlap between the dendritic fields of neighboring TH‐cells. Lastly, individual TH‐immunoreactive amacrine and displaced amacrine cells were often observed in whole‐mounts to provide processes that ramified at more than one level of the inner plexiform layer.