bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential projections of the main and accessory olfactory bulb in the frog
Authors: Scalia Frank , Gallousis Gregory , Roca Suri
Published: January 2005

The central projections of the main olfactory bulb and the accessory olfactory bulb of the adult leopard frog (Rana pipiens) were reexamined, by using a horseradish peroxidase anterograde tracing method that fills axons with a continuous deposit of reaction product. The fine morphology preserved by this method allowed the terminal fields of the projection tracts to be delineated reliably, and for the first time. Herrick's amygdala has been newly subdivided into cortical and medial nuclei on the basis of cytoarchitecture, dendritic morphology, and the differential projections of the main and accessory olfactory tracts.

The main olfactory bulb projects through the medial and lateral olfactory tracts to the postolfactory eminence, the rostral end of the medial cortex, the rostral end of the medial septal nucleus, the cortical amygdaloid nucleus, the nucleus of the hemispheric sulcus, and both the dorsal and ventral divisions of the lateral cortex, including its retrobulbar fringe. The lateral olfactory tract overlaps the dorsal edge of the striatal plate along the ventral border of the lateral cortex, but it is not certain whether any striatal cells are postsynaptic to the tract fibers. The lateral cortex is the largest of these territories, and receives the terminals of the main olfactory projection throughout its extent. It extends from the olfactory bulb to the posterior pole, and from the striatum to the summit of the hemisphere, where it borders the dorsal cortex. The medial and lateral olfactory tracts combine in the region of the amygdala to form a part of the stria medullaris thalami. These fibers cross in the habenular commissure and terminate in the contralateral cortical amygdaloid nucleus and periamygdaloid part of the lateral cortex. Cells projecting to the main olfactory bulb are found in the diagonal band and adjacent cell groups, but there is no evidence of an interbulbar projection arising from either the olfactory bulb proper or a putative anterior olfactory nucleus.

The accessory olfactory bulb projects through the accessory olfactory tract to the medial and cortical amygdaloid nuclei. A fascicle of the tract crosses in the anterior commissure to terminate in the contralateral amygdala. While the main and accessory olfactory projections may converge in the cortical amygdaloid nucleus, the medial amygdaloid nucleus is connected exclusively with the accessory olfactory bulb.
Histamine: A putative afferent neurotransmitter in Limulus eyes
Authors: Battelle B.‐A. , Calman B. G. , Andrews A. W. , Grieco F. D. , Mleziva M. B. , Callaway J. C. , Stuart A. E.
Published: January 2005

Histamine has been proposed as a photoreceptor neurotransmitter in two major groups of arthropods, the insects and the Crustacea. In this study biochemical and immunocytochemical approaches were used to examine the synthesis, endogenous content, and cellular distribution of histamine in the visual system of the horseshoe crab Limulus polyphemus, an ancient chelicerate arthropod. Studies with this animal have been critical to our understanding of the basic processes of vision. High‐voltage paper electrophoresis was used to assay for histamine synthesis in Limulus tissues incubated with radiolabeled histidine; histamine synthesis was detected in the lateral, median, and ventral eyes and optic nerves and in the visual centers in the brain. Endogenous histamine, assayed as its orthophthalaldehyde derivative by high‐performance liquid chromatography and electrochemical detection, was also detected in these tissues. Immunocytochemical analyses, with an antiserum directed against a protein conjugate of histamine, revealed histamine‐like immunoreactivity in the somata of photoreceptors in each of the eyes and in the regions of the brain where the photoreceptors terminate. Histamine‐like immunoreactivity was also intense in the cell bodies and axon collaterals of eccentric cells in the lateral eye and in eccentric cell projections in the brain. These results show that histamine is a major biogenic amine in the Limulus visual system, and they suggest that this amine is involved in transmitting visual information from the eyes to the brain and in lateral inhibition, a fundamental mechanism for processing visual information in the lateral eye.
Guinea pig pancreatic ganglia: Projections, transmitter content, and the type‐specific localization of monoamine oxidase
Authors: Kirchgessner A. L. , Pintar J. E.
Published: January 2005

The ganglionated plexus of the guinea pig pancreas was investigated by using histochemical, immunocytochemical, and tract‐tracing methods in order to determine whether pancreatic ganglia are analogous to the ganglia of the enteric nervous system (ENS). Three lines of evidence suggest that the ganglia of the pancreas appear to be interconnected with one another, as are enteric ganglia. First, microinjections of the retrograde tracer Fluoro‐Gold into individual pancreatic ganglia labeled the perikarya of neurons in distant pancreatic ganglia, whereas no labeling of neurons was observed if injections were placed in the connective tissue adjacent to pancreatic ganglia. Second, when the intercalating dye DiI was microinjected into single pancreatic ganglia in fixed tissues, DiI‐labeled terminals were found in additional pancreatic ganglia. Finally, microinjections of the β subunit of cholera toxin into individual pancreatic ganglia yielded similar results.

The ganglionated plexus of the pancreas also expresses a diversity of transmitter content and cell type‐specific localization of monoamine oxidase (MAO) that is analogous to the ENS. In common with guinea pig enteric ganglia, pancreatic ganglia contain highly varicose 5‐hydroxytryptamine (5‐HT)‐immunoreactive axons and intrinsic neuropeptide Y (NPY)‐ and substance P (SP)‐immunoreactive neurons. The vast majority, but not all, of SP‐immunoreactive fibers in the pancreatic parenchyma also contain calcitonin gene‐related peptide (CGRP) immunoreactivity. MAO‐B was the primary type of MAO found in the intrinsic elements of the pancreas where it was located in neurons and fibers in the pancreatic parenchyma. In common with serotoninergic enteric neurons, MAO‐B immunoreactivity was not found at the LM level in pancreatic serotoninergic neurites. In contrast, NPY‐ and tyrosine hydroxylase (TH)‐immunoreactive perivascular axons were found to contain abundant MAO‐A, but no MAO‐B immunoreactivity. It is concluded that MAO‐B immunoreactivity is characteristic of a portion of the intrinsic innervation of the pancreas, whereas MAO‐A immunoreactivity is a marker for the extrinsic sympathetic innervation of the pancreas. Because of its receipt of a direct neural innervation from myenteric ganglia of the bowel (Kirchgessner and Gershon, '90: J. Neurosci 10:1626–1642), similar connections, transmitter content and localization of type‐specific MAO, the ganglionated plexus of the pancreas should be regarded as an extension or subset of the ENS.
Dendritic morphology of pyramidal neurones of the visual cortex of the rat: II. Parameter correlations
Authors: Larkman Alan U.
Published: January 2005

This study concerns the correlations between the various morphometric parameters obtained for the dendrites of neocortical pyramidal cells. The primary aims were to uncover underlying design principles in dendritic morphology, to see if these differed between different types of dendrite, and to see if estimates of parameters such as total dendritic shaft membrane area could be obtained from a limited number of measurements, avoiding the need to measure every dendritic segment. The data were from a sample of 39 pyramidal neurones, from layers 2/3 and 5 of the visual cortex of the rat, that had been injected with horseradish peroxidase, reconstructed, and measured with the light microscope as part of an earlier study (Larkman and Mason, '90: J. Neurosci. 10:1407–1414).

Correlations between the somal area or the combined diameters of the stem segments and measures of the overall size of the dendrites were generally weak. For basal dendrites, the size of a tree was correlated with both its number of tips and the diameter of its stem segment, but these correlations were weaker for apical dendrites. Within individual cells, the diameter of any basal segment was closely related to the size of the tree arising from it, and quantitatively similar relations applied to apical oblique trees from the same cell. Terminal arbor trees showed relations that were similar in pattern but differed quantitatively, whereas apical trunk segment diameter correlations were often weak. In all cases, the number of tips in a tree was closely related to its size. Segment lengths, however, were not closely related to the size of the trees arising from them.

It appears that at least some aspects of pyramidal dendritic morphology obey simple design rules. There was heterogeneity between trees of different types, although basal and oblique trees were very similar in most respects. It should prove possible to make use of correlations to estimate the sizes of basal, oblique, and terminal arbor trees from a limited number of measurements, but this does not seem to be possible for apical trunks.
Retinohypothalamic tract in the female albino rat: A study using horseradish peroxidase conjugated to cholera toxin
Authors: Levine Joel D. , Weiss Mark L. , Rosenwasser Alan M. , Miselis Richard R.
Published: January 2005

There are several anatomically and functionally distinct retinofugal pathways, one of which is the retinohypothalamic tract (RHT). In this study, horseradish peroxidase conjugated to cholera toxin (CT‐HRP), a sensitive neural tracer, was employed to describe the RHT in the female albino rat. Following uniocular injection of CT‐HRP, both medial and lateral components of the RHT were evident. The medial component swept caudally into and through the suprachiasmatic nucleus (SCN) and dorsally to the subparaventricular zone. Terminal label was seen in the medial preoptic region, peri‐SCN area, retrochiasmatic area, periventricular nucleus, anterior and central parts of the anterior hypothalamic area, and the subparaventricular zone. In contrast to the more focused and symmetrical medial component, the lateral component was diffuse with light terminal label in the lateral preoptic region, olfactory tubercle, lateral hypothalamus, supraoptic nucleus, and medial and posteroventral medial amygdaloid nuclei. The striking exception to this diffuse pattern of the lateral component was an extremely dense columnar terminal field over the dorsal border of the supraoptic nucleus. Whereas the intensity of label in terminal fields of the medial component was often similar on the sides ipsilateral and contralateral to the injection, the lateral component was consistently asymmetrical with greater labeling on the side contralateral to the injection. In addition, alight projection arrived at several thalamic nuclei by returning toward the thalamus from the tectal or pretectal areas via stria medullaris, and thus was not a part of the RHT. Implications for circadian as well as noncircadian photobiologic effects are discussed.
Olfactory projections to the hypothalamus
Authors: Price J. L. , Slotnick B. M. , Revial M.‐F.
Published: January 2005

Electrophysiological recording, together with anterograde and retrograde axonal tracers, was used to provide a comprehensive description of the origin and distribution of the olfactory input to the lateral hypothalamus. This input was much more substantial to the caudal part of the hypothalamus than to the rostral part and originates from several different areas of the olfactory cortex.

Positive responses to electrical stimulation of the olfactory bulb were found consistently in the postero‐lateral hypothalamus, but only occasionally at more rostral levels. In agreement with this, injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) in the posterior half of the lateral hypothalamus labeled cells in four cortical areas that receive input from the olfactory bulb: the anterior olfactory nucleus, the piriform cortex (in the deepest layer or ventral endopiriform nucleus), the olfactory tubercle (in the deep polymorphic layer), and the anterior cortical nucleus of the amygdala. Injections of WGA‐HRP in the anterolateral hypothalamus labeled cells only in the anterior cortical nucleus of the amygdala.

Anterograde axonal tracing confirmed these projections. Injections of 3H‐leucine in the anterior olfactory nucleus, the piriform cortex, and the olfactory tubercle produced axonal label that was light and confined to the medial forebrain bundle in the rostral hypothalamus but was more substantial and extended throughout the lateral hypothalamic area caudally. Injections in the anterior cortical amygdaloid nucleus labeled axons in the anterior hypothalamus and in the premammillary nuclei as well as in the posterolateral hypothalamic area. In addition, a projection was demonstrated to the nuclei gemini from the polymorphic zone deep to the olfactory tubercle.

Injections of two fluorescent retrograde tracers into the mediodorsal nucleus of the thalamus and the posterolateral hypothalamus showed that cells projecting to both diencephalic sites were intermingled in all of the olfactory cortical areas except the anterior olfactory nucleus, where cells were labeled only from the hypothalamus. In the deep layer of the piriform cortex and in the anterior cortical amygdaloid nucleus cells were also double labeled, indicating that they send collateral axons to both parts of the diencephalon.
Cortical connections of dorsal cortex rostral to V II in squirrel monkeys
Authors: Weller R. E. , Steele G. E. , Cusick C. G.
Published: January 2005

A region of dorsal cortex along the rostral border of V II has been described as comprising a visual area or areas separate from more lateral cortex in both New and Old World primates. To evaluate these possibilities in squirrel monkeys, we studied patterns of cortical connections by injecting Fast Blue, Fluoro‐Gold, horseradish peroxidase, and wheat germ agglutinin conjugated to horseradish peroxidase into the dorsal region and related results to distinctions in myeloarchitecture. Our major conclusions are as follows. (1) The dorsal region (D) has distinctly different connections from the area found laterally, the caudal subdivision of the dorsolateral area (DLC). These include major connections with the rostral subdivision of the dorsolateral area (DLR), ventral posterior parietal cortex in the Sylvian fissure, the middle temporal area (MT), the medial superior temporal area (MST), ventral cortex just rostral to V II, and cortex in the inferior temporal sulcus. Weaker connections are with V I, V II, DLC, the fundal superior temporal area (FST), and the frontal lobe. In contrast, DLC, has strong connections with V II and inferior temporal (IT) cortex, weaker connections with DLR, and lacks connections with ventral posterior parietal cortex (Steele et al: J Comp Neurol 306:495–520, 1991). (2) Caudal and rostral aspects of dorsal cortex differ in the magnitude of connections with V I, V II, DLR, and FST. These differences are consistent with the previous proposal that at least two visual areas, caudal and rostral, occupy the dorsal region in squirrel monkeys (Krubitzer and Kaas: Visual Neurosci 5:165, 1990), but they could also reflect regional differences in the connections of a single visual area. (3) The dorsal region is more densely myelinated than surrounding cortex; however, rostral aspects of dorsal cortex are less myelinated than caudal aspects, again suggesting the existence of at least two areas. (4) The distinctiveness of connections between dorsal cortex and rostral as compared to caudal dorsolateral cortex provides further evidence for dividing the region of DL into two visual areas, DLC and DLR (Cusick and Kaas: Visual Neurosci 1:211, 1988; Steele et al: J Comp Neurol 306:495–520, 1991).
Alz‐50 immunoreactivity in the hypothalamus of the normal and Alzheimer human and the rat
Authors: Byne W. , Mattiace L. , Kress Y. , Davies P.
Published: January 2005

Alz‐50 is a monoclonal antibody recognizing a 68 kilodalton protein that is abundant in Alzheimer's disease (AD) but not detectable by immunoblotting methods in normal brains. When used for immunohistochemistry in AD cortex, Alz‐50 recognizes large numbers of neurofibrillary tangles (NFT), neuritic plaques, and some neurons that show no evidence of neurofibrillary degeneration by conventional histopathological staining methods, Alz‐50 immunoreactivity is described at the light and electron microscopic levels in the hypothalamus of brains obtained at autopsy from normal and AD subjects. Alz‐50 immunoreactivity in the rat hypothalamus is also described. A well‐defined population of Alz‐50 immunoreactive hypothalamic neurons was identified in both the normal human and rat. At the light microscopic level in the normal human, immunoreactive neurons were most concentrated in the periventricular region, but were also scattered throughout the arcuate nucleus (ARC), lateral hypothalamic area, and tuberal region. Immunoreactive fibers were seen in the periventricular region, dorsal division of the ventromedial nucleus (VMNd), ARC, and external layer of the median eminence (ME). In the rat, reactive neurons were seen only in the periventricular region, and reactive fibers were seen in the periventricular zone, medial preoptic nuclear complex, suprachiasmatic nucleus, VMNd, ARC, and external layer of the ME. Ultrastructurally, all immunoreactivity in the normal human and rat hypothalamus was associated with intraneuronal vesicles. In the AD hypothalamus, Alz‐50 identified numerous senile plaques and NFT in addition to the cells and fibers that were stained in the normal brains. Immunoreactive plaques and NFT were most numerous in regions previously reported to undergo neurofibrillary degeneration. At the ultrastructural level, the immunoreactivity in the AD hypothalamus was associated with filaments as well as vesicles. The significance of the selective staining of a specific population of vesicles by Alz‐50 is unknown; however, the present results suggest that it is independent of AD pathology.
Differential innervation patterns of three divisions of frog auditory midbrain (torus semicircularis)
Authors: Feng Albert S. , Lin Wenyu
Published: January 2005

The connectivity pattern of the laminar, principal, and magnocellular nuclei of the frog torus semicircularis (TS) was investigated. A small amount of horseradish peroxidase was injected focally into individual divisions of the TS and anterograde and retrograde transport patterns were observed. Results of our tracing study showed that these divisions of the TS possessed distinct innervation patterns. The principal nucleus appeared to be the primary input port of the TS receiving extensive inputs from all caudal brainstem auditory nuclei bilaterally, but especially from the contralateral dorsal medullary nucleus and the ipsilateral superior olivary and lateral lemniscus nuclei. Descending projection to this nucleus was limited to that from the posterior thalamic nucleus. In contrast, the laminar nucleus, but even more markedly the magnocellular nucleus, received extensive descending inputs from numerous structures in the dorsal thalamus and less pronounced ascending afferents from caudal brainstem auditory nuclei. Similar to the afferent connection patterns, the efferent projections originating from these three toral divisions differed substantially. The principal nucleus gave restricted ascending projections, limited mainly to the caudal region of the posterior thalamic nucleus, a region important in processing spectral information of complex sounds, and the pretectal gray. Its descending projection was also somewhat restricted, being limited to the superior olivary and lateral lemniscus nuclei. The laminar nucleus and especially the magnocellular nucleus gave robust descending as well as ascending projections; these nuclei serve as the main output paths for the TS and provide the main routes by which auditory input reaches the central thalamic nucleus, a structure previously shown to be involved in temporal information processing.
Organization of ascending hypothalamic projections to the rostral forebrain with special reference to the innervation of cholinergic projection neurons
Authors: Cullinan William E. , Záborszky László
Published: January 2005

Axonal projections from hypothalamic nuclei to the basal forebrain, and their relation to cholinergic projection neurons in particular, were studied in the rat by using the anterograde tracer Phaseolus vulgaris‐leucoagglutinin (PHA‐L) in combination with choline acetyltransferase (ChAT) immunocytochemistry. Discrete iontophoretic PHA‐L injections were delivered to different portions of the caudal lateral hypothalamus, as well as to various medial hypothalamic areas, including the ventromedial, dorsomedial, and paraventricular nuclei, and anterior hypothalamic and medial preoptic areas. The simultaneous detection of PHA‐L‐labeled fibers/terminals and ChAT‐positive neurons was performed by using nickel‐enhanced diaminobenzidine (DAB) and nonenhanced DAB as chromogens. Selected cases were investigated at the electron microscopic level.

Ascending hypothalamic projections maintained an orderly lateromedial arrangement within the different components of the medial forebrain bundle, as well as with respect to their terminal projection fields (e.g., within the bed nucleus of the stria terminalis and lateral septal nucleus). The distribution pattern of hypothalamic inputs to cholinergic projection neurons corresponded to the topography of ascending hypothalamic axons. Axons originating from neurons in the far‐lateral hypothalamus reached cholinergic neurons in a zone that extended from the dorsal part of the sublenticular substantia innominata (SI) caudolaterally, to the lateral portion of the bed nucleus of the stria terminalis rostromedially, encompassing a narrow band along the ventral part of the globus pallidus and medial portion of the internal capsule. Axons originating from cells in the medial portion of the lateral hypothalamus reached cholinergic cells primarily in more medial and ventral parts of the SI, and in the magnocellular preoptic nucleus and horizontal limb of the diagonal band nucleus (HDB). Axons from medial hypothalamic cells appeared to contact cholinergic neurons primarily in the medial part of the HDB, and in the medial septum/vertical limb of the diagonal band complex. Electron microscopic double‐labeling experiments confirmed contacts between labeled terminals and cholinergic cells in the HDB and SI. Individual hypothalamic axons established synapses with both cholinergic and noncholinergic neuronal elements in the same regions. These findings have important implications for our understanding of the organization of afferents to the basal forebrain cholinergic projection system.
Topographic distribution of connections from the primary motor cortex to the corpus striatum in Aotus trivirgatus
Authors: Whitworth Richard H. , Ledoux's M. S. , Gould Harry J.
Published: January 2005

Connections between the primary motor cortex (MI) and the corpus striatum were studied in the owl monkey. Representations of specific body movements were elicited in MI by microstimulation techniques, and the efferent projections from these stimulation sites were labeled with wheat germ agglutinin‐horseradish peroxidase conjugate (WGA‐HRP).

Dense projections were found in the putamen ipsilateral to the injection site and sparser projections occupied comparable areas in the contralateral putamen. Representations of hindpaw regions projected to the dorsomedial portion of the putamen with only slight extensions across cell bridges into the caudate nucleus. Representations of the forepaw and head projected to progressively more ventrolateral zones of the dorsal two‐thirds of the putamen. Projections from injections of cortex representing discrete body movements terminated in an irregular or patchy distribution over a relatively large portion of the putamen. Extensive projections from relatively discrete injections in MI are indicative of a large degree of divergence and provide evidence for possible overlap from representations of relatively disparate body parts. The results are consistent with observations reported in other species of primates, but different from those seen in carnivores. This difference is discussed with regard to possible general features of corticostriate organization.
Direct observations of synapses between GABA‐immunoreactive boutons and identified spinocervical tract neurons in the cat's spinal cord
Authors: Maxwell D. J. , Christie W. M. , Short A. D. , Brown A. G.
Published: January 2005

Three spinocervical tract neurons in adult cats were physiologically characterized and intracellularly labelled with horseradish peroxidase. The neurons were reconstructed and examined with the light microscope and were prepared for postembedding immunochemical analysis by using an antiserum which specifically recognizes GABA in glutaraldehyde‐fixed tissue. Semithin sections were tested and examined with the light microscope. Somata, proximal, and distal dendrites of all three cells were associated with numerous punctate GABA‐immunoreactive structures. Immunoreactive perikarya of small neurons in the vicinity of spinocervical tract cells were also observed. Ultrastructural analysis, with the immunogold technique, revealed that somata and proximal dendrites of all three neurons received synaptic contacts (about 37% of total synapses) from GABA‐immunoreactive boutons and that distal dendrites were also associated with substantial numbers of immunoreactive structures (about 27% of synapses). Immunoreactive boutons were small (about 1 μm in diameter), contained irregularly shaped agranular vesicles, and formed symmetrical synaptic junctions with identified neurons. An additional group of immunoreactive boutons was observed to be associated with one of the cells only; these contained many large dense‐core vesicles in addition to small agranular vesicles. Boutons containing1 round agranular vesicles and flattened agranular vesicles were not observed to be immunoreactive.

The evidence supports the idea that much of the postsynaptic inhibition observed in spinocervical tract neurons is mediated by GABA and that even the most distal dendrites of these neurons receive inhibitory inputs.
Relationship of retinotopic ordering of axons in the optic pathway to the formation of visual maps in central targets
Authors: Simon David K. , O'Leary Dennis D. M.
Published: January 2005

We examined in rats the relationship between the ordering of retinal axons in the optic pathway and the formation of a retinotopically organized projection to their primary target, the contralateral superior colliculus (SC). We have previously found that axons labeled by focal injections of 1, 1′‐dioctadecyl 3, 3, 3, ′3′ ‐tetramethylindocarbocyanine perchlorate (DiI) made in temporal or nasal retina of perinatal rats commonly mistarget along the medial‐lateral and rostral‐caudal axes of the SC. By postnatal day (P) 11–12, the retinocollicular projection attains an adult‐like topography. Incorrectly targeted axons or axon segments are removed; axons that persist terminate in the topographically appropriate part of the SC (Simon and O'Leary: Dev Biol 137:125, 1990).

In the present study, we made similar DiI injections, covering less than 2% of the retinal area, in peripheral temporal, nasal, superior, or inferior retina, in rats of two age groups, embryonic day (E) 21 to P (postnatal day) 2 and P11‐P17. Whole mounts of retina, optic nerve and tract, and SC, and cross sections of the optic nerve, were examined. In E21‐P2 rats, retinal axons labeled from each retinal site are diffusely distributed in the SC, and poorly ordered in the optic pathway. In retina, labeled axons travel in fascicles directly from the injection site to the optic disc, but neighbor relationships begin to degrade as fascicles split and mix. Retinotopic order is virtually lost in the optic nerve; axons labeled from each injection site disperse throughout its cross‐sectional area, but the labeled axons tend to be concentrated toward a specific half of the nerve depending upon their retinal origin. This slight tendency toward retinotopic order increases in the optic tract, but axons are still poorly ordered as they leave the tract and enter the SC. Targeting errors along the medial‐lateral axis of the SC, but apparently not along its rostral‐caudal axis, are related to the positioning of axons across the width of the optic tract.

In P11–P17 rats, axons labeled from each injection site arborize only in a small, topographically correct part of the SC. However, the distributions of labeled retinal axons observed in whole mounts of the retina and optic pathway have a degree of disorder similar to those in E21‐P2 rats. Further, the scatter of labeled axons in optic nerve cross sections is comparable in both age groups. Therefore, the emergence of topographic order in the retinocollicular projection is not accompanied by an emergence of a retinotopic ordering of axons in the optic nerve. This indicates that axons positioned anywhere within the optic nerve are equally likely to establish a correctly positioned arbor, and survive the phase of map remodeling. Thus, a retinotopic organization of the rat optic nerve at perinatal ages is neither essential nor important for the subsequent development of topographic order in retinal projections.
Disruption of developmental timing in the albino rat retina
Authors: Webster Maree J. , Rowe Michael H.
Published: January 2005

We have examined the spatial and temporal gradients of two developmental processes in albino and pigmented rats: outer plexiform layer (OPL) development, and rate of eel production. The OPL first appears as a thin, discontinuous break in the cytoblast layer that is frequently interrupted by the profiles of migrating neuro‐ and glioblasts. In both strains, this occurs in an area temporal to the optic disc that corresponds to the eventual site of peak ganglion cell density, but is not located along the line of nasotemporal division. The OPL is first evident at P5 in pigmented animals, but its appearance in albino animals is delayed approximately 30 hours, and its development appears Lo follow a flatter spatial gradient than in pigmented animals. In pigmented animals OPL formation is complete over most of the retina by P10, but in albino animals at this age it is yet to be completely formed at any retinal location.

Reductions in mitotic activity are also first evident in temporal retina, but unlike OPL development, appear to follow the same temporal‐spatial gradient in both strains. Reductions in temporal retina are obvious by P4, and mitotic activity has ceased altogether in midtemporal retina by P6 and throughout most remaining retinal regions by P8. Thus, the initial reduction of mitotic activity precedes the onset of OPL formation in both strains, but OPL development lags behind the reduction of mitotic activity to a greater extent in albino than in pigmented animals.

Some aspects of differentiation within the inner nuclear layer (INL) were also examined. Just prior to the time of the onset of OPL formation, three distinct sublaminae are apparent in the INL. Cells in the innermost sublamina appear to be in an early stage of differentiation. Cells in the middle sublamina appear to be postmigratory, but have not yet begun to differentiate. Cells in the outermost sublamina have the appearance of migrating neuroblasts. At least some of these outer cells appear to migrate across the developing OPL to the outer nuclear layer, since the outermost sublamina becomes thinner and eventually disappears at the same time that the OPL becomes a continuous, uninterrupted plexiform layer. Cells of the middle sublamina apparently begin differentiation at about the time that this migration is complete. Although this sequence is the same in both albino and pigmented strains, its onset is delayed in albino animals by the same amount as the onset of OPL formation. In the INL, as well as in the ganglion cell layer, the process of cell death, as judged by the presence of pyknotic profiles, also appears to be delayed in albino animals.

These results illustrate that the temporal relationships between various developmental processes are not fixed, and are consistent with the idea that subtle changes in developmental timing can underlie the orderly evolution of complex neural systems.
Connectivity of glycine immunoreactive amacrine cells in the cat retina
Authors: Pourcho Roberta G. , Owczarzak Michael T.
Published: January 2005

The synaptic relationships of glycine immunoreactive amacrine cells in the cat retina were studied through the use of postembedding immunogold techniques. Glycine immunoreactive amacrine cells were found to synapse extensively with other amacrines and ganglion cells, particularly in strata 1–3 of the inner plexiform layer. This contrasts with GABA immunoreactive amacrine cells which provide major input to bipolar cells in strata 3–5. Glycine containing amacrine terminals exhibited diversity with respect to the morphology of their synaptic vesicles. The three types of terminals which could be distinguished were characterized by small pleomorphic (32–35 nm), medium‐sized flattened (38–45 nm), or larger rounded (48–55 nm) vesicles.

Comparison of retinal sections processed for glycine immunoreactivity with adjacent sections stained for GABA reactivity revealed a colocalization of glycine and GABA in 3% of the cells in the amacrine layer and approximately 40% of the cells in the ganglion cell layer, The amacrine terminals in which glycine and GABA were colocalized typically contained the small pleomorphic type of vesicles.
Pudendal motor and premotor neurons in the male rat: A WGA transneuronal study
Authors: Collins William F. , Erichsen Jonathan T. , Rose Robert D.
Published: January 2005

Anatomical studies using retrograde neuronal tracers were carried out to identify pudendal motoneurons and putative lumbosacral interneurons involved in the generation of penile reflexes in the adult male rat (Sprague‐Dawley). In agreement with previous studies, injection of the direct neuronal tracers, horseradish peroxidase or fluoro‐gold, into the left M. bulbospongiosus (dorsal division) resulted in direct retrograde labeling of motoneurons only in the ipsilateral dorsomedial (DM) nucleus. In contrast, similar injections of the transneuronal tracer, wheat germ agglutinin (WGA), resulted in direct retrograde labeling of ipsilateral DM motoneurons as well as transneuronal labeling of contralateral DM motoneurons and of bilaterally located putative spinal interneurons. The WGA‐labeling was determined to be transneuronal by a series of nerve cut experiments.

The direct retrograde WGA‐labeling of ipsilateral DM motoneurons and the transneuronal WGA‐labeling of contralateral DM motoneurons and bilateral putative spinal interneurons occurred with different time courses. Direct retrograde labeling of ipsilateral DM motoneurons was seen at 20 hours survival and persisted up to 7 days survival. The shortest survival period for detecting transneuronal labeling of contralateral DM motoneurons and putative interneurons was 2 days. Transneuronal WGA‐labeling of contralateral DM motoneurons was transient in that the intensity of label increased from 2 to 3 days survival but was markedly reduced at 7 days survival. At the same time, the number of WGA‐labeled putative interneurons increased with longer survival times up to 7 days.

WGA‐labeled putative interneurons were located primarily in regions receiving dendritic projections from WGA‐labeled DM motoneurons and, in particular, (1) the ventral gray matter between the DM and dorsolateral nuclei and (2) near the central canal and extending dorsally to the dorsal gray commissure. The rapid and extensive transneuronal transport between DM nuclei suggests that direct synaptic coupling may mediate coordinated, bilateral activation of DM motoneurons.
Two systems of branching axons in monkey's retina
Authors: Usai Cesare , Ratto Gian Michele , Bisti Silvia
Published: January 2005

Several monkey retinae were stained, by using the reduced silver technique, in order to analyse long‐distance intraretinal connections. Long, bifurcating processes covering very large areas were identified. Morphological investigation of these processes suggests that they are members of two different systems of branching axons.

The first population of these processes originates as axon collaterals from cells in the ganglion cell layer. These cells have a relatively large, elongated soma and straight, sparsely branching dendrites, stratified in the vitreal half of the inner plexiform layer. The main axon (0.6 μm average diameter) passes along the optic fibre bundles, disappearing into the optic disk, whilst its collaterals run mainly in the inner plexiform layer. A cell showing similar morphology has also been found in the ganglion cell layer of a cat retina.

The second population of processes consists of very thick fibres (2.1 μm average diameter) apparently originating from the optic disk. The main branches run in the space between the optic fibre layer and the ganglion cell layer, with short, secondary processes crossing the ganglion cell layer orthogonally. Many higher‐order processes originate from the second‐order branches; these run almost horizontally in the inner plexiform layer.

The ganglion cells generating axon collaterals may constitute an intraretinal firing synchronization system, or they may be a residual feature of retinal development. The centrifugal fibres may be related to the sensitivity control during retinal dark adaptation.
Phrenic motoneuron morphology in the neonatal rat
Authors: Lindsay Amy D. , Greer John J. , Feldman Jack L.
Published: January 2005

The morphology of neonatal rat phrenic motoneurons was studied following retrograde labeling with horseradish peroxidase, which resulted in Golgi‐like fills of phrenic motoneuron somata and dendrites. At birth, these neurons have well‐developed dendritic trees with many characteristics described for phrenic motoneurons in the adult rat. The dendrites form tightly fasciculated bundles that emerge from the phrenic nucleus primarily along four axes: ventromedial, ventrolateral, dorsolateral, and rostral/caudal, with smaller and more variable projections directly lateral and ventral. Although sparse, some dendritic appendages were also present, and in a few animals, somata clustering was apparent. The most significant difference between adult and neonatal rat phrenic motoneurons is in the extent to which medially and laterally projecting dendrites extend beyond the borders of the ipsilateral gray matter. In the neonate, unlike the adult, these dendrites project extensively past the gray/white border to the edge of the hemicord. Ventromedial dendrites occasionally cross to the contralateral ventral horn in the ventral white commissure and laterally projecting dendrites could be seen reaching the edge of the cord, turning and traveling rostrally or caudally for up to 100 μm. Phrenic motoneurons are not unique in having long dendrites at birth. A brief comparative study showed that neonatal cervical, thoracic, and lumbar motoneurons also have long dendrites that project to the medial and lateral borders of the hemicord.
From embryo to adult: Anatomy and development of a leg sensory organ in Phormia regina, Meigen (Insecta: Diptera). II. Development and persistence of sensory neurons
Authors: Lakes‐Harlan R. , Pollack G. S. , Merritt D. J.
Published: January 2005

The imaginal leg disc of Phormia regina contains eight neurons that arise during embryogenesis. Five of the neurons are associated with Keilin's organ, and of these five, two persist to the adult fly. Two new neurons arise at about the time of pupariation and flank each of these persisting neurons, forming two triplets of cells. Both triplets can be followed throughout metamorphosis; in the late pupa they are situated anteriorly and posteriorly at the tip of the fifth tarsomere. Two triplets of cuticular specializations are found at corresponding positions in the adult fly, each consisting of two campaniform sensilla and a trichoid hair. The central member of each set of sensilla, a campaniform sensillum, is associated with the persisting cell.
Organization of nucleoli and nuclear bodies in osmotically stimulated supraoptic neurons of the rat
Authors: Lafarga M. , Andres M. A. , Berciano M. T. , Maquiera E.
Published: January 2005

This study has analyzed variations in the number of nucleoli and nuclear bodies, as well as in their ultrastructural and cytochemical organization, after the osmotically induced activation of supraoptic nucleus (SON) neurons of the rat. The number of nucleoli and nuclear bodies and also the nucleolar size were determined on smear preparations of previously block‐impregnated SON. The mean number of nucleoli per cell was 1.35 ± 0.6 (mean ± SDM) in control rats. No significant variations in this value were registered either in dehydrated or rehydrated rats. The mean nucleolar volume and the total nucleolar volume per cell showed a significant increase in dehydrated rats with respect to the controls, whereas these two parameters tended to return to control values in rats rehydrated after dehydration. The mean number of nuclear bodies per cell increased significantly from 0.56 ± 0.50 (mean ± SDM) in control rats to 1.54 ± 1.1 after 6 days of dehydration. By electron microscopy, SON neurons displayed a reticulated nucleolar configuration. After the osmotically induced neuronal activation, there was an increase in the proportion of the total nucleolar area occupied by the granular component, and also a reduction in the mean fibrillar‐center area. The most characteristic nucleolar features in rehydrated rats were the tendency for the granular component to be segregated and the occurrence of intranucleolar vacuoles. Ultrastructural cytochemistry with a specific silver method revealed a selective silver reaction on the coiled threads of the nuclear bodies—identified as “coiled bodies”—and on the nucleolar fibrillar components in all animal groups studied. Since nucleoli play a major role in ribosome biogenesis, a relationship between these nucleolar changes and the level of cellular activity of SON neurons is proposed. Furthermore, the response of nuclear “coiled bodies” to neuronal activation suggests their participation in the processing and transport of rRNA precursors.
Distribution of neuropeptide Y (NPY) in the cerebral cortex of the lizards Psammodromus algirus and Podarcis hispanica: Co‐localization of NPY, somatostatin, and GABA
Authors: Dávila Joseé Carlos , de la Calle Adelaida , Gutiérrez Antonia , Megías Manuel , Andreu Manuel José , Guirado Salvador
Published: January 2005

The aim of the present study was to analyze the distribution and characteristics of NPY immunoreactive structures in the cerebral cortex of lizards and to investigate the degree of co‐existence of this neuropeptide with somatostatin and GABA. The immunoperoxidase method was applied to vibratome sections as well as to semithin sections.

NPY neurons are multipolar or fusiform and were unevenly distributed throughout the brain cortex. Within the medial, dorsomedial and dorsal cortices, most NPY perikarya were located in the plexiform layers, especially in the deep one. This suggests that these cells could be regarded as interneurons. In the lateral cortex, NPY neurons were found throughout all layers. The dorsomedial cortex displayed the highest NPY cell density. Here, neuronal perikarya projected many immunoreactive processes toward two distinct zones: the deep plexiform layer of the medial cortex and the superpositio medialis. The NPY neurons of the dorsomedial cortex differed from the other NPY cortical immunoreactive cells in that the latter displayed very few immunoreactive processes.

A high degree of co‐existence among NPY, somatostatin, and GABA (approx. 80%) was found. This co‐existence rate is very similar to that reported in mammals and suggests that co‐localization is a phylogenetically ancient phenomenon.
Postnatal development of thalamic recipient neurons in the monkey striate cortex: Comparison of spine acquisition and dendritic growth of layer 4C alpha and beta spiny stellate neurons
Authors: Lund Jennifer S. , Holbach Suzanne M.
Published: January 2005

A quantitative study has been made from Golgi impregnations of the maturation of dendrites and their spines on spiny stellate neurons in the macaque monkey primary visual cortex. The neurons studied lay within either the alpha or the beta division of lamina 4C; previous workers have shown the alpha division neurons to be contacted by thalamic axon terminals arising from the magnocellular division of the lateral geniculate nucleus (LGN) of the thalamus and the beta division neurons to be contacted by parvocellular LGN inputs. Most thalamic terminals and perhaps the majority of other, type 1 (Colonnier, '81), presumed excitatory, inputs to these cells make synaptic contacts on the tips of their dendritic spines. Measurement was made of relative changes in the total number of spines on these alpha and beta spiny neurons over age by measuring both spine density along the dendrites and dendritic arbor size in single 90‐m̈m sections from Golgi rapid preparations. Our previous work (Lund et al., '77; Boothe et al., '79) showed a marked proliferation and attrition of spines and dendritic branches to occur in the early postnatal weeks; Rakic et al. ('86) have since proposed that there is a cortexwide synchrony of synapse acquisition and loss during this same period. However, different visual capacities channelled via the magnocellular and parvicellular geniculate relays show different maturational rates (Harwerth et al., '86). This study indicates that the anatomical maturation of spines on the alpha and beta neurons is not temporally coincident from birth to 30 weeks. During this period, phases of spine acquisition and loss on alpha neurons precedes similar phases on beta neurons. The alpha neurons carry a peak spine population at 5–8 weeks postnatal, whereas the beta neurons carry their peak spine populations between 8 and 24 weeks postnatal.

At all ages prior to 30 weeks, the two sets of neurons carry quite different total spine populations. Close to 30 weeks of age, the total spine coverage has fallen on both sets of neurons and becomes identical between the alpha and beta neurons. In animals aged 30 weeks to adult, spine coverage per neuron is maintained at a common figure for the alpha and beta neurons despite further growth and disparate dendritic arbor sizes and different local spine densities in the two groups; this suggests that some common sampling paradigm between pre‐ and postsynaptic elements is adopted by the alpha and beta neurons and also suggests the development of a close functional correlation between the two sets of neurons.