bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid changes in ultrastructure during deafferentation‐induced dendritic atrophy
Authors: Deitch Jeffrey S. , Rubel Edwin W
Published: January 2005

This study describes qualitative and quantitative changes in dendritic ultrastructure during the rapid atrophy of nucleus laminaris (NL) dendrites following deafferentation. The dendrites of n. laminaris neurons in the chick auditory system are segregated into dorsal and ventral dendritic tufts, which receive spatially separated innervation from the ipsilateral and contralateral nucleus magnocellularis, respectively. We have previously shown that removing the input to the ventral side of NL results in the rapid atrophy of the ventral dendrites, whereas the nondeafferented dorsal dendrites of the same cells do not change in length.

The ultrastructure of NL was examined in normal animals and after deafferentation. Changes in dendritic ultrastructure were not qualitatively apparent 4 hours after deafferentation. Between 12 and 48 hours the cytoplasm of the ventral dendrites became progressively more lucent, and a gap formed in the transition between the soma and ventral dendritic cytoplasm. Many of the dendrite tips, however, appeared normal even 2 days after deafferentation. Degeneration of dendrite plasma membrane was not visible until 2 days after deafferentation. On the other hand, quantitative measurements revealed a 30% decrease in microtubule density in the initial portion of the ventral dendrite by 4 hours, and a 50–60% decrease from 12 to 48 hours after deafferentation. Neurofilament density in the initial ventral dendrites decreased 50% by 12 hours, and 70% by 2 days after deafferentation. Many of the terminals of the severed afferents remained attached to the atrophying dendrite until 2 days after surgery, when they were in advanced stages of degeneration. Glia apparently were not involved in dendrite loss.

The implications of these results on the role of cytoskeleton in the production and maintenance of dendritic shape are discussed.
Neurogenesis of glutamic acid decarboxylase immunoreactive cells in the hippocampus of the mouse. II: Area dentata
Authors: Soriano Eduardo , Cobas Alberto , Fairén Alfonso
Published: January 2005

The temporal patterns of neurogenesis of cells showing glutamic acid decarboxylase (GAD) immunoreactivity were determined in the area dentata of the mouse. Pregnant C57Bl mice received pulse injections of (3H)thymidine from E11 through E17 (E0 being the day of mating). The distribution of (3H)thymidine‐labeled, GAD‐positive neurons in the hilus and in the different strata of the fascia dentata (stratum infragranulosum, stratum granulosum, stratum moleculare) were recorded in adult animals. A radial gradient of neurogenesis of GAD‐positive cells in the area dentata was not apparent. In the transverse axis, neurogenesis of GAD‐positive cells seemed to follow a faint suprapyramidal to infrapyramidal gradient, which was due to differential timing of neurogenesis of GAD‐positive cells destined for the stratum infragranulosum of the suprapyramidal and infrapyramidal blades of the fascia dentata. GABAergic neurons in the fascia dentata comprise a limited number of welldefined cell types. All of the differet morphologic types of GAD‐positive neurons present in the area dentata were generated prenatally. These diverse forms did not have specific times of neurogenesis. These results support the concept that the adult morphology of GAD‐positive cells in the area dentata of the mouse do not bear any relationship to their times of origin.
Diagonal band projection towards the hypothalamic supraoptic nucleus: Light and electron microscopic observations in the rat
Authors: Jhamandas J. H. , Raby W. , Rogers J. , Buijs R. M. , Renaud L. P.
Published: January 2005

Supraoptic nucleus (SON) neurons receive a prominent gamma‐aminobutyric acid (GABA) input. This study evaluated the hypothesis, partly on the basis of recent electrophysiological data, that this innervation might arise from GABAergic neurons located in the ventral diagonal band of Broca area. For retrograde transport studies, pentobarbital‐anesthetized male Long‐Evans rats received 0.03–0.20‐μl injections of a suspension of rhodamine tagged latex microspheres into the SON. In two cases where such injections were confined to the SON, less than 60 retrogradely labeled neurons were detected in the ipsilateral diagonal band. In three animals where injections extended into the perinuclear zone around the SON, more than 2,000 retrogradely labeled cells were counted in the ipsilateral diagonal band. For anterograde transport studies, another group of animals received either 30% horseradish peroxidase (HRP) in 0.5% poly‐L‐ornithine (0.05–0.10 μl injections) or Phaseolus vulgarus (iontophoresed from a 2% solution) into the diagonal band. After survivals of 18–24 hours (HRP) or 5 days (PHAL‐L) labeled axon terminals invested the perinuclear zone above the SON. The presence of just a single fiber within the nucleus indicated a minor projection to the SON itself. The HRP‐injected material was processed for ultrastructural examination and revealed dense HRP‐labeled axon terminals in this perinuclear zone, most often (98%) forming axodendritic appositions. A postembedding colloidal gold technique to visualize GABA‐synthesizing terminals revealed that fewer than 5% of these perinuclear HRP‐labeled terminals also exhibited GABA‐like immunoreactivity. Within the SON, where GABAergic axon terminals are abundant, few (≤5%) GABAergic terminals contained HRP. Therefore, only a minor component of this prominent GABAergic innervation of SON neurons appears to arise from GABAergic diagonal band neurons. It is proposed that interneurons in the perinuclear zone serve as a relay station for information transfer from the ventral diagonal band to the SON.
Monoclonal antibody to neurofilament protein (SMI‐32) labels a subpopulation of pyramidal neurons in the human and monkey neocortex
Authors: Campbell Michael J. , Morrison John H.
Published: January 2005

A monoclonal antibody that recognizes a nonphosphorylated epitope on the 168 kDa and 200 kDa subunits of neurofilament proteins has been used in an immunohistochemical study of cynomolgus monkey (Macaca fascicularis) and human neocortex. This antibody, SMI‐32, primarily labels the cell body and dendrites of a subset of pyramidal neurons in both species. A greater proportion of neocortical pyramidal neurons were SMI‐32 immunoreactive (ir) in the human than in the monkey. SMI‐32‐ir neurons exhibited consistent differences in the intensity of their immunoreactivity that correlated with cell size. The cellular specificity of SMI‐32 immunoreactivity suggests that a subpopulation of neurons can be distinguished on the basis of differences in the molecular characteristics of basic cytoskeletal elements such as neurofilament proteins.

The size, density, and laminar distribution of SMI‐32‐ir neurons differed substantially across neocortical areas within each species and between species. Differences across cortical areas were particularly striking in the monkey. For example, the anterior parainsular cortex had a substantial population of large SMI‐32‐ir neurons in layer V and a near absence of any immunoreactive neurons in the supragranular layers. This contrasted with the cortical area located more laterally on the superior temporal gyrus, where layers III and V contained substantial populations of large SMI‐32‐ir neurons. Both areas differed significantly from the posterior inferior temporal gyrus, which was distinguished by a bimodal distribution of large SMI‐32‐ir neurons in layer III. Differences across human areas were less obvious because of the increase in the number of SMI‐32‐ir neurons. Perhaps the most notable differences across human areas resulted from shifts in the density of the larger SMI‐32‐ir neurons in deep layer III. A comparison between the species revealed that isocortical areas exhibited greater differences in their representation of SMI‐32‐ir neurons than primary sensory or transitional cortical areas. A comparison of distribution patterns of SMI‐32‐ir neurons across monkey cortical areas and data available on the laminar organization of cortical efferent neurons suggests that a common anatomic characteristic of this chemically identified subpopulation of neurons is that they have a distant axonal projection. Such correlations of cell biological characteristics with specific elements of cortical circuitry will further our understanding of the molecular and cellular properties that are critically linked to a given neuron's role in cortical structure and function.
Distribution of calcitonin gene‐related peptide‐like immunoreactivity in the nucleus ambiguus of the cat
Authors: McWilliam P. N. , Maqbool A. , Batten T. F. C.
Published: January 2005

The distribution of calcitonin gene‐related peptide (CGRP) in the cat nucleus ambiguus was examined by means of a combination of horseradish peroxidase (HRP) tracing and immunohistochemical techniques. Vagal motoneurones in the nucleus ambiguus were identified by applying HRP to either the thoracic vagus or the superior laryngeal nerve or the cervical vagus.

Motoneurones in the nucleus ambiguus labelled with HRP from the thoracic vagus did not contain CGRP‐like immunoreactivity although CGRP‐like immunoreactive cells were present in this nucleus on the same sections. In contrast, a large proportion of the motoneurones labelled from the superior laryngeal nerve and a smaller proportion of cells labelled from the cervical vagus did contain CGRP‐like immunoreactivity.

It is concluded that CGRP‐like immunoreactivity is absent from vagal preganglionic motoneurones projecting to structures in the thorax and abdomen but is present in vagal motoneurones projecting to striated muscle of the larynx and pharynx.
Organization of the projection from the superficial to the deep layers of the hamster's superior colliculus as demonstrated by the anterograde transport of Phaseolus vulgaris leucoagglutinin
Authors: Rhoades Robert W. , Mooney Richard D. , Rohrer William H. , Nikoletseas Michael M. , Fish Steven E.
Published: January 2005

Anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA‐L) was employed to describe the projection from the superficial to the deep layers of the hamster's superior colliculus (SC). Deposits of PHA‐L in the stratum griseum superficiale (SGS) resulted in labelled terminal swellings in the stratum opticum and all of the deep laminae (the stratum griseum intermediate [SGI], stratum album intermedium [SAI], stratum griseum profundum [SGP], and stratum album profundum [SAP]). Labelled terminals were also visible in the periaqueductal gray (PAG). Reconstructions of individual axons showed that many collaterals in the deep laminae arose from axons that projected to targets outside the colliculus.

The projection from the superficial to the deep laminae had a loose topographic organization, and the trajectories of interlaminar axons were generally deflected laterally from “projection” lines that were orthogonal to the SC surface. Physiological recording and receptive field mapping were used to determine actual projection lines, which connect neurons in the superficial and deep layers that have receptive fields with the same elevation. These projection lines closely matched the trajectory of the pathway from the superficial to the deep laminae.
ON/OFF organization in the cat lateral geniculate nucleus: Sublaminae vs. columns
Authors: Bowling D. B. , Caverhill J. I.
Published: January 2005

The hypothesis was tested that ON and OFF cells in the A layers of the cat's lateral geniculate nucleus (l.g.n.) form separate ON and OFF columns, and new evidence for their sublaminar distributions is presented. Evidence for columns was sought in previously published results from 184 electrode tracks oriented parallel to the layers and in new experiments, based on multiple, closely spaced electrode tracks oriented vertically to the layers. The tracks parallel to the layers were analyzed in two ways. First, the distances between cells of like‐sign and unlike‐sign were measured. Second, the signs of response of cells above and below one another, from pairs of tracks made simultaneously in the same layer, were compared. The analyses, which included computer simulations of the experiments based on columnar and noncolumnar models, provided no evidence for columns. The results from the closely spaced, vertical tracks also failed to show columns but confirmed that the organization of ON and OFF cells in the layers is fundamentally sublaminar.
Vasopressin‐ and proctolin‐like immunoreactive efferent neurons in blowfly abdominal ganglia: Development and ultrastructure
Authors: Nässel Dick R. , Holmqvist Bo I. , Movérus Börje J. A.
Published: January 2005

In the neural sheath of the fused thoracicoabdominal ganglia of the blowfly Calliphora erythrocephala, extensive neurohaemal areas can be seen in the electron microscope. A separate set of neurohaemal areas located in the sheath of the lateral abdominal nerve roots contain neural terminals of at least three morphological types. To determine which bioactive substances are stored and possibly released from the neurons supplying these neurohaemal areas, we applied a large number of antisera raised against different neuropeptides of invertebrate and mammalian type. Antisera to two types of neuropeptides react with neurons innervating the sheath of the abdominal nerve roots: antisera to lysine‐vasopressin and proctolin. There are only 14–24 vasopressin‐like immunoreactive (VPLI) neurons in the entire nervous system of Calliphora. These are all restricted to a bilateral cluster in the fused abdominal ganglia. From this cluster, the neurohaemal areas in abdominal nerve roots are supplied. Proctolin‐like immunoreactivity (PLI) can be seen in a large number of neurons in the nervous system of blowflies. The supply of PLI terminals to the abdominal nerve roots is from 12 to 14 neurons in a bilateral cluster of abdominal PLI neurons. It is clear from light‐ and electron‐microscopic immunocytochemistry that the two antisera label two separate populations of neurons that form overlapping terminals in the neural sheath. The immunoreactive terminals are located just below the permeable acellular basal lamina of the neural sheath. Hence, it is likely that at least two different bioactive peptides can be released neurohormonally into the circulation. An additional set of four efferent PLI neurons send axons into the medial abdominal nerve. These do not form neurohaemal terminals in the nerve root, but may innervate the hindgut.

Also in the larval nervous system, VPLI and PLI neurons can be recognized. In the larva, the peptide‐containing neurons are segmentally arranged. The 14 larval VPLI neurons supply segmental abdominal nerves with axons that run inside the nerves to their targets. During metamorphosis, the segmental nerves fuse and the VPLI axons invade the neural sheath where they arborize and form varicose terminals. About the same number of PLI neurons could be detected in the abdominal ganglia of larval and adult flies. Only for a set of four caudal PLI neurons could efferent axons be traced in the larva. These axons run inside the medial abdominal nerves. The same four PLI neurons, with the same axonal projections, can be recognized in the adults.
Convergence and divergence in the afferent projections to cat area 17
Authors: Salin P. A. , Bullier J. , Kennedy H.
Published: January 2005

We have examined the topography of the afferent connections to area 17 in the cat by means of double retrograde label tracing techniques. Injections of two fluorescent retrograde tracers, diamidino yellow and fast blue, were made with variable separations in area 17 and the spatial distributions of the resulting populations of labeled cells examined in afferent cortical areas and subcortical structures.

When injections were separated rostrocaudally, the topographic organizations of the projections were characterized quantitatively with two graphic methods: the labeling density curve and the connectivity graph. The labeling density curve measures labeled neuron density in successive rostrocaudal sections, whereas the connectivity graph provides a two‐dimensional model of the topography of a given connectivity. The connectivity graph makes it possible to define two parameters that characterize the topography of the connection: the convergence and the divergence. The convergence is defined as the extent of an afferent structure that contains neurons converging on a line normal to the cortical surface in area 17. The divergence is the extent of area 17 that is innervated by neurons contained in an infinitely small region of the afferent structure.

The results show that a number of subcortical structures project to area 17 in a nontopographic manner, i.e., that in each of these structures neurons contained in an infinitely small region send projections to the whole of area 17 and that a line normal to the surface of area 17 is innervated by neurons distributed throughout the afferent structure in question. Nontopographic projections are found from the intralaminar nuclei, the ventral mesencephalic tegmental region, the diagonal band of Broca, and the locus coeruleus.

All remaining subcortical structures and cortical areas send topographically organized projections to area 17. The extent of the convergence and divergence, however, varies between structures. Only the projection from the A laminae of the LGN was found to approximate a point‐to‐point projection with a convergence of 0.4 mm and 2 mm in divergence. Much larger convergence and divergence values are found in the projections from the claustrum and the cortical areas. For example, the divergence reaches 20 mm for the projections from area 20 or from the anterior part of the lateral suprasylvian sulcus.

Knowing the convergence and divergence values and the retinotopic organizations of area 17 and a number of its afferents, it becomes possible to test whether connections in the visual system link regions representing the same zone of the visual field. This is the case for the geniculostriate projection only and does not apply for any of the other topographically organized afferents to area 17. For example, the region of area 18 containing neurons projecting to a line normal to the surface of area 17 represents 15 degrees of visual angle, whereas the neurons empaled by this line in area 17 represent only 5 degrees of visual angle.
Neuronal overload in the developing anuran lateral motor column in response to limb removal and thyroid hormone
Authors: Goldberg Joseph F. , Pollack Emanuel D.
Published: January 2005

The lateral motor column (LMC) in the anuran spinal cord normally undergoes a dramatic reduction in motor neuron number during development. At least two factors influence this process: the limb target which is required for the progression of cell loss, and thyroid hormone, a requisite for metamorphosis. This study has examined the relative and combined effects of limb amputation and exogenous thyroxine, initiated at the onset of normal rapid cell loss in Rana pipiens tadpoles, in regulating neuron number in the lumbosacral LMC.

Thyroxine treatment or unilateral limb amputation temporarily resulted in significantly more LMC neurons than in untreated controls. Extraordinary numbers of motor neurons persisted through metamorphic climax when both treatments were combined. Population sizes frequently exceeded the maximum number of neurons observed prior to the onset of natural cell loss. Moreover, thyroxine‐treated tadpoles contained increased numbers of mitotic figures in the ventricular zone of the spinal cord and significantly more newly generated cells in the LMC, as revealed by 3H‐thymidine autoradiography.

These findings suggest that thyroxine‐potentiated mitogenesis promotes greater numbers of new motor neurons to the LMC while, simultaneously, target removal delays the loss of extant cells. It is proposed that this interaction effectively maintains an immature state in the LMC so that neuronal “decisions” for survival and the consequent loss of target‐deprived neurons are postponed far longer than previously reported.
HRP study of the central components of the trigeminal nerve in the larval sea lamprey: Organization and homology of the primary medullary and spinal nucleus of the trigeminus
Authors: Anadón Ramón , De Miguel Encarnacion , Gonzalez‐Fuentes M. Jose , Rodicio Celina
Published: January 2005

The medullary and spinal connections of the trigeminal nerve of larval sea lampreys Petromyzon marinus were studied by anterograde and retrograde HRP transport after application into the orbit. Three components were found, all of them ipsilateral: (1) The motor nucleus was undivided in the larva, and its neurons possessed a rich dendritic tree. The single motor root was well separated from the sensory root. (2) The descending root was laterally located, and its fibers ran compactly to spinal levels. (3) Most medullary and many rostral spinal dorsal cells were labeled. Dorsal cells, which were mostly multipolar, had numerous mutual contacts. Some dorsal cell processes contacted the fourth ventricle. The name “primary medullary and spinal nucleus of the trigeminal nerve” (PMSV) is proposed for these dorsal cells. Medullary dorsal cells were not labeled by applying HRP at the level of spinal nerves, but application to the vagus nerve did label some. The possible relationship of this nucleus with the mesencephalic trigeminal nucleus of jawed vertebrates is discussed.
Nerve growth factor receptor and choline acetyltransferase colocalization in neurons within the rat forebrain: Response to fimbria‐fornix transection
Authors: Batchelor Peter E. , Armstrong David M. , Blaker Scott N. , Gage Fred H.
Published: January 2005

Although it is well known that magnocellular cholinergic basal forebrain neurons are trophically responsive to nerve growth factor (NGF) and contain NGF receptors (NGFr), the exact distribution of forebrain NGFr‐immunoreactive neurons and the degree to which cholinergic neurons are colocalized with them have remained in question. In this study we employed a very sensitive double‐labelling method and examined in the same tissue section the distribution and cellular features of NGFr‐positive and choline acetyltransferase (ChAT)‐immunolabelled neurons within the rat basal forebrain. Throughout this region the majority of magnocellular basal forebrain neurons were immunoreactive for both NGFr and ChAT. However, a small percentage of neurons in the ventral portion of the vertical limb of the diagonal band of Broca were immunoreactive only for NGFr, whereas a larger population of magnocellular neurons in the substantia innominata exhibited only ChAT immunoreactivity. No NGFr‐immunoreactive cells were found associated with ChAT‐positive neurons in the striatum, neocortex, or hippocampus, and no single‐labelled NGFr‐immunoreactive neurons were found outside the basal forebrain area, except for a large number of positive‐labelled cells along the ventricular walls of the third ventricle.

In addition to its function in maintaining the normal integrity of the basal forebrain and cholinergic, peripheral sympathetic, and neural‐crest‐derived sensory neurons, NGF may also have a role in the growth of these neurons after damage to the nervous system. To examine this postulate the hippocampus was denervated of its septal input and examined 8 weeks later. Two populations of neurons were found to have undergone collateral sprouting—namely, the midline magnocellular cholinergic neurons of the dorsal hippocampus and the sympathetic noradrenergic neurons of the superior cervical ganglion. Both of these neuronal populations also stained strongly for NGFr. In contrast, the small intrinsic cholinergic neurons of the hippocampus exhibited neither sprouting response nor staining for NGFr. In view of these results, we suggest that the differing sprouting responses demonstrated by these three neuronal populations may be due to their responsiveness to NGF, as indicated by the presence or absence of NGF receptors.
Morphology of afferent synapses in the mauthner cell of larval Xenopus laevis
Authors: Cioni Carla , De Palma Francesca , Stefanelli Alberto
Published: January 2005

The fine structure of the afferent synapses on the Mauthner cell of larval Xenopus laevis has been studied as a first step toward comparing the fine structure of the afferent synaptic apparatus before and after metamorphosis. There are various types of afferent endings on this cell, some of which are confined to specific cellular regions, while others are distributed over most of the large surface of the neuron. Four different main types of endings have been observed: club endings, round‐vesicle end bulbs, flattened‐vesicle end bulbs and spiral fibers endings. While the myelinated club endings and the spiral fibers endings are located at the distal end of the lateral dendrite and in the axon cap, respectively, the end bulbs are widely distributed over the whole cell. A further type of ending has been observed, although rarely, on the Mauthner cell soma and dendrites: end bulbs characterized by an unusually dense presynaptic substance. Results obtained in the present research suggest that, as in fish, different endings on the anuran Mauthner neuron correspond to different synaptic inputs. The possible origin of some of these inputs is discussed.
Recovery from cortical blindness mediated by destruction of nontectotectal fibers in the commissure of the superior colliculus in the cat
Authors: Wallace Steven F. , Rosenquist Alan C. , Sprague James M.
Published: January 2005

Transection of the commissure of the superior colliculus restores visual orientation behavior to a cat previously rendered hemianopic by a unilateral visual cortical lesion (the Sprague effect). Using two methods, we asked whether this recovery resulted from the severing of the tectotectal component of the commissure or whether the destruction of some other connection was responsible. First, we transected either the rostral or the caudal one‐half of the tectal commissure in hemianopic cats. If destruction of tectotectal fibers is responsible for the Sprague effect, then only rostral transections should produce the recovery since nearly all tectotectal connections lie in the rostral one‐half of the commissure. However, rostral cuts failed to produce a recovery, whereas caudal commisurotomies did. Second, ibotenic acid was used to destroy the cells in the superior colliculus contralateral to the cortical lesion. This lesion eliminated the contralateral tectotectal pathway from the contralateral colliculus but left other fibers (originating elsewhere but coursing through the commissure) largely intact. These ibotenic acid lesions failed to produce the recovery; but when the caudal portion of the tectal commissure was subsequently transected in the same animals, the recovery was observed. The results of both experiments support the conclusion that the transection of a nontectotectal component of the commissure of the superior colliculus is responsible for the recovery of visual orientation behavior in a cortically blind cat.
Development of GABA immunoreactivity in brainstem auditory nuclei of the chick: Ontogeny of gradients in terminal staining
Authors: Code Rebecca A. , Burd Gail D. , Rubel Edwin W
Published: January 2005

The development of gamma‐aminobutyric acid‐immunoreactivity (GABA‐I) in nucleus magnocellularis (NM) and nucleus laminaris (NL) of the chick was studied by using an antiserum to GABA. In posthatch chicks, GABA‐I is localized to small, round punctate structures in the neuropil and surrounding nerve cell bodies. Electron microscopic immunocytochemistry demonstrates that these puncta make synaptic contact with neuronal cell bodies in NM; thus, they are believed to be axon terminals. GABAergic terminals are distributed in a gradient of increasing density from the rostromedial to the caudolateral regions of NM.

The distribution of GABA‐I was studied during embryonic development. At embryonic days (E) 9‐11, there is little GABA‐I staining in either NM or NL. Around E12‐14, a few fibers are immunopositive but no gradient is seen. More GABA‐I structures are present at E14‐15. They are reminiscent of axons with varicosities along their length, preterminal axonal thickenings and fiber plexuses. At E15, terminals become apparent circumscribing neuronal somata and are also discernible in the neuropil of both nuclei. In E16‐17 embryos, terminals are the predominantly labeled GABA‐I structures and they are uniformly distributed throughout NM. The density of GABAergic terminals increases in caudolateral regions of NM such that by E17‐19, there is a gradient of increasing density of GABA‐I terminals from the rostromedial to caudolateral regions of NM. The steepness of this gradient increases during development and is the greatest in posthatch (P) chicks.

Cell bodies labeled with the GABA antiserum are located around the borders of both NM and NL and in the neuropil between these two nuclei. Occasionally, GABA‐I neurons can be found within these auditory brainstem nuclei in both embryonic and posthatch chicks. Nucleus angularis (NA) contains some GABAergic cells.

The appearance of GABA‐I terminals around E15 is correlated in time with the formation of end‐bulbs of Held on NM neurons. Thus, the ontogeny of presumed inhibitory inputs to chick auditory brainstem nuclei temporally correlates with, and could modulate the development of, excitatory auditory afferent structure and function.
Organization of astrocytes in the visual pathways of the goldfish: An immunohistochemical study
Authors: Levine R. L.
Published: January 2005

We have used antisera directed against glial cytoskeletal proteins to examine the distribution and organization of astrocytes in the visual pathways of the goldfish. We describe two different types of cells, which may be distinguished by their unique cytoskeletal proteins. Antibodies raised against a 48 Kd optic nerve protein react with stellate astrocytes in the optic nerve but virtually no glial cells in the brain (although blood vessels and the meninges in the brain were stained). The optic nerve astrocytes form a dense meshwork of processes through which the optic fibers pass. The intraorbital and intracranial segments of the nerve are divided into fascicles, each bounded by a glia limitans, which extend across the optic chiasm. Astroglial cells in the brain bind antibodies raised against a 50 Kd brain cytoskeletal protein. These antibodies show a very limited cross‐reactivity with optic nerve cells. Brain astrocytes have filiform profiles and most appear to be deployed as radial glia. The glial fabric of the brain, as revealed by these antibodies, is far more loosely woven than that of the optic nerve. There is a sharp boundary between the two types of glial cells, immediately behind the optic chiasm. Glial processes in the optic tracts arise from cells in the preoptic area, whereas those in the optic tectum arise from cells that reside locally. In the optic tract, a glia limitans was often difficult to discern, whereas in the tectum one was always evident and composed of endfeet at the pial extremities of radial glial processes.

These findings are discussed both in the context of previous observations by other workers as well as with regard to their possible functional implications.
Time course of expression of neuropeptide Y, calcitonin gene‐related peptide, and NADPH diaphorase activity in neurons of the developing murine bowel and the appearance of 5‐hydroxytryptamine in mucosal enterochromaffin cells
Authors: Branchek Theresa A. , Gershon Michael D.
Published: January 2005

Serotoninergic and cholinergic neurons are known to appear earlier in the ontogeny (day E12) of the murine gut than those containing substance P or vasoactive intestinal peptide (day E14). It has also been demonstrated that proliferating neural precursors coexist with mature neurons in developing enteric ganglia. These observations have led to the hypotheses that peptidergic neurons develop later than those that utilize small molecule neurotransmitters and that the activity of early developing neurons may affect the phenotypic expression of coexisting neuroblasts. As a partial test of these hypotheses we studied the phenotypic expression of neurons recognized by antisera to neuropeptide Y (NPY) and calcitonin gene‐related peptide (CGRP), and of those visualized by the histochemical demonstration of reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity. NADPH diaphorase activity, which is coexpressed with NPY immunoreactivity in all submucosal and many myenteric neurons, was first found on day E11 in clusters of cells in the dorsal mesogastrium. These cells also expressed neurofilament reactivity and thus were developing along a neuronal lineage. Enteric neurons that expressed NADPH diaphorase activity were visualized in the stomach one day later, on day E12. At this time, NADPH diaphorase‐containing cells could no longer be demonstrated in the dorsal mesogastrium. NPY immunoreactivity first appeared in the wall of the bowel on day E12, when it was seen in cells in the presumptive stomach. By day E13, the entire length of the bowel contained NPY‐immunoreactive neurons. Cells that displayed NADPH diaphorase activity were found at this time at both ends of the alimentary tract, but did not appear in the ileum until day E18. In contrast, CGRP immunoreactivity could not be detected anywhere in the gut until day E17, but by day E18 all regions of the bowel contained CGRP‐immunoreactive neurons. Endogenous 5‐HT was first detected at day E16 in mucosal epithelial cells in all segments of the gut except the stomach, where it appeared at day E18. The NPY/NADPH diaphorase set of neurons thus develop before the acquisition of a detectable level of endogenous 5‐HT or enteric neural 5‐HT receptors (which arise in the foregut at day E14). These observations demonstrate that enteric neurons that express small molecule.
Development of the nerve fiber layer in the olfactory bulb of mouse embryos
Authors: Doucette R.
Published: January 2005

The purpose of this study was to provide an ultrastructural description of the development of the olfactory nerve fiber layer (ONL) in the olfactory bulbs of mouse embryos. The developmental age of each embryo was determined by means of the Theiler staging system. During stages 17 and 18, the olfactory axons grew through the mesenchyme toward the cerebral vesicle; they were accompanied by a group of electron‐dense cells which were referred to as peripheral glial progenitor cells (GPCs) because they ensheathed the adjacent axons. In Theiler stage 19–21 embryos, the axons and the peripheral GPCs grew dorsocaudally along the external surface of the bulb primordium forming a presumptive ONL immediately superficial to its glia limitans. Through small breaks in this glia limitans, the axons, but not the peripheral GPCs, penetrated into the marginal zone of the bulb primordium. Even though by the first half of stage 21 there were only short stretches of glia limitans separating the presumptive ONL from the marginal zone, there was no intermingling of the perikarya between the two layers. A definitive ONL could be identified by the second half of Theiler stage 21, by which time the glia limitans of the bulb primordium had totally disappeared. However, up to Theiler stage 24 of development the only cells to be found in this definitive ONL were the peripheral GPCs. Although in Theiler stage 25 and 26 embryos there was an additional population of less‐electron‐dense GPCs within the definitive ONL, these cells were likely derived from the previous group of peripheral GPCs rather than from cells newly emigrated from the deeper layers of the developing bulb. This developmental data necessitated a reevaluation of the cell lineages of the two glial cell types that reside within the ONL of the adult olfactory bulb.
Dendritic maturation of displaced putative cholinergic amacrine cells in the rabbit retina
Authors: Wong R. O. L. , Collin S. P.
Published: January 2005

The dendritic trees of Cb, cholinergic, amacrine cells in the ganglion cell layer of the developing rabbit retina are revealed by intracellular injection with Lucifer yellow to have the adult dendritic branching pattern at birth. It is demonstrated that these cells maintain a constant number of dendritic branches throughout postnatal development and that their dendritic trees increase in size by the growth and subsequent elongation of all branches. Proximal and distal dendrites increase in length by almost the same proportions between birth and adulthood.

Although the adult pattern of dendritic branching of Cb amacrine cells is established by birth, dendrities in the young possess numerous short appendages (1–5 μm in length) resembling the “dendritic spines” of immature cat retinal ganglion cells. Some of these structures remain on the dendrites of adult cells but the majority are lost at the end of the third postnatal week. As dendritic spines disappear, the dendrites of Cb amacrine cells, especially the distal portion of the tree, acquire numerous varicosities. At each stage after P10, the gain in the number of varicosities greatly exceeds the loss in spines; this is not consistent with the hypothesis that all varicosities are retracted dendritic spines. The rapid increase in the number of varicosities on distal dendrites of Cb amacrine cells during the first 3 postnatal weeks coincides with the maturation of amacrine cell physiological responses.

There is no distinct centroperipheral gradient in the postnatal dendritic maturation (acquisition of varicosities, loss of spines, attainment of the adult number of branches) of Cb amacrine cells from the visual streak to the peripheral retina. However, the area of their dendritic tree increases relatively more in the retinal periphery compared to that in the visual streak.
Development of synapses between chick retinal neurons in dispersed culture
Authors: Gleason Evanna , Wilson Martin
Published: January 2005

Morphological criteria allow several kinds of synapse to be recognized in the vertebrate retina. It is, however, not presently known if, or how, these morphological differences reflect physiological distinctions. Since a proper investigation of synaptic physiology in the intact retina is compromised by technical difficulties, we have examined dispersed cultures to discover if they are likely to provide a more tractable physiological preparation. The chief question addressed here concerns the extent to which normal synaptic development takes place in the impoverished conditions of dispersed cell culture.

Cultures were established from embryonic day 8 chick retina and fixed for microscopy on embryonic equivalent (E.E.) days 12, 14, 16, and 18. Neuronal processes appeared shortly after plating and continued to increase in number and extent through E.E. 16. Cone cells were recognizable by virtue of their distinctive oil droplets. Two classes of cone could be distinguished on the basis of the density of their cytoplasmic staining. Presynaptic ribbons could be observed in cone cells on E.E. 12, but characteristic dyad and triad postsynaptic organization was seldom present at this stage nor was it often observed at subsequent times. An increase in the number of ribbon synapses in culture was seen on E.E. 18. These synapses may represent those of bipolar cells. Conventional synapses were found at all times examined but the number of these increased greatly between E.E. 14 and 16. Of these conventional synapses, we found some whose anatomy was characteristic of synapses made by amacrine cells as well as some whose anatomy was characteristic of synapses made by bipolar cells.
Effects of prenatal exposure to ethanol on neocortical development: II. Cell proliferation in the ventricular and subventricular zones of the rat
Authors: Miller Michael W.
Published: January 2005

Prenatal exposure to ethanol alters the generation of neocortical neurons; ethanol reduces the numbers of neurons generated between gestational day (G) 12 and G19 but paradoxically increases neuronogenesis after G19. The present study used [3H]thymidine autoradiography to examine the effects of ethanol on the proliferation of cells in the two cortical germinal zones, the ventricular and subventricular zones. Pregnant rats were fed one of three diets: a liquid ethanol‐containing (6.7% v/v) diet (Et), a nutritionally matched isocaloric liquid diet (Ct), or chow and water (Ch). Fetuses were administered with [3H]thymidine on G13, G17, or G20 and killed 45–60 minutes later. Autoradiographs were prepared to identify radiolabeled and mitotic cells. Additional brains from 13–23‐day‐old fetuses were processed for cytoarchitectonic analyses.

The size of the lateral ventricles in the fetuses was not significantly affected by the prenatal exposure. Both the ventricular and subventricular zones were evident throughout the period from G13 to G23. In all three groups, the ventricular zone was thickest from G13 to G17, but from G15 on, the ventricular zone of Et‐treated fetuses was significantly thinner than those of either controls. On G13, G17, and G20, the labeling index (the ratio of radiolabeled cells to the total population) was significantly less in Et‐treated fetuses. The mitotic index was similar in Et‐, Ch‐, and Ct‐treated fetuses. The subventricular zone of all fetuses was most prominent during later fetal ages and it was thicker in Et‐treated fetuses than in controls. Moreover, the labeling and mitotic indices for the subventricular zone of Et‐treated rats were significantly greater than for controls.

Thus, ethanol had different effects on the two neocortical germinal zones: the proliferation of ventricular cells was inhibited, whereas the proliferation of subventricular cells was stimulated. These data suggest that ethanol‐induced changes in neuronogenesis result from alterations in proliferative activity.
Spinocerebellar projections from spinal border cells in the cat as studied by anterograde transport of wheat germ agglutinin‐horseradish peroxidase
Authors: Matsushita Matsuo , Yaginuma Hiroyuki
Published: January 2005

The cerebellar projections of spinal border cells, which give rise to crossed ascending axons, were studied in the lower lumbar segments by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) in the cat. Prior to the injections, the spinal cord was lesioned rostral and ipsilateral to the WGA‐HRP injections to eliminate labeling of the ipsilaterally ascending axons.

Following injections of WGA‐HRP into the L4‐L6 segments, labeled terminals were seen in sublobules Ib‐Vf of the anterior lobe, sublobules VIf‐VIe, lobule VIII, the paramedian lobule, and crus II. More than 90% of the total number of labeled terminals were in the anterior lobe; the projections were predominantly ipsilateral to their cells of origin (about 90% or more labeled terminals of the total number in each of sublobules IIb‐Va). Many labeled terminals were seen ipsilaterally in sublobules IIb (11.1–17.5% of the total number), IIIa (11.7–12.9%), IIIb (16.1–17.6%), IVa (8.8–10.8%), IVb (6.2–10.5%), and Va (9.7–10.3%). In the posterior lobe, labeled terminals were numerous only in sublobule C of the ipsilateral paramedian lobule (2.7–4.9%).

The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross‐sections through each lobule. In the anteriorlobe, labeled terminals were distributed in four major areas. In sublobules IIa–IVa, area 1 was located between 1.0 and 2.0 mm lateral to the midline in zones B–C1 of Voogd; area 2, between 2.0 and 3.0 mm lateral to the midline in zones C1–C2; area 3, between 3.0 and 4.0 mm in zones C2–C3; and area 4, lateral to 4.0 mm from the midline in zone C3. These areas extended apicobasally in the apical to middle parts of the lobules. On the rostral side of sublobule C1 of the ipsilateral paramedian lobule, the projection areas extended in the entire apicobasal and the mediolateral axis of the sublobule, except in the most lateral part. The present results suggest that the SBCs project to specific areas in the cerebellar lobules.
Ultrastructural analysis of enkephalinergic terminals in parasympathetic ganglia innervating the urinary bladder of the cat
Authors: Kawatani M. , Shioda S. , Nakai Y. , Takeshige C. , de Groat W. C.
Published: January 2005

Leucine enkephalin immunoreactivity was identified in axons and varicosities in parasympathetic ganglia located in the pelvic plexus and on the surface of the urinary bladder of the cat. Electron microscopic immunohistochemical studies revealed that varicosities containing leucine enkephalin exhibited large dense core vesicles and small, clear, spherical vesicles, which were similar to those found in cholinergic terminals. Leucine enkephalin immunoreactivity was primarily associated with large dense core vesicles. The varicosities formed axodendritic and axosomatic synapses with principal ganglion cells. Axoaxonic synapses were not detected. Some axosomatic enkephalinergic synapses were detected embedded within or invaginating the principal ganglion cells. Varicosities containing flattened and/or small dense core vesicles did not exhibit enkephalin immunoreactivity.

Bladder ganglion cells identified by retrograde HRP tracing from the urinary bladder exhibited similar leucine enkephalinergic synapses. These observations, coupled with previous reports that leucine enkephalin is present in sacral preganglionc neurons and released by preganglionic nerve stimulation, suggest that leucine enkephalin and acetylcholine are cotransmitters stored and released from the same nerve terminals in bladder parasympahtitic ganglia.
Distribution of substance P‐like, leucine‐enkephalin‐like, and bombesine‐like immunoreactivity and acetylcholinesterase activity in the visual system of salamanders
Authors: Schmidt Andrea , Roth Gerhard , Ernst Monika
Published: January 2005

In the urodele species Salamandra salamandra and Batrachoseps attenuatus, the distribution of the neuropeptides substance P (SP), leucine‐enkephalin (LENK), and bombesine (BOMB) was investigated by means of immunohistochemistry in brain areas containing retinofugal projection sites (tectum mesencephali, praetectum, thalamus) as well as in brain regions postsynaptic to the tectum. The activity of acetylcholinesterase (AChE) was studied histochemically.

Despite its simplified, two‐layered morphology, the salamander tectum shows a high degree of neurochemical differentiation, characterized by a laminar organization of neuropeptide‐like immunoreactivity and AChE‐activity comparable to that found in the anuran tectum, which has a multi‐layered morphology. SP‐like immunoreactivity constituted four tectal laminae, two of them occurring in the stratum opticum. LENK‐like immunoreactivity formed three laminae, one in the stratum opticum. BOMB‐like immunoreactivity formed one lamina within the stratum opticum and one in the tectal efferent layers. Layers 1 and 2 of the stratum opticum revealed high AChE‐activity, whereas low activity was found in deep fiber layers containing tectal efferents. The outer cellular layer also revealed AChE‐activity. After enucleation of one eye, the contralateral tectum lacked neuropeptide‐like immunoreactivity and AChE‐activity in the layers containing retinofugal projection sites. No reduction of immunoreactivity was found in nuclei postsynaptic to the tectum.

Our experiments suggest that the secondary simplification that has taken place in salamanders with respect to tectal morphology did not affect the neurochemical differentiation of the tectum.