bluuebunny/crossref_metadata_2025 huggingface dataset:
An electron microscope study of synaptic contacts in the abdominal ganglion of Aplysia californica
Authors: Tremblay J. P. , Colonnier M. , McLennan H.
Published: January 2005

The fine structure of the abdominal ganglion of Aplysia californica has been studied in preparations fixed by immersion in aldehydes, either directly or after a survival of a few hours in artificial sea water. The central core of neuropil is surrounded by a rind of neuronal cell bodies floating in a subcapsular space containing a loose mesh work of neuronal and glial processes, separated by wide extracellular spaces. Large primary processes with deeply infolded membranes leave the neuronal perikarya and enter the neuropil where they branch into smaller processes containing either neurofilaments, neurotubules or both. Some have the appearance of initial segments. The neuropil is not a homogenous structure. Rather, four types of zones can be distinguished: (1) zones of fibers of passage coursing together in the neuropil and making few synaptic contacts; (2) zones of neurosecretory fibers containing large granules and dense‐core vesicles, again making few synaptic contacts; (3) zones with a great variety of synaptic contacts between medium size and small profiles; and (4) glomerular zones. The differentiated membranes of the synapses are characterized by a slight increase in density and by being regularly parallel to each other. Presynaptic densities are sometimes quite prominent but specialized dense cytoplasmic opacities have never been seen bordering the postsynaptic membranes, i.e., all synapses are of the symmetrical type. Interlemmal opacities vary considerably in density. In zone 3, the synaptic vesicles are of several sizes, are round, oval or flat, and are either clear or filled with different types of dense material. The population of vesicles within a single profile may consist either of a homogeneous group of similar vesicles, or of various mixtures of two or three kinds of vesicles. In profiles with mixtures of clear and large dense‐core vesicles, it is often only the clear vesicles which agglomerate towards the differentiated membranes. In such cases the large dense‐core vesicles lie as a peripheral halo around the clear vesicles. Here, and especially in other large neuronal profiles not forming contact in the plane of section, they can be seen to associate specifically with mitochondria and glycogen. It is proposed that they do not contain neurotransmitters but are related to mitochondrial activities such as the strorage of ATP or the movement of calcium ions. In profiles with mixtures of clear and small dense‐core vesicles, both types of vesicles often touch the presynaptic membrane, suggesting the release of two transmitters or of a modulator or neurohormone with a transmitter, by a single terminal. Serial synapses are present in this zone. The glomerular zones contain small profiles forming many synaptic contacts, some of which are arranged in such a way as to suggest the existence of “reciprocal” serial synapses.
Spiral ganglion cell counts in an age‐graded series of rat cochleas
Authors: Keithley Elizabeth M. , Feldman Martin L.
Published: January 2005

Spiral ganglion cells in the cochleas of Sprague‐Dawley rats in various age groups were counted in order to assess the extent and location of cell degeneration with age. Cells in every tenth section of serially sectioned plastic embedded cochleas were counted in the light microscope. The median cell number for the 1‐ to 2‐month‐old animals was 15,800 cells. This number was first seen to be significantly reduced ( −14%) in the 23‐ month‐old animals. At 27 to 29 months the ganglion cell number was reduced' by 20%, while at 33 to 34 months there was a 17% loss. Losses were found throughout the length of the ganglion with the greatest losses at the lower basal and apical ends. In the oldest group, these losses amounted to 28% and 33%, respectively.

Type II ganglion cells first showed a significant decrease in number in the 27 ‐ to 29‐month‐old group, when a 32% loss was seen. The same loss was seen in the 33‐ to 34‐month‐old group. Unlike the type I cells which are lost throughout the length of the ganglion, type II cells were not significantly reduced in number at the basal end, but decreased by as much as 42% in the middle and apical regions.
Development of the diencephalon in the rat. IV. Quantitative study of the time of origin of neurons and the internuclear chronological gradients in the thalamus
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Groups of pregnant rats were injected with two successive daily doses of 3H‐thymidine from gestational days 13 and 14 (E13 + 14) until the day before birth (E21 + 22). With this progressively delayed comprehensive labelling procedure we determined the time of origin of neurons in the nuclei of the epithalamus, thalamus, and ventral thalamus. The zona incerta, subthalamic nucleus, are composed of the earliest arising neurons (E13, or before, to E15). The neurons of the lateral habenular nucleus are produced between days E13–16. The neurons of the medial geniculate and lateral geniculate nuclei, the ventrobasal and ventrolateral complexes, and the nucleus lateralis, pars posterior, arise rapidly on days E14–15; the medial geniculate nucleus with a peak on day E14, the others with a peak on day E15. Neurons of a group of nuclei, with ill‐defined boundaries medial to the sensory relay nuclei, arise apparently on days E15–16, with a peak on day E15; these may represent the intralaminar nuclei. The next group is generated on days E15–16 but with peak formation time on day E16: this includes the anteroventral, anterodorsal, anteromedial and mediodorsal nuclei. The rhomboid, reuniens and paratenial nuclei, and the paraventricular nucleus, pars anterior, arise next (E16–17). The medial habenular nucleus forms last and over a protracted period (E15–19). With their lengthy generation time the lateral and medial habenular nuclei resemble more the nuclei of the hypothalamus than the nuclei of the dorsal thalamus.
An autoradiographic study of the retinal projection in Xenopus laevis with comparisons to Rana
Authors: Levine R. L.
Published: January 2005

The retinal projection to the brain in Xenopus has been examined using autoradiographic techniques. The labelled moieties used were 3H‐proline and 3H‐fucose.

There are three anterior thalamic optic terminal sites in Xenopus. These are the nucleus of Bellonci, the corpus geniculatum thalamicum and the rostral visual nucleus. The first two of these are similar to the homonymous nuclei in Rana while the last, the rostral visual nucleus, appears to correspond to the rostral end of the posterior entopeduncular nucleus of Rana. Both the nucleus of Bellonci and the rostral visual nucleus receive strong ipsilateral retinal inputs while the corpus geniculatum receives only a weak ipsilateral projection. In the posterior thalamic: pretectal region there is only one clearly defined optic terminal nucleus—the uncinate field. This structure receives a strong ipsilateral input. In addition there are two other labelled fields in this region whose nature (fibers v. terminals) cannot be clearly discerned in autoradiographs. These are the thalamopretectal field—a horizontal band which extends in the dorsomedial neuropil from midthalamus to the pretectum, and the pretectal field where diffuse labelling is evident, especially ipsilateral to the injected eye. The thalamopretectal field also receives an ipsilateral input. The optic tectum in Xenopus receives a dense contralateral retinal innervation but only a weak ipsilateral projection. Finally, the basal optic nucleus receives both contralateral and ipsilateral retinal innervation with the latter being, by far, the weaker of the two.

In addition to other differences between the two species, it is obvious that there is a much denser and more extensive ipsilateral retinal projection to the thalamic and pretectal brain structures in Xenopus than in Rana. This is presumably due to the greater size of the binocular field in Xenopus.
Coronate cells: Displaced amacrines of the rabbit retina?
Authors: Hughes A. , Vaney David I.
Published: January 2005

The rabbit retinal ganglion cell layer contains a soma population which is morphologically distinct from the demonstrated ganglion cells. These “coronate cells” (Vaney, '80) have many features in common with classical neurons and are qualitatively different from typical glial cells. Detailed investigation by specific staining, ribonuclease treatment, and electron microscopy indicates that coronate cells are microneurons. The coronate cells contain somatic subsurface cisternae typical of rabbit amacrine cells, and are similar in appearance to some neurons of the amacrine cell layer. It is suggested that they represent, at least in part, a population of “displaced” amacrine cells.
Mapping the normal and regenerating retinotectal projection of goldfish with autoradiographic methods
Authors: Meyer Ronald L.
Published: January 2005

In normal goldfish, lesions of various size were made in nasal or temporal retina immediately prior to retinal labeling with tritiated proline. The resulting gaps in retinal innervation of tectum indicated that the projection is retinotopographically ordered to a precision of about 50 μm. Similarly, acute tectal incisions transecting the optic pathways were combined with immediate retinal labeling. The resulting tectal denervation confirmed that most fibers follow highly ordered paths through the stratum opticum of tectum; but a few fibers were found to follow unusual paths to their appropriate tectal positions. In other fish, the optic nerve was crushed. At various times afterwards, retinotopography and pathway order were similarly analyzed by making retinal lesions or tectal incisions just prior to labeling. For up to 40 days after crush, the projection lacked any refined retinotopic order. Only a gross topography could be demonstrated. Over several months, retinotopography gradually improved eventually approaching that of normals. Correlated with this was an initial stereotypic growth through the pathways of the stratum opticum followed by a long period of highly anomalous growth through the innervation layer. Evidently, many regenerated fibers grew in through inappropriate routes to the wrong region of tectum but subsequently arrived at their appropriate locus by circuitous routes within the innervation layer.
The growth of segmental nerves from the brachial myotomes into the proximal muscles of the chick forelimb during development
Authors: Bennett M. R. , Davey D. F. , Uebel K. E.
Published: January 2005

A study has been made of the growth of segmental nerves 13 to 16 (SN 13 to SN 16) into the chick limb bud, from the time when they have just reached the ends of the brachial myotomes (stage 21: Hamburger and Hamilton, '51), until they enter the newly formed ventral (stage 24) and dorsal (stage 25) pre‐muscle cell masses in the limb bud. At stage 22 axon bundles of SN 13 to SN 16 have grown off the ends of their respective myotomes, and converge towards the most densely packed mesenchyme in the limb bud at segmental level 15. As a consequence, the first axon bundles of SN 14 and SN 16 have almost joined those of SN 15, whereas the further removed SN 13 axon bundles have not yet reached the level of SN 15. By stage 23 the first axon bundles from SN 14 to SN 16 have joined at segmental level 15 to form a nerve which grows toward the ventral pre‐muscle cell mass. At stage 24 axon bundles from SN 13 have joined those from SN 14 to SN 16 to form the brachialis longus inferior nerve, which enters the densest region of the ventral pre‐muscle. Other axons from SN 13 to SN 15 grow along the pathways provided by the early arriving axon bundles towards the ventral pre‐muscle, but diverage from those at segmental level 14 to grow to the dorsal pre‐muscle. By stage 25 axon bundles from SN 13 to SN 15 have joined to form the brachialis longus superior nerve which enters the densest region of the dorsal pre‐muscle. At stage 26 a plexus has formed due to this pattern of growth of the segmental nerves between stages 22 and 25. It is suggested that pre‐muscle cells synthesize a nerve growth factor which directs the growth of axons into the limb bud.
Neurons of the periaqueductal gray matter as revealed by Golgi study
Authors: Liu Rita P. C. , Hamilton Betty L.
Published: January 2005

Neurons of the periaqueductal gray matter of the normal adult cat are classified into seven general types, Ia, Ib, II, IIIa, IIIb, IIIc, and IIId, based on the Golgi‐Cox impregnated materials. Types Ia and Ib are spindle shaped bipolar neurons with one straight dendritic process forming varicosities and short stemmed spines. Type Ia is small in size and Ib is larger. The axon of each neuron emerges from another pole and projects beyond the PAG region. Occasionally it may share the origin with a dendrite or a tuft of dendrites. Type II, triangular shaped, has an apical dendrite that traverses a long distance within the PAG and an axon emerging from the basal portion and projecting beyond the PAG. Type IIIa, b, c, and d are pleomorphic multipolar neurons. Type IIIa has a rhomboid‐shaped soma and dichotomically branching dendrites. Type IIIb has a spheroidal soma and short axons that terminate within the PAG. Type IIIc has a piriform soma and spiny dendrites that ramify perfusely and an axon which terminates within the PAG. Type IIId has the largest soma of all these neurons and the structure resembles an undifferentiated motor neuron of the CNS. Axons of the types IIIa and IIId are projecting in nature. Type Ia is found exclusively in the area immediately surrounding the aqueduct, the nucleus medialis. Types IIIc and IIId are found exclusively in the lateral region of the PAG which corresponds to the nucleus lateralis while the remaining cell types are found mostly in nuclei lateralis and dorsalis.
Neurons and synaptic patterns in the deep layers of the superior colliculus of the cat. A Golgi and electron microscopic study
Authors: Norita Masao
Published: January 2005

Golgi and electron microscopic observations were made on the neurons in the deep layers (below the stratum opticum) of the cat superior colliculus. Large neurons, 35–60 μ in somal diameter, occur mainly in the lateral two‐thirds of the colliculus. They have numerous somatic and dendritic spines and receive a large number of axon terminals (bouton covering ratio: more than 70%). The medium‐sized neurons (20–30 μ), with a moderate number of dendritic spines, show a lower bouton covering ratio (25–30%). The ratio for small neurons (8–15 μ), with very few dendritic spines, is less than 10%. The medium‐sized and small neurons are distributed throughout the colliculus and show marked variability in the dendritic arrangement.

Seven different types of axon terminals were distinguished: types I, II, V, and VII form asymmetrical and types III, IV, and VI symmetrical synapses. Type I terminals represent small boutons containing predominantly spherical vesicles, and are in contact mainly with small dendritic profiles. Type II terminals are medium‐sized and slender, contain a mixture of spherical and slightly oval vesicles, and make synaptic contacts with small to medium‐sized dendrites and somatic spines. This type of terminal is occasionally presynaptic to vesicle‐containing dendrites (type VIII). Type III terminals are small, contain flattened vesicles predominantly, and are presynaptic to a wide variety of neuronal elements in the deep layers of the superior colliculus. Type IV terminals are represented by medium to large‐sized boutons that contain pleomorphic vesicles and make synaptic contacts chiefly with the large neurons. Type V and VI terminals exhibit a quite dense axoplasmic matrix and mainly contact the large neurons. Type VII terminals are often in the form of boutons en passant and contain numerous large granular vesicles. Pleomorphic vesicle‐containing dendrites (type VIII terminals) are also observed to participate in the axodendrodendritic serial synapses.
Retinal ganglion cells projecting to the rabbit accessory optic system
Authors: Oyster Clyde W. , Simpson John I. , Takahashi Ellen S. , Soodak Robert E.
Published: January 2005

Recent evidence from extracellular recording studies indicates that the medial terminal nucleus (MTN) of the rabbit accessory optic system receives inputs from a particular functional class of retinal ganglion cells—specifically, the on‐type direction‐selective cells. These ganglion cells have been selectively labeled by the retrograde transport of horseradish peroxidase (HRP) injected into the MTN. The number of labeled cells, their distribution over the retina, and their soma areas were determined. In one animal in which the HRP injection completely filled the nucleus, two thousand ganglion cells were labeled. This number agrees with previous estimates of the number of retinal axons terminating in the MTN. Unlike results in avians, none of the ganglion cells was displaced—i.e., they were not Dogiel cells. The density of labeled cells was highest in the visual streak and, overall, the distribution of labeled cells corresponded to the physiologically determined distribution of on‐type direction‐selective cells. Cells labeled by the HRP injection were among the 20% largest cells in the retina. This result, in conjunction with conclusions from other studies, leads to the prediction that on‐type direction‐selective cells can be characterized morphologically as cells with large cell bodies and a very extensive dendritic spread in which the dendrites ramify in the vitreal sublamina of the inner plexiform layer.
Early development of the brain and spinal cord in dysraphic mice: A transmission electron microscopic study
Authors: Wilson Doris B. , Finta Laurel A.
Published: January 2005

The hindbrain and spinal cord were studied by transmission electron microscopy with and without lanthanum nitrate treatment in nine‐day embryos of the loop‐tail (Lp) mutant mouse. Homozygous (Lp/Lp) individuals exhibit dysraphism from the hindbrain caudally throughout the embryo; in +/+ and Lp/+ individuals, the brains and spinal cords are normal. In contrast, the ventricular cells in the abnormal hindbrain and spinal cord showed increased amounts of intericellular space in an area intermediate between the luminal border and basal zone, and a flattening which occurs variably in their luminal surfaces. A most striking difference occurred in the frequency of gap junctional vesicles, circular structures bounded by a double membrane and containing ribosome‐like material. A quantitative analysis of the distribution of these organelles revealed that they are more numerous in the dysraphic hindbrain and lumbosacral spinal cord of the abnormal animals than in comparable regions of the normal; however, in the cervicothoracic spinal cord, the frequency of these vesicles is similar. In specimens treated with lanthanum, the tracer freely penetrated the luminal junctional complexes in both normal and abnormal animals, but was not present between the membranes of the gap junctional vesicles. The developmental significance of gap junctional vesicles frequently located in juxtaluminal regions of mitotic cells, but also found deeply in dividing cells, is not known; they may relate to cell‐to‐cell attachment and/or communication. In any event, furthe study of them may prove valuable in understanding normal and abnormal development of the neural tube.
Somatotopic and functional organization of the avian trigeminal ganglion: An HRP analysis in the hatchling chick
Authors: Noden Drew M.
Published: January 2005

While the somatotopic organization of many central systems is well characterized, that of peripheral sensory neurons has not been adequately defined. This is especially true for the trigeminal ganglion. By applying HRP subcutaneously at each of 14 sites and also intramuscularly, it is possible to determine whether the location of sensory neurons within the ganglion reflects their peripheral projections.

There is no discernible somatotopic organization of neurons in the ophthalmic lobe. However, the location of maxillary neurons in the maxillo‐mandibular lobe is organized with the most posterior cells projecting to sites closest to the ganglion and with neurons located more anteriorly projecting to progressively more distant sites. There is a less well defined organization in the superior‐inferior axis of the ganglion, and none along its proximal (root) to distal axis.

Mandibular exteroceptive neurons are found primarily in the anterior region of the maxillo‐mandibular lobe, while mandibular proprioceptive cells are located in the proximo‐central part of this lobe. In most cases there is a considerable scattering of horseradish peroxidase (HRP)‐filled neurons. Projections to contralateral ganglia, the trigeminal motor nucleus, and the trigeminal motor nucleus, and the trigeminal mesencephalic nucleus were also examined.

Cytologically, the hatchling trigeminal consists of two interspersed types of neurons: large, lightly staining and smaller, darkly staining cells. Previous experiments have proved that these two cell types do not correspond to each of the embryonic precursorsof trigeminal neurons, the neural crest and placodal cells. In this study HRP was found localized in both classes of neurons following injection at all sites, including jaw‐closing muscles. This indicates that the dual cytology is not correlated with either distribution of peripheral fibers or exteroceptive vs. proprioceptive functions. The possibilities that the two types of neurons may have different central projections and/or may be related to visceral vs. somatic afferent functions are discussed.
Disc morphogenesis in vertebrate photoreceptors
Authors: Steinberg Roy H. , Fisher Steven K. , Anderson Don H.
Published: January 2005

Electron microscopic examination of the bases of adult rod and cone outer segments (rhesus monkey, ground squirrel, and grey squirrel) has led to a new model of disc morphogenesis. In this model the disc surfaces and disc rims develop by separate mechanisms and from separate regions of the membrane of the inner face of the cilium. This membrane is alternately specified into regions that will form either the disc surfaces or the disc rims. The disc surfaces develop by an evagination or outpouching of the ciliary membrane. The two surfaces of an evagination, scleral and vitreal, each form one of the surfaces of adjacent discs. The disc rim is initially specified as a region of ciliary membrane between adjacent disc‐surface evaginations. This region grows bilaterally around the circumferences of adjacent discs, zippering together the apposed surfaces to form the rim and completed disc. At the same time it seals the plasma‐membrane edges of the evaginations, which have become detached from the surfaces. Incisures form in rod discs by infolding of the rim and surfaces together, and they begin to form before the rim is completed around the disc perimeter. When a number of new discs are developing simultaneously the ciliary membrane at the base of an outer segment consists of a stack of rim forming and surface forming growth points. This model provides, in addition, for the continuous renewal of outer‐segment plasma membrane. It also establishes a developmental basis for the structural uniqueness of the disc rim. Finally, it indicates an evolutionary relationship between the discs of vertebrate visual cells and the membrane specializations of invertebrate visual cells.
Effects of indolic neurotoxins on enteric serotonergic neurons
Authors: Gershon Michael D. , Sherman Diane L. , Dreyfus Cheryl F.
Published: January 2005

The effects of the indolic neurotoxins 5,6‐ and 5,7‐dihydroxytryptamine (5,6‐DHT; 5,7‐DHT) on the enteric nervous system were examined. 5,6‐DHT, in moderate dosage, 40 mg/kg, decreased uptake of tritiated 5‐hydroxytryptamine (3H‐5‐HT) but not that of tritiated norepinephrine (3H‐NE). However, selectivity of the neurotoxins for enteric serotonergic rather than adrenergic axons was enhanced by pretreating animals with desmethylimipramine to inhibit the catecholamine uptake mechanism. When this was done, 5,7‐DHT was found to prevent the development of 5‐HT histofluorescence (following injection of L‐tryptophan) without affecting histofluorescence of NE. In contrast, 6‐hydroxydopamine virtually abolished NE histofluorescence and uptake of 3H‐NE without affecting development of 5‐HT histofluorescence or uptake of 3H‐5‐HT. Electron microscopy revealed that 5,7‐DHT induced dose‐dependent lesions of axonal varicosities in the enteric nervous system. Early lesions, 1–4 hours following injection, resembled cytolysosomes and consisted of membrane enclosed regions of opaque cytoplasm containing synaptic vesicles. Affected varicosities contained a mixed population of large dense cored (∼120nm) and small lucent vesicles (∼70nm) but none exhibited pre‐ or postsynaptic membrane specializations. After 24 hours terminals degenerated and were engulfed by surrounding supporting cells. It is concluded that peripheral serotonergic neurons resemble central serotonergic neurons in susceptibility to the toxic effects of indolic neurotoxins. These neurotoxins are useful anatomical markers of serotonergic terminal varicosities.
The nervus terminalis of the guinea pig: A new luteinizing hormone‐releasing hormone (LHRH) neuronal system
Authors: Schwanzel‐Fukuda M. , Silverman A. J.
Published: January 2005

Immunoreactive LHRH‐like material has been found in the cells and fibers of the nervus terminalis in fetal and adult guinea pig brains. LHRH‐containing neurons and axons are seen in the nasal mucosa intermingled with fibers of the olfactory nerves, in ganglia along the ventromedial surfaces of the olfactory bulbs and forebrain, and in clusters surrounding perforating branches of the anterior cerebral artery in the regions of the septal nuclei and olfactory tubercle. Nonreactive neurons are found adjacent to the LHRH‐positive cells in all of the ganglia. LHRH‐immunoreactive cells and axons of the nervus terminalis are in intimate contact with cerebral blood vessels and the cerebrospinal fluid along the intracranial course of this nerve, deep to the meninges. The possible involvement of these structures in the neural mechanisms of sexual behavior and the neurohormonal regulation of reproductive function are discussed.
Time course and pattern of optic fiber regeneration following tectal lobe removal in the goldfish
Authors: Lo Raymond Y. S. , Levine Robert L.
Published: January 2005

Following single tectal lobe removal in the adult goldfish, Carassius auratus, the pattern of regeneration of the optic fibers which had previously projected to that tectum was examined at 1, 2, 4, 6, 8, 10, and 12 weeks postoperative using 3H‐proline radioautography. We found that regenerating optic fibers grew across the midline through the transverse, minor, horizontal, and posterior commissures to innervate the remaining tectum. At early postoperative times innervation of the tectum was continuous, while later, the regenerating fibers segregated into discrete patches in the superficial layers of the tectum. In addition, regenerating fibers also grew into non‐optic centers/pathways such as the habenula, the fasciculus retroflexus, the forebrain, the torus semicircularis, the valvula and corpus cerebelli, the hypothalamus, and the medulla. While optic fibers were no longer apparent in the habenula and the fasciculus retroflexus after 2 weeks postoperative, all other structures were still occupied by the fibers at 12 weeks postoperative. Since most of the innervated pathways were either tectal efferent pathways, which should contain degenerating debris and proliferating glial cells after the tectal removal, or pathways closely associated with traumatized areas, we suggest that degenerating axonal debris and proliferating glia may play an important role in guiding regenerating fibers in this system.
The topographic organization of corticocollicular projections from physiologically identified loci in the AI, AII, and anterior auditory cortical fields of the cat
Authors: Andersen Richard A. , Snyder Russell L. , Merzenich Michael M.
Published: January 2005

The connections of the three auditory fields AI, AII, and the anterior auditory field (AAF) with the inferior colliculus (IC) were studied using anterograde tracing techniques. Microinjections of tracers were placed at physiologically identified loci after these fields had been functionally mapped using microelectrode recording techniques. This methodology ensured that the injections were well within the borders of each cortical field that was studied and enabled the elucidation of the topographies of the projections of AI and AAF onto the IC with respect to their cochleotopicorganizations.

The projection of loci in AI to the caudal aspect of the IC was in the form of sheets of terminals in the dorsomedial division of the central nucleus bilaterally and the pericentral nucleus ipsilaterally. The topography of projection with respect to the cochleotopic organization of AI appeared to be in register with the described cochleotopic organization of the central nucleus and the pericentral nucleus.

The sheets of labeled terminals in the dorsomedial division of the central nucleus that resulted from the projection of single loci in AI were of the proper orientation to be continuous with the morphological laminae described in the ventrolateral division of the central nucleus. These sheets of corticocollicular terminals also paralleled the dorsomedial aspect of the physiologically defined “isofrequency contours” of the central nucleus.

Single injections placed in AAF produced autoradiographic label in the IC that was of the same basic pattern and systematic topography as the labeling recorded with AI injections; however, it was much weaker. The projection from AII was to the lateral (ipsilateral) and medial (bilateral) aspects of the pericentral nucleus.
Degeneration of hippocampal CA3 pyramidal cells induced by intraventricular kainic acid
Authors: Nadler J. Victor , Perry Bruce W. , Gentry Christine , Cotman Carl W.
Published: January 2005

Degeneration of hippocampal CA3 pyramidal cells was investigated by light and electron microscopy after intraventricular injection of the potent convulsant, kainic acid. Electron microscopy revealed evidence of pyramidal cell degeneration within one hour. The earliest degenerative changes were confined to the cell body and proximal dendritic shafts. These included an increased incidence of lysosomal structures, deformation of the perikaryal and nuclear outlines, some increase in background electron density, and dilation of the cisternae of the endoplasmic reticulum accompanied by detachment of polyribosomes. Within the next few hours the pyramidal cells atrophied and became electron dense. Then these cells became electron lucent once more as ribosomes disappeared and their membranes and organelles broke up and disintegrated. Light microscopic changes correlated with these ultrastructural observations. The dendritic spines and the initial portion of the dendritic shaft became electron dense within four hours and degenerated rapidly, whereas the intermediate segment of the dendrites swelled moderately and became more electron lucent. No degenerative changes were evident in pyramidal cell axons and boutons until one day after kainic acid treatment.

Less than one hour after kainic acid administration, astrocytes in the CA3 area swelled, initially in the vicinity of the cell body and mossy fiber layers. It is suggested that the paroxysmal discharges initiated in CA3 pyramidal cells by kainic acid served as the stimulus for this response. Phagocytosis commenced between one and three days after kainic acid administration, but remained incomplete at survival times of 6–8 weeks. Astrocytes, microglia, and probably oligodendroglia phagocytized the degenerating material.

These results point to the pyramidal cell body and possibly also the dendritic spines as primary targets of kainic acid neurotoxicity. In conjunction with other data, they support the view that lesions made by intraventricular kainic acid can serve models of epileptic brain damage.
Single subthalamic nucleus neurons project to both the globus pallidus and substantia nigra in rat
Authors: Van Der Kooy Derek , Hattori T.
Published: January 2005

The organization of the major efferents of the rat subthalamic nucleus (STN) was investigated using a fluorescent retrograde double‐labeling technique. Red fluorcrescent Evans Blue was injected into the globus pallidus and blue fluorescent DAPI‐Primuline was injected into the substantia nigra. After retrograde axonal transport many double‐labeled neurons were seen throughout the STN. Occasional double‐labeled cells were seen in the lateral hypothalamus just medial to the STN and in a thin lateral strip of neurons extending laterally from the STN. Evidence for a mediolateral topography in both the STN‐pallidal and STN‐nigral pathways was obtained.

The STN contains few, if any, local interneurons. Cell counts revealed that at least 94% of, and possibly all, STN neurons send axon collaterals to both the globus pallidus and substantia nigra.
Cells of origin of pathways descending to the spinal cord in some quadrupedal reptiles
Authors: Ten Donkelaar H. J. , Kusuma A. , De Boer‐Van Huizen R.
Published: January 2005

The cells of origin of pathways descending to the spinal cord have been determined in several quadrupedal reptiles, viz., the turtles Pseudemys scripta elegans and Testudo hermanni and the lizards Tupinambis nigropunctatus and Varanus exanthematicus, following a technique introduced by Kuypers and Maisky ('75). This technique was very effective in producing retrograde transport of HRP to a great many neurons in the hypothalamus and in the brain stem. Projections from the hypothalamus (the nucleus paraventricularis and the nucleus periventricularis hypothalami), the interstitial nucleus of the flm, the nucleus periventricularis hypothalami, the interstitial nucleus of the flm, the nucleus ruber, the nucleus of Edinger‐Westphal, the locus coeruleus, the subcoeruleus area, a conspicuous cell group comparable to Kuypers and Maisky's ('75, '77) lateral pontine area, the magnocellular reticular formation, the ventrolateral, ventromedial, and descending vestibular nuclei, the dorsal motor nucleus of the vagus, and the nucleus of the solitary tract, reach at least as far as far as the lumbar intumescence. Projections from two somatosensory nuclei, i.e., the nucleus descendens nervi trigemini and the nucleus funiculi dorsalis, as well as the laminar nucleus of the torus semicircularis, have been demonstrated to at least the ninth spinal segment. The two deep cerebellar nuclei, particularly the medial cerebellar nucleus, were found to project contralaterally to the spinal cord, in the lizard Varanus exanthematicus at least as far as the seventh segment; in the turtles studied so far, only projections as far caudal as the fourth spinal segment could be demonstrated.

Data on the funicular trajectory of various descending pathways could also be obtained. It seems likely that in the reptiles studied, in addition to rubrospinal and reticulospinal pathways, projections from the hypothalamus, the nucleus of Edinger‐Westphal, the cell group comparable to the mammalian lateral pontine area, the locus coeruleus, and subcoeruleus area, and the nucleus of the solitary tract pass via the lateral funiculus.

The pathways descending from the hypothalamus and brain stem to the spinal cord in the quadrupedal reptiles studied appear to show remarkable similarities to pathways in mammals as regards their cells of origin as well as their funicular trajectory. It seems likely that some of the projections demonstrated, viz., from the locus coeruleus, at least part of the cell group comparable to the lateral pontine area, as well as the cells in and around the dorsal motor nucleus of the vagus, are noradrenergic pathways.
Synapse‐to‐neuron ratios of the frontal and cerebellar cortex of 30‐day‐old and adult rats undernourished during early postnatal life
Authors: Bedi K. S. , Thomas Y. M. , Davies C. A. , Dobbing J.
Published: January 2005

Male rats undernourished from birth to 30 days were nutritionally rehabilitated till 160 days of age. Quantitative stereological procedures at the light and electron microscopical levels were employed to estimate, among other things, the synapse‐to‐neuron ratios in the frontal cortex and granular layer of the cerebellum.

In the frontal cortex, the 30‐day‐old undernourished rat had a mean ± SE of about 14,020 ± 1,540 synapses‐per‐neuron compared with 22,270 ± 3,250 for the controls. This was a deficit of 37% (p < 0.05). By 160 days of age the previously undernourished rats showed no statistically significant deficit in this ratio compared with controls (11,800 ± 690 and 13,360 ± 1,110 respectively, p > 0.1). This was due mainly to a fall in the synapse‐to‐neuron ratio with age. A much larger fall in the ratio occurred in the control than in the previously undernourished group.

In the granular layer of the cerebellum the 30‐day‐old undernourished rats had 341 ± 17 synapses‐per‐neuron compared with 495 ± 25 for the controls. This was a deficit of 31% (p < 0.01). By 160 days of age the previously undernourished rats again showed no statistically significant deficit in this ratio compared with controls (627 ± 56 and 688 ± 38, respectively (p > 0.1).

These results show that the previously undernourished rats are capable of at least some (if not complete) “catch‐up” with regard to the synapse‐to‐neuron ratio.
Postnatal development of GABA‐ergic neurons in the rabbit retina
Authors: Man‐Kit Lam Dominic , Fung Sek‐Chung , Kong Yun‐Cheung
Published: January 2005

Uptake, synthesis, storage, and release of γ‐aminobutyric acid (GABA) are some of the characteristic properties of GABA‐ergic neurons. In the present study, we have used these properties as physiological probes to follow the emergence and maturation of GABA‐ergic neurons during postnatal development of the rabbit retina. There is autoradiographic, immunocytochemical, and pharmacological evidence that some amacrine cells and certain neurons in the ganglion cell layer probably use GABA as the neurotransmitter. These neurons take up GABA, contain the GABA‐synthesizing enzyme L‐glutamic acid decarboxylase (GAD, EC 4.1.1.15), and release the accumulated GABA by a Ca++‐dependent mechanism when depolorized with high extracellular K+ concentration. In this study, we show that certain neurons in the newborn retina already possess a specific mechanism for GABA uptake. The positions and numbers of these cells in the developing retina suggest that they will become GABA‐ergic neurons in the adultretina. These putative GABA‐ergic neurons are, however, probably immature an birth because newborn retinas contain only low levels of GABA and GAD. Additionally, there is relatively little K+‐stimulated, Ca++‐dependent release of (3H)‐GABA from the newborn retinas. GABA concentrations and GAD activities in developing retinas increase steadily postnatally, reaching about 80% of the adult levels by day 9. The activities of the GABA‐degrading enzyme, GABA‐glutamate transaminase (GABA‐T, EC 2.6.1.19), follow a similar pattern of maturation during retinal development. K+stimulated GABA release, however, remains low until about day 6, and then increases dramatically from 20% to 85% of the adult level over the next 3 days. Taken together, our results indicate that in the rabbit retina, the commitment by certain neurons to use GABA as the transmitter is made prenatally. These neurons are immature at birth but are biochemically, physiologically, and probably functionally mature by about 9 days after birth.
Retinotopic organization of areas 20 and 21 in the cat
Authors: Tusa R. J. , Palmer L. A.
Published: January 2005

The retinotopic organization of cat cortex, in the vicinity of areas 20 and 21 as defined by Heath and Jones ('71), was determined using electrophysiological mapping techniques. Although the topography of the visual field representations in this region of cortex is more complex than that found in areas 17, 18, and 19, this region appears to contain four representations of the visual hemifield. The four cortical areas these visual field representations occupy have been labeled 20a, 20b, 21a, and 21b. These representations are not as precise as those found in areas 17, 18, and 19; the receptive fields in areas 20a, 20b, 21a, and 21b are larger and there is more scatter in receptive field location among adjacent cells. The upper visual hemifield is emphasized in all four of these areas, but the extent of the representation ranges from just the central 20° found in area 21a to nearly the entire upper visual quadrant found in area 20b. The peak areal magnification factors found in these areas are all at least one order of magnitude less than those found in area 17. The visual field transformations from retina onto cortex in areas 20a, 20b, 21a, and 21b are similar to the types we found in other cortical visual areas, and the significance of these transformations for visual processing is discussed.
Peripheral myelin in the mouse mutant Shiverer
Authors: Rosenbluth J.
Published: January 2005

The mouse mutant Shiverer has been shown previously to lack myelin basic protein and other myelin proteins in both the peripheral and central nervous systems. Examination by electron microscopy shows that the peripheral nervous system, in contrast to the markedly abnormal central nervous system, is grossly normal. Myelin sheaths are of the usual thickness and exhibit normal periodic structure consisting of alternating major dense and intermediate lines. Subtle abnormalities do occur, however, consisting of increased numbers of cytoplasm‐containing lamellae, aberrant terminations of myelin lamellae in internodal regions, invagination of the axon by the inner tongue of the myelin sheath, myelin debrin in both axon and Schwann cells, and disruption of outer myelin lamellae. Such changes have been seen previously in various types of neuropathy and are not pathognomonic of the Shiverer mutation. Despite the absence of myelin basic protein, the peripheral manifestations of this gene are relatively minor and probably not severe enough to compromise peripheral nerve function significantly.
Immunocytochemical localization of enkephalin and substance P in the dorsal tegmental nuclei in human fetal brain
Authors: Pickel Virginia M. , Sumal Khushdev K. , Reis Donald J. , Miller Richard J. , Hervonen Anti
Published: January 2005

The peroxidase‐antiperoxidase (PAP) technique is used to examine the localization of methionine [Met5]‐enkephalin and substance P in the dorsal tegmental nuclei of the human fetal brain. Specific antiserum to both peptides is immunocytochemically detectable in neuronal perikarya and varicose processes in the human dorsal tegmental nuclei at 17–21 weeks of gestation. However the two peptides show a differential distribution in the central versus peripheral portion of the nucleus. Enkephalin‐like immunoreactivity is primarily localized in perikarya along the peripheral borders of the tegmental nuclei, whereas substance P is present primarily in varicose terminals and a few perikarya in the more central portions. These findings suggest that substance P‐containing terminals in dorsal tegmental nuclei are probably derived from afferent axons and that enkephalin is present in intrinsic neurons.
Immunoperoxidase localization of glial fibrillary acidic protein in radial glial cells and astrocytes of the developing rhesus monkey brain
Authors: Levitt Pat , Rakic Pasko
Published: January 2005

Peroxidase‐antiperoxidase (PAP) immunohistochemical staining, utilizing a specific antibody to the glial fibrillary acidic protein (GFA), was employed to analyze gliogenesis in the central nervous system of rhesus monkeys ranging in age from embryonic day 38(E38) to birth (E165) and through the second postnatal month. All major subdivisions of the brain contain glial cells, recognized by the presence of dark brown horseradish peroxidase (HRP) reaction product. Neuronal elements are not stained with this immunocytochemical technique.

The first class of glial cell to appear during development are the radial glial cells; the radial glial fibers fan out from the ventricular and subventricular zones, where their cell bodies reside, to the pial surface where they terminate with conical endfeet. These glial cells appear within the first third of gestation, being present in the spinal cord and brainstem by E41; in the diencephalon by E45; and in the telencephalon and cerebellum by E47. The next class of glia to appear is the Bergmann glial cell of the cerebellar cortex, which can be stained by E54. Bergmann glial cells located below the Purkinje cell layer issue parallel processes which extend up to the pial surface. Within each major subdivision of the brain, massive numbers of elongated glial fibers continually alter their distinctive patterns to maintain constant ventricular‐pial surface relationships during the major tectogenetic changes which occur throughout embryonic development. In Nissl‐counterstained sections columns of migrating neurons are observed juxtaposed to GFA‐positive radial and Bergmann glial fibers.

Radial glial cells assume a variety of transitional forms during the process of their transformation into mature astrocytes. This transformation occurs in each structure at specific embryonic ages and is initiated after neuronal migration has begun to subside. The number of astroglial cells increases at an accelerated pace after neurogenesis is complete.

The immunohistochemical localization of radial glial fibers at relatively early stages of embryonic development indicates that glial cells are present concomitantly with neurons, raising the possibility that at least two distinct populations of cell precursors compose the proliferative zones. Furthermore, the demonstration of large numbers of radial glial cells in all brain regions during the peak of neuronal migration and a close structural relationship between elongated glial fibers and migrating neurons support the concept that glia play a significant role in the guidance and compartmentalization of neuronal elements during development.
Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry: II. Correlative distribution of catecholamine varicosities and magnocellular neurosecretory neurons in the rat supraoptic and paraventricular nuclei
Authors: Mc Neill Thomas H. , Sladek John R.
Published: January 2005

The comparative morphology of catecholamine (CA) varicosities and neurophysin (NP)‐containing perikarya of the supraoptic (SON) and paraventricular nuclei (PVN) was examined. The major CA innervation to the SON and PVN did not coexist with the major distribution of magnocellular perikarya, but was located peripheral to the nuclei. A dense distribution of CA varicosities was found ventral to the neurosecretory perikarya of the SON and overlapped numerous immunoreactive oxytocin‐ and vasopressin‐containing neuritic profiles. Examination of Golgi‐stained sections revealed that dendrites from SON perikarya projected to the CA zone and were likely candidates for the processes identified immunocytochemically. In addition, a heterogenous distribution of axosomatic contacts was found within the SON which suggested a preferential innervation of VP‐containing neurons. The densest concentration of CA varicosities in the PVN occurred in the periventricular region adjacent to the third ventricle and in the contiguous parvocellular portion of the PVN. These CA varicosities overlapped scattered oxytocinerigic perikarya in both areas. In addition the ventromedial as well as the dorsolateral subnuclei of the PVN were contacted by CA varicosities; this heterogeneous distribution suggests that the each subnucleus of the PVN with its individual hypothalamic, neurohypophyseal, brainstem, or cortical projections may possibly receive a catecholaminergic innervation by a select group of CA cells or nuclear groups from the brain stem.