bluuebunny/crossref_metadata_2025 huggingface dataset:
Shape and distribution of an unusual retinal neuron
Authors: Sandell Julie H. , Masland Richard H.
Published: January 2005

Rabbit retinas were exposed to exogenous indoleamines and fixed with mixed aldehydes. The indoleamines were accumulated by two types of amacrine cell and by an unusual cell (type 3) that branches widely in both plexiform layers. The type 3 cells were studied after immunohistochemistry, photooxidation of the fluorescent label, or injection with Lucifer Yellow. Their cell bodies are located at the scleral margin of the inner nuclear layer. The cells' arbors in the outer plexiform layer range from 800 to 1,500 μm in diameter. A descending process crosses the inner nuclear layer and branches in layer 5 of the inner plexiform layer. The arbor in the inner retina can exceed 500 μm in diameter.

The distribution of type 3 cells was mapped in a series of retinal whole mounts. The number of type 3 cells ranged from 58 to 270 in different retinas. In two retinas from a single animal, however, it was virtually identical. Type 3 cells are concentrated in the region ventral to the visual streak, so that large areas of the retina are not covered by any type 3 cell. Because of their incomplete retinal coverage and variable number from animal to animal, the type 3 cells appear to be developmental anomalies. Paradoxically, their generation must be precisely controlled because of the numerical symmetry between an individual animal's two eyes.
Distribution of corticotropin‐releasing factor in the cerebellum and precerbellar nuclei of the opossum: A study utilizing immunohistochemistry, In situ hybridization histochemistry, and receptor autoradiography
Authors: Cummings Sharon L. , Young W. Scott , Bishop Georgia A. , King James S. , De Souza Errol B.
Published: January 2005

This study reports (1) a nonhomogeneous distribution of three morphologically distinct, corticotropin‐releasing factor (CRF)‐immunoreactive axonal phenotypes within the cerebellum of the opossum: climbing fibers, mossy fibers, and beaded fibers within the ganglionic plexus; (2) the existence of CRF binding sites within the cerebellar cortex; and (3) the distribution of CRF‐containing neurons in brainstem precerebellar nuclei identified with immunohistochemistry and in situ hybridization histochemistry. CRF‐immunoreactive climbing and/or mossy fibers were identified within all cerebellar lobules. The density of CRF‐immunoreactive fibers was greatest in the vermis, where longitudinal bands of intensely immunoreactive climbing and mossy fibers were interspersed with regions containing fibers demonstrating lower levels of immunolabeling. CRF‐immunoreactive fibers were present within all deep cerebellar nuclei. The topography of CRF‐containing cerebellar fibers is discussed with respect to possible sites of origin within the brainstem. CRF‐immunoreactive neurons were identified in all nuclei of the inferior olivary complex, although the number and intensity of immunostaining of CRF‐containing cells varied within and among individual nuclei. CRF‐immunoreactive somata were also present in brainstem nuclei known to give rise to cerebellar mossy fibers. In situ hybridization histochemistry utilizing an 35S‐labeled synthetic 48‐base oligodeoxynucleotide complementary to amino acids 22–37 of rat CRF proper revealed that CRF mRNA is transcribed in precerebellar nuclei. Variation in the level of CRF mRNA was detected among inferior olivary nuclei, in correspondence with variations detected in the levels of immunostaining. Data from this study suggest that variation in the level of CRF immunoreactivity detected within cerebellar afferent fibers may correlate with the level of CRF mRNA within cell bodies of origin of the projections. In vitro receptor autoradiography, utilizing 125I‐Tyro‐ovine CRF, revealed correspondence between CRF binding sites and CRF‐immunoreactive fibers in the cerebellar cortex. Results of this study support suggestions for CRF‐mediated circuitry in the cerebellum.
Localization of vasoactive intestinal peptide‐ and peptide histidine isoleucine amide‐like immunoreactivities in the rat superior cervical ganglion and its nerve trunks
Authors: Sasek Cathrine A. , Zigmond Richard E.
Published: January 2005

Electrical stimulation of the preganglionic cervical sympathetic trunk causes an increase in dopa synthesis in the postganglionic neurons in the superior cervical ganglion (SCG). This transsynaptic biochemical effect can be blocked only partially by cholinergic antagonists, suggesting the involvement of a noncholinergic preganglionic sympathetic neurotransmitter(s). A survey of a large number of possible candidates for this neurotransmitter revealed that, in addition to cholinergic agonists, only a small group of peptides (all members of the secretin‐glucagon family) stimulated dopa synthesis in the SCG. The effective peptides included vasoactive intestinal peptide (VIP), peptide histidine isoleucine amide (PHI), and secretin. Consequently we looked for the presence of immunoreactivities for these three peptides in the SCG.

VIP‐ and PHI‐like immunoreactive fibers were found in the SCG and in its major pre‐ and postganglionic nerve trunks. The distributions of the two immunoreactivities were very similar. Immunoreactive fibers were seen both singly and in bundles. In some instances, fibers were found apposed to neuronal cell bodies in the ganglion, and occasionally dense plexuses of fibers were found surrounding the neurons. In addition, punctate immunoreactive profiles were found apposed to the neurons in what appeared to be terminal fields. A small number of immunoreactive neuronal cell bodies were also seen in the ganglion. In a few instances, it was possible to establish, in serial sections, that the same cell body was immunostained with both VIP and PHI antisera. No secretin like‐immunoreactive fibers or cells were observed. The presence of VIP‐like and PHI‐like‐immunoreactive fibers in the cervical sympathetic trunk and in the SCG strengthens the possibility that these peptides, or a related molecule(s), serve as preganglionic neurotransmitters in this ganglion.
Ultrastructural analysis of dynorphin B–immunoreactive cells and terminals in the superficial dorsal horn of the deafferented spinal cord of the rat
Authors: Cho Hee Jung , Basbaum Allan I.
Published: January 2005

Light microscopic studies have demonstrated important differences in the distribution of enkephalin and dynorphin cells and terminals in the dorsal horn. Most importantly, dynorphin neurons are located in regions almost exclusively associated with the transmission and/or control of nociceptive messages (laminae I, IIo, and V); enkephalin neurons, although located in the same regions, are also found in areas involved in the transmission of nonnociceptive messages, e.g., laminae IIi and III. To determine whether there are also differences in the synaptic organization of the two opioid peptides, we have examined the distribution of dynorphin B immunoreactivity at the ultrastructural level. The studies were performed in colchicine‐treated rats that underwent dorsal rhizotomy so that the relationship of dynorphin terminals and cells to primary afferent terminals could be established.

Dynorphin B–immunoreactive cell bodies and dendrites in laminae I and IIo receive convergent primary and nonprimary afferent input, which suggests that dynorphin neurons receive a small‐diameter, nociceptive input. Dynorphin terminals predominantly contain round, agranular vesicles; some terminals also contain a few dense core vesicles. Most dynorphin terminals are presynaptic to unlabelled dendrites; both asymmetric and symmetrical axonal contacts were noted. Dynorphin‐immunoreactive boutons are also presynaptic to unlabelled cell bodies and spines. Twenty‐nine percent of dynorphin terminals were associated with axonal profiles, including degenerating primary afferent terminals; only rarely could a synaptic density be detected. Although some degenerating primary afferent terminals were clearly presynaptic to dynorphin‐immunoreactive terminals, in most cases, the polarity of the relationship between primary afferents and dynorphin terminals could not be established.

These data indicate that synaptic interactions made by and with dynorphin‐immunoreactive cells and terminals in the superficial dorsal horn are not very different from those that were previously reported for enkephalin cells and terminals. Thus, it is unlikely that dynorphin terminals provide a significant presynaptic input to primary afferent fibers. On the other hand, the presence of a primary afferent input to dynorphin cell bodies and dendrites in the superficial dorsal horn suggests that dynorphin cells receive a direct input from small‐diameter, nociceptive primary afferents. That connection might contribute to the increased levels of dynorphin message and peptide that have been reported in rats experiencing a chronic inflammatory condition. The possibility that dynorphin neurons are associated more with the transmission than the control of nociceptive messages is discussed.
Further evidence for excitatory amino acid transmission in lamprey reticulospinal neurons: Selective retrograde labeling with (3H)D‐aspartate
Authors: Brodin Lennart , Ohta Yoshihiro , Hölkfelt Tomas , Grillner Sten
Published: January 2005

The distribution of radiolabeled neurons in the brain stem of Lampetra fluviatilis was studied following unilateral injections of (3H)D‐aspartate in the rostral spinal cord. After survival periods of 1–3 days, labeled perikarya were present within and nearby the posterior, middle, and anterior rhombencephalic reticular nuclei and in the mesencephalic reticular nucleus. The highest number of (3H)D‐aspartate labeled cell bodies were present in the posterior rhombencephalic reticular nucleus. The labeled reticulospinal neurons were distributed mainly ipsilateral to the injection site and included the giant Müller cells as well as medium‐sized and small neurons. Contralateral labeling occurred in cell bodies scattered along the lateral margin of the rhombencephalic reticular formation, the most rostral of these contralaterally projecting neurons being the Mauthner cell. The (3H)D‐aspartate labeling correlates with previous electrophysiological studies showing that lamprey reticulospinal neurons utilize excitatory amino acid transmission.
Gap junction protein in rat hippocampus: Light microscope immunohistochemical localization
Authors: Yamamoto T. , Shiosaka S. , Whittaker M. E. , Hertzberg E. L. , Nagy J. I.
Published: January 2005

An affinity‐purified antibody against a 27‐kD rat liver gap‐junctional protein (GJP) was used to determine the distribution of GJP immunoreactivity in section of rat hippocampus. Four heterogeneously distributed GJP‐immunostaining patterns were observed. The two most common were punctate immunoreactive elements ranging in size from 0.3 to 0.7 μm and networks of immunoreactive varicose fibers coursing in a variety of directions within the various hippocampal layers and ranging in length from a few microns up to 200 μm. The density of punctate immunostaining was highest within a portion of the stratum pyramidale, at the border between the stratum pyramidale and stratum oriens, and at the border between the molecular and granule cell layers of the dentate gyrus. Moderate to low densities were observed in other hippocampal areas. Immunoreactive fibers were most concentrated within the border portions of the stratum pyramidale and oriens, moderately distributed in the stratum radiatum and the remaining part of the stratum oriens, and sparse in the alveus. In the dentate gyrus, fiber networks were most evident at the border between the granule cell and molecular layers and very unevenly distributed in the molecular layer. The two other patterns observed included intense filamentous immunostaining within a small number of neuronal perikarya located mainly in the stratum pyramidale of areas CA2 and CA3, but rarely in area CA1 or the dentate gyrus, and diffuse immunostaining of small cell bodies dispersed throughout the hippocampus but most numerous in the vicinity of the stratum pyramidale and in the alveus. All of these immunostaining patterns were seen at all rostrocaudal hippocampal levels. These results suggest that if GJP‐immunoreactive fibers and neurons observed in the hippocampus have the capacity to form gap junctions, then electrotonic transmission may constitute an important means of information processing within this structure.
Spinocerebellar projections from the upper lumbar segments in the cat, as studied by anterograde transport of wheat germ agglutinin‐horseradish peroxidase
Authors: Yaginuma Hiroyuki , Matsushita Matsuo
Published: January 2005

The projection fields of the dorsal spinocerebellar tract (DSCT) arising from Clarke's column, marginal neurons of Clarke's column, and lamina V neurons in the upper lumbar segments were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) in the cat. To label only these neuron groups with uncrossed ascending axons, the spinal cord was lesioned rostral and contralateral to the WGA‐HRP injections.

Following injections of WGA‐HRP into the L1‐L4 segments, labeled terminals were seen in sublobules Ia‐VIc and VIIb‐VIIIb, the simple lobule, the paramedian lobule, and the dorsal paraflocculus. About 70–80% and 20–30% of the total number of labeled terminals were in the anterior and the posterior lobe, respectively; the projections were predominantly ipsilateral to the cells of origin (about 87% or more labeled terminals of the total number in each of sublobules IIb‐Va). The labeled terminals were abundant in sublobule IIb (6–11%), lobule III (12–27%), and sublobules IVa (14–17%) and IVb (14–21%). In the mediolateral extent of the lobules in the anterior lobe, the labeled terminals were most numerous between 1.1 and 3.0 mm lateral to the midline (45–75% of the total number of labeled terminals on the ipsilateral side). In the posterior lobe labeled terminals were numerous in sublobule VIIIb (13.6%) and sublobule C of the paramedian lobule (15–19%).

The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross sections through each lobule. In the anterior lobe the labeled terminals were distributed in eight major areas. In sublobules IIb‐III, areas 1–3 were located within 1.0 mm of the midline in zone A of Voogd; areas 4–6, between 1.0 and 2.5 mm lateral to the midline in zones B‐C1; and areas 7 and 8, lateral to 3.0 mm from the midline in zones C2 and C3. Areas 1–6 extended apicobasally in the middle part of the lobules. In sublobule VIIIb projections were confined to three longitudinal areas whereas in the paramedian lobule the projection areas were less distinct.

The projection pattern of the lumbar DSCT was different from that of the thoracic DSCT reported previously. In the anterior lobe the thoracic DSCT projects to five areas in the medial (zone A) and the lateral part (zone B) of the vermis and to four areas in the intermediate region of the hemisphere (zones C1‐C3).
Localization of atrial natriuretic factor (ANF) binding sites in the central nervous system of the frog
Authors: Tong Yiai , Netchitaïlo Pierre , Leboulenger Françlois , Vaudry Hubert , Pelletier Georges
Published: January 2005

The distribution of atrial natriuretic factor (ANF) binding sites was investigated in the central nervous system of the frog Rana ridibunda using the technique of in vitro receptor autoradiography by means of [125I]‐labeled ANF‐28. The anatomic distribution of ANF recognition sites was determined on Kodak ARX films apposed onto tissue sections, and their distribution was examined in greater detail by analysis of autoradiograms generated by using emulsion‐coated sections. The highest levels of ANF binding sites were found in the olfactory bulb, the dorsal pallium, the septum, the habenular nucleus, the dorsal infundibular nucleus, the interpeduncular nucleus, and in the tectum. Moderate levels of ANF binding sites were observed in the thalamus and throughout the mesencephalon, whereas low levels were detected in the lateral and medial pallium, the medial forebrain bundle, and the nucleus rotondus. In the pituitary gland, the neural and distal lobes were densely loaded with ANF binding sites, whereas no autoradiographic labeling was observed in the pars intermedia. In general, there was a good correlation between the location of ANF receptors and the distribution of ANF‐containing neurons, as previously determined by immunocytochemistry. Together these results support the view that ANF may act as a neurotransmitter or a neuromodulator in various regions of the frog brain.
Serotoninergic neurons in the retina of Xenopus laevis: Selective staining, identification, development, and content
Authors: Frederick Jeanne M. , Rayborn Mary E. , Hollyfield Joe G.
Published: January 2005

Uptake of 3H‐serotonin followed by autoradiography, and uptake of the serotonin analog 5,7‐dihydroxytryptamine (5,7‐DHT), with subsequent staining, were each used to define a unique set of neurons in the retina of the African clawed frog, Xenopus laevis. Both techniques demonstrated the same population of neurons, on the basis of perikaryal size, shape, and position within the retina. Two classes of amacrine cells accumulated 5,7‐DHT at the proximal (vitread) margin of the inner nuclear layer; the two classes were distinguished by the size of their perikarya. Two similar populations of cells, observed in the ganglion cell layer with lower frequency, may represent “displaced” counterparts of these two amacrine cell types. A class of bipolar cells whose perikarya were located in middle‐to‐distal regions of the inner nuclear layer also accumulated 5,7‐DHT and 3H‐serotonin. Processes of these cells contributed to a dense plexus of fine fibers that appeared evenly distributed throughout the inner plexiform layer. 3H‐Serotonin‐accumulating cells first appeared in the developing retina at stage 35/36, a time immediately after retinal stratification but before elaboration of either plexiform layer. Electron microscopic analysis permitted an identification of 3H‐serotonin‐accumulating terminals in the inner plexiform layer. Serotonin‐labeled terminals containing conventional contacts, suggestive of amacrine cells, were presynaptic to unidentified processes and postsynaptic to bipolar cells. Labeled terminals containing ribbon contacts, indicative of bipolar cells, were postsynaptic to amacrine cells. The amount of serotonin contained in isolated retinas was 15 pmol/mg protein as measured by HPLC with electrochemical detection. We attempted to stimulate the release of accumulated 3H‐serotonin from mature retinas by increasing the K+‐concentration in the bathing medium. Although preloaded glycine is readily released from 14C‐glycine‐accumulating neurons, from the same retinas there was no calcium‐dependent, K+‐stimulated release of 3H‐serotonin. This finding suggests that serotonin and glycine are processed differently by retinal neurons, the consequence of which results in differing responses to 40 mM K+.
Gustatory innervation in the rabbit: Central distribution of sensory and motor components of the chorda tympani, glossopharyngeal, and superior laryngeal nerves
Authors: Hanamori Takamitsu , Smith David V.
Published: January 2005

Although rabbits have been used extensively in neurophysiological studies of the gustatory system, there is little information about the anatomical organization of taste in this species. Afferent and efferent central connections of three nerves innervating oral or laryngeal taste buds in the rabbit, including the chorda tympani (CT), the lingual‐tonsillar branch of the glossopharyngeal (IX), and the superior laryngeal nerve (SLN), were traced by means of horseradish peroxidase neurohistochemistry. After entering the brainstem, most afferent fibers of CT, IX, and SLN turned caudally in the solitary tract, with fibers of the CT terminating in the nucleus of the solitary tract from 1.0 mm rostral to 3.8 mm caudal to the caudal border of the dorsal cochlear nucleus. There was terminal label from the CT also in the principal trigeminal nucleus. Preganglionic parasympathetic cell bodies of the superior salivatory nucleus were labeled retrogradely in the reticular formation ventral to the rostral pole of the solitary nucleus. Afferent fibers of the IXth nerve terminated in the solitary nucleus from 0.6 mm rostral to 5.0 mm caudal to the caudal border of the dorsal cochlear nucleus. There were also labeled terminals in the principal trigeminal nucleus and in all three divisions of the spinal trigeminal nucleus. Cell bodies composing the inferior salivatory nucleus were labeled in and around the solitary nucleus and subadjacent reticular formation just rostral to the caudal border of the dorsal cochlear nucleus. There were also a few lightly labeled cells within the nucleus ambiguus at its most rostral extent. Afferent fibers of the SLN terminated in the solitary nucleus from 1.2 to 6.8 mm caudal to the dorsal cochlear nucleus. There was also some terminal label in the intermediate and caudal divisions of the spinal trigeminal nucleus. Many cells were retrogradely labeled in the nucleus ambiguus following application of HRP to the SLN and a few cells were labeled in and around the solitary nucleus just caudal to the dorsal cochlear nucleus. These three nerves show an overlapping rostral to caudal distribution of afferent input within the nucleus of the solitary tract that may be related to their gustatory and visceral functions.
Brainstem projections to the rat cuneate nucleus
Authors: Weinberg Richard J. , Rustioni Aldo
Published: January 2005

Neurons in the pontomedullary tegmentum have been proposed as a final common pathway subserving descending inhibition in the dorsal column nuclei. To investigate the anatomical substrate for these descending effects, brainstem projections to the cuneate nucleus of rats were studied with injections of lectin‐conjugated horseradish peroxidase. In rats with iontophoretic tracer injections in this nucleus, many labeled neurons were detected near the injection site, especially ventral and caudal to it. Intrinsic reciprocal projections were observed after injections in caudal, middle, or rostral levels of the cuneate nucleus. Neurons were labeled in the red nucleus, in agreement with previous anatomical studies, and also in the trigeminal, vestibular, and cochlear nuclei. An ipsilateral dorsomedial group of neurons was labeled in the upper cervical segments and scattered neurons were also labeled bilaterally near the central canal. Sparse retrograde labeling in the tegmetum was focused in the lateral paragigantocellular nucleus and caudal raphe. Consistent with the retrograde experiments, anterograde labeling after pressure injections of lectin‐conjugated horseradish peroxidase in the pontomedullary tegmentum was very sparse within the dorsal column nuclei; labeling was dense, however, in the region immediately ventral to these nuclei.

These results confirm previous work indicating that the activity of cuneate neurons is modulated by brainstem sensory nuclei. However, it appears that direct projections to the cuneate nucleus from pontine and rostral medullary regions are sparser than previously suggested. The last link of a polysynaptic descending inhibitory pathway may include GABAergic neurons immediately adjacent to the dorsal column nuclei and/or intrinsic to these nuclei.
Structural and functional properties distinguish two types of multipolar cells in the ventral cochlear nucleus
Authors: Smith Philip H. , Rhode William S.
Published: January 2005

We distinguish two types of large multipolar cells designated sustained (Cs) and onset (Oc) choppers in the anterior posteroventral cochlear nucleus (A‐PVCN)/nerve root region on the basis of certain anatomical and physiological features. Cs axons head into the trapezoid body, while Oc axons use the intermediate acoustic stria of Held. At the electron microscopic (EM) level, collateral terminals of Oc axons contain pleomorphic vesicles; Cs terminals contain small round vesicles. Cs dendritic trees tend to be distributed in a stellate fashion while Oc dendritic trees tend to be elongated. At the EM level the sustained chopper somata are sparsely innervated while the proximal dendritic tree receives considerably more input. The Oc somata are highly innervated and this heavy innervation continues out onto the proximal dendrites. Distally the dendritic innervation falls off considerably for both categories. Physiologically, members of the Oc population have wider dynamic ranges at the characteristic frequency (CF), wider response areas that are typically not flanked by inhibitory sidebands, and responses to short tones that do not show the same form of regularity expressed by sustained choppers. Intracellularly the sustained choppers exhibit sustained depolarization to short tones for the duration of the stimulus with resultant regular spiking at a rate that is stimulus level dependent. The response to swept tone shows this same level‐dependent regularity. In response to tones, the Oc cells also show a sustained depolarization whose amplitude is stimulus‐level dependent but whose range is much greater and whose onset is initiated more abruptly. Although the onset component of the Oc spike output is reliably initiated by these levels of depolarization, regular firing to the sustained depolarization is not initiated at levels of depolarization that would surely generate regular firing in sustained choppers. This regularity is also absent in the swept tone response despite marked levels of excitation.
Axonal redirection at the dorsoventral intraretinal boundary
Authors: Springer Alan D. , Morel Kimberly D. , Grobman Steven L. , Wilson Bryan R.
Published: January 2005

Cobaltous‐lysine applied to the goldfish optic nerve backfilled retinal ganglion cells and their axons. Confined to the ventronasal and ventrotemporal retina was a small population of retinal ganglion cells whose axons traveled dorsally and parallel to the retinal margin. On reaching the boundary between dorsal and ventral retina, the axons arched, joined radially oriented bundles of axons, and traveled toward the optic disk. Control studies showed that the axons came from retinal ganglion cells rather than from retinopetal cells. The somatic area of retinal ganglion cells (RGCs) with circumferential axons was 30–50 μm, and was similar to that of average ganglion cells. The axons of these cells coursed between the optic fiber and ganglion cell layers or between the ganglion cell and inner plexiform layers. Many somata were displaced slightly toward the inner plexiform layer, but were not really displaced ganglion cells. The aberrant axonal trajectory may be related to the slightly displaced location of the cell. However, ganglion cells that are displaced to the edge of the inner nuclear layer usually have radially coursing axons.

We digitized the coordinates of the bending points and the dorsoventral retinal boundary. On average, the bending points occurred within 100 μm of the dorsoventral retinal border. These findings suggest that some molecular, rather than mechanical, factor at the dorsoventral retinal boundary alters the course of the circumferential axons. Furthermore, because there are cells with circumferential axons throughout the ventral retina, the data imply that at least ventral RGC axons avoid mingling with the axons from dorsal RGCs.
Pathfinding and target selection of goldfish retinal axons regenerating under TTX‐induced impulse blockade
Authors: Hartlieb Elke , Stuermer Claudia A. O.
Published: January 2005

To define the extent to which impulse blockade interferes with the morphological changes of regenerating retinal axons during their growth through the tectum, axons were deprived of activity by repeated intraocular injections of TTX. At intervals between 24 and 189 days after optic nerve section (ONS), a defined group of TTX‐silenced axons and of axons with normal activity (controls) were labeled by applications of HRP to the ventro‐ or dorsotemporal retina. The trajectories of these labeled axons were traced in DAB processed tectal wholemounts.

As in controls, TTX‐blocked axons went through a phase of exploratory growth at early regeneration stages (24 to 80 days after ONS). Coursing in abnormal routes, the axons initially distributed their growing endings widely over the tectum. Axons with and without activity extended side branches with growth cones and filopodia over all regions of the tectum. These ramifications were of similar dimensions for the TTX‐blocked and control axons. Despite abnormal routes and branching over inappropriate territories, axons showed a preference for the rostral tectum. At late regeneration stages (120–189 days after ONS), axons had lost their side branches and their growth cones. Their preterminal segments exhibited striking bends, suggesting that they had undergone course corrections to achieve access to the retinotopic target. Axonal processes had disappeared from the caudal tectum, and the preferential accumulation of axons over the rostral tectum had increased. The majority of the TTX‐blocked and control axons ended in terminal arbors at retinotopic regions. The labeled arbors of the TTX‐group were no larger than those of the control group. The arbors of each group lay close together in a continuous cluster in the TTX‐group as well as in two‐thirds of the control group. In the other one‐third of the control group, however, terminal arbors were aggregated into separate patches. The clusters of the TTX‐blocked axons covered between 2.2 and 3.9% (mean 2.95%) of the tectal surface and the clusters and/or patches of active axons between 1.9 and 3.4% (mean 2.7%). Thus the terminal arbor clusters of the TTX‐silenced axons were not significantly larger than those of the active axons.

These data show that retinal ganglion cell impulse activity is required for neither the extension of side branches in the early exploratory phase of regeneration nor for the withdrawal of these branches nor for the establishment of target‐directed routes and the deployment of normal‐size terminal arbors at retinotopic loci. Our data further suggest that the retinotopic map is refined considerably with time even in the absence of activity, a finding that is consistent with an abstract by Olsson and Meyer ('87).
Early expression of acetylcholinesterase activity in functionally distinct neurons of the zebrafish
Authors: Hanneman Eric , Westerfield Monte
Published: January 2005

The first expression and distribution of acetylcholinesterase (AChE) activity was studied among a distinct population of early neurons in embryonic zebrafish by using histochemical and retrograde labeling techniques. AChE first appeared in the nervous system in the primary motoneurons of the rostral spinal cord when the embryo had nine somites, approximately 14 hours postfertilization. Subsequent expression of AChE activity in the spinal cord proceeded in a rostral‐to‐caudal sequence. Cranial neurons expressed AChE activity shortly after it appeared in the rostral spinal cord. Several hours later, near the end of the first day, primary neurons in the hindbrain and spinal cord all contained AChE, including sensory neurons, reticulospinal interneurons, and primary motoneurons. AChE activity was also detected in the nucleus of the medial longitudinal fasciculus. Presumptive cranial ganglia transiently expressed AChE activity between 14 and 24 hours of development. These results, combined with previous observations that examined the time of origin and axogenesis of primary neurons, suggest that primary neurons in the embryonic zebrafish contain AChE before they sprout axons. The primary neurons appear to follow a common sequence of development consisting of a withdrawal from the cell division cycle, the expression of AChE, and axogenesis. Although this sequence is followed by all primary neurons, lack of a rostral‐to‐caudal sequence in the time of birth and variability in the time of axon outgrowth demonstrate that the relative timing of these three events is not rigidly programmed in individual neurons. Moreover, the very early expression of AChE in such diverse cell types suggests that it may have a developmental role in addition to its function in transmitter metabolism.
Duration of retinogenesis: Its relationship to retinal organization in two cricetine rodents
Authors: Wikler Kenneth C. , Perez G. , Finlay B. L.
Published: January 2005

The Mongolian gerbil (Meriones unguiculatus) has a prolonged period of development relative to other muroid rodents. We have explored the consequences of this relatively long period of maturation on retinal cell number and topography by comparing the duration and topography of neurogenesis in the gerbil retina with that of a closely related species which develops rapidly, the Syrian hamster (Mesocricetus auratus) (Sengelaub et al.: J. Comp. Neurol. 246:527–543, 1986). An analysis of thymidine‐labeled retinas indicate that cells destined for the gerbil retinal ganglion cell layer are generated for at least 12 embryonic days, twice the duration in the hamster. The period of cell loss in the gerbil retinal ganglion cell layer extends for at least 14 postnatal days, more than twice as long as in the hamster. The gerbil retina is generated in a center‐to‐periphery gradient for both retinal ganglion cells and displaced amacrine cells, while no such gradients are evident in the hamster retina. We conclude that the longer developmental period of the gerbil is associated with (1) a longer period of neurogenesis resulting in greater retinal cell number, (2) the expression of spatial gradients in neurogenesis, and (3) a larger eye at maturity. The last two factors, in part, may be related to the development of a highly differentiated area centralis and visual streak in the retina of this rodent.

Unrelated to duration of growth, early differences in retinal shape between these two species contributes to the development of retinal topography. The gerbil, but not the hamster retina, is initially asymmetric, longer in its nasotemporal than its dorsoventral dimension. The gerbil retina then grows asymmetrically producing a spherical retina, and coincident in time, a nasotemporally extended visual streak.
Type B monoamine‐oxidase‐containing cells and fibers in the cat hypothalamus demonstrated by an improved enzyme histochemical method
Authors: Kitahama Kunio , Sallanon Marcelle , Lin Jian‐Sheng , Maeda Toshihiro , Jouvet Michel
Published: January 2005

The present study, using a diaminobenzidine (DAB)‐coupled peroxidation method, examined the distribution and morphological characteristics of neuronal structures containing type B monoamine oxidase (MAO‐B) in the cat hypothalamus. Large and intensely stained, distinctive MAO‐B‐positive cells, multipolar and with long dendritic arbors, were principally distributed in the ventral hypothalamus extending from A7 to A12.5 of the Horsley‐Clarke plane. These cells were located caudally in the ventral surface of the brain including the tuberomamillary nucleus (TM) and the region surrounding the mamillary nuclei. Rostrally, they were aggregated in the area surrounding the fornix, particularly in the lateral perifornical region, and dispersed in the anterior mamillary nucleus, lateral hypothalamic area (HLA), and the medial tip of the entopeduncular nucleus. The most rostral positive cell group was identified in a narrow space between the optic tract and the entopeduncular nucleus at the A12.5 level.

In addition to these large cells, the present study disclosed the presence of “small” to “very small” MAO‐B‐positive cells in the area surrounding the mamillary recess and the lateral part of the caudal arcuate nucleus.

Distinct MAO‐B‐stained fibers were identified in all regions of the hypothalamus. A large number of thick labeled fibers were observed in the ventral hypothalamus including the TM and premamillary nucleus and posterior and lateral hypothalamic areas. A dense network of MAO‐B‐positive terminal‐like fibers was observed in the dorsomedial nucleus where very small labeled cells were scattered. Many intensely stained thick and straight fibers were seen running ventrolaterally in the anterior part of the HLA and in the narrow space between the entopeduncular nucleus and optic tract. In the area of the tuber cinereum and the ventral part of the HLA, there were many positive fibers cut transversely, possibly projecting to the more anterior parts of the brain such as the diagonal band of Broca or septal nuclei.
Biochemical and immunocytochemical charaterization of olfactory marker protein in the rodent central nervous system
Authors: Baker Harriet , Grillo Mary , Margolis Frank L.
Published: January 2005

Olfactory marker protein (OMP), previously thought to be expressed only by olfactory receptor neurons and their processes, was localized anatomically with immunocytochemical techniques to a number of brain regions in three rodent species, the mouse, rat, and hamster. In addition, the amount of antigen was quantified by radioimmunoassay (RIA) and characterized by an immunoblot procedure. In all three species the antigen could be detected immunocytochemically in the preoptic region and hypothalamus. The rat did not exhibit immunostaining in any other brain region. However, in the mouse neuronal labelling was observed throughout the neural axis, including cellular labelling in the bed nucleus of the anterior commissure, the median preoptic nucleus, the bed nucleus of the stria terminalis, the periventricular region, the anterior parvicellular subnucleus of the paraventricular nucleus, around the dorsomedial hypothalamic nucleus (pars compacta), the subincertal region, the arcuate nucleus, the anterior cortical nucleus of the amygdala, the suprageniculate nucleus, the lateral lemniscal nuclei, the lateraldorsal and lateralventral central gray, the posterior aspects of the commissural and marginal nuclei of the inferior colliculus, the paragenule nucleus, the A‐5 region, the area postrema, the ventromedial nucleus of the solitary tract, area X, the spinal trigeminal nucleus (pars zonale), and superficial laminae of the spinal cord. The hamster displayed a different pattern of labelling including cells in the periventricular gray, the pontine reticular tegmental nucleus, the A‐5 region, the medial vestibular complex, the prepositus hypoglossal nucleus, the parvicellular reticular nucleus, the lateral paragigantocellular nucleus, the raphe obscuras, the lateral reticular nucleus, and the lateral nucleus of the cerebellum. Immunostaining was seen in fibers within the red nucleus and within mossy fibers of the cerebellum. OMP levels could only be quantified by radioimmunoassay in the olfactory bulb of the three species and in the hamster cerebellum where they were 1/1,000 of those determined in the olfactory bulb. The authenticity of OMP measured in the RIA and detected immunocytochemically was verified by a double‐antibody immunoisolation/immunodetection procedure, which confirmed that the antigen being visualized had the molecular properties expected for OMP. In summary, these experiments demonstrate that authentic OMP exists in small groups of neurons in many areas of the central nervous system.
Comparative study of neuronal and glial gap‐junctions in crayfish nerve cords
Authors: Bosch Elizabeth
Published: January 2005

Electrical synapses (neuronal gap‐junctions) and glial gap‐junctions were compared by using thin sectioning, freeze fracturing, and negative staining techniques. Neuronal and glial gap‐junctions differed in the length of the extracellular domains of the channels, in the presence of a cytoskeleton associated to neuronal gap‐junctions, and in their unit cell dimenstions. The difference in length of the channels and the fact that both glial and neuronal gap‐junctions had the same particle diameter suggest that the proteins forming glial and neuronal gap‐junctions might have different molecular weights.

The cytoskeleton associated to neuronal gap‐junctions consisted of a beaded layer of densities located parallel to the membrane in the synaptic regions. Synaptic vesicles associated to neuronal gap‐junctions were attached to this cytoskeleton, which was in turn anchored to the synptic membrane through densities about 20 nm apart, a spacing similar to the neuronal unit cell dimension. These results suggest that the cytoskeleton might be responsible for the association of vesicles to neuronal gap‐junctions and for maintaining the crystalline appearance of neuronal gap‐junctions in situ.
Ultrastructural and neurochemical analysis of synaptic input to trigemino‐thalamic projection neurones in lamina I of the rat: A combined immunocytochemical and retrograde labelling study
Authors: Priestley John V. , Cuello A. Claudio
Published: January 2005

The synaptology of lamina I thalamic projection neurones in the spinal trigeminal nucleus of the rat was investigated by combining electron microscopic immunocytochemistry with the retrograde transport of horseradish peroxidase. Fifteen retrogradely labelled neurones were serially sectioned and their dendrites were traced for up to 160 μm in order to characterise the synaptic input to their cell bodies and proximal dendrites.

Projection neurones receive synapses from dome‐shaped substance P and enkephalin immunoreactive terminals, which make simple axosomatic or axodendritic synapses. In addition, the cells receive synapses from numerous nonimmunoreactive terminals including a wide range of different domeshaped terminals and various scalloped or glomerular terminals. Domeshaped terminals synapse with small stubby spines in addition to cell bodies or dendritic shafts and they are probably derived from lamina II interneurones and from descending bulbospinal pathways. Glomerular terminals occur in two main classes: small type A terminals with dark axoplasm and larger type B terminals. Type B terminals participate in synaptic triads in which a peripheral terminal synapses both axoaxonically with the glomerular terminal and axodendritically with the projection neurone. Type A and type B terminals closely resemble the central terminals of spinal cord lamina II glomeruli and are probably derived from C and Aδ I° afferent fibers.

The results indicate that lamina I projection neurones are under pre‐ and postsynaptic control from diverse sources. Their complex synaptic organisation highlights the key role that such cells play in the rostrad transmission of somatosensory information.
Connections of primary auditory cortex in the new world monkey, Saguinus
Authors: Luethke L. E. , Krubitzer L. A. , Kaas J. H.
Published: January 2005

Connections of primary auditory cortex (A‐I) were investigated in the tamarin (Saguinus fuscicollis), a New World monkey. In each case, A‐I was defined by multiunit recordings, and best frequencies were determined for neurons at different recording sites. Microlesions were placed to mark recording sites for correlation with cortical architecture. Following mapping, separate injections of up to three different tracers (HRP‐WGA and fluorescent dyes) were placed into the representations of different frequencies within A‐I. The results support several conclusions: (1) high to low frequencies are represented in a dorsocaudal to ventrorostral sequence in A‐I, (2) intrinsic connections in A‐I are more pronounced along isofrequency contours, (3) the pattern of connections between A‐I and adjoining cortex suggests that this surrounding auditory cortex contains at least two tonotopically organized fields and possibly one or more additional auditory fields, (4) callosal connections of A‐I are largely between parts of A‐I matched for frequency representation, (5) thalamic connections of A‐I include topographic connections with the ventral division of the medial geniculate complex (MGv) and more diffuse connections with the medial (MGm) and dorsal (MGd) divisions of the medial geniculate complex and the suprageniculate nucleus (Sg), and (6) A‐I projects bilaterally to the dorsal cortex of the inferior colliculus.
Transient GABA immunoreactivity in cranial nerves of the chick embryo
Authors: von Bartheld Christopher S. , Rubel Edwin W.
Published: January 2005

The distribution and time course of γ‐aminobutyric acid (GABA) immunoreactivity was investigated in the cranium of the chick embryo from 2 to 16 days of incubation (E2–16). A fraction of nerve fibers transiently stains GABA‐positive in all cranial motor nerves and in the vestibular nerve. Cranial motor nerves stain GABA‐positive from E4 to E11, including neuromuscular junctions at E8–11; labeled fibers are most frequent in the motor trigeminal root (E6–9.5). Substantial GABA staining is present from E4 to E10 in a subpopulation (1–2%) of vestibular ganglion cells. Their peripheral processes are labeled in the vestibular endorgan, predominantly in the posterior crista. Some GABA‐positive fibers are present in the olfactory nerve (after E5) and in the optic nerve (after E9.5); their immunoreactivity persists throughout the period investigated. Transient GABA immunoreactivity follows “pioneer” fiber outgrowth and coincides with the formation of early synaptic contacts.

GABA‐containing neurons may change their neuronal phenotype (loss of GABA expression) or they may be eliminated by embryological cell death. Periods of cell death were determined in cranial ganglia and motor nuclei by aggregations of pycnotic cells in the same embryonic material. The periods of embryonic cell death partly coincide with transient GABA immunoreactivity. The function(s) of transient GABA expression is unknown. Some lines of evidence suggest that GABA has neurotrophic functions in developing cranial nerves or their target tissue. In the developing neuromuscular junction, GABA may be involved in the regulation of acetylcholine receptors.