bluuebunny/crossref_metadata_2025 huggingface dataset:
Specificity of filiform hair afferent synapses onto giant interneurons in Periplaneta americana: Anatomy is not a sufficient determinant
Authors: Blagburn Jonathan M. , Thompson Kevin S. J.
Published: May 2005

The synapses between the filiform hair sensory afferents and giant interneurons (GIs) 1–6 of embryonic and first instar cockroaches, Periplaneta americana, were used to investigate the role of neuronal anatomy in determining synaptic specificity. The pattern of afferent‐to‐GI synapses was first determined by intracellular recording of excitatory postsynaptic potentials (EPSPs). The lateral (L) axon synapses only with GIs 3, 4, and 6, while the medial (M) axon synapses with the contralateral dendrites of all six GIs but with the ipsilateral dendrites only of GIs 1, 2, and 4. The three‐dimensional anatomy of the filiform afferents and GIs was determined by injection of cobalt. There is little anatomical segregation of the filiform afferents; consequently, there is no correlation between the anatomy of the GIs and their synaptic inputs. The M axon and ipsilateral GI3 were studied in more detail by light and electron microscopy. Despite the presence of an anterior M axon branch which loops around the ipsilateral GI3 neurite at a distance of 2 μm, no synapses are formed between them. This lack of synapses is not due to the presence of physical barriers. Investigation of filiform afferents and GIs in embryonic ganglia shows that at no stage are the afferents sufficiently separated for their anatomy to be an important factor in determining the specificity of the synaptic inputs of the GIs. It was postulated that two pairs of complementary cell surface labels would be sufficient to code for this specificity, and that, in GIs 3, 5, and 6, spatial differences in the expression of these labels allow the M axon to distinguish ipsilateral dendrites from contralateral.
Contribution of brainstem GABAergic circuitry to descending antinociceptive controls: II. Electron microscopic immunocytochemical evidence of gabaergic control over the projection from the periaqueductal gray to the nucleus raphe magnus in the rat
Authors: Reichling David B. , Basbaum Allan I.
Published: May 2005

Pharmacological, physiological, and behavioral studies suggest that inhibitory GABAergic neurons influence the projection from the midbrain periaqueductal gray matter to the medullary nucleus raphe magnus. The present study used electron microscopic immunocytochemical techniques to examine the morphology and synaptic relationships of GABA‐immunoreactive terminals in the ventrolateral periaqueductal gray. These putative GABAergic terminals comprise almost 40% of all axon terminals in the periaqueductal gray. GABA‐immunoreactive terminals contain small, clear, pleomorphic or round, vesicles, and 46% also contain some dense‐cored vesicles. In some experiments we also used a colloidal gold‐conjugated retrograde tracer to label periaqueductal gray neurons that project to the nucleus raphe magnus. About half of the synaptic inputs onto the cell bodies and proximal dendrites of retrogradely labeled neurons are GABA‐immunoreactive; these putative GABAergic synapses, which directly control activity in neurons projecting from the periaqueductal gray to the nucleus raphe magnus, might mediate the antinociception‐related effects of exogenous GABAA receptor ligands.
Architecture of superior and mesial area 6 and the adjacent cingulate cortex in the macaque monkey
Authors: Matelli M. , Luppino G. , Rizzolatti G.
Published: May 2005

The agranular frontal cortex is formed by several distinct functional areas. There is no agreement, however, on its cytoarchitectonic organization. The aim of this study was to redefine the cytoarchitectonic organization of superior and mesial area 6 and the adjacent cingulate cortex in the macaque monkey. A particular goal was to find out whether the so‐called supplementary motor area (SMA) is cytoarchitectonically different from the rest of area 6 and whether it can be considered as a single, independent cytoarchitectonic area.

The results showed that, rostral to F1 (area 4), four architectonic areas can be recognized in the superior (dorsal) and mesial area 6. Two of them are located on mesial cortical surface (F3 caudally and F6 rostrally) and two on superior cortical convexity (F2 caudally and F7 rostrally).

The main cytoarchitectonic features of the five identified areas can be summarized as follows. F1: (1) giant pyramidal cells organized in multiple rows. (2) columnar pattern extending from the white matter to the superficial layers, (3) low cellular density in the lower part of layer III. F3: (1) high cellular density in the lower part of layer III, which fuses with a dense Va, (2) columnar pattern present only in the deepest layer, (3) occasional presence of giant pyramidal cells in layer Vb. F6: (1) prominent layer V, (2) absence of sublayer Vb, (3) homogeneous cell density in superficial layers. F2: (1) thin row of medium‐size pyramids in the lowest part of layer III, (2) columnar pattern extending to the superficial layers, (3) dense layer Va, (4) few, scattered giant pyramids in layer Vb. F7: (1) prominent layer V, (2) bipartite layer VI. Areas F1, F2, and F3, as defined cytoarchitectonically, coincided with the homonymous histochemical areas.

The present data showed also that area 24 is formed by four subareas: 24a, b, c and d. Areas 24a ana b occupy the ventral part of area 24, whereas its dorsal part is formed by area 24c, located rostrally, and area 24d, located caudally. The following features distinguish area 24d from area 24c: (1) larger pyramidal cells in layer V, (2) presence of medium‐size pyramidal cells in the lower part of layer III, (3) more prominent columnar pattern, (4) higher myelinization with the presence of an evident horizontal plexus.

Mesial area 6 is usually considered as a single functional entity (SMA). Our findings show that this cortical region is formed by two distinct cytoarchitectonic areas. In the following article (Luppino et al. 1991: J. Comp. Neurol 311:463–482) physiological evidence is presented that the SMA, as classically defined, corresponds to F3, whereas F6 is an independent functional area.
Glutamate, GABA, and glycine in the human retina: An immunocytochemical investigation
Authors: Davanger Svend , Ottersen Ole P. , Storm‐Mathisen Jon
Published: May 2005

The distribution of the neuroactive amino acids glutamate, GABA, and glycine in the human retina was examined in consecutive semithin sections treated with antisera specific for fixed glutamate, GABA, and glycine, respectively.

Glutamate immunoreactivity was conspicuous in all photoreceptor cells (rods more strongly labelled than cones), and in a majority (85–89%) of the cells in the inner nuclear layer (INL). Rod spherules and cone pedicles showed a greater enrichment of glutamate immunoreactivity than the parent cell bodies and inner segments. Also, structures of the inner plexiform layer (IPL) were labelled. A large majority (83–91%) of cells in the ganglion cell layer (GCL) was strongly stained, as were most axons in the nerve fibre layer. Muller cell processes appeared unstained.

GABA immunoreactivity was present in presumed amacrine but not in bipolar‐like cells. The stained cells were restricted to the inner ⅓ of the INL and were more frequent in central than in peripheral retina (40% and 26% of all cells in the inner ⅓of INL, respectively). GABA positive cell processes, probably originating from interplexiform cells, appeared to traverse the INL and end in the outer plexiform layer. Dense immunolabeling was found in the IPL. GABA immunoreactive cells (some also stained for glutamate) comprised 23% of all GCL cells in the peripheral retina, but only 5% in the central retina. Most of them were localized adjacent to the IPL. A few GABA positive (possibly ganglion) cells extended a single fibre toward the nerve fibre layer. Solitary GABA positive fibres were seen in this layer and in the optic nerve.

Glycine immunoreactivity was observed in cells with the location typical of amacrine and bipolar (peripheral retina) cells, as well as in punctate structures of the IPL. In contrast to the GABA positive cells, the glycine positive cells were more frequent in the peripheral than in the central retina (42% and 23% of all cells in inner ⅓ of INL, respectively). A few cells in the GCL (0.5–1.5%) were glycine positive.

Glutamate colocalized with GABA or glycine in a majority of the cells stained for either of these inhibitory transmitters (90–95% of the GABA positive cells, and 80–86% of the glycine positive cells, in the INL). Some bipolar cells were stained for both glutamate and glycine. Colocalization of GABA and glycine occurred in a subpopulation (3–4%) of presumed amacrine cells, about half of which was also glutamate positive.
Projections from the posteroventral cochlear nucleus to the superior olivary complex in guinea pig: Light and em observations with the PHA‐L method
Authors: Thompson Ann M. , Thompson Glenn C.
Published: May 2005

The efferent neural projections from posteroventral cochlear nucleus to the superior olivary complex in guinea pig were examined with the Phaseolus vulgaris—leucoagglutinin anterograde tract‐tracing method. Light microscopic analysis demonstrated that the posteroventral cochlear nucleus of guinea pig bilaterally projects to the superior paraolivary nucleus and the rostral, medioventral, and lateroventral periolivary regions. Ipsilaterally, the posteroventral cochlear nucleus projects to the lateral superior olive, the caudal periolivary region, and areas immediately surrounding the capsule of the lateral superior olive. Contralaterally, the posteroventral cochlear nucleus projects to the medial nucleus of the trapezoid body. All of these projection axons travel in the trapezoid body and their terminals make, primarily, en passant endings upon their targets. Exclusively within the contralateral medial nucleus of the trapezoid body, some neurons terminate also in calyceal endings.

The assumption that immunolabeled strictures observed with light microscopy made actual synaptic contact in their respective target areas was confirmed with electron microscopy. With postembedding immunocytochemical procedures applied to thin sections, the electron microscope revealed labeled synaptic vesicles and pre‐ and postsynaptic membrane specializations.

The projection pattern from posteroventral cochlear nucleus was found to be topographically organized in three distinct regions. The more dorsally located neurons of the posteroventral cochlear nucleus terminated dorsomedially in the ipsilateral lateral superior olive, ventromedially in the contralateral superior paraolivary nucleus, and medially in the contralateral medioventral periolivary region. The more ventrally located neurons of the posteroventral cochlear nucleus terminated dorsolaterally in the ipsilateral lateral superior olive, dorsolaterally in the contralateral superior paraolivary nucleus, and laterally in the contralateral medioventral periolivary region.
Afferent and efferent projections of the glossopharyngeal‐vagal nerve in the hagfish
Authors: Matsuda Hideki , Goris Richard C. , Kishida Reiji
Published: May 2005

Anterograde and retrograde transport of horseradish peroxidase was used to examine the afferent and efferent projections of the glossopharyngeal‐vagal nerve in the hagfish Eptatretus burgeri. Anterogradely labeled ganglion cells are scattered in the glossopharyngeal‐vagal nerve trunk, in the saccular ganglion, and in the brainstem. Afferent fibers of the glossopharyngeal‐vagal nerve terminate in both the vagal lobe and the fasciculus communis. Close observation showed no morphological differentiation between these two structures, indicating that they are not separate entities, but a single, continuous structure that is homologous with the nucleus and tractus solitarius of other vertebrates. The median part of this structure (the commissura infima) is displaced more rostrally than the same part of the solitary nucleus in many other vertebrates. Some of the afferent fibers invade the ventral portion of the trigeminal sensory nucleus, which receives the maxillo‐mandibular nerve fibers, and terminate there. Our study showed that the hagfish has only one nucleus in the vagal motor system, i.e., the vagal motor nucleus, which contains both parasympathetic and branchiomotor neurons. The dendrites of the vagal motor neurons in the hagfish are more highly developed than those in other vertebrates. This suggests that the motor reflex are of the glossopharyngeal‐vagal nerve in hagfishes may be simpler than in other vertebrates.
Sources of presumptive glutamatergic/aspartatergic afferents to the mediodorsal nucleus of the thalamus in the rat
Authors: Ray James P. , Russchen Fokje T. , Fuller Terry A. , Price Joseph L.
Published: May 2005

The distribution of presumptive glutamatergic and/or aspartatergic neurons retrogradely labeled following injections of 3HD‐aspartate into the mediodorsal nucleus of the thalamus (MD) in the rat was compared to the distribution of neurons labeled by comparable injections of the nonspecific retrograde tracer wheat germ agglutinin conjugated horseradish peroxidase (WGA‐HRP). Cells retrogradely labeled by WGA‐HRP were found in the prefrontal and agranular insular cortices; in forebrain structures such as the amygdaloid complex, the piriform cortex, the ventral pallidum and the reticular nucleus of the thalamus; and in several different parts of the brainstem, such as the superior colliculus, central grey, and substantia nigra, pars reticulata.

Some, but not all, of these projections are presumably glutamatergic and/or aspartatergic. The projections to MD from the prefrontal and agranular insular cortices are well labeled with 3H‐D‐aspartate, as are projections from the anterior cortical amygdaloid nucleus. Projections from the superior colliculus to the lateral portion of MD also label with this tracer. However, other forebrain and brainstem projections to MD are not labeled with 3H‐D‐aspartate, and apparently do not use glutamate or aspartate as a neurotransmitter. These include the projections from the basal and accessory basal amygdaloid nuclei, as well as possibly GABAergic projections from the ventral pallidum and the substantia nigra, pars reticulata. A small fraction of the cells in the piriform cortex that project to MD label with 3H‐D‐aspartate, suggesting that this projection may be heterogeneous.

In other experiments, presumptive GABAergic projections to MD were studied by using 3H‐GABA as a retrograde tracer. Although in these cases the thalamic reticular nucleus is well labeled, the ventral pallidum and the substantia nigra, pars reticulata are only poorly labeled. Pallidal projections to the ventromedial thalamic nucleus (VM), which are likely to be GABAergic, were also studied with this technique. After injections of 3H‐GABA into VM, only a few cells in the substantia nigra, pars reticulata, or entopeduncular nucleus were labeled. This result suggests 3H‐GABA has limited usefulness as a transmitter‐specific retrograde tracer.
The Selective innervation by serotoninergic axons of calbindin‐containing interneurons in the neocortex and hippocampus of the marmoset
Authors: Hornung Jean‐Pierre , Celio M. R.
Published: May 2005

The serotoninergic input to the mammalian cerebral cortex originates in the median and the dorsal raphe nuclei. Median raphe neurons have been previously shown to give rise to beaded varicose axons which form dense pericellular arrays (baskets) surrounding the soma and the proximal dendrites of certain cortical neurons. In the present study, we have searched for specific markers characterizing the neurons of the marmoset neocortex and hippocampus surrounded by these thick varicose serotonin‐containing fibers. The non‐pyramidal nature of these neurons, suggested by their dendritic arborization, was correlated, in immunocytochemical experiments with double‐labelling to demonstrate their surrounding serotonin‐containing basket and their content of glutamic acid decarboxylase (GAD) or of the calcium‐binding protein calbindin. Another calcium‐binding protein common in numerous non‐pyramidal cortical neurons, parvalbumin, was never found in neurons surrounded by serotonin‐containing baskets. This organization was found in all areas of the neocortex and of the hippocampus where serotonin‐containing baskets were present.

One of the serotoninergic cortical inputs which originates from the brainstem tegmentum, traditionally described as «diffuse,» proves to be highly selective in that a subset of its axons terminates preferentially on a subpopulation of inhibitory interneurons of the cerebral cortex. It may be emphasized that this subset of cortical interneurons has now been shown to be characterized not only by its axonal and dendritic arborization and its neurotransmitter, but also by a specific type of input which can modulate cortical function in a unique manner.
Rapid changes in protein synthesis and cell size in the cochlear nucleus following eighth nerve activity blockade or cochlea ablation
Authors: Sie Kathleen C. Y. , Rubel Edwin W.
Published: May 2005

Destruction of the cochlea causes secondary changes in the central auditory pathway through transynaptic regulation. These changes appear to be mediated by an activity‐dependent process and can be detected in the avian auditory system as early as 30 minutes after deafferentation. We compared the early changes in cochlear nucleus neurons following deafferentation by cochlea ablation with those seen following activity deprivation by perilymphatic tetrodotoxin (TTX) exposure. Protein synthesis and size of large spherical cells in the anteroventral cochlear nucleus (AVCN) of 14‐day‐old gerbils were measured during the first 48 hours after the manipulations.

Both cochlea ablation and TTX produced a reliable decrease in protein synthesis by AVCN neurons (30–‐40%) by 1 hour. The magnitude of change in tritiated leucine incorporation was similar at all survival times, in both experimental groups. In contrast to the rapid changes in protein synthesis, the decrease in cell size was first evident 18 hours after TTX exposure and 48 hours after cochlea ablation. There was no significant change in protein synthesis or cell size in control groups at any of the survival times. These findings are consistent with changes in the avian auditory system in response to deafferentation and TTX exposure.

Cochlea ablation and TTX exposure induced similar transneuronal changes, supporting the hypotheses that activity of auditory afferents in young mammals plays a regulatory role in the metabolism and morphology of their target neurons in the central auditory pathway, and that early changes following destruction of the peripheral receptor are due to reduction of activity‐dependent interactions of presynaptic and postsynaptic cells.
Isthmotectal axons make ectopic synapses in monocular regions of the tectum in developing Xenopus laevis frogs
Authors: Udin Susan B. , Fisher Mark D. , Norden Jeanette J.
Published: May 2005

During the development of binocular maps in the tectum of Xenopus laevis, axons that relay input from the ipsilateral eye via the nucleus isthmi undergo a prolonged period of shifting connections. This shifting accompanies the dramatic change in eye position that takes place as the laterally placed eyes of the tadpole move dorsofrontally. There is a concomitant expansion of the proportion of tectum that receives contralateral retinotectal input corresponding to the binocular portion of the visual field. Electrophysiological recording demonstrates that ipsilateral units are present in those rostral tectal zones, and anatomical methods show that the isthmotectal axons arborize densely in the rostral region but also extend sparser branches into the caudal zone, which is occupied by contralateral inputs with receptive fields in the monocular zone of the visual field.

A mechanism that aligns the ipsilateral and contralateral maps is activity‐dependent stabilization of isthmotectal axons that exhibit firing patterns correlated with those of nearby retinotectal axons. In order for activity patterns to function in stabilizing correct connections and promoting the withdrawal of incorrect connections, synaptic communication of some sort is hypothesized to be essential. We have investigated whether isthmotectal axons make morphologically identifiable synapses during development and where such synapses are located.

We find evidence for morphologically identifiable synapses in all regions of the tectum, along with many growth cones and structures that are probably immature synapses. As in the adult, the synapses contain round, clear vesicles, have asymmetric specializations, and terminate on structures that appear to be dendrites. In both adult and tadpole, the rarity of serial synapses involving isthmotectal terminals suggests. That the interactions between retinotectal and isthmotectal inputs are mediated by postsynaptic dendrites. © 1992 Wiley‐Liss, Inc.
Selective innervation of foreign muscles following damage or removal of normal muscle targets
Authors: Boss Valerie , Wigston Donald J.
Published: May 2005

The restoration of a normal pattern of neural connectivity following nerve injury depends upon the selective reinnervation of appropriate postsynaptic targets. Previous studies suggest that, in the neuromuscular system, recognition between regenerating motoneurons and target muscles depends upon the positions of origin of the motoneurons and muscles. In axolotls, portions of the motor pools of adjacent muscles overlap. We found that, following removal of a pair of adjacent hindlimb muscles, anterior and posterior iliotibialis, many regenerating iliotibialis motor axons invaded foreign muscles. A more anterior foreign muscle, puboischiofemoralis internus, received greater innervation from anterior iliotibialis motoneurons, whereas a more posterior muscle, iliofibularis, received greater innervation from posterior iliotibialis motoneurons. Furthermore, anterior iliotibialis motoneurons that reinnervated puboischiofemoralis internus occupied the rostral portion of anterior iliotibialis motor pool, which overlaps that of puboischiofemoralis internus. Anterior iliotibialis motoneurons that reinnervated iliofibularis occupied the caudal portion of the anterior iliotibialis motor pool, which overlaps that of iliofibularis.

When both anterior and posterior iliotibialis were damaged so that their myofibers were permanently destroyed, the rostrocaudal origins of the motoneurons that reinnervated them were virtually the same, suggesting that the motoneurons had difficulty distinguishing between the myofiberless iliotibialis muscles. However, some iliotibialis motoneurons invaded puboischiofemoralis internus instead of their myofiberless targets. Puboischiofemoralis internus received more innervation from the anterior iliotibialis motoneurons than the positionally less appropriate posterior iliotibialis motoneurons. These data are consistent with the hypothesis that selective reinnervation of muscle depends upon a system of recognition cues based on position. © 1992 Wiley‐Liss, Inc.
GABA‐immunoreactive terminals synapse on primate spinothalamic tract cells
Authors: Carlton Susan M. , Westlund Karin N. , Zhang Dongxian , Willis William D.
Published: May 2005

Gamma‐aminobutyric acid (GABA) is a putative inhibitory neurotransmitter in the vertebrate nervous system. Several lines of evidence suggest that GABA plays an important role in the processing and modulation of sensory input in the spinal cord dorsal horn. In the present study, the relationship between GABA‐immunoreactive (GABA‐IR) terminals and spinothalamic tract (STT) cells in the monkey lumbar cord was investigated. Physiologically characterized STT cells, one located in lamina V and two located in lateral lamina IV, were intracellularly injected with horseradish peroxidase (HRP). A fourth STT cell, located in lamina I, was retrogradely labeled following injection of HRP into the contralateral thalamus. Immunogold labeling of ultrathin sections through the cell bodies and proximal dendrites of the STT neurons demonstrated that the percentage of the GABA‐IR terminals in contact with these profiles was 24.7% and 36%, respectively. The average STT surface length contacted by GABA‐IR terminals for cell bodies and proximal dendrites was 18.2% and 26.7%, respectively. For the lamina I cell, 7 out of 35 (20%) of the terminals were GABA‐IR and they covered 9.6% of the surface analyzed. These data demonstrate that GABA‐IR terminals synapse directly on STT cells, constituting a substantial proportion of the terminal population on these cells. Furthermore, compared to the cell bodies, a greater percentage of the input on the proximal dendrites is GABAergic. These anatomical data are consistent with the findings of a previously published iontophoretic study that demonstrated that GABA can exert a strong inhibitory influence on STT cells. These findings are discussed in relation to GABAergic involvement in tonic and phasic inhibition of STT neurons.
5′‐Nucleotidase: A new marker for striosomal organization in the rat caudoputamen
Authors: Schoen Siegfried W. , Graybiel Ann M.
Published: May 2005

The distribution of the adenosine‐producing ectoenzyme 5′‐nucleotidase was studied by means of a histochemical lead technique in the caudoputamen of normal adult rats and of rats in which injections either of 6‐hydroxydopamine in the medial forebrain bundle or of ibotenic acid in the caudoputamen had been made 1–3 weeks previously. The patterns of striatal 5′‐nucleotidase activity in these animals were compared in serial sections to the patterns of calbindin‐D28k immunoreactivity and of 3H‐naloxone ligand binding, which respectively mark the known matrix and striosome (patch) compartments of the caudoputamen. In the normal rats, 5′‐nucleotidase activity was differentially concentrated in striosomes, where it produced a dense staining of the neuropil. The enzymatic staining followed a striosomal distribution in all but the caudal caudoputamen. Within the striatal matrix, 5′‐nucleotidase staining also observed a lateromedial density gradient. Depletion of the dopamine‐containing nigrostriatal innervation of the caudoputamen with 6‐hydroxydopamine did not alter the striosomal selectivity of 5′‐nucleotidase activity. Destruction of intrastriatal neurons by ibotenic acid led to a strongly 5′‐nucleotidase‐positive gliosis within the resulting necrotic region. Elsewhere in the caudoputamen, the enzyme's striosomal distribution was not detectably altered. We conclude that 5′‐nucleotidase histochemistry provides an advantageous tool for detecting the striosomal architecture of the rat's caudoputamen. Moreover, 5′‐nucleotidase is prominently associated with glial membranes in the central nervous system, so that the concentration of this enzyme in striosomes could mark these as sites of selective glial populations within striatum. These properties and actions of 5′‐nucleotidase in purinergic neurotransmission and in neuroadhesion may contribute to the specialized functions of striosomes and matrix. © 1992 Wiley‐Liss, Inc.
Genesis of neurons in the retinal ganglion cell layer of the monkey
Authors: Rapaport David H. , Fletcher Jeffery T. , LaVail Matthew M. , Rakic Pasko
Published: May 2005

We have analyzed the genesis of various neuronal classes and subclasses in the ganglion cell layer of the primate retina. Neurons were classified according to their size and the time of their origin was determined by pulse labeling with 3H‐thymidine administered to female monkeys 38 to 70 days pregnant. All offspring were sacrificed postnatally, and their retinas processed for auto radiography.

The somata of cells in the retinal ganglion cell layer generated on embryonic day (E) 38 ranged from 9 to 14 μm in diameter. Between E40 and E56, the minimum soma diameter remained around 8–9 μm, while the maximum gradually increased to 22 μm. As a consequence, the means of the distributions of labeled cells also increased with age, from 11.8 μm diameter for cells generated on ESS to 14.6 μm diameter at E56. Over this period the percentage of labeled cells in the 10.5–16.5 μm and > 16.5 μm diameter range gradually increased. The proportion of the labeled cells in the < 10.5 μm diameter range decreased from ESS to E45, but subsequently increased rapidly. At the end of neurogenesis in the retinal ganglion cell layer, around E70, most labeled cells were considerably smaller (7–9 μm) than those generated earlier.

Our results indicate that within the ganglion cell layer of the macaque, neurons of small caliber are generated first, followed successively by medium sized cells. Large, putative Pα cells are generated late. The production between E56 and E70 of cells with the smallest somata suggests that the last‐generated neurons in the ganglion cell layer are predominantly displaced amacrine cells. Within the same sector of retina, different classes of neurons in the ganglion cell layer of the rhesus monkey appear to have a sequential schedule of production. © 1992 Wiley‐Liss, Inc.
Multiple neurotransmitters in the tuberomammillary nucleus: Comparison of rat, mouse, and guinea pig
Authors: Airaksinen Matti S. , Alanen Sari , Szabat Ewa , Visser Theo J. , Panula Pertti
Published: May 2005

Tuberomammillary neurons in the posterior hypothalamus are the sole source of neuronal histamine in adult mammalian brain. In the rat, these cells are reported to contain immunoreactivity for γM‐aminobutyric acid (GABA) and several neuropeptides. We compared the presence of these substances in the tuberomammillary cells of the rat, mouse, and guinea pig.

In all three species, all histamine‐immunoreactive neuronal cell bodies were positive for GABA. This suggests that GABAergic transmission may be important in tuberomammillary function. No cell bodies immunoreactive for thyrotropin releasing hormone (TRH) were found in the guinea pig or mouse tuberomammillary area. In contrast, about 14% of the histamine‐immunoreactive tuberomammillary cells in the rat were TRH‐positive. These cells were small or medium‐sized and were located only in the medial part of the tuberomammillary complex. An antibody against porcine galanin stained about 45% of the tuberomammillary cell bodies in the rat and about 28% in the mouse, but none in the guinea pig. A large proportion of the cells in the rat and mouse, but none in the guinea pig, were positive for met‐enkephalin‐arg‐phe. In contrast, all histamine‐containing tuberomammillary cells in the guinea pig, but none in the rat or mouse, were immunoreactive for met‐enkephalin. This may indicate a different expression of proenkephalin‐derived peptides in the tuberomammillary neurons in these species. Some substance P‐immunoreactive cell bodies were located in the tuberomammillary area in all three species. However, only 3% of the histamine‐immunoreactive cell bodies in the rat and mouse but none in the guinea pig were substance P‐positive.

The neurochemical properties of the tuberomammillary nucleus that exhibited species commonality deserve to be studied neurochemically and electrophysiologically in order to determine the functional relevance of coexisting transmitters in this nucleus. © 1992 Wiley‐Liss, Inc.
The structure of the diencephalic prepacemaker nucleus revisited: Light microscopic and ultrastructural studies
Authors: Zupanc Günther K. H. , Heiligenberg Walter
Published: May 2005

The prepacemaker nucleus (PPn), a bilateral cluster of neurons at the boundary of diencephalon and mesencephalon, controls frequency modulations of the electric organ discharge in weakly electric knifefish (Eigenmannia sp.). Previous light microscopic studies employing retrograde labelling with horseradish peroxidase suggested that the PPn is restricted to a small area, located approximately 400 μm laterally from the third ventricle and fusing at its medial edge with the thalamic central posterior nucleus (CP). In the present investigation we used Phaseolus vulgaris‐leucoagglutinin and cholera toxin as highly sensitive markers. In contrast to the previous studies, these experiments yielded a large number of labelled cells not only in the region of the traditionally defined PPn but also in an area reaching far into the CP. Since the PPn has been defined by retrograde labelling rather than by topographic criteria, this result questions the traditional separation between PPn and CP. Such a notion is in agreement with observations of Nissl‐stained sections at the light microscopic level and with a quantitative analysis of several morphological characteristics of the cell bodies in the PPn and CP at the ultrastructural level. Both sets of experiments failed to find differences between the two nuclei. Furthermore, autoradiographic studies have shown that, even in adulthood, cells are continuously born within the ventricular zone of the CP, and at least some of these newborn cells differentiate into CP cells and migrate laterally towards the PPn. Therefore, we postulate that CP and PPn form one large complex, with the medial CP providing precursors of neurons in the lateral CP and PPn. © 1992 Wiley‐Liss, Inc.
Fine structure and blood‐brain barrier properties of the central nervous system of a dipteran larva
Authors: Juang Jyh‐Lyh , Carlson Stanley D.
Published: May 2005

Using scanning and transmission electron microscopy, we studied basic ultrastructure, membrane specializations, and blood‐brain barrier properties of the ventral ganglion and abdominal nerves of the last (third) instar larva of a dipteran fly, Delia platura. Both ganglion and nerves are covered with a non‐cellular neural lamella. A monolayer of flattened perineurial cells lies beneath the neural lamella. Perineurial cells contain stores of metabolites and nutrients and these cells extensively interdigitate with one another. An extensive extracellular series of channels pervades perineurial cells. Glial cells beneath the perineurium envelope but do not entwine axons. In a minority of cases, adjacent axons in nerve and neuropil appear to be contiguous without glial intervention. Extensive (pleated) septate junctions with triangular septa are present between perineurial cells. Hemidesmosomes, half desmosomes (a first report for invertebrates), and desmosomes were also observed. Although no tight junctions were discovered, an effective blood‐brain barrier exists, and tracer (ionic lanthanum) in no case reached neuronal surfaces. Extracellular tracer halted within the extensive septate junctions between perineurial cells. We postulate that in the absence of tight junctions the functional blood‐brain barrier is effected by the septate junctions in the central nervous system of the Delia larva.
Projections from the laterodorsal nucleus of the thalamus to the limbic and visual cortices in the rat
Authors: Van Groen Thomas , Wyss J. Michael
Published: May 2005

The laterodorsal nucleus (LD) of the thalamus is an important source of thalamic afferents to the limbic cortex, but the topography and lamination of these projections has not been investigated in detail. Using the anterograde transport of Phaseolus vulgaris leucoagglutinin and Fluoro‐Ruby, the present study demonstrates that in the rat, LD projects to infraradiata, precentral agranular, retrosplenial, visual (area 18b), subicular, and entorhinal cortices. Each subregion of LD has a distinct pattern of terminals within these cortical areas. The rostral part and the dorsalmost part of LD project densely to retrosplenial granular a (Rga) cortex, presubiculum and parasubiculum. Slightly more caudal parts of dorsal LD project primarily to the postsubiculum. More ventral parts of LD project primarily to retrosplenial dysgranular (Rdg) and retrosplenial granular b (Rgb) cortices. The projection of LD to area 18b originates from cells in the caudalmost part of LD. In each cortical region, LD terminals display distinct laminar patterns. In area 18b and the adjacent Rdg cortex, the LD terminal field is in layers I, III, and IV, but in both the Rgb and Rga cortices the terminal field is located predominantly in layer I. In the postsubiculum the LD terminals are distributed to layers I and III/IV and extend into superficial layer V; in the presubiculum and the parasubiculum the LD terminals are only in the deep layers (i.e., layers IV–VI). A small number of LD axons terminate in the deep layers (i.e., layers IV–VI) of the medial entorhinal cortex. These results indicate that each area of LD has a distinct projection to limbic and adjacent neocortex.
The superficial plexiform layer: A third retinal association area
Authors: Wieniawa‐Narkiewicz Elzbieta , Hughes A.
Published: May 2005

Electron microscopy enables the identification of a new association area in the mammalian retina. It is a region whose processes and synaptic junctions form a diffuse and intermittent layer bridging the boundary between the optic nerve fibre layer and ganglion cell layer. It involves displaced amacrine cells, retinal ganglion cells and probably interplexiform cell processes. Because it is close to the vitreal surface of the retina and has several properties of a plexiform layer, it has been named the superficial plexiform layer. It is much more sparse than the outer or inner plexiform layers in the rabbit, but contains a significant and substantial density of 6,100 synapses/mm2 near the visual streak.

Morphological criteria distinguish two classes of synapses in the new association area. One has features of Colonnier's symmetric type and is formed by amacrine‐like processes or their terminals, onto other amacrine‐like processes or the cell bodies, dendrites and axon hillocks of some large ganglion cells. It makes up 79% of the population at a density of 4,800 synapses/mm2 in the examined sample.

The second class arises from large processes of the fibre layer, which resemble axons rather than amacrine cell branches, has Colonnier's asymmetric form, and synapses onto a variety of other neuronal processes and cells. At a local density of 1,300/mm2 this type forms 21% of the population.

A series of experiments including Wallerian degeneration, retrograde degeneration, electron microscopy and horseradish peroxidase (HRP) transport was employed to determine the nature of the large synapse‐forming processes of the fibre layer that were the most amenable to investigation. It is concluded that the processes project into the optic nerve because they can be filled with HRP by retrograde transport from the end of the transected optic nerve. Although this result is based on limited evidence, it is complemented by the observation that the majority of the fibres undergo retrograde degeneration within 25 days of optic nerve section. It is concluded that the processes are either centrifugal fibres or the axons of retinal ganglion cells. The persistence of a relatively normal density of synapse‐forming large fibres for seven days after optic nerve section, without Wallerian degeneration, argues that they are not the terminals of centrifugal axons. This conclusion is complemented by a separate class of profiles that did degenerate in this short period and are concluded to represent the centrifugal fibres.

The large synapsing processes of the fibre layer are concluded to be the axons of some large ganglion cells. Their connections indicate the presence of feedback loops onto other large retinal ganglion cells both directly and indirectly through amacrine pathways. The superficial plexiform layer thus contains a rich variety of organised synaptic connections whose functional significance remains to be established.
A multiterminal stretch receptor, chordotonal organ, and hair plate at the wing‐hinge of Manduca sexta: Unravelling the mystery of the noctuid moth ear B cell
Authors: Yack Jayne E.
Published: May 2005

The present study aims to shed light on the evolutionary origin of the B cell, a sensory element of unknown function in the noctuid moth ear.

Peripheral projections of the metathoracic nerve IIIN1b1, homologue of the noctuid moth tympanic nerve, are described in the atympanate moth Manduca sexta on the basis of dissections with the aid of Janus Green B, and intracellular tracer dyes Lucifer yellow and cobalt lysine. A large multiterminal (Type II) neurone, attaching to membranous cuticle ventral to the hind wing axillary cord, was discovered. This cell appears to be homologous to the B cell in the noctuid moth ear. Recordings from the IIIN1b1 nerve in M. sexta reveal a continuous train of large, uniform spikes, presumed to originate From the multiterminal cell. This unit increases its rate of firing in response to hind wing elevation, suggesting that it functions as a stretch receptor monitoring wing movements during flight. Also identified in the tympanic nerve homologue, and closely associated with the multiterminal cell, were a chordotonal organ and hair plate. The chordotonal organ consists of a proximal scolopidial region and a distal strand that attaches to the sclerotized epimeron slightly medial to the multiterminal cell. This simple chordotonal organ, having three uniterminal (Type I) sensory cells, is homologous to the auditory cells of the noctuid moth ear.

The significance of these receptors as proprioceptors in M. sexta, and as evolutionary precursors to the noctuid moth ear, is discussed.
Ultrastructural development of the medial superior olive (MSO) in the ferret
Authors: Brunso‐Bechtold J. K. , Henkel C. K. , Linville C.
Published: May 2005

When ferrets are born, four weeks before the onset of hearing, few synapses are evident in the medial superior olive (MSO). The synapses present are immature and almost exclusively found in the neuropil. The MSO somata are virtually devoid of synaptic contacts but are contacted by fine glial processes that increasingly ensheathe the somata during the first postnatal week. By P12, somatic synaptogenesis in the MSO is evident. Initially the terminals contain vesicles of irregular shape, size, and distribution. The glial lamellae appear to withdraw as the synaptic contacts form but continue to cover the asynaptic portions of the cell surface. The lamellae frequently extend from an sheathing the soma to encapsulate the immature terminals. During the next two weeks, synaptic density and terminal encapsulation proceed until the somata is surrounded by encapsulated synaptic terminals as in the adult ferret MSO. While most immature terminals contain round vesicles, during the first postnatal week some terminals with nonround vesicles can be distinguished. The first distinction between types of nonround vesicle‐containing terminals, i.e., pleiomorphic and ovoid, is in the second postnatal week. This distinction becomes increasingly clear and by the end of the first postnatal month, terminal types can be reliably categorized. These observations indicate that: (1) synapses are present in the MSO neuropil one month prior to the onset of hearing, (2) the major period of synaptogenesis begins approximately two weeks prior to the onset of hearing, and (3) glial lamellae ensheathe MSO somata prior to the onset of somatic synaptogenesis, withdraw as synapses form, and subsequently re‐extend to encapsulate newly formed synapses.
Redeployment of trigeminal motor axons during metamorphosis
Authors: Omerza Frank F. , Alley Keith E.
Published: May 2005

As a consequence of the degeneration and replacement of the jaw muscle fibers in the leopard frog, Rana pipiens, trigeminal motoneurons innervate different targets before and after metamorphosis. This investigation examined the morphological correlates of the reassignment of trigeminal motoneurons during the initial phases of myofiber turnover. Specifically, silver‐cholinesterase histochemistry and electron microscopy were used to 1) identify the fate of motor axons within the neuromuscular junctions (NMJs) applied to degenerating larval myofibers and 2) to determine the origin(s) of the motor axons that innervate the postmetamorphic muscle fibers of the jaw.

The results demonstrate that the NMJs are retained on larval myofibers throughout their degeneration and are readily identifiable on the residual larval basal laminae that remain after involution of the sarcoplasm. Light and electron microscopic observations provide evidence that both pre‐ and post‐synaptic elements are present on the degenerating fibers. Furthermore, morphometric analyses indicate that the preponderance (86%) of motor axons supplying adult muscle fibers originates from the larval NMJs. This condition suggests that metamorphic redeployment of trigeminal motoneurons occurs through the resumption of growth at the axon terminal supplying larval muscle rather than through the proximal collateralization of these axons and resorption of larval terminals. © 1992 Wiley‐Liss, Inc.
Independent efferent populations in the nucleus of the optic tract: An anatomical and physiological study in rat and cat
Authors: Schmidt Matthias , Schiff Daniel , Bentivoglio Marina
Published: May 2005

The efferent projections of the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic system (DTN) to the contralateral NOT‐DTN, ipsilateral inferior olive (IO), ipsilateral nucleus prepositus hypoglossi (NPH), and ipsilateral dorsal lateral geniculate. nucleus (LGNd) were examined in pigmented rats and in cats by using anterograde and retrograde tract tracing, as well as extracellular recording and electrical stimulation.

Anterograde tracing in the rat revealed a dense termination field of NOT‐DTN efferents throughout the homologous contralateral territory.

In both species three different cell populations, projecting to the contralateral NOT‐DTN, ipsilateral IO, and ipsilateral LGNd, respectively, were distinguished by means of multiple retrograde tracing. No clear topographical segregation of the different NOT‐DTN relay cell populations was observed. On the other hand, a large proportion (at least 60%) of NOT‐DTN neurons projecting to the ipsilateral NPH were found to bifurcate upon the IO in the rat.

Electrophysiologically, NOT‐DTN neurons projecting to the IO were identified by their directionally selective responses. Such neurons were never activated by electrical stimulation of either the contralateral NOT‐DTN or the ipsilateral LGNd. Neurons antidromically activated from the contralateral NOT‐DTN could not be activated from the ipsilateral LGNd.

Thus, in both cat and rat the NOT‐DTN includes at least three independent relay cell populations. As a consequence, the NOT‐DTN must serve functions additional to the generation of eye movements during optokinetic nystagnus, a function subserved by the directionally selective NOT‐DTN cells. © 1995 Wiley‐Liss, Inc.
Ultrastructure of the synaptic terminals of the dorsal giant serotonin‐IR neuron and deutocerebral commissure interneurons in the accessory and olfactory lobes of the crayfish
Authors: Sandeman R. E. , Watson A. H. D. , Sandeman D. C.
Published: May 2005

The olfactory and accessory lobes in the crayfish are large spherical neuropils found on each side of its brain. The olfactory lobes receive the afferent axons of chemoreceptors that are located along the outer branches of the biramous first antennae. The accessory lobes receive a large input from interneurons whose axons lie in the deutocerebral commissure. A pair of large serotonergic neurons (the dorsal giant neurons) branch unilaterally in the accessory and olfactory lobes of each side. From physiological recordings, it has been proposed that the deutocerebral commissure interneurons synapse with elements in the accessory lobes that in turn connect to the dorsal giant neuron. It has also been proposed that the dorsal giant neuron is activated by inputs in the accessory lobe and that its output is in the olfactory lobe. This ultrastructural study tests this hypotheses by examining the polarity of synaptic terminals on dorsal giant neurons and deutocerebral interneurons that have been filled with neurobiotin. In double‐labelled preparations, we found the deutocerebral interneurons to be presynaptic to elements in the accessory lobes, but none of these postsynaptic elements was identifiable as the dorsal giant neuron. The dorsal giant neurons receive many more synaptic inputs in the accessory lobes than in the olfactory lobe. Very few giant serotonin neuron output synapses were found in either lobe. © 1995 Wiley‐Liss, Inc.