bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructural and morphometric analysis of nuclear and nuclear changes during the early growth period in hamster facial neurons
Authors: Clark Pamela , Jones Kathryn J. , LaVelle Arthur
Published: January 2005

In this study, progressive developmental changes in the nucleus and associated organelles, including the nucleolus, coiled bodies, nuclear envelope, and nucleoplasm, of hamster facial motor neurons were characterized by two parallel analyses: ultrastructural and morphometric. Golden hamsters (Mesocricetus auratus) used for this series were the 14‐day fetus, newborn (<6 hr), and 1, 2, 3, 4, 5, 7, 9, 11, and 13 days postnatal ages, with 3 animals per group. Following anesthesia and perfusion fixation, facial nuclear groups were dissected and processed for electron microscopy. Electron micrographs and camera lucida tracings of nuclear profiles were collected and analyzed. The ultrastructural analysis revealed progressive changes in the nucleolus from a compact, segregated type to a reticulated form characteristic of actively protein‐secreting cells. Nucleolar microbodies and fibrillar centers were seen at all ages; the latter structures appeared to decrease in size and increase with age in the series. The nucleolus‐associated chromatin became less condensed, suggesting an increase in the incorporation of rDNA into the nucleolus proper. Coiled bodies, both free and attached to nucleoli, were found in varying frequencies. The nucleoplasm of neurons at the earliest stages contained large numbers of heterochromatin clumps, which decreased concomitantly with an increase in interchromatin granules and fibrils during the later stages. Nuclear envelope imaginations, polarized along one side of the nucleus, increased throughout the developmental period examined. These changes occurred in concert with a 61% increase in nuclear size and a 47% increase in the length of nuclear envelope. The sequence of nuclear changes observed during this early period of normal facial neuronal growth completes the study of a series of distinctly defined cytomorphic events in this cell type, the lability of which can be experimentally tested for their functional roles in neuronal development.
Auditory brainstem of the ferret: Early cessation of developmental sensitivity of neurons in the cochlear nucleus to removal of the cochlea
Authors: Moore David R.
Published: January 2005

The role of primary afferent innervation in the maintenance of neurons in the mammalian auditory system was assessed by performing unilateral removals of the cochlea in neonatal and mature ferrets of known birth dates. Removals were performed under steroid anesthesia and resulted in the complete destruction of the organ of Corti and the loss of at least 80% of type I spiral ganglion neurons. Four main age groups [postnatal days (P)5, P24, P90, and P180] were used. Additional animals received no surgery, partial removals, or complete removals at older ages. Three months after the cochlear removal the animals were reanesthetized and perfused. The brainstem and the temporal bones were wax‐embedded, frontally sectioned, and Nissl‐stained. Sections of the right and left cochlear nuclei were compared quantitatively. Removal of the cochlea at P5 resulted in the loss of more than 50% of large (nongranular) neurons throughout the ipsilateral cochlear nucleus. Lesions at older ages did not produce any neuron loss. The size of the remaining neurons was reduced by 10–15% in all age groups. Partial lesions at P5 produced a graded response in the cochlear nucleus that was related to the extent of the lesion. The developmental sensitive period for the effects of cochlear removal on the ferret cochlear nucleus is therefore over before the age (P28–P30) at which the animal begins to hear. The present result differs markedly from the chicken, in which the sensitive period for removal of the cochlea persists for at least 2 months after the onset of hearing.
Crossing fiber arrays in the rat hippocampus as demonstrated by three‐dimensional reconstruction
Authors: Tamamaki Nobuaki , Nojyo Yoshiaki
Published: January 2005

The hippocampus is a neural substrate playing a key role in short‐term memory. In order to achieve a better understand‐ding of how the hippocampus functions in “learning and memory,” we conducted an intracellular horseradish peroxidase (HRP) study of the CA3 pyramidal neurons and the granule cells of the fascia dentata. The axon of the CA3 pyramidal neurons has two components, the longitudinal association system and the Schaffer collateral system. The latter component is organized in a lamellar fashion and follows the alvear fiber stream. An electron microscopic analysis of myelinated fibers suggested that most myelinated fibers in the hippocampus are organized parallel to the alvear fibers. The mossy fibers of the granule cells, however, do not follow the alvear fiber stream. We propose a new model of the organization of the intrinsic excitatory circuitry of the rat hippocampus in which the distinct lamellar organization of the pyramidal and granule cells creates a crossing neural network.
Effects of testosterone on a selected neuronal population within the preoptic sexually dimorphic nucleus of the Japanese quail
Authors: Panzica Giancarlo , Viglietti‐Panzica Carla , Sanchez Fernando , Sante Philippe , Balthazart Jacques
Published: January 2005

The effects of testosterone on the volume and cytoarchitecture of the sexually dimorphic nucleus of the preoptic area (POM) were investigated in male and female Japanese quail. It was confirmed that castration decreases the POM volume in males and that, in gonadectomized birds of both sexes, testosterone increases this volume to values similar to those observed in intact sexually mature males. This suggests that the sex difference in POM volume results from a differential activation by T so that this brain morphological characteristic is not truly differentiated in the organizational sense. This conclusion was extended here by demonstrating that males exposed to a photoperiod simulating long days and that are known to have high plasma levels of testosterone have a larger POM than short‐day males that have inactive testes. Detailed morphometric studies of POM neurons revealed a structural heterogeneity within the nucleus. A population of large neurons (cross‐sectional area larger than 70–80 μm2) was well represented in the dorsolateral but was almost absent in the medial part of POM. This lateral population of neurons was sensitive to variations of testosterone levels in males but not in females. The cross‐sectional area, diameter, and perimeter of the dorsolateral neurons were significantly increased in males exposed to high testosterone levels (intact birds exposed to long days or castrated birds treated with the steroid). These changes were not observed in the medial part of the nucleus. Interestingly, the size of the dorsolateral neurons was not affected by testosterone treatments in females. These results suggest that the swelling of neurons in the lateral POM of males might be responsible for the increase in total volume of the nucleus, which is observed in physiological situations associated with a high testosteronemia. In addition, the sensitivity to testosterone of the dorsolateral neurons in the POM appears to be sexually differentiated. This differential response to testosterone might represent a truly dimorphic feature in the organizational sense and additional studies manipulating the early steroid environment should be performed to test this possibility.
Development of the olfactory nerve in the African clawed frog, Xenopus laevis: I. Normal development
Authors: Burd Gail D.
Published: January 2005

Quantitative and morphological data were obtained on developing olfactory axons in the African clawed frog, Xenopus laevis, during late premetamorphosis (stages 48–54), prometamorphosis (stages 55–57), and halfway through metamorphic climax (stages 58–62). Larval axons throughout these stages of development did not change with respect to morphology or diameter and were similar in all respects to olfactory axons described in other vertebrate species. The number of axons in the olfactory nerve increased throughout development, more rapidly after stage 54. Based on comparisons of the number of axons in proximal and distal regions of the nerve, there also appeared to be more axons growing into the olfactory nerve at early metamorphic climax than during premetamorphosis. Through the onset of metamorphic climax, the number of olfactory axons was correlated with other measures of body growth. In the later stages of climax, however, the number of olfactory axons continued to rise, whereas body weight, length, and width, as well as olfactory nerve length, decreased. Not all animals developed at the same rate, but for all quantitative measurements in this study, stage was a better predictor of any given parameter than age of the animal. Rearing conditions affected the rate of development but did not have a significant effect on most of the features analyzed quantitatively. Although most of the new olfactory axons in these larval animals probably represent addition of fibers resulting from development, the ensheathing glial cells at all stages showed evidence of phagocytic activity, suggesting that there might be turnover of olfactory receptor cells during larval development. The results presented here provide a baseline for future reports on various factors that may influence normal development in this system.
Ultrastructure of the ganglion cells of the terminal nerve in the dwarf gourami (Colisa lalia)
Authors: Oka Yoshitaka , Ichikawa Masumi
Published: January 2005

In our previous light microscopic studies (Oka et al., Brain Res. 367:341–345, '86; Oka and Ichikawa, J. Comp. Neurol. 300:511–522, '90), we reported that there are at least two types of terminal nerve (TN) cells based on cell size and immunoreactivity: type I cells had large cell bodies, while type II cells had smaller cell bodies. Type I TN cells were immunoreactive to gonadotropin‐releasing hormone (GnRH) and may be the major source of GnRH‐immunoreactive fibers that are widely distributed throughout the brain. Type if TN cells, on the other Hand, were not immunoreactive to GnRH. In the present paper, we examined the cytology and synaptology of these two types of TN cells with electron microscopy. Type I TN cell bodies were found to have morphological characteristics similar to those of other peptide‐synthesizing neurons and are likely to be actively synthesizing GnRH. The frequent occurrence of coated vesicles close to the plasma membrane of the cell body was suggestive of membrane retrieval following exocytosis of the vesicular contents from the cell surface. Neighboring TN cells were either in direct juxtaposition with one another or made specialized “glomeruloid” cell‐to‐cell contacts; these specializations may be relevant for nonsynaptic intercellular communications among the TN cells. Within these glomeruloid complexes, the somatic processes of TN cells received inputs from two types of synaptic terminals: one containing only spherical synaptic vesicles and another containing a small number of dense‐cored vesicles in addition to the spherical synaptic vesicles. Axosomatic synapses were rare on type I TN cell bodies. In contrast, type II TN cell bodies had morphological characteristics similar to those of neurons in other brain regions. These receive axosomatic inputs from synaptic terminals containing only spherical synaptic vesicles and those with a small number of dense‐cored vesicles in addition to the spherical synaptic vesicles. Thus, each type of TN cell has unique fine structural characteristics which may correlate to their different functional roles.
Sprouting of peripherally regenerating primary sensory neurones in the adult central nervous system
Authors: McMahon Stephen B. , Kett‐White Rupert
Published: January 2005

We have studied the ability of primary afferent neurones to proliferate within the grey matter of the dorsal horn following the degeneration of other, nearby, afferent fibres. The peripheral branches of primary afferents have the capacity to regenerate successfully over long distances, and we have examined the possibility that when they are so doing, the neurones' status changes to facilitate greatly the sprouting of afferent fibres within the dorsal horn.

“Spared root” preparations (rhizotomies of L3, L4, L6, S1, and the caudal half of L5, sparing the rostral half of the L5 dorsal root) were made in adult rats. In some animals (acute preparations) the distribution of the central terminals of the spared root was assessed by labelling the sciatic nerve with WGA‐HRP at the time of the rhizotomies. In other animals (chronic preparations, symmetrical bilateral spared roots were made and the sciatic nerve on one side was concomitantly crushed to trigger regrowth of the peripheral branches of these axons. Eight to 10 weeks later the sciatic nerves on both sides were labelled with HRP‐WGA.

In the acute preparations the reaction product was found in a limited rostrocaudal and mediolateral region of the dorsal horn. In lamina II (the lamina of densest labelling the labelled terminals occupied an average of 1.17 ± 0.21 mm2. In chronic preparations, the area of labelled terminals on the side of the uncrushed sciatic nerve was 1.34 ± 0.28 mm2 (not significantly different from acute animals). However, the labelled area on the side of the crushed sciatic nerve was significantly greater, averaging 2.17 ± 0.14 mm2. Hence, primary afferent nerve fibres show greatly enhanced sprouting within the grey matter of the dorsal horn of the spinal cord when two conditions are fulfilled; 1) vacant synaptic sites are created by the degeneration of other primary afferent fibres; and 2) the peripheral branches of the axons are actively regenerating.
Distribution of motoneurons supplying dorsal suboccipital and intervertebral muscles in the cat neck
Authors: Gordon D. C. , Richmond F. J. R.
Published: January 2005

Multiple labelling methods were used to examine the topographical organization of motoneurons supplying the suboccipital muscles, rectus capitis posterior (RCP) and obliquus capitis inferior (OCI); the intervertebral muscles, spinalis dorsi (SD) and semispinalis cervicis (SSC); and the dorsal extensor biventer cervicis (BC). Muscle nerves were isolated, cut, and exposed in the same animal to one of three different retrograde tracers, Fluorogold, Fast Blue, and horseradish peroxidase. Motoneurons supplying suboccipital muscles were found to be located in the rostral two cervical segments. The RCP motor nucleus was confined to C1 and the caudal brainstem, whereas the OCI nucleus usually originated in mid‐C1 and extended caudally as far as mid‐C2. Most motoneurons supplying OCI and SD were concentrated in the deepest part of the ventral horn, but some cells were found in the commissural region, the contralateral ventral horn, the dorso‐medial aspect of the ipsilateral ventral horn, and the ventromedial white matter. Cells supplying the functional extensor RCP were intermingled with those supplying the turning muscle OCI, although a gradient in mediolateral distribution was detected. Motoneurons supplying the intervertebral muscles SD and SSC were found caudal to C3. Within the ventral horn, they occupied locations similar to those occupied by suboccipital motoneurons in C1 and C2. The cell column for intervertebral motoneurons was just medial to that of BC and some cells supplying SD and SSC were found in the territory occupied by BC motoneurons. Motoneurons supplying intervertebral and suboccipital muscles had unimodal diameter spectra, and most cells had mean equivalent diameters smaller than 35 μm.
Distribution of motoneurons supplying cat sartorius and tensor fasciae latae, demonstrated by retrograde multiple‐labelling methods
Authors: Gordon D. C. , Loeb G. E. , Richmond F. J. R.
Published: January 2005

Sartorius (SART) and tensor fasciae latae (TFL) in the cat hindlimb are functionally heterogeneous muscles with regions that differ in their skeletal actions and electromyographic recruitment during normal activity. The topographical organization of motoneurons supplying different regions of SART or TFL has been investigated by exposing cut nerve branches supplying different peripheral territories to a combination of retrograde tracers, including Fast Blue (FB), Fluorogold (FG), and horseradish peroxidase (HRP). Motoneurons supplying medial, central, and anterior regions of SART were intermixed extensively throughout a single columnar nucleus located in the ventrolateral part of segments L4 and L5. Within this column, motoneurons supplying medial SART tended to lie more rostrally than those supplying anterior regions, but the gradient was modest and showed some cat‐to‐cat variation. Two major branches entered anterior SART at different proximodistal levels. When these two branches were exposed to different tracers, most motoneurons contained a single tracer; only a few double‐labelled cells were apparent. The labelling suggests that anterior SART may contain two separate, in‐series divisions of motor units. In TFL, motoneurons supplying nerve branches to posterior, central, and anterior parts of the muscle were intermingled indiscriminately in a single ventrolateral cell column in L6 and rostral L7. These results suggest that topographical organization in lumbar motor nuclei does not always reflect the highly ordered biomechanical and functional specialization evident in the peripheral organization of the muscles themselves.
Postnatal development of the noradrenergic projection from locus coeruleus to the olfactory bulb in the rat
Authors: McLean John H. , Shipley Michael T.
Published: January 2005

Norepinephrine (NE) may play a role in the developing brain by modulating synaptic plasticity during critical periods of circuit formation (Kasamatsu and Pettigrew, 1976; 1979; Bear and Singer, 1986). In the olfactory bulb, NE input from the locus coeruleus (LC) appears to be necessary for the newborn rat to form a learned odor preference (Sullivan and Leon, 1986; Wilson and Leon, 1988; Sullivan et al., 1989). However, little is known about the development of NE innervation of the olfactory bulb. Thus, it is not clear how the maturation of the LC projection to the bulb correlates with the formation of olfactory bulb circuits during the period when NE modulates early olfactory learning. In this study, the postnatal development of the NE input from the LC to the main and accessory bulbs was characterized with tract tracing, immunocytochemistry, and quantitative image analysis methods.

By birth there is already a substantial input to the olfactory bulb from the LC; as many as 200 LC neurons can be retrogradely labelled with wheatgerm agglutinin‐horseradish peroxidase injection in the olfactory bulb. This compares with an estimated 400–600 neurons labelled by similar procedures in adult rats (Shipley et al., 1985).

In order to study the development of NE fibers innervating the olfactory bulb, immunocytochemistry with antibodies to dopamine‐β‐hydroxylase was employed. Image analysis was used to facilitate visualization and to quantitate the development of fiber densities. At birth, immunocytochemically labelled NE fibers were identified in all layers of the main and accessory olfactory bulb. The innervation was strongly preferential for infraglomerular layers at all stages of postnatal development. The fibers were densest in the internal plexiform and granule cell layers, less dense in the external plexiform layer, and sparse in the glomerular layer. The density of the fibers increased during development. There were no significant shifts in the relative distribution of the fibers in different layers of the bulb during development. This consistent laminar innervation by NE fibers suggests that if these fibers have a developmental role, their influence is probably limited to neuronal elements in inframitral cell layers.
In situ hybridization analysis of the FMRFamide neuropeptide gene in Drosophila. I. Restricted expression in embryonic and larval stages
Authors: Schneider Lynne E. , O'Brien Martha A. , Taghert Paul H.
Published: January 2005

We have used in situ hybridization techniques to describe the cellular distribution of transcripts from a Drosophila gene that encodes multiple FMRFamide‐related neuropeptides. The Drosophila FMRFamide gene consists of two exons and is expressed predominantly as a ∼ 1.7 kb RNA throughout postembryonic stages (Nambu et al., '88; Schneider and Taghert, '88, '90). We used exon‐specific oligonucleotide probes to assay transcription in both embryonic and larval stages and found a pattern of hybridization signals that was restricted to the central nervous system and, within that tissue, was cell‐specific. The pattern included 36 distinct signals distributed throughout both the brain and segmental nerve cord (ventral ganglion). These observations suggest that the cell‐specific pattern of FMRFamide‐like neuropeptide expression in the Drosophila CNS (White et al., '86; Taghert and Schneider, '90) is due to the restricted expression of specific gene transcripts. The results also indicate that, with few exceptions, all previously identified FMRFamide‐immunoreactive neurons in Drosophila larvae express FMRFamide gene transcripts. The 36 hybridization regions of the CNS could be divided into three categories, based on their signal intensities (strong, moderate, and weak). The differences in intensity were reproducible and suggest that steady‐state levels of specific neuropeptide RNA differ among individual neurons. The two exon‐specific probes produced patterns that were indistinguishable both in pattern and in intensity. This result supports the previous conclusion that the one detectable FMRFamide transcript contains both exons (Schneider and Taghert, '90). A single identifiable signal was detected during embryogenesis (beginning at stage 16), but the mature complement of signals was not fully established until the final larval stages.
Fine structure and synaptic architecture of HRP‐labelled primary afferent terminations in lamina IIi of the rat dorsal horn
Authors: Cruz F. , Lima D. , Zieglgänsberger W. , Coimbra Antonio
Published: January 2005

The fine structure and synaptic architecture of the afferent terminations in dorsal horn lamina II are studied using a combined light and electron microscopic procedure after anterograde labelling with horseradish peroxidase. Vibratome parasagittal sections, stained with heavy metal intensified diaminobenzidine after tracer application to the dorsal roots, were flat‐embedded in Epon. The five types of labelled terminal arbors occurring in lamina IIi (Cruz et al., '87: J. Comp. Neurol. 261:221–236) were drawn and relocated in 5‐μm sections cut serially from the thick sections. Ultrathin sections were then cut from the 5‐μm sections so that the terminal fibers and swellings observed in the light microscope could be traced in the electron microscope. The flame‐shaped arbors arose from fine myelinated stem fibers. Terminal strands generated large oval central terminals of type II synaptic glomeruli (CII), which established frequent axoaxonal contacts. Similar terminals have been labelled in the cat after tracer injections into hair‐follicle fibers (Réthelyi et al., '82: J. Comp. Neurol. 207:381–393). The other four plexuses arose from unmyelinated stem fibers. The swarms of ultrafine boutons consisted of extremely thin terminal fibers generating very small, round, or polygonal glomerular terminals containing tightly packed agranular synaptic vesicles of variable size and one mitochondrion at best. The terminal strands of the bouquet plexus bore long and scalloped central varicosities of type I synaptic glomeruli (CI) with pleomorphic agranular vesicles and a relative abundance of dendroaxonal contacts. These features, together with the location in dorsal lamina IIi, suggest their belonging to the fluoride resistant acid phosphatase (FRAP)‐reactive population. The boutons of the undulating fibers and those of the lateral plexus were, like those of the bouquets, scalloped and elongated rostrocaudally (CI), but contained a few large granular vesicles. The occurrence of the swarm, undulating, and lateral plexuses in ventral lamina IIi, which seems to lack FRAP or peptidergic terminals, suggests an origin from other, still unidentified neurochemical populations of fine primary afferents.
Increase in a focal population of juxtaglomerular cells in the olfactory bulb associated with early learning
Authors: Woo Cynthia C. , Leon Michael
Published: January 2005

Young rats learn to approach an odor that had been experienced in the presence of reinforcing tactile stimulation. Subsequent presentation of the conditioned odor also evokes an enhanced focal uptake of 2‐deoxyglucose (2‐DG) in the glomerular layer of the olfactory bulb, and the glomerular‐layer width of such foci increases in conditioned pups. In the present study, we determined whether an increase in the glomerular‐layer cell population contributes to this structural and functional change. We therefore counted and measured glomerular‐layer cells in Nissl‐stained sections from focal regions of radiolabeled 2‐DG uptake. While cell size did not differ between groups, conditioned pups had a 19% increase in the number of glomerular‐layer cells associated with the 2‐DG foci compared to controls. The increase in cell number may contribute to the enhanced 2‐DG uptake in glomerular‐layer foci.
Conditioning nerve crush accelerates cytoskeletal protein transport in sprouts that form after a subsequent crush
Authors: McQuarrie Irvine G. , Jacob Jane M.
Published: January 2005

To examine the relationship between axonal outgrowth and the delivery of cytoskeletal proteins to the growing axon tip, outgrowth was accelerated by using a conditioning nerve crush. Because slow component b (SCb) of axonal transport is the most rapid vehicle for carrying cytoskeletal proteins to the axon tip, the rate of SCb was measured in conditioned vs. sham‐conditioned sprouts. In young Sprague‐Dawley rats, the conditioning crush was made to sciatic nerve branches at the knee; 14 days later, the test crush was made where the L4 and L5 spinal nerves join to form the sciatic nerve in the flank. Newly synthesized proteins were labeled in motor neurons by injecting 35S‐methionine into the lumbar spinal cord 7 days before the test crush. The wave of pulse‐labeled SCb proteins reached the crush by the time it was made and subsequently entered sprouts. The nerve was removed and sectioned for SDS‐PAGE and fluorography 4–12 days after the crush. Tubulins, neurofilament proteins, and representative “cytomatrix” proteins (actin, calmodulin, and putative microtubule‐associated proteins) were removed from gels for liquid scintillation counting. Labeled SCb proteins entered sprouts without first accumulating in parent axon stumps, presumably because sprouts begin to grow within hours after axotomy. The peak of SCb moved 11% faster in conditioned than in sham‐conditioned sprouts: 3.0 vs. 2.7 mm/d (p <.05). To confirm that sprouts elongate more rapidly when a test crush is preceded by a conditioning crush, outgrowth distances were measured in a separate group of rats by labeling fast axonal transport with 3H‐proline 24 hours before nerve retrieval. The rate of outgrowth was 17% faster in conditioned than in sham‐conditioned sprouts: 5.13 vs. 4.38 mm/d (p <.01). The increase in outgrowth rate correlated with the increase in SCb rate, suggesting that outgrowth is a function of cytoskeletal protein transport.
Detection and characterization of a sensory microganglion associated with the spinal accessory nerve: A scanning laser confocal microscopic study of the neurons and their processes
Authors: Wetmore Cynthia , Elde Robert
Published: January 2005

The spinal accessory nerve has been generally thought to be a cranial nerve with purely motor function, innervating the trapezius and sternocleidomastoid muscles. The present study identified clusters of sensory neurons consistently associated with this cranial nerve in adult rats. Either a single microganglion or several dispersed microganglia were found that adhered to the spinal root of the nerve, to small vessels, or were free within the subarachnoid space. The neurons of the ganglion had axons that joined the spinal root of the nerve proximal to its exit from the skull. Additional branches appeared to have an intracranial distribution within the arachnoid of the brainstem and along its vessels.

Several findings suggest that the function of the ganglion is sensory and not autonomic. First, the architectural features of neurons within the ganglion (including their size, pseudounipolar morphology, and the lack of synaptic contacts) are similar to those of neurons in other sensory ganglia. Second, substance P and calcitonin gene‐related peptide coexist within neurons of the microganglion, whereas markers for the major transmitters found in autonomic ganglia in rats are absent. Third, the expression of peptides in neurons of the ganglion was sensitive to neonatal capsaicin treatment. Finally, neurons within the ganglion were filled with a retrogradely transported dye after injection of the dye into the cervical spinal cord. Although the function of the ganglion is not known, its features are consistent with a role in nociception from the muscles of the spinal accessory complex, and it may be involved in headaches that have an occipital distribution.
Ultrastructure and aspects of functional organization of pyramidal and nonpyramidal entorhinal projection neurons contributing to the perforant path
Authors: Germroth Peter , Schwerdtfeger Walter K. , Buhl Eberhard H.
Published: January 2005

Identified entorhino‐hippocampal projection neurons were investigated for their ultrastructure. Spinous projection neurons (pyramidal and spiny stellate cells) display common features such as symmetric axosomatic terminals on their somata, asymmetric synapses on the spines, and both types of synapses on the dendritic shafts. Their axons descend towards the white matter, branching occasionally via collaterals which establish contact with local spines and rarely on dendritic shafts and somata. The sparsely spinous projection neurons (multipolar and horizontal‐bipolar) typically show deep nuclear infolds and symmetric and asymmetric synapses on their somata and dendritic shafts. Axons also collateralize in the soma vicinity and form local synapses. It is concluded that the entorhino‐hippocampal projection neurons (both spiny and sparsely spinous) act locally and distally thus performing simultaneously as local‐circuit and as projection neurons. In accordance with other morphological and electrophysiological reports it appears likely that the generation, modulation, and suppression of entorhinal excitation waves is mediated by these neurons through direct excitation, feed‐forward and feed‐back inhibition, and disinhibition.
Targets of horizontal connections in macaque primary visual cortex
Authors: McGuire Barbara A. , Gilbert Charles D. , Rivlin Patricia K. , Wiesel Torsten N.
Published: January 2005

Pyramidal neurons within the cerebral cortex are known to make long‐range horizontal connections via an extensive axonal collateral system. The synaptic characteristics and specificities of these connections were studied at the ultrastructural level. Two superficial layer pyramidal cells in the primate striate cortex were labeled by intracellular injections with horseradish peroxidase (HRP) and their axon terminals were subsequently examined with the technique of electron microscopic (EM) serial reconstruction. At the light microscopic level both cells showed the characteristic pattern of widespread, clustered axon collaterals. We examined collateral clusters located near the dendritic field (proximal) and approximately 0.5 mm away (distal). The synapses were of the asymmetric/round vesicle variety (type I), and were therefore presumably excitatory. Three‐quarters of the postsynaptic targets were the dendritic spines of other pyramidal cells. A few of the axodendritic synapses were with the shafts of pyramidal cells, bringing the proportion of pyramidal cell targets to 80%. The remaining labeled endings were made with the dendritic shafts of smooth stellate cells, which are presumed to be (GABA)ergic inhibitory cells. On the basis of serial reconstruction of a few of these cells and their dendrites, a likely candidate for one target inhibitory cell is the small‐medium basket cell. Taken together, this pattern of outputs suggests a mixture of postsynaptic effects mediated by monosynaptic excitation followed by combined disynaptic inhibition and excitation. As a consequence the horizontal connections may well be the substrate for the variety of influences observed between the receptive field center and its surround.
Evidence for enkephalin‐ and endorphin‐immunoreactive cells in the anterior pituitary of the axolotl Ambystoma mexicanum
Authors: Leon‐Olea Martha , Sanchez‐Alvarez Marcela , Pĩa Ana Luisa , Bayon Alejandro
Published: January 2005

An immunohistochemical study of opioid peptides in the hypophysis of the axolotl, Ambystoma mexicanum, was carried out with antisera against leu‐enkephalin, beta‐endorphin, met‐enkephalin, and dynorphin A (1–8). We found leu‐enkephalin immunoreactivity in some fibers of the neural lobe and the median eminence. In contrast to previous reports on mammals and other vertebrates, we found leu‐enkephalin immunoreactivity in many cells scattered throughout the anterior lobe. As in other vertebrates, the beta‐endorphin immunoreactivity was present in all the cells of the intermediate lobe and in a few cells of the anterior lobe. Met‐enkephalin and dynorphin A (1–8) immunoreactivities were only present in the neural lobe and the median eminence. The presence of leu‐enkephalin and beta‐endorphin in the anterior lobe suggests that these peptides could be acting as hormones released from the hypophysis of the unmetamorphosed amphibian.
GABA‐like immunoreactivity in the tuberomammillary nucleus: An electron microscopic study in the rat
Authors: Ericson Hans , Köhler Christer , Blomqvist Anders
Published: January 2005

The organization of GABAergic elements in the histaminergic tuberomammillary nucleus has been examined by using antibodies against γ‐aminobutyric acid (GABA) and light and electron microscopy.

Most neuronal perikarya of the ventral subgroup of the tuberomammillary nucleus were GABA immunoreactive (GABA‐i). The morphology of the GABA‐i perikarya was similar to the morphology of histaminergic perikarya described by Hayashi et al. ('84: J. Comp. Neurol. 229:233–241) and Wouterlood et al. ('86: J. Comp. Neurol. 252:227–243).

The GABA‐i perikarya were contacted by relatively few terminals. The mean bouton covering ratio of GABA‐i perikarya was 6.1%, whereas the mean bouton covering ratio for GABA‐i dendrites in the tuberomammillary nucleus was 31%. Some of the presynaptic terminals were GABA‐i. In addition, GABA‐i perikarya and dendrites formed close contacts that never presented synaptic specializations. These results suggest that neurons of the histaminergic tuberomammillary nucleus contain the neurotransmitter GABA. Furthermore, GABA may act as a modulator of cellular processes within the tuberomammillary nucleus.
Evidence for subdivisions in the human suprachiasmatic nucleus
Authors: Mai J. K. , Kedziora O. , Teckhaus L. , Sofroniew M. V.
Published: January 2005

The human suprachiasmatic nucleus was analysed by immunohistochemical demonstration of various substances in combination with 3‐dimensional computerized reconstruction and video overlay facilities. In the human, the suprachiasmatic nucleus is not as compact as in the rodent. Its boundaries are not easily delineated using conventional stains, and it shows no obvious cytoarchitectonic structure. However, based on its chemoarchitecture, the human suprachiasmatic nucleus can be apportioned into five major subdivisions: Dorsal, comprising a crescent shaped mass of densely packed neurophysin/vasopressin‐neurons as well as neurotensin‐neurons, and also containing 3‐fucosyl‐N‐acetyl‐lactosamine (FAL)‐positive neurons in its medial part. Central, occupying the core of the nucleus and consisting precisely of a region devoid of neurophysin/vasopressin neurons but demarcated by calbindin, synaptophysin, and a circumscribed cluster of vasoactive intestinal polypeptide‐neurons and containing neurotensin neurons as well. Anteroventrally this division also contains some intermingled neurons positive for neurotensin, neuropeptide Y, somatostatin, and FAL. Ventral, extending from the anterior extreme of the preoptic recess caudolaterally to a field between the optic chiasm and the anteroventral margin of the supraoptic nucleus. This subdivision is specified by synaptophysin, calhindin, and substance P immunoreactivity and is almost free of glial fibrillary acidic protein. From its rostral portion, fibers immunoreactive for calbindin, vasoactive intestinal polypeptide, synaptophysin, and substance P protrude deeply into the optic chiasm. Medial, comprising a thin band between the subependymal zone and the dorsal subdivision, containing scattered somatostatin neurons. External, extending as a band around the dorsal and lateral borders of the nucleus, containing astrocytes expressing the FAL‐epitope and scattered neurophysin/vasopressin and neurotensin neurons.

These findings indicate that the human suprachiasmatic nucleus contains well‐defined subdivisions with different, chemically specific, connections and provides a basis for comparing these subdivisions with the structure and function of subdivisions previously described for the suprachiasmatic nucleus in experimental animals. In addition, the findings strengthen the concept that the human suprachiasmatic nucleus generates and expresses circadian rhythms in a manner similar to that documented for the suprachiasmatic nucleus in experimental animals, and suggest that different subdivisions may subserve specific functional roles.
Organization of pyramidal neurons in area 17 of monkey visual cortex
Authors: Peters Alan , Sethares Claire
Published: January 2005

In sections of area 17 of monkey visual cortex treated with an antibody to MAP2 the disposition of the cell bodies and dendrites of the neurons is readily visible. In such preparations it is evident that the apical dendrites of the pyramidal cells of layer VI form fascicles that pass into layer IV, where most of them gradually taper and form their terminal tufts. In contrast, the apical dendrites of the smaller layer V pyramidal cells come together in a more regular fashion. They form clusters that pass through layer IV and into layer II/III where the apical dendrites of many of the pyramidal cells in that layer add to the clusters. In horizontal sections taken through the middle of layer IV, these clusters of apical dendrites are found to have an average center‐to‐center spacing of about 30 μm, and it is proposed that each cluster of apical dendrites represents the axis of a module of pyramidal cells that has a diameter of about 30 μm and contains about 142 neurons.

The MAP2 antibody reaction also reveals that some pyramidal cells in layers IVA and IVB have their cell bodies arranged into cones. There are about 118 such cones beneath 1 mm2 of cortical surface and the apical dendrites of the pyramidal cells within them bundle together at the apex of each cone to pass into layer III. Surrounding the cones of neurons there are horizontally aligned, thin dendrites. The location of these dendrites coincides with the dark walls of the honeycomb pattern seen in layer IVA after cytochrome oxidase reactions, or after the parvocellular input from the lateral geniculate nucleus has been labeled. Thus the cones of pyramidal cells within upper layer IV fit into the pockets of the honeycomb pattern. Below the cones of pyramidal cells are the outer Meynert cells within layer IVB, and the cell bodies of these large neurons are disposed so that they preferentially lie beneath the neuropil between the cones of pyramids.

It is suggested that pyramidal cell modules are a basic feature of the cerebral cortex, and that these are combined together by afferent inputs to the cortex to generate the systems of functional columns.
Ultrastructural localization of substance P, met‐enkephalin, and somatostatin immunoreactivity in lamina X of the primate spinal cord
Authors: Lamotte Carole C. , Shapiro Christine M.
Published: January 2005

The ultrastructural localization of substance P (SP), met‐enkephalin (MENK), and somatostatin (SS) in the lamina X area surrounding the central canal of the macaque monkey was examined by the indirect peroxidase‐antiperoxidase method. The most common synaptic terminals in lamina X were simple terminals (S) with small rounded or pleomorphic clear vesicles: one to two dense‐core vesicles were occasionally also present. These were found on soma, dendrites, and dendritic spines, in all regions of lamina X. A second class of terminal with round or oval clear vesicles was glomerular (G) in shape, with scalloped edges, and contained many mitochondria. These large terminals had several synaptic contacts onto dendrites, spines, and small terminals and were found mainly in the lateral region. The third class (L) contained small clear vesicles and several vesicles with large, dense cores (100–125 nm), and also contacted dendrites, mainly lateral to the canal. The fourth class of terminal (D) contained small clear vesicles and several vesicles with small, dense cores (75–100 nm): these contacted dendrites and somata in all areas. Very few terminals with fiat vesicles were identified. There was an unequal distribution of immunoreactivity among the several terminal classes identified in lamina X. Most SP terminals were S terminals, but SP L terminals were also common: few were D terminals. MENK terminals were usually either S terminals or D terminals: L terminals were rarely MENK positive. SS terminals were commonly D terminals or S terminals: L terminals were also rarely SS positive. Only SP terminals were identified as G terminals. Synaptic targets of SP, MENK, and SS terminals were most commonly dendrites. In addition to unlabelled neurons, peptidergic neurons and their processes were also synaptic targets of terminals containing the same peptide. The distributions of these peptides in primate lamina X differ from that of the same peptides in primate superficial dorsal horn. These differences are important, in consideration of some of the parallels that may be drawn between the lamina X area and the superficial dorsal horn: both areas have high concentrations of the same peptides, receive nociceptive primary afferents, and contain spinothalamic and other projection neurons. Nevertheless, comparison of the distribution of immunoreactivity among terminal classes indicates that neurochemical organization at the ultrastructural level is quite distinct in each of the two areas. This may also reflect other roles of the lamina X area, including its involvement in visceral functions, although it would be expected that this element might be less prominent at the cervical levels we investigated.
Dendritic morphology of pyramidal neurones of the visual cortex of the rat: I. Branching patterns
Authors: Larkman Alan U.
Published: January 2005

The aim of this study was to provide quantitative descriptions of the branching patterns of basal and apical dendrites of pyramidal neurones from the visual cortex of the rat. Thirty‐nine neurones from cortical layers 2/3 and 5, that had been injected with horseradish peroxidase, reconstructed, and measured with the light microscope as part of an earlier study (Larkman and Mason, '90; J. Neurosci. 10:1407–1414), were used. The cells had previously been divided into three classes, layer 2/3 cells and thick and slender layer 5 cells, on the basis of their dendritic morphology.

The branching pattern of the basal and apical oblique dendrites was similar for all the cells. Between 3 and 9 basal trees arose from the soma and the number of tips in each tree varied widely, between 1 and 13. The path lengths of all the basal dendrites of a given cell were relatively constant, however. Most basal dendritic branching occurred close to the soma, such that terminal segments were much longer than intermediate segments and contributed approximately 90% of the total dendritic length of each tree. Terminal segments showed only a narrow range of diameters. Most apical oblique trees arose from the proximal part of the apical trunk. They tended to be less highly branched but were otherwise extremely similar to basal trees. Distal oblique trees were unbranched or branched only once, and their terminal segments tended to be shorter and thinner than those of basal trees.

The branching pattern of the apical terminal arbors was different, with many longer intermediate segments. The terminal segments tended to be thinner than those of basal or proximal oblique trees. Slender layer 5 cells were without obvious terminal arbors.

The basal and proximal oblique dendrites jointly sampled a roughly spherical volume of cortex centred about the soma, and together they accounted for the substantial majority of the cell's total dendritic shaft membrane area. Comparisons with previous studies suggest that intracellular HRP injection can yield a more complete visualization of dendritic morphology than is obtained using Golgi‐based methods (unless cells are reconstructed across tissue slabs), and can therefore result in a different view of the relative importance of the various components that make up the cell's dendritic system.
Reorganization of the area dentata serotoninergic plexus after lesions of the median raphe nucleus
Authors: Haring John H.
Published: January 2005

Serotoninergic projections from the dorsal and median raphe nuclei to the area dentata of the hippocampal formation terminate mainly in the molecular layer and hilus, respectively. Consequently, a reduction in the density of the hilar serotoninergic plexus is seen by immunocytochemistry 2 weeks after lesions of the median raphe nucleus. Hippocampal serotonin concentration and serotonin high affinity uptake are also significantly reduced. Six weeks after lesion, surviving serotoninergic axons form a dense band in the inner molecular layer of the dorsal area dentata, a region that usually contains a sparse serotoninergic plexus. Moreover, serotoninergic fibers traverse the molecular layer and pass through the granule cell layer to reinnervate the hilus. Serotonin concentration and high affinity uptake have recovered to near normal levels by 6 weeks postlesion. Changes in the anatomical distribution of the area dentata serotoninergic plexus have not been reported in cases in which serotoninergic sprouting follows axotomy of serotoninergic projections. Thus direct lesions of serotoninergic neurons can produce a homotypic compensatory response that is qualitatively different from that generated by axotomy. The mechanistic basis for this reorganization is unclear, but the apparent extension of serotoninergic axon collaterals toward the hilus suggests that the denervated hilar neuropil is guiding reinnervation. Finally, anatomical evidence from animals studied 10 weeks postlesion suggests that the compensatory proliferation of serotoninergic axons observed 6 weeks after median raphe lesion is a transient event.