bluuebunny/crossref_metadata_2025 huggingface dataset:
A morphological correlate of target recognition by regenerating motor axons in the cockroach
Authors: Denburg Jeffrey L. , Caldwell Robert T.
Published: January 2005

A specific cell recognition process during regeneration of severed axons of identified cockroach motor neurons eventually leads to the reformation of the original innervation pattern of target muscles in the leg. This occurs even though, at early times after nerve crush, the multiple branches of each regenerating axon grow into both appropriate and inappropriate muscles. In this study, we sought to examine whether there are any structural differences between regenerating axon branches in appropriate and inappropriate muscles that could lead to an understanding of why only those in inappropriate muscles are eliminated. A neuron subset‐specific monoclonal antibody, NSS‐2A, which labels the inhibitory motor neurons, was used to make their axon branches visible at various times after nerve crush. In inappropriate muscles, these axons grow primarily parallel to the muscle fibers and are later eliminated. In the appropriate muscles, these axon branches initially also grow parallel to the muscle fibers, but subsequently grow many interstitial collaterals. The formation of the collateral branches is a morphological correlate of the specific interaction of a neuron with its appropriate muscle. The simultaneous occurrence of axonal elimination and collateral sprouting supports the idea that the two processes are causally related, as suggested by the sibling neurite bias hypothesis.
Structural and functional consequences of neonatal deafferentation in the superficial layers of the hamster's superior colliculus
Authors: Mooney Richard D. , Nikoletseas Michael M. , King Tod D. , Savage Steven V. , Weaver Michael T. , Rhoades Robert W.
Published: January 2005

Intracellular recording and horseradish peroxidase (HRP) injection techniques were used to evaluate the effects of neonatal enucleation upon the structural and functional properties of cells in the superficial retinorecipient laminae of the hamster's superior colliculus (SC). The physiological recordings confirmed previous results that normally visual superficial layer neurons develop somatosensory receptive fields in the enucleated animals. This study further showed that all of the physiological subclasses of somatosensory neurons normally encountered in the deep layers were present in the superficial laminae. With the exception of marginal cells, all of the morphological classes of neurons in the superficial SC laminae of sighted hamsters (narrowfield vertical cells, widen eld vertical cells, stellate cells, horizontal cells, and giant stellate cells) were recovered from the blinded animals. Quantitative comparison of neurons within a given morphological class demonstrated only slight differences between cells from blind and sighted hamsters. However, there was a significant reduction in the percentage of neurons with dorsally directed dendrites in the neonatally enucleated animals. Additional experiments with the Golgi technique also demonstrated that neonatal enucleation altered the distribution of morphological cell types in the superficial SC laminae. These results suggest that enucleation in the hamster may result in relative reductions in specific cell types in the superficial SC laminae rather than dendritic changes in all of the cell classes present in these layers.
Sensory reinnervation after partial removal of the olfactory bulb
Authors: Monti‐Graziadei A. G. , Graziadei P. P. C.
Published: January 2005

In this study, in order to provide the anatomical basis for future behavioral and electrophysiological experiments, we describe the effects of unilateral bulbar lesion on the peripheral sensory neurons and the parameters of reinnervation of the damaged olfactory bulb. Neonatal mice and rats were subjected to removal of portions of the olfactory bulb. At survival times from 2 to 6 months, the animals were killed by transcardial perfusion and processed for light (histological, immunohistochemical, autoradiographic) and electron microscopic observations. As a result of this surgery, in the basal layer of the olfactory neuroepithelium the rate of mitotic activity increased while the number of mature olfactory neurons was greatly reduced. The regrowing olfactory axons, by forming ectopic glomerular structures in the damaged target, profoundly influenced its reorganization. The typical layered morphology of the olfactory bulb was often disrupted in the bulbar remnant; the large dendrites of the deafferented mitral cells bent toward the ectopically located glomerular structures establishing numerous synaptic contacts. The results from this study indicate that the olfactory input plays an important role in the reorganization of the damaged olfactory bulb. Behavioral experiments in partially bulbectomized animals should provide essential information about the importance of a topological map in the processing of olfactory cues.
Axonal sprouting and frank regeneration in the lizard tail spinal cord: Correlation between changes in synaptic circuitry and axonal growth
Authors: Duffy Mark T. , Liebich Diana R. , Garner Laurie K. , Hawrych Andrew , Simpson Sidney B. , Davis B. M.
Published: January 2005

In our previous studies, we found that the number of supraspinal neurons projecting to the level of tail spinal cord increases by 74% during tail regeneration and that the number of local spinal neurons with descending projections increases 233%. However, only a small fraction of the supraspinal axons (< 4%) and half of the local spinal axons actually enter the regenerated spinal cord. We suggested that this may be the result of “synaptic capture” in which regrowing axons make synapses on denervated targets rostral to the transection, aborting further regeneration. To examine this hypothesis, morphometric analysis of electron microscope (EM) photomontages was used to test for changes in synaptic distribution on ventral horn neurons rostral to regenerating tail spinal cord. In addition, 3H‐thymidine and retrograde markers were used to determine whether the regenerate axons arose from cut axons, neurogenesis, or sprouting from uninjured neurons.

3H‐thymidine injections during regeneration, combined with retrograde HRP pathway tracing, did not reveal the production of new neurons in the tail spinal cord. To test whether cut axons regenerate, fluorescein isothiocyanate conjugated latex beads were applied to the exposed end of the tail spinal cord. After tail regeneration, HRP was applied to the new spinal cord in the regenerated tail. Examination of local spinal neurons (the primary source of axons that enter the regenerated tail spinal cord) revealed that 28% of the neurons contained both labels. This indicated that cut axons successfully regrew into the new tail spinal cord.

The regenerated axons that fail to enter the new tail spinal cord can be found in the normal spinal cord immediately rostral to the regenerated tail. To determine whether these axons were making synaptic contacts, lamina IX ventral horn neurons were examined. EM photomontages of the spinal cord rostral to the regenerate tail revealed the following properties: (1) neurons rostral to regenerated tails are larger in area compare to non‐regenerates (mean increase = 112%); (2) axosomatic contacts cover a greater percentage of the neuronal soma following regeneration compared to normal (mean increase = 23%); and (3) this increased innervation is the result of an increase in the number of synaptic boutons rather than larger boutons. The number of synaptic contacts in regenerated lizards returned to normal following lumbar transection, indicating that supraspinal and/or long descending propriospinal afferents were the major source of the increased synaptic contacts. These results suggest that increased synaptogenic activity in the spinal cord immediately rostral to the junction of normal and regenerating spinal cord, could be an important mechanism for inhibiting CNS axonal regeneration.
Phenylethanolamine N‐methyltransferase (PNMT)‐expressing horizontal cells in the rat retina: A study employing double‐label immunohistochemistry
Authors: Hammang Joseph P. , Bohn Martha C. , Messing Albee
Published: January 2005

Phenylethanolamine N‐methyltransferase (PNMT), the final enzyme in the catecholamine biosynthetic pathway that converts norepinephrine to epinephrine, has been detected in the retinas of various vertebrate species. The expression of PNMT has generally been thought to occur in amacrine cells of the ganglion cell and inner nuclear layers. By using immunohistochemical techniques, we have found a population of PNMT‐ and neurofilament‐positive neurons at the border of the inner nuclear layer and the outer plexiform layer in the rat retina. We have classified these cells as horizontal neurons based on their location adjacent to the outer plexiform layer, their morphology, and their expression of vimentin and neurofilaments.
Polyaxonal amacrine cells of rabbit retina: Morphology and stratification of PA1 cells
Authors: Famiglietti Edward V.
Published: January 2005

Polyaxonal amacrine cells are a new class of amacrine cell bearing one to six branching, axon‐like processes, closely resembling the axons of Golgi type II cells found elsewhere in the central nervous system. Of the four types of polyaxonal amacrine cell that we have recognized in rabbit retina, three have been described previously in brief communications, and one is the subject of this paper.

Type 1 polyaxonal (PA1) amacrine cells have larger cell bodies than most amacrine cells in Golgi preparations, averaging about 13 μm in diameter. These are typically positioned interstitially in the middle of the inner plexiform layer (IPL), although some are also found in the amacrine and ganglion cell layers. Axons and dendrites are broadly stratified in the middle of the IPL, in the vicinity of the a/b sublaminar border. Sparsely branching dendrites have a conventional appearance, branching at a narrow angle, and giving rise to smaller daughter branches, which taper gradually toward their termination. An unusual feature of the dendrites is the zig‐zag course of some terminal branches. Clusters of small, pedunculated spines are common on proximal dendrites, and spines are virtually absent on axons.

Axons emerge from proximal dendrites within 50 μm of the soma, and more rarely from the soma, in a tapering initial segment, commonly interrupted by one or two large swellings. Subsequent branching is at a wide angle, and the fine caliber is maintained in the transition from parent to daughter branches. The uniform thickness of the axonal branches is interrupted at intervals by boutons en passant. Although the extent of the dendritic tree is large, exceeding 500 μm in radial extent from the cell body, for cells a few millimeters distant from the visual streak, the axonal tree is much larger, and its radial extent is measured in millimeters. PA1 amacrine cells are believed to be polarized in their functional organization, with a primarily recipient dendritic tree and a primarily transmissive axonal tree.

PA1 amacrine cells co‐stratify with nab cone bipolar cells and with certain small tufted amacrine and ganglion cells at the a/b sublaminar border. The co‐stratification of both axons and dendrites at the a/b sublaminar border of the IPL suggests that PA1 amacrine cells are important modulators of neural activity in the middle of the IPL, affecting both ON and OFF responses, and perhaps ON‐OFF cells selectively.
Astrocytes in cat visual cortex studied by GFAP and S‐100 immunocytochemistry during postnatal development
Authors: Müller Christian M.
Published: January 2005

A monoclonal antibody to glial fibrillary acidic protein (GFAP) and a polyclonal antiserum to the S‐100 protein were used to study the expression of these astrocytic proteins in the postnatal visual cortex of the cat. Three changes in antigen expression of these astroglial markers could be distinguished over development. First, the density of cells in the white matter, which are heavily labelled with both antibodies from birth until adulthood, diminishes after the third postnatal week. By intracellular filling with Lucifer Yellow the reduction of the cell density can be attributed to the disappearance of large astrocytes with a morphology of transforming radial glia, present only in early postnatal development. Second, heavily labelled, large cells present in the grey matter at the seventh postnatal day have disappeared by the fifth postnatal week. On the basis of their morphology these cells can also be classified as radial glial cells. Finally, astroglial cells of the adult‐like stellate form appear to be labelled in the cortical layers between the third and seventh postnatal weeks. While the density of these cells and the S‐100 immunoreactivity of the cell bodies is adult‐like at the fourth postnatal week, there is a gradual increase of the staining intensity with the GFAP antibody up to the seventh postnatal week. This developmental period is paralleled by the appearance of S‐100‐positive astrocytic processes. The gradual expression of GFAP immunoreactivity and the increased expression of S‐100 is interpreted as reflecting the time course of astrocytic maturation. A possible relation of the maturation of astrocytes and cortical development, both of which are prominent in the time period between the third and seventh postnatal week, is discussed.
Neurofilaments are prominent in bullfrog olfactory axons but are rarely seen in those of the tiger salamander, Ambystoma tigrinum
Authors: Burton Paul R. , Wentz Mark A.
Published: January 2005

Bullfrog olfactory axons show variable numbers (0–29) of structurally typical neurofilaments (NFs) about 10 nm in diameter. In studies tracking these NFs through serial sections of axons in cross section, they were found to be discontinuous, with a calculated average length of about 118 μm. In contrast to olfactory axons in bullfrogs, those of the tiger salamander Ambystoma trigrinum rarely show NFs. To be certain that the absence of NFs is a specific characteristic of olfactory axons, pieces of salamander spinal cord, optic nerve, and sciatic nerve were examined and found to contain typical NFs. To minimize the possibility that NFs in salamander olfactory axons were degraded or poorly fixed during preparation for electron microscopy, samples were fixed by using a variety of fixative and buffer combinations. To exclude the possibility that proteases degraded NFs during processing, prior to fixation some pieces of olfactory nerve were incubated in physiological saline containing protease inhibitors. Regardless of the preparation method, NFs were generally not seen in salamander olfactory axons. Extracts of salamander olfactory nerve were subjected to SDS‐polyacrylamide gel electrophoresis (PAGE) and immunoblotting studies with monoclonal antibodies to the three NF subunit proteins. The immunoblots showed negligible or trace amounts of NF‐L (light) and NF‐H (heavy), while an NF‐M (medium) protein having a molecular mass (Mr) of 160 kD was present in abundance. Extracts of salamander spinal cord, on the other hand, showed all three subunit proteins (with Mrs of 230, 160, and 77 kD). If one assumes that cells assemble structural elements to provide for a given function, the findings suggest that NFs in olfactory neurons of bullfrogs provide a function that may be missing in olfactory neurons of the salamander; the evidence also suggests that the absence of NFs in the salamander may be clue to a deficiency in two of the three NF subunit proteins.
Comparative distribution of messenger RNAs encoding glutamic acid decarboxylases (Mr 65,000 and Mr 67,000) in the basal ganglia of the rat
Authors: Mercugliano M. , Soghomonian J.‐J. , Qin Y. , Nguyen H. Q. , Feldblum S. , Erlander M. G. , Tobin A. J. , Chesselet M.‐F.
Published: January 2005

Glutamic acid decarboxylase, the enzyme required for GABA synthesis, exists as distinct isoforms, which have recently been found to be encoded by different genes. The relative expression of messenger RNAs encoding two isoforms of glutamic acid decarboxylase (Mr 67,000 and Mr 65,000) was measured at the single‐cell level in neurons of the rat basal ganglia with in situ hybridization histochemistry. Both messenger RNAs were expressed in neurons of the striatum, pallidum, and substantia nigra pars reticulata, but marked differences in the relative level of labelling were observed with the two probes. In striatum, efferent neurons were more densely labelled for the messenger RNA encoding glutamic acid decarboxylase (Mr 65,000) than for the messenger RNA encoding glutamic acid decarboxylase (Mr 67,000), whereas the reverse was observed for GABA‐ergic interneurons. Neurons of the entopeduncular nucleus were much more densely labelled for messenger RNA encoding glutamic acid decarboxylase (Mr 65,000) than for messenger RNA encoding glutamic acid decarboxylase (Mr 67,000). In addition, labelling for messenger RNA encoding glutamic acid decarboxylase (Mr 65,000) was higher in the entopeduncular nucleus (internal pallidum) than in the globus pallidus (external pallidum), a structure which expressed similar levels of both mRNAs. In contrast to neurons of the internal pallidum, efferent neurons of the substantia nigra pars reticulata expressed slightly more messenger RNA encoding glutamic acid decarboxylase (Mr 67,000) than that encoding the other isoform of the enzyme. The results suggest a differential expression of the messenger RNAs encoding the two isoforms of glutamic acid decarboxylase in subpopulations of basal ganglia neurons in rats.
Antennular projections to the midbrain of the spiny lobster. II. Sensory innervation of the olfactory lobe
Authors: Schmidt Manfred , Ache Barry W.
Published: January 2005

The projection pattern of antennular sensory afferents in the olfactory lobe (OL) of the spiny lobster, Panulirus argus, was examined by backfilling axons in the antennular nerve (AN) with biocytin. Thin, presumptive olfactory afferents from the lateral division of the AN form a tract in the brain that diverges into a dense plexus that completely envelops the glomerular cortex of the OL. Most of the thin (diameter ≤ 0.3–1 μm) afferents project to single glomeruli. About 10% of the thin afferents, however, branch in the plexus and project to multiple glomeruli. A smaller number of medium‐sized to thick (diameter 2–10 μm), presumably mechanosensory, afferents also innervate the OL and co‐project to multiple glomeruli with the thin afferents. Afferents arborize profusely within the columnar glomeruli into very fine processes that penetrate to the base of the columns, but selectively terminate in either the cap/subcap region‐or in the innermost part of the base of the columns, often with conspicuous terminal boutons, forming two distinct regions of presumptive synaptic output. These results suggest that 1) The majority of the OL innervation is provided by olfactory sensilla (aesthetascs), but that other types of sensilla provide additional, likely mechanosensory, input to the OL. 2) The projection of olfactory afferents is not strictly uniglomerular. 3) The columnar organization of crustacean olfactory glomeruli is functionally significant and may provide an evolutionary correlate of the recently proposed subdivision of the vertebrate olfactory bulb into “functional columns”.
Restorative effects of reinnervation on the size and dendritic arborization patterns of axotomized cat spinal α‐motoneurons
Authors: Brännström Thomas , Havton Leif , Kellerth Jan‐Olof
Published: January 2005

In a preceding paper [Brännström, et al. (1992) J. Comp. Neurol. 318:439–451] a marked reduction in dendritic size was observed in cat spinal motoneurons following permanent axotomy. The aim of the present study was to analyse the possible restorative effects of peripheral reinnervation on the size and dendritic branching patterns of cat spinal motoneurons which had been deprived of neuromuscular contact for an extended period of time.

In adult cats the medial gastrocnemius (MG) nerve was transected and ligated. After 6 weeks the nerve was allowed to reinnervate its muscle through a nerve graft. With approximately 6 weeks needed for muscle reinnervation [Foehring, et al. (1986) J. Neurophysiol. 55:947–965], the MG motoneurons were devoid of neuromuscular contact for altogether about 12 weeks. Two years later reinnervated MG α‐motoneurons were intracellularly labelled with horseradish peroxidase to allow quantitative analyses of the cell bodies and dendritic trees. Comparisons were made with previous data from normal and permanently axotomized MG motoneurons.

The reinnervated motoneurons exhibited positive correlations between dendritic stem diameter, on one hand, and combined length, volume, membrane area, and number of end branches of the whole dendrite, on the other. By using the regression equations for these correlations, the total dendritic size of whole reinnervated motoneurons could be estimated. Such calculations showed that in comparison with the reduction in dendritic size found at 12 weeks after permanent axotomy (Brännström et al., see above), peripheral reinnervation caused the dendritic volume and membrane area to return to normal values. However, the values for combined dendritic length and number of dendritic end branches were still reduced by more than 25% as compared to the normal situation.

The results indicate that following reinnervation of the target muscle, the axotomized motoneurons did not recover their original number of dendritic branches. The normalization of dendritic membrane area and volume was instead accomplished by two other mechanisms, namely an increase in dendritic diameters and an increased number of dendrites per neuron.
Somatic sensory responses in the rostral sector of the posterior group (POm) and in the ventral posterior medial nucleus (VPM) of the rat thalamus: Dependence on the barrel field cortex
Authors: Diamond Mathew E. , Armstrong‐James Michael , Budway Matthew J. , Ebner Ford F.
Published: January 2005

The projection from the whiskers of the rat to the S‐I (barrel) cortex is segregated into two separate pathways—a lemniscal pathway relayed by the ventral posterior medial nucleus (VPM) to cortical barrels, and a paralemniscal pathway relayed by the rostral sector of the posterior complex (POm) to the matrix between, above, and below barrels. Before investigating how the barrel cortex integrates these sensory pathways, it is important to learn more about the influence of the various inputs to the two thalamic nuclei. Based on the greater density of descending versus ascending projections to POm, it seemed likely that corticofugal inputs play an important role in the sensory activity of POm. To test this, the responses of POm and VPM cells to sensory stimuli were measured before, during, and after suppression of the S‐I cortex. S‐I was suppressed by application of magnesium or by cooling; the status of the barrel cortex was assessed continuously by an electrocorticogram. All VPM cells (n = 8) responded vigorously to whisker movement even when the barrel cortex was profoundly depressed. In contrast, all POm cells (n = 9) failed to respond to whisker movement once the barrel cortex became depressed, typically about 25 minutes after the start of cortical cooling or magnesium application. POm cells regained responsiveness about 30 minutes after the cessation of cortical cooling or the washoff of magnesium. These findings indicate that the transmission of sensory information through the lemniscal pathway occurs independently of the state of cortex, whereas transmission through the paralemniscal pathway depends upon the state of the cortex itself. © 1992 Wiley‐Liss, Inc.
Structural changes of the soleus and the tibialis anterior motoneuron pool during development in the rat
Authors: Westerga J. , Gramsbergen A.
Published: January 2005

The morphological development of motoneuron pools of two hindlimb muscles of the rat, soleus (SOL) and tibialis anterior (TA), was studied in rats ranging in age between 8 and 30 postnatal days (P8—P30). Motoneurons were retrogradely labelled by injecting a cholera toxin B subunit solution directly into the muscles. This resulted in extensive labelling of motoneurons as well as their dendritic trees.

The distribution of cross sectional areas of neuronal somata was determined for both muscles at various ages. Somal size increased considerably between P8 and P12, whereas growth was moderate between P12 and P20. The size distribution of SOL motoneurons was bimodal from P20, whereas the size distribution of TA motoneurons remained largely unimodal.

The morphological development of the dendritic tree was studied qualitatively. The development of dendritic arborization within the SOL and the TA motoneuron pool showed major differences. The arborization pattern of dendrites of TA motoneurons was basically multipolar at all ages. In contrast, dendrites of SOL neurons tended to line up with the rostro‐caudal axis and became organized in longitudinal bundles from P16 onwards.

The relatively late appearance of dendrite bundles in the soleus motoneuron pool suggests that they might be related to the fine‐tuning of neuronal activity rather than patterning of motor activity. The occurrence of dendrite bundles in SOL and not in TA motoneuron pools suggests that they may be related to the different afferent organization of this postural muscle or to its tonic activation pattern. © 1992 Wiley‐Liss, Inc.
Segmental distribution and peptide content of primary afferent neurons innervating the urogenital organs and colon of male rats
Authors: Keast J. R. , de Groat W. C.
Published: January 2005

Many visceral afferent neurons contain peptides, which have been proposed as histochemical markers for nerve pathways of particular targets or as transmitter candidates. The former possibility was investigated in the present study. Primary afferent neurons which project to the urinary bladder, distal colon or penis of rats, and the colon of cats were labelled with retrogradely transported fluorescent dyes (Fast Blue, True Blue, or Fluoro Gold). One to six weeks after dye injection into the organs, lumbosacral dorsal root ganglia were removed, treated with colchicine, and processed for immunohistochemical identification of five peptides. Dye‐labelled neurons were distributed in an organ‐specific manner in the lower lumbosacral ganglia, where colon afferent neurons were almost exclusively found in S1 ganglia, penis neurons primarily in L6, and bladder neurons at both levels. Substance P‐ (SP), calcitonin gene‐related peptide‐(CGRP), vasoactive intestinal peptide‐ (VIP), enkephalin‐ (ENK), and somatostatin‐ (SOM) immunoreactivity (IR) were detected in neurons in all lumbosacral ganglia but only some of these peptides were present in a large percentage of labelled neurons. The numbers of peptide‐containing neurons innervating each organ were CGRP > SP > VIP > ENK > SOM; however some differences were observed in the relative proportions of these neuronal populations between upper lumbar and lower lumbosacral ganglia and between different organs. The major difference seen at the upper lumbar level was amongst the SP‐IR neurons, which were common (25–30%) amongst bladder and colon afferent neurons but absent in penis neurons. At the lower lumbar‐sacral level CGRP‐IR was present in a greater proportion (70%) of colon neurons than neurons which supplied the bladder (52%) or penis (35%). VIP‐IR was found in fewer (2–12%) neurons of each group. The afferent innervation of the cat colon exhibited a similar peptide distribution but with smaller numbers of CGRP‐IR neurons (45% vs. 70%) and larger numbers of VIP‐ (18% vs. 2%) and ENK‐IR (5% vs. 0–2%) neurons. SOM‐IR was rarely found in any dye‐labelled neurons and may therefore be more important in the sensory supply of other pelvic organs or of somatic organs. In summary, these studies have revealed that primary afferent neurons supplying the urogenital organs and colon of male rats differ in their segmental distribution and also exhibit some differences in the percentage of cells containing certain peptides (SP, CGRP, and VIP). © 1992 Wiley‐Liss, Inc.
Effects of ethanol on development of dorsal raphe transplants in oculo: A morphological and electrophysiological study
Authors: Backman C. , Granholm A.‐C.
Published: January 2005

The purpose of this project was to investigate ethanol influence on the development of serotonin‐containing (5‐HT) neurons of the dorsal raphe nucleus in rat. Fetal tissue of embryonic day 17 from the dorsal brainstem was grafted to the anterior chamber of the eye of adult albino rats. The experimental group was exposed to 16% ethanol in the drinking water, and the control group received water ad libitum. After 4 weeks, morphological and electrophysiological evaluations were performed. Immunohistochemical analysis showed that 5‐HT‐immunoreactive fibers from ethanol treated transplants had a disturbed outgrowth pattern into the host iris as compared to the control group. Furthermore, the outgrowth area and axon bundle formation was significantly greater in the control group than in the ethanol group. Electrophysiological recordings revealed a dose‐dependent biphasic effect of locally applied ethanol on transplanted monoaminergic neurons. Low doses of ethanol (0.5–3 mM)induced an increase in basal firing rate of control neurons, while higher doses (10–100 mM)caused inhibition. However, monoaminergic neurons in the ethanol group showed a decreased neuronal sensitivity to locally applied ethanol. The same dose of locally applied ethanol which produced an excitation of neuronal activity in the ethanol transplants produced an inhibition in the control grafts. The dose‐response curve was shifted to the right. The present results suggest that chronic ethanol exposure during early development leads to altered axonal outgrowth from brainstem 5‐HT neurons, as well as decreased sensitivity of these neurons to locally applied ethanol.
Immunocytochemical demonstration of neural cell adhesion molecule (NCAM) along the migration route of luteinizing hormone‐releasing hormone (LHRH) neurons in mice
Authors: Schwanzel‐Fukuda Marlene , Abraham S. , Crossin K. L. , Edelman G. M. , Pfaff D. W.
Published: January 2005

Contact between the developing forebrain and the ingrowing central processes of the olfactory, vomeronasal and terminal nerves is preceded by a migration of neural cell adhesion molecule (NCAM)‐immunoreactive cells from the epithelium of the olfactory pit and the formation of an NCAM‐immunoreactive cellular aggregate in the mesenchyme between the olfactory pit and the forebrain. The axons of the olfactory, vomeronasal, and terminal nerves, also NCAM‐immunoreactive, grow into the cellular aggregate, which as development proceeds, becomes continuous with the rostral tip of the forebrain. The lateral and more rostral part of the cellular aggregate receives the ingrowing axons of the olfactory nerves and becomes the olfactory nerve layer of the olfactory bulb. The medial, more caudal part receives the central processes of the vomeronasal and terminal nerves. The vomeronasal nerve ends in the accessory olfactory bulb. The central processes of the terminal nerve end in the medial forebrain. Luteinizing hormone‐releasing hormone (LHRH)‐immunoreactive neurons, like the vomeronasal and terminal nerves, originate from the medial part of the olfactory pit. These LHRH cells migrate into the brain along and within a scaffolding formed by the NCAM‐immunoreactive axons of the vomeronasal and terminal nerves, and they are never seen independent of this NCAM scaffold as they cross the nasal lamina propria.

The results suggest that: (1) NCAM is likely to be necessary for scaffold formation, and (2) the scaffold may be essential for the subsequent migration of LHRH neurons into the brain. Because they aggregate, migrating LHRH‐immunoreactive neurons, on which we did not detect NCAM immunoreactivity, may interact via other cell adhesion molecules (CAM). Inasmuch as the interaction between the LHRH‐immunoreactive neurons and the NCAM‐immunoreactive scaffold is heterotypic, the possibility of a heterophilic (NCAM to other CAM) interaction is not ruled out. These findings focus our attention on the functional role of NCAM in this migratory system. © 1992 Wiley‐Liss, Inc.
A quantitative light and electron microscopic analysis of taurine‐like immunoreactivity in the dorsal horn of the rat spinal cord
Authors: Lee Inse S. , Renno Waleed M. , Beitz Alvin J.
Published: January 2005

Taurine has been proposed as an inhibitory neurotransmitter or neuromodulator in the vertebrate central nervous system. Within the spinal cord, taurine has been shown to have a direct inhibitory effect on spinal neurons and to have a selective antinociceptive effect on chemically induced nociception. Although sufficient data exists to suggest that taurine plays a neurotransmitter or neuromodulatory role in the spinal cord, it is not known whether this amino acid is present in axon terminals nor if this amino acid has a unique pattern of distribution within spinal tissue. To address these questions a monoclonal antibody against taurine was employed to localize taurine‐like immunoreactivity in the dorsal horn of the rat spinal cord by using both light and electron microscopic techniques. Taurine‐like immunoreactivity was most dense and most prominent in laminae I and II of the dorsal horn. A moderate amount of immunoreactivity was also present in laminae VIII and IX and X while the remaining laminae were only lightly stained. In laminae I and II taurine‐like immunostaining was evident within neuronal cell bodies, dendrites, myelinated and unmyelinated axons, axon terminals, and astrocytes and their processes. Cell counts of these two laminae indicated that approximately 30% of neuronal perikarya at the C2 level, 52% of neuronal perikarya at the T6 level, and 18% of neuronal perikarya at the L2 level of the cord exhibited taurine‐like immunoreactivity. With preembedding diaminobenzidine staining, approximately 20% of the axons examined in laminae I and II were found to be immunoreactive for taurine. Using postembedding immunogold staining in combination with quantitative procedures, the highest densities of gold particles were found in axon terminals containing pleomorphic vesicles and forming symmetrical synapses (36.8 particles/μm2), in a subpopulation of myelinated axons (34.2 particles/μm2), in a subpopulation of neuronal dendrites (32.6 particles/μm2), and in capillary endothelial cells (39.8 particles/μm2). Moderate labeling occurred in astrocytes (20.9 particles/μm2) and neuronal perikarya (18.7 particles/μm2). The localization of taurine to presumptive inhibitory axon terminals provides anatomical support for the hypothesis that taurine may serve an inhibitory neurotransmitter role in the superficial dorsal horn of the spinal cord. On the other hand, its localization to astrocytes and endothelial cells within both the dorsal ventral horns implies that it serves other nonneuronal functions as well. © 1992 Wiley‐Liss, Inc.
Morphology of bipolar cells labeled by DAPI in the rabbit retina
Authors: Mills Stephen L. , Massey Stephen C.
Published: January 2005

The morphology, distribution, and coverage of certain cone bipolar cell types were investigated in rabbit retina. Brief in vitro incubation of isolated rabbit retina in the fluorescent dye 4,6‐diamino‐2‐phenylindole labeled only a few cell types in the inner nuclear layer. Intracellular injection of Lucifer Yellow into these types showed them to be horizontal cells and cone bipolar cells. All stained bipolar cells ramified in sublamina a of the inner plexiform layer (IPL) and formed three classes. Two types ranged from 20 to 60 μm in diameter in both plexiform layers; the other large bipolar cell was 40–70 μm in diameter in the outer plexiform layer (OPL) and up to 150 μm in diameter in the IPL. The brightest type was narrowly stratified in the outer portion of sublamina a. Its density increased from about 500 cells/mm2 in the periphery to about 2,500 cells/mm2 in the visual streak. Staining of neighboring cells of this type showed that processes in the IPL rarely crossed, but often converged at a common site so as to impart a “honeycomb” appearance to a single sublayer of retina. The other small bipolar cell was similar in density and coverage, but stratified diffusely throughout sublamina a. The large bipolar cell stratified narrowly in the distal portion of sublamina a and was more sparsely distributed. Whether determined by staining adjacent cells or by density vs. area calculations, coverage in the OPL approached 1 for each type, as did coverage in the IPL for the two types with narrow fields. © 1992 Wiley‐Liss, Inc.
Retinal growth and cell addition during embryogenesis in the teleost, Haplochromis burtoni
Authors: Hagedorn Mary , Fernald Russell D.
Published: January 2005

Neurogenesis of the developing embryonic retina is described for the African cichlid fish, Haplochromis burtoni, from 4 days post fertilization until all cell phenotypes are generated (day 7). Cell addition and differentiation both begin at the same absolute location which later becomes the central retina. As observed in most other vertebrates, cones and ganglion cells differentiate first, followed by amacrine and bipolar cells. Rod photoreceptors, which are added late, differentiate last. Changes in retinal thickness, retinal stretching, cell size, and cell density were measured during development. From day 4 through 7, there is an increase in retinal thickness largely due to the expansion of the inner plexiform layer (IPL) and outer nuclear layer (ONL). The inner nuclear layer (INL) decreases in thickness and there is a transient decrease in the density of cells in the scleral portion of the INL. Cells increase in size in the ganglion cell layer (GCL) and the vitread INL, decrease in size in the sclerad INL, and remain the same in the ONL. Changes in the density of the cell layers were observed: the density of ONL cells increased, the density of GCL cells decreased, and INL cells increased then decreased. From day 4 to day 6, eye growth is entirely due to cell addition because no retinal stretching was observed in the ONL or the horizontal layer.

During this same developmental period, the pattern and rate of neurogenesis were measured in the differentiated portion of the retina by means of 3H‐thymidine labeling. A small number of cell divisions within the differentiated INL precede the onset of cell divisions in the ONL. The number of 3H‐thymidine labeled cells within the INL increases at a low rate consistent with an asymmetric pattern of cell division characteristic of stem cells. In contrast, cell divisions in the ONL increase exponentially, consistent with a symmetric pattern of cell division characteristic of progenitor cells. Double‐label experiments (3H‐thymidine and a rod specific opsin antibody) show that some of the symmetrically dividing cells in the ONL express the rod specific opsin within 2 days, suggesting that these dividing cells are rod progenitors. Although we do not have conclusive evidence, these developmental processes support the hypothesis that stem cells within the INL could be the source of rod precursors in the embryonic teleost retina. © 1992 Wiley‐Liss, Inc.
Light and electron microscopic characterization of dopamine‐immunoreactive axons in human cerebral cortex
Authors: Smiley John F. , Williams S. Mark , Szigeti Klara , Goldman‐Rakic Patricia S.
Published: January 2005

The distribution and synaptic connections of dopamine axons were studied by light and electron microscopy in human cerebral cortex. For this purpose, dopamine immunoreactivity was characterized in apparently normal anteriolateral temporal cortex, which was removed to gain access to the medial temporal lobe during tumor excision or treatment of epilepsy. Nissl sections showed this to be granular neocortex. Dopamine fibers were distributed throughout this cortex, although there were relatively more fibers in layers I–II and in layers V–VIa, compared to layers III–IV and VIb, resulting in a bilaminar pattern of labeling. In all layers, fibers were seen to form numerous varicosities, and to vary in size from thick to very fine. Fibers were relatively straight, sparsely branched and were oriented in various planes within the cortex. However, in layer I, they often ran parallel to the pial surface.

In order to analyze the functional interactions of dopamine fibers, individual cortical layers were surveyed for dopamine synapses. These were usually symmetrical (Gray's type II), although 13% of them were asymmetrical. Approximately 60% of dopamine synapses were made with dendritic spines, and 40% with dendritic shafts, and this ratio was similar in all layers. On both spines and shafts, it was common to see dopamine synapses closely apposed to an unlabeled asymmetric input, suggesting a dopamine modulation of excitatory input. Some postsynaptic dendritic shafts had features of pyramidal cells, including formation of spines. Since pyramidal cells are the major type of cortical spiny neuron, they probably represent the main target of dopamine synapses in this cortex. There were also dopamine profiles apposed to membrane densities on unlabeled axon terminals, suggesting another type of synaptic interaction. These findings provide the first documentation of dopamine synapses in the human cortex, and show that they form classical synaptic junctions. The location of these synapses on spines and distal dendrites, and their proximity to asymmetric synapses, suggest a modulatory role on excitatory input to pyramidal cells. © 1992 Wiley‐Liss, Inc.
Area 3a in the cat. I. A reevaluation of its location and architecture on the basis of Nissl, myelin, acetylcholinesterase, and cytochrome oxidase staining
Authors: Avendaño Carlos , Verdu Alfonso
Published: January 2005

Current knowledge on the anatomy of area 3a of the cat mainly derives from the cyto‐ and myeloarchitectonic study of Hassler and Muhs‐Clement (J Hirnforsch 6:377, 1964). Previous investigations in the cat had failed to identify a cortical region comparable to monkey's area 3a. In the present study, Nissl, myelin, acetylcholinesterase, and cytochrome oxidase staining techniques were applied to coronal and sagittal serial sections of the cat brain. Area 3a appears as a slender band of cortex between areas 4 and 3b, and in Nissl‐stained sections it is mainly characterized by an attenuated granular layer IV, overlying a thin layer V with pyramidal cells of various sizes, including a few large ones. These cytoarchitectonic features are sufficient to differentiate area 3a from neighboring areas, although the borders between them are not sharp in many cases. After the Nissl staining, the acetylcholinesterase staining proved to be the most helpful in defining the structure and borders of area 3a. Acetylcholinesterase staining was dense in layer I (in contrast with a lighter staining of outer layer I in area 4), and light in layers II and IIIa, changing to moderate in IIIc and IV (a pattern which is accentuated in area 3b). Myelin and cytochrome oxidase techniques also yielded differential staining patterns of area 3a and neighboring areas 4 and 3b, although the borders were not easily drawn with these techniques. Whereas our cyto‐ and myeloarchitectonic findings were comparable to those of Hassler and Muhs‐Clement ('64) and applied well to area 3a in the convexity of the hemisphere, we found that most of the area 3a described by these authors in the medial face of the hemisphere had a number of distinguishing architectonic (as well as connectional and physiological) features which enabled us to define it as a separate area (7m). The techniques we used to delineate area 3a are compatible with most current procedures of histo‐ and immunohistochemical staining of the brain, and may also provide valuable supporting data for electrophysiological studies. © 1992 Wiley‐Liss, Inc.
Restoration of ascending noradrenergic projections by residual locus coeruleus neurons: Compensatory response to neurotoxin‐induced cell death in the adult rat brain
Authors: Fritschy Jean‐Marc , Grzanna Reinhard
Published: January 2005

There is clinical and experimental evidence that monoamine neurons respond to lesions with a wide range of compensatory adaptations aimed at preserving their functional integrity. Neurotoxin‐induced lesions are followed by increased synthesis and release of transmitter from residual monoamine fibers and by axonal sprouting. However, the fate of lesioned neurons after long survival periods remains largely unknown. Whether regenerative sprouting may contribute significantly to recovery of function following lesions which induce cell loss has been questioned. We have previously analyzed the response of locus coeruleus (LC) neurons to systemic administration of the noradrenergic (NE) neurotoxin N‐(2‐chloroethyl)‐N‐ethyl‐2‐bromobenzylamine (DSP‐4) to adult rats. This drug causes ablation of nearly all LC axon terminals within 2 weeks after administration, followed by a profound loss of LC cell bodies 6 months later. The present study was conducted to determine the fate of surviving LC neurons and to characterize their potential for regenerative sprouting during a 16 month period after DSP‐4 treatment. The time‐course and extent of LC neuron degeneration were analyzed quantitatively in Nissl‐stained sections, and the regenerative response of residual neurons was characterized by dopamine‐β‐hydroxylase immunohistochemistry. The results document that LC neurons degenerate gradually after DSP‐4 treatment, cell loss reaching on average 57% after 1 year. LC neurons which survive the lesion exhibit a vigorous regenerative response, even in those animals in which cell loss exceeds 60–70%. This regenerative process leads progressively to restoration of the NE innervation pattern in the forebrain, with some regions becoming markedly hyperinnervated. In stark contrast to the forebrain, very little reinnervation takes place in the brainstem, cerebellum and spinal cord. These findings suggest that regenerative sprouting of residual neurons is an important compensatory mechanism by which the LC may regain much of its functional integrity in the presence of extensive cell loss. Furthermore, regeneration of LC axons after DSP‐4 treatment is region‐specific, suggesting that the pattern of reinnervation is controlled by target areas. Elucidation of the factors underlying recovery of LC neurons after DSP‐4 treatment may provide insights into the compensatory mechanisms of central neurons after injury and in disease states. © 1992 Wiley‐Liss, Inc.
Sex differences in the gross size of the rat neocortex
Authors: Reid Silvia N. M. , Juraska Janice M.
Published: January 2005

The pervasiveness of sex differences in the size of the rat cerebral cortex was investigated in ten littermate pairs of socially housed Long‐Evans hooded rats at 90 days of age. Overall, the cortex was longer and wider in male than in female rats. Sex differences were detected in most cortical regions with this sample size; the exception was the temporal cortex. While some asymmetries were found, they did not vary with the sex of the animal nor were they consistently in one direction. The contribution of the cortical layers to sex differences in cortical thickness was examined in four locations: the primary motor cortex, the forelimb area of the sensorimotor cortex and the monocular and the binocular areas of the visual cortex. The layers that showed sex differences varied among the areas but were confined to layers II–III, V and VI. Sex differences in cortical size were widespread in the adult rat but showed some regional and laminar specificity. © 1992 Wiley‐Liss, Inc.