Rostrocaudal Extension Research Articles

Cell proliferation in the brains of NMDAR NR1 transgenic mice

We have used genetically engineered NMDA receptor NR1+/− mice in which the gene for the NR1 subunit was modified in such a way that these mice express only 50% of the NR1 subunit. The NR1 subunit is necessary for NMDA receptor channel function. We investigated the effects of reduced NMDA receptor function on cell proliferation in the hippocampus and the amygdala of the adult mouse brain. Transgenic (NR1+/−) and wild-type (NR1+/+) mice were injected with BrdU. We collected brain sections cutting through the rostro-caudal extension of the entire hippocampus of the NR1+/− and NR1+/+ (wild-type) mice. The phenotype of BrdU-positive cells was identified by double labeling with antibodies to neuronal or glial markers. Our results show that the NR1+/− mice, which express the NMDAR NR1 subunit at a low level, have a significant ( p < 0.01) increase in the number of BrdU-positive cells in the dentate gyrus and the amygdala compared to NR1+/+ mice. Some of these dividing cells express the neuronal marker NeuN. Our results indicate that low expression of the NR1 subunit significantly increases cell proliferation and neurogenesis, suggesting that low NMDARs activity contributes to the increase in cell proliferation in the adult brain.

Novel applications of common stereology software to represent the complete distribution, density and spatial organization of anterogradely labelled fibers in neuroanatomical tract-tracing studies

In a recent study we have adapted for the first time available software used in spatial neuronal organization studies to represent the complete fiber distribution of a brain projection [Leite-Almeida H, Valle-Fernandes A, Almeida A. Brain projections from the medullary dorsal reticular nucleus: an anterograde and retrograde tracing study in the rat. Neuroscience 2006;140:577–95]. Here we describe the technique in detail using the injection of biotinylated-dextran amine (BDA) in the rat cuneate nucleus and its projection through the pyramidal decussation as an example. Camera-lucida-like computer drawings were produced with StereoInvestigator software. Using high magnification lens, rat brain sections were screened and lines superimposed with virtually all fibers and terminal boutons present in each brain section. Additionally, in each screening field of the section, all focal planes were inspected and lines depicted only on focused fibers and/or fiber segments. Later, NeuroExplorer software was used to interpret fiber depth information and obtain the three-dimensional pathway of each fiber bundle along the rostrocaudal extension of each section. This computer methodology presents several advantages over classical camera-lucida hand-made drawings: (i) the software is prepared to work interchangeably in different magnifications without misplacements, which allows the representation of virtually all labelled fibers and, therefore, results in a much more accurate fiber location in each brain section; (ii) three-dimensional information of all individual fibers and fiber bundles is recorded; (iii) the method is more flexible allowing, for example, to colour differently labelled fibers according to their profiles (e.g. terminal or ramified fiber arborizations and terminal boutons).

Prenatal carbocyanine dye tracing of septo-hypothalamic connections

This is the first study of the prenatal development of septal projections to the hypothalamus in rats, using carbocyanine dyes (DiI and DiA) as retrograde tracers. First septal neurons send axons to the preoptic area and anterior hypothalamus on embryonic day 14,5 (E14,5) and on E15 numerous labeled neurons are visualized in the septum after DiI insertion into the preoptic region. On E18 and E20 these neurons develop numerous spiny dendrites that occupy all rostrocaudal extension of the septum with concentration in the ventral part of the septum. Only a few septal neurons send their axons to the mediobasal hypothalamus at E15 confirmed by double-labeling (DiI + DiA) experiments on E20–E21. All septo-hypothalamic connections are unilateral and the number of the neurons revealed in the septum correlates with the place and size of the DiI insertion in the hypothalamus: more lateral and anterior hypothalamic marker insertions always resulted in significant neuronal labeling in the septum. No septal connections with the posterior hypothalamus specifically, the mammillary bodies are formed prenatally. We have demonstrated that the development of septal projections to various rostrocaudal regions of the hypothalamus take place during different stages of development. Prominent parts of the septal projections are to the preoptic area and anterior hypothalamus while few connections with the mediobasal hypothalamus are formed prenatally. These data provide basic knowledge of early steps of the development of the septo-hypothalamic connections.

Distribution of vesicular glutamate transporters 1 and 2 in the rat spinal cord, with a note on the spinocervical tract

To evaluate whether the organization of glutamatergic fibers systems in the lumbar cord is also evident at other spinal levels, we examined the immunocytochemical distribution of vesicle glutamate transporters 1 and 2 (VGLUT1, VGLUT2) at several different levels of the rat spinal cord. We also examined the expression of VGLUTs in an ascending sensory pathway, the spinocervical tract, and colocalization of VGLUT1 and VGLUT2. Mainly small VGLUT2-immunoreactive varicosities occurred at relatively high densities in most areas, with the highest density in laminae I-II. VGLUT1 immunolabeling, including small and medium-sized to large varicosities, was more differentiated, with the highest density in the deep dorsal horn and in certain nuclei such as the internal basilar nucleus, the central cervical nucleus, and the column of Clarke. Lamina I and IIo displayed a moderate density of small VGLUT1 varicosities at all spinal levels, although in the spinal enlargements a uniform density of such varicosities was evident throughout laminae I-II in the medial half of the dorsal horn. Corticospinal tract axons displayed VGLUT1, indicating that the corticospinal tract is an important source of small VGLUT1 varicosities. VGLUT1 and VGLUT2 were cocontained in small numbers of varicosities in laminae III-IV and IX. Anterogradely labeled spinocervical tract terminals in the lateral cervical nucleus were VGLUT2 immunoreactive. In conclusion, the principal distribution patterns of VGLUT1 and VGLUT2 are essentially similar throughout the rostrocaudal extension of the spinal cord. The mediolateral differences in VGLUT1 distribution in laminae I-II suggest dual origins of VGLUT1-immunoreactive varicosities in this region.

Leptin fragments induce Fos immunoreactivity in rat hypothalamus

Leptin presents an important role in energy balance and neuroendocrine control in mammals. In an attempt to identify regions of the leptin molecule responsible for its bioactivity, we have synthesized six peptides based on the protein three-dimensional structure. Fragments were synthesized by the solid-phase methodology, purified by reverse-phase high-performance liquid chromatography (RP-HPLC), and characterized by liquid chromatography–electrospray ionization mass spectrometry (LC/ESI-MS). They were injected intravenously and their ability to induce Fos immunoreactivity (Fos-ir) in rat hypothalamus was compared with that of the recombinant human leptin and saline. Fragment Ac-[Ser 117]Lep 116–140–NH 2 (V) induced Fos-ir in hypothalamic nuclei that express leptin receptor long form. No similar ability was observed for the other five fragments. To investigate whether Fos-ir was induced in the same neuronal group activated by leptin, we proceeded with a dual-label immunohistochemistry for cocaine- and amphetamine-regulated transcript (CART), a neuropeptide related to leptin action in rat hypothalamus. We found that Ac-[Ser 117]Lep 116–140–NH 2 (V) differentially activates CART neurons through the rostrocaudal extension of the arcuate nucleus. These results suggest that this fragment acts in the same group of neurons that mediate leptin response. This approach may offer the basis for the development of leptin-related compounds, having potential application in human or veterinary medicine.

Electric Source Imaging in Temporal Lobe Epilepsy

The objective of this study was to determine the validity of interictal spike (IIS) source localization in temporal lobe epilepsies (TLE) using stereoelectroencephalography as a validating method. Twenty patients with drug-resistant TLE were studied with high-resolution EEG and stereoelectroencephalography. Sixty-four scalp channels, a realistic head model, and different algorithms were used. For each patient, the intracerebral interictal distribution was studied and classified into one of three groups: L (mainly lateral), ML (mediolateral), and M (medial). In group L (three patients), surface IIS were recorded with a high signal-to-noise ratio. Source localizations designated all or part of the intracerebral interictal distribution. In group ML (11 patients), 8 patients had surface IIS, only 5 of which were localizable. High-resolution EEG permitted localization of the more lateral portion and definition of its rostrocaudal extension. A common pattern was identified in three patients with a predominant role of the temporal pole. In group M (six patients), four patients had rare surface IIS, none of which were localizable. Surface EEG does not record IIS limited to medial temporal lobe structures. In TLE with a mediolateral or a lateral interictal distribution, only the lateral component is detectable on surface EEG and accurately localizable by source localization tools.

Résection d’un schwannome rétropéritonéal en sablier par abord combiné

We report a remarkable case of retroperitoneal schwannoma with significant spinal growth illustrating the effectiveness of a combined surgical approach. A 41-year-old man presented with a long history of back pain and unexplained weight loss. An abdominal mass was found in the right upper quadrant. The CT-scan revealed a partially cystic lesion located in the right psoas muscle. Spinal extension was noticed through the L1-L2 neural foramen. MRI better showed the wide rostro-caudal extension in the spinal canal. Bilateral L1 and L2 laminectomy was performed to remove the spinal portion of the tumor. It was extradural but attached to the dura. The roots were not infiltrated. The retroperitoneal mass was removed by an anterior transperitoneal approach. The histological examination did not reveal criteria of malignancy. Retroperitoneal schwannomas are rare and their preoperative diagnosis remains difficult. In case of significant spinal growth, a combined surgical exposure should be preferred to allow total removal of the lesion and control of the neurological structures.

From head to tail: the myoseptal system in basal actinopterygians.

Experimental studies indicated that myomeres play several functional roles during swimming. Some of the functions in question are thought to change rostrocaudally, e.g., anterior myomeres are thought to generate forces, whereas posterior myomeres are thought to transmit forces. In order to determine whether these putative functions are reflected in myoseptal morphology we carried out an analysis of the myoseptal system that includes epaxial and hypaxial myosepta of all body regions for the first time. We combined clearing and staining, microdissections, polarized light microscopy, SEM technique, and length measurements of myoseptal parts to reveal the spatial arrangement, collagen fiber architecture, and rostrocaudal gradients of myosepta. We included representatives of the four basal actinopterygian clades to evaluate our findings in an evolutionary and in a functional context. Our comparison revealed a set of actinopterygian groundplan features. This includes a set of specifically arranged myoseptal tendons (epineural, epipleural, lateral, and myorhabdoid tendons) in all epaxial and postanal hypaxial myosepta. Only preanal hypaxial myosepta lack tendons and exclusively consist of mediolateral fibers. Laterally, myosepta generally align with the helically wound fibers of the dermis in order not to limit the body's maximum curvature. Medially, the relationship of myosepta to vertebrae clearly differs from a 1:1 relationship: a myoseptum attaches to the anterior margin of a vertebra, turns caudally, and traverses at least three vertebrae in an almost horizontal orientation in all body regions. By this arrangement, horizontal multiple layers of myosepta are formed along the trunk dorsal and ventral to the horizontal septum. Due to their reinforcement by epineural or epipleural tendons, these multiple layers are hypothesized to resist the radial expansion of underlying muscle fibers and thus contribute to modulation of body stiffness. Rostrocaudally, a dorsoventral symmetry of epaxial and hypaxial myosepta in terms of spatial arrangement and collagen fiber architecture is gradually developed towards the postanal region. Furthermore, the rostrocaudal extension of myosepta measured between anterior and posterior cones gradually increases. This myoseptal region is reinforced by longitudinal fibers of lateral tendons. Furthermore, the percentage of connective tissue in a cross section increases. These morphological data indicate that posterior myosepta are equipped for multisegmental force transmission towards the caudal fin. Anteriormost myosepta have reinforced and elongated dorsal posterior cones. They are adequately designed to transmit epaxial muscular forces to the neurocranium in order to cause its elevation during suction feeding.

Immunocytochemical characterization of rat brainstem neurons with vagal afferent input from the stomach challenged by acid or ammonia.

Exposure of the gastric mucosa to backdiffusing acid is signalled to the brainstem via vagal afferents. This study examined whether exposure of the Sprague-Dawley rat stomach to hydrochloric acid (HCl) or ammonium hydroxide (NH4OH), a noxious chemical produced by Helicobacter pylori, activates different vagal afferent pathways as reflected by different circuitries in the medullary brainstem. Two hours after intragastric treatment with HCl or NH4OH the activation of neurons in the nucleus tractus solitarii at the rostrocaudal extension of the area postrema (NTSAP) was visualized by c-Fos immunohistochemistry and their chemical coding characterized by double-labelling immunohistochemistry. Exposure of the rat gastric mucosa to HCl (0.15-0.5 M) or NH4OH (0.1-0.3 M) led to a concentration-dependent expression of c-Fos in the NTSAP. The number and distribution of NTSAP neurons activated by 0.35 M HCl and 0.3 M NH4OH were similar; the highest number of activated neurons occurring in the medial part of the NTSAP. Some 60% of the NTSAP neurons activated by intragastric HCl and NH4OH stained for the high affinity glutamate transporter EAAC1, while some 30% contained calbindin or neuropeptide Y. Glutamate receptors of the N-methyl-D-aspartate type were found on approximately 50% of the c-Fos-positive cells in the NTSAP, whereas tachykinin NK1, NK2 and NK3 receptors were present on 5-10% of the activated neurons. The similar number and distribution of c-Fos-expressing neurons within the NTSAP and their identical chemical coding indicate that exposure of the rat stomach to backdiffusing concentrations of HCl and NH4OH activates the same vagal afferent-NTSAP pathway.

Orexin-B-immunoreactive fibers make close appositions on cell bodies and fibers immunoreactive for Neuropeptide Y within the intergeniculate leaflet of the Djungarian hamster (Phodopus sungorus)

The intergeniculate leaflet (IGL) is part of the neural network involved in the regulation of the circadian timing processes. The IGL receives photic- and non-photic-inputs from retina and midbrain and projects this information to the suprachiasmatic nucleus (SCN) through the geniculohypothalamic tract (GHT) arising mostly from neuropeptide Y (NPY) containing neurons in the IGL. Based on distribution of orexin-B-ir fibers and terminal boutons in the IGL we suggest that one pathway by which orexin-B may influence circadian timing could be through interaction with NPY, the most abundant neuropeptide/neurotransmitter in the IGL of the Djungarian hamster. In order to test this idea we investigated the anatomical basis for such a interaction using dual-label immunofluorescence. Orexin B-ir fibers with terminals had close apposition on NPY-lir perikarya and fibers with terminal boutons in the rostro-caudal extension of the IGL. Furthermore, NPY-lir fibers in the peripheral structures of the SCN had apposition from orexin-B-ir fibers and terminals. These observations provide anatomical basis for orexin-B to interact with NPY and influence the circadian timing system. This study was supported by Deutsche Forschungsgemeinschaft (DFG KL973–5) and Danish Research Agancy.

Chondroitin sulfate proteoglycans in the rat thalamus: expression during postnatal development and correlation with calcium-binding proteins in adults.

Postnatal expression of chondroitin sulfate proteoglycans was studied in the rat thalamus by immunocytochemistry and Western immunoblotting techniques with monoclonal antibodies that recognize carbohydrate epitopes (clones CS-56, 1-B-5, 2-B-6). The complex of the results shows that these antibodies recognize mostly nonoverlapping molecules whose expression is regulated during postnatal development. Chondroitin sulfate proteoglycans, recognized by antibody CS-56, and hyaluronan, identified by antibody 1-B-5 after hyaluronidase digestion, are abundant in the neuropil of most thalamic nuclei at the perinatal stage and progressively decrease during the second week of life, attaining levels barely detectable by immunocytochemistry at the end of the third week. In adult thalamus, chondroitin sulfate proteoglycans of high molecular mass, bearing glycosaminoglycans unsulfated in the linking region, and recognized by antibody 1-B-5 are confined to perineuronal nets around neurons chiefly localized in thalamic reticular nucleus. The immunoreactvity for antibody 2-B-6, specific for chondroitin-4-sulfate, is low at the perinatal stage and is not detectable in adult thalamus. Double-immunolabeling has shown that, along the rostrocaudal extension of reticular nucleus, the most developed perineuronal nets are associated with a subset of neurons expressing calretinin, and not with parvalbumin-positive neurons, which represent the largest neuronal population of the nucleus. The distribution of perineuronal nets supports the presence, in thalamic reticular nucleus, of neuronal subpopulations with different morphological and physiological features.

Vertebrate floor plate transiently expresses a compound recognized by antisera raised against subcommissural organ secretion.

Located along the ventral midline of the neural tube, the floor plate (FP) performs an essential role in central nervous system development, especially in the patterning of the ventral region of the neural tube and axonal guidance. Several studies have been directed to the identification of molecules mediating some of the functions of the FP. Most of the models proposed for floor plate actions involve contact-mediated- and/or gradients of diffusible-signals acting throughout the nervous tissue. This report presents and discusses findings showing that the FP cells secrete a novel compound, which is recognized by antisera raised against secretory products of the subcommissural organ (SCO). This immunoreactive compound appears to be very similar to one of the glycoproteins secreted by the SCO. This immunoreactivity is expressed transiently during central nervous system development, and its rostro-caudal extension along the anterior-posterior axis of the FP displays some species variations. However, a constant feature in all species investigated is that this immunoreactive compound is highly expressed in the FP located in the mesencephalic-metencephalic boundary. The distribution of this compound is compatible with basal and apical pathways of release from FP cells. The former might participate in the formation of some brain commissures. The latter might involve the use of the cerebrospinal fluid as a route for performing actions on distant targets, a pathway somehow disregarded by most models accounting for morphogen actions.

The pre-Bötzinger complex and phase-spanning neurons in the adult rat

Recent in vitro studies indicate that neurons in the pre-Botzinger (pre-Bot) complex of neonatal rats play an essential role in respiratory rhythm generation. In the adult rat, however, the location and physiology of pre-Bot neurons is less clearly understood. The present study aims to investigate the firing patterns of neurons that are located between Botzinger and rVRG area, and the precise location of this transition zone in relation to other medullary nuclei. Sprague-Dawley rats (weighted between 400–550 g) were anaesthetised with 72 mg/kg sodium pentobarbitone and 0.4 mg/kg atropine (i.p.), and paralysed with 1 mg/kg pancuronium dibromide (i.v.), followed by additional doses as required. Extracellular recordings were made from 302 respiratory units located between 0 and 1.6 mm caudal to the facial nucleus and ventral to the nucleus ambiguus. As expected, expiratory units were mostly recorded from the rostral medulla (80%, 125/157) and inspiratory units were concentrated in the more caudal area (80%, 36/45). However, we report here that, between the Botzinger expiratory and rVRG inspiratory units, there exists a transition zone containing a mixture of phase-spanning units (41%, 41/100) as well as inspiratory (37%) and expiratory units (22%). The phase-spanning units are active across the expiratory-inspiratory phase, or vice versa. The rostrocaudal extension of this transition zone is about 400 μm, with the caudal end at the level of the caudal pole of the ambigual compact formation. Our preliminary data suggest that this transition zone could be the locus of pre-Bot neurons in the adult rat.

Distribution of a glucocorticoid-induced orphan receptor (JP05) mRNA in the central nervous system of the mouse

JP05 (originally referred to as glucocorticoid-induced receptor gene or cDNA clone 4.2) designates a gene originally isolated from murine thymoma WEHI-7TG cells after being treated with glucocorticoids and forskolin. This gene is also induced by dexamethasone (a potent glucocorticoid receptor agonist) in isolated normal murine thymocytes. The predicted amino acid sequence was found to share significant similarity to the family of G-protein-coupled receptors, in particular to the tachykinin receptors NK-1, NK-2 and NK-3, with which it has an overall identity of 32%, 31% and 33%, respectively. The results of the present in situ hybridization analysis reveal that JP05 mRNA containing cells are extensively distributed throughout the rostrocaudal extension of the brain and spinal cord. However, the vast majority of the areas with high to moderate levels of JP05 mRNA were localized in the forebrain, primarily within limbic system structures, the dorsal and ventral striatum and in some hypothalamic nuclei. These results are discussed in relation to the central nervous system distribution of glucocorticoid receptor-containing cells and to the tachykinin system.

The caudal neurosecretory system and its afferent synapses in the goldfish, Carassius auratus: Morphology, immunohistochemistry, and fine structure

Morphological features of the goldfish caudal neurosecretory system were investigated by means of immunohistochemical localization of urotensins I and II (UI and UII) and electron microscopic examination of the caudal neurosecretory neurons, the urophysis, and the synaptic neuropil. The aim of the work is to provide a detailed morphological description of the afferent synapses to the caudal neurons and to analyze their distribution through the rostrocaudal extension of the caudal neurosecretory system. Three morphologically different types of neurosecretory cells have been identified according to size and shape: large, medium, and small Dahlgren cells. The three different-sized cells share similar patterns of immunoreactivity with the UI (or oCRF) and the UII antisera. Electron microscopic examination of the synaptic neuropil throughout the caudal system revealed the presence of four types of terminals: dense-cored-vesicle end bulbs (DC), spherical-vesicle end bulbs (S), flattened-vesicle end bulbs (F), and granular-vesicle end bulbs (G). The present study demonstrates that the small Dahlgren cells receive different synaptic inputs from the large and the medium neurosecretory cells. Indeed, G terminals are only found on the small Dahlgren cells, whereas DC, S, and F terminals are distributed on the large, medium, and small Dahlgren cell bodies and proximal processes. J. Morphol. 235:59–76, 1998. © 1998 Wiley-Liss, Inc.

The caudal neurosecretory system and its afferent synapses in the goldfish, Carassius auratus: morphology, immunohistochemistry, and fine structure.

Morphological features of the goldfish caudal neurosecretory system were investigated by means of immunohistochemical localization of urotensins I and II (UI and UII) and electron microscopic examination of the caudal neurosecretory neurons, the urophysis, and the synaptic neuropil. The aim of the work is to provide a detailed morphological description of the afferent synapses to the caudal neurons and to analyze their distribution through the rostrocaudal extension of the caudal neurosecretory system. Three morphologically different types of neurosecretory cells have been identified according to size and shape: large, medium, and small Dahlgren cells. The three different-sized cells share similar patterns of immunoreactivity with the UI (or oCRF) and the UII antisera. Electron microscopic examination of the synaptic neuropil throughout the caudal system revealed the presence of four types of terminals: dense-cored-vesicle end bulbs (DC), spherical-vesicle end bulbs (S), flattened-vesicle end bulbs (F), and granular-vesicle end bulbs (G). The present study demonstrates that the small Dahlgren cells receive different synaptic inputs from the large and the medium neurosecretory cells. Indeed, G terminals are only found on the small Dahlgren cells, whereas DC, S, and F terminals are distributed on the large, medium, and small Dahlgren cell bodies and proximal processes.

Loss of primary afferent nerve terminals in the brainstem after peripheral nerve transection: an anatomical study in monkeys.

In order to investigate the changes in the somatosensory organization that occur after a peripheral nerve injury, a purely sensory nerve (radial nerve - superficial branch) was divided in adult monkeys (Macaca fascicularis). The nerve ends were immediately rejoined by an epineural suturing technique. After 6-21 months the nerve investigated was exposed to an intra-axonal nerve tracer (horseradish peroxidase conjugate) in order to label the primary afferent terminals within the cuneate nucleus of the brainstem. The non-transected nerve on the contralateral side was similarly exposed and served as a control. Terminal labelling was seen throughout the cuneate nucleus, mainly in the middle of its rostro-caudal extension, and in this part it showed a patchy appearance superimposed on cell clusters within the pars rotunda. This pattern of distribution was seen both on the experimental and control sides. On the experimental side there was an obvious loss of terminal labelling within the terminal field as estimated using an image-analysing system: Compared with the contralateral side the median loss (peroxidase activity) was 83% and between 6 and 21 months only minor restoration of the terminal intensity was observed. These results in the primate confirm earlier results in the cat that transection and microsurgical repair of a sensory nerve causes a considerable loss of neurons capable of intraaxonal transport.

Catecholaminergic systems in the zebrafish. III. organization and projection pattern of medullary dopaminergic and noradrenergic neurons

To characterize the catecholaminergic systems in the zebrafish medulla, immunocytological studies were performed by using antibodies directed against tyrosine hydroxylase and dopamine-beta-hydroxylase. Catecholaminergic neurons could be categorized into three populations based on location, dendritic morphology, axonal projection pattern, and targets: an interfascicular group, a vagal area group, and an area postrema group. All groups contained both dopaminergic and noradrenergic neurons. Interfascicular neurons formed a loose longitudinal column of approximately 16-20 multipolar neurons on each side of the medulla, whose rostrocaudal extension coincided roughly with the vagal lobe. These neurons were relatively large and had dendrites that arborized throughout the reticular formation and in the vagal lobe. They also contributed axonal processes to the longitudinal catecholamine bundle. Neurons associated with structures in the vagal area were mostly dopaminergic. Some cells had a short, thin apical process that arborized into a dense plexus near the ventricular surface, and all cells had a basal dendrite that divided into two main branches: one extended caudally to terminate in the commissural nucleus of Cajal and among the postobecular catecholaminergic cell group; the other extended laterally and joined the longitudinal catecholamine bundle. The caudal extent of this cell group reached the medullospinal junction. The area postrema cell group consisted of densely packed, bipolar neurons. One process of these neurons contacted the ventricular surface in the area postrema, and one terminated in the commissural nucleus of Cajal. Collaterals from the latter innervated the superficial laminae of the vagal lobe and joined the longitudinal catecholamine bundle. The longitudinal catecholamine bundle ascended through the medulla ventral to the secondary gustatory tract. Whether some fibers extended more rostrally is not known. The majority of the terminal fields of medullary catecholaminergic neurons appeared to be restricted to the medulla and were strongly associated with sensory systems. With the exception of some cells in the vagal area, catecholamine-containing neurons in the zebrafish medulla were not obviously homologous to those in the mammalian brainstem.

An electrophysiological demonstration of axonal projections of single ventral inspiratory neurons to the phrenic nucleus of the cat

Axonal branching patterns of single inspiratory (I) neurons of the nucleus retroambigualis (NRA) were studied electrophysiologically in cat phrenic nucleus (C4–C6). Experiments were performed on Nembutal anesthetized, artificially ventilated cats, and extracellular spikes of I neurons were recorded. The cervical spinal gray matter was microstimulated from dorsal to ventral sites at 100 μm intervals with an intensity of 150–250 μA using a glass insulated tungsten microelectrode. The stimulations were made at 1 mm intervals rostrocaudally along the spinal cord, and effective stimulating sites of antidromic activation in axonal collaterals were systematically mapped. I neurons examined ( n = 8) descending contralaterally distributed multiple collaterals in the phrenic nucleus. These collaterals were found throughout the rostrocaudal phrenic nucleus. An I neuron ( n = 1) descending ipsilaterally also distributed collaterals in the ipsilateral phrenic nucleus. Axonal collaterals in the contralateral phrenic nucleus occupied 44.2% of the total length of the cervical spinal cord examined. To determine the detailed trajectory of collaterals in the cervical gray matter, microstimulation was performed in and around the collateral arborizations at the maximum intensity of 50 μA. The descending stem axons could be localized in the lateral funiculus in four I neurons and in the ventral funiculus in one I neuron. I neurons distributed axonal collaterals within the phrenic nucleus. Some part of the collaterals ran to the medial region of the gray matter, re-crossed the midline under the central canal and reached the phrenic nucleus ipsilateral to the I neuron. Re-crossed collaterals arborized in the phrenic nucleus, but did not extend to the gray matter more lateral than the phrenic nucleus. Rostrocaudal extension of the re-crossed collaterals was found to be narrow.

Local projections of GABAergic neurons in the dentate gyrus and CA1 region in the rat hippocampal formation

Using retrograde transport of wheat germ agglutinin conjugated colloidal gold (WGA-gold) combined with immunoreactivity for glutamate decarboxylase (GAD), a specific synthesizing enzyme for γ-aminobutyric acid (GABA), local projections of GABAergic neurons in the dentate gyrus and CAI were examined. In the hilus of the dentate gyrus, it was found that GABAergic neurons in the granule cell layer projected to the ipsilateral upper leaf of the molecular layer, with a mediolateral extension of more than 1.2 mm and a rostrocaudal extension of over 0.8 mm. Non-GABAergic neurons in nearly the entire hilar area were found to project to the ipsilateral upper leaf of the molecular layer. In the dorsal CAI region, GABAergic neurons in the stratum pyramidale and radiatum converged onto the ipsilateral stratum pyramidal/oriens, with a mediolateral extension of over 1 mm and a rostrocaudal extension of over 0.7 mm. These results provide direct evidence that in both the dentate gyrus and CAI, GABAergic interneurons from a fairly large field converge onto a very small target area. This suggests that the output signals from GABAergic neurons in the dentate gyrus and CAI, and non-GABAergic neurons in the dentate gyrus, may propagate beyond the anatomical limits contained in conventional slice preparations of the hippocampal formation.