Small Fusiform Neurons Research Articles

Synaptic relationship between somatostatin‐ and neurokinin‐1 receptor‐immunoreactive neurons in the pre‐Bötzinger complex of rats

The pre-Bötzinger complex (pre-BötC) in the ventrolateral medulla oblongata is critical for the generation of respiratory rhythm in mammals. Somatostatin (SST) and neurokinin 1 receptor (NK1R) immunoreactivity have been used as markers of the pre-BötC. SST immunoreactivity almost completely overlaps with small fusiform NK1R-immunoreactive (ir) neurons, the presumed rhythmogenic neurons, but not with large multipolar NK1R-ir neurons. Understanding the neurochemical characteristics, especially the synaptic relationship of SST/NK1R-ir neurons within the pre-BötC network is essential in providing cellular and structural bases for understanding their physiological significance. This work has not been documented so far. We found that SST immunoreactivity was highly expressed in terminals, somas, and primary dendrites in the pre-BötC. Besides the small fusiform neurons, a small population of medium-sized NK1R-ir neurons also colocalized with SST. Large NK1R-ir neurons were not SST-ir, but received somatostatinergic inputs. SST-ir terminals were glutamatergic or GABAergic, and synapsed with NK1R-ir neurons. Most of synapses between them were of the symmetric type, indicating their inhibitory nature. Asymmetric synapses were evident between SST-ir terminals and NK1R-ir dendrites, strongly suggesting an excitatory innervation from the presumed rhythmogenic neurons as these neurons are glutamatergic. We speculate that SST-mediated excitatory and inhibitory synaptic transmission onto NK1R-ir rhythmogenic and follower neurons synchronizes their activity to contribute to respiratory rhythmogenesis and control.

Neurokinin-1 Receptor-Expressing Cells of the Ventral Respiratory Group Are Functionally Heterogeneous and Predominantly Glutamatergic

According to a recent theory (Gray et al., 1999) the neurokinin-1 receptor (NK1R)-immunoreactive (ir) neurons of the ventral respiratory group (VRG) are confined to the pre-Bötzinger complex (pre-BötC) and might be glutamatergic interneurons that drive respiratory rhythmogenesis. In this study we tested whether the NK1R-ir neurons of the VRG are glutamatergic. We also examined whether different groups of NK1R-ir neurons coexist in the VRG on the basis of whether these cells contain preproenkephalin (PPE) mRNA or project to the spinal cord. NK1R immunoreactivity was found in two populations of VRG neurons that are both predominantly glutamatergic because most of them contained vesicular glutamate transporter 2 mRNA (77 ± 9%;<i>n</i> = 3). A group of small fusiform neurons (somatic cross section: 91 ± 3.6 μm²) that has neither PPE mRNA nor spinal projections is primarily restricted to the pre-BötC. These cells may be the interneurons the destruction of which produces massive disruptions of the respiratory rhythm (Gray et al., 2001). The rest of the NK1R-ir neurons of the VRG are multipolar, are larger (somatic cross section: 252 ± 15 μm²), and express high levels of PPE mRNA. Some of these cells located in the rostral half of the rostral VRG project to the spinal cord (C4 or T3). Using electrophysiological methods, we showed that these bulbospinal NK1R-ir neurons are slowly discharging inspiratory-augmenting neurons, suggesting that they may control phrenic or intercostal motor neurons. In summary, NK1R-expressing cells of the VRG are a heterogeneous group of predominantly glutamatergic neurons that include subpopulations of respiratory premotor neurons.

Neurokinin-1 receptor-expressing cells of the ventral respiratory group are functionally heterogeneous and predominantly glutamatergic.

According to a recent theory (Gray et al., 1999) the neurokinin-1 receptor (NK1R)-immunoreactive (ir) neurons of the ventral respiratory group (VRG) are confined to the pre-Bötzinger complex (pre-BötC) and might be glutamatergic interneurons that drive respiratory rhythmogenesis. In this study we tested whether the NK1R-ir neurons of the VRG are glutamatergic. We also examined whether different groups of NK1R-ir neurons coexist in the VRG on the basis of whether these cells contain preproenkephalin (PPE) mRNA or project to the spinal cord. NK1R immunoreactivity was found in two populations of VRG neurons that are both predominantly glutamatergic because most of them contained vesicular glutamate transporter 2 mRNA (77 +/- 9%; n = 3). A group of small fusiform neurons (somatic cross section: 91 +/- 3.6 microm2) that has neither PPE mRNA nor spinal projections is primarily restricted to the pre-BötC. These cells may be the interneurons the destruction of which produces massive disruptions of the respiratory rhythm (Gray et al., 2001). The rest of the NK1R-ir neurons of the VRG are multipolar, are larger (somatic cross section: 252 +/- 15 microm2), and express high levels of PPE mRNA. Some of these cells located in the rostral half of the rostral VRG project to the spinal cord (C4 or T3). Using electrophysiological methods, we showed that these bulbospinal NK1R-ir neurons are slowly discharging inspiratory-augmenting neurons, suggesting that they may control phrenic or intercostal motor neurons. In summary, NK1R-expressing cells of the VRG are a heterogeneous group of predominantly glutamatergic neurons that include subpopulations of respiratory premotor neurons.

A reticuloreticular commissural pathway in the rat thalamus.

To further characterize the communication between the thalami of the two hemispheres, a connection linking the rostral reticular nuclei of the two thalamic sides was investigated in the rat by retrograde and anterograde tracing. The rostral reticular nucleus can be divided into a medial region, with densely packed fusiform neurons, and a lateral region, with less densely packed, polymorphic neurons. After injections of Fluorogold (FG) in the medial region, retrogradely labeled, small fusiform neurons were found in the corresponding contralateral region. The retrograde labeling data were confirmed by the anterograde-tracing experiments. Thin, beaded axons, anterogradely labeled after injection of biocytin or biotinylated dextranamine in the medial region, innervate the corresponding region in the contralateral reticular nucleus. The present data suggest the existence of a commissural pathway specifically devoted to the crosstalk between the rostral reticular nuclei of the two thalamic sides. The commissural gamma aminobutyric acid (GABA)-ergic input on the GABAergic neurons of the rostral reticular nucleus could modulate the generation of sleep spindles. The reticuloreticular pathway may, moreover, synchronize the diffuse modulatory effect of the rostral reticular nucleus on nonprimary cortical areas through the bilateral projections of the nucleus to the ventromedial, intralaminar, and anterior thalamic nuclei.

Immunohistochemical localization of γ-aminobutyric acid- and aspartate-containing neurons in the guinea pig superior olivary complex

The immunohistochemical localization of γ-aminobutyric acid (GABA)- and aspartate-containing neurons was demonstrated in the guinea pig superior olivary complex, using purified antisera to GABA and aspartate, respectively. Medium-sized oval GABA-containing neurons were found in the lateral superior olive, and bipolar medium-sized GABA-containing neurons were observed in the dorsal hilus of the lateral superior olive. Medium-sized to large round GABA-containing neurons were observed in the ventral nucleus of the trapezoid body. GABA-containing terminals were found throughout the superior olivary complex with the highest density in the ventral nucleus of the trapezoid body. Aspartate-like immunoreactivity was observed in medium-sized round or oval neurons in the lateral superior olive, small fusiform neurons in the ventral nucleus of the trapezoid body, fusiform medium-sized neurons in the medial superior olive and oval medium-sized neurons in the superior paraolivary nucleus and round medium-sized neurons in the medial nucleus of the trapezoid body. Double staining method demonstrated that aspartate-containing neurons in the medial nucleus of the trapezoid body were surrounded by GABA-containing terminals. The present results suggested the possible origin of GABAergic and aspartatergic olivocochlear bundles.

The reticular thalamic nucleus (RTN) of the rat: Cytoarchitectural, Golgi, immunocytochemical, and horseradish peroxidase study

Experiments have been performed on adult albino rats in order to study the cellular organization of the thalamic reticular nucleus. For this purpose four approaches have been used: Nissl stain, Golgi impregnation, retrograde transport of horseradish peroxidase after injection in different thalamic nuclei, and immunocytochemistry with antibodies against GABA and glutamic acid decarboxylase. In sections through the horizontal plane, three morphologically different neurons have been observed. Cells with round perikarya and with multipolar dendrites were found predominantly in the rostral pole of the nucleus. Neurons with large fusiform cell body and with dendrites arborizing mainly on the horizontal plane were detected through the whole extent of the nucleus. Small fusiform neurons were observed almost exclusively in the medial third of the dorso-ventral extent of the nucleus. The Golgi impregnation method demonstrated that dendrites of small fusiform neurons develop in the vertical plane perpendicular to the dendritic arborization of large fusiform neurons. In coronal sections neurons with round perikarya and with large fusiform cell bodies are detectable while small fusiform neurons are only rarely visible. These data have been confirmed by statistical form factor analysis. Moreover, by means of the horseradish peroxidase and the immunocytochemical study, it has been confirmed that all three groups of neurons project within the thalamus and that they are GABAergic. The data concerning the distribution within the nucleus of the three morphologically different neurons are discussed in relation to the topographic distribution of cortical sensory afferents and to the topographic maps within different sectors of the reticular nucleus.

Identification and electrophysiology of isolated pars compacta neurons from guinea-pig substantia nigra

Single nuerons from the substantia nigra of the adult guinea-pig were dissociated. Two morphological types of neurons were identified: (i) large multipolar neurons (20–40 μm greatest diameter) and (ii) small fusiform neurons ( <20 μm diameter). Neurons of both types showed catecholamine fluorescence and were retrogradely labelled by rhodamine-conjugated microspheres injected into the striatum. Two types of neuron (Type A and Type B) were also identified electrophysiologically in perforated patch recordings of membrane potential and whole-cell current. Type A neurons had a low spontaneous firing frequency (5 Hz) broad action potentials (4 ms) and a threshold of ∼−45 mV. They were inhibited by the dopamine D 2 receptor agonist, quinpirole. Type B neurons were characterized by a faster firing frequency (25 Hz), shorter action potential duration (1.5 ms) and a threshold of ∼−50 mV. These cells were unaffected by quinpirole. Large multipolar neurons were usually found to be of the A type and small fusiform, neurons of the B type. The properties of the large multipolar, Type A neurons suggest that they form part of the nigrostriatal, dopaminergic population of the pars compacta.

Neurons with galanin innervate cholinergic cells in the human basal forebrain and galanin and acetylcholine coexist

Immunocytochemistry with antibodies against cholinacetyltransferase (ChAT) and the novel peptide galanin (GA) were conducted as a single label or as double label experiments on the basal forebrain nuclei of brains from eleven human subjects without prior history of neurological disease. ChAT positive or cholinergic neurons form the major population of cells in the basal nucleus of Meynert. A minor portion of these ChAT positive neurons demonstrate a coexistence with GA positive immunoreactivity suggesting that they are cholinergic/GA neurons. Small fusiform neurons with long dendrites and complex local axonal networks are GA immunoreactive and are local circuit interneurons. The cholinergic cells in the basal nucleus are innervated by a fine network of GA immunoreactive axons and terminals which enwrap their perikarya and dendrites. It is suggested that GA in local circuit interneurons may provide a significant control or modulation of the cholinergic neurons and of cholinergic functions within the basal nucleus. In human diseases which feature a destruction of the basal forebrain cholinergic neurons, surviving GA neurons may inhibit most remaining cholinergic neurons and their function, with severe consequences.

Localization of cytochrome oxidase in the mammalian spinal cord and dorsal root ganglia, with quantitative analysis of ventral horn cells in monkeys

The spinal cord and dorsal root ganglia of mice, rats, cats, squirrel monkeys, and macaque monkeys were examined at both the light and electron microscopic levels for cytochrome oxidase activity. A similar histochemical pattern prevailed in all of the species examined. While the spinal gray exhibited a heterogeneous but consistent distribution of the enzyme, the white matter was only lightly stained. Highly reactive neurons were either singly scattered or aggregated into discrete clusters. The dorsal nucleus of Clarke, the lateral cervical nucleus (cat), the intermediolateral cell columns of the thoracic and upper lumbar levels, and selected groups of ventral horn neurons formed moderate to darkly reactive cell clusters, whereas fusiform and multipolar cells of Waldeyer in the marginal layer, small fusiform neurons in the ventral gray, funicular cells in the white matter, and ventral horn neurons of varying sizes tended to stand out against the neuropil as singly reactive neurons. At the electron microscopic level, reactive neurons were characterized by a greater packing density of darkly reactive mitochondria, while lightly reactive ones had fewer mitochondria, most of which showed very little reaction product. Reactive mitochondria were also found in the neuropil, mainly in dendritic profiles and some axon terminals. Glial cells, in general, were not very reactive. Ventral horn neurons from three macaque monkeys were measured for somatic areas and optical densities of cytochrome oxidase reaction product. A total of 1,770 neurons from representative sections of the cervical, thoracic, lumbar, and sacral cords of these animals were analyzed. The results indicated that the distribution of cell sizes as well as optical densities at every level of the cord fell on a continuum. Analysis of the regression coefficients revealed that the slopes were negative for all levels, indicating that there was a general inverse relationship between cell size and optical densities. However, there were representations of dark, moderate, and lightly reactive neurons in all three size categories (large, medium, and small). Thus, the level of oxidative metabolism of ventral horn neurons cannot be correlated strictly with size, but it is likely to reflect their total synaptic and spontaneous activities. Neurons of the dorsal root ganglia likewise exhibited heterogeneous distribution of cell sizes and levels of enzyme reactivity, while satellite cells, in general, were only lightly reactive. As in the case of the ventral horn, representatives of dark, moderate, and light levels of reactivity occurred in every size category of neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Sympathetic preganglionic efferent and afferent neurons mediated by the greater splanchnic nerve in rabbit

Motion sickness, a multisymptom disorder characterized by abnormal gastrointestinal motility and emesis, can be induced by vestibular effects on the sympathetic portion of the autonomic nervous system. However, the vestibular-autonomic pathways are unknown. As a first step in the analysis, we identified the locus of preganglionic sympathetic neurons (PSNs) and dorsal root afferent ganglionic neurons (DRGs) which supply sympathetic innervation to major portions of the gastrointestinal tract in the rabbit. Retrograde labeling of neurons was obtained by application of horseradish peroxidase (HRP) to the cut end of the greater splanchnic nerve. Labeled PSNs were found, ipsilaterally, within the T1 to T11 spinal cord segments, with the highest density of neurons in T6. Most PSNs were located within the intermediolateral column (IML), but a significant portion also occurred within the lateral funiculus (LF), the intercalated region (IC) and the central autonomic area (CA). The proportion of labeling between the four regions depended on the spinal cord segment. In the midthoracic levels, the distribution of labeled neurons was denser in the IML and LF, and in the caudal thoracic segments, the majority were localized in the IC and CA. Labeled cells in these four areas varied morphologically from large fusiform neurons in the IC to small fusiform neurons in the LF, small stellate neurons in the CA, and medium-size stellate neurons in the IML. The DRGs were labeled in thoracic segments T1 to T12, with the majority between T5 and T11. These labeled DRG somata of the greater splanchnic nerve were smaller in comparison with unlabeled ones.

A correlative HRP, Golgi, and EM study of the intrinsic organization of the feline dorsal column nuclei.

AbstractThe retrograde transport of horseradish peroxidase (HRP), Golgi impregnations, and electron microscopic (EM) observations have been employed to investigate the intrinsic organization of one cytoarchitectonic subdivision of the feline dorsal column nuclei (DCN): the “clusters” region. Previous studies have demonstrated that neurons arranged in typical cell clusters in the dorsal two‐thirds of the feline DCN project to the ventrobasal complex (VB) of the thalamus. Following injections of HRP in the VB of adult cats, over 90% of the neurons in this region contain detectable reaction product. These thalamic projecting neurons (TPN) are typically round, range from 20 to 35 μm in diameter, and have round nuclei and abundant cytoplasm.In Golgi preparations, TPN are identified by their characteristic arrangement in the cell clusters. Observations of their cytological characteristics in gold‐toned preparations in both 1‐μm‐thick sections, and in thin sections at the EM level, supplement the data from HRP material. The dendrites of TPN in the clusters region characteristically converge in the perikarya‐free center of each cluster, and appendages originate from both proximal and distal portions of the major dendrites of these neurons. These appendages vary in morphology from short‐stalked, occasionally multi‐lobed, bulbous thorns to long‐stalked processes terminating in a single or multilobed swelling. Other appendages often display beaded swellings along their length (moniliform appendages).Neurons in the clusters region unlabelled by HRP injected in the VB have cytological charateristics quite distinct from those of TPN in the same region. Typically located at the periphery of the cell clusters, unlabelled neurons have fusiform perikarya, range in diameter from 8 to 12 μm along their short axis, and have highly indented nuclei and sparse cytoplasm. In Golgi preparations, small fusiform neurons located at the periphery of cell clusters typically have two major dendritic trunks originating from opposite poles of their perikarya. Observations in 1‐μm‐thick plastic sections of re‐embedded Golgi‐impregnated neurons of this type support their identifications as neurons which are unlabelled after HRP injection in VB. Dendritic appendages are present also on this type of neuron, although they do not appear to be as frequent as in the case of the TPN. Although the axon of the small, fusiform neurons have not been impregnated beyond the initial segment in the present Golgi material, thus precluding the classification of this type of neuron as a Golgi type II neuron, a combination of the HRP and Golgi observations suggest that these neurons are distinct from TPN, and are possibly interneurons.In addition to the previously described synaptic complexes of primary afferent terminals associated with, or postsynaptic to, small boutons with flattened vesicles (F‐boutons, of presumed interneuronal origin), EM observations of serial sections demonstrate triadic synaptic arrangements similar to those encountered in other CNS nuclei. In such instances, a primary afferent terminal is presynaptic to a pale profile containing polymorphicvesicles (P‐bouton), and both boutons are presynaptic to a dendrite. In serial sections, P‐boutons are demonstrated to be of dendritic origin, while F‐boutons are observed to arise frommyelinated fibers. By comparison with Golgi observations, P‐boutons are believed to corre‐spond to the dendritic appendages of TPN, suggesting that TPN, as well as interneurons, contribute to the intrinsic synaptology of the cell clusters region.