Quantitative morphologic classification of layer 5 neurons from mouse primary visual cortexTsiola, Areti; Hamzei‐Sichani, Farid; Peterlin, Zita; Yuste, Rafael
doi: 10.1002/cne.10628pmid: 12746859
The understanding of any neural circuit requires the identification and characterization of all its components. Morphologic classifications of neurons are, therefore, of central importance to neuroscience. We use a quantitative method to classify neurons from layer 5 of mouse primary visual cortex, based on multidimensional clustering. To reconstruct neurons, we used Golgi impregnations and biocytin injections, as well as DiOlistics, a novel technique of labeling neurons with lipophilic dyes. We performed computerized 3‐D reconstructions of 158 layer 5 cells to measure a series of morphologic variables. Principal component analysis and cluster analysis were used for the classification of cell types. Five major classes of cells were found: group 1 includes large pyramidal neurons with apical dendrites that reach layer 1 with an apical tuft; group 2 consists of short pyramidal neurons and large multipolar cells with “polarized” dendritic trees; group 3 is composed of less extensive pyramidal neurons; group 4 includes small cells; and group 5 includes another set of short pyramidal neurons in addition to “atypically oriented” cells. Our sample included a relatively homogeneous group of 27 neurons that project to the superior colliculus, which clustered mainly in group 1, thus supporting the validity of the classification. Cluster analysis of neuronal morphologies provides an objective method to quantitatively define different neuronal phenotypes and may serve as a basis for describing neocortical circuits. J. Comp. Neurol. 461:415–428, 2003. © 2003 Wiley‐Liss, Inc.
Synaptic targets of commissural interneurons in the lumbar spinal cord of neonatal ratsBirinyi, András; Viszokay, Kornél; Wéber, Ildikó; Kiehn, Ole; Antal, Miklós
doi: 10.1002/cne.10696pmid: 12746860
There is strong evidence that commissural interneurons, neurons with axons that extend to the contralateral side of the spinal cord, play an important role in the coordination of left/right alternation during locomotion. In this study we investigated the projections of commissural interneurons to motor neurons and other commissural interneurons on the other side of the spinal cord in neonatal rats. To establish whether there are direct contacts between axons of commissural interneurons and motor neurons, we carried out two series of experiments. In the first experiment we injected biotinylated dextran amine (BDA) into the lateral motor column to retrogradely label commissural interneurons that may have direct projections to motor neurons. Stained neurons were recovered in the ventromedial areas of the contralateral gray matter in substantial numbers. In the second experiment BDA was injected into the ventromedial gray matter on one side of the lumbar spinal cord, whereas motor neurons were simultaneously labeled on the opposite side by applying biocytin onto the ventral roots. BDA injections into the ventromedial gray matter labeled a strong axon bundle that arose from the site of injection, crossed the midline in the ventral commissure, and extensively arborized in the contralateral ventral gray matter. Many of these axons made close appositions with dendrites and somata of motor neurons and also with commissural interneurons retrogradely labeled with BDA. The results suggest that commissural interneurons may establish monosynaptic contacts with motor neurons on the opposite side of the spinal cord. Our findings also indicate that direct reciprocal connections between commissural interneurons on the two sides of the spinal cord may also exist. J. Comp. Neurol. 461:429–440, 2003. © 2003 Wiley‐Liss, Inc.
Characterization of the cDNA encoding a somatostatin variant in the chicken brain: Comparison of the distribution of the two somatostatin precursor mRNAsTrabucchi, Michele; Tostivint, Hervé; Lihrmann, Isabelle; Blähser, Sabine; Vallarino, Mauro; Vaudry, Hubert
doi: 10.1002/cne.10690pmid: 12746861
Although the existence of two somatostatin variants (SS1 and SS2) has now been demonstrated in the brain of mammals, amphibians, and fish, only one isoform of somatostatin (SS1) has been characterized to date in the brain of birds. Here we report cloning of the cDNA encoding a 101‐amino‐acid protein (PSS2) that encompasses the somatostatin variant [Pro2]somatostatin‐14 (SS2) at its C‐terminus. Sequence analysis indicated that chicken PSS2 is more closely related to fish PSS2 than to mammalian cortistatin precursors. Northern blot analysis showed that the chicken PSS1 gene is expressed in the central nervous system (CNS) and in the pancreas, whereas the PSS2 gene is expressed only in the CNS and not in peripheral organs. In situ hybridization histochemistry revealed that, in the chicken brain, PSS1 mRNA is more widely distributed than PSS2 mRNA. In particular, PSS1 mRNA expression was found in the hippocampus, the hyperstriatum, the preoptic area, the ventricular hypothalamic nuclei, the optic tectum, and several nuclei of the mesencephalon and rhombencephalon. In contrast, the distribution of PSS2 mRNA was restricted to a few regions of the brain, including the paraolfactory lobe, the paleostriatum, and some nuclei of the mesencephalon and rhombencephalon. The fact that the PSS1 and PSS2 genes are differently expressed in the brain and in peripheral organs indicates that, in chicken, the two somatostatin variants likely exert distinct functions. In particular, the observation that PSS1 mRNA, but not PSS2 mRNA, occurs in the preoptic area and in the ventral hypothalamic nuclei suggests that, of the two somatostatin isoforms, only SS1 acts as a hypophysiotropic factor. J. Comp. Neurol. 461:441–451, 2003. © 2003 Wiley‐Liss, Inc.
Axonal pathways to the lateral superior olive labeled with biotinylated dextran amine injections in the dorsal cochlear nucleus of ratsDoucet, John R.; Ryugo, David K.
doi: 10.1002/cne.10722pmid: 12746862
The lateral superior olive (LSO) contains cells that are sensitive to intensity differences between the two ears, a feature used by the brain to localize sounds in space. This report describes a source of input to the LSO that complements bushy cell projections from the ventral cochlear nucleus (VCN). Injections of biotinylated dextran amine (BDA) into the dorsal cochlear nucleus (DCN) of the rat label axons and swellings in several brainstem structures, including the ipsilateral LSO. Labeling in the ipsilateral LSO was confined to a thin band that extended throughout the length of the structure such that it resembled an LSO isofrequency lamina. The source of this labeled pathway was not obvious, because DCN neurons do not project to the LSO, and VCN bushy cells were not filled by these injections. Filled neurons in several brainstem structures emerged as possible sources. Three observations suggest that most of the axonal labeling in the LSO derives from a single source. First, the number of labeled VCN planar multipolar cells and the amount of labeling in the LSO were consistent and robust across animals. In contrast, the number of labeled cells in most other structures was small and highly variable. Second, the locations of planar cells and filled axons in the LSO were related topographically to the position of the DCN injection site. Third, labeled terminal arborizations in the LSO arose from collaterals of axons in the trapezoid body (output tract of planar cells). We infer that planar multipolar cells, in addition to bushy cells, are a source of ascending input from the cochlear nucleus to the LSO. J. Comp. Neurol. 461:452–465, 2003. © 2003 Wiley‐Liss, Inc.
Developmental change in expression and subcellular localization of two Shaker‐related potassium channel proteins (Kv1.1 and Kv1.2) in the chick tangential vestibular nucleusPopratiloff, Anastas; Giaume, Christian; Peusner, Kenna D.
doi: 10.1002/cne.10702pmid: 12746863
The chick tangential nucleus is a major avian vestibular nucleus whose principal cells participate in two vestibular reflexes. Intracellular recordings have shown that the principal cells acquire their mature firing pattern gradually during development. At embryonic day 16 (E16), most principal cells fire a single spike, whereas shortly after hatching (H) the vast majority fire repetitively on depolarization. The transition in firing pattern was likely due in part to a downregulation of a low‐threshold, sustained, dendrotoxin‐sensitive (DTX) potassium current, IDS. Since the DTX‐sensitive potassium channel subunits Kv1.1 and Kv1.2 generate sustained currents, in the present study we applied fluorescence immunocytochemistry and confocal microscopy to characterize their developmental expression at E16, H1, and H9. At E16, both Kv1.1 and Kv1.2 staining were confined to the principal cell bodies. Immunolabeling decreased significantly for both proteins at H1, and more so by H9. Double‐labeling with a monoclonal antibody against microtubule‐associated protein 2 (MAP2) in hatchlings showed that some Kv1.1 remained as clusters within the cell body, at the base of the dendrites, and in the axon initial segment. In hatchlings, Kv1.2 staining decreased in the cell bodies and simultaneously appeared in the neuropil, colocalized with biocytin‐labeled primary vestibular fibers and vestibular “spoon” terminals. Also, double‐labeling with synaptotagmin showed that Kv1.2 colocalized with many nonvestibular terminals surrounding the principal cell bodies. These results identified developmental decreases in the staining of these two potassium channel protein subunits and changes in their subcellular localization corresponding to the downregulation of IDS defined electrophysiologically around hatching. Accordingly, both of these protein subunits could be involved in regulating excitability of the principal cells. J. Comp. Neurol. 461:466–482, 2003. © 2003 Wiley‐Liss, Inc.
Distribution of NTS3 receptor/sortilin mRNA and protein in the rat central nervous systemSarret, Philippe; Krzywkowski, Pascale; Segal, Laura; Nielsen, Morten S.; Petersen, Claus M.; Mazella, Jean; Stroh, Thomas; Beaudet, Alain
doi: 10.1002/cne.10708pmid: 12746864
The neurotensin (NT) receptor, NTS3, originally identified as the intracellular sorting protein sortilin, is a member of a recently discovered family of receptors characterized by a single transmembrane domain. The present study provides the first comprehensive description of the distribution of NTS3/sortilin mRNA and protein in adult rat brain using in situ hybridization and immunocytochemistry. Both NTS3/sortilin mRNA and immunoreactivity displayed a widespread distribution throughout the brain. High levels of NTS3/sortilin expression and immunoreactivity were found in neuronal cell bodies and dendrites of allocortical areas such as the piriform cortex and hippocampus. Regions expressing both high levels of NTS3/sortilin mRNA and protein also included several neocortical areas, the islands of Calleja, medial and lateral septal nuclei, amygdaloid nuclei, thalamic nuclei, the supraoptic nucleus, the substantia nigra, and the Purkinje cell layer of the cerebellar cortex. In the brainstem, all cranial nerve motor nuclei were strongly labeled. NTS3/sortilin mRNA and immunoreactivity were also detected over oligodendrocytes in major fiber tracts. Subcellularly, NTS3/sortilin was predominantly concentrated over intracytoplasmic membrane‐bound organelles. Many of the areas exhibiting high levels of NTS3/sortilin (e.g., olfactory cortex, medial septum, and periaqueductal gray) have been documented to contain high concentrations of NT nerve cell bodies and axons, supporting the concept that NTS3/sortilin may play a role in NT sorting and/or signaling. Other areas (e.g., hippocampal CA fields, cerebellar cortex, and cranial nerve motor nuclei), however, are NT‐negative, suggesting that NTS3/sortilin also exerts functions unrelated to NT signaling. J. Comp. Neurol. 461:483–505, 2003. © 2003 Wiley‐Liss, Inc.
Autoradiographic analysis of rat brain kinin B1 and B2 receptors: Normal distribution and alterations induced by epilepsyOngali, Brice; Campos, Maria Martha; Bregola, Gianni; Rodi, Donata; Regoli, Domenico; Thibault, Gaétan; Simonato, Michele; Couture, Réjean
doi: 10.1002/cne.10706pmid: 12746865
Kindling‐induced seizures constitute an experimental model of human temporal lobe epilepsy that is associated with changes in the expression of several inflammatory proteins and/or their receptors in distinct brain regions. In the present study, alterations of kinin receptors in the brain of amygdaloid‐kindled rats were assessed by means of in vitro autoradiography, using 125I‐labeled 3‐4 hydroxyphenyl‐propionyl‐desArg9‐D‐Arg°‐[Hyp3, Thi5, D‐Tic7, Oic8]‐bradykinin (B1 receptors) and 125I‐labeled 3‐4 hydroxyphenyl‐propionyl‐D‐Arg°‐[Hyp3, Thi5, D‐Tic7, Oic8]‐bradykinin (B2 receptors) as ligands. Results demonstrate that B2 receptors are widely distributed throughout the brain of control rats. The highest densities were observed in lateral septal nucleus, median preoptic nucleus, dentate gyrus, amygdala, spinal trigeminal nucleus, mediovestibular nucleus, inferior cerebellar peduncles, and in most of cortical regions (0.81–1.4 fmol/mg tissue). In contrast, very low densities of B1 receptors were detected in all analyzed areas from control rats (0.18–0.26 fmol/mg tissue). When assessed in kindled rats, specific binding sites for B2 receptors were significantly decreased (41 to 76%) in various brain areas. Conversely, B1 receptor binding sites were markedly increased in kindled rats, especially in hippocampus (CA2 ≅ CA1 ≅ CA3), Amy and entorhinal, peririnal/piriform, and occipital cortices (152–258%). Data show for the first time that kindling‐induced epilepsy results in a significant decline of B2 receptor binding sites, accompanied by a striking increase of B1 receptor labeling in the rat brain. An altered balance between B1 and B2 receptor populations may play a pivotal role in the onset and/or maintenance of epilepsy. J. Comp. Neurol. 461:506–519, 2003. © 2003 Wiley‐Liss, Inc.
Immunohistochemical distribution of NTS2 neurotensin receptors in the rat central nervous systemSarret, Philippe; Perron, Amélie; Stroh, Thomas; Beaudet, Alain
doi: 10.1002/cne.10718pmid: 12746866
In the present study, we localized the levocabastine‐sensitive neurotensin receptor (NTS2) protein in adult rat brain by using an N‐terminally‐directed antibody. NTS2‐like immunoreactivity was broadly distributed throughout the rat brain. At the cellular level, the reaction product was exclusively associated with neurons and predominantly, although not exclusively, with their dendritic arbors. No NTS2 signal was observed over astrocytes, as confirmed by dual confocal microscopic immunofluorescence studies using the astrocytic marker S100β. High densities of NTS2‐like immunoreactive nerve cell bodies and/or processes were detected in many regions documented to receive a dense neurotensinergic innervation, such as the olfactory bulb, bed nucleus of the stria terminalis, magnocellular preoptic nucleus, amygdaloid complex, anterodorsal thalamic nucleus, substantia nigra, ventral tegmental area, and several brainstem nuclei. Most conspicuous among the latter were structures implicated in the descending control of nociceptive inputs (e.g., the periaqueductal gray, dorsal raphe, gigantocellular reticular nucleus, pars alpha, lateral paragigantocellular, and raphe magnus), in keeping with the postulated role of NTS2 receptors in the mediation of neurotensin's supraspinal antinociceptive actions. However, the distribution of NTS2‐like immunoreactivity largely exceeded that of neurotensin terminal fields, and some of the highest concentrations of the receptor were found in areas devoid of neurotensinergic inputs such as the cerebral cortex, the hippocampus, and the cerebellum, suggesting that neurotensin may not be the exclusive endogenous ligand for this receptor subtype. J. Comp. Neurol. 461:520–538, 2003. © 2003 Wiley‐Liss, Inc.
Contractile cochlear frame in the gecko Teratoscincus scincusGaneshina, Olga; Vorobyev, Misha
doi: 10.1002/cne.10717pmid: 12746867
It is generally accepted that the cartilaginous frame of the reptilian cochlea has only a passive supportive function. In this study, a ribbon of contractile tissue was revealed within the cartilaginous frame of the cochlea of the gecko Teratoscincus scincus. It consisted of tightly packed cells and received an extensive blood supply. The cytoplasm of the cells was filled with cytoskeletal filaments 5–7 nm thick as revealed by electron microscopy. Isolated tissue permeabilized with Triton X‐100 or glycerol reversibly contracted in the presence of ATP. Noradrenaline caused slow relaxation of the freshly isolated tissue placed in artificial perilymph. We suggest that slow motility of the contractile tissue may adjust passive cochlear mechanics to sounds of high intensities. J. Comp. Neurol. 461:539–547, 2003. © 2003 Wiley‐Liss, Inc.