Neuronal nitric oxide synthase is localized in extrinsic nerves regulating perireceptor processes in the chemosensory nasal mucosae of rats and humans

Nitric oxide synthase is the enzyme responsible for the production of the free radical gas nitric oxide, which has been implicated as an intercellular messenger in both the central and peripheral nervous systems. Immunoreactivity for nitric oxide synthase is often coincident with the histochemical demonstration of NADPH-diaphorase activity. Using an antibody to the neuronal form of nitric oxide synthase and a histochemical technique for NADPH-diaphorase, we have compared the localization of immunoreactivity and histochemical reaction product in the nasal mucosae of rats and humans. Immunoreactivity for neuronal nitric oxide synthase was localized in the extrinsic perivascular innervation of the olfactory and vomeronasal mucosae of rats and in the olfactory mucosa of humans. In the rat nasal mucosa, specific groups of glands were also innervated; the density of nitrinergic innervation varied among them, with vomeronasal glands and posterior glands of the nasal septum being the most densely innervated. In contrast, NADPH-diaphorase activity was present in olfactory, vomeronasal, and septal organ receptor neurons in rats and in olfactory receptor neurons in humans as well as in numerous nerve fibers, glands, and surface epithelial cells. The localization of neuronal nitric oxide synthase in extrinsic perivascular and periglandular nerve fibers suggests that nitric oxide may modulate the perireceptor processes of local blood flow and mucus secretion that influence the access to and clearance of chemical stimuli from rat and human chemosensory mucosae. © Wiley-Liss, Inc.     

Association of ecto-5′-nucleotidase with specific cell types in the adult and developing rat olfactory organ

A unique feature of the olfactory epithelium is its ability to give rise to new sensory neurons throughout life and also following injury. Cells at the basal side of the epithelium serve as neurogenic progenitor cells. The enzyme ecto-5′-nucleotidase is expressed at the surface of developing nerve cells and is regarded as a marker of neural development. To study the expression pattern of the enzyme, we analyzed its distribution in the adult and developing rat olfactory organ. Labeling is restricted to specific cell types and varies between the epithelia investigated. At the basal side of the olfactory epithelium, activity of 5′-nucleotidase is associated specifically with the dark/horizontal basal cells. Neither the light/globose basal cells, which are the immediate precursors of the sensory receptor cells, nor subsets of potentially immature olfactory receptor cells are labeled. On the other hand, microvillar cells dispersed at the lumenal side of the epithelium contain 5′-nucleotidase activity. The enzyme is also present at the inner lining of the ducts of Bowman's glands as they traverse the epithelium. Within the respiratory epithelium, activity of 5′-nucleotidase is associated with basal cells as well as with the epithelial surface. During development, 5′-nucleotidase is initially limited to the respiratory epithelium, including its basal cells. Dark/horizontal basal cells of the olfactory epithelium, which are positive for 5′-nucleotidase, first appear at the border of the respiratory epithelium, suggesting that they might originate from immigrating basal cells of the respiratory epithelium. Within the vomeronasal organ, labeling is largely restricted to the receptor-free epithelium. Although the functional role of 5′-nucleotidase in the olfactory system needs to be further defined, the distribution of the enzyme can be used successfully as a marker for defined cell types. J. Comp. Neurol. 393:528–537, 1998. © 1998 Wiley-Liss, Inc.     

Differential projections of ciliated and microvillous olfactory receptor cells in the catfish,Ictalurus punctatus

The primary olfactory projections of channel catfish Ictalurus punctatus have been examined with postmortem tracing by using either 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate or 1,1-dilinoleyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI). Following DiI deposition into small areas in different parts of the posterior olfactory bulb, olfactory sensory neurons always were labeled throughout the olfactory epithelium. No obvious topographical mapping exists between the epithelium and olfactory bulb. The different dye placements, however, did result in labeling of different morphologies of receptor cells, depending on the site of injection. Retrogradely labeled neurons in the olfactory epithelium were classified into three types on the basis of their height: tall, intermediate, and short. Tall olfactory sensory neurons had perikarya at the bottom one-fourth of the epithelium, extended slender dendrites to the epithelial surface, and possessed numerous cilia on the apical dendritic tips. These tall olfactory sensory neurons were labeled predominantly following DiI applications to the ventral part of the posterior olfactory bulb. In contrast, the short olfactory sensory neurons had perikarya situated within the superficial half of the epithelium and with short apical dendrites bearing microvilli. These short olfactory sensory neurons projected predominantly to the dorsal, posterior olfactory bulb. Thus, short microvillous receptor cells and tall ciliated receptor cells connect to different parts of the olfactory bulb, although the receptor cells are intermingled within the olfactory epithelium. Because different parts of the olfactory bulb are thought to respond preferentially to different classes of odorants, these results suggest that receptor cell morphology may be related to odorant quality detection. In addition, to compare this study with previous in vivo studies, Fluoro-Gold was injected in vivo into either the olfactory bulb or intraperotineally. These in vivo studies show that so-called “type II ciliar receptor cells” of the nonsensory epithelium are labeled nonselectively by blood-borne substances, but they are not labeled by postmortem injections of DiI anywhere in the olfactory bulb. J. Comp. Neurol. 398:539–550, 1998. © 1998 Wiley-Liss, Inc.     

Immunocytochemical localization of luteinizing hormone-releasing hormone (LHRH) in the brain and nervus terminalis of the adult and early neonatal gray short-tailed opossum (Monodelphis domestica)

Luteinizing hormone-releasing hormone (LHRH) was detected by immunocytochemical procedures in cells and fibers in the brain and in the nervus terminalis of the adult and neonatal gray, short-tailed opossum (Monodelphis domestica). As in several species of eutherian mammals, LHRH-immunoreactive cells and fibers were seen in the medial septal nuclei, nucleus, and tract of the diagonal band and olfactory tubercle. Surprisingly, few LHRH-immunoreactive cells were found in the hypothalamus or in the preoptic area in either the adult or neonate. LHRH-immunoreactive fibers were seen in these regions and were numerous in the median eminence. The nervus terminalis in the gray opossum showed several distinctive characteristics. Immunoreactive and nonreactive cells, in ganglia along the peripheral and intracranial course of this nerve, were accompanied by thick fascicles of LHRH fibers and frequently lay adjacent to blood vessels. No LHRH-immunoreactive branches of the nervus terminalis were found in contact with the vomeronasal nerves as they traversed the medial surfaces of the main olfactory bulbs en route to the accessory olfactory bulbs. The LHRH-immunoreactive fibers in the central roots of the nervus terminalis formed a compact bundle on either side of midline, which coursed obliquely from clusters of ganglion cells on the ventromedial surface of the olfactory bulbs into the septum. Traced through serial sagittal sections, LHRH-immunoreactive fibers, in continuity with those in the triangular nucleus of the septum, ran down and around the rostral face of the anterior commissure and fanned out into the medial preoptic area. As previously observed in the fetal guinea pig and rat, LHRH was detected in ganglion cells of the nervus terminalis of the newborn gray opossum preceding its detection in any other area of the brain.     

Expression of a vomeronasal receptor gene (V1r) and G protein alpha subunits in goat, Capra hircus, olfactory receptor neurons

Most mammals have two distinct olfactory epithelia, the olfactory epithelium (OE) and vomeronasal epithelium (VNE), containing, respectively, olfactory receptor neurons (ORNs) and vomeronasal receptor neurons (VRNs). Olfactory receptors (ORs), which couple to G alpha olf, are generally expressed by ORNs, whereas two vomeronasal receptor families (V1rs and V2rs) coupled respectively to G alpha i2 and G alpha o, are expressed by VRNs. Previously, we reported that one goat V1rs (gV1ra1) is expressed by ORNs and VRNs. To investigate the characteristics of vomeronasal-receptor-expressing ORNs in mammals we performed double-label in situ hybridization for gV1ra1, G alpha i2, G alpha olf, olfactory marker protein (OMP), and growth association protein 43 (GAP43). Goat V1r-expressing ORNs are categorized into two types situated in different areas of the epithelium. The first type of V1r-expressing ORN coexpressed G alpha i2, but not OMP or GAP43. The second type of V1r-expressing ORN expresses G alpha olf and OMP, but not G alpha i2 or GAP43. These findings suggest that the two types of V1r-expressing ORN in goat OE function using different G protein alpha subunits for chemoreception.     

Differential expression of cadherins in the developing and adult zebrafish olfactory system

Cadherins are cell adhesion molecules that play important roles in development of a variety of tissues and maintenance of adult structures. Although cadherin expression has been studied in detail in the central nervous system of several vertebrate species, little is known of their distribution in the developing and adult olfactory structures, and there is no published report, to our knowledge, of cadherin expression in fish olfactory system. In this study, we examined expression patterns of three cadherins, cadherin-1 (E-cadherin), cadherin-2 (N-cadherin), and cadherin-4 (R-cadherin), in the olfactory system of developing and adult zebrafish by using both in situ hybridization and immunocytochemical methods. Cadherin-1 is detected in the newly formed olfactory placode, and its expression is maintained in the developing and adult olfactory epithelium and olfactory nerve. Cadherin-2 is expressed in the olfactory epithelium, olfactory nerve, and olfactory bulb of the embryonic and larval zebrafish, and its expression is reduced in the adult olfactory system. In contrast to the cadherin-1 and cadherin-2 expression, cadherin-4 is not found in the olfactory epithelium, but it is detected in the larval and adult olfactory bulb, in the olfactory tract, and its targets in the telencephalon. We hypothesize that the differential expression of these three cadherins in the developing zebrafish major olfactory structures reflects functionally different roles in the development of the vertebrate olfactory system.     

Expression and localization of the prion protein PrPC in the olfactory system of the mouse

The normal physiological function of the prion protein PrP^C remains elusive despite its widespread expression, particularly throughout the nervous system. A critical step toward identifying its function is to precisely localize its pattern of expression. Historically, the immunolocalization of PrP^C has proved to be notoriously difficult and nonconsensual. We have thus undertaken a detailed expression analysis by means of a combination of in situ hybridization, knockout mice, and immunohistochemistry, using recently generated highly specific antibodies. We have attempted to accurately localize PrP^C expression in a tissue that is highly structured and of crucial behavioral importance to mice, the olfactory system. We found that PrP^C was expressed in both peripheral and central neurons of the olfactory system and that its distribution was axonal‐specific in both olfactory sensory neurons of the olfactory epithelium and mitral cells of the olfactory bulb. Our detailed expression analysis and the axonal localization we observed may provide important hints toward potential functions of PrP^C. J. Comp. Neurol. 508:487–499, 2008. © 2008 Wiley‐Liss, Inc.     

Differential expression of manganese and copper-zinc superoxide dismutases in the olfactory and vomeronasal receptor neurons of rats during ontogeny

Superoxide dismutases (SODs) protect cells from damage by oxygen free radicals. Manganese (Mn) SOD is preferentially induced in terminally differentiating cells; induction of copper-zinc (CuZn) SOD is more closely associated with postnatal exposure to environmental sources of oxygen free radicals. The purpose of this study was to investigate ontogenetic changes in immunoreactivity for MnSOD and CuZnSOD relative to the expression of markers of neuronal and chemosensory differentiation in olfactory and vomeronasal receptor neurons (ORNs and VRNs, respectively), which mature with different time courses. Immunoreactivity for both SODs was detected in rat ORNs at embryonic day (E) 14, the earliest time point investigated, but not until E16 in vomeronasal neuroblasts. ORNs also expressed the neuronal marker protein gene product (PGP) 9.5 and the chemosensory cell marker olfactory marker protein (OMP) at E14; vomeronasal neuroblasts expressed PGP 9.5 at E16 but were not immunoreactive for OMP until postnatal day (P) 2. Immunoreactivity for MnSOD in ORNs and VRNs generally increased pre- and postnatally to a maximum at P11. Immunoreactivity for CuZnSOD did not increase markedly until after birth, reaching maximal levels at P11-P24. Within ORNs and VRNs, the most intense immunoreactivity was localized in the dendritic and supranuclear regions. The results indicate that in ORNs and VRNs, increases in MnSOD immunoreactivity during ontogeny parallel the ongoing differentiation and maturation of chemosensory receptor neurons; in contrast, the induction of immunoreactivity for CuZnSOD is associated with postnatal exposure to the ambient oxygen and xenobiotic environment. J. Comp. Neurol. 381:31-40, 1997. © 1997 Wiley-Liss, Inc.     

Cellular expression of H and B antigens in the rat olfactory system during development

Developmental expression of H and B antigens in the rat olfactory system was studied from the embryonic day 14 up to the postnatal day 30. The H antigen was detected in the olfactory and vomeronasal epithelia as early as fetal day 14, whereas the B antigen first appeared 2 days later. The anti-H reagent reacted strongly with sensory receptors and weakly with supporting cells in both epithelia, whereas the anti-B reagent was specific for olfactory receptors. In the main olfactory epithelium, the H antigen was expressed from fetal day 19 by most of the receptor cells, whereas the B determinant was expressed from fetal day 16 to postnatal day 3 by only a few neuroreceptors mostly located near the epithelial surface. After the postnatal day 3, B positive neurons increased in number from the periphery toward the deeper mucosal layers and they were distributed over 3/4 of the epithelial thickness in 15- and 30-day-old rats. In the main olfactory bulb, a widespread glomerular B staining with variable binding intensity between adjacent glomeruli was already observed at birth. The vomeronasal receptor cells and their axon terminals in the accessory olfactory bulb exhibited a comparable developmental expression of the B antigen. Results suggest that the B antigen could be regarded as a marker of neuronal maturation of both the olfactory and vomeronasal receptor cells; moreover, its first appearance in the receptor cells might be temporally related to the formation of synapses between receptor axons and deutoneurons in the bulb.     

二乙基二硫化氨基甲酸盐对大鼠外侧嗅束髓鞘碱性蛋白表达的影响

BACKGROUND： Dithiocarbamates can cause demyelination of axons in the peripheral nervous system. Its derivate, diethyldithiocarbamate, is cytotoxic, and causes olfactory mucosal damage and atrophy of the olfactory bulb. However, it is still unclear whether the myelin sheath of the lateral olfactory tract is affected by diethyldithiocarbamate. OBJECTIVE： To investigate the effects of diethyldithiocarbamate on the myelin sheath of the rat lateral olfactory tract. This was done by examining changes in myelin basic protein expression after diethyldithiocarbamate treatment. DESIGN, TIME AND SETTING： A randomized, controlled, animal study was performed at the Laboratory of the Department of Human Anatomy and Neurobiology, Xiangya School of Medicine, Central South University, China from July to November 2007. MATERIALS： A total of 72 Sprague Dawley rats were randomly assigned into a diethyldithiocarbamate group （n = 32）, a solvent control group （n = 32）, and a blank control group （n = 8）. The diethyldithiocarbamate and solvent control groups were separately divided into 3-d, 7-d, 14-d and 28-d survival subgroups, with eight rats in each. Diethyldithiocarbamate （Sigma, USA） and goat anti-myelin basic protein polyclonal antibody （Santa Cruz, USA） were used in this study. METHODS： Rats in the diethyldithiocarbamate and solvent control groups were subcutaneously injected with diethyldithiocarbamate （600 mg/kg） and 0.01 mol/L phosphate buffered saline （600 mg/kg） at the posterior neck, respectively. Rats in the blank control group received no treatment. MAIN OUTCOME MEASURES： Immunohistochemical staining and Western blot assay were used to measure myelin basic protein expression in the rat lateral olfactory tract. RESULTS： Following immunohistochemical staining, myelin basic protein was uniformly distributed in the rat lateral olfactory tract in the blank control and solvent control groups. Western blot assay showed 21.5, 18, 17 and 14 ku positive bands. No significant difference was found in myelin basic protein distribution and blot pattern, in the rat lateral olfactory tract, in the diethyldithiocarbamate group, following immunohistochemical staining and Western blot assay. Myelin basic protein expression gradually decreased at day 3, reached the lowest level at day 7, and gradually increased again at days 14 and 28. CONCLUSION： Demyelination is induced by diethyldithiocarbamate in the rat lateral olfactory tract in an early stage, followed by remyelination at later stages.     

Effects of diethyldithiocarbamate on myelin basic protein expression in the rat lateral olfactory tract

BACKGROUND: Dithiocarbamates can cause demyelination of axons in the peripheral nervous system. Its derivate, diethyldithiocarbamate, is cytotoxic, and causes olfactory mucosal damage and atrophy of the olfactory bulb. However, it is still unclear whether the myelin sheath of the lateral olfactory tract is affected by diethyldithiocarbamate.OBJECTIVE: To investigate the effects of diethyldithiocarbamate on the myelin sheath of the rat lateral olfactory tract. This was done by examining changes in myelin basic protein expression after diethyldithiocarbamate treatment.DESIGN, TIME AND SETTING: A randomized, controlled, animal study was performed at the Laboratory of the Department of Human Anatomy and Neurobiology, Xiangya School of Medicine, Central South University, China from July to November 2007.MATERIALS: A total of 72 Sprague Dawley rats were randomly assigned into a diethyldithiocarbamate group (n=32), a solvent control group (n=32), and a blank control group (n=8). The diethyldithiocarbamate and solvent control groups were separately divided into 3-d, 7-d, 14-d and 28-d survival subgroups, with eight rats in each. Diethyldithiocarbamate (Sigma, USA) and goat anti-myelin basic protein polyclonal antibody (Santa Cruz, USA) were used in this study.METHODS: Rats in the diethyldithiocarbamate and solvent control groups were subcutaneously injected with diethyldithiocarbamate (600 mg/kg) and 0.01 mol/L phosphate buffered saline (600 mg/kg) at the posterior neck, respectively. Rats in the blank control group received no treatment.MAIN OUTCOME MEASURES: Immunohistochemical staining and Western blot assay were used to measure myelin basic protein expression in the rat lateral olfactory tract.RESULTS: Following immunohistochemical staining, myelin basic protein was uniformly distributed in the rat lateral olfactory tract in the blank control and solvent control groups. Western blot assay showed 21.5, 18, 17 and 14 ku positive bands. No significant difference was found in myelin basic protein distribution and blot pattern, in the rat lateral olfactory tract, in the diethyldithiocarbamate group, following immunohistoehemical staining and Western blot assay. Myelin basic protein expression gradually decreased at day 3, reached the lowest level at day 7, and gradually increased again at days 14 and 26.CONCLUSION: Demyelination is induced by diethyldithiocarbamate in the rat lateral olfactory tract in an early stage, followed by remyelination at later stages.     

Differential expression and cellular localization of doublecortin in the developing rat retina

Doublecortin is 40 kDa microtubule-associated phosphoprotein required for neuronal migration and differentiation in various regions of the developing central nervous system. We have investigated the expression and cellular localization of doublecortin in the developing rat retina using immunocytochemistry and Western blot analysis. The expression of doublecortin was high from embryonic day 18 (E18) until E20 and was low during the postnatal period. The doublecortin immunoreactivity first appeared in a few radially orientated cells in the mantle zone of the primitive retina at E15. From E16 onward, the immunoreactivity appeared in two different regions: the inner part of the retina and middle of the neuroblastic layer. In the inner part, the somata of cells in the ganglion cell layer, in the distal row of the neuroblastic layer and profiles in the inner plexiform layer showed doublecortin immunoreactivity up to postnatal day 1 (P1). Afterwards, the doublecortin immunoreactivity persisted in the inner plexiform layer until P15, although the intensity decreased gradually with the maturation of the retina. In the middle of the neuroblastic layer, doublecortin immunoreactivity appeared in the radially orientated cells. These cells transformed into horizontal cells. The doublecortin immunoreactivity persisted in these cells up to P21. Given these results, doublecortin may play an important role in the migration and differentiation of specific neuronal populations in developmental stages of the rat retina.     

Differential expression of neuregulins and their receptors in the olfactory bulb layers of the developing mouse

Neuregulins (NRGs), and their cognate receptors (ErbBs), play essential roles in numerous aspects of neural development and adult synaptic plasticity. The goal of this study was to investigate the developmental expression profiles of these molecules during the olfactory bulb (OB) maturation. The OB is a highly organized structure with cell types and synaptic connections segregated into discrete anatomical layers. We employed a novel approach by combining single-layer microdissection at different development ages, with isoform-specific semi-quantitative RT-PCR and Western blotting to monitor layer-specific developmental profiles of these molecules and alternate splice variants. Layer and age specific regulation was observed for the ErbB4 splice variants JMa/JMb and NRG-1-beta1/beta2 forms. With the exception of the outermost (nerve) layer, ErbB4-JMb and NRG-1-beta1 are expressed throughout the OB and their expressions decrease in the adult age in most layers. In contrast both ErbB4-JMa and NRG-1-beta2 are highly expressed in the granule cell layer in the early postnatal OB. This early postnatal expression correlates with the dramatic change from radial glia to astrocytes and appearance of the bulk of granule cells occurring at this developmental stage.     

Localization of taurine transporters, taurine, and (3)H taurine accumulation in the rat retina, pituitary, and brain.

The nervous system contains an abundance of taurine, a neuroactive sulfonic acid. Antibodies were generated against two cloned high-affinity taurine transporters, referred to in this study as TAUT-1 and TAUT-2. The distribution of such was compared with the distribution of taurine in the rat brain, pituitary, and retina. The cellular pattern of [(3)H] taurine uptake in brain slices, pituitary slices, and retinas was examined by autoradiography. TAUT-2 was predominantly associated with glial cells, including the Bergmann glial cells of the cerebellum and astrocytes in brain areas such as hippocampus. Low-level labeling for TAUT-2 was also observed in some neurones such as CA1 pyramidal cells. TAUT-1 distribution was more limited; in the posterior pituitary TAUT-1 was associated with the pituicytes but was absent from glial cells in the intermediate and anterior lobes. Conversely, in the brain TAUT-1 was associated with cerebellar Purkinje cells and, in the retina, with photoreceptors and bipolar cells. Our data suggest that intracellular taurine levels in glial cells and neurons may be regulated in part by specific high-affinity taurine transporters. The heterogeneous distribution of taurine and its transporters in the brain does not reconcile well with the possibility that taurine acts solely as a ubiquitous osmolyte in nervous tissues.     

Sequential expression, activity and nuclear localization of prolyl oligopeptidase protein in the developing rat brain

Prolyl oligopeptidase (POP) is a serine protease that hydrolyzes peptides shorter than 30-mer. Some evidence has recently been obtained that POP can generate protein-protein interactions and therefore participate in various physiological and pathological events. Several studies have reported that POP may be involved in neurogenesis since its activity increases during development and can be found in the nucleus of proliferating tissues. In cell cultures, POP has been shown to be localized in the nucleus, but only early in the development, since during maturation it is moved to the cytosol. We have now studied for the first time the expression of POP protein, its enzymatic activity and nuclear localization in vivo in the developing rat brain. We observed that enzymatic activity of POP is highest on embryonic day 18 while the protein amounts reach their peak at birth. Furthermore, POP is located in the nucleus only early in the development but is transferred to the cytosol already before parturition. Our in vivo results confirm the previous cell culture results supporting the role of POP in neurogenesis. A discordance of antenatal protein amounts and enzymatic activities is suggesting a tight regulation of POP activity and possibly even a nonhydrolytic role at that stage.     

Differential expression of kainate receptors in the basal ganglia of the developing and adult rat brain

Glutamate is the principal excitatory transmitter of the mammalian brain and plays a particularly important role in the physiology of the basal ganglia structures responsible for movement regulation. Using in situ hybridization with oligonucleotide probes, we examined the expression patterns of the five known kainate type glutamate receptor subunit genes, KA1, KA2 and GluR5–7, in the basal ganglia of adult and developing rat brain. In the adult rat, a highly organized and selective pattern of expression of the kainate subunits was observed in the basal ganglia and associated structures as well as in other regions of the brain. KA2 mRNA was abundant in the striatum, nucleus accumbens, subthalamic nucleus and substantia nigra pars compacta, and was present at lower levels in the globus pallidus and substantia nigra pars reticulata. Neither KA1 nor GluR5 expression was observed in the basal ganglia of adult rats, although these messages were present in other regions. GluR6 was highly expressed in the striatum and subthalamic nucleus and to a lesser extent in the substantia nigra pars reticulata, while no hybridization signal was detectable in the large, presumably dopaminergic neurons of the substantia nigra pars compacta. In contrast, GluR7 was strongly expressed in the substantia nigra pars compacta, was present at lower levels in the striatum, globus pallidus and substantia nigra pars reticulata, and was not detectable in the subthalamic nucleus. During postnatal development, expression of the kainate receptor subunits was characteristically highest on postnatal day 1 and declined to adult levels by day 20; however, in the globus pallidus we did observe the transient expression of KA1 and GluR5 between day 1 and day 10. These results demonstrate that the neuronal structures comprising the basal ganglia express a distinct combination of kainate receptor subunit genes, suggesting that the pharmacological properties of the resultant glutamate receptors are likely to be regionally specific. The organization of expression of these genes is established early in life, which is consistent with the important role they may play in establishing the functions of the motor system.     

Differential localization of high- and low-molecular-weight variants of microtubule-associated protein 2 in the developing rat telencephalon

Microtubule-associated protein 2 (MAP2) occurs in developing mammalian neuronal tissue as both high- and low-molecular-weight forms with temporally regulated expression. We studied the MAP2 expression in the developing rat telencephalon with monoclonal antibodies that recognized both the high- and low-molecular-weight forms of MAP2 variants or that specifically recognized high-molecular-weight forms of MAP2 variants. Differences in the staining patterns of these antibodies reflected differences in the distribution of the high- and low-molecular-weight MAP2s. The immunoreactive sites of high- and low-molecular-weight MAP2 had a more widespread distribution in the embryonic telencephalon than those of high-molecular-weight MAP2. Many bipolar cells in the ganglionic eminence (GE) and in the intermediate zone (IZ) of the neocortex showed low-molecular-weight MAP2 immunoreactivity, but they showed weak or no high-molecular-weight MAP2 immunoreactivity. Expression of mRNA containing exons common to high- and low-molecular-weight MAP2 was detected in the tangentially ellipsoidal cells in the IZ, but expression of mRNA containing an exon specific to high-molecular-weight MAP2 was not detected in these cells by in situ hybridization. We interpreted these observations as indicating that the bipolar cells contained MAP2c preferentially, but contained MAP2a and MAP2b (MAP2a/b) at a very low or negligible level. The cells that expressed MAP2c preferentially among the MAP2 splicing variants composed 50% of the preplate cells, most of the MAP2-positive cells in the hippocampus and the corpus callosum. Double labeling by DiI staining and Dlx2 immunohistochemistry, or by Dlx2 and MAP2 immunohistochemistry, revealed that most of the Dlx2-positive cells in the IZ expressed MAP2c preferentially at embryonic day 16. Another double-labeling study revealed that most GAD-positive cells in the preplate were MAP2a/b positive, whereas most GAD-positive cells in the IZ expressed MAP2c preferentially, with only a negligible level of MAP2a/b immunoreactivity. We conclude that MAP2 immunoreactivity in the IZ was localized in the tangentially migrating neurons. The tangentially migrating neurons seemed to acquire MAP2a/b immunoreactivity as they entered the preplate or cortical plate and developed into mature neurons. Radially migrating neurons in the IZ were MAP2 negative. After entering to the preplate or the cortical plate, they became MAP2a/b positive as they developed into mature neurons.