Vasoactive intestinal polypeptide-containing elements in the olfactory bulb of the hedgehog (Erinaceus europaeus)

The distribution of vasoactive intestinal polypeptide (VIP)-immunopositive elements was analyzed in the olfactory bulb (OB) of the Western European hedgehog (Erinaceus europaeus) under light and electron microscopy. The immunoreactivity appeared in an abundant population of periglomerular cells of the glomerular layer, in interneurons of the external plexiform layer, and in a restricted group of deep short-axon cells of the internal plexiform layer, the granule cell layer and the white matter. In the glomerular layer, VIP-containing periglomerular cells constituted a population of non-GABAergic neurons and did not receive synapses from olfactory axons. In the EPL, VIP-immunoreactivity appeared in a morphologically heterogeneous population of GABAergic interneurons, most of them identified as satellite cells and Van Gehuchten cells. These interneurons exerted an abundant and selective innervation of the somata, primary and secondary dendrites of the principal mitral and tufted cells, but did not contact granule cells. Perisomatic innervation of the principal cells followed two different patterns. The first included 'normal' basket-like arrangements of VIP-containing varicosities surrounding the somata of mitral and tufted cells. In the second, a set of satellite cells gave rise to short dendritic shafts that embraced the somata of principal cells in an 'exuberant' basket-like arrangement. These two morphological patterns of perisomatic innervation of principal cells were correlated with a neurochemical specificity of the target. In this sense, the 'exuberant' basket-like structures were always found surrounding a subpopulation of principal cells that did not contain the calcium-binding protein parvalbumin (PV). By contrast, they were never found surrounding the subpopulation of PV-containing principal cells, which only showed 'normal' basket-like structures. This study provides new data on the connectivity and neurochemical features of the hedgehog olfactory bulb and suggests that the olfactory circuits in this species are more complex than those described in other mammals.     

Tyrosine hydroxylase-like immunoreactive neurons in the olfactory bulb of the snake,Elaphe quadrivirgata,with special reference to the colocalization of tyrosine hydroxylase- and GABA-like immunoreactivities

Summary The distribution and structural features of tyrosine hydroxylase-like immunoreactive (TH-LI) neurons were studied in the olfactory bulb of a snake, Elaphe quadrivirgata, by using pre-and post-embedding immunocytochemistry at the light microscopic level. In contrast to rodent olfactory bulbs previously reported, many TH-LI neurons were seen not only in the main olfactory bulb (MOB) but also in the accessory olfactory bulb (AOB). With regard to the TH-like immunoreactivity, there appeared no appreciable differences between MOB and AOB. As in mammalian MOB, the majority of TH-LI neurons were clustered in the periglomerular region and appeared to send their dendritic branches into glomeruli, which as a whole make an intense TH-LI band in the glomerular layer (GML). In the external plexiform/mitral cell layer (EPL/ML) of MOB and AOB as well as in the outer sublamina of the internal plexiform layer (OSL) of AOB, an appreciable number of TH-LI neurons were scattered, extending dendritic processes which appeared to make a loose meshwork. TH-LI neurons in EPL/ML (including OSL) appeared to consist of at least two morphologically different types. The first had a small perikaryon and one or two smooth dendrites which usually extended to GML and were frequently confirmed to enter into glomeruli. The second had a larger perikaryon and 2–3 dendrites which branched into several varicose processes extending in EPL/ML/OSL but appeared not to enter into glomeruli. The TH-like immunoreactivity was rarely seen in the internal plexiform layer and internal granule cell layer. The colocalization of GABA-like and TH-like immunoreactivities was further studied. Almost all TH-LI neurons in both EPL/ ML/OSL and GML contained GABA-like immunoreactivity irrespectively of the type of TH-LI cells.Abbreviations in Figures AOB accessory olfactory bulb - MOB main olfactory bulb - Hem hemisphere - ON olfactory nerve layer - VN vomeronasal nerve layer - GM glomerular layer - EP/M external plexiform layer/Mitral cell layer - IP internal plexiform layer - IG internal granular layer - OS outer sublamina of the IPL of AOB - MS middle sublamina of the IPL of AOB - IS inner sublamina of the IPL of AOB     

Ciliary neurotrophic factor in the olfactory bulb of rats and mice

Ciliary neurotrophic factor (CNTF) is primarily regarded as an astrocytic lesion factor, promoting neuronal survival and influencing plasticity processes in deafferented areas of the CNS. Postnatal loss of neurons in CNTF-deficient mice indicates a function of the factor also under physiological conditions. In the olfactory bulb, where neurogenesis, axo- and synaptogenesis continue throughout life, CNTF content is constitutively high. The cellular localization of CNTF in the rat olfactory bulb is not fully resolved, and species differences between mouse and rat are not yet characterized. In the present study, four different CNTF antibodies and double immunolabeling with specific markers for glial and neuronal cells were used to study the cellular localization of CNTF in rat and mouse olfactory bulb. Specificity of the detection was checked with tissue from CNTF-deficient mice, and investigations were complemented by immunolocalization of reporter protein in mice synthesizing beta-galactosidase under control of the CNTF promoter (CNTF lacZ-knock-in mice). In both species, CNTF localized to ensheathing cell nuclei, cell bodies and axon-enveloping processes. Additionally, individual axons of olfactory neurons were CNTF immunoreactive. Both CNTF protein content and immunoreaction intensity were lower in mice than in rats. Scattered lightly CNTF-reactive cells were found in the granular and external plexiform layers in rats. Some CNTF-positive cells were associated with immunoreactivity for the polysialylated form of the neural cell adhesion molecule, which is expressed by maturing interneurons derived from the rostral migratory stream. In CNTF lacZ-knock-in mice, beta-galactosidase reactivity was found in ensheathing cells of the olfactory nerve layer, and in cells of the glomerular, external plexiform and granular layers. The study proves that CNTF is localized in glial and neuronal structures in the rodent olfactory bulb. Results in mice provide a basis for investigations concerning the effects of a lack of the factor in CNTF-deficient mice.     

Origin and migration of interneurons of the olfactory bulb in the musk shrew,Suncus murinus

The olfactory bulb of the musk shrew, Suncus murinus, is characterized by the presence of various interneurons. Our previous report (Kakuta et al., 2001) demonstrated that positive immunoreactions for calretinin were observed in periglomerular and perinidal cells in the glomerular layer, small ovoid neurons in the external plexiform layer, and granule cells in the granule cell layer of the olfactory bulb in the musk shrew aged 1 to 5 weeks, in addition to calretinin-immunoreactive bipolar cells distributed in the anterior subependymal layer and in each layer of the olfactory bulb. To examine the origin and migration of interneurons of the olfactory bulb, we labeled generated cells by injecting 28-day-old musk shrews with 5-bromo-2'-deoxyuridine (BrdU), and detected the labeled progeny cells that survived after several intervals. BrdU-labeled cells originated in the subependymal layer around the anterior horn of the lateral ventricle, and rostrally migrated in the subependymal layer from the anterior wall of the lateral ventricle into the center of the olfactory bulb, where they radially migrated into the granule cell layer, external plexiform layer, and glomerular layer. It took 2 days to migrate rostrally in the subependymal layer from the anterior lateral ventricle to the center of the olfactory bulb, and 2 to 6 days to migrate radially from the bulbar subependymal layer into the three layers mentioned. The rate of rostralward migration of the labeled cells was estimated to be 38 microm/h, while that of radial migration, 7 to 25 microm/h. The present BrdU-labeling study, together with our previous immunohistochemical study (Kakuta et al., 2001), indicates that anterior subependymal cells differentiate into granule cells in the granule cell layer, into Van Gehuchten cells in the external plexiform layer, and into periglomerular and perinidal cells in the glomerular layer of the olfactory bulb in the musk shrew.     

Distribution of enkephalin-like immunoreactivity in the rat main olfactory bulb

Enkephalin-like immunoreactivity was localized within the main olfactory bulb of the rat using immunohistochemical techniques. These studies utilized well characterized antisera directed to either leu⁵- or met⁵-enkephalin. Specificity was established by absorption of the antisera with either 10 μM synthetic leu⁵- or met⁵-enkephalin.Specific enkephalin-like immunoreactivity was observed within several different cell populations including (1) periglomerular cells, (2) granule cells and their processes within the external plexiform layer and (3) occasional short-axon (horizontal) cells within the granule and external plaxiform layers. The granule cell layer contained the greatest number of immunoreactive cells. Only a limited number of immunoreactive cells were found in both the periglomerular and granule cell layers, suggesting the enkephalin-containing neurons represent a sub-population within each layer.The absence of immunoreactive processes in the periventribular white matter, as well as the morphologies of immunoreactive bulbar neurons, indicates that enkephalin is found exclusively within intrinsic olfactory bulb neurons.     

Analysis of synaptic events in the mouse accessory olfactory bulb with current source-density techniques.

The accessory olfactory bulb of the mouse was studied by current source-density analysis of field potentials to determine the laminar and temporal distribution of synaptic currents evoked by electrical stimulation of the vomeronasal organ. The one-dimensional current source-density analysis revealed two major spatially and temporally distinct inward membrane currents (sinks): one in the glomerular layer and the other in the external plexiform layer. The glomerular layer sink preceded the external plexiform layer sink by a mean of 5.5 ms. Local infusions of the broad-spectrum excitatory amino acid antagonist, kynurenate, into the accessory olfactory bulb blocked the external plexiform layer sink without an obvious effect on the glomerular layer sink. The selective non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione produced a dose-dependent blockade of the external plexiform layer sink, whereas the selective N-methyl-D-aspartate receptor antagonist D-2-amino-5-phosphonovalerate was without effect. These results, taken together with the cytoarchitecture of the accessory olfactory bulb, suggest that the glomerular layer sink results mainly from synaptic excitation evoked in the glomerular dendritic branches of mitral cells by the vomeronasal afferent fibres and the external plexiform layer sink mainly from non-N-methyl-D-aspartate receptor-mediated synaptic excitation in the peripheral processes of granule cells via the mitral to granule cell dendrodendritic synapse.     

Morphological characteristics of dopaminergic immunoreactive neurons in the olfactory bulb of the common marmoset monkey (Callithrix jacchus)

The present study describes the distribution of tyrosine hydroxylase (TH)-immunoreactive (IR) elements in the olfactory bulb of the common marmoset monkey (Callithrix jacchus), a primate species by immunohistochemistry. We identified six layers of the olfactory bulb of the common marmoset monkey in sections stained with cresyl violet. The majority of TH-IR cells were found in the glomerular layer. A few TH-IR cells were present in the external plexiform and granule cell layers. TH-IR fibers were identified in all layers of the olfactory bulb. The density of these nerve fibers was high in the internal plexiform and granule cell layers. The results in the olfactory bulb of the common marmoset monkey are generally similar to previous reports in some mammals. These data suggest that TH in the olfactory bulb of the common marmoset monkey may play a role in olfactory transmission via the glomeruli like in other mammals.     

Changes in mitotic rate and GFAP expression in the primary olfactory axis of streptozotocin-induced diabetic rats

Many diabetic individuals develop anosmia but the mechanism(s) causing the dysfunction in the olfactory system is (are) unknown. Glial fibrillary acidic protein expression is reduced in diabetic retinopathy and is also reduced, with unknown consequences, in other brain regions of diabetic rats. We used immunohistochemistry and immunoblotting from untreated control and streptozotocin-induced type 1 (insulin dependent) diabetic rats to investigate main olfactory epithelial mitotic rate and glial fibrillary acidic protein expression in the lamina propria of the sensory epithelium and in the olfactory bulb. Numbers of bromodeoxyuridine-positive cells were significantly lower in the diabetic sensory epithelium compared to non-diabetic controls. Immunohistochemical observations suggested a qualitative difference in glial fibrillary acidic protein expression in both regions examined especially in the olfactory bulb external plexiform layer and the lamina propria. Immunoblot analysis confirmed that the diabetic olfactory bulb and lamina propria expressed less glial fibrillary acidic protein compared to the non-diabetic control group. The lower expression levels in the olfactory bulb external plexiform layer suggested by immunohistochemistry do not reflect a change in the number of astrocytes since the numbers of S100B(+) cells were not different between the two groups.     

Calbindin-D-28k-like immunoreactive structures in the olfactory bulb and anterior olfactory nucleus of the human adult: distribution and cell typology--partial complementarity with parvalbumin

Calbindin-D-28k and parvalbumin are calcium-binding proteins. The laminar distribution and morphological features of calbindin-D-28k-like immunoreactive structures were studied in 60-microns-thick sections of the human olfactory bulb. Except for the olfactory nerve layer, immunoreactive neurons were present in all layers of the olfactory bulb. They reached highest densities in the external plexiform layer and internal granule cell layer. Considerable numbers of calbindin-like nerve cells were also found in the olfactory tract and in distal portions of the anterior olfactory nucleus. When comparing the distribution of calbindin-positive structures to that of parvalbumin-positive ones a partially complementary distribution pattern was found. Calbindin-like immunoreactive portions of the anterior olfactory nucleus and olfactory tract were mirrored by immunonegative areas in adjacent sections stained for parvalbumin. Using the combined pigment-Nissl procedure we observed the presence of lipofuscin deposits in nearly 80% of all the calbindin-immunoreactive neurons analysed. Moreover, analysis of their lipofuscin deposits rendered the further differentiation of morphologically similar neuronal subpopulations possible. In contrast, all parvalbumin-like immunoreactive neurons remained free of lipofuscin granules.     

Mapping of benzodiazepine-like immunoreactivity in the rat brain as revealed by a monoclonal antibody to benzodiazepines.

A monoclonal antibody against benzodiazepines (21-7F9) was used to study the distribution of benzodiazepine-like immunoreactivity in the rat brain. Immunodensitometry in combination with image analysis were used for quantification. The results showed a ubiquitous distribution of benzodiazepine-like immunoreactivity throughout the brain. Very high levels of benzodiazepine-like immunoreactivity were found in the Purkinje cell layer of the cerebellum, in the primary olfactory cortex, in the stratum pyramidale of the hippocampus and in the mitral cell layer of the olfactory bulb. High densities of benzodiazepine-like immunoreactivity were found in the granule cell layer of the cerebellum, the pyramidal cell layer of the olfactory tubercle, the granule layer of the dentate gyrus, the arcuate nucleus of the hypothalamus, the mammillary bodies, the interstitial nucleus of Cajal and superficial grey layer of superior colliculus. The substantia nigra pars compacta, the islands of Calleja and layers II, III, V and VI of the cerebral cortex had moderate levels of benzodiazepine-like immunoreactivity. Lower densities were found in the internal granular layer and the external plexiform layer of the olfactory bulb, in the molecular layer of the dentate gyrus, in layers I and IV of the cerebral cortex, in the nucleus caudate-putamen and most of the thalamic nuclei. The lowest density of immunoreactivity was found in the globus pallidus, and the strata radiatum, oriens and lacunosum-moleculare of the hippocampus. The distribution of endogenous benzodiazepine-like immunoreactivity was compared with the distribution of the GABA/benzodiazepine receptor by using both immunocytochemistry and receptor autoradiography. Our studies have shown a clear mismatch between the localization of the benzodiazepine-like immunoreactivity and the GABA/benzodiazepine receptors.     

Tyrosine hydroxylase immunoreactive structures in the aged human olfactory bulb and olfactory peduncle

We studied the anatomical distribution of dopaminergic structures in the normal, aged, human olfactory bulb and olfactory peduncle with a monoclonal antibody against tyrosine hydroxylase. Three different tyrosine hydroxylase containing cell groups are present in the olfactory bulbs: (1) a group of round, medium-sized cells within and around the glomeruli; (2) cells in the external plexiform layer; and (3) cells that are scattered in the stratum album. Occasionally, a few labeled neurons can be observed in the granule cell layer. In the olfactory peduncle a few labeled cells are present in the superficial layers just underneath the pia. Tyrosine hydroxylase containing terminal-like structures are present in the glomerular layer and the external plexiform layer. In a few cases dense terminal labeling is also observed in the cell groups that constitute the anterior olfactory nucleus. In the olfactory peduncle scattered labeled fibers are present. In addition, the present study makes clear that quantitative differences exist between the individual cases for which no explanation could be found.     

Intraglomerular dendritic link connected by gap junctions and chemical synapses in the mouse main olfactory bulb: electron microscopic serial section analyses

Glomeruli of the main olfactory bulb are considered to serve as functional units in processing the olfactory information. Thus the fine tuning of the output level from each glomerulus is important to the information processing in the olfactory system. The interactions among neuronal elements in glomeruli might be one of main mechanisms regulating this output level. In the mouse main olfactory bulb neuronal connections via chemical synapses and gap junction in glomeruli were analyzed by the serial electron microscopical reconstruction. Gap junctions were encountered between diverse types of dendritic processes, between mitral/tufted cell dendrites, between mitral/tufted cell dendrites and periglomerular cell dendrites and between mitral/tufted cell dendrites and dendrites of some interneurons different from periglomerular cells. Then these morphological observations indicate that we must consider both direct coupling between mitral/tufted cells via gap junctions and indirect coupling between mitral/tufted cells via intervening interneuronal processes. One of gap junction-forming processes presynaptic in asymmetrical synapses was traced back to the soma of its origin located in the glomerular layer, which was thus identified as an external tufted cell. However, interestingly, it showed apparently different ultrastructural features from other external tufted cells located at the border between the glomerular and external plexiform layers; the latter resemble so-called mitral/tufted cells located in the external plexiform and mitral cell layers. Then external tufted cells were assumed to be heterogeneous in their ultrastructural features. We occasionally encountered several dendrites connected by gap junctions, which furthermore made chemical synapses with each other and with other surrounding processes. Thus both chemical synapses and gap junctions interconnect complexly various processes in the glomerulus, where the local circuit among intermingled olfactory nerves, mitral/tufted cell dendrites and interneuron dendrites is far more complex than previously schematized.     

A Golgi study on the olfactory bulb in the lamprey, Lampetra japonica

The intrinsic organization of the olfactory bulb in the lamprey was studied using the rapid Golgi method. Although not as discrete as in many vertebrates, a laminar organization was recognized. From the periphery inward, the following layers were discernible: the layer of the olfactory fibers, the olfactory glomeruli with the mitral cells, the granule cells, and the ependymal cells. Just beneath the surface of the olfactory bulb, the olfactory fibers extended over the entire bulb forming a dense fiber plexus terminating in the olfactory glomeruli which were arranged in one to two layers internally to the layer of the olfactory fibers. The mitral cells formed no discrete layer and were located mainly around the olfactory glomeruli. The mitral cells in the lamprey were lacking in secondary dendrites, but had two or more primary dendrites which terminated in the olfactory glomeruli. The axons of the mitral cells proceeded inwardly and accumulated diffusely in the granule cell layer which occupied a wide area internally to the layer of the olfactory glomeruli with the mitral cells. The granule cell layer was composed of densely packed small spindle or fusiform axonless cells, the processes of which extended superficially to be distributed in the olfactory glomeruli. At the deepest region of the bulb was a layer of the ependymal cells lining the surface of the olfactory ventricle. The external and internal plexiform layers were not evident. Thus, while the major constituents of the olfactory bulb of the vertebrate could be identified in that of the lamprey, the general laminar organization seemed indiscrete.     

Localisation of neuronal nitric oxide synthase-immunoreactivity in rat and rabbit retinas

The distribution of neuronal nitric oxide synthase (NOS) immunoreactivity was examined in rat and rabbit retinas and was compared with the distribution of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase reactivity and vasoactive intestinal peptide (VIP) immunoreactivity. An antibody raised against a C-terminal fragment of a cloned rat cerebellar NOS was used to localise NOS immunoreactivity. NOS immunoreactive cells were not detected in rat retinas at postnatal day 1 or 4, but were seen from postnatal day 7 onwards. NOS immunolabelling was seen in a small population of cells in the proximal inner nuclear layer. Most of the labelled cells had the position of amacrine cells and were seen to send processes into the inner plexiform layer. A few labelled cells were at times also seen in the ganglion cell layer, which are likely to correspond to displaced amacrine cells. The same NOS-labelling pattern was seen in rat and rabbit retinas.NADPH-diaphorase staining was observed in both species, in photoreceptor inner segments, in cells with the position of horizontal cells, in a subset of amacrine and displaced amacrine cells, in large cell bodies in the ganglion cell layer, in both plexiform layers, and in endothelium. Colocalisation of NOS immunoreactivity and NADPH-diaphorase staining was only observed among amacrine cells. However, not all NADPH-diaphorase-reactive amacrine cells were found to be NOS immunoreactive. VIP immunoreactivity was also localised in rat retinas in a subpopulation of amacrine cells, but no colocalisation of NOS and VIP immunoreactivity was observed.Our observations indicate that only amacrine cells contain the NOS form recognisable by the antibody used, and suggest that different isoforms of neuronal NOS may be present in retinal cells. Further, the onset of NOS expression in rat amacrine cells appears to occur independently of neuronal activity.Paper in honour of Professor Rolf Elofsson on the occasion of his retirement from the chair of Zoology at the University of Lund     

Microglia in the olfactory bulb of rats during postnatal development and olfactory nerve injury with zinc sulfate: a lectin labeling and ultrastrucutural study

Using isolectin (GSA I-B4) as a marker, this study examined the possible alterations of lectin-labeled membranous glycoproteins in microglial cells in the olfactory bulb of normal development and under experimentally induced degeneration. In light microscopy, several morphological types of microglial cells representing different degrees of cell differentiation were distributed in the bulb laminae. A gradient of microglial differentiation extending from the intermediate to superficial and intermediate to deep occurs in the bulb layers. The differentiation gradient and lectin labeling pattern of microglial cells in the developing bulb resembled those in other areas of the brain tissues. Differentiating microglia showed a gradual diminution of lectin staining when the nascent round cells transformed into the mature ramified cells. Microglia in the external plexiform layer of the olfactory bulb were the first to mature and the cells expressed very weak lectin reactivity. In mature or adult rats, some microglial cells showing intense lectin labeling were observed in the olfactory nerve layer, granule cell layer and subependymal layer. Ultrastructurally, lectin labeling was localized at the trans saccules of the Golgi apparatus. Microglial cells in other bulb laminae, however, exhibited a negative reaction for the isolectin at the Golgi apparatus. Following intranasal irrigation of zinc sulfate, some microglial cells in the olfactory nerve layer and glomerular layer were activated to become phagocytic cells with increased lectin labeling at their ramified processes. GSA I-B4 staining was also localized at their trans saccules of the Golgi apparatus. The lectin labeling pattern of these phagocytic cells resembled that of differentiating microglia in postnatal bulbs, suggesting that bulb microglia in the lesioned sites were activated through cell dedifferentiation into macrophages.     

A Golgi study on the main olfactory bulb in the snake Elaphe quadrivirgata

The intrinsic organization of the main olfactory bulb in the snake was studied using the rapid Golgi method. A distinct laminar structure was recognized. From the periphery inward, the following layers were distinguished: the layer of the olfactory fibers, the olfactory glomeruli, the mitral cells, the deep fiber plexus, the granule cells and the ependymal cells. Olfactory fibers derived from the nasal cavity reached the entire surface of the bulb, forming a dense fiber plexus, then swung deeply and terminated in the olfactory glomeruli which were arranged in 2-4 rows. The mitral cell layer occupied a wide zone and was composed of scattered mitral cells. The mitral cells had 2-9 primary dendrites proceeding externally to terminate in the olfactory glomeruli and 2-4 secondary dendrites extending tangentially in the mitral cell layer to be distributed therein. The axons of the mitral cells travelled deeply and entered the layer of the deep fiber plexus. The deep fiber plexus was the path for the bulbar efferent and afferent fibers and could be traced caudally as the main olfactory tract, up to the anterior olfactory nucleus and vicinity. The granule cell layer was composed of small cells, the granule cells, packed closely with no special arrangement. The granule cells had long processes which extended superficially to be distributed mainly in the mitral cell layer. The ependymal cells were located at the deepest layer forming the wall of the olfactory ventricle and generated a long process which extended towards the surface to terminate in the peripheral portion of the bulb. In the snake bulb, the well-documented external and internal plexiform layers were considered to be included in the wide mitral cell layer. Thus, while several specific structures were observed, the fundamental organization of the main olfactory bulb in the snake seemed to be identical to that of the main olfactory bulb in various other vertebrate species.     

The distribution of taurine,cysteinyl sulphinilic acid decarboxylase and crysteinyl sulphinlic acid α-ketoglutarate transaminase in the rat olfactory bulb and olfactory nucleus

Taurine, a putative neurotransmitter, cysteinyl sulphinlic acid α-ketogluraric acid transaminase (CSA-T) and cysteinyl sulphinlic acid decarboxylase (CSA-D) were measured in the different structures of the rat olfactory bulb and olfactory nucleus. It appears there are significant differences between the level of taurine in internal layers (mitral cells, plexiform) and external layer such as fibrorum. The CSA-T and CSA-D activities followed approximately the distribution of taurine in the different areas of the rat olfactory bulb and nucleus.A very high activity of CSA-T was present in all areas studied and a role for the enzyme is proposed. The cellular distribution of CSA-T, CSA-D and taurine is compared with the distribution in retina.     

Chromogranin A in the olfactory system of the rat

The olfactory bulb of the rat contains chromogranin A at a similar level as the adrenal gland or the hypophysis as revealed by immunoblots. Olfactory chromogranin A also displays the same size as chromogranin A of endocrine cells. In the hippocampus and other brain regions, we could not detect chromogranin A by immunoblotting. In contrast, chromogranin A messenger ribonucleic acid (using S1 nuclease protection assays) was observed in all brain regions examined, including the olfactory bulb. By in situ hybridization histochemistry with a complementary ribonucleic acid probe (280 nucleotides), and by immunocytochemistry, chromogranin A synthesis could be localized to cell bodies of the mitral cell layer, of the external plexiform layer and of the periglomerular region of the olfactory bulb. Immunocytochemically, chromogranin A was also detected in the central projection areas of mitral and tufted cells in the primary olfactory cortex and the anterior amygdaloid area but not in the olfactory glomeruli, where the incoming olfactory nerve fibers of the primary olfactory neurons establish synaptic contacts. Taken together the data show that chromogranin A, following biosynthesis in the perikarya of the mitral and tufted cells, is specifically transported into their axonal terminals but not into their primary dendrites. We propose that the rat olfactory system could serve as a model for the study of chromogranin A regulation and function in neurons.     

Early X-irradiation of rats--II. Effect on granule cells and their dendrodendritic synapses in the olfactory bulb

Low, repeated doses of X-rays from a Co60 source were used to impair the development of the granule cells and their dendritic terminals in the olfactory bulb, and the resulting effect was studied under light and electron microscopes at 9 days of age. Irradiation of rats from embryonic day 18 (in utero) to postnatal day 5 resulted, among others, in maldevelopment of the (internal) granule cell and external plexiform layers. This was accompanied by a decrease in the number and the density of the granule cells, and the remaining granule cells contained less ribosomes, regardless of their position within the layer. This implies that both supposed subtypes of granule cells were effected. In the external plexiform layer, a reduced number of mature dendrodendritic synapses and signs of harmed granule gemmules were observed. The results suggest that intrauterinal plus postnatal irradiation with low, repeated doses of X-rays may be an effective tool impairing the development of prenatally forming neurons.