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     

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.     

Heterogeneity of parvalbumin-containing neurons in the mouse main olfactory bulb, with special reference to short-axon cells and betaIV-spectrin positive dendritic segments

The structural features of parvalbumin-positive neurons were studied in the mouse main olfactory bulb (MOB). Parvalbumin-positive neurons were heterogeneous, including numerous medium-sized interneurons in the external plexiform layer (EPL), some few large short-axon cells and a few periglomerular cells. Their overall distribution pattern and structural features resembled those of the rat MOB. However, large short-axon cells were frequently encountered in the internal plexiform and granule cell layers, which were rare in the rat MOB. In addition a few large short-axon cells were also encountered throughout the EPL. These short-axon cells extended their axons mainly in the EPL, usually making columnar axonal fields. Most parvalbumin-positive cells except periglomerular cells were confirmed to be glutamic acid decarboxylase positive. We examined the immuno-localization of the markers for the axon initial segments (AISs), betaIV-spectrin and sodium channels, to determine whether or not heterogeneous parvalbumin-positive neurons have axons. We confirmed their localization on the AISs of the large short-axon cells and periglomerular cells. However, these markers were encountered on some patch-like segments on the dendritic processes instead of the thin axon-like processes of the medium-sized EPL interneurons. The present study revealed the diversity of parvalbumin-positive neurons in the mouse MOB and their particular structural properties hitherto unknown.     

Expression and regulation of the immediate-early gene product Arc in the accessory olfactory bulb after mating in male rat

Recent studies of the accessory olfactory bulb have shown that the expression of immediate-early genes, e.g., c-fos, c-jun and egr-1, can be used as a marker of neuronal activity in response to pheromonal cues. In this study, we analyzed the expression pattern, in response to mating, of the novel immediate-early gene product Arc (an activity-regulated cytoskeleton-associated protein). Arc is hypothesized to play a role in activity-dependent neuronal plasticity in the hippocampus. In a control group of male rats, only a small number of Arc-immunoreactive cells were observed in the accessory olfactory bulb. In a mating group, however, a marked increase in the number of Arc-immunoreactive cells was observed only in the granule cell layer of the accessory olfactory bulb. The increase in the number of Arc-immunoreactive cells after mating was similar to that observed for other immediate-early genes. However, for the mating group, the increase in Arc-positive cells was limited to the granule cell layer. Granule cells have been shown to exhibit a strong synaptic plasticity in response to pheromonal stimulation.From these findings we suggest that Arc plays an important role in neuronal plasticity in the accessory olfactory bulb.     

Expression of connexin 57 in the olfactory epithelium and olfactory bulb

In the visual system, deletion of connexin 57 (Cx57) reduces gap junction coupling among horizontal cells and results in smaller receptive fields. To explore potential functions of Cx57 in olfaction, in situ hybridization and immunohistochemistry methods were used to investigate expression of Cx57 in the olfactory epithelium and olfactory bulb. Hybridization signal was stronger in the olfactory epithelial layer compared to the connective tissue underneath. Within the sensory epithelial layer, hybridization signal was visible in sublayers containing cell bodies of basal cells and olfactory neurons but not evident at the apical sublayer comprising cell bodies of sustentacular cells. These Cx57 positive cells were clustered into small groups to form different patterns in the olfactory epithelium. However, individual patterns did not associate with specific regions of olfactory turbinates or specific olfactory receptor zones. Patched distribution of hybridization positive cells was also observed in the olfactory bulb and accessory olfactory bulb in layers where granule cells, mitral cells, and juxtaglomerular cells reside. Immunostaining was observed in the cell types described above but the intensity was weaker than that in the retina. This study has provided anatomical basis for future studies on the function of Cx57 in the olfactory system.     

大鼠嗅球向梨状皮质的纤维投射及其一氧化氮合酶阳性神经元的分布

目的观察大鼠嗅球向梨状皮质的纤维投射及嗅球内一氧化氮合酶(NOS)阳性神经元的分布。方法采用还原型尼克酰胺腺嘌呤二核苷酸脱氢酶(NADPH-d)组织化学法结合辣根过氧化物酶(HRP)逆行追踪技术对20只SD大鼠嗅球向梨状皮质的纤维投射进行逆行追踪观察。结果同侧嗅球僧帽细胞层观察到HRP标记细胞。嗅球内丛层、颗粒细胞层观察到NOS阳性神经元,但未观察到HRP/NOS双标记细胞。结论嗅球僧帽细胞层发出纤维投射到同侧梨状皮质。嗅球内有NO的表达,但嗅球的NOS阳性神经元不投射到梨状皮质。     

Vasoactive intestinal polypeptide-immunoreactive neurons in the main olfactory bulb of the hedgehog (Erinaceus europaeus)

Vasoactive intestinal polypeptide (VIP) immunoreactivity was localized by the indirect antibody enzyme method (PAP technique) in the main olfactory bulb of the hedgehog. Most VIP-immunoreactive cells were located in the glomerular layer and throughout the external plexiform layer. Fewer cells were observed in the granule cell layer. At the morphological level they exhibit the characteristics of periglomerular, external tufted, superficial short axon, horizontal and Van Gehuchten cells. It should be mentioned that another specific neuronal type was found in the inner third of the external plexiform layer, which is not described in other animals. These results revealed that a high number of intrinsic neuronal types of the olfactory bulb of the hedgehog display a strong VIP immunoreactivity.     

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 somatostatin mRNA in the rat nervous system as visualized by a novel non-radioactive in situ hybridization histochemistry procedure

The cellular localization of preprosomatostatin mRNA in the rat brain and sensory ganglia has been examined in detail using a newly developed highly sensitive non-radioactive in situ hybridization histochemistry procedure. An alkaline phosphatase labelled anti-sense 30mer oligodeoxynucleotide probe was used for detection of somatostatin mRNA. This probe readily demonstrated somatostatin gene expression throughout the rat CNS with very high contrast and good cellular localization. As a result, we visualized numerous somatostatin mRNA-positive cells in many CNS areas which had previously not been shown to contain a mRNA signal. This method detected a number of somatostatin mRNA-positive cells, in the mitral cell layer of accessory olfactory bulb, the glomerular layer of the main olfactory bulb, the dorsal part of the lateral septum, superficial gray layer of superior colliculus, inferior colliculus, anterior ventral cochlear nucleus, granular layer and Purkinje cell layer of cerebellum, and substantia gelatinosa of medulla and spinal cord, all areas where signal detection using radiolabelled in situ probes has previously been rather difficult. The principle advantages of the present method include the very precise cellular resolution of signal, the rapid reaction time and low background. The sensitivity of the present method seems to be at least equivalent to most immunocytochemical procedures and more sensitive than most isotopic in situ hybridization methods.     

Cholinergic innervation of the main and the accessory olfactory bulbs of the rat as revealed by a monoclonal antibody against choline acetyltransferase

Summary The main and accessory olfactory bulbs (MOB and AOB) of the rat were immunohistochemically stained with a monoclonal antibody against choline acetyltransferase (ChAT) in order to know the difference in the distribution patterns of cholinergic fibers between these two structures. A few ChAT-immunoreactive cell bodies were found in the superficial and middle parts of the external plexiform layer (EPL) of the MOB, in the granule cell layer (GCL) of the MOB, and in the GCL of the AOB. The frequency in appearance of these cells was 0.9 cells/section in the MOB and 0.3 cells/section in the AOB. While the glomerular layer (GL) and the superficial part of the EPL were most densely innervated in the MOB, the internal plexiform layer received the richest innervation in the AOB. There were no immunoreactive structures in the olfactory nerve layer of the MOB and in the vomeronasal nerve layer and glomerular layer of the AOB. In addition to a relatively homogenous distribution of cholinergic fibers in the MOB and AOB, there were several foci of very dense network of immunoreactive fibers at the posterior level of the OB. These foci formed a part of the modified glomerular complex that was recently identified using 2-deoxyglucose method and was presumed to be related to suckling behaviour in the neonatal rat.     

Autoradiographic localization of insulin receptors in rat brain: prominence in olfactory and limbic areas

The binding of 125I-labeled insulin in thin sections of frozen fresh rat brain (95% specific binding) was shown using autoradiography. By several criteria including structure-activity relationship analysis, the brain insulin receptors were qualitatively indistinguishable from insulin receptors previously characterized on brain and other more typical target tissues and distinct from receptors for the insulin-like growth factors. The 125I-labeled insulin binding sites in brain formed a distinct pattern with high levels of binding in all olfactory areas and in closely related limbic regions. Binding was also prominent in the neocortex and the accessory motor areas of the basal ganglia and the cerebellum. Among ancillary brain structures only the choroid plexus demonstrated a high density of insulin receptors. When insulin receptors were located on cortical or laminated structures, the highest binding occurred in the superficial ("molecular" or "plexiform") layer, i.e. the layer which receives afferent input and/or is rich in the dendritic branches of principal neurons (e.g. external plexiform layer of the olfactory bulb and the molecular layer of the dentate gyrus). The enrichment of insulin receptors in the olfactory and limbic systems, which is a characteristic feature of other known neuropeptides, in addition to their prevalence in the strata occupied by the dendritic fields of principle neurons, suggests a neuromodulatory function for insulin in the brain.     

Neonatal sensory deprivation reduces tufted cell number in mouse olfactory bulbs

Quantitative morphometric methods were used in mice to study the effect postnatal olfactory deprivation has on tufted cell size and number. The two layers containing tufted cells, the external plexiform and glomerular layers, are considerably smaller in the deprived olfactory bulbs than in the contralateral, experienced olfactory bulbs. While most of this volumetric deficit may be due to an attenuation of synaptogenesis and dendritic elaboration, an additional factor contributing to the reduced volume of these bulbar layers is a substantial loss of tufted cells. Since tufted cells are generated prenatally, their reduced number in the postnatally deprived olfactory bulb is probably a consequence of retarded migration or cell death.     

A light and electron microscopic study of taurine-like immunoreactivity in the main olfactory bulb of frogs

The distribution of taurine in the frog olfactory bulb was studied using light and electron microscopic immunohistochemical techniques. At the light microscopic level, taurine-like immunoreactivity (taurine-LI) was found in (i) fibers coursing from the olfactory nerve layer to the glomerular layer, (ii) cell bodies and processes primarily located in the caudal part of the granule cell layer (GCL), and (iii) puncta outlining unstained somata of mitral cells and cells in the GCL. In consecutive sections processed for taurine or GABA, numerous cells of the caudal GCL displayed taurine-LI and GABA-like immunoreactivity (GABA-LI). A bimodal distribution of the cross-sectional cell area for GABA-LI cells implied their morphological diversity, and the peak for larger GABA-LI cells coincided with the maximum for taurine-LI cells. At the electron microscopic level, single immunogold labeling showed that GABA-LI, but not taurine-LI, is present in granule cells, whereas both taurine-LI and GABA-LI were localized in a ‘non-granule’ type of cell. The double labeling procedure demonstrated coexistence of taurine-LI and GABA-LI in neurons of a ‘non-granule’ type. These cells had some ultrastructural features typical of short axon cells in the GCL of the mammalian olfactory bulb and were tentatively considered as short axon-like cells. Results suggest that, in the frog olfactory bulb, taurine is contained in primary olfactory afferents and short axon-like cells of the GCL co-localizing GABA and taurine.     

Calcium-binding protein parvalbumin-immunoreactive neurons in the rat olfactory bulb

The laminar distribution and morphological features of parvalbumin-immunoreactive [PV(+l)] neurons, one of the subpopulations of GABAergic neurons, were studied in the rat olfactory bulb at a light microscopic level. In the main olfactory bulb of adult rats, PV(+) neurons were mainly located in the external plexiform layer (EPL), and a few were scattered in the glomerular layer (GL), mitral cell layer (ML), and granule cell layer (GRL); whereas PV(+) neurons were rarely seen in the accessory olfactory bulb. The inner and outer sublayers of the EPL (ISL and OSL) appeared to be somewhat different in the distribution of PV(+) somata and features of PV(+) processes. PV(+) somata were located throughout the OSL, and PV(+) processes intermingled with one another, making a dense meshwork in the OSL; whereas, in the ISL, PV(+) somata were mainly located near the inner border of the EPL, and PV(+) processes made a sparser meshwork than that in the OSL. PV(+) neurons in the EPL were apparently heterogeneous in their structural features and appeared to be classifiable into several groups. Among them there appeared five distinctive types of PV(+) neurons. The most prominent group of PV(+) neurons in the OSL were superficial short-axon cells, located in the superficial portion of this sublayer and giving rise to relatively thick processes, in horizontal or oblique directions, which usually bore spines and varicosities. Another prominent group of PV(+) neurons extended several short, branched dendrites with spines and varicosities, which appeared to intermingle with one another, making a relatively small, spherical or ovoid dendritic field around the cell bodies; most of them resembled Van Gehuchten cells reported in previous Golgi studies. A third distinctive and most numerous group of PV(+) neurons were of the multipolar type; their somata and processes were located throughout the EPL. Their relatively smooth processes with frequent varicosities and a few spines were extended horizontally or diagonally throughout the EPL. A fourth group, which could be a subtype of the multipolar type, were located in or just above th ML and extended several thin, smooth dendrites in the EPL, some of which appeared to reach the border between the GL and EPL. Occasionally, axonlike processes arose from their cell bodies and extended into the ML. This fourth type of PV(+) neuron was named inner short-axon cells. A fifth group of neuron was located in the ML; processes of these neurons were extended horizontally, so they were named inner horizontal cells. PV(+) processes from the fourth and the fifth group of cells appeared to make contacts on mitral cell somata. In the GL some presumably periglomerular cells were also PV(+). In the GRL, PV(+) neurons were small in number, but they were also heterogeneous in their structural features; Some were identified as Golgi cells. This study shows a tremendous heterogeneity in morphological features of a chemically defined subpopulation of GABAergic interneurons in the olfactory bulb.     

Immunohistochemical localization of vascular endothelial growth factor and its receptor Flk-1 in the amphibian developing principal and accessory olfactory system

In the last years several studies have shown that vascular endothelial growth factor (VEGF) is present in neural stem cells and mature neurons from different neural tissues where it may play an important role as a neuroproliferative and/or antiapoptotic factor. The olfactory neuroepithelium has the capability to replace dying neurons with new neurons formed by cell division from stem cells in the basal region of the epithelium. The present study demonstrates, for the first time, that VEGF is present in the olfactory epithelium, nerves and bulbs (both main and accessory) during the development of the toad Bufo arenarum. In this report, we detected VEGF immunoreactivity in mature olfactory neurons from early larval stages until the beginning of the metamorphic climax. VEGF expression decreases dramatically after metamorphosis. VEGF receptor Flk-1 was localized by immunohistochemistry, from premetamorphic larval stages until the climax in the neurons of the olfactory epithelium with a more intense labeling in the basal cell layer. Double-label immunofluorescence studies localized VEGF to the cytoplasm and the nucleus of mature neurons whereas Flk-1 was expressed in cell membranes. Flk-1 was present in neurons of both the main and accessory olfactory bulbs. After the end of metamorphosis, Flk-1 expression was limited to basal cells in the olfactory epithelium and Bowman’s glands. The main and accessory olfactory bulbs showed the same pattern of Flk-1 immunostaining before and after the end of metamorphosis. The presence of VEGF and its receptor in the olfactory system suggests that VEGF may play an important role during neural development.     

Volatile female odors activate the accessory olfactory system of male mice without physical contact

We previously reported that male mice are more attracted to volatile odors from intact female mice than from ovariectomized female mice. In the present study, we investigated male attraction to volatile odors from soiled bedding collected from the cages of estrous or ovariectomized female mice. There was no difference in the total time spent sniffing volatile odors from estrous and ovariectomized female mice, suggesting that female mice emit volatile odors which are not excreted into bedding. To test this possibility, we investigated c-Fos expression in the mitral cell layer and granule cell layer of the accessory olfactory bulb 60 min after exposure of male mice to volatile odors without physical contact. Volatile odors from an estrous female mouse significantly increased the total number of c-Fos positive cells in each of the rostral and caudal granule cell layer, but not in the mitral cell layer. After exposure to volatile odors from estrous bedding, the total number of c-Fos positive cells did not increase. Volatile odors from a male mouse did not increase the total number of c-Fos positive cells. Volatile odors from an ovariectomized female mouse increased c-Fos expression only in the caudal granule cell layer. These results suggest that female mice emit specific volatile odors which are not excreted into bedding, and that the volatile odors activate the accessory olfactory system of male mice without physical contact. To characterize the female-specific volatile odors, we conducted habituation-dishabituation tests. Whereas sham-operated male mice discriminated between volatile odors of estrous and ovariectomized female mice, vomeronasal organ-removed male mice did not. These results suggest that male mice discriminated whether or not female mice were ovariectomized, by volatile odors via the accessory olfactory system, and that the female-specific volatile odors are involved in reproduction.     

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.     

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.     

Estrogen-induced region specific decrease in the density of 5-bromo-2-deoxyuridine-labeled cells in the olfactory bulb of adult female rats

Effects of chronic estrogen treatment on the survival rate of newly integrated interneurons were studied in the olfactory bulb of adult (250-300 g) female rats. Ovariectomized rats received 17-beta estradiol dissolved in sesame oil (i.p., 100 microg/100 g body weight [b.w.]) during six consecutive days, and on day 6 they were also injected with the mitotic marker 5-bromo-2-deoxyuridine (BrdU, i.p., 50 mg/kg b.w.) in every 2 hours during 8 hours. After 21 days of survival animals were killed and the density of BrdU-immunoreactive cells was analyzed in the granule cell and glomerular layer both in the main and accessory olfactory bulb. A significant decrease was found in the density of BrdU-labeled cells in both layers examined in the accessory olfactory bulb of ovariectomized and estradiol-treated rats when compared with those of ovariectomized and vehicle-treated animals. In the main olfactory bulb, in contrast, no difference was observed in the density of BrdU-immunoreactive cells in either of the two layers. Our results suggest that cells destined to the glomerular and granule cell layers react in the same way to chronic estrogen treatment, and the effect of estradiol is region specific, at least, within the olfactory bulb. 17-Beta estradiol reduces the density of newly generated cells in the accessory olfactory bulb, an area involved in the perception of pheromones, thus having a role in regulating sexual behavior, while the rate of integration and survival of newly born cells in the first relay station of the main olfactory pathway, i.e. the main olfactory bulb, remains unchanged.