Effects of chronic perinatal odour exposure on odour sensitivity ans olfactory system homeostasis in preweaning mice

Chez les mammifères, le système olfactif principal est fonctionnel dans le dernier tiers du stade gestationnel. Le fœtus est donc capable de détecter avec sensibilité, discriminer, et mémoriser les odorants présents dans le liquide amniotique dans lequel il baigne. Chez le rongeur, ces odorants mémorisés in utero sont fondamentaux pour la survie du nouveau-né à la naissance en lui permettant de s’orienter vers la mamelle et de déclencher la tétée. Par la suite, ces odorants vont guider le nouveau-né dans ses choix olfactifs et alimentaires et favoriser ses apprentissages ultérieurs. Or, on sait que l’alimentation de la mère fait varier les clés olfactives des fluides biologiques (liquide amniotique, lait) et donc modifie la nature des sources olfactives rencontrées par le fœtus, puis le nouveau-né dans la période périnatale. Dans le but d’évaluer l’impact d’une exposition odorante périnatale sur le fonctionnement et la maturation du système olfactif en relation avec le développement de préférences médiées par l’olfaction et la modulation du stress au moment du sevrage, nous avons mis en place un modèle d’exposition odorante périnatale via l’alimentation maternelle dans une lignée transgénique murine exprimant le récepteur olfactif I7 couplé à une protéine fluorescente, dont l’odorant préférentiel est l’heptanal. Après validation de la présence d’heptanal dans le liquide amniotique et le lait de ces souris par GC-MS-MS, nos résultats montrent que l’exposition périnatale à l’heptanal entraine une augmentation significative du nombre de glomérules I7 présents au niveau du bulbe olfactif à PN12 par rapport aux animaux contrôles sans modification notable de l’homéostasie tissulaire ou de la transcription du gène I7 au niveau de la muqueuse olfactive. Ce changement structural important au niveau des projections axonales du bulbe olfactif s’accompagne d’un faible effet sur le comportement olfactif des souriceaux dont les capacités de discrimination ne sont que très faiblement améliorées par rapport aux souriceaux non exposés. A PN21, l’effet de l’exposition odorante sur le nombre de glomérules I7 est atténué, mais reste significatif. A ce stade, les souriceaux odorisés montrent une attraction olfactive pour l’heptanal par rapport au groupe contrôle non exposé, bien que l’effet sur un choix entre aliment odorisé ou pas soit plus contrasté. D’un point de vue moléculaire, ces effets sont associés à une diminution de l’expression du récepteur I7, et de gènes de la signalisation neuronale pouvant traduire une modification de la dynamique cellulaire. Et comme le montrent les résultats obtenus en électro-olfactogramme à cet âge, la sensibilité de la muqueuse olfactive vis-à-vis de l’heptanal est diminuée alors qu’elle ne l’est pas pour d’autres composés odorants. Ces travaux montrent que l’exposition périnatale à un odorant s’accompagne d’effets précoces sur le système olfactif qui impactent son organisation et d’effets sur les choix olfactifs qui se renforcent au cours du développement. Enfin, l’effet d’une exposition périnatale à l’heptanal sur la réponse à des conditions stressantes après séparation maternelle au moment du sevrage a été évaluée en enregistrant des souriceaux CD1 élevés dans les mêmes conditions d’odorisation que les souriceaux mI7-GFP adoptés, en open-field odorisé ou non. Nous avons montré que la réaction de stress des souriceaux à PN21, exposés en périnatal à l’heptanal, dans l’open field, est atténuée lorsque l’heptanal est présent dans l’environnement, comparé à la réaction des souriceaux non exposés qui affichent un comportement d’anxiété. Dans l’ensemble, cette étude a donc permis de mettre en évidence les conséquences en terme d’effets comportementaux (préférences médiées par l’olfaction et diminution du stress), structuraux et moléculaires, d’une exposition odorante périnatale chez le jeune, à l’aide d’une lignée transgénique pour laquelle nous disposions de peu de données.In mammals, the main olfactory system displays all the structural and functional characteristics at the last third of the gestational stage. Thus, the fetus is able to detect, to discriminate, but also to memorize the odorants present in the amniotic fluid in which it bathes. In the rodent, these odors memorized in utero are fundamental for the survival of the newborn at birth by allowing it to trend itself towards food sources. Afterwards, odorants are guiding the newborn to olfactory and food choices and are promoting subsequent learning. It is known that the mother's diet varies the olfactory keys of the biological fluids (amniotic fluid, milk) and thus modifies the nature of the olfactory sources encountered by the fetus and then the newborn in the perinatal period. The neuroanatomic and functional consequences of this impregnation are the subject of recent studies. The objective of this thesis was to characterize the effects of perinatal odor exposure on the maturation and functioning of the olfactory system in relation to the development of olfactory preferences and to a stressing challenge at weaning. For that, we set up a model of perinatal odor exposure through maternal feeding in the mI7-GFP murine transgenic strain expressing the olfactory receptor I7 coupled with the Green Fluorescent Protein (GFP). We evaluated the neuroanatomic, molecular and behavioral consequences on the pups before weaning, and their evolution over time by focusing our efforts on the postnatal stages 3 (PND3), PND12-14 and PND21. Due to the fragility of the transgenic strain, we worked on mI7-GFP mice pups crossfostered by CD1 mice mothers raised under the same conditions after having validated the presence of heptanal in the amniotic fluid of mI7-GFP mice and the milk of CD1 mice by GC-MSMS. We characterized the effects of perinatal odor exposure on the maturation and functioning of the olfactory system in relation to the olfactory preference until weaning (mI7-GFP mice pups under CD1 adoptive mothers) and on the stress reaction to maternal separation at weaning (CD1 mice pups under biological mother). Our results show that perinatal exposure to heptanal leads to a significant increase in the number of I7 glomeruli in the olfactory bulb (OB) associated to a slight modification of the tissue homeostasis in the olfactory mucosa (OM) and to subtle differencies in heptanal sensitivity and preferences, that are amplified at PND21. From a molecular point of view, these effects are associated to a down-regulation of the expression of the I7 receptor and genes of neuronal signaling and an odorantspecific decrease in EOG response which may highlight a modification of the cellular dynamics. Finally, the effect of perinatal exposure to heptanal on the response to stressing conditions after maternal separation was assessed by recording CD1 mice pups grown under the same conditions than fostered mi7 mice on odorized and non odorized open-field. We showed that the reaction of odorized mice in the open field at PND21 is attenuated when the odorant is present in the environment, compared to non odorized mice that display anxiety-like behavior. Overall, this study demonstrates the consequences of a perinatal odorant exposure in the young, in terms of behavior (olfactory preference and anxiety), structural and molecular plasticity of the olfactory system, on a transgenic strain for which we had little available data

Effet d'une exposition odorante pré et post-natale sur le développement des préférences médiées par l'olfaction chez la souris - Mécanismes de neuromodulation: Mécanismes de neuromodulation

In mammals, the main olfactory system displays all the structural and functional characteristics at the last third of the gestational stage. Thus, the fetus is able to detect, to discriminate, but also to memorize the odorants present in the amniotic fluid in which it bathes. In the rodent, these odors memorized in utero are fundamental for the survival of the newborn at birth by allowing it to trend itself towards food sources. Afterwards, odorants are guiding the newborn to olfactory and food choices and are promoting subsequent learning. It is known that the mother's diet varies the olfactory keys of the biological fluids (amniotic fluid, milk) and thus modifies the nature of the olfactory sources encountered by the fetus and then the newborn in the perinatal period. The neuroanatomic and functional consequences of this impregnation are the subject of recent studies. The objective of this thesis was to characterize the effects of perinatal odor exposure on the maturation and functioning of the olfactory system in relation to the development of olfactory preferences and to a stressing challenge at weaning. For that, we set up a model of perinatal odor exposure through maternal feeding in the mI7-GFP murine transgenic strain expressing the olfactory receptor I7 coupled with the Green Fluorescent Protein (GFP). We evaluated the neuroanatomic, molecular and behavioral consequences on the pups before weaning, and their evolution over time by focusing our efforts on the postnatal stages 3 (PND3), PND12-14 and PND21. Due to the fragility of the transgenic strain, we worked on mI7-GFP mice pups crossfostered by CD1 mice mothers raised under the same conditions after having validated the presence of heptanal in the amniotic fluid of mI7-GFP mice and the milk of CD1 mice by GC-MSMS. We characterized the effects of perinatal odor exposure on the maturation and functioning of the olfactory system in relation to the olfactory preference until weaning (mI7-GFP mice pups under CD1 adoptive mothers) and on the stress reaction to maternal separation at weaning (CD1 mice pups under biological mother). Our results show that perinatal exposure to heptanal leads to a significant increase in the number of I7 glomeruli in the olfactory bulb (OB) associated to a slight modification of the tissue homeostasis in the olfactory mucosa (OM) and to subtle differencies in heptanal sensitivity and preferences, that are amplified at PND21. From a molecular point of view, these effects are associated to a down-regulation of the expression of the I7 receptor and genes of neuronal signaling and an odorantspecific decrease in EOG response which may highlight a modification of the cellular dynamics. Finally, the effect of perinatal exposure to heptanal on the response to stressing conditions after maternal separation was assessed by recording CD1 mice pups grown under the same conditions than fostered mi7 mice on odorized and non odorized open-field. We showed that the reaction of odorized mice in the open field at PND21 is attenuated when the odorant is present in the environment, compared to non odorized mice that display anxiety-like behavior. Overall, this study demonstrates the consequences of a perinatal odorant exposure in the young, in terms of behavior (olfactory preference and anxiety), structural and molecular plasticity of the olfactory system, on a transgenic strain for which we had little available data.Chez les mammifères, le système olfactif principal est fonctionnel dans le dernier tiers du stade gestationnel. Le fœtus est donc capable de détecter avec sensibilité, discriminer, et mémoriser les odorants présents dans le liquide amniotique dans lequel il baigne. Chez le rongeur, ces odorants mémorisés in utero sont fondamentaux pour la survie du nouveau-né à la naissance en lui permettant de s’orienter vers la mamelle et de déclencher la tétée. Par la suite, ces odorants vont guider le nouveau-né dans ses choix olfactifs et alimentaires et favoriser ses apprentissages ultérieurs. Or, on sait que l’alimentation de la mère fait varier les clés olfactives des fluides biologiques (liquide amniotique, lait) et donc modifie la nature des sources olfactives rencontrées par le fœtus, puis le nouveau-né dans la période périnatale. Dans le but d’évaluer l’impact d’une exposition odorante périnatale sur le fonctionnement et la maturation du système olfactif en relation avec le développement de préférences médiées par l’olfaction et la modulation du stress au moment du sevrage, nous avons mis en place un modèle d’exposition odorante périnatale via l’alimentation maternelle dans une lignée transgénique murine exprimant le récepteur olfactif I7 couplé à une protéine fluorescente, dont l’odorant préférentiel est l’heptanal. Après validation de la présence d’heptanal dans le liquide amniotique et le lait de ces souris par GC-MS-MS, nos résultats montrent que l’exposition périnatale à l’heptanal entraine une augmentation significative du nombre de glomérules I7 présents au niveau du bulbe olfactif à PN12 par rapport aux animaux contrôles sans modification notable de l’homéostasie tissulaire ou de la transcription du gène I7 au niveau de la muqueuse olfactive. Ce changement structural important au niveau des projections axonales du bulbe olfactif s’accompagne d’un faible effet sur le comportement olfactif des souriceaux dont les capacités de discrimination ne sont que très faiblement améliorées par rapport aux souriceaux non exposés. A PN21, l’effet de l’exposition odorante sur le nombre de glomérules I7 est atténué, mais reste significatif. A ce stade, les souriceaux odorisés montrent une attraction olfactive pour l’heptanal par rapport au groupe contrôle non exposé, bien que l’effet sur un choix entre aliment odorisé ou pas soit plus contrasté. D’un point de vue moléculaire, ces effets sont associés à une diminution de l’expression du récepteur I7, et de gènes de la signalisation neuronale pouvant traduire une modification de la dynamique cellulaire. Et comme le montrent les résultats obtenus en électro-olfactogramme à cet âge, la sensibilité de la muqueuse olfactive vis-à-vis de l’heptanal est diminuée alors qu’elle ne l’est pas pour d’autres composés odorants. Ces travaux montrent que l’exposition périnatale à un odorant s’accompagne d’effets précoces sur le système olfactif qui impactent son organisation et d’effets sur les choix olfactifs qui se renforcent au cours du développement. Enfin, l’effet d’une exposition périnatale à l’heptanal sur la réponse à des conditions stressantes après séparation maternelle au moment du sevrage a été évaluée en enregistrant des souriceaux CD1 élevés dans les mêmes conditions d’odorisation que les souriceaux mI7-GFP adoptés, en open-field odorisé ou non. Nous avons montré que la réaction de stress des souriceaux à PN21, exposés en périnatal à l’heptanal, dans l’open field, est atténuée lorsque l’heptanal est présent dans l’environnement, comparé à la réaction des souriceaux non exposés qui affichent un comportement d’anxiété. Dans l’ensemble, cette étude a donc permis de mettre en évidence les conséquences en terme d’effets comportementaux (préférences médiées par l’olfaction et diminution du stress), structuraux et moléculaires, d’une exposition odorante périnatale chez le jeune, à l’aide d’une lignée transgénique pour laquelle nous disposions de peu de données

DMRT1 is Required for Fetal Germ Cell Development in Rabbit Ovary

International audienceDMRT1 (doublesex and mab-3 related transcription factor 1) is a conserved transcriptional factor expressed in the genital ridge in both sexes and plays a critical role in mammals, nonmammalian vertebrates and non-vertebrate testis development. A lack of Dmrt1 expression induces Sertoli cell fate reprogramming into Granulosa-like cells and formation of feminized germ cells in the mouse adult testis. Although, most of the female mouse lacking Dmrt1 expression in fetal germ cells are fertile, we discovered that homozygous DMRT1 mutant female rabbits are infertile and have smaller ovaries starting at 28 days post conception (dpc) when germ cell should be proliferating. We showed that DMRT1 expression is enriched in female germ cells and reaches its higher levels of expression between 28 dpc and 4 days postpartum (dpp) which corresponds to the onset of meiosis in the rabbit ovary. Thus, we hypothesize that DMRT1 could play a regulatory role on female germ cells differentiation by controlling expression of meiotic genes. Histological analysis confirmed a disruption of ovarian cells formation specifically marked by a failure of meiosis initiation leading to follicular development arrest and associated with a reduction of DDX4 and STRA8 expression at 28 dpc. These results suggest a potential role of DMRT1 in rabbit ovarian development and provide new insights in the regulatory mechanisms involved in germ cell differentiation. Therefore, to complete our understanding of the mechanisms that underly the effects of DMRT1 in germ cells we are currently performing the transcriptomic analysis of ovaries lacking DMRT1 at birth combined with a DMRT1-ChIP sequencing in order to identify specific targets of DMRT1

Effect of environmental exposure to a maternally-learned odorant on anxiety-like behaviors at weaning in mice

International audienceEarly sensory experience, such as exposure to maternal or other environmental factors, is considered to influence neurocognitive development and behaviors. In many species, exposure to odorants during pregnancy or lactation impacts the morpho-functional development of the olfactory circuitry with changes in olfactory sensitivity, feeding behavior and food preferences at birth or later. However, few studies have investigated the impact of a perinatal exposure to odorants on the anxiety-like behavior of animals to stressfull stimuli. Here, we exposed mice to heptaldehyde (HEP) during pregnancy and lactation and measured the anxiety-like behavior of their offspring to stress-inducing novel stimuli at weaning in presence or absence of odorants. We applied a combined social and maternal separation as a stressor and measured the anxiety-like behavior in an open field (OF) in presence of two odorants, HEP or alpha-pinene (AP) as a control odorant. Although the presence of the odorant during the social separation did not influence anxiety-like behavior, we found that, if mice born to non-odorized mothers exhibited a decreased exploratory behavior in the presence of both odorants, the effect was restricted to AP for the mice perinatally exposed to HEP. These results show that anxiety-like behaviors during a stress-inducing event could be reduced by the presence of a familiar odorant. We propose that the recall of an early olfactory experience could contribute to the improvement of animal welfare in various situations associated with husbandry practices

Développement de biocapteurs en diamant porteurs de récepteurs olfactifs sensibles à une molécule odorante signature de l'oestrus

National audienceNotre laboratoire a récemment breveté une odeur signature de l’oestrus [1] retrouvée chez différents mammifères, la 6-methyl-5-hepten-2-one. Nous avons lors de cette étude cherché à identifier des récepteurs olfactifs (RO) sensibles à cette odeur afin de les greffer sur des capteurs en diamant développés par des collaborateurs du CEA List. Notre stratégie a consisté à prélever des neurones sensoriels olfactifs (NSO) de souris sensibles à la 6-methyl-5-hepten-2-one, puis à réaliser une RT-PCR sur cellule unique permettant d’identifier les RO exprimés par les NSO prélevés. Par ailleurs, nous avons utilisé une approche de production et de purification des RO que nous avions développée antérieurement. Les récepteurs ainsi produits et purifiés peuvent être greffés via un tag poly-histidine sur des micro-capteurs en diamant, lesquels sont alors capables de détecter spécifiquement les ligands odorants des RO greffés [2]. Nous ne sommes pas parvenus à identifier des RO de souris sensibles à la 6-methyl-5-hepten-2-one étant donné les difficultés méthodologiques rencontrées. Notamment, l’approche mise en oeuvre ne permet pas un criblage suffisamment performant pour obtenir des résultats dans le temps imparti pour cette étude. Toutefois, via d’autres recherches menées au laboratoire sur les RO et leurs ligands odorants [3, 4], nous avons pu mettre en évidence que deux récepteurs humains sont sensibles à la 6-methyl-5-hepten-2-one avec des niveaux de sensibilité différents (cf. figure). Nous avons par conséquent produit et purifié le récepteur le plus sensible et nos collaborateurs du CEA List ont réussi à le greffer sur les capteurs en diamant. Les essais de mesure de la sensibilité de ces capteurs à la 6-methyl-5-hepten-2-one sont en cours. Etant donné que la 6-methyl-5-hepten-2-one se trouve en quantité plus importante au moment de l’oestrus, mais qu’elle est également présente en période de dioestrus, une détection sensible et quantitative des capteurs sera indispensable. De plus, étant donné que les RO peuvent reconnaître plusieurs molécules odorantes différentes, l’identification de RO de sensibilités différentes à la 6-methyl-5-hepten-2-one s’avère nécessaire pour assurer la spécificité de détection des capteurs. Nous prévoyons donc de greffer sur les capteurs le second récepteur humain présentant une sensibilité moins importante à la 6-methyl-5-hepten-2-one ainsi qu’un autre RO humain dont nous savons qu’il n’est pas activé par cette molécule

Chronic perinatal odour exposure with heptaldehyde affects odour sensitivity and olfactory system homeostasis in preweaning mice

International audienceExposure to specific odorants in the womb during pregnancy or in the milk during early nursing is known to impact morpho-functional development of the olfactory circuitry of pups. This can be associated with a modification in olfactory sensitivity and behavioural olfactory-based preferences to the perinatally encountered odorants measured at birth, weaning or adult stage. Effects depend on a multitude of factors, such as odorant type, concentration, administration mode and frequency, as well as timing and mice strain. Here, we examined the effect of perinatal exposure to heptaldehyde on the neuro-anatomical development of the olfactory receptor Olfr2 circuitry, olfactory sensitivity and odour preferences of preweaning pups using mI7-IRES-tau-green fluorescent protein mice. We found that perinatal odour exposure through the feed of the dam reduces the response to heptaldehyde and modulates transcript levels of neuronal transduction proteins in the olfactory epithelium of the pups. Furthermore, the number of I7 glomeruli related to Olfr2-expressing OSN is altered in a way similar to that seen with restricted post-natal exposure, in an age-dependent way. These variations are associated with a modification of olfactory behaviours associated with early post-natal odour preferences at weaning

DMRT1 is a Sex-Determining Gene in Rabbits

International audienceDMRT1 is a transcription factor containing a DNA-binding domain (DM domain) highly conserved across evolution. It shows gonad-specific expression and it is considered as the Testis Determining Factor in many non-mammalian species. In mice, Dmrt1 disruptions had no impact on testicular differentiation during fetal development, whereas in humans, mutations induce gonadal dysgenesis with XY women phenotype (46, XY DSD). In some others mammals, DMRT1 expression was shown to precede SOX9 up-regulation like in XX sex-reversed goats (FOXL2-/-) or in wild type XY rabbits where SRY and DMRT1 are both expressed in XY genital ridges a few days before testis cords formation. We thus assumed that DMRT1 was involved in sex determination in non-murine species, by directly targeting SOX9 expression. Thanks to CRISPR/Cas9 technology, we generated DMRT1 mutant rabbits. We show that the absence of DMRT1 leads to male-to-female sex reversal in XY homozygous mutants. At 20 days post conception, few days after sex-determination, XY DMRT1-/- gonads are devoid of testis cords structures but rather present a typical ovarian organization with cortical germ cells. Molecular studies confirmed the expressional up-regulation of ovary-driving genes (RSPO1, WNT4, FOXL2 and CYP19A1) and the downregulation of testis-specific ones (SOX9, SOX10 and DHH) while SRY expression is highly maintained in the developing XY ovary (RNA-sequencing and RT-qPCR data). Interestingly, some somatic cells of the XY DMRT1-/- gonads still present SOX9 protein expression. Nevertheless, this is not sufficient to trigger its target genes expression (e.g. AMH) in the developing XY ovary. Our data clearly involved DMRT1 as a key player in sex determination in rabbits. DMRT1 is required to SRY action on SOX9 expression and may also be necessary to SOX9 function on its own target genes. Interestingly, DMRT1 was recently shown to act as a pioneer factor, opening the chromatin and favouring the action of SOX protein such as SOX9. Investigation on DMRT1 targets and epigenetic mark (H3K4me1, H3K27ac and H3K27me3) deposition on these targets are in progress at early stages of rabbit gonadal differentiation

The olfactory function is affected by exposure to glucocorticoid: stressed animals might perceive smells differently.

The welfare and health of farm animals are of critical importance for sustainable use of our environment. Paradoxically, while food quality impacts human health, modern rearing practices can be stressful for animals and affect the quality of animal production. The perception of smells and the olfactory environment have been linked to animal welfare and health (e.g. anxiety or depressive-like symptoms). There is evidence that the olfactory epithelium and bulb are responsive to stress hormones (glucocorticoids). However, the actions of glucocorticoids in these two tissues are still not fully explained. We have received seed funding (Credits Incitatifs PHASE) to evaluate those links in our model species (rat). Do glucocorticoids affect olfactorytissue and function in rat stress model? The initial step was to evaluate the potential for hormone response in the tissues of interest, by confirming the presence and localisation of the glucocorticoid receptor (GR).Immunohistochemistry showed the expression of GR is restricted to olfactory ensheathing cells (OEC), glial cells involved in processing of the olfactory signal propagation and neurone regeneration. We tested the functional significance of this observation in vitro using primary OEC cultures treated with a synthetic GR agonist (dexamethasone). The expression of various genes was affected, including ion transporters (ATP1B1), a macrophage chemoattractant (MCP1) and elements of the endothelin signalling pathways (the ETB receptor gene is repressed). We are currently exploring the significance of this latter observation by measuring endothelin response in our cells using calcium imaging. In vivo, acute administration of dexamethasone altered gene expression patterns in the OM and OB, as well as electrical activity induced by odorant exposure (measured by ElectroOlfactoGram, EOG). EOG signal recovery was delayed post-odorantstimulation in dexamethasone treated animals, this suggests olfactory neurone repolarisation might be slower. In addition to these acute stress models, we have developed a chronic unpredictable stress model in rats and we are assessing its impact on EOG and gene expression patterns. Our data shows stress hormones clearly affect olfactory response in the olfactory epithelium, at the first step of odorant detection. We currently do not know whether these changes affect smell perception in animals. To address this issue, we are in the process of developing olfactory learning tests in rats in order to study the impact of glucocorticoids on behavioural aspects of odour detection. This might allow us to determine whether stress-induced changes in olfactoryfunction can affect animal welfare and physiology

DMRT1 is Required For Sex Determination in Rabbits

International audienc

The olfactory function is affected by exposure to glucocorticoid: stressed animals might perceive smells differently.

The welfare and health of farm animals are of critical importance for sustainable use of our environment. Paradoxically, while food quality impacts human health, modern rearing practices can be stressful for animals and affect the quality of animal production. The perception of smells and the olfactory environment have been linked to animal welfare and health (e.g. anxiety or depressive-like symptoms). There is evidence that the olfactory epithelium and bulb are responsive to stress hormones (glucocorticoids). However, the actions of glucocorticoids in these two tissues are still not fully explained. We have received seed funding (Credits Incitatifs PHASE) to evaluate those links in our model species (rat). Do glucocorticoids affect olfactorytissue and function in rat stress model? The initial step was to evaluate the potential for hormone response in the tissues of interest, by confirming the presence and localisation of the glucocorticoid receptor (GR).Immunohistochemistry showed the expression of GR is restricted to olfactory ensheathing cells (OEC), glial cells involved in processing of the olfactory signal propagation and neurone regeneration. We tested the functional significance of this observation in vitro using primary OEC cultures treated with a synthetic GR agonist (dexamethasone). The expression of various genes was affected, including ion transporters (ATP1B1), a macrophage chemoattractant (MCP1) and elements of the endothelin signalling pathways (the ETB receptor gene is repressed). We are currently exploring the significance of this latter observation by measuring endothelin response in our cells using calcium imaging. In vivo, acute administration of dexamethasone altered gene expression patterns in the OM and OB, as well as electrical activity induced by odorant exposure (measured by ElectroOlfactoGram, EOG). EOG signal recovery was delayed post-odorantstimulation in dexamethasone treated animals, this suggests olfactory neurone repolarisation might be slower. In addition to these acute stress models, we have developed a chronic unpredictable stress model in rats and we are assessing its impact on EOG and gene expression patterns. Our data shows stress hormones clearly affect olfactory response in the olfactory epithelium, at the first step of odorant detection. We currently do not know whether these changes affect smell perception in animals. To address this issue, we are in the process of developing olfactory learning tests in rats in order to study the impact of glucocorticoids on behavioural aspects of odour detection. This might allow us to determine whether stress-induced changes in olfactoryfunction can affect animal welfare and physiology