Reproductive Seasonality and the Effects of Thyroid Hormone on Neurotrophin Expression in the Ewe.
Notice bibliographique
Résumé
Many animals exhibit an annual cycle of fertility that synchronizes the timing of reproductive activity and the birth of offspring. In the sheep, the transition from the breeding season to anestrus is associated with morphological and molecular changes resulting in an altered responsiveness of the gonadotropin-releasing hormone neurosecretory system to the negative feedback effects of estradiol. This transition to anestrus is known to be dependent on the thyroid hormone, thyroxine (T4), as removal of the thyroid gland (THX) during the late breeding season prevents the onset of anestrus. T4 can act in multiple sites to regulate this seasonal transition, including the ventral medial preoptic area (vmPOA) and premammillary region (PMR) of the hypothalamus, where T4 microimplants prevent the effects of THX. Moreover, the anatomy of dopamine neurons in the A15 region of the hypothalamus, which are involved in seasonal changes in estrogen negative feedback, is influenced by T4. Glutamatergic and synapsin-positive inputs onto A15 dopamine neurons are increased in anestrus, an effect correlated with longer dendrites of these A15 neurons. This latter observation is dependent on T4. Since neurotrophins and their receptors play an important role in mediating T4-dependent neuroplasticity during development, we examined neurotrophins as mediators of T4's influence during the transition to anestrus. In this study, we used Real Time-PCR to examine expression of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in hypothalamic regions of THX ewes compared to thyroid-intact controls during the transition to anestrus. Results indicate that thyroid-intact ewes have decreased BDNF mRNA expression in the A15 and PMR but increased expression in the vmPOA compared to THX ewes. In contrast, NGF mRNA expression is increased in the A15 and decreased in the vmPOA of thyroid-intact ewes. Thus both neurotrophins may be involved in mediating the T4 dependent changes by acting in different regions of the hypothalamus. In a second experiment, immunohistological staining for the receptor for BDNF, tyrosine kinase B (TrkB), was conducted in late breeding season thyroid-intact and THX animals. Preliminary analysis suggests that thyroid-intact animals may have decreased TrkB fiber density staining in the A15 compared to THX animals. This decreased receptor expression correlated with decreased BDNF mRNA expression in the A15 observed in the first study. The functional importance of this change in expression of BDNF and its receptor is currently unknown; however, it is clear that these factors are regulated by T4 and correlated with synaptic and morphological changes in the A15. Thus, our findings provide initial evidence pointing to alterations in NGF, BDNF and TrkB expression as possible mediators of the actions of T4 necessary for seasonal alterations in the neural circuitry mediating estrogen negative feedback in the sheep. (poster)
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».