Le contrôle environnemental et neuroendocrinien de l’activité saisonnière de la reproduction chez le dromadaire

Le dromadaire (Camelus dromedarius), qui est un mammifère bien adapté au désert est une espèce à reproduction saisonnière. Sa saison sexuelle a lieu durant l’hiver et le printemps. Ces périodes coïncident avec l’abondance des ressources alimentaires et des conditions climatiques favorables pour la survie de la progéniture. Toutefois les mécanismes impliqués dans le contrôle de cette saisonnalité restent encore mal élucidés. L’objectif de cette revue est de décrire les caractéristiques de la reproduction chez le dromadaire. Cela inclue la distribution géographique de sa saison sexuelle et son déclenchement possible par plusieurs paramètres environnementaux physiques, notamment la température ambiante, la photopériode et la quantité de précipitations. De plus, plusieurs aspects de cette saisonnalité ont été discutés chez le mâle et la femelle. Finalement, cette revue analyse les facteurs neuroendocriniens impliqués dans la saisonnalité de reproduction, notamment, le rôle putatif de deux neuropeptides hypothalamiques, le kisspeptin et le (Arg) (Phe) peptide apparenté. Mots-clés: Dromadaire, saisonnalité de reproduction, précipitations, photopériode, température ambiante, disponibilité alimentaire, kisspeptin, RFRP. The dromedary camel (Camelus dromedarius), a well-adapted desert mammal, is a seasonal breeder whose sexual activity occurs during the winter and spring. These periods coincide with food resources and climate conditions are favorable for offspring’s survival. The mechanisms involved in the control of this seasonality however still need to be elucidated. The aim of this review is to describe the reproductive patterns of the dromedary camel. This includes the geographical seasonal breeding distribution of this species taking into account the role of various physical environmental parameters notably temperature, day length and the amount of rainfall. Further, various aspects of seasonal breeding in male and female camels are discussed as well as the neuroendocrine factors that may control seasonal such phenomena. Finally, the putative roles of two hypothalamic neuropeptides, kisspeptin and (Arg) (Phe) related peptide, are proposed for the control of camel’s seasonal reproduction. Keywords: Dromedary camel, seasonal breeding, rainfall, photoperiod, ambient temperature, food availability, Kisspeptin, RFRP

Environmental and neuroendocrine control of breeding activity in the dromedary camel

The dromedary camel (Camelus dromedarius), a well-adapted desert mammal, is a seasonal breeder whose sexual activity occurs during the winter and spring. These periods coincide with food resources and climate conditions are favorable for offspring’s survival. The mechanisms involved in the control of this seasonality however still need to be elucidated. The aim of this review is to describe the reproductive patterns of the dromedary camel. This includes the geographical seasonal breeding distribution of this species taking into account the role of various physical environmental parameters notably temperature, day length and the amount of rainfall. Further, various aspects of seasonal breeding in male and female camels are discussed as well as the neuroendocrine factors that may control seasonal such phenomena. Finally, the putative roles of two hypothalamic neuropeptides, kisspeptin and (Arg) (Phe) related peptide, are proposed for the control of camel’s seasonal reproduction

Effects of muscarinic receptor stimulation on Ca2+ transient, cAMP production and pacemaker frequency of rabbit sinoatrial node cells

We investigated the contribution of the intracellular calcium (Cai2+) transient to acetylcholine (ACh)-mediated reduction of pacemaker frequency and cAMP content in rabbit sinoatrial nodal (SAN) cells. Action potentials (whole cell perforated patch clamp) and Cai2+ transients (Indo-1 fluorescence) were recorded from single isolated rabbit SAN cells, whereas intracellular cAMP content was measured in SAN cell suspensions using a cAMP assay (LANCE®). Our data show that the Cai2+ transient, like the hyperpolarization-activated “funny current” (If) and the ACh-sensitive potassium current (IK,ACh), is an important determinant of ACh-mediated pacemaker slowing. When If and IK,ACh were both inhibited, by cesium (2 mM) and tertiapin (100 nM), respectively, 1 μM ACh was still able to reduce pacemaker frequency by 72%. In these If and IK,ACh-inhibited SAN cells, good correlations were found between the ACh-mediated change in interbeat interval and the ACh-mediated change in Cai2+ transient decay (r2 = 0.98) and slow diastolic Cai2+ rise (r2 = 0.73). Inhibition of the Cai2+ transient by ryanodine (3 μM) or BAPTA-AM (5 μM) facilitated ACh-mediated pacemaker slowing. Furthermore, ACh depressed the Cai2+ transient and reduced the sarcoplasmic reticulum (SR) Ca2+ content, all in a concentration-dependent fashion. At 1 μM ACh, the spontaneous activity and Cai2+ transient were abolished, but completely recovered when cAMP production was stimulated by forskolin (10 μM) and IK,ACh was inhibited by tertiapin (100 nM). Also, inhibition of the Cai2+ transient by ryanodine (3 μM) or BAPTA-AM (25 μM) exaggerated the ACh-mediated inhibition of cAMP content, indicating that Cai2+ affects cAMP production in SAN cells. In conclusion, muscarinic receptor stimulation inhibits the Cai2+ transient via a cAMP-dependent signaling pathway. Inhibition of the Cai2+ transient contributes to pacemaker slowing and inhibits Cai2+-stimulated cAMP production. Thus, we provide functional evidence for the contribution of the Cai2+ transient to ACh-induced inhibition of pacemaker activity and cAMP content in rabbit SAN cells

The role of the pineal gland in the photoperiodic control of reproduction in different hamster species

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