title: Control of motor activity in crayfish by the steroid hormone 20-hydroxyecdysone via motoneuron excitability and sensory-motor integration.
abstract: We studied the effects of the molting hormone 20-hydroxyecdysone (20E) on leg sensory-motor networks of the red swamp crayfish, Procambarus clarkii. The hormone was injected in isolated crayfish and network activity was analyzed 3 days after injection using electrophysiology on an in vitro preparation of the leg locomotor network. This 20E treatment deeply reduced motor activity, by affecting both intrinsic motoneuron (MN) properties and sensory-motor integration. Indeed, we noticed a general decrease in motor nerve tonic activities, principally in depressor and promotor nerves. Moreover, intracellular recordings of depressor MNs confirmed a decrease of MN excitability due to a drop in input resistance. In parallel, sensory inputs originating from a proprioceptor, which codes joint movements controlled by these MNs, were also reduced. The shape of excitatory post-synaptic potentials (PSPs) triggered in MNs by sensory activity of this proprioceptor showed a reduction of polysynaptic components, whereas inhibitory PSPs were suppressed, demonstrating that 20E acted also on interneurons relaying sensory to motor inputs. Consequently, 20E injection modified the whole sensory-motor loop, as demonstrated by the alteration of the resistance reflex amplitude. These locomotor network changes induced by 20E were consistent with the decrease of locomotion observed in a behavioral test. In summary, 20E controls locomotion during crayfish premolt by acting on both MN excitability and sensory-motor integration. Among these cooperative effects, the drop of input resistance of MNs seems to be mostly responsible for the reduction of motor activity.
authors: Université de Bordeaux, Centre National de la Recherche Scientifique (CNRS), Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA), Biologie Animale, Bâtiment B2, 33405 Talence Cedex, France.
authors: Julien
authors: J
authors: Bacqué-Cazenave
authors: Flora
authors: F
authors: Bouvet
authors: Pascal
authors: P
authors: Fossat
authors: Daniel
authors: D
authors: Cattaert
authors: Jean Paul
authors: JP
authors: Delbecque
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D003400:Astacoidea / Q000187:drug effects / Q000502:physiology*; D001522:Behavior, Animal / Q000187:drug effects; D004441:Ecdysterone / Q000494:pharmacology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D042541:Intracellular Space / Q000187:drug effects / Q000502:physiology; D008124:Locomotion / Q000187:drug effects; D008297:Male; D018978:Molting / Q000187:drug effects; D009043:Motor Activity / Q000187:drug effects*; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D012018:Reflex / Q000187:drug effects; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology*
chemical_list: D004441:Ecdysterone
keywords: Crustacea; behavior; ecdysteroids; molt; neuromodulation; posture; stretch reflex