title: Cellular substrates of action selection: a cluster of higher-order descending neurons shapes body posture and locomotion.
abstract: The selection of distinct movements involved in various body postures and locomotion is often dependent on higher-order descending neurons. To study how such cells select different actions, we used a nearly-intact leech preparation (Hirudo sp.) in which cephalic projection interneurons were recorded and stimulated while the leech generated overt behaviors. Two long-distance projecting neurons were identified in the sub-packet of the third neuromere (R3b) of the subesophageal ganglion. These interneurons, named R3b2 and R3b3, produced changes in whole-body posture, crawling and swimming. Cell R3b2 reliably caused the body to become turgid, to hyper-elongate, and to thrash cyclically. Such robust activity resembled struggling behavior exhibited by intact leeches when grasped. The neighboring cell R3b3 elicited body elongation accompanied by a static whole-body bend to the left or right. R3b3 activity was context-dependent, oscillated in phase with crawling, reset the crawl rhythm, and terminated swimming. Both neuronal types responded to multi-modal sensory stimulation delivered to various rostral and caudal regions of the body. Our study illustrates the need to study behavioral selection with a neuroethological approach, and provides a cellular substrate for the motor action-selection cluster proposed for the vertebrate brainstem.
authors.affiliation: Departments of Entomology and Neuroscience, University of Minnesota, 219 Hodson Hall, 1980 Folwell Ave, St Paul, MN 55108, USA. mesce001@umn.edu
authors.forename: Karen A
authors.initials: KA
authors.lastname: Mesce
authors.forename: Teresa
authors.initials: T
authors.lastname: Esch
authors.forename: William B
authors.initials: WB
authors.lastname: Kristan
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D004594:Electrophysiology; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000502:physiology; D007865:Leeches; D008124:Locomotion / Q000502:physiology*; D009474:Neurons / Q000166:cytology* / Q000502:physiology*; D011187:Posture / Q000502:physiology*