title: The whisking rhythm generator: a novel mammalian network for the generation of movement.
abstract: Using the rat vibrissa system, we provide evidence for a novel mechanism for the generation of movement. Like other central pattern generators (CPGs) that underlie many movements, the rhythm generator for whisking can operate without cortical inputs or sensory feedback. However, unlike conventional mammalian CPGs, vibrissa motoneurons (vMNs) actively participate in the rhythmogenesis by converting tonic serotonergic inputs into the patterned motor output responsible for movement of the vibrissae. We find that, in vitro, a serotonin receptor agonist, alpha-Me-5HT, facilitates a persistent inward current (PIC) and evokes rhythmic firing in vMNs. Within each motoneuron, increasing the concentration of alpha-Me-5HT significantly increases the both the magnitude of the PIC and the motoneuron's firing rate. Riluzole, which selectively suppresses the Na(+) component of PICs at low concentrations, causes a reduction in both of these phenomena. The magnitude of this reduction is directly correlated with the concentration of riluzole. The joint effects of riluzole on PIC magnitude and firing rate in vMNs suggest that the two are causally related. In vivo we find that the tonic activity of putative serotonergic premotoneurons is positively correlated with the frequency of whisking evoked by cortical stimulation. Taken together, these results support the hypothesized novel mammalian mechanism for movement generation in the vibrissa motor system where vMNs actively participate in the rhythmogenesis in response to tonic drive from serotonergic premotoneurons.
authors.affiliation: Department of Anatomy and Neurobiology, University of Maryland School of Medicine, 20 Penn St., Rm S251, Baltimore, MD 21201, USA.
authors.forename: Nathan P
authors.initials: NP
authors.lastname: Cramer
authors.forename: Ying
authors.initials: Y
authors.lastname: Li
authors.forename: Asaf
authors.initials: A
authors.lastname: Keller
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000166:cytology / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004558:Electric Stimulation; D004576:Electromyography; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009068:Movement / Q000502:physiology*; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D010507:Periodicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014738:Vibrissae / Q000294:innervation*
chemical_list: D017366:Serotonin Receptor Agonists; D026941:Sodium Channel Blockers; C042390:alpha-methylserotonin; D012701:Serotonin; D013779:Tetrodotoxin