title: Membrane excitability changes in hindlimb motoneurons induced by stimulation of the locus coeruleus in cats.
abstract: The present analysis describes the cellular mechanisms underlying the heightened membrane excitability of hindlimb flexor and extensor motoneurons upon stimulation of the locus coeruleus (LC) in unanesthetized, decerebrate cats. In a total of 73 cells, brief train stimuli to the LC at 50-300 microA intensity evoked one of 4 patterns of motoneuronal responses: a simple excitatory postsynaptic potential (EPSP) with weak trailing depolarization, a double-peak EPSP, an EPSP succeeded by a weak hyperpolarization, or a slow rising EPSP. As the initial dominant EPSP was a consistent finding among all cells and the ensuing potentials were variable in polarity, quantitative characterization was focused on the initial EPSP only. In all cells tested (n = 11), the LC-EPSP was accompanied by a decrease in input resistance. The excitatory LC action was further demonstrated by the consistent (n = 25 cells) motoneuron rheobase decrease when the latter was measured coincident with the summit of an LC-EPSP. Furthermore, the time course of the single-spike afterhyperpolarization became shortened during the LC conditioning stimuli (n = 16 motoneurons). Our data show that the descending LC action on motoneurons is typified by an EPSP accompanied by a net decrease in input resistance as well as a concurrent increase in motoneuron electrical excitability.
mesh_terms: D000818:Animals; D002415:Cats; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D004558:Electric Stimulation; D004594:Electrophysiology; D006614:Hindlimb / Q000294:innervation*; D008125:Locus Coeruleus / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D013569:Synapses / Q000502:physiology