Norepinephrine effects on spinal motoneurons.
Intracellular recordings from cat spinal motoneurons in situ demonstrated that microiontophoretic application of NE with low-intensity ejection currents produces a slowly developing, small-amplitude depolarization of the cells, in contrast to early reports of NE-induced hyperpolarization. This depolarization was associated with an increase in excitability of the cells and a decrease in membrane conductance. These observations are consistent with the hypothesis that NE reduces potassium conductance in spinal motoneurons as has been proposed for facial motoneurons (VanderMaelen and Aghajanian, 1980) and thalamic neurons (McCormick and Prince, 1988). The time course of the facilitatory effects of NE on cat motoneuron excitability recorded intracellularly agreed very closely with the time course of NE-induced facilitation of glutamate-evoked excitability in rat spinal motoneurons recorded extracellularly. The similarity of the observations in rats and cats suggests that NE functions generally to enhance mammalian motoneuron responsiveness to excitatory input.
White
S R
SR
Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman.
Fung
S J
SJ
Barnes
C D
CD
D000200:Action Potentials / Q000187:drug effects; D000320:Adrenergic Fibers / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002415:Cats; D003655:Decerebrate State / Q000503:physiopathology; D005154:Facial Nerve / Q000187:drug effects / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects; D007478:Iontophoresis; D008125:Locus Coeruleus / Q000502:physiology; D009046:Motor Neurons / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology / Q000502:physiology*; D011149:Pons / Q000502:physiology; D011188:Potassium / Q000502:physiology; D051381:Rats; D012701:Serotonin / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects*
D012701:Serotonin; D011188:Potassium; D009638:Norepinephrine