Chapter 11 Serotonin, norepinephrine and associated neuropeptides: effects on somatic motoneuron excitability

Publisher Summary In a laboratory electrophysiological techniques are used to address the question of how monoaminergic and peptidergic inputs may affect the excitability of the motoneurons in rats and cats in situ. This chapter reviews these in situ findings and compares them to in situ and in vitro studies from laboratories. Some new evidence about interactive effects of serotonin and neuropeptides on motoneurons is also presented. Monoaminergic and peptidergic effects on brainstem and spinal cord motoneurons are discussed within the framework of an emotional motor system that has a modulatory effect on motoneuronal excitability. The chapter also chapter considers postsynaptic effects of serotonin, colocalized neuropeptides and norepinephrine on motoneuron excitability. However, all of these substances have actions on interneurons that are presynaptic to the motoneurons. These indirect actions on interneurons may interact with postsynaptic effects on the motoneurons in simple or complex fashions. Similarly, norepinephrine appears to enhance spinal motoneuron excitability by both direct postsynaptic actions that lead to motoneuron depolarization and increased excitability, and by indirect actions on interneurons that prevent interneuronal-mediated inhibition of the motoneurons.