Acetylcholine At Motor Nerves: Storage, Release, and Presynaptic Modulati On By Autoreceptors and Adrenoceptors

Abstract

Publisher Summary This chapter focuses on the modulation of acetylcholine release from the motor endplate by presynaptic receptors. An individual neuron can regulate its function, the release of transmitters or modulators, through the activation of local feedback loops. After escaping the neuronal membrane and entering the synaptic cleft (or extracellular space), the transmitter activates both the receptors localized at the endorgan (postsynaptic receptors) and the receptors localized at the nerve terminal within its diffusion radius (so-called presynaptic or neuronal receptors). Stimulation of presynaptic receptors triggers the generation of intracellular signals that modify ion channels or regulatory proteins and, in consequence, modify the subsequent release of the transmitter. This is shown for the classic transmitters, particularly those released from the peripheral autonomic nervous system (acetylcholine, adrenaline, noradrenaline), as well as for dopamine, serotonin, histamine, γ-aminobutyric acid (GABA), and opioid peptides. The chapter summarizes clear and basic evidence that the release of acetylcholine from the motor nerve (phrenic nerve) measured by a radiotracer method under the condition of unblocked acetylcholinesterase, which is a crucial condition for the operation of presynaptic nicotine receptors, is regulated by nicotine and muscarine autoreceptors.