CURRENT EXCITEMENT FROM INSECT MUSCARINIC RECEPTORS

Recent electrophysiological, pharmacological and molecular studies sug gest that muscarinic ACh receptors (mAChRs) in insects are related to, but distinct from, their mammalian counterparts. Insect mAChRs perfor m two primary roles that are distinguished by their locations. Presyna ptic mAChRs, present on sensory terminals, inhibit transmitter release , thereby reducing the effectiveness of specific afferent inputs. In c ontrast, post-synaptic mAChRs depolarize and increase the excitability of motoneurons and interneurons, thereby acting as dynamic-gain contr ols. This postsynaptic modulation is achieved in different ways in spe cific neurons but generally results from the activation of persistent inward and outward currents. At the level of neural processing, these distinct roles enable insect mAChRs to regulate the transfer of sensor y information, and modulate the contributions of central neurons to ce ntral pattern generators and reflexes. Because these phenomena can be studied in identified neurons, a combination of physiological and mole cular studies of mAChRs in insects should help to elucidate some of th eir behavioral roles. Furthermore, such studies could lead to the iden tification of general mechanisms of functional plasticity in neuronal networks.