Modulation of Neuromodulators

'Metamodulation' or second-order modulation of neurons and neural networks is emerging as a recognized and important mechanism contributing to behavioral plasticity. This issue provides a unique and timely synthesis of articles detailing how potent chemical modulators of behavior are themselves modulated by a variety of influences including social and developmental events, hormones and other neuroactive substances, parasitism, and specific network configurations. Reports of original research as well as insightful reviews of previously published studies are included. The contributed papers describe a number of diverse ways by which the biogenic amines are modulated, and how synaptic interactions and peptidase activity can regulate peptidergic signaling and motor pattern generation. By addressing how the physiology and external world of an animal can shape the suite of neuromodulators that regulates the activity of the nervous system, each article highlights the capacity of such regulatory mechanisms to expand the operational range in which animals can behave adaptively.