“…The limited number of serotonin immunoreactive neurons in the insect brain allows a detailed analysis of the morphology of these neurons throughout postembryonic development and indicates that they are developmentally conserved (Breidbach, 1990;Granger et al, 1989;Radwan et al, 1989;Seidel and Bicker, 1996;White, 1986, 1988;Wegerhoff and Breidbach, 1992). For serotonin containing wide-field neurons that centrifugally invade sensory neuropils, a role in modulation of the integration of sensory inputs has been shown for different insect species (Erber and Kloppenburg, 1995;Erber et al, 1991Erber et al, , 1993Muszynska-Pytel and Cymborowski, 1978;Salecker and Distler, 1990), whereas serotonin or other amines in small field neurons may serve as a conventional transmitter in local neuronal circuits (for review see Homberg, 1994). In contrast to serotonin, GABA immunoreactivity is found in numerous neurons within the insect brain.…”