ORIGINAL PAPER Y. Zilberstein Æ E. Fuchs Æ L. Hershtik Æ A. Ayali Neuromodulation for behavior in the locust frontal ganglion Received: 28 October 2003 / Revised: 8 January 2004 / Accepted: 11 January 2004 / Published online: 5 February 2004 Ó Springer-Verlag 2004 Abstract Neuromodulators orchestrate complex behav- ioral routines by their multiple and combined effects on the nervous system. In the desert locust, Schistocerca gregaria, frontal ganglion neurons innervate foregut dilator muscles and play a key role in the control of foregut motor patterns. To further investigate the role of the frontal ganglion in locust behavior, we currently fo- cus on the frontal ganglion central pattern generator as a target for neuromodulation. Application of octopamine, a well-studied insect neuromodulator, generated revers- ible disruption of frontal ganglion rhythmic activity. The threshold for the modulatory effects of octopamine was 10 )6 mol l )1 , and 10 )4 mol l )1 always abolished the ongoing rhythm. In contrast to this straightforward modulation, allatostatin, previously reported to be a myoinhibitor of insect gut muscles, showed complex, tri-modal, dose-dependent effects on frontal ganglion rhythmic pattern. Using a novel cross-correlation anal- ysis technique, we show that different allatostatin con- centrations have very different effects not only on cycle period but also on temporal characteristics of the rhyth- mic bursts of action potentials. Allatostatin also altered the frontal ganglion rhythm in vivo. The analysis tech- nique we introduce may be instrumental in the study of not fully characterized neural circuits and their modula- tion. The physiological significance of our results and the role of the modulators in locust behavior are discussed. Keywords Allatostatin Æ Cross-correlation Æ Neuromodulation Æ Octopamine Æ Schistocerca gregaria Abbreviation CPG central pattern generator Æ FG frontal ganglion Æ JH juvenile hormone Æ STNS stomatogastric nervous system Introduction A fundamental question in neurobiology concerns the way by which the function of the nervous system is modified to allow an animal the behavioral plasticity needed to adapt to the changing demands of its envi- ronment. Modulation of neural circuits for behavior has been the focus of considerable work over the last two decades (e.g., Harris-Warrick and Marder 1991; Harris-Warrick et al. 1992; Grillner et al. 1994; Marder et al. 1994; Kupfermann and Weiss 2001; Marder and Bucher 2001; Marder and Thirumalai 2002; Nusbaum and Beenhakker 2002). Neuromodulators, primarily biogenic amines and peptides, coordinate and shape behavior by acting simultaneously at many target points in the nervous systems to integrate neuronal activity. Substantial progress has been made by studying modulation of rhythmic behaviors and the central pat- tern generator (CPG) circuits that control them (Delc- omyn 1980; Stein et al. 1997). The ability of a CPG network to produce a variety of different motor pat- terns, and thus a number of related behaviors dependent on sensory and modulatory inputs, is a fundamental feature of these networks (Harris-Warrick and Marder 1991; Harris-Warrick 1994; Grillner et al. 1994; Marder et al. 1994; Ayali and Harris-Warrick 1999; Pearson 2000; Marder and Thirumalai 2002). We have recently described a CPG network in the frontal ganglion (FG) of the desert locust, Schistocerca gregaria (Ayali et al. 2002). The FG is part of the insect stomatogastric ner- vous system (STNS) and is found in most insect orders (Penzlin 1985; Ayali 2003). The FG network(s) consti- tutes a major source of innervation to the foregut dilator muscles and plays a key role in control of foregut movements in two fundamental behaviors in insect life: feeding and molting (Allum 1973; Aubele and Klemm 1977; Zilberstein and Ayali 2002). Both behaviors con- stitute a complex set of motor patterns that need to be carefully coordinated and controlled. Our previously Y. Zilberstein Æ E. Fuchs Æ L. Hershtik Æ A. Ayali (&) Department of Zoology, Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel E-mail: ayali@post.tau.ac.il Tel.: +972-3-6409820 Fax: +972-3-6409403 J Comp Physiol A (2004) 190: 301–309 DOI 10.1007/s00359-004-0496-5