The brain can eat: Establishing the existence of a central pattern generator for feeding in third instar larvae of Drosophila virilis and Drosophila melanogaster Andreas Schoofs a , Senta Niederegger b , Andre ` van Ooyen c , Hans-Georg Heinzel a , Roland Spieß a, * a Zoologisches Institut der Universita ¨t Bonn, Abteilung Neurobiologie, Poppelsdorfer Schloß, 53115 Bonn, Germany b Universita ¨tsklinikum Jena, Institut fu ¨r Rechtsmedizin, Fu ¨rstengraben 23, 07743 Jena, Germany c RWTH Aachen, Institut fu ¨r Werkstoffe der Elektrotechnik, Lehrstuhl 1, Sommerfeldstraße 24, 52074 Aachen, Germany 1. Introduction Central pattern generators (CPGs) are often responsible for the basic motor patterns of rhythmic movements like walking, breathing, swimming and feeding in both vertebrate and inverte- brate animals (Ba ¨ ssler, 1993; Burrows, 1996; Eisenhart et al., 2000; MacKay-Lyons, 2002; Marder, 2000; Marder and Bucher, 2001; Marder et al., 2005; Marder and Calabrese, 1996). Due to the relative simplicity of the invertebrate nervous system considerable knowledge was accumulated about the functionality of the underlying circuits to the level of intrinsic properties of identified neurons in Crustaceans (Harris-Warrick et al., 1992; Selverston and Moulins, 1987), snails (Benjamin and Rose, 1979; Benjamin et al., 1979; Kyriakides and McCrohan, 1988; Rose and Benjamin, 1979; Straub and Benjamin, 2001; Straub et al., 2002), insects (Ayali and Zilberstein, 2004; Ayali et al., 2002; Miles and Booker, 1994) and leeches (Arbas and Calabrese, 1984; Eisenhart et al., 2000). Diptera, especially Drosophila larvae present an ideal new system to investigate the neural circuitry of feeding behavior. Given that the eggs were laid on a adequate substrate, Drosophila larvae spend proximally 84% of their life with feeding (Green et al., 1983). The expressed behavior is simple and consists of rhythmic pro- and retraction of the head and shoveling movements of the mouth hooks (Green et al., 1983; Harrison and Cooper, 2003; Hobson, 1932; Sokolowski, 1982). These movements resemble the feeding behavior of Calliphora larvae which was recently described as repetitive cycles with four distinct phases (Schoofs et al., 2009). Each phase is characterized by specific movements of the mouth hooks and the cephalopharyngeal skeleton (CPS). The information available on the muscular and neural architecture of the thoracic segments which are predominantly involved in feeding behavior, is restricted to Calliphora larvae (Bolwig, 1946; Lowne, 1890; Ludwig, 1949; Schoofs et al., 2009), although the anatomy and innervation of the abdominal muscles of Diptera larvae were thoroughly investigated (Bate, 1990; Broadie and Bate, 1993; Budnik et al., 1990; Choi et al., 2004; Crossley, 1965; Harrison and Cooper, 2003; Hooper, 1986; Jan and Jan, 1976; Keshishian et al., 1996; Magazanik and Fedorova, 2003; Robinson, 1981). Schoofs et al. (2009) could establish for Calliphora larvae that the motor pathways to the cibarial dilator muscles which mediate food ingestion project through the antennal nerve. The maxillary nerve innervates the elevator and depressor system of the mouth hooks and the prothoracic accessory nerve contains the Journal of Insect Physiology 56 (2010) 695–705 ARTICLE INFO Article history: Received 13 October 2009 Received in revised form 8 December 2009 Accepted 9 December 2009 Keywords: Diptera larvae Feeding Central pattern generator ABSTRACT To establish the existence of a central pattern generator for feeding in the larval central nervous system of two Drosophila species, the gross anatomy of feeding related muscles and their innervation is described, the motor units of the muscles identified and rhythmic motor output recorded from the isolated CNS. The cibarial dilator muscles that mediate food ingestion are innervated by the frontal nerve. Their motor pathway projects from the brain through the antennal nerves, the frontal connectives and the frontal nerve junction. The mouth hook elevator and depressor system is innervated by side branches of the maxillary nerve. The motor units of the two muscle groups differ in amplitude: the elevator is always activated by a small unit, the depressor by a large one. The dorsal protractors span the cephalopharyngeal skeleton and the body wall hence mediating an extension of the CPS. These muscles are innervated by the prothoracic accessory nerve. Rhythmic motor output produced by the isolated central nervous system can simultaneously be recorded from all three nerves. The temporal pattern of the identified motor units resembles the sequence of muscle contractions deduced from natural feeding behavior and is therefore considered as fictive feeding. Phase diagrams show an almost identical fictive feeding pattern is in both species. ß 2009 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +49 228 735495. E-mail address: roland.spiess@uni-bonn.de (R. Spieß). Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys 0022-1910/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2009.12.008