Octopamine Neuromodulation Regulates Gr32a-Linked Aggression and Courtship Pathways in Drosophila Males

et al. (2014) Octopamine Neuromodulation Regulates Gr32a-Linked Aggression and Courtship Pathways in Drosophila Males. PLoS Genet 10(5): e1004356. doi:10.1371/journal.pgen.1004356 Octopamine Neuromodulation Regulates Gr32a-Linked Aggression and Courtship Pathways in Drosophila Males Jonathan C. Andrews 0 1 Mara Paz Ferna ndez 0 1 Qin Yu 0 1 Greg P. Leary 0 1 Adelaine K. W. Leung 0 1 Michael P. Kavanaugh 0 1 Edward A. Kravitz 0 1 Sarah J. Certel 0 1 Thomas Clandinin, Stanford University, United States of America 0 a Current address: Instituto de Investigacio n en Biomedicina de Buenos Aires - CONICET - Partner Institute of the Max Planck Society, Buenos Aires, Argentina b Current address: Department of Veterinary Biomedical Sciences, University of Saskatchewan , Saskatoon , Canada 1 1 Center for Structural and Functional Neuroscience, University of Montana, Missoula, Montana, United States of America, 2 Department of Neurobiology, Harvard Medical School , Boston , Massachusetts, United States of America, 3 Division of Biological Sciences, University of Montana , Missoula, Montana , United States of America Chemosensory pheromonal information regulates aggression and reproduction in many species, but how pheromonal signals are transduced to reliably produce behavior is not well understood. Here we demonstrate that the pheromonal signals detected by Gr32a-expressing chemosensory neurons to enhance male aggression are filtered through octopamine (OA, invertebrate equivalent of norepinephrine) neurons. Using behavioral assays, we find males lacking both octopamine and Gr32a gustatory receptors exhibit parallel delays in the onset of aggression and reductions in aggression. Physiological and anatomical experiments identify Gr32a to octopamine neuron synaptic and functional connections in the suboesophageal ganglion. Refining the Gr32a-expressing population indicates that mouth Gr32a neurons promote male aggression and form synaptic contacts with OA neurons. By restricting the monoamine neuron target population, we show that three previously identified OA-FruM neurons involved in behavioral choice are among the Gr32a-OA connections. Our findings demonstrate that octopaminergic neuromodulatory neurons function as early as a second-order step in this chemosensory-driven male social behavior pathway. - Funding: Funding was provided by a Pew Latin American Fellowship to MPF, grants from the National Institute of General Medical Sciences (GM0067645 and GM074675) to EAK, NIH COBRE grant P20RR015583, NSF 1257730, and Whitehall Foundation Grant 2013-08-29 to SJC. This work was also supported by National Center for Research Resources Grant 2P20RR017670, which supports the University of Montana Molecular Histology and Fluorescence Imaging core. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Organisms live in complicated environments requiring successful interaction with their surroundings for reproduction and survival. Information about the environment is transformed into neural activity by specialized sensory organs that detect signals via touch-, taste-, vibration-, odor- and image-sensitive neurons. Pheromones commonly used as olfactory or contact signals in social behavior like courtship and aggression provide information about gender, receptivity, or conspecificity [13]. In many systems, chemosensory signal-detecting systems are regulated by biogenic amines including dopamine, serotonin, and norepinephrine (or octopamine, its invertebrate analog) acting as neuromodulators [46]. Despite extensive investigation in a wide variety of organisms, it has proven difficult to assign specific roles to individual amines in the circuitry concerned with social behavior [710]. In this study, we directly connect amine regulation to pheromonal communication by identifying specific chemosensory to octopamine neuron contacts and then investigating their tissuespecific functional roles in male aggression and courtship selection. In Drosophila, pheromonal signals are communicated primarily via cuticular hydrocarbons (CHC) and long carbon chain esters that trigger olfactory (volatile) or gustatory (contact) receiving pathways in conspecifics [1113]. Contact pheromones are detected by gustatory receptor-expressing sensory neurons (GRNs) found in taste sensilla in mouth, leg, and wing segments. Despite the importance of this non-volatile sensory information, only a small number of gustatory receptors (GRs) have been reported to be involved in the perception of pheromones that regulate social behavior. In one well-studied example, the behavior of males lacking the gustatory receptor Gr32a is altered in at least three ways; levels of male courtship towards females are reduced, levels of male courtship towards second males are elevated, and aggression as measured by the numbers of lunges (a key higher level behavioral pattern) is reduced [1416]. In addition, a recent study describes a role of tarsal/leg Gr32a-expressing neurons in the inhibition of interspecies courtship between Drosophila species [17]. To transduce pheromonal stimuli, axons of Gr32a-expressing neurons project to distinct zones in the suboesophageal ganglion (SOG) [15,18], and other sites within the central nervous system [19]. The SOG is a central brain region that in addition to axons of gustatory neurons contains extensive neuronal processes of octopamine neurons [2022]. Reduced levels of the amine octopamine (OA) yield phenotypes similar to those seen in flies lacking Gr32a function [2325]. Males without OA exhibit increased male-male courtship [23] and a delay in the initiation of male aggressive behavior [25], as do Gr32a loss-of-function flies [16]. OA function is also necessary for To mate or fight? When meeting other members of their species, male fruit flies must determine whether a second fly is male or female and proceed with the appropriate behavioral patterns. The taste receptor, Gr32a, has been reported to respond to chemical messages (pheromones) that are important for gender recognition, as eliminating Gr32a function impairs both male courtship and aggressive behavior. Here we demonstrate that different subsets of Gr32a-expressing neuron populations mediate these mutually exclusive behaviors and the male Gr32a-mediated behavioral response is amplified through neurons that contain the neuromodulator octopamine (OA, an invertebrate equivalent of norepinephrine). Gr32a-expressing neurons connect functionally and synaptically with distinct OA neurons indicating these amine neurons may function as early as a second-order step in a chemosensory-driven circuit. Our results contribute to understanding how an organism selects an appropriate behavioral response upon receiving external sensory signals. males to make correct choices between courtship and aggression (...truncated)