Neurons that Control Social States in Drosophila melanogaster

Animal behaviors are influences not only by the immediate stimuli they are receiving but also by internal states. Internal states such as fear, hunger, and arousal can change subjective "feeling", and result in complex behavioral outcome even if animals receive the same stimuli. In most cases, these state-dependent behavioral changes persist long after the sensory input that caused internal state change is removed, and affect future behavior, reflexing previous experience. This feature of state-control allows animals to adapt their behavior to be more suitable for their internal demands. The influence of the internal state on animal behavior has been emphasized for decades. There are multiple studies and attempts to identify persistent neuronal mechanisms which are the important feature of the internal state. However, how persistency makes the behavioral state interact with behavioral process to induce input/output relationship has been largely unknown. In addition, it is not clear what the behavioral functions of the persistence are, and what the circuit implementation of persistent activity is. Are there neurons that are persistently activated by external stimulus? Here we approached these questions by investigating social state of fruit flies, Drosophila melanogaster. Fruit flies exhibit complex social behaviors that are appropriate for given social cues. For example, male flies show courtship behavior toward female flies, and show aggressive behavior such as wing threat and fighting when they encounter opponent male files. Previous studies have been focused on what sensory cues induce these behaviors: detection of female specific pheromones, 7,11-HD, causes male files to court, and male specific pheromone, cVA, induces inter-male aggression. In this study, we have focused more on how these cues might affect internal state changes rather than immediate behavioral response. Studying persistent social state change has been challenging due to the difficulty of precise, time-resolved presentation of the social cues. For instance, courtship behaviors require constant presence of female object toward which male flies show oriented behavior. The male-male aggressive behaviors such as lunging and tussling require constant interaction between two animals, and removal of opponent male fly is technically impossible. Therefore, we first developed an optogenetic tool in fly systems to study persistent feature of the social state change to mimic transient presentation of the social cue. In Chapter II, we describe an optogenetic tool that allows the manipulation of neural activity in a freely moving fly. We used Red activatable Channelrhodopsin (ReachR), which enabled us to manipulate activation of neurons in freely behaving adult flies in millisecond precision without interfering normal visual function. Using such an activation tool, we show that activation of female sensing neurons, P1 neurons, induces persistent courtship behaviors in male flies that last several minutes after the stimulation of P1 neurons. Although we show that persistent internal state change can be induced by transient stimulation of the sensory cues in Chapter II, the circuit implementation of such a persistency is not clear. In Chapter III, we show that activation of P1 neurons triggers persistent activity in its downstream neurons, pCd neurons, that is necessary for the persistent social behavior induced by transient social behaviors. Interestingly, manipulation of the pCd neurons do not affect immediate behavioral response that are shown during the presentation of social cues (P1 stimulation), implying that there are parallel and dissociable pathways for the immediate response and enduring response derived from persistent internal state change, although these responses are caused by common cue. Although the neural mechanism to encode persistent activity is still unclear, this finding shows how internal state and command pathway interact with each other to affect behavioral outcome. Altogether, these findings described in this dissertation offer new insights for future researchers to understand behavioral state control.</p

P1 interneurons promote a persistent internal state that enhances inter-male aggression in Drosophila

How brains are hardwired to produce aggressive behavior, and how aggression circuits are related to those that mediate courtship, is not well understood. A large-scale screen for aggression-promoting neurons in Drosophila identified several independent hits that enhanced both inter-male aggression and courtship. Genetic intersections revealed that P1 interneurons, previously thought to exclusively control male courtship, were responsible for both phenotypes. The aggression phenotype was fly-intrinsic, and required male-specific chemosensory cues on the opponent. Optogenetic experiments indicated that P1 activation promoted aggression vs. wing extension at low vs. high thresholds, respectively. High frequency photostimulation promoted wing extension and aggression in an inverse manner, during light ON and OFF, respectively. P1 activation enhanced aggression by promoting a persistent internal state, which could endure for minutes prior to social contact. Thus P1 neurons promote an internal state that facilitates both aggression and courtship, and can control these social behaviors in a threshold-dependent manner

Neurons that Function within an Integrator to Promote a Persistent Behavioral State in Drosophila

Innate behaviors involve both reflexive motor programs and enduring internal states, but how these responses are coordinated by the brain is not clear. In Drosophila, male-specific P1 interneurons promote courtship song, as well as a persistent internal state that prolongs courtship and enhances aggressiveness. However, P1 neurons themselves are not persistently active. Here, we identify pCd neurons as persistently active, indirect P1 targets that are required for P1-evoked persistent courtship and aggression. Acute activation of pCd neurons alone is inefficacious but enhances and prolongs courtship or aggression promoted by female cues. Brief female exposure induces a persistent increase in male aggressiveness, an effect abrogated by interruption of pCd activity. pCd activity is not sufficient but necessary for persistent physiological activity, implying an essential role in a persistence network. Thus, P1 neurons coordinate both command-like control of courtship song and a persistent internal state of social arousal mediated by pCd neurons

Internal States and Behavioral Decision-Making: Toward an Integration of Emotion and Cognition

Social interactions, such as an aggressive encounter between two conspecific males or a mating encounter between a male and a female, typically progress from an initial appetitive or motivational phase, to a final consummatory phase. This progression involves both changes in the intensity of the animals’ internal state of arousal or motivation and sequential changes in their behavior. How are these internal states, and their escalating intensity, encoded in the brain? Does this escalation drive the progression from the appetitive/motivational to the consummatory phase of a social interaction and, if so, how are appropriate behaviors chosen during this progression? Recent work on social behaviors in flies and mice suggests possible ways in which changes in internal state intensity during a social encounter may be encoded and coupled to appropriate behavioral decisions at appropriate phases of the interaction. These studies may have relevance to understanding how emotion states influence cognitive behavioral decisions at higher levels of brain function

optogenetic control of Drosophila using a red-shifted channelrhodopsin reveals experience-dependent influences on courtship

Articles nAture methods | ADVANCE ONLINE PUBLICATION | optogenetics allows the manipulation of neural activity in freely moving animals with millisecond precision, but its application in Drosophila melanogaster has been limited. here we show that a recently described red activatable channelrhodopsin (reachr) permits control of complex behavior in freely moving adult flies, at wavelengths that are not thought to interfere with normal visual function. this tool affords the opportunity to control neural activity over a broad dynamic range of stimulation intensities. using time-resolved activation, we show that the neural control of male courtship song can be separated into (i) probabilistic, persistent and (ii) deterministic, command-like components. the former, but not the latter, neurons are subject to functional modulation by social experience, which supports the idea that they constitute a locus of state-dependent influence. this separation is not evident using thermogenetic tools, a result underscoring the importance of temporally precise control of neuronal activation in the functional dissection of neural circuits in Drosophila. D. melanogaster is one of the most powerful model organisms available for the genetic dissection of neural circuit function 1,2 . Likewise, the use of light-sensitive microbial opsins, such as channelrhodopsin, has revolutionized the functional dissection of neural circuits in behaving animals In the absence of facile optogenetic manipulation, dTRPA1, a thermosensitive cation channel, has been the preferred metho

Optogenetic control of Drosophila using a red-shifted channelrhodopsin reveals experience-dependent influences on courtship

Optogenetics allows the manipulation of neural activity in freely moving animals with millisecond precision, but its application in Drosophila melanogaster has been limited. Here we show that a recently described red activatable channelrhodopsin (ReaChR) permits control of complex behavior in freely moving adult flies, at wavelengths that are not thought to interfere with normal visual function. This tool affords the opportunity to control neural activity over a broad dynamic range of stimulation intensities. Using time-resolved activation, we show that the neural control of male courtship song can be separated into (i) probabilistic, persistent and (ii) deterministic, command-like components. The former, but not the latter, neurons are subject to functional modulation by social experience, which supports the idea that they constitute a locus of state-dependent influence. This separation is not evident using thermogenetic tools, a result underscoring the importance of temporally precise control of neuronal activation in the functional dissection of neural circuits in Drosophila

Optogenetic control of Drosophila using a red-shifted channelrhodopsin reveals experience-dependent influences on courtship.

Optogenetics allows the manipulation of neural activity in freely moving animals with millisecond precision, but its application in Drosophila melanogaster has been limited. Here we show that a recently described red activatable channelrhodopsin (ReaChR) permits control of complex behavior in freely moving adult flies, at wavelengths that are not thought to interfere with normal visual function. This tool affords the opportunity to control neural activity over a broad dynamic range of stimulation intensities. Using time-resolved activation, we show that the neural control of male courtship song can be separated into (i) probabilistic, persistent and (ii) deterministic, command-like components. The former, but not the latter, neurons are subject to functional modulation by social experience, which supports the idea that they constitute a locus of state-dependent influence. This separation is not evident using thermogenetic tools, a result underscoring the importance of temporally precise control of neuronal activation in the functional dissection of neural circuits in Drosophila