Time is the fundamental dimension for animal’s survival. The animal brain is the result of evolution to orchestrate temporal information across a wide spectrum of time scales. Especially, interval timing is a pivotal function of the human brain to support our cognitive ability such as memory, attention, and decision-making. Interval timing refers to the discrimination of durations in the seconds-to-minutes ranges. The genetic aspects of interval timing have not been vigorously investigated because of the lack of a genetically-traceable model organism. Here we present two novel behavioural paradigms of male Drosophila that fits the current ‘internal clock model’ of interval timing.
1. LMD, Rival induced prolonged mating: Drosophila males respond to the presence of rivals by prolonging mating duration to guard female and pass their genes. In previous studies, we examined the genetic network and neural circuits that regulate rival-induced longer mating duration (LMD). LMD can be induced solely via visual stimuli. LMD depends on the circadian clock genes timeless and period, but not Clock or cycle. LMD involves the memory circuit of the ellipsoid body (EB) (Kim et al., Nat. neuroscience). Further, we identified a small subset of clock neurons in the male brain that regulates LMD via neuropeptide signaling (Kim et al., Neuron).
2. SMD, Sexual experience-based shortened mating: Drosophila males exhibit a shortened mating duration for guarding female when sexually satiated, called ‘Shorter-Mating-Duration (SMD)’. Both sexual experiences and contact-based chemoreception is necessary to induce SMD. SMD requires the sexually dimorphic Gr5a-positive neurons to detect female body pheromones, and can be induced by gustatory stimuli. The memory circuitry within the ellipsoid body (EB) and mushroom body (MB) brain regions are crucial to process this satiety state. SMD depends on the circadian clock genes Clock and cycle, but not timeless or period. SMD also relies on signaling via the neuropeptide sNPF, but not PDF or NPF. Sexual experience modifies the neuronal activity of a subset of sNPF-positive neurons involved in neuropeptide signaling, which modulates SMD (Current Biol. in revision).
Internal clock model (pacemaker-accumulator model PAM) constitutes of a pacemaker, mode switch, accumulator, memory circuit, and a comparator circuit. We have found that LMD/SMD provides all of these components, which are all identified in the fly brain. This presentation will provide 1) how the fly model of interval timing is similar with that of human and 2) what is the merit of this system.