An olfactory system is one of the complicatedly-equipped sensory facilities in the insect sensory systems, which is most essential for insect olfactory-driven behaviors relevant to survival such as finding hosts, mates, oviposition sites, and food resources. These behaviors are mostly controlled by circadian rhythm. The american cockroach, Periplaneta americana, has been an ideal model to extensively study olfactory system associated with complex behavioral repertoires and circadian controls of certain behaviors, respectively. Even though it is known that olfactory-related physiology in peripheral and central olfactory systems seems to be highly variable by circadian rhythms, little is known about how these are controlled at the neuronal and molecular levels. It has been reported that the plasticity in the olfactory system is modulated by a set of neuropeptides. However, it remains still elusive how these neuropeptides and neuroendocrine system interact in the peripheral systems to change olfactory responses in cockroaches. Here, current study focuses on the localization of neuropeptides and their receptors by using in situ hybridization and immunostaining methods. Also, expression level of these genes are evaulated by qRT-PCR methods. Circadian fluctuation of these genes seem to be important neurotransmission machineries in the periphery. Our current study suggests that microcircuits of neuronal systems in the peripheral olfactory organ play an important in olfactory modulation by circadian rhythm

Olfactory sense is an essential modality for insects to locate hosts, mates, oviposition sites, and food resources in nature. Based on many studies so far, insect olfactory systems in periphery as well as central nervous systems seem to be highly plastic with behavioral and physiological changes associated with learning and memory, sensory processes, and other developmental processes. Eventually, it is also evident that these plasticity and processes in olfactory systems are modulated by a various ensemble or sets of neuropeptides. The olfactory reception in the peripheral systems of the cockroach, Periplaneta americana, associated with learning behaviors, is fluctuated by the circadian rhythm, which is subsequently thought to control the titer of hormones and various neuropeptides concomitantly. However, it remains still elusive how neuropeptides and neuroendocrine systems modulate olfactory system in the peripheral systems in cockroaches as well as any other insects. Here, our aims to characterize the ultrastructure of these neuro-endocrine systems in the peripheral olfactory systems in American cockroach, Periplaneta americana. Using in situ hybridization methods, we found out that tachykinin and its receptors seem to be important neurotransmission machineries in the periphery to convey the arousal signals from the insect brain. Our findings also indicate complicated endocrine systems connected with central nervous systems may modulate the olfactory reception in the periphery.