ROLES OF CIRCADIAN CLOCKS IN REGULATION OF THE ENDOCRINE SYSTEM IN AN INSECT

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This research program analyzes the functional significance and mechanisms of control of circadian rhythms in hormones. Circadian rhythms are daily rhythms that are controlled by internal mechanisms called 'biological clocks', which are synchronized by external light cycles. Clocks occur in many body tissues; our thesis is that these are coordinated into a synchronized network mainly by rhythms in hormones. This network creates the internal organization of cells and tissues that is essential for life; its breakdown, as in human shift workers, leads to illness and premature death. Our goal is to find out how this organization is achieved. This research employs an insect Rhodnius prolixus as it has many unique attributes for hormone rhythm studies that are not found in higher animals. The data apply to all animals and will lead to advances in medicine, agriculture and pest control. All these will benefit Canada.We analyzed the complex neural structure of the brain clock and showed it controls rhythmic release of numerous hormones into the blood. This system is closely parallel to the hypothalamic control of pituitary hormone rhythms in mammals. One of these hormones acts as a 'messenger of time' that synchronizes clocks located in endocrine glands with the brain clock. This is a novel type of function for a hormone. This proposal analyzes other clocks in peripheral tissues and the roles of various other brain hormones (and also direct light sensitivity) in coordinating them with each other and with the brain clock, into the timing network that we envisage. We will analyze the actions of these hormones, and also steroids and melatonin on the molecular oscillator within clock cells that generates timekeeping. Are there additional hormonal 'messengers of time'? The brain clock receives 'temporal feedback' from a steroid hormone rhythm, enabling novel experiments on how it integrates light signals with internal hormonal time signals. Hormone rhythms are found in both larval and adult stages, and both testes and ovaries will be examined for clocks and the actions of hormones (and light) on them. The work will produce major advances in understanding how hormone rhythms coordinate cells and tissues both with each other and with the external world.