Charles Bourque, McGill University – How the Brain’s Clock Drives Thirst Before Sleep

Do you have a drink of water before bed?

Charles Bourque, professor of neurosurgery at McGill University, details why you might want to be hydrated before zonking out for the night.

Dr. Bourque obtained a Ph.D. degree in Physiology from McGill University (Montreal, 1985) complemented with a Certificate in Biophysics from the Marine Biological Laboratory (Woods Hole, USA). He pursued Post-Doctoral studies in Pharmacology at the School of Pharmacy, University College (London, UK) and was recruited to McGill University’s Centre for Research in Neuroscience in 1987. He now occupies the positions listed above. Dr Bourque has published over 130 scientific papers, co-edited 1 book, and has delivered over 150 invited presentations at National and International venues.

Dr. Bourque’s laboratory research focuses on understanding the molecular and cellular mechanisms by which the brain monitors body hydration, fluid electrolytes and core temperature. Dr. Bourque and his team are particularly interested in defining how networks of thermosensitive and salt-sensitive neurons communicate with neurons in the central clock and other cells to control the sensation of thirst and the release of antidiuretic hormone to mediate hydromineral homeostasis.

Life-threatening defects in osmoregulation are featured in many clinical conditions, including heart failure, sepsis and following head trauma. Moreover changes in osmoregulation likely link dietary salt intake to many forms of hypertension. The Bourque team is therefore interested in how changes in neuronal properties and inter-neuronal communication contribute to the pathogenesis of several hydromineral disorders.

Honors awarded to Dr. Bourque have included the Medical Research Council’s Scholarship, Scientist and Senior Scientist awards, as well as a Senior Investigator award from the Canadian Institutes of Health Research. He has received the Joseph Erlanger Distinguished Lecturer Award from the American Physiological Society, the Jacques Benoit Lectureship from the Société de Neuroendocrinologie (France), the Stevenson Lectureship (Western University, Ontario) and a Distinguished Lectureship from the University of Saskatchewan. Dr. Bourque was inducted as a Fellow of the Royal Society of Canada in 2016.

How the Brain’s Clock Drives Thirst Before Sleep

A requirement for life to evolve on this planet was a need to anticipate the impact of earth’s 24 hour light cycle. In single cells, Clock genes soon evolved to optimize metabolism during the absence and presence of warmth and light. Multicellular organisms later evolved master clocks that can orchestrate several different rhythms to adapt behavior and optimize organ function according to the time of day.

In vertebrates, this master clock is located in a small region of the brain called the suprachiasmatic nucleus. This structure is located near where the optic nerves enter the brain, and receives light information captured by the eye to synchronize its timing.  Although much is known about the anatomy and time-keeping ability of this clock, little is known about how it mediates circadian rhythms.

Recent work by PhD student Claire Gizowski, with help from Cristian Zaelzer and myself at McGill University, revealed that mice increase water intake before sleep, and that preventing this increase causes them to be dehydrated at wake time. Therefore this behavior protects the body by anticipating a need for water reserves during the sleep period. Because we knew that thirst-promoting neurons are located in a brain region termed the OVLT, we investigated the mechanism by which the clock communicates with this area to promote thirst before sleep.

Claire discovered that clock neurons and thirst neurons both increase their electrical activity before sleep. Moreover, clock neurons extend long processes known as axons toward the thirst neurons. Using a technique that uses laser light to control neuronal activity, she showed that clock neurons drive thirst behavior by exciting thirst neurons through the release of a neuropeptide called vasopressin from the axons terminals of the clock neurons.  Understanding how the clock regulates circadian rhythms will eventually improve our ability to treat disorders related to clock malfunction, and to better cope with shift work or jet lag.