V to the L-izzo, D to the M-izza: The Circadian Pacemaker

This morning, I attended one of the nanosymposia on the circadian pacemaker. Many presented data pertinent to the role of VIP in photic phase-resetting, entrainment, and clock gene expression. Mary Harrington of Smith College utilized chronic simulated jet lag (multiple 8 hr shifts in the photocycle) to illustrate marked internal circadian desynchronization between clock gene expression in the SCN and peripheral tissue. In the past, this internal desynchronization has also been achieved under constant dark/photic conditions. In Harrington’s study, the deleterious effects of chronic jet lag on circadian pacemaker activity are potentiated by advances of the photocycle more than delays.

Mike Schwartz through collaboration with the University of Maryland School of Medicine and the University of Washington presented a model of cross-talking between the ventrolateral and dorsomedial regions of the SCN that mediates phase-resetting of the circadian clock; light stimulates a response within the ventrolateral region of the SCN that is transmitted to the dorsalmedial region, ultimately manifesting in phase-resetting.

Finally, The Antle Lab from the University of Calgary presented data on the minor, almost trivial role of Substance P in the mediation of photic phase-resetting. Substance P is co-localized within the core region of the SCN (there are two regions of the SCN called the shell and the core) along with gastrin-releasing peptide (GRP). Though intracerebroventricular administration of GRP into the third ventricle alone effectively elicits behavioral shifts of locomotor activity and parallels changes in c-fos expression, substance P does not.

From a purely aesthetic perspective, below is a photomicrograph of VIP expression within the SCN from my own lab (i.e. the Glass Lab) per Jessica M. Francl (alias GirlJessie) who will be presenting this data today during the poster sessions.



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