Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid peptide that was first isolated from ovine hypothalamic extracts. It has been previously observed that light information reaches the suprachiasmatic nucleus through a population of retinal ganglion cells that contain PACAP, however the involvement of PACAP and its receptor is not well studied. In order to study the role of PACAP in vivo, a new mouse model was developed in which the gene encoding for PACAP was disrupted by homologous recombination.
PACAP deficient mice exhibit significant impairment in the magnitude of the response to brief light exposures. Researches observed about a 50% reduction in the magnitude of both light-induced phase delays and advances of the circadian system in the PACAP deficient mice. Overall, loss of PACAP produced selective deficits in the light response of the circadian system.
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