Disrupted circadian rhythms in VIP- and PHI-deficient mice

Area of Science:

• Neuroscience
• Chronobiology
• Molecular Biology

Background:

• Vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) are neuropeptides found in the suprachiasmatic nucleus (SCN).
• Their precise role in regulating circadian rhythms remains largely uncharacterized.
• The SCN is the master circadian clock in mammals.

Purpose of the Study:

• To investigate the in vivo function of VIP and PHI in the regulation of circadian rhythms.
• To elucidate the contribution of VIP/PHI to circadian system's response to light and its internal oscillations.

Main Methods:

• Development of a novel mouse model with disrupted VIP and PHI genes via homologous recombination.
• Observation of circadian locomotor activity patterns under light-dark cycles and constant darkness.
• Electrophysiological analysis of synaptic transmission within the SCN.

Main Results:

• VIP/PHI-deficient mice showed normal diurnal rhythms in light-dark cycles but significant abnormalities in constant darkness.
• Mutant mice exhibited advanced activity onset, shortened free-running periods, and loss of rhythm precision, with some becoming arrhythmic.
• Deficits in light response and altered synaptic transmission within the SCN were observed.

Conclusions:

• VIP and PHI peptides are essential for the generation and precise synchronization of circadian rhythms.
• These peptides play a critical role in mediating the SCN's response to photic cues.
• Disruption of VIP/PHI impacts both the internal clock's stability and its entrainment to external light cycles.