The role of Clock in the developmental expression of neuropeptides in the suprachiasmatic nucleus.

The number of vasopressin (AVP) neurons is significantly reduced in Clock mutant mice compared to wild type.

• Clock homozygous mice do not exhibit the increase in VIP-immunoreactive neurons from postnatal day 6 to P30 seen in wild type mice.
• AVP-immunoreactive neurons remain relatively constant in the postnatal suprachiasmatic nucleus (SCN) but are significantly lower in Clock mutant mice.
• The impact of the Clock mutation on AVP and VIP expression varies by position within the SCN.
• Densitometry analysis shows that Clock mutation specifically reduces AVP expression in the SCN, with no effects observed in other brain regions.
• The neonatal mouse SCN contains its full complement of cells, although some are not fully mature regarding neuropeptide content.
• The findings suggest heterogeneity among AVP and VIP cell classes within the SCN.

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