Local biological clocks made of groups of rhythm neurons in the rat's daily time-keeping center

Robust circadian rhythms in arginine vasopressin release were observed peaking consistently at the middle of the original light phase.

• Circadian rhythms of arginine vasopressin (AVP) release were detected in organotypic slice cultures of the suprachiasmatic nucleus (SCN) from neonatal rats.
• The release of vasoactive intestinal polypeptide (VIP) showed varied rhythmicity, with some profiles being arrhythmic and others exhibiting a phase delay of 5-7 hours compared to AVP.
• Out of 67 examined neurons in the SCN, 51 (76.1%) exhibited circadian firing rate rhythms, with a higher percentage of rhythmic neurons in the dorsal region (86.8%) compared to the ventral region (62.1%).
• Twenty-seven percent of the firing rhythms were nearly out of sync with the majority, but there was no specific regional distribution of these antiphasic rhythms.
• Dorsal and ventral regions of the SCN may contain distinct circadian pacemakers that regulate AVP and VIP release differently, potentially linked to variations in neuron coupling strength.

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