Blocking nerve signals in the brain's body clock stops NMDA from lowering night-time melatonin without changing clock gene activity

Sodium-dependent action potentials in the suprachiasmatic nucleus are necessary for light to suppress melatonin levels but not for increasing circadian clock gene mRNA levels.

• Light exposure during the night increases mRNA levels of the circadian clock genes Per1 and Per2 in the suprachiasmatic nucleus.
• Light exposure also suppresses melatonin levels in the pineal gland.
• Tetrodotoxin (TTX) inhibits the ability of light to increase Per1 and Per2 mRNA levels and to suppress pineal melatonin levels.
• N-methyl-D-aspartate (NMDA) can still increase Per1 and Per2 mRNA levels even when TTX is present, indicating that action potentials are not required for this response.
• However, NMDA's ability to suppress pineal melatonin levels is inhibited by TTX, suggesting a separate mechanism for this action.

Simplified