Physiology Exposure to darkness leads to increased melatonin secretion. It is brought about by: A Decreasing the activity of suprachiasmatic nuclei B Increasing the serotonin N-acetyl transferase. C Decreasing the hydroxy-indole-o-methyl transferase, activity D Blocking the release of norepinephrine from sympathetic nerve terminals 💡 Explanation Exposure to darkness leads to increased melatonin secretion. It is brought about by: ✓ Correct Answer: B. Increasing the serotonin N-acetyl transferase.