Pituitary and pineal glands.

In addition to the endocrine effects of the hypothalamus, the brain also produces a number of brain peptides, released from axonal branches at various parts of the brain to exert relatively long-lasting effects on the polarized states of neurons.

The pineal gland releases melatonin, a derivative of tryptophan, when the environment is dark. The pineal gland also has an internal rhythm. Also important in regulating biological rhythms are the regions of the hypothalamus called the suprachiasmatic nuclei (SCN), which operates as a master control of biological rhythms, sending regulatory impulses to other parts of the brain.