are released by neurons acting as neurotransmitters into the local tissue which include: include the endogenous opioids (e.g., enkephalin and endorphin)- peptides found in both the brain and the peripheral nervous system (e.g., substance p and neurotensin)- hypothalamic releasing hormones (e.g., thyrotropin-releasing hormone)- pituitary hormones (e.g., growth hormone and prolactin)- and other circulating peptides (e.g., atrial natriuretic peptide and bradykinin).

NEUROPEPTIDE: "A neuropeptide is a precursor molecule for a wide range of other larger proteins, they are released by neurons into local tissue."