The endocrine system is a complex system of ductless glands.

The CNS controls the endocrine system through the neuro-chemical feedback loops involving the hypothalamus and the pituitary gland.

The CNS receives and integrates information affecting endocrine functioning. This includes sensory information from the environment, interoceptive information from the body, feedback from the hormones in the bloodstream, and built-in biological patterns and species-specific biological rhythms.

There are two classes of hormones- steroid hormones and peptide hormones.

Steroid hormones include corticoids and sex hormones (testosterone and estrogens)

Peptides & Neuropeptides

Peptide hormones include substances like CRF and ACTH released by the hypothalamus and the pituitary gland.

Peptides are very old substances found even in plants, worms, bacteria, and single-celled organisms.

Peptides & Neuropeptides

Peptides influence not just the peripheral nervous system, but even the central nervous system.

Peptides that are found in the CNS are called neuropeptides.

Neuropeptides released by the hypothalamus and the pituitary gland carry information to the brain structures that influence emotion, motivation, learning and memory.

Newer research suggests that the hypothalamus also releases neuropeptides into the cerebrospinal fluid that fills the ventricles of the brain.


In the early 1970s, it was discovered that human and other animal bodies produce endogenous morphines. These were called endorphins.

Endorphins are peptides that have pain-killing effects similar to opium.

They are found both in the brain and in the peripheral nervous system (gut, pancreas, etc)


A peptide (substance – P), present in some pathways in sensory nerves and the brain, is though to be specifically associated with the transmission of pain from the peripheral receptors.

The larger the amount of substance – P released, the greater the transmission, and thus the perception of pain.

Endorphins act to regulate the sensation of pain by modulating the release of substance P, both in the spinal cord and  at the higher regions.

Several studies have shown that stressful situations and stimuli associated with stress, can trigger the release of endorphins. This has analgesic effects which helps reduce subjective experience of pain.

Koplik and his associates (1982) found that rats that had been injected with a peptide (DSIP), were more than four times more resistant to stress as compared to normal rats.

Fields demonstrated that placebo effect is absent in patients who were injected with the drug naloxone, which interferes with the functioning of endorphins.

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