Dynorphin

Dynorphin is a class of peptides produced by many different populations of neurons, which has some opiate-like activity. It is thus classed as an endogenous opioid peptide.

Dynorphin functions primarily as a kappa opioid receptor agonist, meaning that it acts mainly at kappa opioid receptors. Other opioid peptides include beta-endorphin, met-enkephalin, leu-enkephalin and endomorphins.

The dynorphins, which include dynorphin A, dynorphin B, alpha- and beta-neoendorphin, and big dynorphin, are all the products of a single gene, 'preprodynorphin'.

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Production

Dynorphin is produced in many different parts of the brain, including the hypothalamus, the hippocampus and the spinal cord, and has many different physiological actions, depending upon its site of production.

• For example, dynorphin that is made in magnocellular vasopressin neurons of the supraoptic nucleus is important in the patterning of electrical activity. Dynorphin produced in magnocellular oxytocin neurons is a negative feedback inhibitor of oxytocin secretion.
• Dynorphin produced in the arcuate nucleus and in orexin neurons of the lateral hypothalamus affects the control of appetite.

Clinical significance

Dynorphin may act as an antidote to pleasurable effects of cocaine. As such, it may help some individuals against addiction.^[1]

Blocking dynorphin may help alleviate depression.^[2]

Recent research has demonstrated that pulmonary delivery may be an effective means of distributing dynorphin derivatives.^[3]

Discovery

It was discovered in the mid-1970s in the laboratory of Avram Goldstein, one of the most important researchers in the field of opioid receptors and endogenous opioid peptides. At first, it was described as an opioid activity present in porcine pituitary extract that proved resistant to chemical degradation by cyanogen bromide, indicating that the activity was not due to the well-known pituitary endogenous opioid peptide beta-endorphin. The molecular identification was achieved by Goldstein in collaboration with the Japanese biochemist, Shinro Tachibana for purification, and M. Hunkapiller and L. Hood, who performed the microsequencing.^[4]

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