What are the post-climax effects of opioids in the brain?

The endogenous opioid system consists of 3 families of opioid peptides, β-endorphin, enkephalins, and dynorphins, and their receptors. Opioid peptides and their receptors have widespread, but selective, distribution in the central and peripheral nervous systems. They are particularly found in circuits involved in pain modulation, reward, responses to stress, and autonomic control.

It’s believed that one class of opioids (endorphins) is particularly involved with feelings of euphoria during sex, while the other two classes have roles in inhibition of sexual desire and dopamine release.

Animal studies

Activation of mu opioid receptors in the medial preoptic area following copulation in male rats

Different amounts of ejaculatory activity, a natural rewarding behavior, induce differential mu and delta opioid receptor internalization in the rat’s ventral tegmental area

Endogenous opioid-induced neuroplasticity of dopaminergic neurons in the ventral tegmental area influences natural and opiate reward

Endogenous opioids mediate the sexual inhibition but not the drug hypersensitivity induced by sexual satiation in male rats

Evidence for changes in brain enkephalin contents associated to male rat sexual activity

Involvement of endogenous opioidergic neurons in modulation of prolactin secretion in response to mating in the female rat.

IRS2-Akt pathway in midbrain dopamine neurons regulates behavioral and cellular responses to opiates

Opiate-Induced Molecular and Cellular Plasticity of Ventral Tegmental Area and Locus Coeruleus Catecholamine Neurons

Opioid receptor and β-arrestin2 densities and distribution change after sexual experience in the ventral tegmental area of male rats

The mesolimbic system participates in the naltrexone-induced reversal of sexual exhaustion: Opposite effects of intra-VTA naltrexone administration on copulation of sexually experienced and sexually exhausted male rats