Abstract
The endogenous mu-opioid receptor (MOR) system modulates a multitude of social and reward-related functions, and exogenous opiates also influence sex drive in humans and animals. Sex drive shows substantial variation across humans, and it is possible that individual differences in MOR availability underlie interindividual of variation in human sex drive. We measured healthy male subjects’ (n = 52) brain’s MOR availability with positron emission tomography (PET) using an agonist radioligand, [11C]carfentanil, that has high affinity for MORs. Sex drive was measured using self-reports of engaging in sexual behaviour (sex with partner and masturbating). Bayesian hierarchical regression analysis revealed that sex drive was positively associated with MOR availability in cortical and subcortical areas, notably in caudate nucleus, hippocampus, and cingulate cortices. These results were replicated in full-volume GLM analysis. These widespread effects are in line with high spatial autocorrelation in MOR expression in human brain. Complementary voxel-based morphometry analysis (n = 108) of anatomical MR images provided limited evidence for positive association between sex drive and cortical density in the midcingulate cortex. We conclude that endogenous MOR tone is associated with individual differences in sex drive in human males.
Highlights
Endogenous opioids modulate behaviors ranging from analgesia to socioemotional processes and pleasure (Nummenmaa & Tuominen, 2018)
Regional Bayesian analysis revealed that sex drive was in general positively associated with mu-opioid receptor (MOR) availability (Fig. 2)
The more frequently the subjects reported in engaging in sexual activities, the more μ-opioid receptors they had in the striatum, thalamus, amygdala, and middle cingulate cortex
Summary
Endogenous opioids modulate behaviors ranging from analgesia to socioemotional processes and pleasure (Nummenmaa & Tuominen, 2018). Dopamine is the principal neurotransmitter responsible for reward processing, murine models show that opioids produce reward independent of dopamine (Hnasko et al, 2005). Μ-opioid receptor (MOR) stimulation of the FI‐20521 Turku, Finland nucleus accumbens increases both incentive motivation and consummatory rewards (Berridge et al, 2010; DiFeliceantonio & Berridge, 2016; Peciña & Berridge, 2013), and injection of μ-opioid agonists into the mesolimbic reward system induces reward (Bozarth & Wise, 1981). Molecular imaging studies in humans have further demonstrated central opioidergic activation following administration of various rewards ranging from feeding to social contact and exercise-induced “runner’s high” (Boecker et al, 2008; Burghardt et al, 2015; Manninen et al, 2017). Human sex drive varies both between sexes as well as between and within individuals (Baumeister et al, 2001; Twenge et al, 2017), and multiple lines of evidence suggest that the MOR system could be involved in maintenance of human sex drive (Pfaus & Gorzalka, 1987)
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