Female Syrian hamster analyses of bremelanotide, a US FDA approved drug for the treatment of female hypoactive sexual desire disorder.
This study used female Syrian hamsters as an animal model to investigate how bremelanotide (Vyleesi), an FDA-approved drug for hypoactive sexual desire disorder (HSDD), affects the brain's reward system. Researchers examined melanocortin receptor (MC3R and MC4R) expression in the mesolimbic dopamine system — specifically the ventral tegmental area (VTA) and nucleus accumbens (NAc) — and assessed whether the drug enhanced sexual reward using a conditioned place preference (CPP) paradigm. Key findings attributed to the study include: MC4R mRNA was predominantly expressed in dopamine neurons in the VTA, while in the NAc and dorsal striatum, MC4R was rarely co-expressed with dopamine D1 or D2 receptor neurons, appearing instead in interneurons. Neither dose of bremelanotide tested altered melanocortin receptor mRNA expression in the mesolimbic system. Although sexual experience itself produced a CPP in female hamsters, bremelanotide did not enhance this sexual reward response. The authors conclude that bremelanotide does not appear to act through the VTA-NAc reward circuit in this model. A key limitation is that findings are derived entirely from an animal model and may not directly translate to human neurobiology or clinical outcomes.
Why this grade: All experiments were conducted exclusively in female Syrian hamsters; no human participants or clinical data were involved, limiting direct translation to human efficacy or mechanism.
Hypoactive sexual desire disorder (HSDD) is the most reported sexual dysfunction among premenopausal women worldwide. Bremelanotide, trade name Vyleesi, has been approved by the United States Food and Drug Administration to treat HSDD. However, despite approval, very little is known about its neurobiological mechanism of action. In this study, we utilized a female Syrian hamster model to investigate the effects of bremelanotide on melanocortin receptor expression in the mesolimbic dopamine system and sexual reward. We found that the majority of melanocortin 3 and 4 (MC4R) receptor mRNA is expressed in dopamine neurons in the ventral tegmental area (VTA). Fewer neurons express MC4R in the nucleus accumbens (NAc) or dorsal striatum, where they rarely colocalize with neurons expressing dopamine D1 or D2 receptors. Instead, MC4R mRNA is expressed in nucleus accumbens interneurons. Neither the low nor the high dose of bremelanotide had an effect on the expression of melanocortin receptor mRNA in the mesolimbic dopamine system. Finally, sexual experience resulted in a conditioned place preference (CPP) in female Syrian hamsters, though bremelanotide treatment failed to enhance sexual reward in this test. The results of this study are discussed in conjunction with similar studies in rats, with the conclusion that bremelanotide does not act on the VTA-NAc reward circuit and does not enhance the rewarding effects of sexual interactions.
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