Serotonergic 5-HT7 Receptors as Modulators of the Nociceptive System

Non-hallucinogenic compounds derived from iboga alkaloids alleviate neuropathic and visceral pain in mice through a mechanism involving 5-HT2A receptor activation

The aim of this study was to determine the anti-hypersensitivity activity of novel non-hallucinogenic compounds derived from iboga alkaloids (i.e., ibogalogs), including tabernanthalog (TBG), ibogainalog (IBG), and ibogaminalog (DM506), using mouse models of neuropathic (Chronic Constriction Injury; CCI) and visceral pain (dextrane sulfate sodium; DSS). Ibogalogs decreased mechanical hyperalgesia and allodynia induced by CCI in a dose- and timeframe-dependent manner, where IBG showed the longest anti-hyperalgesic activity at a comparatively lower dose, whereas DM506 displayed the quickest response. These compounds also decreased hypersensitivity induced by colitis, where DM506 showed the longest activity. To understand the mechanisms involved in these effects, two approaches were utilized: ibogalogs were challenged with the 5-HT2A receptor antagonist ketanserin and the pharmacological activity of these compounds was assessed at the respective 5-HT2A, 5-HT6, and 5-HT7 receptor subtypes. The behavioral results clearly demonstrated that ketanserin abolishes the pain-relieving activity of ibogalogs without inducing any effect per se, supporting the concept that 5-HT2A receptor activation, but not inhibition, is involved in this process. The functional results showed that ibogalogs potently activate the 5-HT2A and 5-HT6 receptor subtypes, whereas they behave as inverse agonists (except TBG) at the 5-HT7 receptor. Considering previous studies showing that 5-HT6 receptor inhibition, but not activation, and 5-HT7 receptor activation, but not inhibition, relieved chronic pain, we can discard these two receptor subtypes as participating in the pain-relieving activity of ibogalogs. The potential involvement of 5-HT2B/2 C receptor subtypes was also ruled out. In conclusion, the anti-hypersensitivity activity of ibogalogs in mice is mediated by a mechanism involving 5-HT2A receptor activation.

Effectiveness of Brexpiprazole in a Patient With Bipolar Disorder and Comorbid Persistent Genital Arousal Disorder/Genito-Pelvic Dysesthesia: A Case Report

Although the symptoms of persistent genital arousal disorder/genito-pelvic dysesthesia (PGAD/GPD) can have negative impacts on patients' lives, it is an under-recognized clinical entity. We describe the case of a 61-year-old Japanese female who suffered simultaneously from bipolar disorder and PGAD/GPD. She developed PGAD/GPD approx. 10 years after being diagnosed with bipolar disorder. Despite 20 years of various drug treatments, her bipolar disorder and PGAD/GPD symptoms showed little improvement. She had also undergone multiple sessions of cognitive behavioral therapy (CBT) and mindfulness, nerve block, botulinum toxin injections, and laser treatment for PGAD/GPD. Her PGAD/GPD symptoms remained with no significant improvement, and her bipolar disorder symptoms had also not responded well to medication. With the administration of brexpiprazole, she achieved remission of her bipolar disorder. Her PGAD/GPD symptoms also eventually improved. When PGAD/GPD is comorbid with bipolar disorder, the improvement of bipolar disorder may also lead to relief of PGAD/GPD symptoms. This case reveals that brexpiprazole, which has a unique profile, may be effective for PGAD/GPD.