Novel 5-HT7 receptor antagonists modulate intestinal immune responses and reduce severity of colitis.

Inflammatory bowel disease (IBD) encompasses a number of debilitating chronic gastrointestinal (GI) inflammatory disorders, including Crohn's disease and ulcerative colitis. In both conditions, mucosal inflammation is a key clinical presentation and is associated with altered serotonin (5-hydroxytryptamine; 5-HT) signaling. This altered 5-HT signaling is also found across various animal models of colitis. Of the 14 known receptor subtypes, 5-HT receptor type 7 (5-HT7) is one of the most recently discovered. We previously reported that blocking 5-HT signaling, with either a selective 5-HT7 receptor antagonist (SB-269970) or genetic ablation alleviated intestinal inflammation in murine experimental models of colitis. Here, we developed novel antagonists, namely MC-170073 and MC-230078, which target 5-HT7 receptors with high selectivity. We also investigated the in vivo efficacy of these antagonists in experimental colitis by utilizing dextran sulfate sodium (DSS) and the transfer of CD4+CD45RBhigh T cells to induce intestinal inflammation. Inhibition of 5-HT7 receptor signaling with the antagonists, MC-170073 and MC-230078, ameliorated intestinal inflammation in both acute and chronic colitis models, which was accompanied by lower histopathological damage and diminished levels of pro-inflammatory cytokines in comparison to vehicle-treated controls. Together, the data reveal that the pharmacological inhibition of 5-HT7 receptors by these selective antagonists ameliorates the severity of colitis across various experimental models and may, in the future, serve as a potential treatment option for patients with IBD. In addition, these findings support that 5-HT7 is a viable therapeutic target for IBD.

5-HT1B receptor agonist enhances breakpoint for cocaine on a progressive ratio (PR) schedule during maintenance of self-administration in female rats but reduces breakpoint for sucrose.

Background: Previous research showed that the 5-HT1B receptor agonist CP94253 enhanced cocaine reinforcement rate during maintenance of daily self-administration (SA), but inhibited reinforcement rate after 21 days of abstinence in male rats. Here we examined whether female rats show similar effects of CP94253 during maintenance as males across estrous cycle phases. Methods: Female rats trained on a fixed ratio 5 (FR5) cocaine reinforcement schedule were tested for the effects of CP94253 (5.6 mg/kg, s.c.) on cocaine reinforcement rate during each phase of the estrous cycle, with access to either low (0.075 and 0.1875) or high (0.375 and 0.75) cocaine doses available for 1 h sequentially in descending dose order. Other female and male rats trained on a progressive ratio (PR) schedule of cocaine or sucrose reinforcement were tested for CP94253 (0, 3.2, 5.6, and 10 mg/kg, s.c.) effects on reinforcement rate in 3-h sessions. CP94253 effects on responding during sucrose cue-reactivity were also examined post-abstinence. Results: Regardless of sex, CP94253 enhanced breakpoints on the PR schedule during maintenance of cocaine SA but attenuated breakpoints for sucrose reinforcement and decreased responding during sucrose cue-reactivity. FR results showed that CP94253 attenuated cocaine reinforcement rate during all estrous cycle phases except metestrus. Conclusions: Overall, we suggest that CP94253 increased incentive motivation for cocaine during maintenance of SA in female and male rats, yet decreased motivation for sucrose. We also suggest that 5-HT1BRs modulate motivation similarly across sexes except when females are in metestrus.

5-HT1B receptor agonist attenuates cocaine self-administration after protracted abstinence and relapse in rats.

BACKGROUND: The 5-HT1B receptor (5-HT1BR) agonist, CP94253, enhances cocaine intake during maintenance of self-administration (SA) but attenuates intake after 21 days of forced abstinence in male rats. AIMS: We examined whether CP94253 attenuates cocaine intake in female rats after a period of abstinence, and if these attenuating effects persist or revert to enhancing cocaine intake during resumption (i.e. relapse) of daily cocaine SA. METHODS: Male and female rats trained to lever press on a fixed ratio 5 schedule of cocaine reinforcement underwent ⩾21 days of forced abstinence. They were then tested for the effects of CP94253 (5.6 mg/kg, SC) or vehicle on cocaine SA. During the test session, rats had 1-h access to the training dose of cocaine (0.75 mg/kg, IV) followed by 1-h access to a lower cocaine dose (0.075 mg/kg, IV). Rats then resumed cocaine SA for 15 days to mimic relapse and were retested as done previously. Subsequently, rats underwent abstinence again (21-60 days) and were tested for CP94253 effects on locomotion and cue reactivity (i.e. responding for light/tone cues previously paired with cocaine infusions). RESULTS: Regardless of sex, CP94253 decreased cocaine intake after abstinence and during resumption of SA and decreased cue reactivity while having no effect on locomotion. CONCLUSIONS: CP94253 decreases cocaine intake and cocaine seeking in both males and females even after resumption of cocaine SA. These findings suggest that the inhibitory effects of CP94253 observed after abstinence are long-lasting, and therefore, 5-HT1BR agonists may have clinical efficacy as anti-relapse medications for cocaine use disorders.

Pharmacology and Therapeutic Potential of the 5-HT7 Receptor.

It is well-documented that serotonin (5-HT) exerts its pharmacological effects through a series of 5-HT receptors. The most recently identified member of this family, 5-HT7, was first identified in 1993. Over the course of the last 25 years, this receptor has been the subject of intense investigation, and it has been demonstrated that 5-HT7 plays an important role in a wide range of pharmacological processes. As a result of these findings, modulation of 5-HT7 activity has been the focus of numerous drug discovery and development programs. This review provides an overview of the roles of 5-HT7 in normal physiology and the therapeutic potential of this interesting drug target.