Behavioral Effects of a Novel Benzofuranyl-Piperazine Serotonin-2C Receptor Agonist Suggest a Potential Therapeutic Application in the Treatment of Obsessive-Compulsive Disorder

Abstract

Selective serotonin reuptake inhibitors (SSRIs) are the only effective pharmacological treatments for obsessive-compulsive disorder (OCD). Nonetheless, their generally limited efficacy, side-effects, and delayed onset of action require improved medications for this highly prevalent disorder. Preclinical and clinical findings have suggested serotonin2C (5-HT_2C) receptors as a potential drug target. Data in rats and mice are presented here on the effects of a novel 5-HT_2C receptor agonist ((3S)-3-Methyl-1-[4-(trifluoromethyl)-7-benzofuranyl]-piperazine) (CPD 1) with high potency and full efficacy at 5-HT_2C receptors and less potency and partial agonism at 5-HT_2A and 5-HT_2B receptors. Effects of CPD 1 on consummatory (schedule-induced polydipsia in rats) and non-consummatory behaviors (marble-burying and nestlet-shredding in mice) that are repetitive and non-habituating were studied. We also evaluated the effects of CPD 1 in rats with isoproterenol- and deprivation-induced drinking in rats to compare with the polydipsia studies. The SSRIs, fluoxetine, and chlomipramine decreased the high rates of drinking in rats engendered by a schedule of intermittent food delivery (schedule-induced polydipsia). The effects of fluoxetine, but not of d-amphetamine, were prevented by the selective 5-HT_2C receptor antagonist SB242084. The 5-HT_2C receptor agonists Ro 60-0175 and CPD 1 also decreased drinking, but unlike the SSRIs and Ro 60-0175, CPD 1 dose-dependently decreased excessive drinking without affecting lever press responses that produced food. The effects of CPD 1 were prevented by SB242084. CPD 1 also suppressed drinking induced by isoproterenol and by water deprivation without affecting normative drinking behavior. CPD 1, like fluoxetine, also suppressed marble-burying and nestlet-shredding in mice at doses that did not affect rotarod performance or locomotor activity. The behavioral specificity of effects of CPD 1 against repetitive and excessive behaviors suggests a potential therapeutic application in OCD.

Keywords: 5-HT2C receptors; Ro 60-0175; SB242084; fluoxetine; marble-burying; obsessive–compulsive disorder; schedule-induced polydipsia.

Figure 1

Functional activity of CPD1 at 5-HT_2A,B,C receptors. Data are from experiments conducted with n = 15. Each data point represents the mean ± SEM.

Figure 2

Effects of SSRIs on schedule-induced polydipsia. Significant effects on the number of responses and amount of water consumed were produced by both fluoxetine (F_2,23 = 4.4, p < 0.001—responses; F_2,23 = 25, p < 0.0001—water) and clomipriamine (F_3,31 = 12.6, p < 0.0001—responses; F_3,31 = 20.5, p < 0.0001). Each point represents the mean ± SEM of eight rats.

Figure 3

Prevention of effects of fluoxetine by a 5HT_2C receptor antagonist. Fluoxetine (30 mg/kg, i.p.) significantly suppressed both the number of responses emitted and the amount of water consumed in rats under a schedule of food delivery engendering excessive drinking. Co-dosing with SB-242084 (3 mg/kg) significantly attenuated these decreases. Each bar represents the mean ± SEM of five to eight rats. *p < 0.05 compared to vehicle (Dunnett’s test). ^#p < 0.05 compared to fluoxetine alone (30 mg/kg) (Dunnett’s test).

Figure 4

Effects of 5-HT_2C receptor antagonism on the reductions in schedule-induced polydipsia produced by d-amphetamine. d-Amphetamine significantly enhanced the number of responses emitted (F_2,19 = 18.4, p < 0.0001) and significantly decreased the amount of water consumed (F_2,19 = 24.9, p < 0.0001). SB-242084 did not block these effects of d-amphetamine Each bar represents the mean ± SEM of five to eight rats. *p < 0.05 compared to vehicle (Dunnett’s test).

Figure 5

Effects of 5HT_2C receptor agonists on schedule-induced polydipsia. mCPP and Ro 60-0175 significantly decreased both the number of responses emitted and the amount of water consumed (mCPP: reponses—F_2,23 = 17.1, p < 0.0001; water—F_2,23 = 13.5, p < 0.001) (Ro-60-0175: responses—F_4,39 = 8.6, p < 0.0001; water—F_2,23 = 13.5, p < 0.001). In contrast, CPD1 dose-dependently suppressed excessive water drinking (F_3,31 = 9.5, p < 0.001) without affecting response output (F_3,31 = 0.37, p = 0.78). Each point represents the mean ± SEM of five to eight rats. *p < 0.05 compared to vehicle (Dunnett’s test).

Figure 6

Effects of 5-HT_2C receptor antagonism on the reductions in schedule-induced polydipsia produced by CPD 1. SB-242084prevented the decreases in excessive water consumption produced by CPD 1 (5.6 mg/kg) (F_4,25 = 6.0, p < 0.001) and significantly enhanced the number of responses emitted (F_4,25 = 3.1, p < 0.05). Each point represents the mean ± SEM of 6 rats/group. *p < 0.05 compared to vehicle (Dunnett’s test).

Figure 7

Effects of CPD1 on deprivation-induced drinking. Water deprivation significantly increased the amount of water consumed and this enhancement was prevented by CPD 1 (F_2,18 = 7.5, p < 0.01). Data are means ± SEM of 6–8 rats/group. *p < 0.05 compared to vehicle (Dunnett’s test).

Figure 8

Effects of CPD1 on isoproterenol-induced drinking. Isoproterenol significantly increased the amount of water consumed and this enhancement was prevented by 5.6 mg/kg CPD 1 (F_3,48 = 24.9, p < 0.0001) that did not significantly affect normal drinking (LY + Veh). Data are means ± SEM of 5 (vehicle)-20 rats/group. *p < 0.05 compared to vehicle (Dunnett’s test).

Figure 9

Effects if CPD1 on marble-burying behavior of mice over five consecutive days. Marble-burying was significantly decreased by CPD 1 (10 mg/kg) compared to vehicle-treated mice (F_1,110 = 59.4, p < 0.0001). There was also a significant impact of dosing day (F_4,110 = 5.2, p < 0.001) but no significant day × treatment interaction (F_4,110 = 0.31, p = 0.87). Data are means ± SEM of 12 mice/group. *p < 0.05 compared to day 1 (Dunnett’s test).

Figure 10

Effects of CPD1 on schedule-induced polydipsia over five consecutive days of dosing. CPD 1 (10 mg/kg) significantly decreased excessive water consumption (F_1,40 = 128.5, p < 0.0001) and to a lesser extent response output over 5 days (F_1,40 = 11.7, p < 0.05). The factor of day of dosing did not significantly impact effects of CPD1 (responses: F_4,40 = 0.11, p = 0.98; water: F_4,40 = 0.49, p = 0.74) nor was there any significant day × treatment interaction (responses: F_4,40 = 0.06, p = 0.99; water: F_4,40 = 1.37, p = 0.26). There was not a significant attenuation of the effect of CPD 1 over 5 days (F_4,20 = 1.46, p = 0.25). Data are means ± SEM of 5 rats/group.