Evidence for Distinct Forms of Compulsivity in the SAPAP3 Mutant-Mouse Model for Obsessive-Compulsive Disorder

Abstract

The specific mechanisms underlying compulsive behavior in obsessive-compulsive disorder (OCD) are unknown. It has been suggested that such compulsivity may have its origin in cognitive dysfunction such as impaired processing of feedback information, received after the completion of goal-directed actions. The signal attenuation (SA) task models such a processing deficit in animals by attenuating the association strength between food reward and audiovisual feedback (signal) presented after performance of an operant response. The compulsive-like responding resulting from SA is well characterized in rats, but was so far not established in mice, a species for which powerful genetic OCD models exist. Thus, first, we demonstrate that the SA task can be implemented in mice and show that attenuation of reward-associated response feedback produces similar behavior in C57BL/6 mice as previously reported in rats. Second, we tested the hypothesis that SAPAP3 knock-out mice (SAPAP3^-/-), prone to exhibit several OCD-like abnormalities including excessive grooming, show enhanced compulsive-like behavior in the SA task compared with their wild-type (WT) littermates. However, task-related compulsivity measures in SAPAP3^-/- and WT did not yield significant differences, neither following SA nor during "regular" extinction of operant behavior. Thus, compulsive-like instrumental behavior following feedback distortion was not potentiated in compulsively grooming mice, implicating specifically that (1) a general deficit in feedback processing is not related to excessive grooming in SAPAP3^-/- and (2) different manifestations of compulsivity may be driven by independent mechanisms.

Keywords: SAPAP3 knock-out mice; compulsivity; feedback processing; obsessive-compulsive disorder; signal attenuation.

Figure 1.

Experimental design of the mouse SA task. Training and testing procedures are based on the original rat version of the SA task (Joel and Avisar, 2001; Joel, 2006). At the beginning of the task animals learn to associate delivery of a food reward with an audiovisual feedback signal that indicates that food is available in the food magazine (stage 1, Mag training). Thereafter, animals learn that making a nose poke during illumination of a cue light leads to delivery of a food reward, accompanied by the signal (stage 2, nose-poke training; NP). Subsequently, half of the animals are exposed to the SA procedure (stage 3, SA) in which the information value of the signal is decreased by presenting the signal without food reward (simulation of feedback deficiency). Finally, all animals are tested under extinction conditions (stage 4, extinction test). Compulsivity measures (UCTs, ENPs) will be compared between animals that were exposed to SA prior and those that were not (experienced the extinction test only, i.e., RE without prior manipulation of the feedback signal).

Figure 2.

Validation of the SA task in mice. A, Number of training sessions until reaching criteria (in Mag and nose-poke training; stages 1 and 2). Stage 2 consisted of two parts: nose-poke training with 30 trials (NP 30) and nose-poke training with 50 trials (NP 50). B, Magazine entries of C57BL/6-SA mice declined across SA sessions (stage 3), demonstrating effective ‘attenuation’ of the feedback signal (i.e., attenuation of the association strength between signal and reward). C, In the final extinction test (stage 4), C57BL/6-SA mice (n = 12) showed significantly more UCTs in comparison with C57BL/6-RE mice (i.e., mice that underwent only RE in stage 4 without prior SA; n = 12). D, The mean number of UCT was significantly higher in SA mice in four out of five trial blocks. E, All animals increased the number of ENPs in the final extinction test. However, ENP of C57BL/6-SA mice were significantly higher compared with C57BL/6-RE mice in the final extinction test (stage 4). F, Examination of ENP in UCT showed increased compulsivity in C57BL/6-SA compared with C57BL/6-RE, demonstrating successful implementation of the SA task in mice. Mag, food magazine; NP, nose poke. Data are expressed as mean ± SEM. *p < 0.05.

Figure 3.

Training performance of SAPAP3^-/- and WT in the SA task. A, Number of training sessions until reaching criteria (in Mag and nose-poke training; stages 1 and 2). Stage 2 consisted of two parts: nose-poke training with 30 trials (NP 30) and nose-poke training with 50 trials (NP 50). WT-RE and WT-SA required a similar number of training sessions to reach task criteria. B, There was no difference between SAPAP3^-/--RE and SAPAP3^-/--SA in the number of training sessions until reaching task criteria. While SAPAP3^-/- required a few more sessions of Mag and NP 30 training than WT, overall genotype comparison in SA and RE condition did not reveal significant differences, confirming that both genotypes acquired the task equally. C, Following NP 50 training, half of the WT and half of the SAPAP3^-/- were subjected to the SA procedure (stage 3, SA) in which the information value of the signal is decreased by presenting the signal without food reward (simulation of feedback deficiency). In WT-SA, magazine entries declined across three successive SA sessions, demonstrating effective attenuation of the feedback signal. D, In SAPAP3^-/--SA, effective attenuation of the feedback signal was also demonstrated by decreasing magazine entries of across SA training sessions. No difference was observed between the number of magazine entries of WT and SAPAP3^-/-, suggesting that the association between signal and reward was attenuated effectively in both genotypes (SAPAP3^-/-: SA = 15, RE = 16; WT: SA = 17, RE = 13). Data are expressed as mean ± SEM. *p < 0.05.

Figure 4.

SAPAP3^-/- are not more compulsive than WT in the SA task. A, SAPAP3^-/- do not show a general deficit in feedback processing, as compulsive responding during the extinction test (stage 4) of the SA paradigm was similar to that of normal WT controls. Both WT-SA and SAPAP3^-/--SA showed more UCTs than WT-RE and SAPAP3^-/--RE, respectively, confirming that the SA stage (stage 3) was effective in inducing compulsive-like responding. B, ENPs in UCT, an important indicator of compulsivity, was similar between SAPAP3^-/- and WT mice that underwent SA, suggesting that genetic deletion of SAPAP3 does not potentiate SA-induced compulsivity. ENP in UCT were increased in WT-SA and SAPAP3^-/--SA compared with WT-RE and SAPAP3^-/--RE, respectively, confirming that the SA stage was effective. C, A genotype difference was found in the number of ENP in CTs. During RE, SAPAP3^-/- showed reduced numbers of ENP in CT, indicative of rapid extinction learning or altered vigor for obtaining rewards. D, During the extinction test (stage 4), SAPAP3^-/--RE groomed significantly more than WT-RE. In contrast, grooming was similar between genotypes after SA. E, F, During the extinction test (stage 4), a positive correlation was observed between grooming and ENP in UCT for SAPAP3^-/--SA but not for SAPAP3^-/--RE. WT mice showed a positive correlation between grooming and ENP in UCT in the regular-extinction condition but not following SA. The average duration of the extinction test varied between 39 and 41 min (SAPAP3^-/-: SA =15, RE = 16; WT: SA = 17, RE = 13). Data are expressed as mean ± SEM. *p < 0.05.

Figure 5.

SAPAP3^-/- groom significantly more than WT in various contexts. A, During the extinction test (stage 4), grooming is significantly higher in SAPAP3^-/- compared with WT in the RE condition, both during the ITI and during illumination of the cue light (indicator that an operant response is required). However, grooming during cue light presentation was not correlated with overall task performance (data not shown), suggesting that attention to behaviorally relevant cues was not diminished in SAPAP3^-/-. B, Additionally, grooming was scored in the open field (OF). Results show increased grooming behavior of SAPAP3^-/- compared with WT. C, SAPAP3^-/- and WT were exposed to a 5-min test on the elevated plus maze (EPM). SAPAP3^-/- spent more time grooming than WT mice on the EPM; RE, average duration extinction test 39–41 min; OF, test duration 60 min; EPM, test duration 5 min (SAPAP3^-/-: SA = 15, RE = 16; WT: SA = 17, RE = 13). Data are expressed as mean ± SEM. *p < 0.05.