Olfactory Bulbectomy Model of Depression Lowers Responding for Food in Male and Female Rats: The Modulating Role of Caloric Restriction and Response Requirement

Abstract

Depression is a psychiatric disorder characterized by a marked decrease in reward sensitivity. By using the olfactory bulbectomy (OBX) model of depression, it was shown that OBX rats display enhanced drug-taking and seeking behaviors in a self-administration paradigm than sham-operated (SHAM) controls, and sex is an important regulating factor. To reveal potential strain effects, we compared the operant behavior of male and female Sprague-Dawley and Wistar OBX and SHAM rats trained to self-administer palatable food pellets. Results showed that Sprague-Dawley OBX rats of both sexes exhibited lower operant responding rates and food intake than SHAM controls. Food restriction increased responding in both OBX and SHAM groups. Female rats responded more than males, but the OBX lesion abolished this effect. In Wistar rats, bulbectomy lowered food self-administration only during the last training days. Food self-administration was not significantly affected in Wistar rats by sex. In summary, this study showed that bulbectomy significantly reduces operant responding and food intake in male and female Sprague-Dawley rats while inducing a mild reducing effect only in the Wistar strain. Strain-dependent effects were also observed in the modulating role of sex and food restriction on operant responding and palatable food intake.

Keywords: depression; olfactory bulbectomy; reward; self-administration; sex; strain.

Figure 1

Self-administration of sweet pellets in male SD rats. The graphs present the mean ± SEM of daily numbers of active lever presses (A), inactive lever presses (B), and cumulative numbers of self-administered pellets (C) in all experimental groups. The tables summarize the results of RM ANOVA and Bonferroni’s post-test for each variable (* p < 0.05, ** p < 0.01, *** p < 0.001 and ^# p < 0.05, ^### p < 0.001 for day*feeding interaction). N/A: not applicable; n.s.: not significant.

Figure 2

Self-administration of sweet pellets in female SD rats. The graphs present the mean ± SEM of daily numbers of active lever presses (A), inactive lever presses (B), and cumulative numbers of self-administered pellets (C) in all experimental groups. The tables summarize the results of RM ANOVA and Bonferroni’s post-test for each variable (* p < 0.05, ** p < 0.01, *** p < 0.001 and ^## p < 0.01, ^### p < 0.001 for day*feeding interaction). N/A: not applicable; n.s.: not significant.

Figure 3

Sex differences in the self-administration of sweet pellets in SD rats. The graphs present the mean ± SEM of daily numbers of active lever presses (A) and cumulative numbers of self-administered pellets (B) in ad libitum-fed experimental groups of both sexes. The tables summarize the results of RM ANOVA and Bonferroni’s post-test for each variable (* p < 0.05, ** p < 0.01, *** p < 0.001). N/A: not applicable; n.s.: not significant.

Figure 4

Self-administration of sweet pellets in male WI rats. The graphs present the mean ± SEM of daily numbers of active lever presses (A), inactive lever presses (B), and cumulative numbers of self-administered pellets (C) in all experimental groups. The tables summarize the results of RM ANOVA and Bonferroni’s post-test for each variable (* p < 0.05, ** p < 0.01, *** p < 0.001). N/A: not applicable; n.s.: not significant.

Figure 5

Self-administration of sweet pellets in FEMALE WI rats. The graphs present the mean ± SEM of daily numbers of active lever presses (A), inactive lever presses (B), and cumulative numbers of self-administered pellets (C) in all experimental groups. The tables summarize the results of RM ANOVA and Bonferroni’s post-test for each variable (* p < 0.05, ** p < 0.01, *** p < 0.001). N/A: not applicable; n.s.: not significant.

Figure 6

Sex differences in the self-administration of sweet pellets in WI rats. The graphs present the mean ± SEM of daily numbers of active nose-pokes (A) and cumulative numbers of self-administered pellets (B) in ad libitum-fed experimental groups of both sexes. The tables summarize RM ANOVA and Bonferroni’s post-test results for each variable (* p < 0.05, *** p < 0.001). N/A: not applicable; n.s.: not significant.