Anhedonia in the Shadow of Chronic Social Defeat Stress, or when the Experimental Context Matters

Abstract

One of the core symptoms of major depression in human is anhedonia. For that reason, one of the main requirements towards experimental depression models is that they be able to demonstrate anhedonia in animals, that have been exposed to stressful events, and other behavioral changes attributable to a depression-like state. However, the results presented in the literature are contradictory: sweet solution intake, which is considered as a parameter of hedonic/anhedonic behavior in animals, responds quite differently to stressful situations in that it is either unaffected or increased or decreased. Different experimental designs used for the study of anhedonia in male mice exposed to chronic social defeat stress were tried to understand the reasons for so contradictory responses. Anhedonia appears as an abrupt reduction in sweet solution consumption in stressed animals and by failure to attain recovery after deprivation. However, it was also demonstrated that sucrose solution intake and preference strongly depend on the experimental context; that the possible critical factor may be prior acquaintance with the hedonic stimulus -or the lack whereof. Analysis of literature data and ours allowed us to conclude that the lack of a significant decrease in sweet solution intake in stressed animals is no evidence of lack of depression. This decrease is evidence of anhedonia only provided other symptoms of depression are present. Hedonic consumable intake can be decreased over various motivations, conditions or diseases, in particular, a high level of anxiety or pathological aggression.

Extended Effect of Chronic Social Defeat Stress in Childhood on Behaviors in Adulthood

“…Notably, the changes in adolescent behaviors under chronic SDS are similar to those in adult males in similar experimental paradigms. In adult mice, long SDS dramatically increases anxiety and depressiveness, decreases sucrose consumption [ 35 ] , [36] , [ 37 ] , disturbs social communications, and increases repetitive behaviors [ 38 ] . However, there are also important distinctions in the response of adults and adolescents to SDS: while in adult males depressiveness was shown to develop after 21 days of SDS in our experimental paradigm [ 35 ] , in SDS adolescents a depressive-like state develops faster, appearing after 14 days in the Porsolt test as longer periods of passive behavior ( Fig.…”

Correlation of Expression Changes between Genes Controlling 5-HT Synthesis and Genes Crh and Trh in the Midbrain Raphe Nuclei of Chronically Aggressive and Defeated Male Mice

“…Male mice exhibiting repeated aggression in daily agonistic interactions enter a pathological psychotic-like state characterized, e.g., by symptoms of increased aggressiveness, hyperactivity, stereotypical behavior, and disturbances in social recognition (reviewed in [20,21]). Mice with chronic social defeat experience develop a mixed anxiety/depression-like state with symptoms of hypoactivity, behavioral deficits, anhedonia, and other problems [22][23][24][25][26]. We have previously demonstrated that, in the MRNs of both groups of animals with the opposite social experiences, there is underexpression of several key genes responsible for the synthesis, transport, and binding of serotonin [27][28][29].…”