Assessment of Operant Learning and Memory in Mice Born through Intracytoplasmic Sperm Injection

Abstract

21Study question: Are there differences in operant learning and memory between mice born 22 through intracytoplasmic sperm injection (ICSI) and naturally-conceived control (CTL) mice? 23 Summary answer: ICSI females exhibited deficits in acquisition learning relative to CTL 24 females, whereas ICSI males exhibited deficiency in discrimination learning and memory 25 relative to CTL males during initial assessments. ICSI and CTL groups exhibited equally poor 26 long-term retention of learned discrimination and memory performances at old age. 27What is known already: Some human outcome studies have suggested that ICSI might be 28 associated with an increased risk of certain cognitive disorders, but only one of two behavioral 29 studies with ICSI mouse models have reported differences between ICSI and CTL females. No 30 studies to date have investigated associative learning in ICSI mice. 31 Study design, size, duration: 36 ICSI mice (18 male, 18 female) and 37 CTL mice (19 male, 18 32 female) aged 3-6 months were compared in a series of operant learning procedures that assessed 33 acquisition of a new behavior, discrimination learning, and memory. 16 ICSI mice (9 male, 7 34 female) and 17 CTL mice (10 males, 7 females) received follow-up discrimination learning and 35 memory assessments at 12 months of age (six months after the end of initial training) to evaluate 36 retention and reacquisition of learned performances. 37 Participants/materials, setting, methods: Mice received daily operant learning sessions in 38 experimental chambers in which all stimulus events and the recording of responses were 39 automated. Food rewards were delivered for responding under different conditions of 40 reinforcement, which varied by procedure. Subjects received a successive series of sessions of 41 nose poke acquisition training, discrimination training, and the delayed non-matching-to-position 42 (DNTMP) memory procedure. Mixed repeated measures ANOVAs in which the between-43Operant Learning in ICSI Mice 3 subjects factor was group (ICSI vs. CTL) and the within-subjects factor was repeated exposures 44 to learning procedures (i.e., sessions) were used to analyze data. 45Main results and the role of chance: In comparisons between all mice (i.e., males and females 46 combined), CTL mice exhibited superior performance relative to ICSI in response acquisition (p 47 = 0.03), discrimination (p = 0.001), and memory (p = 0.007). Sex-specific comparisons between 48 the groups yielded evidence of sexual dimorphism. ICSI females exhibited a deficit in 49 acquisition learning relative to CTL females (p < 0.001) but there was not a significant difference 50 between CTL and ICSI males. In the discrimination and memory tasks, ICSI males exhibited 51 deficits relative to CTL males (p = 0.002 and p = 0.02, respectively) but the differences between 52 females in these tasks were not significant. There was no difference in discrimination or memory 53 retention/re-acquisition assessments conducted with mice at 12 months of age. ICSI males and 54 fema...