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

Study question: Are there differences in operant learning and memory between mice born through intracytoplasmic sperm injection (ICSI) and naturally-conceived control (CTL) mice? Summary answer: ICSI females exhibited deficits in acquisition learning relative to CTL females, whereas ICSI males exhibited deficiency in discrimination learning and memory relative to CTL males during initial assessments. ICSI and CTL groups exhibited equally poor long-term retention of learned discrimination and memory performances at old age. What is known already: Some human outcome studies have suggested that ICSI might be associated with an increased risk of certain cognitive disorders, but only one of two behavioral studies with ICSI mouse models have reported differences between ICSI and CTL females. No studies to date have investigated associative learning in ICSI mice. Study design, size, duration: 36 ICSI mice (18 male, 18 female) and 37 CTL mice (19 male, 18 female) aged 3-6 months were compared in a series of operant learning procedures that assessed acquisition of a new behavior, discrimination learning, and memory. 16 ICSI mice (9 male, 7 female) and 17 CTL mice (10 males, 7 females) received follow-up discrimination learning and memory assessments at 12 months of age (six months after the end of initial training) to evaluate retention and reacquisition of learned performances. Participants/materials, setting, methods: Mice received daily operant learning sessions in experimental chambers in which all stimulus events and the recording of responses were automated. Food rewards were delivered for responding under different conditions of reinforcement, which varied by procedure. Subjects received a successive series of sessions of nose poke acquisition training, discrimination training, and the delayed non-matching-to-position (DNTMP) memory procedure. Mixed repeated measures ANOVAs in which the between-subjects factor was group (ICSI vs. CTL) and the within-subjects factor was repeated exposures to learning procedures (i.e., sessions) were used to analyze data. Main results and the role of chance: In comparisons between all mice (i.e., males and females combined), CTL mice exhibited superior performance relative to ICSI in response acquisition (p = 0.03), discrimination (p = 0.001), and memory (p = 0.007). Sex-specific comparisons between the groups yielded evidence of sexual dimorphism. ICSI females exhibited a deficit in acquisition learning relative to CTL females (p