Fig. 2: Chemogenetic inactivation of CA2 alters investigation of a CD1 mouse 24 h after defeat.
From: Hippocampal area CA2 activity supports social investigation following an acute social stress
a Acute social defeat experimental timeline. Five mg/kg of clozapine-N-oxide (CNO) was delivered on day 1, 45 min prior to defeat by a CD1 aggressor mouse via IP injection in Amigo2-icreERT2 male mice (15–19wks of age) that either did (Cre + ) or did not (Cre-) express cre-recombinase in area CA2 neurons. Twenty-four hours after defeat, day 2, mice were tested for avoidance/investigation in a novel context containing a littermate of the CD1 aggressor mouse. b (right) Amigo2-icreERT2-Cre+ mice show CA2 specific expression of the intracranially injected Gi-DREADD-mCherry construct 3+ weeks following injection (left). No expression of the Gi-DREADD construct was observed in Cre- mice. c Day 2, 24 h after defeat, both defeat populations spent significantly more time in the far zone of the novel arena, opposite the CD1 mouse (i.e. avoidance behavior), when compared to no defeat control mice. Cre+ defeated males, with CA2 activity inhibited, spent significantly more time in the far zone than Cre- defeated mice (No Defeat controls: 119.44 ± 5.7 s vs. Defeat Cre-: 188.60 ± 16.4 s vs. Defeat Cre + : 241.64 ± 12.7 s, N = 22, 18, 18, respectively, one-way ANOVA F = 28.19 p < 0.0001; No Defeat vs. Defeat Cre-, Holm-Sidak multiple comparisons test p = 0.0.0002, No Defeat vs. Defeat Cre + , Holm-Sidak multiple comparisons test p < 0.0001, Defeat Cre- vs. Defeat Cre + , Holm-Sidak multiple comparisons test p = 0.003). d Day 2, 24 h after defeat, Cre+ mice entered the interaction zone, surrounding the CD1 mouse, at a significantly lower frequency than both Defeat Cre- and No Defeat control mice (No Defeat controls: 73.09 ± 6.5 entries vs. Defeat Cre-: 32.5 ± 6.5 entries vs. Defeat Cre + : 16.17 ± 3.4 entries, N = 22, 18, 18 mice, respectively, one-way ANOVA F = 26.34 p < 0.0001; No Defeat vs. Defeat Cre-, Holm-Sidak p < 0.0001, No Defeat vs. Defeat Cre + , Holm-Sidak p < 0.0001, Defeat Cre- vs. Defeat Cre + , Holm-Sidak p = 0.062, unpaired t-test p = 0.034). e The increase in avoidance behavior (red) in Defeat Cre+ mice was driven by a loss of the more investigative phenotype (green) when CA2 activity was inhibited during aSD (Cre-: 61.1% investigative and 38.9% avoidance versus Cre + : 16.7% investigative and 83.3% avoidant, N = 18 & 18 mice respectively, Chi-square 40.69, z = 6.38, p < 0.0001). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.
