Figure 3. Cocaine-conditioned oestrus females exhibit enhanced VTA and NAc responses to cocaine-associated cues.

(a) Timeline of CPP experiments and paired fibre photometry recordings during choice test 24 h after the last conditioning session. (b) Schematic of recording experiments for VTA cell body recordings, which were taken during the choice test, 24 h after the last conditioning session. (c) Representative VTA Ca²⁺ activity trace during choice test demonstrating increases in activity preceding entry (dashed line) into the drug-paired (blue) chamber (left); averaged Ca²⁺ activity in a 10 s window around paired chamber entry (right). (d) The amplitude (ΔF/F) of the spike in Ca²⁺ activity preceding cocaine-paired chamber entry was increased in oestrus-conditioned female mice (one-way analysis of variance (ANOVA); F_{(2, 9)}=6.603, P<0.05; *P<0.05; ^#P<0.05) when compared with males (#) or dioestrus females (*). (e) Heat maps of Ca²⁺ activity over time during successive entries (rows) into the cocaine-paired chamber across groups. (f) Correlation between the amplitude of VTA response to the cocaine-paired context and preference score for cocaine (r=0.881; P<0.0001). (g) Schematic of recording experiments for NAc recordings taken at the same time as VTA recordings during the choice test 24 h after the last conditioning session. (h) Representative Ca²⁺ activity trace, from the same animal as depicted in c, showing VTA terminal activity in the NAc around cocaine-paired (blue) and unpaired (red) entry where dashed lines denote entry into the cocaine-paired chamber (left); averaged Ca²⁺ activity in a 10 s window around paired chamber entry (right). (i) The amplitude of the spike in VTA terminal Ca²⁺ activity in NAc preceding cocaine-paired chamber entry was increased in oestrus-conditioned female mice (Kruskal–Wallis (KW); χ² ₍₂₎=8.122, P<0.01; *P<0.05). (j) Heat maps of Ca²⁺ activity over time during successive entries (rows) into the cocaine-paired chamber across groups. (k) Correlation between the amplitude of VTA terminal Ca²⁺ activity in NAc to the cocaine-paired context and CPP for cocaine (r=0.883; P<0.0001). *P<0.05 versus dioestrus; ^#P<0.05 versus male. Data represented as mean±s.e.m.