a–d, In situ hybridization for Esr1 mRNA in Esr1cre/+ male (a, b, red) and female (c, d, red) mice (Bregma ∼−1.65 mm). b, d are the boxed areas in a–c. Note that the expression of Esr1 mRNA in VMHvl (dotted outline) is higher in females than in males. e–g, Immunofluorescence showing that expression of a Cre-dependent hrGFP reporter expressed from a stereotaxically injected AAV (f, green) is restricted to VMHvl, without detectable spillover expression in the nearby arcuate hypothalamic nucleus (ARH). h–s, Double labelling for behaviourally-induced c-Fos (h, k, n, q, anti-c-Fos, green) and Esr1 (i, l, o, r, anti-Esr1, red) in wild-type male residents following a 30-min resident–intruder test with no (h–j, n = 3), male (k–m, close investigation without attack, n = 4; q–s, attack, n = 5) or female (n–p, mating, n = 5) intruders. t–v, Quantification of the fraction of total (NISSL+) cells that were c-Fos+ following different behaviours (t), fraction of c-Fos+ that were Esr1+ for each behaviour (u), and fraction of NISSL+ cells that are Esr1+ (v) in VMHvl, quantified from data as illustrated in h–s. *P < 0.05, ***P < 0.001, ****P < 0.0001; one-way ANOVA with Dunnett’s multiple comparisons test.