A, example ratemeter recordings of vasopressin neurone firing rate (in 30 s bins) from urethane‐anaesthetised virgin (left) and lactating (right) female Sprague–Dawley rats, showing that i.c.v. administration of 2 μg prolactin (PRL) reduces firing rate in the neurone from the lactating rat but not in the neurone from the virgin rat. B, mean (±SEM) vasopressin neurone firing rate (in 30 s bins) before and after i.c.v. administration of 2 μg prolactin in virgin rats (blue symbols) and lactating rats (red symbols); data from 1 μg prolactin injections have been omitted for clarity. C, mean vasopressin neurone firing rate averaged over 5 min before and after i.c.v. administration of 1 and 2 μg prolactin in virgin rats (left panel) and lactating rats (right panel); ns
P > 0.05 (t
13 = 1.15 after 1 μg in virgin rats, t
10 = 0.26 after 2 μg in virgin rats and t
7 = 1.84 after 1 μg in lactating rats), **
P < 0.01 (t
5 = 4.40) vs. pre‐prolactin, paired t test. [Color figure can be viewed at wileyonlinelibrary.com]