Figure 4. Continuously active vasopressin neurones express functional κ-opioid receptors in euhydrated rats and dehydrated rats.

A and B, ratemeter records (in 10 s bins) of the activity of continuously active vasopressin neurones in a euhydrated rat (A) and a dehydrated rat (B). Injection of the κ-opioid receptor agonist U50,488H (U50; 1 mg kg⁻¹, i.v.) profoundly inhibited the firing rate of both neurones. C and E, the mean firing rates of continuously active vasopressin neurones recorded from euhydrated rats (C, n= 5) and dehydrated rats (E, n= 9) before (Pre-U50) and after injection of U50,488H (*P < 0.05 and ***P < 0.001, paired t test). D and F, the mean firing rates of continuously active vasopressin neurones recorded from euhydrated (D, n= 5) and dehydrated rats (F, n= 2) before (Pre-BNI) and during intra-supraoptic nucleus administration of the κ-opioid receptor antagonist nor-BNI over 60 min (BNI, 200 μg ml⁻¹).