Figure 3. κ-Opioid receptor antagonism increases the activity of phasic vasopressin neurones in euhydrated and dehydrated rats.

A and B, ratemeter recordings (in 1 s bins) of the firing rates of phasic vasopressin neurones in a euhydrated rat (A) and a dehydrated rat (B) before and during microdialysis administration of nor-binaltorphimine (BNI, 200 μg ml⁻¹). The insets show a 2 min period of firing before and during nor-BNI administration. C–F, the mean firing rate (C), intraburst firing rate (D), burst duration (E) and interburst interval (F) of nine phasic vasopressin neurones recorded from euhydrated rats (n= 5) and dehydrated (n= 4) rats. Note that the nor-BNI induced changes in activity were independent of the hydration status of the animals: two-way repeated measures ANOVA showed that dehydration increased firing rate (P= 0.01) as did nor-BNI (P= 0.005), but with no interaction between hydration status and nor-BNI (P= 0.51); dehydration (P= 0.009), but not nor-BNI (P= 0.08), increased intraburst firing rate; nor-BNI (P= 0.003), but not dehydration (P= 0.73), increased burst duration; nor-BNI (P= 0.04), but not dehydration (P= 0.30), decreased interburst interval; (*P≤ 0.05 and **P≤ 0.01). G, the mean intraburst firing rates (in 5 s bins, and aligned to peak intraburst firing) of the nine phasic neurones (euhydrated and dehydrated), recorded before and during administration of nor-BNI. H, the difference in intraburst firing rate of the cells from G, showing a progressive increase in the nor-BNI-induced difference in firing rate over the first 50 s of bursts (Pearson product moment correlation coefficient = 0.67, P= 0.03).