Voluntary locomotion linked with cerebral activation is reduced in vasopressin V1a receptor knockout mice

Abstract

We have reported that cerebral activation suppressed baroreflex control of heart rate (BR), followed by voluntary locomotion at higher probability. In this study, we examined whether vasopressin V1a receptor was involved in these responses by using free-moving V1a receptor knockout (KO, n=8) and wild-type mice (WT, n=8). BR sensitivity (ΔHR/ΔMAP) was determined from heart rate response (ΔHR) to spontaneous change in mean arterial pressure (ΔMAP) every 4 s during a total resting period for ~8.5 h of 12 daytime hours. ΔHR/ΔMAP was adopted in the periods where cross-correlation function (R(t)) between ΔHR and ΔMAP was significant (P<0.05). The cerebral activity was determined from the power density ratio of θ to δ wave band (θ/δ) in electroencephalogram every 4 s. We found that spontaneous change in θ/δ synchronized with R(t) in both groups; however, the significant correlation occurred during 38±4% of the total resting period in KO, shorter than 62±3% in WT (P<0.001). When R(t) and ΔHR/ΔMAP were divided into 6 bins according to θ/δ, neither was positively correlated with θ/δ in KO (both, P>0.1) while both were in WT (both, P<0.001). Moreover, the probability that mice started to move after an increase in θ/δ was 24±4% in KO, lower than 61±5% in WT (P<0.001) with less suppression of BR. Thus, V1a receptor plays an important role in starting voluntary locomotion after cerebral activation through suppression of BR.