Voluntary locomotion linked with cerebral activation is mediated by vasopressin V1a receptors in free-moving mice

We previously reported that cerebral activation suppressed baroreflex control of heart rate (HR) at the onset of voluntary locomotion. In the present study, we examined whether vasopressin V1a receptors in the brain were involved in these responses by using free-moving V1a receptor knockout (KO, n= 8), wild-type mice locally infused with a V1a receptor antagonist into the nucleus tractus solitarii (BLK, n= 8) and control mice (CNT, n= 8). Baroreflex sensitivity (HR/MAP) was determined from HR response (HR) to a spontaneous change in mean arterial pressure (MAP) every 4 s during the total resting period, which was similar to 8.7 h, of the 12 h measuring period in the three groups. HR/MAP was determined during the periods when the cross-correlation function (R(t)) between HR and MAP was significant (P < 0.05). Cerebral activity was determined from the power density ratio of to wave band (/) on the electroencephalogram every 4 s. Spontaneous changes in / were significantly correlated with R(t) during 62 +/- 3% of the total resting period in CNT (P < 0.05), but only 38 +/- 4% in KO and 47 +/- 2% in BLK (vs. CNT, both P < 0.001). When R(t) and HR/MAP were divided into six bins according to the level of /, both were positively correlated with / in CNT (both P < 0.001), while neither was correlated in KO or BLK (all P > 0.05). Moreover, the probability that mice started to move after an increase in / was 24 +/- 4% in KO and 24 +/- 6% in BLK, markedly lower than 61 +/- 5% in CNT (both P < 0.001), with no suppression of the baroreflex control of HR. Thus, central V1a receptors might play an important role in suppressing baroreflex control of HR during cerebral activation at the onset of voluntary locomotion.