Cholinergic activation of brain stem neurons increases intravesical pressure mediated by vasopressin release in female rats

      Background: Previous findings of our laboratory have shown that injection of the cholinergic agonist carbachol into the 4th brain ventricle (4th V) increases intravesical pressure (IP) with peak response at 30 minutes after injection. Aim: We investigated if carbachol injection into the 4th V induces vasopressin (AVP) or oxytocin (OT) release and the existence of AVP and OT receptors in the urinary bladder (UB). Methods: Female Wistar rats (~250 g, N = 6/group) implanted with guide cannulas into the 4th V five days prior to the experiments were anesthetized with 2% isoflurane in 100% O2, and carbachol (4 nmol/μL) or saline (1 μL) was injected into the 4th V. Thirty minutes after injection, a blood sample was collected and plasma AVP and OT was determined by ELISA kit (Cayman Chemical). In a different group of rats, gene expression in the UB for AVP1A, AVP1B, AVP2, OT recepμtors and cyclophilin (housekeeping gene) were investigated by qPCR. Data are as mean ± SE and were submitted to Student t-test (p < 0.05). Results: Carbachol induced plasma AVP release (3051 ± 85 pg/mL) compared to saline into the 4th V (2628 ± 276 pg/mL). No difference was observed in plasma OT in rats which received carbachol (532 ± 33 pg/mL) or saline (508 ± 38 pg/mL). All subytpes of AVP and OT receptors showed their genes expressed in the UB. Conclusion: Cholinergic activation of brain stem neurons by carbachol induces plasma AVP release. The increase in IP evoked by carbachol is likely due to AVP release which binds to AVP receptors in the urinary bladder. Financial support: FAPESP (grant# 2013/04550-5) and NEPAS.
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