Postnatal development of excitatory innervations in longitudinal smooth muscle of the chicken anterior mesenteric artery

AimsThe anterior mesenteric artery of chickens contains a well-developed outer longitudinal smooth muscle layer in addition to an inner circular layer. Cholinergic and purinergic neurons play crucial roles in excitatory transmission at the longitudinal smooth muscle. The aim of this study was to clarify postnatal development of excitatory neurotransmission of the longitudinal smooth muscle.Main methodsMembrane potentials of smooth muscle were recorded with a microelectrode technique. Perivascular nerves were stimulated by applying electrical field stimulation (EFS).Key findingsHistological examination showed that longitudinal smooth muscles exist in the artery at birth. EFS failed to evoke membrane response in 1-day-old chickens, though it caused depolarization (excitatory junction potential; EJP) in 12-week-old chickens. However, exogenous application of acetylcholine (ACh) or ATP produced depolarization in longitudinal smooth muscle of 1-day-old chickens, suggesting that responsiveness of smooth muscle to excitatory neurotransmitters is already established at birth. In preparations isolated from 10-day-old chickens, EFS caused EJP, which was totally blocked by atropine but not by a non-specific purinoceptor antagonist, suramin. Several purinoceptor subtypes including P2Y1, which may be related to depolarizing response in smooth muscle of adult chickens, were expressed in the anterior mesenteric artery of 10-day-old chickens.SignificanceExcitatory innervation in longitudinal smooth muscle of the chicken anterior mesenteric artery is not established at birth but develops during the early postnatal period. Moreover, development of cholinergic excitatory innervation precedes that of purinergic excitatory innervation, although receptors that mediate purinergic control are already expressed in smooth muscle.