Dudley J S, Paul J W, Teh V, Mackenzie T E, Butler T A, Tolosa J M, Smith R, Foley M, Dowland S, Thompson M B, Whittington C M
The University of Sydney, School of Life and Environmental Sciences, Heydon-Laurence Building (A08), Sydney, NSW, 2006, Australia.
School of Medicine and Public Health, College of Health, Medicine and Wellbeing, University of Newcastle, Callaghan, NSW, 2308, Australia; Hunter Medical Research Institute, 1 Kookaburra Circuit, New Lambton Heights, NSW, 2305, Australia.
Placenta. 2022 Sep;127:88-94. doi: 10.1016/j.placenta.2022.07.015. Epub 2022 Aug 6.
Syngnathids (seahorses, pipefishes and seadragons) are among the few vertebrates that display male pregnancy. During seahorse pregnancy, males incubate developing embryos embedded in a placenta within a fleshy brood pouch, before expelling fully developed neonates at parturition. The mechanisms underpinning seahorse parturition are poorly understood.
We examined the morphology of the brood pouch using microcomputed tomography and histological techniques, in combination with physiological assays, to examine how male pot-bellied seahorses (Hippocampus abdominalis) control labour. In female-pregnant vertebrates, nonapeptide hormones (such as vasopressin- and oxytocin-like hormones) produce contractions of gestational smooth muscle to produce labour.
Histological analysis of the seahorse brood pouch reveals only scattered small smooth muscle bundles in the brood pouch, and in-vitro application of isotocin (a teleost nonapeptide hormone) to the brood pouch do not produce measurable muscle contractions. Micro-computed tomography shows differences in size and orientation of the anal fin assembly between male and female pot-bellied seahorses, and histological analysis reveals large skeletal muscle bundles attached to the anal fin bones at the male brood pouch opening.
We conclude that seahorse parturition may be facilitated by contraction of these muscles, which, in combination with body movements, serves to gape open the pouch and expel the neonates. Future biomechanical studies are needed to test this hypothesis.
海龙科鱼类（海马、管口鱼和叶形海龙）是少数表现出雄性怀孕的脊椎动物。在海马怀孕期间，雄性会在肉质育儿袋中孵化嵌入胎盘的发育中胚胎，然后在分娩时排出完全发育的幼体。海马分娩的机制尚不清楚。
我们使用微型计算机断层扫描和组织学技术，并结合生理学分析，研究了大腹海马（Hippocampus abdominalis）育儿袋的形态，以探究雄性如何控制分娩。在雌性怀孕的脊椎动物中，九肽激素（如加压素和催产素样激素）会引起妊娠平滑肌收缩以引发分娩。
对海马育儿袋的组织学分析显示，育儿袋中只有散在的小平滑肌束，并且在体外将异催产素（一种硬骨鱼九肽激素）应用于育儿袋并不会产生可测量的肌肉收缩。微型计算机断层扫描显示，雄性和雌性大腹海马的臀鳍组件在大小和方向上存在差异，组织学分析显示，在雄性育儿袋开口处有大的骨骼肌束附着在臀鳍骨上。
我们得出结论，这些肌肉的收缩可能有助于海马分娩，这些肌肉与身体运动相结合，有助于张开育儿袋并排出幼体。未来需要进行生物力学研究来验证这一假设。
