Structure and innervation of retia mirabilia of Bottlenose dolphin (Tursiops truncatus).

The cetaceans retia mirabilia represent a vascular network that supplies a preferred vascularization to organs that require high amounts of oxygen during diving. The present study, conducted in the perispinal retia mir-abilia of bottlenose dolphin (Tursiops truncatus), analyzed: nature of the blood vessels; innervation by the tyrosine hydroxylase (TH)-, neuronal nitric oxide synthase (nNOS)-, and substance P (SP)-immunoreactive (IR) fibers; co-localization in the nerve fibers of the antigens mentioned above. The results demonstrated that the perispinal retia mirabilia consists of arterial vessels (muscular arteries and arterioles) and, minimally, of venous vessels. In all types of vessels, the innervation was supplied mainly from TH-IR fibers. Even nNOS-IR fibers were numerous, especially at the level of arterioles; on the contrary, SP-IR fibers were observed in a small number of vessels. The fibers were located mainly in the tunica adventitia, but also between media and ad-ventitia tunicae. This research indicates that the perispinal retia mirabilia of bottlenose dolphin is innervated by sympathetic system (TH-IR fibers) and primary afferent neurons of the spinal ganglia (nNOS- and SP-IR fibers).The sympathetic system probably induces vasoconstriction and vasodilation by increasing and lowering its level of activity, respectively. Sensory fibers, especially through the local release of nitric oxide, are proba-bly involved in the regulation of vasodilatory processes. Since the sympathetic fibers appear in greater num-bers than those containing nNOS and SP, it is reasonable to hypothesize that the vasodilatory activity of pri-mary afferent fibers can be realized only by means of a simultaneous inhibition of sympathetic tone.