Immunohistochemical localization of substance P and neuronal nitric oxide synthase in the spinal ganglia of the bottlenose dolphin (Tursiops truncatus)

Spinal ganglia (SG) contain the somata of primary afferent neurons that transmit sensory information from the periphery into the spinal cord. A subpopulation of ganglionic neurons containing neuronal nitric oxide synthase (nNOS), an enzyme known to generate nitric oxide, has been detected in a number of mammalian species. In this study, the presence of nNOS-immunoreactive (IR) neurons was examined in the bottlenose dolphin SG by immunohistochemical techniques. Double immunostaining was used to verify whether there was colocalization of nNOS with substance P (SP). In all SG, a subpopulation of small- and medium-sized neurons exhibited nNOS immunoreactivity. Data analysis revealed that the majority of nNOS-IR neurons expressed SP. On the contrary, few SP-IR neurons were also nNOS-positive The density of nNOS-immunoreactive and nNOS/SP-double immunopositive cells was relatively constant throughout the ganglia. The results of the present study suggest that nNOS-IR neurons may be involved in the afferent transmission of visceral and nociceptive information as well as in the control of the flow circulation in the retia mirabilia.