The presence of substance P (SP) and cholecystokinin (CCK) immunoreactive neurons was examined in the bottlenose dolphin dorsal root ganglia (DRGs) and spinal cord by immunohistochemical techniques. SPpositive and CCK-immunoreactive neurons were respectively $50% and 1% of the total number of ganglion cells examined and especially belonged to small and medium-sized cell populations. Using double labeling techniques we observed that SP-and CCK-immunoreactivity coexisted in a very low number of primary afferent neurons (2.7%). Few SPimmunoreactive (IR) neurons (2.7%) were also CCK-positive. On the contrary, 65% of CCK-immunoreactive neurons contained SP. Interestingly, we observed CCK-immunoreactive satellite glial cells located around large cell class somata. Virtually no SP-IR and CCK-positive neurons were surrounded by peripheral CCK-immunoreactive satellite glial cells. The SP-IR and CCK-positive nerve fibers were particularly conspicuous in the superficial layers of the spinal cord. The present study indicates that SP and CCK only partially overlap in the thoracic, lumbar, and caudal DRGs of the bottlenose dolphin, suggesting that the majority of SP-IR ganglion neurons are lacking in CCK-immunoreactivity. The role of SPcontaining DRG neurons is discussed also in relation to the huge vascular spinal retia mirabilia typical of cetaceans. Anat Rec, 293:477-484, 2010. V V C 2010 Wiley-Liss, Inc.

Dorsal root ganglia (DRGs) contain the cell bodies of primary afferent neurons that transmit sensory information from the periphery into the spinal cord. Distinct populations of DRG neurons have been characterized by a variety of different immunohistochemical markers. 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. Despite previous studies, no information is known on the presence and exact distribution of nNOS-immunoreactive neurons in the DRGs of the bottlenose dolphin. In this investigation, immunoperoxidase for nNOS was used to determine the distribution and the perikaryal size of nitrergic neurons in the DRGs of this species. Double immunofluorescence protocol was used to determine the percentage of nNOS-immunoreactive (IR) neurons over the total primary afferent neurons. In addition, double immunostaining was used to verify whether there was colocalization of nNOS with substance P (SP). In all DRGs, a subpopulation of small-and medium-sized neurons (about 9%) exhibited nNOS immunoreactivity. Data analysis revealed that the majority of nNOS-IR neurons (81.3%) expressed SP. The density of nNOS-immunoreactive and nNOS/SP-double immunopositive cells was relatively constant throughout the ganglia. However, as observed in others mammals, the number of nitrergic neurons decreased in the caudalmost DRGs. Our results, in conjunction with previous observations, suggest that nNOS-IR neurons may be involved in the afferent transmission of visceral and nociceptive information as well as in the regulation of the vascular tone. Anat Rec, 294:1066Rec, 294: -1073Rec, 294: , 2011. V V C 2011 Wiley-Liss, Inc.Key words: bottlenose dolphin; dorsal root ganglia; neuronal nitric oxide synthase; substance P Dorsal root ganglia (DRGs) contain the cell bodies of primary afferent neurons that convey somatic and visceral input from the body to the spinal cord. Several studies have indicated that primary afferent neurons of the DRGs can be classified in different populations on the basis of their morphological, physiological, and biochemical features (Lawson, 1992;Willis and Coggeshall, 2004). On the basis of cell body size, the DRG neurons of