Retrospective study of vascular structures within the SDNPOA.This experiment was conducted in two steps. The initialstep included (a) review of thousands of histological and immunofluorescentimages that contained the SDN-POA and itssurrounding structures, obtained from 201 male and femaleSprague-Dawley rats (24 adults and 177 weanlings) fromtwo previous research projects (NCTR Protocol Nos. 00706and 00710); (b) identification and characterization of thesuspected vascular structures within or close to the SDNPOA;and (c) establishment of criteria for identifying vascularstructures. In subsequent steps, all images containing vascularstructures were identified logged and some were recopied andoptimized if necessary. Briefly, any pipe-like structure (arrowsin Fig. 1a), having a diameter between 10 and 20 μm andentering the SDN-POA in an ascending course (i.e., from thedirection of the cranial base), was counted as an identifiablesupply artery/arteriole of the SDN-POA.