Localization of nitric oxide-synthesizing neurons sending projections to the dorsal raphe nucleus of the rat

The origin of the nerve fibers immunoreactive for neuronal nitric oxide syn thase (nNOS) in the rat dorsal raphe nucleus (DRN) was determined by combin ing the use of cholera toxin subunit b (CTb) as a retrograde tracer and nNO S immunohistochemistry with a monoclonal anti-nNOS antibody. Double labeled CTb-nNOS cell bodies were distributed from the rostral diencephalon to the caudal medulla oblongata, in about 20 areas of the brain. Several of the a reas displaying double labeled cells are known for their involvement in the control of the sleep-wake cycle and/or transmission of nociception. (C) 19 98 Elsevier Science Ireland Ltd. All rights reserved.