Distribution and colocalization of neurotransmitters and receptors in the pre-Botzinger complex of rats

The pre- Botzinger complex (PBC), thought to be the center of respiratory r hythm generation, is a cell column ventrolateral to the nucleus ambiguus. T he present study analyzed its cellular and neurochemical composition in adu lt rats. PBC neurons were mainly oval, fusiform, or multipolar in shape and small to medium in size. Neurokinin-1 receptor, a marker of the PBC, was p resent in the plasma membrane of mostly medium and small neurons and their associated processes and boutons. Among neurons immunoreactive for differen t neurotransmitter or receptor candidates, various numbers were colocalized with neurokinin-1 receptor. The highest ratio was with nitric oxide syntha se (52.72%), and the lowest was with glycine receptors (31.93%). Glutamic a cid decarboxylase- and glycine transporter 2-immunoreactive boutons, as wel l as GABAA receptor-immunoreactive plasma membrane processes and boutons, w ere also identified in the PBC. PBC neurons exhibited different levels of c ytochrome oxidase activity, indicating their various energy demands. Our re sults suggest that synaptic interactions within the PBC of adult rats invol ve a variety of neurotransmitter and receptor types and that nitric oxide m ay play an important role in addition to glutamate, GABA, glycine, and neur okinin.