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 rhythm generation, is a cell column ventrolateral to the nucleus ambiguus. The present study analyzed its cellular and neurochemical composition in adult 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 present in the plasma membrane of mostly medium and small neurons and their associated processes and boutons. Among neurons immunoreactive for different neurotransmitter or receptor candidates, various numbers were colocalized with neurokinin-1 receptor. The highest ratio was with nitric oxide synthase (52.72%), and the lowest was with glycine receptors (31.93%). Glutamic acid decarboxylase- and glycine transporter 2-immunoreactive boutons, as well as GABAA receptor-immunoreactive plasma membrane processes and boutons, were also identified in the PBC. PBC neurons exhibited different levels of cytochrome oxidase activity, indicating their various energy demands. Our results suggest that synaptic interactions within the PBC of adult rats involve a variety of neurotransmitter and receptor types and that nitric oxide may play an important role in addition to glutamate, GABA, glycine, and neurokinin.