NK1 receptor and the ventral medulla of the rat: bulbospinal and catecholaminergic neurons.

Bulbospinal C1 neurons are sympathoexcitatory and excited by substance P. However the substance P receptor (NK1 receptor), has been reported to be absent from the somata of C1 neurons. In this study, using double and triple labelling immunofluorescence and retrograde tracing, we provide evidence that the NK1 receptor is present on 5.3% of C1 neurons, and that 4.7% of C1 neurons receive close oppositions from NK1 receptor immunoreactive terminals, indicating a pre-synaptic and post-synaptic site for the action of substance P. These results provide support for the sympathoexcitatory actions of substance P on C1 neurons. We also demonstrate the NK1 receptor on bulbospinal neurons of the ventral respiratory group, in a region overlapping the pre-Bötzinger Complex.