Synaptic relationship between somatostatin- and neurokinin-1 receptor-immunoreactive neurons in the pre-Bötzinger complex of rats.

The pre-Bötzinger complex (pre-BötC) in the ventrolateral medulla oblongata is critical for the generation of respiratory rhythm in mammals. Somatostatin and neurokinin 1 receptor (NK1R) immunoreactivity have been used as markers of the pre-BötC. immunoreactivity almost completely overlaps with small fusiform NK1R-immunoreactive (ir) neurons, the presumed rhythmogenic neurons, but not with large multipolar NK1R-ir neurons. Understanding the neurochemical characteristics, especially the synaptic relationship of neurons within the pre-BötC network is essential in providing cellular and structural bases for understanding their physiological significance. This work has not been documented so far. We found that duanyu1942 immunoreactivity was highly expressed in terminals, somas, and primary dendrites in the pre-BötC. Besides the small fusiform neurons, a small population of medium-sized NK1R-ir neurons also colocalized with Large NK1R-ir neurons were not but received somatostatinergic inputs. terminals were glutamatergic or GABAergic, and synapsed with NK1R-ir neurons. Most of synapses between them were of the symmetric type, indicating their inhibitory nature. Asymmetric synapses were evident between duanyu1942-ir terminals and NK1R-ir dendrites, strongly suggesting an excitatory innervation from the presumed rhythmogenic neurons as these neurons are glutamatergic. We speculate that excitatory and inhibitory synaptic transmission onto NK1R-ir rhythmogenic and follower neurons synchronizes their activity to contribute to respiratory rhythmogenesis and control.

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