Activity of rat pump neurons is modulated with central respiratory rhythm.

The firing properties of the second-order neurons of the slowly-adapting pulmonary stretch receptors called pump neurons (P-cells), were studied in Nembutal-anesthetized, paralyzed, and artificially-ventilated rats. Extracellular recording was made from single P-cells which were monosynaptically activated by electrical stimulation of the vagal afferents and fired in phase with lung inflations. In the majority of the P-cells examined (49/52), the firing was suppressed to various extents in the inspiratory phase: in effect, their firing was accentuated at the time of the inspiratory off-switch. This issue has never been reported in cat P-cells, on which relatively rich data have been accumulated. The present results suggest that rat P-cells do not only relay information from the lung stretch receptors but also integrate the central respiratory inputs.