Local Spinal GABAergic Mechanisms Regulate Expiratory Phrenic Nerve Activity

Although GABAergic inhibitiory mechanisms have been implicated in respiratory rhythm generation, the role of local spinal GABAergic neurons in controlling phrenic output is poorly understood. In 6 isoflurane‐anesthetized rats, anti‐glutamate amino decarboxilase (65 and 67 subunits) short interference RNA (anti‐GAD 65/67 siRNA) was injected unilaterally into the phrenic nucleus at the C 4 level, after physiological identification via 10 nl of 10mM L‐glutamate injection. A second barrel in the injection pipette was used for anti‐GAD 65/67 siRNA microinjection (20μM, 5 nl every 2 min for 2.5 h). No changes in left and right phrenic nerve (PN) activity were observed during the first hour, save for some irregular expiratory activity ipsilateral to the injection. After 60–90 min this low‐amplitude expiratory discharge transformed into a regular tonic pattern (145 ± 12.7 % of background pre‐injections; % BC), and saturated after 2 hours a significant expiratory discharge was evident (203 ±18.4 % BC). No changes in respiratory rhythm, blood pressure, amplitude or inspiratory burst duration of either PN were observed. Each spinal cord was removed and processed immunohistochemically. The number of GAD+ cells showed a decreased of 43 ± 8.3% in the region of the phrenic nucleus on the side of siRNA injection. Our data suggests a specific role for local spinal GABAergic neuronal control in shaping the expiratory phase.