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Sample records of significantly reduced increases.
After hindlimb loading, rats show increased GABA(A), which inhibits the RVLM.
Moffitt, Julia A.; Heesch, Cheryl M.; Hasser, Eileen M.
The central nervous system is responsible for the attenuated baroreflex mediated increases in renal sympathic nerve activity (RSNA). After hindlimb unloading, we hypothesized an increase in GABA(A), receptor-mediated inhibition of rostral medulla. The effects of bilateral microinjections of the GABA (A) antagonist (-)-bicucullinemethiodide into the RVLM before and after CVLM inhibition were studied in Inactin anesthetized controls and HU rats. HU rats showed a significant increase in heart rate, mean arterial pressure and RSNA after BIC was injected into the RVLM. The responses to bilateral CVLM blocking were similar. BIC blocked the remaining GABA(A), which inhibits the RVLM, during CVLM blockade. The additional increases in MAP or RSNA in HU rats were significant. These results indicate that GABA receptor-mediated inhibitory inhibition of RVLM neuronal activity is enhanced after hindlimb deloading. The CVLM input had no effect. After cardiovascular deconditioning, rodents' increased sympathetic nerve activity is attenuated in response to hypotension. This attenuation of sympathetic nerve activity is associated with greater GABA (A) receptor-mediated inhibitory inhibition of RVLM neuronal cells originating from sources other than CVLM.