Acute reverse microdialysis (MD) of atropine into the pontine respiratory group (PRG) during the day has chronic affects on the control of breathing and metabolic rate

Abstract

To further study the importance of acetylcholine as a neurotransmitter in the PRG, we chronically implanted microtubules into the PRG of 12 goats to assess the acute ventilatory response of reverse microdialysis (MD) of atropine (50mM) into the PRG during the day. Ipsi‐unilateral MD of atropine increased pulmonary ventilation (VI) by 6.4% (P=0.004) compared to MD of mock cerebral spinal fluid (mCSF), due to increases in both breathing frequency (P=0.042) and tidal volume (P=0.002). Unexpectedly, subsequent (2 to 4 days later) contra‐unilateral and bilateral MD of mCSF alone increased VI by 9.3% (P<0.001) and 4.1% (P<0.001), respectively. This change is presumed due to a carryover effect of the ipsilateral MD of atropine. Interestingly, following the increases in VI due to MD of mCSF, MD of atropine immediately attenuated these increases back to pre‐MD control levels. pH, pCO2, pO2, and body temperature were unaffected, but changes in VI were matched by changes in VO2 and VCO2, with significance on the contralateral side (P=0.015 and 0.045, respectively). These findings are consistent with previous studies where MD of atropine into the PRG of goats chronically attenuated a secondary physiologic response to hypoxia (FASEB J. 2008 22:1233.7). We conclude that MD of atropine elicits chronic effects, which subsequent MD of atropine attenuates. Supported by the Department of Veterans Affairs and NIH 25739.