| 12611760 |
Solomon IC: Focal CO2/H+ alters phrenic motor output response to chemical stimulation of cat pre-Botzinger complex in vivo. J Appl Physiol. 2003 Jun;94(6):2151-7. Epub 2003 Feb 28.
Microinjection of dl-homocysteic acid (DLH), a glutamate analog, into the pre-Botzinger complex (pre-BotC) can produce tonic excitation of phrenic nerve discharge. Although this DLH-induced tonic excitation can be modified by systemic hypercapnia, the role of focal increases in pre-BotC CO (2)/H (+) in this modulation of the DLH-induced response remains to be determined. Therefore, we examined the effects of unilateral microinjection of DLH (10 mM; 10-20 nl) into the pre-BotC before and during increased focal pre-BotC CO (2)/H (+) (i.e., focal tissue acidosis) in chloralose-anesthetized, vagotomized, mechanically ventilated cats. Focal tissue acidosis was produced by blockade of carbonic anhydrase with either focal acetazolamide (AZ) or methazolamide (MZ) microinjection. For these experiments, sites were selected in which unilateral microinjection of DLH into the pre-BotC produced a nonphasic tonic excitation of phrenic nerve discharge (n = 10). Microinjection of 10-20 nl AZ (50 microM) or MZ (50 microM) into these 10 sites in the pre-BotC increased the amplitude and/or frequency of eupneic phrenic bursts, as previously reported. Subsequent microinjection of DLH produced excitation in which phasic respiratory bursts were superimposed on tonic discharge. These DLH-induced phasic respiratory bursts had an increased frequency compared with the preinjection baseline frequency (P < 0.05). These findings demonstrate that modulation of phrenic motor activity evoked by DLH-induced activation of the pre-BotC is influenced by focal CO (2)/H (+) chemosensitivity in this region. Furthermore, these findings suggest that focal increases in pre-BotC CO (2)/H (+) may have contributed to the modulation of the DLH-induced responses previously observed during systemic hypercapnia. |
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