Are pacemaker properties required for respiratory rhythm generation in adult turtle brain stems in vitro?
The role of pacemaker properties in vertebrate respiratory rhythm generation is not well understood. To address this question from a comparative perspective, brain stems from adult turtles were isolated in vitro, and respiratory motor bursts were recorded on hypoglossal (XII) nerve rootlets. The goal was to test whether burst frequency could be altered by conditions known to alter respiratory pacemaker neuron activity in mammals (e.g., increased bath KCl or blockade of specific inward currents). While bathed in artificial cerebrospinal fluid (aCSF), respiratory burst frequency was not correlated with changes in bath KCl (0.5–10.0 mM). Riluzole (50 µM; persistent Na+ channel blocker) increased burst frequency by 31 ± 5% (P < 0.05) and decreased burst amplitude by 42 ± 4% (P < 0.05). In contrast, flufenamic acid (FFA, 20–500 µM; Ca2+-activated cation channel blocker) reduced and abolished burst frequency in a dose- and time-dependent manner (P < 0.05). During synaptic inhibition blockade
