Figure 6.

Generation of fictive sighs depends on the activation of P/Q-type calcium channels. Pharmacological blockade of the P/Q type channels with ω-agatoxin TK specifically abolishes sighs. (A) Sighs recorded under control conditions in population recordings from the preBötC (sighs indicated by red arrows) and (B) after bath application of ω-agatoxin TK, at low concentrations (modified, with permission, from reference 297). (C) Reduction of the amplitude of intracellularly recorded evoked EPSPs (by electrical stimulation of the contralateral preBötC) in respiratory neurons by pharmacological blockade of P/Q-type calcium channels. Individual responses of five neurons to ω-agatoxin TK [120 nmol/L] show a variable response, with a minimum of 8% reduction and a maximum of 90% reduction. (D) Individual responses to the N-type specific calcium channel blocker GVIA [0.5 µmol/L], showing a homogeneous 40% reduction of evoked EPSPs (modified, with permission, from reference 297). (E) Activation of the metabotropic glutamate receptors (mGluR8) leads to specific inhibition of “fictive sighs” recorded from the preBötC (modified, with permission, from reference 296). (F) Hypothesized mechanism of action for the inhibition of P/Q-type calcium channels by activated mGluR8 receptors, through a direct inhibitory interaction with the β-subunit of the heterotrimeric G-protein.