Figure 4.
Effects of activation and inhibition of the various steps along the NO/cGMP/PKG pathway on KCl-induced SD-like events. A, Single SD-like events were evoked by injecting saline (50 nl) containing elevated potassium chloride (150 mm vs 10 mm) directly into the MTG. During SD-like events, ventilatory motor activity monitored EMG, ceased, and recovered during restoration of the potassium ion gradient. We measured the duration of the [K+]o event at half its maximal amplitude and the time from failure of the ventilatory motor pattern to the recovery of the rhythm. After recovery (20 min) of ventilatory motor pattern activity, a second injection was delivered into the MTG, evoking a second SD-like event, permitting within-animal comparisons. Before the second injection (10 min), various pharmacological antagonists or agonists were bath applied to manipulate steps along the NO/cGMP/PKG pathway or protein phosphatase 2A activity. B, In control preparations, the second event was ∼30% longer than the first. Event duration was increased by T-0156 (phosphodiesterase inhibitor), although not by 8-Br-cGMP, and reduced by KT5823 and cantharidin (PP2A antagonist). The effect of T-0156 was offset by cantharidin but not significantly reduced. C, In control preparations, motor pattern recovery time was ∼10% longer for the second event compared with the first. The recovery time was increased by 8-Br-cGMP and T-0156 and reduced by KT5823 and cantharidin. The effect of T-0156 was significantly offset by cotreatment with cantharidin. These data indicate that PKG inhibition (KT5823) reduces the duration of SD-like events and hastened the time to recover neural function after KCl-induced SD-like events, whereas activation of the pathway (8-Br-cGMP, T-0156) had the opposite effect. D, Animals were treated with either the NOS inhibitor l-NAME, the NO donors SNAP or SNOG, or a combination of l-NAME and SNOG 10 min before the second injection. Animals treated with l-NAME had significantly shorter SD-like event durations than animals treated with SNOG. E, After l-NAME treatment, the length of time taken to recover CPG function after KCl-evoked SD-like events was shorter than for all other drug treatments. This effect was abolished by concurrent exposure to the NO donor SNOG (l-NAME plus SNOG). Letters represent statistical groupings using a post hoc test, whereby bars with different letters are significantly different and bars that share a letter are not (1-way ANOVA, Tukey, p < 0.10).