Figure 4. Release of medullary burster activity following a blockade of fast synaptic transmission.

Control recordings (A) are of integrated activity of the phrenic nerve (∫ PNA) and of activity of a single medullary ramp inspiratory neurone. Peripheral chemoreceptors were stimulated by an intra-arterial bolus injection of sodium cyanide (NaCN; 50 μl, 0.03%): note the pre-inspiratory discharge evoked in this neurone (B). * and ‡ indicated the bursts prior to and during the chemoreceptor reflex-evoked response; the burst labelled ‡ exhibits the pre-inspiratory discharge. In C, bicuculline, strychnine and kynurenic acid (8.0 mm) were added to the perfusate to block inhibitory synaptic transmission at GABA_A receptors, at receptors for glycine, and ionotropic glutamate receptors respectively. Phrenic discharge ceased and burster discharges commenced. No increase in extracellular potassium was required to evoke this activity which persisted for the duration of the recording (>20 min).