EFFECT OF CARDIOPULMONARY C-FIBER ACTIVATION ON THE FIRING ACTIVITY OF VENTRAL RESPIRATORY GROUP NEURONS IN THE RAT

1. Cardiopulmonary C fibre receptor stimulation elicits apnoea and rap id shallow breathing, but the effects on the firing activity of centra l respiratory neurones are not well understood. This study examined th e responses of ventral respiratory group neurones: decrementing expira tory (E-dec), augmenting expiratory (E-aug), and inspiratory (I) neuro nes during cardiopulmonary C fibre receptor-evoked apnoea and rapid sh allow breathing. 2. Extracellular neuronal activity, phrenic nerve act ivity and arterial pressure were recorded in urethane-anaesthetized ra ts. Cardiopulmonary C fibre receptors were stimulated by right atrial injections of phenylbiguanide. Neurones were tested for antidromic act ivation from the contra-and ipsilateral ventral respiratory group (VRG ), spinal cord and cervical va;gus nerve. 3. E-dec neurones discharged tonically during cardiopulmonary C fibre-evoked apnoea and rapid shal low breathing, displaying increased burst durations, number of impulse s per burst, and mean impulse frequencies. E-dec neurones recovered ei ther with the phrenic nerve activity (25 s) or much later (3 min). 4. By contrast, the firing activity of E-aug and most I neurones was decr eased, featuring decreased burst durations and number of impulses per burst and increased interburst intervals. E-aug activity recovered in similar to 3 min and inspiratory activity in similar to 1 min. 5. The results indicate that cardiopulmonary C fibre receptor stimulation cau ses tonic firing of E-dec neurones and decreases in E-aug and I neuron al activity coincident with apnoea or rapid shallow breathing.