Barbiturate alteration of respiratory rhythm and drive in isolated brainstem-spinal cord of newborn rat: Studies at normal and hyperbaric pressure

High pressure and anaesthetic agents are mutual antagonists in intact animals, but antagonism is not observed in isolated nerve cells. In order to test the hypothesis that a neural network might display pressure-anaesthetic antagonism not found in simpler systems, we have examined the effects of pentobarbitone at normal pressure and at 10.1 MPa helium pressure on the rhythmic activity of medullary respiratory centres of isolated brainstem and spinal cord from 0-3 day old rats. Pentobarbitone 5-80 μmol litre^-1 depressed the frequency, amplitude and area of spontaneous bursts recorded from C₅ reduced respiratory drive, and altered the response to trigeminal nerve root stimulation. Compression to 10.1 MPa decreased ventilatory frequency and respiratory drive, and either did not interact with or enhanced the depressant effects of pentobarbitone. Pentobarbitone and helium pressure altered the response to trigeminal nerve root stimulation in the same manner. The results are consistent with additive rather than antagonistic effects of pressure and a barbiturate on the determinants of output from the respiratory centre-motor neurone pathway. Pressure-anaesthetic antagonism may be a property unique to the neural circuitry which underlies awake behaviour and pressure-induced seizures, rather than reflecting a fundamental molecular-level antagonism.