Effects of electrical and chemical stimulation of the Bötzinger complex on respiratory activity in the cat.

The effects of electrical and chemical stimulation of the expiratory neuronal population in the region of the retrofacial nucleus, the so called 'Bötzinger complex' (Böt. c.), on respiratory activity were investigated in vagotomized cats under pentobarbitone anaesthesia. Some of the experiments were performed on paralyzed or bilaterally thoracotomized, artificially ventilated animals. Sustained tetanic electrical stimulation (20 to 100-Hz, 0.5-ms current pulses at intensities of 5-60 microA) induced strong depressant effects on the inspiratory motor output which could lead to complete apnoea. The apnoeic response was accompanied by tonic activation of expiratory muscles; the appearance and the strength of tonic expiratory activity were dependent upon the frequency of stimulation. Brief tetani (40 to 100 ms trains of 0.5-ms rectangular pulses at 100-300 Hz) timed either during the inspiratory or the expiratory phase caused depression of inspiratory activity and prolongation of expiratory time, respectively. These effects increased gradually as the onset of stimulation was progressively delayed during each respiratory phase. The effects of sustained tetanic stimulation were mimicked by microinjections (25-100 nl) of 0.5 M L-glutamate or 0.16 M DL-homocysteic acid in the same region, thus indicating that they were the result of the stimulation of cell bodies and not of axons of passage. The present results support the hypothesis that Böt. c. neurons play an important role in the control of the breathing pattern by exerting inhibitory influences on inspiratory activity and, possibly, by contributing to the off-switch mechanisms. Furthermore, they suggest that these neurons are involved in the central control of expiratory activity.