Effects of reversible elimination of some bulbar structures on the generation of respiratory pattern in rabbits

The regions of (i) nucl. n. VII (N. VII), (ii) nucl. retrofacialis (N. r. VII), (iii) nucl. Ambiguus (A.c) and (iv) nucl. ret. parvocellularis (n.rp) were explored with microelectrodes and then the active sites were injected with 5 microliters of lignocaine. The activity of both phrenic nerves, blood pressure and end-tidal CO2 percent were recorded throughout the experiment. Blockade of the n.VII region elicited apneustic discharge in both phrenic nerves; blockade of N.r.VII gave variable frequency responses but always reduced phrenic amplitude of discharges; microinjection of lignocaine into the region of A.c. invariably accelerated central respiratory rhythm, the amplitude of discharges being reduced predominantly contralaterally to the injection site; blockade of the R.pc elicited a dramatic prolongation of expiratory pause, decrease in amplitude and rate of rise of phrenic activity. All effects disappeared within 30 min after injection and histological examinations revealed only minor lesions at the sites of injections. It is concluded that the respiratory neurons of the medulla form a complex, strongly interconnected network.