Respiratory effects mapped by focal stimulation in the rostral brain stem of the anaesthetised rabbit

Abstract

The brain stem of the rabbit, anaesthetised with a mixture of chloralose and urethane, was explored with stimulating microelectrodes between the anterior commissure and the superior colliculus. At many points stimulation evoked changes in the pattern of ventilatory movements. The changes could be in rate, amplitude or baseline volume, or combinations of these. A set of symbols are shown which indicate the qualitative nature of the evoked changes in ventilation and these symbols are used in a set of 13 maps, based on transverse sections of the rabbit brain stem, to show the location of the responsive areas. An important zone was found, extending from the lateral hypothalamic area, dorsal to the lateral mammillary nucleus, to the mesencephalon near the ventral tegmental decussation. Stimulation within this zone evoked strong respiratory and cardiovascular effects, accompanied by other autonomic and somatic responses. The respiratory rate rose, remaining high for some time after stimulation had ceased. The amplitude of ventilation diminished greatly, with a rise in baseline volume, sometimes to apnoea in inspiration. The evidence suggests that this zone may be homologous with that concerned with the defence reaction in cats. In many other regions of the brain stem focal stimulation resulted in highly significant changes in ventilation, suggesting that there are several mechanisms present in the rostral brain stem that may play some part in the integrated regulation of respiration.