Effects of focal cooling of medulla oblongata structures on quiet breathing in cats

Experiments were carried out on 16 anaesthetized, non-paralysed cats to determine the effects of unilateral, successive focal cooling of the nuclei of the dorsal and ventral respiratory groups (DRG, VRG) of the medulla oblongata on quiet breathing parameters. The results of cold block tests of the respiratory nuclei showed that: 1. Compared with the control state, cooling of the ventrolateral part of the nucleus solitarii (vl. NTS) and the rostral part of the nucleus retroambigualis (r. NRA) to 20 degrees C or 15 degrees C decreased the respiration rate (p less than 0.001), prolonged the inspiration time (p less than 0.01 and p less than 0.001 respectively) and the development of apneustic breathing. A decrease in the inspiratory pleural pressure values (p less than 0.01) was found after cooling the r. NRA region to 15 degrees C. In 45% of the cases of cooling of the vl. NTS and 66.7% of cooling of the r. NRA to 15 degrees C, an incidence of short inspiratory efforts was observed. 2. Focal cooling of the nucleus retrofacialis (nucl. RF) region to 20 degrees C always arrested rhythmic respiration. 3. The effects of unilateral focal cooling of the respiratory nuclei were always bilaterally symmetrical and, after discontinuing cooling, reversible. 4. The findings indicate that the inspiratory neurones of the r. NRA participate more in regulation of the intensity of inspiration than those of the vl. NTS, while the nucl. RF region may be a part of central regulatory mechanisms essential for the maintenance of rhythmic breathing in cats.