Although there is considerable evidence that the H fields of Forel of the posterior diencephalon play an important role in the regulation of cardiovascular function, little is known about the role these areas play in the control of airway caliber. In chloralose-anesthetized paralyzed dogs, we used both electrical and chemical means to stimulate the H fields of Ford, while we monitored breath-by-breath changes in total lung resistance (TLR), a functional index of airway caliber. Electrical stimulation (200-250 μA, 80 Hz, 0.75 ms) of 82 histologically confirmed sites significantly decreased TLR from 9.2 ± 0.4 to 7.9 ± 0.4 cmH2O·l-1·s (P < 0.01). The bronchodilation evoked by electrical stimulation was unaffected by β-adrenergic blockade with propranolol but was abolished by cholinergic blockade with atropine. The increases in airway caliber evoked by stimulation were often accompanied by increases in phrenic nerve activity. Chemical stimulation of 21 of 82 sites with microinjections of DL-homocysteic acid (82 nl, 0.2 and 0.5 M), which stimulates cell bodies but not fibers of passage, also decreased TLR from 8.3 ± 0.5 to 7.3 ± 0.5 cmH2O·l-1·s (P < 0.03). We conclude that stimulation of cell bodies in the H fields of Forel produces bronchodilation by withdrawal of cholinergic tone to airway smooth muscle.
All Science Journal Classification (ASJC) codes
- Physiology (medical)