Journal of Applied Physiology, Vol 65, Issue 5 2156-2163, Copyright © 1988 by American Physiological Society
Stimulation of H fields of Forel decreases total lung resistance in dogs
L. W. McCallister, J. C. Connelly and M. P. Kaufman
Department of Physiology, University of Texas Southwestern Medical School, Dallas 75235.
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
Forel, while we monitored breath-by-breath changes in total lung resistance
(TLR), a functional index of airway caliber. Electrical stimulation
(200-250 microA, 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
less than 0.01). The bronchodilation evoked by electrical stimulation was
unaffected by beta-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 (83 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 less than 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.
