Control of discharge patterns of medullary respiratory neurons by pulmonary vagal afferent inputs.
To provide a better understanding of the central mechanisms by which pulmonary afferents reflexly control breathing, the responses of single respiratory neurons to vagal afferent patterns were analyzed. Respiratory-related unit (RRU) recordings were obtained from inspiratory (I), expiratory (E), and phase-spanning neurons in the ventral medulla of halothane-anesthetized, paralyzed, ventilated, vagotomized, mongrel dogs. Electrical stimulation of the largest vagal fibers was used to reflexly alter I and E durations (TI and TE) and to present various temporal input patterns to RRU. The net response was quantified by taking the difference between cycle-triggered histograms (CTH) of activity obtained during an input and the spontaneous control (no input) CTH. For step frequency patterns confined to either the I or E phase, 127 responses in 41 neurons were analyzed. The average step response time was greater than 500 ms. In general the time courses of the control and test-input discharge patterns were linearly related to one another. For I neurons the slopes (beta) of these relationships were linear functions of the vagal step frequency (Fv). Linear relationships were also obtained for 1/TI vs. Fv and 1/beta vs. TI. These results suggest that the vagal control of the discharge patterns of these neurons and phase timing is mediated via a process similar to gain modulation.
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee.
E J
EJ
Zuperku
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FA
Hopp
D000818:Animals; D004285:Dogs; D004558:Electric Stimulation; D004594:Electrophysiology; D008168:Lung / Q000294:innervation*; D008526:Medulla Oblongata / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D010791:Phrenic Nerve / Q000502:physiology; D012018:Reflex / Q000502:physiology; D012119:Respiration; D014630:Vagus Nerve / Q000502:physiology*