Journal of Neuroscience, Vol 2, 744-757, Copyright © 1982 by Society for Neuroscience
The effects of microstimulation and microlesions in the ventral and dorsal respiratory groups in medulla of cat
DF Speck and JL Feldman
The responses in respiratory outflow resulting from microstimulation and
successive microlesions of the dorsal (DRG) and ventral (VRG) respiratory
groups of neurons in the brainstem were studied in anesthetized, paralyzed,
artificially ventilated cats. Microstimulation (2 to 120 Hz; 5 to 50
microA; 100 musec pulse duration) at almost every point within the DRG or
VRG produced a bilateral short latency inhibition of phrenic nerve activity
which had an onset latency of 4 to 9 msec and a duration of 4 to 24 msec.
This global stereotyped phrenic inhibition was elicited by single pulses
and often was accompanied by a postinhibitory excitation. In 48% (92/193)
of the stimulation trials, trains of stimulus pulses during inspiration
decreased the duration of inspiration. In 25% of the expiratory
microstimulation trials, expiratory duration was increased and in 11%,
expiration was shortened markedly by trains of pulses. Single shocks
delivered to the right VRG or DRG produced a short latency excitation in
the ipsilateral recurrent laryngeal nerve (RRL). This RRL excitation had an
onset latency of 2 to 5 msec and a duration of 3 to 15 msec. Evidence
suggests that the RRL excitation is due to a paucisynaptic activation of
expiratory motoneurons in the caudal VRG. This activation is synchronous
with the inhibition of inspiratory neurons in DRG and VRG. Despite the
powerful short latency effects of microstimulation in VRG and DRG,
extensive bilateral destruction of these neuronal populations had only
modest effects on respiratory rhythm, while it decreased (or abolished)
respiratory outflow in phrenic and recurrent laryngeal nerves. The combined
results of the microstimulation and microlesion portions of this study
suggest that a region (or regions) outside of the DRG and VRG might be
important in the control of the respiratory pattern and that the DRG and
VRG are important in determining the depth of inspiration; their role in
generating respiratory rhythm needs to be critically re-examined.
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