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Abstract
The pontomedullary connections of the rostral division of the ventral respiratory
group (rVRG), the largest medullary population of inspiratory bulbospinal and propriobulbar
neurons, were identified in the rat by retrograde and anterograde tracing techniques.
These experiments revealed that: (i) the Kölliker-Fuse nucleus, portions of the medial
and lateral parabrachial nuclei, and all levels of the ipsilateral and contralateral
VRG complex have dense reciprocal connections with the rVRG; (ii) the lateral paragigantocellular
nucleus has reciprocal but less dense connections with rVRG; (iii) portions of the
nucleus of the solitary tract have prominent projections to, but weaker inputs from
rVRG; (iv) the raphe, magnocellular tegmental field and spinal trigeminal nuclei have
minor projections to rVRG and receive only sparse inputs from rVRG, and; (v) the retrotrapezoid
nucleus, pontine lateral tegmental field and area postrema each have only efferent
projections to rVRG. These findings are consistent with previous studies of pontomedullary
connections of rVRG in the cat, and further document the extensive reciprocal connections
between principal respiratory groups. These connections are likely to be important
for generation of the respiratory pattern, for the coordination of effector responses
of the cranial and spinal respiratory motor neurons to afferent stimuli, and coordination
of the central respiratory and cardiovascular control systems.