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Cobalt injections into the pedunculopontine nuclei attenuate the reflex diaphragmatic responses to muscle contraction in rats

¹Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801; and ²Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599

Submitted 24 June 2003 ; accepted in final form 9 September 2003

Previous studies have suggested that neurons in the pedunculopontine nucleus (PPN) are activated during static muscle contraction. Furthermore, activation of the PPN, via electrical stimulation or chemical disinhibition, is associated with increases in respiratory activity observed via diaphragmatic electromyogram recordings. The present experiments address the potential for PPN involvement in the regulation of the reflex diaphragmatic responses to muscle contraction in chloralose-urethane anesthetized rats. Diaphragmatic responses to unilateral static hindlimb muscle contraction, evoked via electrical stimulation of the tibial nerve, were recorded before and subsequent to bilateral microinjections of a synaptic blockade agent (CoCl₂) into the PPN. The peak reflex increases in respiratory frequency (9.0 ± 1.0 breaths/min) and minute integrated diaphragmatic electromyogram activity (14.6 ± 3.3 units/min) were attenuated after microinjection of CoCl₂ into the PPN (2.6 ± 0.9 breaths/min and 4.6 ± 2.1 units/min, respectively). Consistent diaphragmatic responses were observed in the subset of animals that were barodenervated. Control experiments suggest no effects of PPN synaptic blockade on the cardiovascular responses to muscle contraction. The results are discussed in terms of a potential role for the PPN in modulation of the reflex respiratory adjustments that accompany muscular activity.

mesencephalic locomotor region

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