Entrainment of the medullary respiratory generators by electrical stimulation in the cervical grey matter on in vitro preparations of newborn rat.
The present study describes how the medullary respiratory generators (mRGs) can be driven by periodic electrical stimulations applied to the ventral part of the spinal grey matter at the C5 level. The general effect of an electrical stimulus (5 pulses at 200 Hz and between 50 and 80 microA) was either to delay or to advance the occurrence of the medullary respiratory burst via a resetting process, depending on its time of application within the corresponding cycle. Compared to the spontaneous medullary periods, the phase-response curves show that the non-spontaneous medullary period increased progressively when the electrical stimulus was applied within the first two-thirds of the corresponding medullary cycle and decreased when it was applied within the last third of the latter one. These curves were constructed in order to predict the limits of a stable 1:1 entrainment. As predicted, the 1:1 entrainment was obtained when we stimulated repetitively at resetting intensity within the frequency limits determined by the phase-response curves. The entrainment became harmonic (2:1, 3:1, 4:1) when the stimulation frequency increased near submultiples of the fundamental mRGs frequency. From these data, we conclude on the presence of ascending connections from the C5 segment of the spinal cord which might be involved in the realisation of the locomotor-respiratory coupling.
Dubayle
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Laboratoire des Neurosciences de la Motricité, CNRS URA 339, Université de Bordeaux I, Talence, France.
Viala
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D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001933:Brain Stem / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D008526:Medulla Oblongata / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016897:Respiratory Burst / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology