Afferent Inputs Modulate the Activity of a Rhythmic Burst Generator in the Rat Disinhibited Spinal Cord In Vitro

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Abstract
Bracci, E., M. Beato, and A. Nistri. Afferent inputs modulate the activity of a rhythmic burst generator in the rat disinhibited spinal cord in vitro. J. Neurophysiol. 77: 3157–3167, 1997. Application of strychnine and bicuculline to the isolated spinal cord of the neonatal rat induces spontaneous bursting of regular rhythmicity (cycle period ∼30 s). This phenomenon is important because it shows that a spinal network, made up by excitatory connections only, generates a very reliable rhythmic pattern. To find out how signals from the periphery or higher centres might influence the operation of the rhythmogenic network, the present experiments examined whether synaptic inputs from dorsal root (DR) or ventrolateral (VL) afferent fibers could modulate this spontaneous rhythmicity. This issue was addressed with intracellular recording from motoneurons or extracellular recording from ventral roots after eliciting bursting with strychnine plus bicuculline. Single electrical shocks (0.1 ms; intensity 1–4 times threshold) applied to one DR reset spontaneous bursting without altering its period or duration. Repetitive stimulations at periods ranging from 20 to 2 s entrained bursts on a 1:1 basis. Burst duration was shorter at lower stimulation periods whereas burst amplitude was unchanged. The lowest stimulation period compatible with burst entrainment depended on stimulus strength. At stimulation periods

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