Synaptic drive in spinal motoneurons during scratch network activity.

Synaptic activity in motoneurons may provide unique insight in the relation between functional network activity and behavior. During scratch network activity in an ex vivo preparation from red-eared turtles ( Trachemys scripta elegans), excitatory and inhibitory synaptic current can be separated and quantified in voltage-clamp recordings. With this technique, we confirm the reciprocal synaptic excitation and inhibition in hip flexor motoneurons during ipsilateral scratching and show that out-of-phase inhibition and excitation also characterize hip extensor motoneurons during ipsi- and contralateral scratching. In contrast, inhibition precedes and partly overlaps excitation in hip flexor-like motoneurons and delays depolarization of membrane potential. We conclude that out-of-phase excitation and inhibition during rhythmic network activity is a common feature in spinal motoneurons. NEW & NOTEWORTHY During network activity, the firing pattern of individual neurons is shaped by their intrinsic conductances and synaptic input. Quantification of synaptic input is, therefore, essential to understand how the properties of individual neurons contribute to function and help to reveal the structure of the network. Here, we show how a combination of recording techniques can be used to quantify and compare the pattern of synaptic activity in different groups of motoneurons during rhythmic network activity.