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.

Synaptic Excitation in Spinal Motoneurons Alternates with Synaptic Inhibition and Is Balanced by Outward Rectification during Rhythmic Motor Network Activity.

Regular firing in spinal motoneurons of red-eared turtles (, either sex) evoked by steady depolarization at rest is replaced by irregular firing during functional network activity. The transition caused by increased input conductance and synaptic fluctuations in membrane potential was suggested to originate from intense concurrent inhibition and excitation. We show that the conductance increase in motoneurons during functional network activity is mainly caused by intrinsic outward rectification near threshold for action potentials by activation of voltage and Ca gated K channels.

Motor Neurons.

Motor neurons translate synaptic input from widely distributed premotor networks into patterns of action potentials that orchestrate motor unit force and motor behavior. Intercalated between the CNS and muscles, motor neurons add to and adjust the final motor command. The identity and functional properties of this facility in the path from synaptic sites to the motor axon is reviewed with emphasis on voltage sensitive ion channels and regulatory metabotropic transmitter pathways.

Irregular Firing and High-Conductance States in Spinal Motoneurons during Scratching and Swimming.

Unlabelled: Intense synaptic transmission during scratch network activity increases conductance and induces irregular firing in spinal motoneurons. It is not known whether this high-conductance state is a select feature for scratching or a property that goes with spinal motor network activity in general. Here we compare conductance and firing patterns in spinal motoneurons during network activity for scratching and swimming in an ex vivo carapace-spinal cord preparation from adult turtles (Trachemys scripta elegans).