J. Schmidt et al., Pattern generation for walking and searching movements of a stick insect leg. II. Control of motoneuronal activity, J NEUROPHYS, 85(1), 2001, pp. 354-361
In the stick insect, Cuniculina impigra, intracellular recordings from meso
thoracic motoneurons that control flexion and extension of the tibia and de
pression and levation of the trochantero-femur were made while the leg perf
ormed walking-like movements on a treadband or stereotyped rhythmic searchi
ng movements. We were interested in how synaptic input and intrinsic proper
ties contribute to form the activity pattern of motoneurons during rhythmic
leg movements without sensory feedback from other legs. During searching a
nd walking, motoneurons expressed a rhythmic bursting pattern that was form
ed by a depolarizing input followed by a hyperpolarizing input in the inter
-burst interval. This basic pattern was similar in all fast, semi-fast, and
slow motoneurons that were recorded. Hyperpolarizations were in synchrony
with activity in the antagonistic motoneurons. De- and hyperpolarizations w
ere associated with a decrease in input resistance. All motoneurons showed
spike frequency adaptation when depolarized by current injection to a membr
ane potential similar to that observed during walking. In the hyperpolarizi
ng phase of fast flexor motoneurons, the initial maximum hyperpolarization
was followed by a sag in potential toward more depolarized values. Consiste
nt with this observation, only fast flexor motoneurons developed a depolari
zing sag potential when hyperpolarized by injection of constant negative cu
rrent.