Cholinergic Currents in Leg Motoneurons of Carausius morosus

Oliveira EE, Pippow A, Salgado VL, Buschges A, Schmidt J, Kloppenburg P. Cholinergic currents in leg motoneurons of Carausius morosus. J Neurophysiol 103: 2770-2782, 2010. First published March 17, 2010; doi: 10.1152/jn.00963.2009. We used patch-clamp recordings and fast optical Ca2+ imaging to characterize an acetylcholine-induced current (I-ACh) in leg motoneurons of the stick insect Carausius morosus. Our long-term goal is to better understand the synaptic and integrative properties of the leg sensory-motor system, which has served extremely successfully as a model to study basic principles of walking and locomotion on the network level. The experiments were performed under biophysically controlled conditions on freshly dissociated leg motoneurons to avoid secondary effects from the network. To allow for unequivocal identification, the leg motoneurons were backfilled with a fluorescent label through the main leg nerve prior to cell dissociation. In 87% of the motoneurons, I-ACh consisted of a fast-desensitizing (I-ACh1) and a slow-desensitizing component (I-ACh2), both of which were concentration dependent, with EC50 values of 3.7 x 10(-5) and 2.0 x 10(-5) M, respectively. Ca2+ imaging revealed that a considerable portion of I-ACh (similar to 18%) is carried by Ca-,(2+) suggesting that I-ACh, besides mediating fast synaptic transmission, could also induce Ca2+-dependent processes. Using specific nicotinic and muscarinic acetylcholine receptor ligands, we showed that I-ACh was exclusively mediated by nicotinic acetylcholine receptors. Distinct concentration-response relations of I-ACh1 and I-ACh2 for these ligands indicated that they are mediated by different types of nicotinic acetylcholine receptors.