ORIGINAL PAPER Mobility of acetylcholine receptors in command Helix lucorum neurons in a cellular analog of habituation Arkady S. Pivovarov • Galina B. Murzina • Denis A. Makhnovsky • Mariya S. Tret’yakova • Natalya A. Vasil’yeva Received: 16 October 2012 / Accepted: 6 April 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract We investigated the role of the mobility of acetylcholine receptors in the depression of an acetylcho- line-induced inward current (ACh-current) of Helix luco- rum (a land snail) command neurons of defensive behavior in a cellular analog of habituation. The inhibitors of endocytosis and exocytosis, actin microfilaments and cytoskeleton microtubules, serine/threonine protein kinases (PKA, PKG, calcium calmodulin-dependent PK II, p38 mitogen-activated PK), tyrosine kinases (including Src- family kinases), serine/threonine phosphatases (PP1, PP2A, PP2B, PPM1D), and tyrosine protein phosphatases altered the depression of the ACh-current. A comparison of experimentally calculated curves of the ACh-current of these neurons and those obtained by mathematical model- ing revealed the following: (a) ACh-current depression is caused by the reduction in the number of membranous ACh-receptors, which results from the shift in the balance of multidirectional transport processes of receptors toward the predominance of ACh-receptor internalization over their recycling; (b) depression of ACh-current depends on the activity of serine/threonine and tyrosine protein kinases and protein phosphatases, whose one of the main targets is the neuron transport system—actin microfilaments and microtubules of cytoskeleton, as well as motor proteins. Keywords Mobility of acetylcholine receptors Á Cytoskeleton Á Protein kinases Á Protein phosphatases Á Command Helix lucorum neurons Á Habituation Introduction In behavioral experiments, rhythmic tactile stimulation of the skin of a land snail, Helix lucorum, caused habitua- tion—the animal’s defensive response was reduced. Once tactile stimulation was terminated, the response was spontaneously restored (Nistratova and Pivovarov 2004). We imitated the stimulation protocol, evoking behavioral habituation of the animal, in electrophysiological experi- ments on command neurons LPa2, LPa3, RPa3, and RPa2 controlling defensive behavior of the snail. Rhythmic local application of acetylcholine (ACh) on the soma led to a reversible decrease in the amplitude of ACh-induced inward current (ACh-current). Depression curves of the defensive reaction and the ACh-current had similar dynamics (Nistratova and Pivovarov 2004). The described change in the current can be regarded as a cellular analog of behavioral habituation. The cellular mechanism of ACh- current depression can include reversible reduction in the number of ACh-receptors (AChRs) in the test zone. It has been established that chemoreceptor agonists stimulate endocytosis of membrane receptors. Thus, car- bachol, a muscarinic receptor agonist, causes rapid desen- sitization and internalization of muscarinic receptors in human neuroblastoma cells (Szekeres et al. 1998). The number of plasma membrane receptors is reduced and then restored after the carbachol washout (Szekeres et al. 1998). These results suggest that the short-term reduction in an ACh-current in neurons of a snail is a cellular analog of habituation (Nistratova and Pivovarov 2004; Pivovarov A. S. Pivovarov (&) Á D. A. Makhnovsky Á M. S. Tret’yakova Á N. A. Vasil’yeva Department of Higher Nervous Activity, Biological Faculty, Lomonosov State University, Moscow 119991, Russia e-mail: as_pivovarov@mail.ru G. B. Murzina Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow 117485, Russia 123 Invert Neurosci DOI 10.1007/s10158-013-0155-z