ИСТИНА

Hebbian synapses are between the main problems of modern neuroscience. There are several solutions and most of them are based on hippocampal PTP data. But there is no an answer today why long-lasting plastic changes arise in synchronously activated pre- and postsynaptic cells only. We try to answer the question using identified synapses of edible snail Helix pomatia. Visceral sensory and aversive command neurons with monosynaptic connections were identified in parietal ganglia of the snail (for rev.: Sokolov, Palikhova, 1999). Simultaneous intracellular recording from pre- and postsynaptic cells were used to identify the synapses. These synapses are cholinergic and changes according to presynaptic spike pattern. An associative plasticity is also took place: homo- and hetero-synaptic post-tetanic potentiation was recorded. Intestinal nerve stimulation followed by three time increase of EPSPs’ amplitudes evoked by the tested visceral input activation. These changes were recorded about hour after intestinal nerve stimulation but background EPSPs analysis showed that tetanic stimulation increased frequency but not to amplitudes of background EPSPs recorded in the postsynaptic command neurons. To explain such selectivity of plastic changes we suggested “presynaptic waiting hypothesis” (Palikhova, 2003. The 13 Neuropharm. Conference. New Orleans, USA). This is based on Ca2+ dependent changes of sensitivity of presynaptic receptors to backward messengers such as serotonin or growth factors and suggests both synaptic and non-synaptic neuronal nets. Perspectives to compare plasticity of cholinergic and glutamatergic synaptic inputs to the identified neuron might be discussed for the snail experimental model.