[The neuronal mechanisms of site-specific nociceptive sensitization in the snail Helix lucorum]

Electrophysiological effects of site-specific sensitization after application of strong quinine solution onto snail head or snail mantle were studied in Helix lucorum LPl1 and RPl1 interneurons. Sensitizing stimulation (strong quinine solution) applied onto the snail head or mantle produced synapse-specific facilitation of neural responses evoked by tactile stimulation: synaptic facilitation was more expressed in neural responses evoked by tactile stimulation of the sensitized body site. Synaptic facilitation of the neural responses evoked by tactile stimulation of the snail head was observed 1 hour after corresponding sensitizing stimulation. Two definite phases were separated in the synaptic facilitation. The first phase persisted for 1 hour and was characterized by a "peak-shaped" increase of the EPSP square, in the second phase the EPSP facilitation was maintained at a relatively constant level for more than 3 hours. The synaptic facilitation of the neural responses to tactile stimulation of the snail mantle began 40-60 min later than that of the responses to the stimulation of the head and was characterized by the absence of the first phase. It was suggested that specific character of synaptic facilitation in a command interneuron is determined by peculiarities of genetical regulation of different neural inputs.