[Long-term synaptic facilitation depends on RNA synthesis in LP11 neuron of sensitized Helix]

Effects of actinomycin D (transcription inhibitor) on neural mechanisms of nociceptive sensitization were studied in Helix lucorum LP11 command neurons of defensive behavior. In control snails, the sensitizing stimulation (three applications of 10% quinine solution with 15-min intervals) produced an increase in membrane excitability and two-phase changes in neural responses to tactile or chemical sensory stimuli. In the first (within one hour after the beginning of the sensitization) phase the responses were depressed; they were facilitated in the second phase (to 24r). Application of 20 microM actinomycin D to LPl1 neuron during sensitization of a snail semi-intact preparation did not affect the increase in membrane excitability and short-term depressions of neural responses but suppressed the long-term synaptic facilitation. Actinomycin D application 30 min after the third sensitizing stimulus prevented neither increase in membrane excitability nor the long-term synaptic facilitation of the neural responses evoked by sensory stimuli. It is suggested that the long-term synaptic facilitation in Helix LPl1 neurons depends on the RNA synthesis in the critical time window (within one hour after the sensitization beginning), whereas membrane excitability changes do not depend on transcription within two-three hours.