Protein changes underlying long-term facilitation in Aplysia

In vivo investigation of genome activity and synaptic plasticity of neurons in snails during learning

The present report describes in vivo investigations of genome activity and its role in the mechanisms forming long-term synaptic plasticity in defensive behavior command neuron LPl1 during the acquisition of nociceptive sensitization by common snails. Transcription processes were recorded using SYTO 16, a specific fluorescent indicator of DNA activity, along with in vivo computer image analysis. Studies in control snails showed that application of nociceptive stimuli to the head led to biphasic changes in the bioelectrical responses of neurons to tactile and chemical stimulation--depression of responses in the short-term stage (during the 1 h after training) and their facilitation during the long-term stage of sensitization (more than 24 h). There were marked increases in fluorescence over the nucleus of the command neuron stained with SYTO 16 at 15-20 min from the start of training, this lasting 4-5 h. Acquisition of sensitization in the presence of the RNA synthesis inhibitor actinomycin D (20 microM) to the neuron led to the complete elimination of changes in fluorescence and synaptic facilitation in the responses of LPl1 to sensory stimulation in the long-term stage of sensitization but had no effect during the short-term stage of sensitization. Actinomycin D given 30 min after the end of acquisition of sensitization (1 h after the start) had no effect on the dynamics of fluorescence or synaptic facilitation. Thus, the acquisition of nociceptive sensitization is accompanied by a rapid (within 15-20 min) activation of the DNA of neuron LPl1 and subsequent (about 1 h) display of long-term synaptic facilitation. Induction of both processes was suppressed by the RNA synthesis inhibitor over a relatively short time period--1 h from the moment at which training started.