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My lab:
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This talk was all about long-term memory of classical conditioning in the pond snail Lymnaea stagnalis. Paul Benjamin is the eminent researcher studying this topic.
To study this, the scientists in this lab condition feeding behavior. Sucrose works fine as the unconditioned stimulus (US) and either a tactile stimulus or amyl acetate serve as conditioned stimulus (CS). Depending on the number and spacing of CS-US pairings (trials) the formed memory can last up to 20 days. But even single trial conditioning can lead to long-term memory. The procedure is to train the animals and then dissect the preparation to probe the neuronal changes in the various ganglia.
Apparently, much of the learning takes place in a set of modulatory interneurons in the cerebral ganglion which are located between the sensory input and the feeding central pattern generator. These modulatory interneurons have to fire at a certain rate for the buccal CPG to actually function. One of the changes after training is a depolarization of the CGC (cerebral giant cell) neuron. The CGC shows no changes in firing rate, spike threshold, input resistance or spike shape. This change is important as artificial manipulation of the membrane potential can mimic training. The increase in CGC potential leads to increased synaptic output apparently mediated by calcium. It seems as if this change in the CBC is potentiating the CS pathway. Also involved in these processes is nitric oxide (NO). NO synthase (NOs) genes are expressed in the snail CNS along with unusual anti-NOs genes, yielding complementary mRNAs.
Posted on Saturday 09 June 2007 - 00:51:30 comment: 0
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