Cellular And Molecular Analysis of Associative Learning
Cellular and molecular analyses of associative learning and memory are the research interests of this laboratory. The experimental preparation we use to study mechanisms of Pavlovian conditioning is the Pacific nudibranch Hermissenda crassicornis. Cellular neurophysiological, biophysical and biochemical studies of the isolated central nervous system of conditioned Hermissenda have identified long-term intrinsic modifications of identified sensory neurons in the pathway supporting the conditioned stimulus. We have found that conditioning produces an enhancement of the excitability of identified sensory neurons elicited by the conditioned stimulus and an enhancement of specific synaptic connections between identified sensory neurons.
Hermissenda is an attractive preparation for studies of cellular and synaptic mechanisms underlying memory consolidation since behavior can be modified by one conditioning trial and cellular correlates can be studied in identified neurons that previously have been shown to contribute to long-term memory produced by Pavlovian conditioning. Cellular and synaptic mechanisms underlying short- and long-term memory for this example of associative learning are currently under investigation. Our recent studies have shown that one-trial conditioning results in an intermediate phase of memory that is characterized by enhanced cellular excitability and the phosphorylation of CSP24, a beta-thymosin-like protein. Inhibition of CSP24 protein expression blocks the development of intermediate-term memory in Hermissenda. The mechanisms underlying memory associated with Pavlovian conditioning of Hermissenda are being investigated using molecular and cellular neurophysiological techniques.
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Selected Reading
Crow, T, Tian, L-M. (2004) Statocyst hair cell activation of identified interneurons and foot contraction motor neurons in Hermissenda. Journal of Neurophysiology, 92: 2874-2883.
Crow, T. (2004) Pavlovian conditioning of Hermissenda: Current cellular, molecular, and circuit perspectives. Learning and Memory 11: 229-238.
Yamoah, EN, Levic, S, Redell, J, Crow, T. (2005) Inhibition of conditioned stimulus pathway phosphoprotein 24 expression blocks the reduction in A-type transient K+ current produced by one-trial in vitro conditioning of Hermissenda. Journal of Neuroscience, 25: 4793-4800.
Tian, L-M, Kawai, R, Crow, T. (2006) Serotonin-immunoreactive CPT interneurons in Hermissenda: Identification of sensory input and motor projections. Journal of Neurophysiology, 96: 327-335.
Crow, T, Tian, L-M. (2006) Pavlovian conditioning in Hermissenda: a circuit analysis. The Biological Bulletin, 210: 289-297. A contribution to The Biological Bulletin Virtual Symposium on Marine Invertebrate Models of Learning and Memory.
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