The extracellular levels of selected amino acids in the cerebellar posterior interpositus nucleus (PIN) during classical eyeblink conditioning was analyzed in alert cats using a delay paradigm. Animals were prepared for the chronic recording of eyelid movements (with the magnetic search-coil technique) and the electromyographic activity of the orbicularis oculi muscle. With the help of a guide and push-pull cannulae, selected PIN sites were perfused daily during classical eyeblink conditioning. The perfusate was sampled at intervals of 5 min and analyzed with a high-pressure liquid chromatography- electrochemical detection (HPLC-EC) method. The analysis of push-pull perfusate revealed a significant increase in the release of glycine, taurine, and glutamate across the successive conditioning sessions, in parallel with the acquisition of eyelid conditioned responses (CRs). Both CRs and extracellular levels of these three amino acids returned to control values during extinction. Other amino acids (alanine, GABA, glutamine, serine, and threonine) did not undergo modifications in their extracellular concentrations across the training. Results are discussed with regard to the role of PIN in this type of associative learning.
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