LEARNING AND FEAR
A puzzling problem in fear research is whether plasticity in the amygdala related to fear conditioning is mediated solely by NMDA receptors or other receptors, such as AMPA receptors, are involved.
Both NMDA and AMPA are glutamate receptors. NMDA (from N-methyl-D-aspartate) receptors cause long-term potentiation (LTP) essential for the associative learning in fear conditioning, while AMPA (from α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors or metabotropic glutamate receptors alters fear conditioning in a still unclear way.
Goosens & Maren (Goosens K. A. & Maren S., NMDA receptors are essential for the acquisition, but not expression, of conditional fear and associative spike firing in the lateral amygdala. Eur. J. of Neurosci. 20, 537-548, 2004) in a new study, published in the European Journal of Neuroscience, show that NMDA receptors are essential for the acquisition of both fear conditioning and the associated neurophysiological changes in the lateral amygdala, but not for the expression of these changes. AMPA receptors in the amygdala seem not to be able to support either conditioned fear learning or associative neuronal plasticity after training, but they are sufficient for the expression of the conditioned fear response.
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