sentence: The putative cellular mechanisms that underlie LTP1 , including enhanced release of neurotransmitter ( Bayazitov et al ., 2007 ) , protein kinase activation ( Sacktor et al ., 1993 ; Lisman et al ., 2012 ) , and trafficking of both α - amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ( AMPA ) and N-methyl-D-aspartate ( NMDA ) subtypes of glutamate receptors to synapses ( Williams et al ., 1998 ; Hayashi et al ., 2000 ; Shi et al ., 2001 ) , are likely to only explain short term synaptic strengthening .