(A) Diagram illustrating the PKMζ-compensation hypothesis tested by pharmacogenetic analysis of LTP. The Prkcz gene consists of an autoinhibitory PKCζ regulatory domain exon region (Reg, shown in red) and a catalytic domain exon region (Cat, green). In neurons in wild-type mice, PKMζ is produced by an internal promoter within the Prkcz gene, transcribing a PKMζ mRNA that expresses an independent ζ catalytic domain (indicated as step  [Hernandez et al., 2003]). The PKMζ mRNA is transported to dendrites (Muslimov et al., 2004) but is translationally repressed ( [Hernandez et al., 2003]). During tetanic stimulation, glutamate (Glu) activates the NMDAR to stimulate Ca2+-dependent induction mechanisms that release the translational block ( [Hernandez et al., 2003]), resulting in synthesis of PKMζ ( [Hernandez et al., 2003]), which potentiates postsynaptic AMPARs ( [Ling et al., 2002; Serrano et al., 2005]). If wild-type mice express persistently enhanced AMPAR-mediated synaptic transmission through synthesis of PKMζ and PKMζ-null mice through compensatory mechanisms, then PKMζ-antisense will block LTP in wild-type mice (left) but have no effect in PKMζ-null mice (right). (B) The PKMζ-antisense (20 µM) blocks the new synthesis of PKMζ, but not PKCι/λ or the eukaryotic elongation factor 1A (eEF1A) that are also rapidly synthesized in LTP. In the presence of antisense or scrambled oligodeoxynucleotides, adjacent slices from the same hippocampus are either tetanized or untetanized, and 30-min post-tetanization CA1 regions are assayed by immunoblot. The levels of protein in the untetanized slices are set at 100%. Mean ± SEM; *denotes significance; n.s., no significance. PKMζ: scrambled, tetanized (n = 17) vs. untetanized (n = 19), t34 = 3.81, p = 0.00056, d = 1.27; antisense, tetanized (n = 12) vs. untetanized (n = 18), t28 = 1.35, p = 0.19, d = 0.50; antisense vs. scrambled, t27 = 2.12, p = 0.043, d = 0.80; PKCι/λ: scrambled, tetanized (n = 17) vs. untetanized (n = 18), t33 = 3.72, p = 0.00074, d = 1.26; antisense, tetanized (n = 12) vs. untetanized (n = 17), t27 = 3.59, p = 0.0013, d = 1.35; antisense vs. scrambled, t27 = 0.71, p = 0.49, d = 0.27; eEF1A: scrambled, tetanized (n = 9) vs. untetanized (n = 10), t17 = 2.40, p = 0.028, d = 1.10; antisense, tetanized (n = 12) vs. untetanized (n = 18), t28 = 2.07, p = 0.048, d = 0.77; antisense vs. scrambled, t19 = 0.47, p = 0.64, d = 0.21. (C) PKMζ-antisense blocks late-LTP in wild-type mice but has no effect on LTP in PKMζ-null mice. Left, representative fEPSPs; numbers correspond to time points at right. Right, mean ± SEM. Scrambled version of the oligodeoxynucleotide has no effect on either genotype. Circles show tetanized pathways, and color-coded squares show control untetanized pathways within each slice that receive only test stimulation. Tetanization is at arrow. N’s are: wild-type + antisense: 7; PKMζ-null + antisense: 5; wild-type + scrambled: 8; PKMζ-null + scrambled: 6. The genotype X drug X time ANOVA with repeated measures on time (average of the 5 min ending at 30 min post-tetanization and 180 min post-tetanization) confirmed a significant genotype X drug interaction, F1,22 = 4.7; p = 0.041, η2 = 0.0026. Post-hoc tests confirmed antisense on wild-type at 180 min post-tetanization is significantly less than all other responses.