Korean J Physiol Pharmacol.  2013 Feb;17(1):51-56. 10.4196/kjpp.2013.17.1.51.

Phorbol 12-Myristate 13-Acetate Enhances Long-Term Potentiation in the Hippocampus through Activation of Protein Kinase Cdelta and epsilon

• Kim EC
• Lee MJ
• Shin SY
• Seol GH
• Han SH
• Yee J
• Kim C
• Min SS

• KMID: 1432763
• DOI: http://doi.org/10.4196/kjpp.2013.17.1.51

Abstract

Many intracellular proteins and signaling cascades contribute to the sensitivity of N-methyl-D-aspartate receptors (NMDARs). One such putative contributor is the serine/threonine kinase, protein kinase C (PKC). Activation of PKC by phorbol 12-myristate 13-acetate (PMA) causes activation of extracellular signal-regulated kinase (ERK) and promotes the formation of new spines in cultured hippocampal neurons. The purpose of this study was to examine which PKC isoforms are responsible for the PMA-induced augmentation of long-term potentiation (LTP) in the CA1 stratum radiatum of the hippocampus in vitro and verify that this facilitation requires NMDAR activation. We found that PMA enhanced the induction of LTP by a single episode of theta-burst stimulation in a concentration-dependent manner without affecting to magnitude of baseline field excitatory postsynaptic potentials. Facilitation of LTP by PMA (200 nM) was blocked by the nonspecific PKC inhibitor, Ro 31-8220 (10microM); the selective PKCdelta inhibitor, rottlerin (1microM); and the PKCepsilon inhibitor, TAT-epsilonV1-2 peptide (500 nM). Moreover, the NMDAR blocker DL-APV (50microM) prevented enhancement of LTP by PMA. Our results suggest that PMA contributes to synaptic plasticity in the nervous system via activation of PKCdelta and/or PKCepsilon, and confirm that NMDAR activity is required for this effect.

Keyword

Hippocampus; Long-term potentiation (LTP); Phorbol 12-myristate 13-acetate; Protein kinase C (PKC); Synaptic plasticity

MeSH Terms

2-Amino-5-phosphonovalerate
Acetophenones
Benzopyrans
Excitatory Postsynaptic Potentials
Hippocampus
Indoles
Long-Term Potentiation
Nervous System
Neurons
Phorbols
Phosphotransferases
Protein Isoforms
Protein Kinases
Proteins
Receptors, N-Methyl-D-Aspartate
Spine
2-Amino-5-phosphonovalerate
Acetophenones
Benzopyrans
Indoles
Phorbols
Phosphotransferases
Protein Isoforms
Protein Kinases
Proteins
Receptors, N-Methyl-D-Aspartate

Figure

• 

  Fig. 1 Effects of PMA on the induction of LTP by one episode of TBS. (A) PMA enhanced LTP induced by one episode of TBS in a concentration-dependent manner. fEPSP values (as percentages of baseline) are plotted against time. (B) Averaged values from 58 to 60 min after TBS in the experiment reported on the left are represented as a bar graph. All values are expressed as means±SEMs (error bars). Values in parentheses are numbers of animals and slices tested. *p<0.05, **p<0.01 compared to vehicle.

• 

  Fig. 2 Effects of PKCδ and PKCε inhibitors on facilitation of LTP by PMA. (A) The potentiating effect of PMA (200 nM) was blocked in the presence of Ro 31-8220 (10µM; a nonspecific PKC inhibitor), (B) rottlerin (1µM; a selective PKCδ inhibitor), and (C) TAT-εV1-2 peptide (500 nM; a PKCε inhibitor). (D) Averaged values from 58 to 60 min after a single episode of TBS from the experiment reported in A, B and C, are represented in bar graph form. All values are expressed as means±SEMs (error bars). Values in parentheses are numbers of animals and slices tested. *p<0.05 compared to vehicle. Rot, rottlerin; εV1-2, TAT-εV1-2.

• 

  Fig. 3 Involvement of NMDA receptors in PMA-induced facilitation of LTP and PPF. (A) In the presence of DL-APV, PMA did not facilitate the induction of LTP by one episode of TBS. (B) Averaged values from 58 to 60 min after TBS in the experiment shown on the left are represented as bar graphs. (C) PPF ratios were similar between PMA and control groups. (D) Areas under the curves (AUC) of PPF ratio were calculated to compared the basal levels of synaptic transmission. All values are expressed as means±SEMs (error bars). Values in parentheses are numbers of animals and slices tested. *p<0.05 compared to vehicle. DAP5, DL-APV.

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