Memantine, an NMDA receptor antagonist, improves working memory deficits in DGKβ knockout mice

Neuroscience Letters 630 (2016) 228–232

Contents lists available at ScienceDirect

Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet

Research article

Memantine, an NMDA receptor antagonist, improves working memory deficits in DGK␤ knockout mice Kenichi Kakefuda, Mitsue Ishisaka, Kazuhiro Tsuruma, Masamitsu Shimazawa, Hideaki Hara (Ph.D.) (Professor) ∗ Department of Biofunctional Evaluation, Molecular Pharmacology, Gifu Pharmaceutical University, Gifu, Japan

h i g h l i g h t s • Memantine improved the working memory deficit observed in DGK␤ KO mice. • NR2A and NR2B NMDA receptor subunit levels were increased in the prefrontal cortex of DGK␤ KO mice. • NR2A and NR2B NMDA receptor subunit levels were decreased in the hippocampus of DGK␤ KO mice.

a r t i c l e

i n f o

Article history: Received 26 June 2016 Received in revised form 20 July 2016 Accepted 30 July 2016 Available online 2 August 2016 Keywords: DGK␤ Working memory Memantine NMDA

a b s t r a c t Diacylglycerol kinase (DGK) ␤ is a type 1 isozyme of the DGK family. We previously reported that DGK␤ was deeply involved in neurite spine formation, and DGK␤ knockout (KO) mice exhibited behavioral abnormalities concerning spine formation, such as cognitive, emotional, and attentional impairment. Moreover, some of these abnormalities were ameliorated by the administration of a mood stabilizer. However, there is no data about how memory-improving drugs used in the treatment of Alzheimer’s disease affect DGK␤ KO mice. In the present study, we evaluated the effect of an anti-Alzheimer’s drug, memantine on the working memory deficit observed in DGK␤ KO mice. In the Y-maze test, the administration of memantine significantly improved working memory of DGK␤ KO mice. We also found that the expression levels of the NR2A and NR2B N-methyl-d-aspartate (NMDA) receptor subunits were increased in the prefrontal cortex, but decreased in the hippocampus of DGK␤ KO mice. These altered expression levels of NR2 subunits might be related to the effect of an NMDA receptor antagonist, memantine. Taken together, these findings may support the hypothesis that DGK␤ has a pivotal role in cognitive function. © 2016 Elsevier Ireland Ltd. All rights reserved.

1. Introduction Diacylglycerol kinase (DGK) is a member of the lipid kinases, and it phosphorylates diacylglycerol (DG) into phosphatidic acid (PA) downstream of Gq protein–coupled receptor signaling [18,31–33]. DG modulates not only protein kinase C function, but also other functional proteins such as Ras guanyl-releasing protein, protein kinase D, transient receptor potential cation channel C, and chimerins [18,31–33]. PA also has functions as a signal mediator, regulating the mammalian target of rapamycin, phosphatidylinositol 4-phosphate 5-kinase, and Akt [18,31–33]. Hence, DGK is a

∗ Corresponding author at: Department of Biofunctional Evaluation, Molecular Pharmacology, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu 5011196, Japan. E-mail address: [email protected] (H. Hara). http://dx.doi.org/10.1016/j.neulet.2016.07.061 0304-3940/© 2016 Elsevier Ireland Ltd. All rights reserved.

key second messenger that plays multiple roles in regulating cell signaling. In mammals, 10 DGK isozymes have been identified so far [26], and recently the function of each isozyme has become clearer. Among DGK isozymes, DGK␤ is classified as type 1, has EF-hand and recoverin homology, and shows Ca2+ sensitivity. DGK␤ is widely distributed in the brain, especially in the olfactory bulb, cerebral cortex, striatum, and hippocampus [10]. We previously investigated the various roles of DGK␤ in higher brain function, and found the following: (i) DGK␤ is involved in neurite spine formation. DGK␤ knock out (KO) mice showed significant reduction of spine density in the cortex, striatum, and hippocampus, which resulted in impairment of hippocampal long-term potentiation (LTP) and cognitive dysfunction [12,17,29]. (ii) DGK␤ KO mice also showed hyper locomotion, reduced anxiety, and attention deficit behaviors [13,17]. These behaviors indicate that DGK␤ also has a key role in emotion. It has been reported that a splice variant at the COOH-

K. Kakefuda et al. / Neuroscience Letters 630 (2016) 228–232

terminal of DGK␤ was related to bipolar disorder [5]. (iii) Finally, DGK␤ influenced the sensitivity to seizure-inducing stimuli [15]. Memantine is a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist [7]. In many countries, it has been approved for the treatment of moderate to severe Alzheimer’s disease (AD). Memantine has relatively low affinity for the NMDA receptor, strong voltage dependency, fast kinetics, and inhibits only low firing responses to the NMDA receptor [7]. These characteristics of memantine may enable the filtering of only the abnormal synaptic noise of AD patients without affecting the physiological stimuli of the NMDA receptor [16]. Therefore, memantine is of clinical benefit to AD patients. In preclinical studies, memantine also improved cognitive function and had neuroprotective effects not only in an AD animal model, but also in many other animal models such as the aged rodent, psychiatric disease model, and pharmacologically induced dementia animal model [2,4,6,8,19,20]. In the present study, to explore the characteristics of cognitive dysfunction in DGK␤ KO mice and the involvement of NMDA receptor signaling in it, we evaluated the effects of memantine on the cognitive deficits in DGK␤ KO mice and investigated the expression levels of NMDA receptor subunits in DGK␤ KO mice. 2. Materials and methods 2.1. Animals DGK␤ KO mice were generated using the Sleeping Beauty transposon system and backcrossed for more than nine generations onto a C57BL/N genetic background, as described previously [29]. In all experiments, we used littermates of DGK␤ KO mice and wild-type (WT) mice generated by breeding heterozygous mutants. The animals (male, 10–48 weeks old) were housed at 24 ± 2 ◦ C under a 12 h light-dark cycle (lights on from 08:00 to 20:00) and had ad libitum access to food and water. Behavioral experiments were performed between 10:00 and 18:00. All procedures relating to animal care and treatment conformed to the animal care guidelines of the Animal Experiment Committee of Gifu Pharmaceutical University. All efforts were made to minimize both suffering and the number of animals used. 2.2. Drug treatments Memantine hydrochloride (R&D Systems, Minneapolis, MN, USA) (2.5 mg/kg) was dissolved in distilled water. Thirty minutes before testing, we administered memantine or vehicle to mice perorally at a volume of 10 mL/kg. 2.3. Y-maze test The Y-maze test was performed to evaluate spatial working memory as previously described [29]. The apparatus consists of three identical arms (length × width × height, 40 × 10 × 12 cm). Thirty minutes after drug or vehicle administration, each mouse was placed at the end of a fixed arm and allowed to freely explore the maze for 8 min. The sequence of arm entries was recorded manually. An alternation was defined as entering each of the three arms consecutively. The maximum number of alternations was thus the total number of arms entered minus two, and the percentage of alternations was calculated as (actual alternations/maximum alternations) × 100. The total number of arms entered during the session was also recorded. 2.4. Western blot analysis Each mouse was decapitated under deep anesthesia induced by sodium pentobarbital (80 mg/kg, i.p.; Nacalai Tesque, Kyoto,

229

Japan). The brain was quickly removed from the skull, briefly washed in ice-cold saline, and laid on a cooled (4 ◦ C) metal plate, on which the brain was rapidly dissected to separate the hippocampus and prefrontal cortex (PFC). Brain samples were homogenized in 10 mL/g tissue ice-cold lysis buffer [50 mM Tris-HCl (pH8.0) containing 150 mM NaCl, 50 mM EDTA, 1% Triton X-100, and protease/phosphatase inhibitor mixture] and centrifuged at 12,000g for 20 min at 4 ◦ C. An aliquot of 5 ␮g of protein was subjected to 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with the separated protein being transferred onto a polyvinylidene difluoride membrane (Immobilon-P; Millipore, Billerica, MA, USA). For immunoblotting, the following primary antibodies were used: rabbit anti-GluR␧1 (NR2A) polyclonal antibody (1:1000 dilution; Frontier Science, Ishikari, Japan), rabbit anti-GluR␧2 (NR2B) polyclonal antibody (1:1000; Frontier Science), and anti-␤-actin (1:5000; Sigma Aldrich, St. Louis, MO, USA). The secondary antibodies were as follows: HRP-conjugated goat anti-mouse IgG and HRP-conjugated goat anti-rabbit IgG (1:4000; Pierce Biotechnology, Rockford, IL, USA). The immunoreactive bands were visualized using Super Signal West Femto Maximum Sensitivity Substrate (Thermo Scientific, Waltham, MA, USA). The band intensity was measured using a Luminescent image analyzer LAS-4000 UV mini (Fujifilm, Tokyo, Japan) and a Multi Gauge Ver. 3.0 (Fujifilm). For quantitative analysis, total proteins were used as loading controls for the phosphoprotein signal. 2.5. Statistical analysis Data are presented as the mean ± SEM. Statistical comparisons were made using a t-test or one-way ANOVA followed by Bonferroni’s Multiple Comparison Test using GraphPad Prism 5 (GraphPad Software, San Diego, CA, USA), with p < 0.05 considered to indicate statistical significance. 3. Results 3.1. Memantine improved working memory deficit in DGKˇ KO mice We previously determined that DGK␤ had an essential role in neurite spine formation, and demonstrated that DGK␤ KO mice showed cognitive deficits in both behavioral and electrophysiological aspects [29]. The cognitive dysfunctions of DGK␤ KO mice were ameliorated by administering a mood stabilizer, valproate [14]. However, there have been no data about how memory-improving drugs, like anti-Alzheimer’s drugs, may affect cognition in DGK␤ KO mice. Therefore, we evaluated the effect of memantine, an antiAlzheimer’s drug, on the cognition of DGK␤ KO mice using a Y-maze test. In this test, DGK␤ KO mice showed significantly lowered alternation rate, indicating a working memory deficit (Fig. 1A). A single administration of memantine significantly improved the alternation rate of DGK␤ KO mice to the WT levels (Fig. 1A). Memantine did not affect cognition in WT mice (Fig. 1A). There was no significant difference in the total entry number between the groups (Fig. 1B). 3.2. Expression levels of NMDA receptor subtypes were altered in DGKˇ KO mice Memantine improves cognitive function in AD patients by inhibiting the NMDA receptor. Memantine also ameliorated the working memory deficit in DGK␤ KO mice. We then compared protein expression levels of NMDA receptor subtypes in the PFC and hippocampus of DGK␤ KO mice. In the PFC, the protein expression levels of NR2A and NR2B subunits were significantly increased as compared to levels in WT (Fig. 2A–D). In contrast, both NR2A and

230

K. Kakefuda et al. / Neuroscience Letters 630 (2016) 228–232

Fig. 1. The effects of memantine on the cognitive deficit of DGK␤ KO mice. Each mouse (n = 10 for each group) was treated with either memantine (2.5 mg/kg, p.o.) or vehicle and performed the Y-maze test 30 min later. (A) The effect of memantine on spontaneous alternation behavior in Y-maze test. Values are expressed as the mean ± S.E.M. **; p < 0.01 (with one-way ANOVA and followed by Bonferroni’s multiple comparison test.) (B) The effect of memantine on the number of total arm entries in the Y-maze test. Values are expressed as the mean ± S.E.M. V; vehicle treated group, M; memantine treated group.

NR2B protein levels were decreased in the hippocampus of DGK␤ KO mice (Fig. 3A–D). 4. Discussion Since the cloning of DGK␤ in 1993 [10], the distribution, localization, and developmental expression of DGK␤ in the central nervous system (CNS) have been elucidated [1,10]. By generating and screening the phenotype of DGK␤ KO mice, we have also progressively clarified the function of DGK␤ in the CNS. In the present study, we found that acute administration of an NMDA receptor inhibitor, memantine, attenuated the working memory deficit in DGK␤ KO mice. We also detected altered expression levels of NR2 subunits in the PFC and hippocampus of DGK␤ KO mice. These data provide a hint in understanding the role of DGK␤ in cognitive function. Memantine can improve cognitive function not only in AD patients but also in some animal models as described in the introduction. Our data in the present study support these positive aspects of memantine. On the other hand, some reports

Fig. 2. NR2A and 2 B expression in the cortex of DGK␤ KO mice. NR2A and NR2B, subunits of the NMDA receptor, levels in the prefrontal cortex were measured using western blot analysis. (A) Representative immunoblot bands showing the expression levels of NR2A and ␤-actin in the prefrontal cortex of WT (n = 4) and DGK␤ KO (n = 4) mice. (B) Density of NR2A quantified relative to ␤-actin. Values are expressed as the mean ± S.E.M. **; p < 0.01 vs. WT mice group (t-test). (C) Representative immunoblot bands showing the expression levels of NR2B and ␤-actin in the prefrontal cortex of WT (n = 7) and DGK␤ KO (n = 7) mice. (D) Density of NR2B quantified relative to ␤-actin. Values are expressed as the mean ± S.E.M. **; p < 0.01 vs. WT mice group (t-test).

have demonstrated that memantine can worsen cognitive function in animals [24,25]. It is known that memantine shows a concentration-dependent biphasic effect on cognitive function [9,11]. Wise et al. reported that memantine enhanced the cognitive performance of the aged rat in an inverted U-shaped dose-response relationship [35]. These reports indicate that adequate inhibition of NMDA receptor by memantine is beneficial for cognition, though excessive inhibition worsens cognition. When discussing these issues, it would be helpful to evaluate the pharmacokinetic information of a compound. We decided the dose and route

K. Kakefuda et al. / Neuroscience Letters 630 (2016) 228–232

231

the abnormal spatial performance [34]. Moreover, hippocampus specific NR2B disrupted mice also showed the spatial working memory deficit [34]. These cognitive impairments described above are all hippocampal-dependent behavior, indicating the presence of NR2 subunits is crucial for hippocampal memory function. DGK␤ KO mice also showed decreased the expression of NR2A and NR2B in the hippocampus. These alterations might be related to reduced LTP and spatial memory deficit in DGK␤ KO mice [29]. In contrast, the effect of increased NR2 expression on cognitive function is still under debate. It has been reported that genetic overexpression of the NR2B subunit in mice enhanced cognitive function [30]. On the other hand, rats neonatally administrated phencyclidine (PCP) exhibited elevated expressions of both NR2A and NR2B subunits in PFC, but not hippocampus [22]. This neonatal PCP model mouse showed the schizophrenia-like behavioral abnormalities, including a spatial working memory deficit [21,28]. The difference of these two reports is the brain area of NR2 overexpression. PFC specific NR2 overexpression might be related to the cognitive dysfunction. The neonatal PCP model and our DGK␤ KO mice have a number of shared characteristics. Both animals showed hyperactivity, impaired working memory, and decreased neurite spine density, in addition to an elevated NR2 expression level, in the PFC [21,22,28]. According to the literature described above and the results we obtained in this study, alteration of the NR2 subunit in both brain areas of DGK␤ KO mice could result in the cognitive impairment. In addition, working memory improving action of memantine in this study might be an adequate regulation of altered NMDA receptor conditions in PFC. Because the working memory deficit expressed in the Y-maze test is generally known as a cortical region-dependent memory In the present study, we have not clarified the mechanism of action of memantine totally, and further studies are needed to elucidate how DGK␤ modulates the effects of memantine or NR2 subunits expression. To evaluate the effects of memantine on hippocampal-dependent behavior is also helpful to elucidate the detail of NR2 subunits function in DGK␤ KO mice. However, the data suggest that role of NMDA receptors may be involved in the cognitive dysfunction observed in DGK␤ KO mice. References

Fig. 3. NR2A and 2 B expressions in the hippocampus of DGK␤ KO mice. NR2A and NR2B, subunits of the NMDA receptor, levels in the hippocampus were measured using western blot analysis. (A) Representative immunoblot bands showing expression levels of NR2A and ␤-actin in the hippocampus of WT (n = 4) and DGK␤ KO (n = 4) mice. (B) Density of NR2A quantified relative to ␤-actin. Values are expressed as the mean ± S.E.M. *; p < 0.05 vs. WT mice group (t-test). (C) Representative immunoblot bands showing the expression levels of NR2B and ␤-actin in the hippocampus of WT (n = 7) and DGK␤ KO (n = 7) mice. (D) Density of NR2B quantified relative to ␤-actin. Values are expressed as the mean ± S.E.M. **; p < 0.01 vs. WT mice group (t-test).

of memantine (2.5 mg/kg, p.o.) by referring to the protocol of Nagakura et al. [20]. They found that the plasma concentration of memantine reached approximately 1 ␮M when 2.5 mg of memantine was administered orally to an AD model mice. Because a therapeutically relevant plasma concentration is approximately 1 ␮M in a clinical setting [23], this dosage might also be suitable for experimentation in mice. A number of studies have been performed investigating the involvement of NR2 subunit expression levels in cognitive function. Genetically NR2A-disrupted mice showed impaired spatial memory [3,27]. Mice lacking the NR2B subunit in the forebrain presented

[1] N. Adachi, M. Oyasu, T. Taniguchi, Y. Yamaguchi, R. Takenaka, Y. Shirai, N. Saito, Immunocytochemical localization of a neuron-specific diacylglycerol kinase beta and gamma in the developing rat brain, Brain Res. Mol. Brain Res. 139 (2005) 288–299. [2] S.N. Amin, A.A. El-Aidi, M.M. Ali, Y.M. Attia, L.A. Rashed, Modification of hippocampal markers of synaptic plasticity by memantine in animal models of acute and repeated restraint stress: implications for memory and behavior, Neuromol. Med. 17 (2015) 121–136. [3] D.M. Bannerman, B. Niewoehner, L. Lyon, C. Romberg, W.B. Schmitt, A. Taylor, D.J. Sanderson, J. Cottam, R. Sprengel, P.H. Seeburg, G. Kohr, J.N. Rawlins, NMDA receptor subunit NR2A is required for rapidly acquired spatial working memory but not incremental spatial reference memory, J. Neurosci. 28 (2008) 3623–3630. [4] C.A. Barnes, W. Danysz, C.G. Parsons, Effects of the uncompetitive NMDA receptor antagonist memantine on hippocampal long-term potentiation short-term exploratory modulation and spatial memory in awake, freely moving rats, Eur. J. Neurosci. 8 (1996) 565–571. [5] A. Caricasole, E. Bettini, C. Sala, R. Roncarati, N. Kobayashi, F. Caldara, K. Goto, G.C. Terstappen, Molecular cloning and characterization of the human diacylglycerol kinase beta (DGKbeta) gene: alternative splicing generates DGKbeta isotypes with different properties, J. Biol. Chem. 277 (2002) 4790–4796. [6] W. Chung, S.Y. Choi, E. Lee, H. Park, J. Kang, H. Park, Y. Choi, D. Lee, S.G. Park, R. Kim, Y.S. Cho, J. Choi, M.H. Kim, J.W. Lee, S. Lee, I. Rhim, M.W. Jung, D. Kim, Y.C. Bae, E. Kim, Social deficits in IRSp53 mutant mice improved by NMDAR and mGluR5 suppression, Nat. Neurosci. 18 (2015) 435–443. [7] W. Danysz, C.G. Parsons, The NMDA receptor antagonist memantine as a symptomatological and neuroprotective treatment for Alzheimer’s disease: preclinical evidence, Int. J. Geriatr. Psychiatry 18 (2003) S23–32. [8] B.D. Drever, W.G. Anderson, H. Johnson, M. O’Callaghan, S. Seo, D.Y. Choi, G. Riedel, B. Platt, Memantine acts as a cholinergic stimulant in the mouse hippocampus, J. Alzheimers Dis. 12 (2007) 319–333.

232

K. Kakefuda et al. / Neuroscience Letters 630 (2016) 228–232

[9] M.H. Gharedaghi, R. Rahimian, A.R. Dehpour, Y. Yousefzadeh-Fard, A. Mohammadi-Farani, Dinitrobenzene sulphonic acid-induced colitis impairs spatial recognition memory in mice: roles of N-methyl D-aspartate receptors and nitric oxide, Psychopharmacology (Berl.) 232 (2015) 3081–3090. [10] K. Goto, H. Kondo, Molecular cloning and expression of a 90-kDa diacylglycerol kinase that predominantly localizes in neurons, Proc. Natl. Acad. Sci. U. S. A. 90 (1993) 7598–7602. [11] S. Guadagna, C. Bundgaard, N. Hovelso, C. Volbracht, P.T. Francis, J. Egebjerg, F. Sotty, Memantine potentiates hippocampal theta oscillations at a therapeutic dose in anesthetized mice: a mechanistic link to its cognitive-enhancing properties, Neuropharmacology 62 (2012) 2208–2218. [12] Y. Hozumi, K. Kakefuda, M. Yamasaki, M. Watanabe, H. Hara, K. Goto, Involvement of diacylglycerol kinase beta in the spine formation at distal dendrites of striatal medium spiny neurons, Brain Res. 1594 (2015) 36–45. [13] M. Ishisaka, K. Kakefuda, A. Oyagi, Y. Ono, K. Tsuruma, M. Shimazawa, K. Kitaichi, H. Hara, Diacylglycerol kinase beta knockout mice exhibit attention-deficit behavior and an abnormal response on methylphenidate-induced hyperactivity, PLoS One 7 (2012) e37058. [14] M. Ishisaka, S. Tsujii, T. Mizoguchi, K. Tsuruma, M. Shimazawa, H. Hara, The effects of valproate and olanzapine on the abnormal behavior of diacylglycerol kinase beta knockout mice, Pharmacol. Rep. 67 (2015) 275–280. [15] M. Ishisaka, K. Tsuruma, M. Shimazawa, Y. Shirai, N. Saito, H. Hara, Increased seizure susceptibility in a mouse with diacylglycerol kinase beta deficiency, J. Pharmacol. Sci. 121 (2013) 181. [16] M.W. Jones, M. McClean, C.G. Parsons, P.M. Headley, The in vivo relevance of the varied channel-blocking properties of uncompetitive NMDA antagonists: tests on spinal neurones, Neuropharmacology 41 (2001) 50–61. [17] K. Kakefuda, A. Oyagi, M. Ishisaka, K. Tsuruma, M. Shimazawa, K. Yokota, Y. Shirai, K. Horie, N. Saito, J. Takeda, H. Hara, Diacylglycerol kinase beta knockout mice exhibit lithium-sensitive behavioral abnormalities, PLoS One 5 (2010) e13447. [18] S. Krishna, X.P. Zhong, Regulation of lipid signaling by diacylglycerol kinases during t cell development and function, Front. Immunol. 4 (2013) 178. [19] R. Minkeviciene, P. Banerjee, H. Tanila, Memantine improves spatial learning in a transgenic mouse model of Alzheimer’s disease, J. Pharmacol. Exp. Ther. 311 (2004) 677–682. [20] A. Nagakura, Y. Shitaka, J. Yarimizu, N. Matsuoka, Characterization of cognitive deficits in a transgenic mouse model of Alzheimer’s disease and effects of donepezil and memantine, Eur. J. Pharmacol. 703 (2013) 53–61. [21] A. Nakatani-Pawlak, K. Yamaguchi, Y. Tatsumi, H. Mizoguchi, Y. Yoneda, Neonatal phencyclidine treatment in mice induces behavioral, histological and neurochemical abnormalities in adulthood, Biol. Pharm. Bull. 32 (2009) 1576–1583.

[22] S. Owczarek, J. Hou, T. Secher, L.V. Kristiansen, Phencyclidine treatment increases NR2A and NR2B N-methyl-D-aspartate receptor subunit expression in rats, Neuroreport 22 (2011) 935–938. [23] C.G. Parsons, W.G. Danysz Quack, Memantine is a clinically well tolerated N-methyl-D-aspartate (NMDA) receptor antagonist–a review of preclinical data, Neuropharmacology 38 (1999) 735–767. [24] M.N. Quan, N. Zhang, Y.Y. Wang, T. Zhang, Z. Yang, Possible antidepressant effects and mechanisms of memantine in behaviors and synaptic plasticity of a depression rat model, Neuroscience 182 (2011) 88–97. [25] B.J. Saab, R.M. Luca, W.B. Yuen, A.M. Saab, J.C. Roder, Memantine affects cognitive flexibility in the Morris water maze, J. Alzheimers Dis. 27 (2011) 477–482. [26] F. Sakane, S. Imai, M. Kai, S. Yasuda, H. Kanoh, Diacylglycerol kinases: why so many of them? Biochim. Biophys. Acta 1771 (2007) 793–806. [27] K. Sakimura, T. Kutsuwada, I. Ito, T. Manabe, C. Takayama, E. Kushiya, T. Yagi, S. Aizawa, Y. Inoue, H. Sugiyama, et al., Reduced hippocampal LTP and spatial learning in mice lacking NMDA receptor epsilon 1 subunit, Nature 373 (1995) 151–155. [28] T. Secher, V. Berezin, E. Bock, B. Glenthoj, Effect of an NCAM mimetic peptide FGL on impairment in spatial learning and memory after neonatal phencyclidine treatment in rats, Behav. Brain Res. 199 (2009) 288–297. [29] Y. Shirai, T. Kouzuki, K. Kakefuda, S. Moriguchi, A. Oyagi, K. Horie, S.Y. Morita, M. Shimazawa, K. Fukunaga, J. Takeda, N. Saito, H. Hara, Essential role of neuron-enriched diacylglycerol kinase (DGK), DGKbeta in neurite spine formation, contributing to cognitive function, PLoS One 5 (2010) e11602. [30] Y.P. Tang, E. Shimizu, G.R. Dube, C. Rampon, G.A. Kerchner, M. Zhuo, G. Liu, J.Z. Tsien, Genetic enhancement of learning and memory in mice, Nature 401 (1999) 63–69. [31] M.K. Topham, R.M. Epand, Mammalian diacylglycerol kinases: molecular interactions and biological functions of selected isoforms, Biochim. Biophys. Acta 1790 (2009) 416–424. [32] M.K. Topham, S.M. Prescott, Mammalian diacylglycerol kinases, a family of lipid kinases with signaling functions, J. Biol. Chem. 274 (1999) 11447–11450. [33] W.J. van Blitterswijk, B. Houssa, Properties and functions of diacylglycerol kinases, Cell. Signal. 12 (2000) 595–605. [34] J. von Engelhardt, B. Doganci, V. Jensen, O. Hvalby, C. Gongrich, A. Taylor, C. Barkus, D.J. Sanderson, J.N. Rawlins, P.H. Seeburg, D.M. Bannerman, H. Monyer, Contribution of hippocampal and extra-hippocampal NR2B-containing NMDA receptors to performance on spatial learning tasks, Neuron 60 (2008) 846–860. [35] L.E. Wise, A.H. Lichtman, The uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist memantine prolongs spatial memory in a rat delayed radial-arm maze memory task, Eur. J. Pharmacol. 575 (2007) 98–102.