Modulation of NMDA receptors by pregnenolone sulphate, eicosapentaenoic acid, docosahexanoic acid, and linolenic acid D. Gunner, A. Macaulay, K.A. Wafford, S. Clark. Merck Sharp & Dohme Research Laboratories, Neuroscience Research Centre, Terlings Park, Harlow, Essex, CM20 2QR.

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Evidence suggests that hypofunction of glutamatergic neurotransmission may result in the behavioural symptoms of schizophrenia (Tsai and Coyle, 2002). Here we report on the effects of four compounds, pregnenolone sulphate (PS), eicosapentaenoic acid (EPA), docosahexanoic acid (DHA), and linolenic acid on cloned NMDA receptors.

Whole cell patch clamp recordings were obtained from cell lines stably expressing NR1a + NR2A, NR2B, or NR2D NMDA receptor subunits. All recordings were made as described by Priestley et al. (1995). Data are mean ± sem from between 3 and 11 cells, statistical analysis was performed using a paired student's t test. Glycine was used at 10µM throughout. Glutamate concentration-response curves were normalised to the control response to 10µM glutamate.

At 1-100µM all four compounds produced a concentration dependent potentiation of the EC₂₀ glutamate response (0.3µM) in cells expressing both NR2A and NR2B. At 100µM, PS, EPA, and linolenic acid potentiated the response at NR2A receptors by 108.1 ± 6.5%, 135.0 ± 17.0% and 104.2 ± 15.0% respectively. DHA at 30µM potentiated the response by 140.5±12.5%. At NR2B receptors 100µM PS, EPA and linolenic acid potentiated the EC₂₀ response by 124.3 ± 10.6% 100.9% ± 4.8 and 130.2% ± 13.1 respectively. 30µM DHA potentiated the response by 55.3 ± 6.3%. Conversely 100µM PS and EPA inhibited responses to 1µM glutamate at NR1a + NR2D by 40.5% ± 2.1 and 50.7% ± 11.2 respectively. Glutamate dose response curves were obtained in the presence and absence of 100µM PS, EPA, and 50µM DHA. PS significantly decreased the EC₅₀ for both NR2A and NR2B receptors (NR2A: 1.9 ± 0.03µM vs. 1.1 ± 0.04µM, p<0.003; NR2B: 0.54 ± 0.08µM vs. 0.30 ± 0.03µM, p<0.03). The maximal NR2A current was significantly increased (1.09 ± 0.04 vs. 1.32 ± 0.03, p<0.002) while the maximal NR2B current was unaffected (1.06 ± 0.07 vs. 1.06 ± 0.01, p> 0.1). In contrast, EPA caused a significant increase in both NR2A and NR2B maximal currents (NR2A: 1.01 ± 0.02 vs. 1.33 ± 0.02, p<0.03; NR2B: 0.99 ± 0.04 vs. 1.15 ± 0.04, p<0.04). EPA significantly reduced the NR2A EC₅₀ but had no effect on NR2B (NR2A: 0.81 ± 0.02µM vs. 0.71 ± 0.02µM, p<0.04; NR2B: 0.64 ± 0.07µM vs. 0.59 ± 0.05µM, p>0.1). DHA had no effect on the maximal current for either NR2A or NR2B receptors (NR2A: 1.17 ± 0.08 vs. 1.67 ± 0.25, p>0.1; NR2B: 1.06 ± 0.07 vs. 0.97 ± 0.06, p>0.5). It did however significantly reduce the NR2B EC₅₀ (0.75 ± 0.07µM vs. 0.46 ± 0.08µM, p< 0.03).

In conclusion we have shown that PS, EPA, DHA, and linolenic acid potentiate glutamate responses of NR2A and NR2B NMDA receptors. The modulatory effects of these compounds are subunit specific since both EPA and PS inhibit NR2D receptors.

Priestley T. et al. (1995) Mol. Pharmacol. 48: 841-8.
Tsai G. and Coyle J.T. (2002). Ann. Rev. Pharmacol. Toxicol. 42:165