S18986: a positive modulator of AMPA-receptors enhances (S)-AMPA-mediated BDNF mRNA and protein expression in rat primary cortical neuronal cultures.

The present study describes the effect of (S)-2,3-dihydro-[3,4]cyclopentano-1,2,4-benzothiadiazine-1,1-dioxide (S18986), a positive allosteric modulator of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors, on (S)-AMPA-mediated increases in brain-derived neurotrophic factor (BDNF) mRNA and protein expression in rat primary cortical neuronal cultures. (S)-AMPA (0.01-300 microM) induced a concentration-dependent increase in BDNF mRNA and protein expression (EC(50)=7 microM) with maximal increases (50-fold) compared to untreated cultures observed between 5 and 12 h, whereas for cellular protein levels, maximal expression was detected at 24 h. S18986 alone (< or =300 microM) failed to increase basal BDNF expression. However, S18986 (300 microM) in the presence of increasing concentrations of (S)-AMPA maximally enhanced AMPA-induced expression of BDNF mRNA and protein levels (3-5-fold). S18986 (100-300 microM) potentiated BDNF mRNA induced by 3 microM (S)-AMPA (2-3-fold). Under similar conditions, the AMPA allosteric modulator cyclothiazide induced a potent stimulation of (S)-AMPA-mediated BDNF expression (40-fold; EC(50)=18 microM), whereas IDRA-21 was inactive. Kinetic studies indicated that S18986 (300 microM) in the presence of 3 microM (S)-AMPA was capable of enhancing BDNF mRNA levels for up to 25 h, compared to 3 microM (S)-AMPA alone. On the other hand, S18986 only partially enhanced kainate-mediated expression of BDNF mRNA, but failed to significantly enhance N-methyl-D-aspartate-stimulated BDNF expression levels. In support of these observations, the competitive AMPA receptor antagonist NBQX (1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide) but not the selective NMDA-receptor antagonist, (+)-MK-801 [(5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine], abrogated S18986-induced effects on BDNF expression. S18986-mediated enhancement of (S)-AMPA-evoked BDNF protein expression was markedly attenuated in Ca(2+)-free culture conditions. Furthermore, from a series of kinase inhibitors only the Calmodulin-Kinase II/IV inhibitor (KN-62, 25 microM) significantly inhibited (-85%, P<0.001) AMPA+S18986 stimulated expression of BDNF mRNA. The present study supports the observations that AMPA receptor allosteric modulators can enhance the expression of BDNF mRNA and protein expression via the AMPA receptor in cultured primary neurones. Consequently, the long-term elevation of endogenous BDNF expression by pharmacological intervention with this class of compounds represents a potentially promising therapeutic approach for behavioural disorders implicating cognitive deficits.