Figure 5. TGF-β1-deficient hippocampal neurons are sensitive to high extracellular glutamate concentrations.

(A) Treatment with TGF-β1 (25 ng ml⁻¹, 2 hrs) does not affect glutamate uptake in dissociated hippocampal neurons. TBOA treatment (2 hrs) reduces glutamate uptake in dissociated neurons. (B) Photomicrographs illustrate calcium-induced fluorescence signals in the somata of dissociated hippocampal neurons (t 1–7.5 min). Heat map indicates fluorescence intensity (Ratio F340/380). (C) Pre-treatment with TGF-β1 (25 ng ml⁻¹, 2 hrs) decreases cytosolic calcium responses in a dose-dependent fashion. (D) Effect of TGF-β1 on BIC/4-AP-induced calcium responses (t_AUC = 2.0–5.5 min). (E) Effect of TGF-β1 on NMDA-induced calcium responses (t_AUC = 7.0–8.5 min). (F) Effect of TGF-β1 on the ratio of synaptic to extrasynaptic calcium signals. (G) TGF-β1 deficiency does not affect synaptic calcium signals. (H) TGF-β1-deficiency increases extrasynaptic calcium signals. (I) TGF-β1-deficiency decreases the ratio of synaptic to extrasynaptic calcium responses. (J) Treatment with TGF-β1 (25 ng ml⁻¹, 2 hrs) prevents neuronal death induced by stimulation of extrasynaptic NMDARs. (K) Effect of co-perfusion of Ro 25-6189 (2.5 μM) and the subunit-unspecific NMDAR antagonist D-AP5 (100 μM) on extrasynaptic NMDAR-mediated calcium responses in cultured hippocampal neurons. (L) Co-perfusion of low-dose memantine (10 μM) had no effect on synaptic calcium responses blocked NMDA-mediated calcium responses. (M) Memantine blocks extrasynaptic calcium responses. (N) Application of memantine during BIC/4-AP pulses increases the number of BIC-evoked peaks/cell (O) Application of memantine has no effect on the synaptic peak area/#peaks. [*p < 0.05; **p<0.01; ***p<0.001]