Article Figures & Data
Figures
- Figure 1.
MSO causes an acute decrease in synaptic transmission that appears to be independent of glutamate–glutamine cycle inhibition. A, fEPSPs recorded in stratum radiatum of CA1 in rat hippocampal slices (n = 9) are inhibited by MSO (10 mm); however, glutamine (Gln; 4 mm) does not prevent the effect. B, Input–output relationships in slices incubated in MSO (40 mm; n = 11) or control solution (n = 9) for >4 h are not significantly different (p > 0.05 for all fiber volley amplitudes). Representative traces at three fiber volley amplitudes are shown to the right for a control slice (top) and a MSO incubated slice (bottom). FV, Fiber volley. Calibration: 0.5 mV, 10 ms.
- Figure 2.
MeAIB produces a rapidly reversible acute depression of synaptic transmission. A, Depression of fEPSPs recorded in stratum radiatum of CA1 is observed after MeAIB (25 mm) application (n = 7). B, Incubation in MeAIB (25 mm) for more than 4 h does not change the input–output curve (control, n = 16; MeAIB, n = 14; p > 0.05 for all fiber volley amplitudes). Representative traces in control slices (top) and MeAIB-incubated slices (bottom) are shown to the right. FV, Fiber volley. Calibration: 0.5 mV, 10 ms.
- Figure 3.
Increasing extracellular glutamine enhances synaptic transmission and vesicular glutamate content in hippocampal slice. A, Input–output relationship of the AMPA-mediated fEPSPs in hippocampal slices incubated in 4 mm glutamine (n = 16) compared with a 4 mm sucrose osmotic control (n = 15) are statistically greater at all fiber volley amplitudes (p < 0.05). Sample fEPSPs at different fiber volley amplitudes from each group are shown to the right. Calibration: 0.5 mV, 10 ms. B, Input–output curve of NMDA-mediated fEPSP in 4 mm glutamine-incubated slices (n = 13) is significantly enhanced over control slices (n = 12). Representative traces from three fiber volley amplitudes are shown to the right for glutamine-incubated (top) and control (bottom) slices. Calibration: 0.1 mV, 10 ms. C, Inhibition of evoked EPSCs by the low-affinity AMPA receptor antagonist γ-DGG (0.5 mm) is reduced in 4 mm glutamine-incubated slices (n = 12) relative to control (n = 10; * p < 0.05). However, the high-affinity antagonist CNQX (400 nm) produces similar inhibition in both control (n = 7) and glutamine-incubated slices (n = 6; p > 0.05). Inset, Sample traces before (black traces) and after (gray traces) γ-DGG and CNQX application. Calibration: 25 pA, 10 ms.
- Figure 4.
Prolonged incubation in glutamine increases quantal amplitude through a system A-dependent mechanism. A, Quantal amplitude does not change in slices incubated in glutamine (Gln; 4 mm) for <4 h. Cumulative distribution function of amplitudes are not different between glutamine (n = 7) and control slices (n = 9; p > 0.05, Kolmogorov–Smirnov test). Sample recordings from control (top) and glutamine-incubated (bottom) cells. Calibration: 10 pA, 100 ms. B, After more than 4 h of glutamine incubation, quantal amplitude is increased. Cumulative distribution function of amplitudes are significantly increased in glutamine (n = 8) slices over control slices (n = 7; p < 0.05, Kolmogorov–Smirnov test). Sample recordings from control (top) and glutamine-incubated (bottom) cells are shown. Calibration: 10 pA, 100 ms. C, Glutamine enhancement relies on system A transporters. Cumulative distribution function of amplitudes is reduced in slices incubated in glutamine and MeAIB (n = 18) relative to slices incubated in glutamine alone (n = 18; p < 0.05, Kolmogorov–Smirnov test). Sample recordings from glutamine-incubated (top) and glutamine-incubated (bottom) cells. Calibration: 10 pA, 100 ms.
- Figure 5.
Glutamine enhances quantal amplitude in dissociated hippocampal culture with the same time course as in hippocampal slices. A, Cumulative distribution function of amplitudes is not different between 4 mm glutamine (Gln)-incubated (n = 18) and control cultures (n = 20; p > 0.05, Kolmogorov–Smirnov test). Sample recordings from control (top) and glutamine-incubated (bottom) cells. Calibration: 10 pA, 100 ms. B, Cumulative distribution function of amplitudes is different between 4 mm glutamine-incubated (n = 15) and control cultures (n = 14; p < 0.05, Kolmogorov–Smirnov test). Sample recordings from control (top) and glutamine-incubated (bottom) cells. Calibration: 10 pA, 100 ms. C, Current evoked by sucrose (500 mm) does not differ between cultures incubated in 4 mm glutamine (<4 h, n = 19; >4 h, n = 16) relative to control coverslips (<4 h, n = 16; >4 h, n = 16; p > 0.05). Inset, Representative traces show sucrose-evoked currents. Black bars indicate application of 500 mm sucrose. Calibration: 400 pA, 1 s.
- Figure 6.
Glutamine enhancement of synaptic transmission is activity-dependent. A, Time course of glutamine enhancement shows that population activity does not increase appreciably until 1 h after application. Sample traces in control (top) and 4 mm glutamine (Gln)-incubated (bottom) slices at baseline, 1, 2, 3, and 4 h after glutamine application. Calibration: 0.5 mV, 10 ms. B, Application of hyperkalemic solution results in an immediate increase in fEPSP slope in the presence of 4 mm glutamine (n = 11) relative to control (n = 6) and produces an enhancement over baseline after 60 min. C, Immediate enhancement by 4 mm glutamine (n = 7) after hyperkalemic stimulation is lessened by addition of 25 mm MeAIB (n = 8), whereas the persistent enhancement after 60 min is abolished. D, Recovery of synaptic transmission after intense hyperkalemic stimulation does not differ in the presence of 40 mm MSO and 25 mm MeAIB (n = 7) relative to control (n = 5) slices.
