Neurosteroid-induced plasticity of immature synapses via retrograde modulation of presynaptic NMDA receptors - PubMed (original) (raw)

The PREGS-induced long-term enhancement of postsynaptic AMPA responses in P3-P4 slices is NMDA receptor and Ca2+ dependent. a1, Traces illustrating that the late phase of the 25 μ

m

PREGS-induced increase of AMPA mEPSC frequency cannot be observed when the Ca2+ chelator BAPTA (10 m

m

) is internally dialyzed via the patch electrode. Calibration: 15 pA, 100 ms. a2, time course of the effect of 25 μ

m

PREGS on a neuron internally dialyzed with BAPTA and a control neuron from the same batch of slices. a3, Summary of the effect of 25 μ

m

PREGS on neurons internally dialyzed with 10 m

m

BAPTA (**p < 0.01; ***p < 0.001; n = 6). b1, NMDA receptor-mediated EPSCs (_V_hold = +40 m

m

; calibration: 20 pA, 200 ms) are significantly inhibited by intracellular dialysis of MK-801 (5 m

m

; see Results for more details; ***p < 0.001; n = 11 by t test). To promote entrance of MK-801 to the pore, neurons were depolarized from -70 to -15 mV (5 times for 10 s each). b2, In six of these 11 neurons, after NMDA EPSC inhibition was confirmed, 500 n

m

tetrodotoxin was applied, and the effect of 25 μ

m

PREGS on mEPSC frequency was assessed [experiment (Exp.) 1]. Under these conditions, application of PREGS did not induce a long-lasting increase in mEPSC frequency. In a separate batch of neurons, tetrodotoxin was present from the start of the experiment, and basal mEPSC frequency was recorded (experiment 2; see Results for more details). Neurons were then depolarized as described above to promote entrance of MK-801 to the pore. mEPSC frequency was recorded again and found to be unchanged by the depolarization procedure (see Results). As shown in the summary graph, 25 μ

m

PREGS did not induce a long-lasting increase in mEPSC frequency under these conditions (n = 4). *p < 0.05; **p < 0.01; ***p < 0.001. c1, Extracellular application of 10 μ

m

ifenprodil (ifen) induces a long-lasting decrease in the amplitude of NMDA EPSCs (recorded at _V_hold = -10 mV). Note that these events are blocked by 100 μ

m dl

-AP-5. Calibration: 20 pA, 200 ms. c2, In a separate batch of neurons, mEPSC frequency was recorded in the presence of tetrodotoxin (500 n

m

). Under these conditions, ifenprodil blocked the late phase of the 25 μ

m

PREGS effect on mEPSC frequency. Ifenprodil alone did not have an effect on mEPSC frequency (see Results). *p < 0.05; **p < 0.01; n = 6. Ctrl, Control. Error bars represent SEM.