Prolonged exposure to NMDAR antagonist induces cell-type specific changes of glutamatergic receptors in rat prefrontal cortex - PubMed (original) (raw)

Prolonged exposure to NMDAR antagonist induces cell-type specific changes of glutamatergic receptors in rat prefrontal cortex

Huai-Xing Wang et al. Neuropharmacology. 2012 Mar.

Abstract

N-methyl-d-aspartic acid (NMDA) receptors are critical for both normal brain functions and the pathogenesis of schizophrenia. We investigated the functional changes of glutamatergic receptors in the pyramidal cells and fast-spiking (FS) interneurons in the adolescent rat prefrontal cortex in MK-801 model of schizophrenia. We found that although both pyramidal cells and FS interneurons were affected by in vivo subchronic blockade of NMDA receptors, MK-801 induced distinct changes in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and NMDA receptors in the FS interneurons compared with pyramidal cells. Specifically, the amplitude, but not the frequency, of AMPA-mediated miniature excitatory postsynaptic currents (mEPSCs) in FS interneurons was significantly decreased whereas both the frequency and amplitude in pyramidal neurons were increased. In addition, MK-801-induced new presynaptic NMDA receptors were detected in the glutamatergic terminals targeting pyramidal neurons but not FS interneurons. MK-801 also induced distinct alterations in FS interneurons but not in pyramidal neurons, including significantly decreased rectification index and increased calcium permeability. These data suggest a distinct cell-type specific and homeostatic synaptic scaling and redistribution of AMPA and NMDA receptors in response to the subchronic blockade of NMDA receptors and thus provide a direct mechanistic explanation for the NMDA hypofunction hypothesis that have long been proposed for the schizophrenia pathophysiology.

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Figures

Figure 1

Both pyramidal cells and FS interneurons were depolarized by treatment with MK-801. A, The firing patterns of pyramidal cells and FS interneurons (dash-lines denote the expanded spikes within the boxed areas) in response to injection of current in the soma. B, The numbers of action potentials in both FS and pyramidal cells were not significantly different overall compared with saline vehicle control groups (two-way ANOVA: n = 7; F = 0.975, p = 0.448 for pyramidal cells; n = 5, F = 1.022, p = 0.427 for FS interneurons). C, The summary graphs show the significant shift of I–V curves toward depolarization induced by MK-801 in both FS and pyramidal cells (P: n = 7 for both control and MK 801, F = 4.764, p < 0.001; FS: n = 5 for both control and MK 801, F = 2.943, p < 0.01). Overall, pyramidal neurons appeared to be easily excited; FS interneurons were more difficult to study due to rapid rundown during recordings in the MK-801-treated rats. Although MK-801 treatment causes changes in membrane properties in both pyramidal cells and FS interneurons, these neurons are basically healthy and thus the results were comparable. FS, fast-spiking; P, pyramidal.

Figure 2

Prolonged treatment with MK-801 induces opposite homeostatic synaptic scaling of AMPA receptor-mediated mEPSCs in FS interneurons compared with pyramidal cells. A, The sample traces of mEPSC recordings in pyramidal cells and FS interneurons at −70 mV with TTX and PTX in the bath solution. B, Sample traces show that MK-801 induced opposite alterations of mEPSC amplitude in FS and pyramidal cells, with a significant decrease of mEPSC amplitude in FS and an increase in the pyramidal cells. The time constants were, however, unaltered (see scaled traces). C, Cumulative probability histograms show the mEPSC amplitude in the control and the MK-801 model. Insets: average AMPA mEPSCs (p < 0.001, n = 7 for both control and MK-801 in FS cells; and p < 0.05, n = 9 both control and MK-801 in pyramidal neurons). D, Cumulative probability histograms of mEPSCs interevent interval from control and the MK-801 model. Insets: average frequency of AMPA mEPSCs. The frequency was unaltered in FS interneurons but was significantly increased in pyramidal cells (p < 0.01, n = 7).

Figure 3

Presynaptic NMDA receptors exist in excitatory synaptic terminals targeting on pyramidal neurons in adolescent rat PFC. A, The upper panel shows the sample traces of evoked EPSCs with paired-pulse stimuli in baseline and AP5 application. The bottom panel shows the changes of input resistance (Rinput) and holding current (Ihold) in the recorded neuron. The EPSCs were pharmacologically isolated by recording the neuron at −70 mV in the presence of 50 μM picrotoxin, 1 μM CGP55845 to block both GABAA and GABAB receptors. The postsynaptic NMDA receptors were blocked with intracellular solution containing 1 mM MK-801. AP5 wash-in clearly altered the amplitude of both first and second EPSCs without affecting the input resistance and holding current. B, Summary histograms showing the effects of AP5 on EPSC amplitudes and paired-pulse ratio (PPR). Most of the neurons exhibited paired-pulse facilitation with the amplitudes of the second EPSCs larger than the first ones in the baseline recordings, while wash-in of AP5 (50 μM) significantly decreased PPR (n = 15, p < 0.0001). C, The effects of AP5 on eEPSCs induced with minimal stimulation which produced about 50% synaptic failures in all stimulus trials. The evoked EPSCs in pyramidal neurons were recorded in the presence of GABAA receptor antagonist picrotoxin (50 μM) and AP5 (50 μM) with minimal stimulus. The upper panel shows the average sample traces of AMPA receptor-mediated EPSCs in baseline (1), AP5 (2), and washout (3). Lower panel: plot of eEPSC amplitudes versus recording time shows the depressive AP5 effect on the minimal eEPSCs in a pyramidal cell. Shadow area denotes synaptic failure which was determined as same or below 3 times mean root square of the baseline under our recording condition. D, Summary histograms exhibited that AP5 application significantly decreased the EPSC amplitude (n = 6; p = 0.001) but increased the failure rate (n = 6; p = 0.012). These results further confirm the existence of presynaptic NMDA receptors in the axon terminals targeting pyramidal neurons in the adolescent PFC.

Figure 4

Treatment with MK-801 induces new insertions of NMDA receptors to the presynaptic terminals targeting pyramidal cells. A, Sample traces of AMPA mEPSCs in pre-AP5 and AP5 in the pyramidal neurons. B, Average mEPSCs before and after application of AP5. C Although mEPSC amplitude was significantly increased in the MK-801 model compared with the control, it was not affected by AP5 in either the control or the MK-801 treatment group. D, Cumulative probability of mEPSC interevent interval before and after application of AP5. E, In contrast to the unaltered frequency in FS interneurons in the MK-801 model, the frequencies of AMPA mEPSCs in pyramidal cells were significantly reduced by AP5 in both the control and the MK-801 groups. The frequency was significantly increased 3-fold in MK-801 compared with the control. F, G, The histograms show that mEPSC events on pyramidal cells were significantly decreased by application of AP5 in both control and MK-801 groups. H, The mEPSC amplitude was not affected by AP5 application (n = 9, p = 0.119) but the mEPSC frequency was significantly decreased by AP5 (n = 9, p = 0.017) when postsynaptic NMDA receptors were blocked with 1 mM MK-801 loaded into the pipette solution. I, CV analysis of the mEPSCs projected a reduced presynaptic release probability after AP5 application because the ratio (AP5/pre-AP5) of CV2 was located under 45° line. The trend of changes was similar to those exhibited in Figure 4C, E and G. These data indicated that MK-801 treatment induced new additions of presynaptic NMDA receptors to the glutamatergic axon terminals targeting pyramidal neurons.

Figure 5

Presynaptic NMDA receptors in the axon terminals targeting FS interneurons were completely blocked by treatment with MK-801. A, Sample traces of mEPSCs in pre-AP5 and AP5 applications from saline control and MK-801-treated animals. The mEPSCs were recorded at −70 mV in the presence of PTX and TTX. B, Average mEPSCs from both pre-AP5 and AP5 applications showing a significantly reduced mEPSC amplitude and unaltered kinetics in the MK-801 model. C, Summary histogram shows that despite the significantly smaller mEPSC amplitude in the MK-801-treated group compared with the saline vehicle control, the mEPSC amplitudes in the FS interneurons were not affected by application of AP5 in either the control or the MK-801-treated group. D, Cumulative probability of mEPSC interevent intervals in pre-AP5 and AP5 applications. E, Frequency histograms in pre-AP5 and AP5 applications from control and the MK-801 model show that the mEPSC frequency was significantly reduced by AP5 in the control but not in the MK-801-treated group. F, G, The histograms show that mEPSC events were significantly decreased by AP5 administration in vehicle control but not in MK-801 model. n.s., not significant.

Figure 6

MK-801 treatment induced dramatic changes in AMPA receptor-mediated current in both pyramidal cells and FS interneurons. A, Sample traces and I–V curves showing the rectification of AMPA receptor-mediated EPSCs recorded at −60, 0, and +60 mV, respectively, in the presence of AP5 and PTX. The AMPA-EPSCs in FS interneurons exhibited both large and small RIs whereas those in pyramidal neurons displayed large RIs only in the vehicle control rats. Dramatic decreases in RIs were observed in both pyramidal cells and FS interneurons in MK-801-treated rats. B, Summary scatter plot shows that RIs in both pyramidal cells and FS interneurons were significantly decreased in the MK-801 model compared with controls.

Figure 7

MK-801 increased CP-AMPA receptor expressions in both pyramidal cells and FS interneurons in adolescent rat PFC. A, The sample traces of AMPA-EPSCs in baseline, NASPM administration, and wash-out for pyramidal cells and FS interneuron under both conditions of normal control and MK-801 model. The recorded neurons were clamped at -70 mV and bathed with 50 μM PTX and 50 μM AP5 to isolate AMPA currents. After the currents were stable, we recorded 5 minutes as baseline and then recorded another 10 minutes with wash-in of 50 μM NASPM, followed by washing out with ACSF containing PTX and AP5. B. Summary histograms of EPSC amplitude changes with NASPM administration. In the normal control animals, the EPSC amplitude was not altered by NASPM in pyramidal cells (n = 9, p = 0.240) but was significantly decreased by 20.8 % in FS interneurons (n = 6, p = 0.036). In contrast, in the MK-801 model, NASPM significantly reduced the EPSC amplitude by more than 30% in pyramidal cells (n = 6, p = 0.0014) and about 42% in FS interneurons (n = 6, p = 0.011). The percent changes of EPSC amplitude in MK-801-treated neurons were significantly higher than those in the control for both pyramidal neurons and FS interneurons (p = 0.048 for pyramidal cells and p = 0.048 for FS interneurons), suggesting that CP-AMPA receptors were indeed increased in both pyramidal neurons and FS interneurons in the MK-801-treated animals.

Figure 8

Differential Ca2+ permeability of synaptic AMPA receptors in pyramidal cells and FS interneurons in the MK-801 model. A, Representative traces (at −60, 0, and +60 mV) from the administration of control (2 mM) and highly concentrated Ca2+ (30 mM) solutions in pyramidal cells and FS interneurons in the MK-801-treated rats. B, The RIs of FS interneurons but not of pyramidal neurons were significantly decreased by administration of highly concentrated Ca2+ solution (p < 0.05, n = 7), indicating a differential calcium permeability in FS interneurons versus pyramidal neurons.

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Prolonged exposure to NMDAR antagonist induces cell-type specific changes of glutamatergic receptors in rat prefrontal cortex - PubMed (original) (raw)