A critical role for NMDA receptors in parvalbumin interneurons for gamma rhythm induction and behavior

Abstract

Synchronous recruitment of fast-spiking (FS) parvalbumin (PV) interneurons generates gamma oscillations, rhythms that emerge during performance of cognitive tasks. Administration of N-methyl-D-aspartate (NMDA) receptor antagonists alters gamma rhythms, and can induce cognitive as well as psychosis-like symptoms in humans. The disruption of NMDA receptor (NMDAR) signaling specifically in FS PV interneurons is therefore hypothesized to give rise to neural network dysfunction that could underlie these symptoms. To address the connection between NMDAR activity, FS PV interneurons, gamma oscillations and behavior, we generated mice lacking NMDAR neurotransmission only in PV cells (PV-Cre/NR1f/f mice). Here, we show that mutant mice exhibit enhanced baseline cortical gamma rhythms, impaired gamma rhythm induction after optogenetic drive of PV interneurons and reduced sensitivity to the effects of NMDAR antagonists on gamma oscillations and stereotypies. Mutant mice show largely normal behaviors except for selective cognitive impairments, including deficits in habituation, working memory and associative learning. Our results provide evidence for the critical role of NMDAR in PV interneurons for expression of normal gamma rhythms and specific cognitive behaviors.

Figure 1

Genetic ablation of NMDA receptor (NMDAR) specifically in parvalbumin (PV) interneurons. (a) Quantification of recombination from the PV locus in somatosensory cortex and hippocampus at different time points. (b, c) NMDAR-mediated synaptic transmission in PV interneurons is abolished in PV-Cre/NR1f/f mice. (b) Sample EPSC traces mediated by the AMPAR (downward) and NMDAR (upward) from a control PV-Cre mouse and a PV-Cre/NR1f/f mouse. (c) NMDAR EPSC/AMPAR EPSC ratio in control PV-Cre and PV-Cre/NR1f/f mice. (d) Distribution of PV interneurons in NR1f/f and PV-Cre/NR1f/f mice, respectively, at 11 weeks. (e) Immunohistochemistry for PV interneurons in somatosensory cortex of an adult NR1f/f and PV-Cre/NR1f/f mouse, respectively. ^*P<0.05; error bars, mean±s.e.m. Scale bar: (e) 200 μm. See also Supplementary Figure 1. AMPAR, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor; EPSC, excitatory postsynaptic current.

Figure 2

Spontaneous and induced cortical gamma oscillations require NMDA receptor (NMDAR) in parvalbumin (PV) interneurons. (a, b, d–g) Local field potential (LFP) activity in anesthetized control (black) and PV-Cre/NR1f/f (red) mice. (a, b) Spontaneous LFP activity. (a) Relative power from 1–100 Hz in control and PV-Cre/NR1f/f mice. (b) Relative LFP power in the 6–10, 12–24 and 36–44 Hz frequency bands. (c) Single-unit recordings during optogenetic activation of FS–PV+ interneurons. Middle trace: control mice, lower trace: PV-Cre/NR1f/f mice. In each case, a series of 1 ms light pulses (blue trace) was given in a random pattern drawn from a broadband distribution (5–200 Hz). In both cases, each light pulse evoked a single spike from the cell. Both cells followed the light stimulus with a high degree of reliability. (d–g) Optogenetic activation of FS–PV interneurons in somatosensory cortex in control and PV-Cre/NR1f/f mice. (d) Mean power ratio in each LFP frequency band in response to light activation of channelrhodopsin-2 (ChR2)-expressing FS–PV interneurons at varying frequencies. PV-Cre/NR1f/f mice generate significantly less 30–60 Hz oscillations (gamma) than control mice. (e) Comparison of the effect of activating FS–PV interneurons in the control and PV-Cre/NR1f/f mice at 8, 24, and 40 Hz on relative LFP power in those frequency bands. (f) Relative LFP power in the 8, 24 and 40 Hz frequency bands in the PV-Cre/NR1f/f mice during spontaneous (solid bars) and light-evoked (striped bars) activity. (g) Relative power in the 6–10, 15–19, 20–30 and 36–44 Hz frequency bands in response to broadband light stimulation in control and PV-Cre/NR1f/f mice. ^*P<0.05, ^**P<0.01; error bars, mean±s.e.m.

Figure 3

Baseline cortical oscillations and NMDA receptor (NMDAR) antagonist induced gamma rhythms in awake behaving animals. (a–g) Local field potential (LFP) activity in somatosensory cortex in awake control and parvalbumin (PV)-Cre/NR1f/f mice. (a) Examples of single-trial gamma activity from a PV-Cre/NR1f/f and control mouse. Thin lines: LFP filtered between 5–300 Hz; thick lines: LFP filtered in the 30–50 Hz gamma frequency range. (b, c) Awake baseline activity. (b) Mean power spectra 1–100 Hz. Lighter regions indicate s.e.m. (c) Characteristics of 30–50 Hz gamma events. Mean event duration is significantly increased in freely moving PV-Cre/NR1f/f mice, whereas number of events are not. (d–g) NMDAR antagonist (MK-801) challenge. (d, e) Average relative power in the 30–50 Hz gamma frequency band 15 min before administration of MK-801 (dashed line), to 35 min after. Lighter regions indicate s.e.m. Administration of MK-801 gives a significant increase in relative gamma power in control mice and a significant reduction in relative gamma power in PV-Cre/NR1f/f mice. (f) Average power changes (dB) between pre and post1. Lighter regions indicate s.e.m. (g) Average power changes (dB) between pre and post2. Pre, 5–15 min before MK-801; post1, 5–15 min after MK-801; post2, 25–35 min after MK-801. ^*P<0.05; error bars, mean±s.e.m. See also Supplementary Figures 3 and 4.

Figure 4

Parvalbumin (PV)-Cre/NR1f/f mice display no behavioral changes in the open field but reduced sensitivity to pharmacological NMDA receptor (NMDAR) treatment. (a) Total distance traveled over 60 min in the open field of PV-Cre/NR1f/f and control mice at 7 weeks. (b–d) Open field behavior over 60 min at 11 weeks. (b) Total distance traveled over 60 min in the open field of PV-Cre/NR1f/f and control mice at 11 weeks. (c) No significant difference in the time spent in the center of the field between the genotypes. (d) PV-Cre/NR1f/f mice do not display stereotypy behavior. (e) MK-801 treatment induces significant increase in horizontal activity only in control mice. (f) MK-801 treatment results in marked increase in stereotypy behavior only in control mice. HACT, horizontal activity; STR TIME, stereotypy time; STR CNT, stereotypy count; STR NO, stereotypy numbers; ns P>0.05, ^**P<0.01, ^***P<0.001, ^****P<0.0001; error bars, mean±s.e.m.

Figure 5

Loss of NMDA receptor (NMDAR) in parvalbumin (PV) interneurons results in selective cognitive disruptions. (a) PV-Cre/NR1f/f mice show no deficiency in sensorimotor gating as measured by prepulse inhibition (PPI). (b) PV-Cre/NR1f/f display deficiencies in habituation. (c, d), PV-Cre/NR1f/f mice exhibit impaired freezing behavior both to a tone-dependent (cued) and a contextual version of fear conditioning. (e) PV-Cre/NR1f/f mice perform similarly to control mice during training in a hidden platform version of water maze. (f) Time spent (%) in each quadrant during the water maze probe trial. There is no significant difference between the genotypes. (g) Time spent (%) in each quadrant during the water maze probe trial after reversal training. There is no significant difference between the genotypes. (h) PV-Cre/NR1f/f mice perform at a similar accuracy levels independent of working memory load in the discrete paired-trial variable-delay T-maze task. PPI, prepulse inhibition; FC, fear conditioning; T, target quadrant; R, right quadrant; O, opposite quadrant; L, left quadrant. ^*P<0.05, ^**P<0.01; error bars, mean±s.e.m. See also Supplementary Figure 5.