Mouse neurexin-1alpha deletion causes correlated electrophysiological and behavioral changes consistent with cognitive impairments

Abstract

Deletions in the neurexin-1alpha gene were identified in large-scale unbiased screens for copy-number variations in patients with autism or schizophrenia. To explore the underlying biology, we studied the electrophysiological and behavioral phenotype of mice lacking neurexin-1alpha. Hippocampal slice physiology uncovered a defect in excitatory synaptic strength in neurexin-1alpha deficient mice, as revealed by a decrease in miniature excitatory postsynaptic current (EPSC) frequency and in the input-output relation of evoked postsynaptic potentials. This defect was specific for excitatory synaptic transmission, because no change in inhibitory synaptic transmission was observed in the hippocampus. Behavioral studies revealed that, compared with littermate control mice, neurexin-1alpha deficient mice displayed a decrease in prepulse inhibition, an increase in grooming behaviors, an impairment in nest-building activity, and an improvement in motor learning. However, neurexin-1alpha deficient mice did not exhibit any obvious changes in social behaviors or in spatial learning. Together, these data indicate that the neurexin-1alpha deficiency induces a discrete neural phenotype whose extent correlates, at least in part, with impairments observed in human patients.

Fig. 1.

Neurexin-1α KO mice exhibit a reduced mEPSC frequency in the CA1 region of the hippocampus. (A) Representative traces of mEPSCs (Left) and mIPSCs (Right) recorded in hippocampal CA1 pyramidal neurons in the presence of 0.5 μM TTX with a high-chloride (mIPSCs) or methanesulfonate (mEPSCs) internal pipette solution. (B and C) Cumulative distributions of the interevent intervals (B) and amplitudes (C) of mEPSCs (WT, nine cells per three mice; KO, nine cells per three mice) (Left) and mIPSCs (WT, 11 cells per three mice; KO, nine cells per three mice) (Right). Statistical significance was assessed with a Kolmogorov–Smirnov test (**, P < 0.01). (D and E) Representative traces (D) and summary graphs (E) of sequential measurements of the frequency and amplitudes of mEPSCs (Left) and mIPSCs (Right; monitored at −60 and 0 mV holding potentials, respectively) in the same pyramidal CA1 neuron (WT, eight cells per three mice; KO, eight cells per three mice). Recordings were obtained with a modified methanesulfonate internal pipette solution. Representative traces are depicted on top, and summary plots with each cell represented by a dot on the bottom. Means ± SEMs are indicated by the cross symbols; statistical significance was evaluated with Student's t test (*, P < 0.05; ns, nonsignificant).

Fig. 2.

Neurexin-1α KO mice exhibit a decrease in excitatory synaptic strength in the CA1 region of the hippocampus. (A) Sample traces for extracellular field EPSP recordings performed in stratum radiatum of CA1 region of hippocampus. (B) Summary graph of input-output measurements. The slope of the fEPSP is plotted as a function of the fiber-volley amplitude (WT, three mice per nine slices; KO, three mice per eight slices). Linear fit slopes were calculated for WT (4.815 ± 0.285) and KO (3.616 ± 0.296) slices and were significantly different (P = 0.011, unpaired Student's t test). (C) Summary graph of linear fit slopes for WT and KO input-output curves. (D and E) Sample traces and summary graph for whole-cell voltage clamp recordings of NMDA/AMPA ratio in CA1 pyramidal neurons (WT, three mice per six cells; KO, three mice per eight cells). (F and G) Sample traces and summary graph for paired-pulse facilitation measurements (fEPSP2/fEPSP1) recorded at various interstimulus intervals (WT, three mice per nine slices; KO, three mice per six slices). Data represent means ± SEM.

Fig. 3.

Neurexin-1α KO mice exhibit impaired PPI. (A) Mean startle amplitude to an initial 120 dB sound pulse (repeated six times). (B) Startle responses to eight presentations of the following sound pulses (presented in pseudorandom order): no stimulus, 80, 90, 100, 110, and 120 dB pulse. For each pulse, the mean startle amplitudes were averaged. (C) PPI measurements, performed in mice randomly exposed to five trial types: pulse alone (120 dB), three different prepulse/pulse pairings [prepulses at 4, 8, or 16 dB above the background noise (70 dB), followed by a 120 dB pulse with a 100-ms onset-onset interval], and no stimulus. Data show the percentage inhibition of the mean startle amplitude. Data shown are means ± SEMs (*, P < 0.05; **, P < 0.01; and ***, P < 0.001 compared with WT; for a full description of statistical tests and results, see SI Appendix).

Fig. 4.

Neurexin-1α KO mice exhibit increased grooming behavior. Mice were habituated in an empty cage without bedding, and grooming of all body regions was monitored for 10 min. (A) Mean time spent self-grooming. (B) Mean number of grooming bouts. (C) Mean time spent per grooming bout. Data shown are means ± SEMs (*, P < 0.05; ns compared with WT; for a full description of statistical tests and results, see SI Appendix).

Fig. 5.

Neurexin-1α KO mice exhibit impaired nest-building behaviors. (A and B) Mice were habituated in an empty cage for 15 min, and a 5 × 5 cm square of pressed cotton was placed in a random cage corner. The width (A) and height (B) of the nest built by the mouse, with subtraction of the original width and height of the cotton pad, was measured at 30, 60, and 90 min. Data shown are means ± SEMs (*, P < 0.05; **, P < 0.01; and ***, P < 0.001 compared with WT; for a full description of statistical tests and results, see SI Appendix).

Fig. 6.

Neurexin-1α KO mice exhibit enhanced motor learning on the rotarod. (A) Mean time WT and neurexin-1α KO mice stay on an accelerating rotarod (4–45 rpm in 5 min). Mice were tested in 10 trials, with four trials per day with a 45–60 min intertrial interval over 3 days. The time to either fall off the rod or turn one full revolution was measured. (B) After the experiments described in A, mice were subjected to an additional two trials with a higher acceleration rate (4–45 rpm in 1 min) to test the improved performance of the KO mice. Data shown are means ± SEMs (*, P < 0.05; **, P < 0.01; and ***, P < 0.001 compared with WT; for a full description of statistical tests and results, see SI Appendix).