Selective modulation of some forms of schaffer collateral-CA1 synaptic plasticity in mice with a disruption of the CPEB-1 gene

Abstract

CPEB-1 is a sequence-specific RNA binding protein that stimulates the polyadenylation-induced translation of mRNAs containing the cytoplasmic polyadenylation element (CPE). Although CPEB-1 was identified originally in Xenopus oocytes, it has also been found at postsynaptic sites of hippocampal neurons where, in response to N-methyl-D-aspartate receptor activation, it is thought to induce the polyadenylation and translation of alphaCaMKII and perhaps other CPE-containing mRNAs. Because some forms of synaptic modification appear to be influenced by local (synaptic) protein synthesis, we examined long-term potentiation (LTP) in CPEB-1 knockout mice. Although the basal synaptic transmission of Schaffer collateral-CA1 neurons was not affected in the knockout mice, we found that there was a modest deficit in LTP evoked by a single train of 100 Hz stimulation, but a greater deficit in LTP evoked by one train of theta-burst stimulation. In contrast, LTP evoked by either four trains of 100 Hz stimulation or five trains of theta-burst stimulation were not or were only modestly affected, respectively. The deficit in LTP evoked by single stimulation in knockout mice appeared several minutes after tetanic stimulation. Long-term depression (LTD) evoked by 1 Hz stimulation was moderately facilitated; however, a stronger and more enduring form of LTD induced by paired-pulse 1 Hz stimulation was unaffected. These data suggest that CPEB-1 contributes in the translational control of mRNAs that is critical only for some selected forms of LTP and LTD.

Figure 1

(A) Northern blot for CPEB-1 in the brain from wild-type and CPEB-1 KO mice. Tubulin is shown as loading control. Wild type (+/+), CPEB-1 KO (-/-), CPEB-1 KO heterozygote (+/-). (B) Hippocampal section showing Nissl staining from a wild-type and a CPEB-1 KO mouse. (C) Input-output curve (left) and PSFV versus voltage plot (right) (n = 12). Inset: Scheme of the mouse hippocampal slice preparation. (D) Scatter plot shows paired pulse facilitation responses (n = 12). Interpulse interval, msec: 5, 10, 50, 100, 150, and 200. In all figures, the data points represent mean ± SD.

Figure 2

(A) Long-term potentiation (LTP) evoked by one train of 100 Hz in CPEB-1 KO and wild-type mice (n = 12/12). (B) LTP evoked by four trains of 100 Hz in CPEB-1 KO and wild-type mice (n = 8/8). (C) LTP evoked by one train of TBS in CPEB-1 KO and wild-type mice (n = 10/10). (D) LTP evoked by five trains of TBS in CPEB-1 KO and wild-type mice (n = 8/8). Each arrow represents a train of electrical stimulation. TBS: theta-burst stimulation. In all figures the data points represent mean ± SE. Traces represent baseline (black line, 1) and after 100 Hz stimulation or TBS (gray line, 2) fEPSPs from wild-type (WT) and CPEB-1 KO (KO) mice. Calibration bars: 3 mV, 10 ms.

Figure 3

(A), Long-term potentiation (LTP) evoked by two trains of theta-burst stimulation in CPEB-1 KO and wild-type mice (n = 6/6). (B) LTP evoked by three trains of theta-burst stimulation in CPEB-1 KO and wild-type mice (n = 5/5). Each arrow represents a train of electrical stimulation. In all figures the data points represent mean ± SE. Histograms showing amplitude of LTP evoked by 1-5 TBS for the 20-30 min (C), 90-120 min (D), and 150-180 min (E) for CPEB-1 KO and wild-type mice. Each bracket represents statistical significance (p < 0.05) between two columns. Data-columns represent mean ± SD.

Figure 4

(A) Long-term potentiation evoked by 10 Hz (90 sec) stimulation in CPEB-1 KO and wild-type mice (n = 6/6). (B) Short-term depression evoked by 5 Hz (180 sec) stimulation in CPEB-1 KO and wild-type mice (n = 6/6). (C) Long-term depression evoked by 1 Hz (15 min) stimulation in CPEB-1 KO and wild-type mice (n = 10/8). Frequency response curves for the 20-30 min (D) and 50-60 min (E) time traces from CPEB-1 KO and wild-type mice. (F) Long-term depression evoked by paired-pulse (50 msec interpulse interval) 1 Hz (15 min) stimulation in CPEB-1 KO and wild-type mice (n = 10/8). In all figures the data points represent mean ± SE.

Figure 5

(A) Rapamycin effect on a single train of theta-bursts-evoked long-term potentiation (theta-burst stimulation) in wild type (left) and CPEB-1 KO (right) mice. The horizontal bar represents the time of rapamycin application. Wild-type control (n = 5), wild-type rap (n = 6), CPEB-1 KO control (n = 5), CPEB-1 KO rap (n = 6). Data points represent mean ± SE. (B) Amplitude histogram for three time frames (1-10, 10-50, and 120-150 min) for each Long-term potentiation showed in (A). Data points represent mean ± SD. Bars show statistical significance (P < .05) between two data sets.

Figure 6

(A) Rapamycin effect on five trains of theta-bursts-evoked long-term potentiation in wild-type and CPEB-1 KO mice. The horizontal bar represents the time of rapamycin application. Wild-type control (n = 5), wild-type rap (n = 6), CPEB-1 KO control (n = 5), CPEB-1 KO rap (n = 6). Data points represent mean ± SE. (B) Amplitude histogram for two time frames (25-45 min and 120-150 min) for each long-term potentiation shown in (A). Data points represent mean ± SD. Bars show statistical significance (P < .05) between two data sets. (C) Human brain-derived neurotrophic factor-evoked long-term potentiation in wild-type and CPEB-1 KO mice (n = 5). The horizontal bar represents the time of human brain-derived neurotrophic factor application.

Figure 7

(A) Synaptic fatigue responses during a train at 14 Hz in CPEB-1 KO and wild-type mice (n = 12/9). Data normalized to the first response. (B) Field depolarization induced by 100 Hz stimulation for 1 sec (horizontal bar) in CPEB-1 KO and wild-type mice (n = 8/8). Column/bar plot shows peak amplitudes obtained from (B) (upper graph). Column/bar plot shows area under the curves obtained from (B) (lower graph). In all figures the data points represent mean ± SD.

Figure 8

Top panel, Late phase of long-term potentiation evoked by four trains of 100 Hz stimulation delivered to pathway S1 observed in CPEB-1 KO and wild-type mice. Bottom panel, Capture of late long-term potentiation evoked by one train of 100 Hz delivered to the pathway S2 observed in CPEB-1 KO and wild-type mice. Data points represent mean ± SE (n = 5/5). The scheme represents the two pathways (S1 and S2) stimulated by electrodes placed in the proximal and distal region of the stratum radiatum, respectively.