Research Article

Regulation of Hippocampal and Behavioral Excitability by Cyclin-Dependent Kinase 5

  • Ammar H. Hawasli,

    Affiliation: Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America

  • Della Koovakkattu,


  • Kanehiro Hayashi,


  • Anne E. Anderson,

    Affiliation: Departments of Pediatrics, Neurology and Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America

  • Craig M. Powell,

    Affiliations: Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America, Department of Neurology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America

  • Christopher M. Sinton,


  • James A. Bibb mail,


  • Donald C. Cooper

    Affiliation: Department of Psychology and Neuroscience, Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado, United States of America

  • Published: June 04, 2009
  • DOI: 10.1371/journal.pone.0005808








Conditional knockout of Cdk5





Figure 1. Altered theta burst topography in SC/CA1 pathway accompanies enhanced LTP in Cdk5 KO mice.

A, An acute hippocampal slice resting on MED-64 multi-electrode array. fEPSPs were recorded (blue) after stimulation of the SC/CA1 pathway (red). B, LTP after a ten-burst theta stimulus in representative WT and KO slices plotted as percent amplitude of baseline (−10 to 0 min). C, Effects of Cdk5 KO on theta-burst responses. Representative theta burst traces were extracted from LTP experiment illustrated in B, Quantitation plotted as percentage change in amplitude (relative to the 1st fEPSP) of the 2nd, 3rd, and 4th field EPSP within a single stimulus train of 4 pulses at 100 Hz in control and KO slices. The measures are shown for bursts 1–4 of a train. Similar results were obtained with slope calculations, n = 5–8. *P<0.05 vs. WT; post hoc t-test. Data represent mean±s.e.m.


Responses to CA1 hippocampal tetanic stimuli in WT and Cdk5 KO mice



Figure 2. Tetanic stimulation and post-tetanic potentiation after conditional loss of Cdk5.

A, fEPSPs during high frequency tetanus. fEPSPs amplitudes during 100 Hz tetani are plotted relative to the 1st response in the presence of 75 µM AP5. Asterisk indicates that the 2nd fEPSP during the train was significantly different between WT and KO (P<0.05, student's t-test). B, Effects of Cdk5 KO on fEPSPs during low frequency tetanus. fEPSPs amplitudes during 14 Hz tetani are plotted relative to the 1st response in the presence of 75 µM AP5. C, Post-tetanic potentiation after a 100 Hz stimulus. Representative traces and fEPSP amplitudes were measured and plotted relative to baseline (75 µM AP5, n = 5–8; P<0.05, student's t-test). Data represent mean±s.e.m.




Conditional loss of Cdk5 leads to elevated Mg2+-sensitive potentials



Figure 3. Increased Mg2+-sensitive post-synaptic potential and reduced threshold for epileptiform activity after conditional loss of Cdk5.

A, Representative traces and quantitation of fEPSP amplitude (n = 12) and area (n = 6) in the stratum radiatum relative to baseline following Mg2+ wash-out. B, Representative traces and quantitation showing reduced threshold for population spikes in the stratum pyramidale of KO slices after stimulation in the hippocampal SC/CA1 pathway in Mg2+-free conditions. Quantitation shows % of slices displaying population spikes at indicated stimulation intensities (% of maximum). Recordings were performed 4–6 weeks post-KO. n = 16–18; ANOVA revealed a main effect of genotype (F1,217 = 36.16, p<0.0001), stimulation (F6,217 = 115.41, p<0.0001) and interaction between genotype and stimulation (F6,217 = 11.76, p<0.0001). **P<0.05, *P<0.01, P = 0.067 vs. WT, post hoc t-test. Data represent mean±s.e.m.


Chronic loss of Cdk5 reduced threshold for epileptiform population-spike activity




Figure 4. GABAA-mediated signaling partially compensates for increased fEPSP half-width in Cdk5 KO mice.

A, Effect of partial Na+-channel blockade on fEPSP amplitude. Representative fEPSPs traces from WT (red) and KO (black) are shown before and after TTX treatment (n = 12). B, Increased basal fEPSP half-width in SC/CA1 pathway of KO hippocampus. Representative fEPSPs traces from WT (red) and KO (black) are shown with quantitation (n = 9–10). C, Representative fEPSPs traces before and after GABAA blockade (top) are shown with quantitation (bottom). Histograms show the changes in amplitude and half-width following treatment with 2 µM SR95531 (n = 7). 1 and 2 indicate traces before and after treatment with SR95531, respectively. SR95531 had similar effects on fEPSP slope measurement. *P<0.05 vs. WT; post hoc t-test.



Increased behavioral seizure susceptibility follows chronic loss of Cdk5



Figure 5. Elevated seizure susceptibility after chronic conditional Cdk5 loss.

A, Kaplan-Meier seizure morbidity and survival curves. Percent of animals observed to have handling-induced seizures and percent survival are plotted against weeks post-KO; n = 10–14; the differences for morbidity and mortality were statistically significant, P<0.01, log-rank test. B, Latency to pilocarpine-induced wet-dog shakes (WDS), clonus (Cl), and rearing/falling (RF) seizures in mice, 8 weeks post-KO (n = 7–10). *P<0.05 vs. WT, Student's t-test. Data represent means±s.e.m. C–F, Representative spontaneous EEG/EMG recordings from a conditional KO mouse, 8 weeks post-KO. C, Appearance of multiple bursts (at 3–4 Hz) of spike waves which were frequently clustered as shown and accompanied by evident tremor and clonic seizures. D, Expanded view of 10 sec of the recording period shown in Figure C, displaying two spike bursts separated by about 2 sec. E, Post-ictally, there was rapid return to normal EEG/EMG and resumption of ongoing activity as displayed here during a period of wakefulness. F, Expanded view of 10 sec of the recording period shown in Figure E, Calibration 1 sec and 50 µV; the recording periods shown in panels D and F are annotated by the 10 sec bars in C and E respectively.


Table 1. Long-term conditional Cdk5 knockout increases susceptibility to seizures.




Increased acoustic startle reactivity in Cdk5 KO mice



Figure 6. Increased acoustic startle reactivity with normal short-term acoustic habituation and prepulse inhibition in Cdk5 KO mice.

A, Acoustic startle reactivity in Cdk5 KO mice (4–8 weeks post-KO, n = 17–19). ANOVA revealed a main effect of genotype (F1,204 = 16.35, p<0.0001), decibels (F5,204 = 19.67, p<0.0001) and interaction between genotype and decibels (F5,204 = 3.72, p = 0.003). *P<0.01, **P<0.001, P = 0.08 vs. WT, post hoc t-test. B, Habituation to a 120 db sound is shown as startle reactivity in three consecutive time blocks. ANOVA revealed effects of genotype (F1,68 = 8.62, p<0.006) and trial (F2,68 = 14.65, p<0.0001) but no interaction between genotype and trial (F2,68 = 0.31, p = 0.7326). n = 17–19. C, Prepulse inhibition in Cdk5 KO mice. Prepulse at indicated decibels were given 5 ms prior to a 120 db sound. Prepulse inhibition is represented as percent decrease compared to an isolated 120 db sound. ANOVA revealed effect of decibel (F2,32 = 143.74, p<0.0001) but no effect of genotype (F1,32 = 2.03, p = 0.1735) or interaction (F2,32 = 0.78, p = 0.469). n = 8–10. Vehicle-treated animals behaved similarly to WT. Data represent mean±s.e.m.


Audiogenic behavioral seizures after chronic loss of Cdk5



Table 2. Audiogenic seizures after long-term conditional Cdk5 knockout1.





Figure 7. p25 generation in the hippocampus after pharmacologically-induced status epilepticus and electroconvulsive shock.

A, Representative immunoblots (top) and quantitation of p25 per tubulin (middle) and p25/35 ratio (bottom) after treatment with kainate and pilocarpine. VEH = saline; KA = kainate (50 mg/kg); SC = scopolamine (2 mg/kg)/saline; and SC/PI = scopolamine (2 mg/kg)/pilocarpine (280 mg/kg). n = 4; *P<0.05 vs. VEH and SC in; Student's t-test. B, Representative immunoblots of p25 and quantitation of p25/p35 ratio 15, 30, and 60 min following electroconvulsive shock administration compared to unshocked controls (time = 0); n = 2. C, Hippocampal p25:p35 ratio 6–8 weeks post-KO. Crude lysates were immunoblotted for p25 and p35. Double asterisk indicates P<0.05 versus aged WT, Student's t-test; n = 3–4. Data represent means±s.e.m.















Materials and Methods

Animals and reagents


Electrophysiological recordings


Post-tetanic potentiation


fEPSP measurements in Mg2+-free conditions and epileptiform activity



fEPSP repolarization


Electronencephalographic (EEG)-Electromyographic (EMG) recordings



Seizures and startle response behaviors



Pharmacologically-induced status epilepticus and electroconvulsive shock



Immunoblot analysis

Frozen samples were sonicated in boiling 1% SDS containing 50 mM NaF and boiled for an additional 5 min. Protein concentrations were determined by the BCA protein assay (Pierce) using bovine serum albumin standards. An equal amount of total protein (100 µg) from each sample was subjected to SDS-PAGE followed by electrophoretic transfer to nitrocellulose membranes (Whatman). The membranes were immunoblotted using antibodies for p35/p25 (1:200; C-19 Santa Cruz) and alpha-tubulin (1:5000), followed by incubation with a horseradish peroxidase-conjugated anti-rabbit or anti-mouse secondary antibody (1:8000; Chemicon). Antibody binding was detected by autoradiography using the enhanced chemiluminescence immunoblotting detection system (Amersham Biosciences) and quantified by densitometry using Image J software (NIH).

Statistical analysis


Supporting Information

Figure S1.



(0.19 MB TIF)



Author Contributions

Conceived and designed the experiments: AHH JAB DCC. Performed the experiments: AHH. Analyzed the data: AHH JAB DCC. Contributed reagents/materials/analysis tools: AHH CMS JAB DCC. Wrote the paper: AHH JAB DCC. Designed and supervised the experiments conducted in his/her laboratory: JAB AEA CMP CMS. Performed experiments: DK KH. Designed and supervised the experiments conducted in his/her laboratory: JAB AEA CMP CMS DCC. Performed experiments: DK KH.


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