Impaired spatial learning and defective theta burst induced LTP in mice lacking fibroblast growth factor 14

Abstract

Spinocerebellar ataxia 27 (SCA27) is a recently described syndrome characterized by impaired cognitive abilities and a slowly progressive ataxia. SCA27 is caused by an autosomal dominant missense mutation in Fibroblast Growth Factor 14 (FGF14). Mice lacking FGF14 (Fgf14(-/-) mice) have impaired sensorimotor functions, ataxia and paroxysmal dyskinesia, a phenotype that led to the discovery of the human mutation. Here we extend the similarities between Fgf14(-/-) mice and FGF14(F145S) humans by showing that Fgf14(-/-) mice exhibit reliable acquisition (place learning) deficits in the Morris water maze. This cognitive deficit appears to be independent of sensorimotor disturbances and relatively selective since Fgf14(-/-) mice performed similarly to wild type littermates during cued water maze trials and on conditioned fear and passive avoidance tests. Impaired theta burst initiated long-term synaptic potentiation was also found in hippocampal slices from Fgf14(-/-) mice. These results suggest a role for FGF14 in certain spatial learning functions and synaptic plasticity.

Fig. 1

FGF14 expression in hippocampus and PHR. (A) FGF14-β-gal expression in the forebrain. (B) FGF14-β-gal expression in the PHR (PRh, LEnt, medial entorhinal cortex), Pir and DEn showing expression in neurons in layers II, III, V and VI of the PRh in Fgf14^−/+ mice. (C) FGF14-β-gal expression in major nuclei of the amygdala. (D) In situ detection of Fgf14 in the forebrain. (E) FGF14-β-gal expression in the PHR showing similar patterns of expression to that of FGF14-β-gal. (F) Fgf14 mRNA expression in the amygdala showing a similar expression pattern to FGF14-β-gal. BLA, anterior basolateral amygdaloid nucleus; BMA, anterior basolateral amygdala; DEn, dorsal endopiriform nucleus; LaDL, dorsolateral amygdaloid nucleus; LEnt, lateral entorhinal cortex; Pir, piriform cortex; PRh, perirhinal cortex; rf, rhinal fissure. Bar=200 µm.

Fig. 2

Fgf14^−/− mice exhibited hyperactivity and impaired grip strength. (A) Fgf14^−/− mice exhibited significantly more total ambulations (mean±SEM, *, p<0.005) during 1-h locomotor activity tests relative to WT littermate controls in both study 1 and study 2, providing good evidence that the Fgf14^−/− mice are hyperactive. (B) Fgf14^−/− mice demonstrated impaired forelimb grip strength relative to WT control mice on both Test Day 1 and Day 2 (p<0.0005; p<Bonferroni corrected p=0.025).

Fig. 3

Fgf14^−/− mice have impaired spatial learning as evaluated by the water navigation test. (A) In study 1, Fgf14^−/− mice did not differ significantly from WT littermate controls in terms of escape path length (mean±SEM) during cued (visible platform) trials. (B) In contrast to the lack of group differences in the cued trials data, Fgf14^−/− mice exhibited significantly impaired acquisition performance in terms of escape path length (mean±SEM) during place (submerged platform) trials compared to WT controls. *p<0.001 (Bonferroni corrected p=0.01), **p=0.011. (C) The Fgf14^−/− mice also exhibited significantly impaired acquisition performance in terms of escape latency (mean±SEM) during place trials compared to WT controls. *p<0.003, **p=0.03. (D) Similar to the cued trials results in study 1, Fgf14^−/− mice in study 2 did not differ significantly from WT littermate controls in terms of escape path length (mean±SEM) during cued trials. (E) The acquisition performance of the Fgf14^−/− mice in study 2 was impaired during place trials in terms of path length (mean±SEM), which was also consistent with the place trials data from study 1. *p=0.007. (F) The Fgf14^−/− mice also demonstrated performance deficits during place trials in study 2 in terms of escape latency (mean±SEM). **p=0.011. (G, H) A significant main effect of genotype was found for both path length (G) and latency (H), [F(1,13)=9.3, p=0.009; and F(1,13)=5.9, p=0.03, respectively], for study 2B, thus documenting generally-impaired performance across blocks of trials on the part of the Fgf14^−/− mice to learn new platform locations. (I) Retention performance during the probe trial in study 1 was not highly “resolved” in either the Fgf14^−/− or WT groups since neither showed a “spatial bias” for the target quadrant (increased time spent in the target quadrant versus time in each of the other quadrants). (J) In contrast, both the Fgf14^−/− and WT mice showed a spatial bias for the target quadrant in study 2, where each group spent significantly (*p<0.003) more time in the target quadrant compared to each of the other quadrants. (K) However, when the same mice were required to learn a new platform location during the place trials in study 2B, only the WT mice showed a significant spatial bias for the target quadrant during the probe trial. *p<0.002. Pool Quadrants: T=target quadrant that contained the platform; L=quadrant to the left of the target quadrant; O=quadrant opposite the target quadrant; R=quadrant to the right of the target quadrant.

Fig. 4

Swimming speeds, retention deficits and normal passive avoidance and conditioned fear performance in Fgf14^−/− mice. (A) A significant genotype by blocks of trials interaction and subsequent contrasts pertaining to the swimming speeds data from the place trials in study 1 suggested that the Fgf14^−/− mice were slower than the WT mice early in acquisition training but that similar speeds were observed in the two groups at the end of training. *p=0.0005; **p=0.046. (B) In contrast, no differences in swimming speeds were observed between groups during the place trials in study 2, suggesting that compromised swimming abilities were not responsible for the impaired spatial learning performance in Fgf14^−/− mice. (C) The swimming speeds of Fgf14^−/− and WT mice were also found not to differ during the place trials in study 2B when the mice were required to learn a new submerged platform location. (D, E) Fgf14^−/− mice exhibited significant (*) impairment compared to WT controls on trial 1 but not trial 2 in terms of path length to the submerged platform averaged across test days during place trials in both study 1 (D) and study 2 (E) (p=0.001 and 0.008, respectively). The memory demands present during trial 1 were greater than those present for trial 2 since there was an interval of 24 h between acquisition trials with respect to trial 1, whereas only 60 s intervened between acquisition trials for trial 2. (F) Fgf14^−/− mice did not differ significantly from WT controls in trials to criterion (mean±SEM) during passive avoidance acquisition in study 1. (G) Although the latencies (mean±SEM) to enter the dark-shock chamber tended to be shorter for the Fgf14^−/− mice, they were not significantly different from WT controls when tested 24 h (retention) or 48 h (extinction) after passive avoidance acquisition. (H) A significant main effect of genotype [F(1,14)=6.6, p=0.02] was found on the baseline data from min 1 and 2 during day 1 of conditioned fear testing. However, subsequent pairwise comparisons showed that the Fgf14^−/− mice and WT littermate controls did not differ significantly in the percent of time spent freezing (mean±SEM) for either minute. In addition, no significant differences were observed between Fgf14^−/− mice and WT controls in the percent of time spent freezing (mean±SEM) during CS-US [t-s (tone-shock)] training for min 3 to 5. (I) Fgf14^−/− mice also did not differ significantly from WT controls (mean±SEM) in percent of time freezing during the contextual fear test conducted 24 h after tone-shock training when the mice were placed back into the same chamber.

Fig. 5

Impaired Schaffer Collateral LTP in Fgf14^−/− mice. (A) Representative recordings from a hippocampal slice from a WT mouse exhibit stable fEPSP baseline responses to stimuli applied every minute for 20 min (labeled Baseline, 20 consecutive traces superimposed, red line indicates the first response). 55–60 min after 3 applications of theta burst stimuli (3TB), the fEPSP slope remains significantly potentiated relative to the baseline responses, indicating successful induction and maintenance of LTP (middle panel labeled 55–60 min after 3TB). The fEPSP shows a normally graded increase in amplitude with increasing stimulus intensity (0–250 mA stimulus, labeled Input/Output). (B) Representative recordings from a hippocampal slice from an Fgf14^−/− mouse exhibit stable baseline responses (Baseline), normal input output responses (Input/Output), but failed to maintain LTP (55–60 min after 3TB). (C) Cumulative data from LTP experiments from all slices were combined by normalizing fEPSP slopes to the baseline responses. Numbers in parentheses indicate when representative traces in A and B were obtained (1, Baseline; 2, 55–60 min after 3TB). The arrow indicates when 3TB were applied. Approximately 58% potentiation of the baseline response was observed in the WT slices (open circles). Although there is initially some post 3TB potentiation, LTP is not maintained in slices from Fgf14^−/− mice (closed circles). (D) LTP compared between WT and Fgf14^−/− slices at 55–60 min after 3TB (corresponding to 2 in C) demonstrates impaired LTP maintenance in Fgf14^−/− mice (p<0.001 one-way ANOVA). Scale bar, 0.5 mV and 5 ms. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Normal PHR and amygdala anatomy in Fgf14^−/− mice. (A) Normal hippocampal cytoarchitecture in the s.o., s.p. and s.r. of CA1 revealed by Nissl staining in Fgf14^−/− and WT mice. (B–F) No difference was observed in the staining intensity of GFAP (B), SNAP-25 (C), Synaptophysin (Syn38) (D), PKCγ (E) and CaMKII (F) in CA1 regions of Fgf14^−/− and WT mice. (G–H) Normal cytoarchitecture in the entorhinal cortex (G) and amygdala (H) in WT and Fgf14^−/− mice (Nissl stain). BLA, anterior basolateral amygdaloid nucleus; BMA, anterior basolateral amygdala; LaDL, dorsolateral amygdaloid nucleus DEn, dorsal endopiriform nucleus; Pir, piriform cortex; rf, rhinal fissure; s.l-m., stratum lacunosum moleculare; s.o., stratum oriens; s.p., stratum pyramidal; s.r., stratum radiatum. Bar=125 µm (A, B); Bar=50 µm (C, D); Bar=500 µm (E–H).