Characterization of cognitive deficits in mice with an alternating hemiplegia-linked mutation

Abstract

Cognitive impairment is a prominent feature in a range of different movement disorders. Children with Alternating Hemiplegia of Childhood are prone to developmental delay, with deficits in cognitive functioning becoming progressively more evident as they grow older. Heterozygous mutations of the ATP1A3 gene, encoding the Na+,K+-ATPase α3 subunit, have been identified as the primary cause of Alternating Hemiplegia. Heterozygous Myshkin mice have an amino acid change (I810N) in Na+,K+-ATPase α3 that is also found in Alternating Hemiplegia. To investigate whether Myshkin mice exhibit learning and memory deficits resembling the cognitive impairments of patients with Alternating Hemiplegia, we subjected them to a range of behavioral tests that interrogate various cognitive domains. Myshkin mice showed impairments in spatial memory, spatial habituation, locomotor habituation, object recognition, social recognition, and trace fear conditioning, as well as in the visible platform version of the Morris water maze. Increasing the duration of training ameliorated the deficit in social recognition but not in spatial habituation. The deficits of Myshkin mice in all of the learning and memory tests used are consistent with the cognitive impairment of the vast majority of AHC patients. These mice could thus help advance our understanding of the underlying neural mechanisms influencing cognitive impairment in patients with ATP1A3-related disorders.

Figure 1

Y-maze spontaneous alternation. (A) Total number of arm entries (mean ± SEM) of Myk/+ (n = 10) and +/+ (n = 10) mice. (B) Percentage of alternation (mean ± SEM). *** p < .001 compared with +/+ mice. ^### p < .001 compared with chance level (50%).

Figure 2

Object recognition. (A) Percentage of exploration time (mean ± SEM) spent by Myk/+ (n = 10) and +/+ (n = 10) mice exploring four identical objects. Broken line indicates 25% chance level. (B) Percentage of exploration time (mean ± SEM) with displaced objects versus nondisplaced objects. Broken line indicates 50% chance level. (C) Percentage of exploration time (mean ± SEM) with a novel object versus a familiar object. Broken line indicates 50% chance level. ** p < .01; *** p < .001 compared with +/+ mice. ^## p < .01; ^#### p < .0001 compared with chance level (50%).

Figure 3

T-maze habituation. Exploration ratio (mean ± SEM) of Myk/+ (n = 10) and +/+ (n = 10) mice allowed to explore two arms of a T-maze for 10 min or 1 hr before the third (novel) arm was revealed. * p < .05; ** p < .01 compared with +/+ mice. ^## p < .01 compared with 10-min exploration ratio.

Figure 4

Water maze and fear conditioning. (A) Escape latency (s; mean ± SEM) and (B) swim path length (m; mean ± SEM) of Myk/+ (n = 10) and +/+ (n = 10) mice in the visible platform version of the Morris water maze test. (C) Freezing levels (mean ± SEM) of Myk/+ (n = 10) and +/+ (n = 10) mice in the trace fear conditioning procedure. Baseline, baseline (test-naïve) freezing; Tone, freezing during the auditory tone in the training phase; Pre-CS, freezing in the altered chamber before the auditory tone; CS, freezing in the altered chamber during the auditory tone. ** p < .01; *** p < .001 compared with +/+ mice. ^†† p < .01 compared with Baseline. ^#### p < .0001 compared with Pre-CS.

Figure 5

Social recognition and locomotor habituation. (A) Recognition ratio (mean ± SEM) of male Myk/+ and +/+ mice after exposure to a novel juvenile mouse for 2 min (n = 9/genotype) or 10 min (n = 6/genotype) the day before. Broken line indicates “null recognition” level (ratio of 1.0). (B) Total distance traveled (m) in an open field during each 1-hr session on four consecutive days. * p < .05 compared with +/+ mice. ^## p < .01; ^### p < .001 compared with null recognition level. ⁺⁺⁺⁺ p < .0001 compared with Day 1.