Seizure susceptibility, phenotype, and resultant growth delay in the nclf and mnd mouse models of neuronal ceroid lipofuscinoses

Abstract

We examined flurothyl gas-induced seizure latencies and phenotype in 2 mouse models of neuronal ceroid lipofuscinoses: the nclf (Cln6 mutant) variant late-infantile model and the mnd (Cln8 mutant) Northern epilepsy model. Mnd mice on postnatal days 35 to 42 had increased latency to loss of posture compared with wild-type controls. Nclf, mnd, and wild-type mice on postnatal days 21 days to 25 displayed similar latency profiles during repeated seizure induction (kindling) and retesting; seizure phenotypes were different, however. Kindled wild-type mice reexposed to flurothyl after a 28-day recovery displayed brainstem generalized seizures exclusively. Neuronal ceroid lipofuscinoses mutants demonstrated a lack of brainstem seizures at retesting after 28 days. Repeated induction of generalized seizures delayed weight gain in both nclf and mnd mice compared with wild-type mice. These and our previous results suggest that abnormal seizure-related neuronal connectivity and/or plasticity are shared characteristics of the neuronal ceroid lipofuscinoses.

Keywords: Batten disease; epilepsy; flurothyl; neuronal ceroid lipofuscinoses; seizure induction latencies.

Figure 1

Age-dependent increase in the latency to flurothyl-induced seizure in mnd mice. Male wild-type, mnd, and nclf mice at 3 different ages (21 days to 25 days, 35 days to 42 days, and 6 months to 9 months) were used in the experiments. Seizure was induced by inhalation of flurothyl gas, and the latency until loss of posture was measured. Columns and bars represent mean ± standard error of the mean (n = 4–7). At the age of 35 days to 42 days, the mean latency to flurothyl-induced loss of posture was 532.1 ± 47.8 s for mnd mice and 420.9 ± 17.6 s for 35-day to 42-day wild-type mice (P < .05 by unpaired t test). No significant differences were observed between mnd and wild-type mice at earlier (21 days to 25 days) or later (6 months to 9 months) developmental time points. No statistically significant differences existed between nclf and age-matched wild-type mice.

Figure 2

Immature wild-type, nclf, and mnd mice show similar seizure latencies but an altered seizure phenotype during kindling and retesting. Wild-type, nclf, and mnd mice at 21 days to 25 days of age underwent kindling (seizure induction by flurothyl once a day for 8 consecutive days) and subsequent retesting (seizure induction by flurothyl once a week for 4 weeks). Columns and bars represent mean ± standard error of the mean (n = 3–5). (A) Seizure induction latencies during the 8 days of kindling (day 1 through day 8) and in the 4th (28th day) post kindling retest (RT-28 days). Statistical analysis was performed using unpaired t test: P < .05 as compared with wild-type; NS: not significant. (B) Seizure phenotypes during the 8 days of kindling and in the 4th (28th day) post kindling retest. Eight-day kindling in wild-type mice produced the expected shift from cortical to brainstem seizures when the animals were retested 28 days later. All (100%) wild-type mice demonstrated a brainstem seizure, whereas none (0%) of the nclf or mnd mice converted to the expected phenotype.

Figure 3

Repeated flurothyl-induced seizure activity inhibits the growth of nclf and mnd mice. Wild-type, nclf, and mnd mice at 21 days to 24 days of age underwent kindling (seizure induction by flurothyl once a day for 8 consecutive days) and subsequent retesting (seizure induction by flurothyl once a week for 4 weeks). After the last retesting (at 57 days to 60 days of age), the mice were weighed. Age-matched naïve (no seizure induction), same-strain control mice also were weighed. Columns and bars represent mean ± standard error of the mean (n = 3–5). Repeated seizure activity significantly decreased the total body weight of nclf and mnd mice when compared with naïve same-strain controls (P < .01 for nclf and P < .001 for mnd by unpaired t test). Wild-type animals showed normal growth despite repeated seizure activity (NS: not significant by unpaired t test).