Exposure of developing well-nourished and malnourished rats to environmental heating facilitates cortical spreading depression propagation at adulthood

Cortical spreading depression (CSD) is a brain electrical response related to neural activity and probably also related to diseases like migraine and epilepsy. Adverse conditions like malnutrition and exposure to a warm environment early-in-life can permanently alter brain development, changing electrophysiological features of the brain responses and rendering the brain prone to febrile seizures. Here we investigated the lasting effects of heat exposure on brain CSD propagation in well-nourished and malnourished developing rats. From postnatal days 10–29, rats were exposed to daily sessions (one session per day, five sessions per week during 3 weeks; total of 15 sessions) of a warm environment (40 ± 2 °C). At 30–40 days and 90–120 days of life (young and adult age-ranges, respectively), they were anesthetized (urethane + chloralose; 1000 + 40 mg/kg ip) and the electrocorticogram plus the slow potential change accompanying CSD were recorded on two parietal points for 4 h. Compared to controls (maintained on the normal environment temperature, 23 ± 2 °C), heat-exposed rats displayed higher CSD velocities of propagation (P < 0.05; ANOVA plus Tukey test) at both age-ranges and nutritional statuses. The mean ± S.D. CSD velocities (in mm/min) were: for control- and heat-exposed well-nourished rats, 3.75 ± 0.15 and 4.17 ± 0.19 (young groups), and 3.33 ± 0.06 and 3.88 ± 0.26 (adult); for the same control and heat exposure conditions in the malnourished rats, 4.30 ± 0.22 and 5.31 ± 0.46 (young), and 4.18 ± 0.20 and 4.88 ± 0.35 (adult). In contrast to early malnutrition, heat exposure did not affect body and brain weights. Data support the hypotheses that (1) early heat exposure long-lasting facilitates CSD propagation and (2) this effect is not modified by early malnutrition.