Ethanolic extract from bulbs of Cipura paludosa reduced long-lasting learning and memory deficits induced by prenatal methylmercury exposure in rats

Abstract

Previous studies from our group have indicated important biological properties of the ethanolic extract (EE) and isolated compounds from the bulbs of Cipura paludosa (Iridaceae), a native plant widely distributed in northern Brazil. In the present study, the effects of chronic treatment with the EE on the memory of adult rats exposed to methylmercury (MeHg) during early development were assessed. Pregnant rats were treated by gavage with a single dose of MeHg (8 mg/kg) on gestational day 15, the developmental stage critical for cortical neuron proliferation. Adult offspring were administered orally with the EE of C. paludosa (1, 10 or 100mg/kg) over 14 consecutive days. EE improved short-term social memory in a specific manner and facilitated the step-down inhibitory avoidance of short- and long-term memory. MeHg exposure induced pronounced long-lasting impairments in social recognition memory that were improved by EE. Moreover, EE significantly increased the step-down latencies specifically during the short-term session in prenatal MeHg-exposed rats. These results demonstrate that EE reduced the long-lasting short-term learning and memory deficits induced by MeHg exposure. These findings may encourage further studies evaluating the cognitive enhancing properties of C. paludosa and its components on neuropathological conditions associated with exposure to environmental contaminants.

Fig. 1

Effects of repeated oral administration of the ethanolic extract of Cipura paludosa (1, 10 or 100mg/kg, once daily for 14 days) or vehicle (V) on social investigation times of prenatally methylmercury (MeHg)-exposed adult rats when the same juvenile was re-exposed at 30min after the first presentation (n=10 per group). Bars represent investigation times (mean±S.E.M., in seconds) in the first (white) and second presentation (grey). *p≤0.05 compared to the first presentation of the same group. ^#p≤0.05 compared to the second presentation of the vehicle-treated animals of the control group (Newman–Keuls test).

Fig. 2

Effects of repeated oral administration of the ethanolic extract of Cipura paludosa (1, 10 or 100mg/kg, once daily for 14 days) or vehicle (V) on social investigation times of prenatally methylmercury (MeHg)-exposed adult rats when the same juvenile was re-exposed at 120min after the first presentation (n=10 per group). Bars represent investigation times (mean±S.E.M., in seconds) in the first (white) and second presentation (grey). *p≤0.05 compared to the first presentation of the same group (Newman–Keuls test).

Fig. 3

Effects of repeated oral administration of the ethanolic extract of Cipura paludosa (1, 10 or 100mg/kg, once daily for 14 days) or vehicle (V) on social investigation times of adult rats exposed prenatally methylmercury (MeHg)-exposed adult rats when a different juvenile was re-exposed at 120min after the first presentation (n=10 per group). Bars represent investigation times (mean±S.E.M., in seconds) in the first (white) and second presentation (hatched).

Fig. 4

Effects of repeated oral administration of the ethanolic extract of Cipura paludosa (1, 10 or 100mg/kg, once daily for 14 days) or vehicle (V) on the short-term (1.5h) and long-term (24h) memory evaluated in the step-down inhibitory avoidance task in adult rats exposed prenatally to methylmercury (MeHg). Data are shown as the medians (interquartile ranges) of latencies to step-down in the training (white) and test (1.5h: grey; 24h: hatched) sessions (n=10 animals per group). *p≤0.05 compared to the respective session of the control-treated group (Dunn's test).