Developmental 3,4-methylenedioxymethamphetamine (MDMA) impairs sequential and spatial but not cued learning independent of growth, litter effects or injection stress

Rats given MDMA from postnatal days 11 to 20 showed lasting deficits in spatial learning and memory, even when growth restriction from the drug was matched by raising rats in larger litters. Males exposed to MDMA took longer and made more errors in the Cincinnati water maze than control males. In the Morris water maze, MDMA-treated rats of both sexes were impaired during initial learning. Only females showed deficits when the platform was first moved, but both sexes were impaired after a second move with a smaller platform. No differences appeared in swimming ability, cued navigation, or stress hormone responses. Growth retardation, injections, or litter size did not account for the learning impairments.

Study at a glance

Abstract

Previously, we have shown that rats administered MDMA from postnatal (P) days 11-20 had reductions in body weight during the period of treatment and as adults they had deficits in sequential and spatial learning and memory. In the present study, to control for weight reductions, we used litters with double the number of offspring to induce growth restriction comparable to that of standard size litters treated with MDMA. Litters were treated twice daily from P11 to 20 with vehicle or MDMA (20 mg/kg) or only weighed. Males, but not females, exposed to MDMA had longer latencies and more errors in the Cincinnati water maze compared to males of the other treatments. In the Morris water maze (210 cm pool, 10x10 cm platform), the MDMA animals were impaired relative to all other treatments during acquisition. Only the MDMA females showed deficits when the platform was shifted to a new location, however, both MDMA males and females were impaired when the location of the platform was again shifted and a reduced platform (5x5 cm) used. No differences were observed in the ability to swim a straight channel, locate a platform with a cue, or the endocrine response to forced swim among the treatment groups. No differences were seen between animals injected with saline and those only weighed. The data suggest that factors, such as growth retardation, multiple injections, or the composition of the litter, do not affect the development of learning and memory impairments resulting from P11 to 20 MDMA exposure. The large litter approach offers a novel method to control for undernutrition during the preweaning period in rodents.