Possible changes in production of tachykinin after chronic MDMA treatment were investigated in rats given daily injections of saline or 5 mg/kg MDMA for 8 consecutive days. Rats were killed 9 days post-drug, and brain slices were treated with radiolabeled oligonucleotide for preprotachykinin A mRNA. Social memory was assessed in saline and MDMA-treated rats given saline, 1, 5 or 10 mg/kg MDMA by exposing rats to a juvenile "stranger" rat in their home cage for 5 minutes. Acute effects of MDMA on social interactions were apparently measured (but not reported) in assessments conducted 30 min post-drug on each day. Memory was measured by comparing a second presentation of the same rat 120 min after the first presentation on treatment day 8. Chronic MDMA treatment reduced preprotachykinin A mRNA in nucleus accumbens core and shell, olfactory tubercle, islands of Calleja, in the bed nucleus of the stria terminalis, posterior-dorsal medial amygdala, pre-optic area and medial habenular nucleus. When compared with saline-treated animals, MDMA-treated animals had increased preprotachykinin A mRNA in the dorsal and ventral caudate-putamen. All rats apparently spent more time investigating the strange rat on second presentation, but rats given 1 and 5 mg/kg MDMA spent more time investigating the strange rat than did controls or rats given 10 mg/kg on day 8. The authors interpret their findings as relating to a compensatory mechanism responding to chronic dopamine release in the forebrain, possibly related to activity at 5HT2A and 5HT4 receptors. Given that MDMA releases serotonin, dopamine and norepinephrine, and given that no histological examinations of 5HT or DA activity were performed, it is difficult to draw conclusions from study findings. It is also difficult to interpret the data from the social memory task for a number of reasons, including possible confounding of acute MDMA effects with measurement of social memory. In addition, if it is assumed that rats will spend less time investigating the rat on second presentation, it is puzzling that this is not the case even for controls. Conversely, if the authors subtracted the first investigation times from the second investigation times, it would then appear that MDMA-treated rats spent even less time investigating the stranger, as difference scores are larger and negative.