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049P
University
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MDMA (ecstasy) dose-dependently attenuates defensive burying behaviour in mice
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When mice are placed in a cage with an aversive stimulus they displace the bedding with forepaws or head movements and bury the object, a behaviour termed defensive burying (De Boer & Koolhaas, 2003). One simple aversive object used is a group of marbles (Njung'e & Handley, 1991). We have now examined the effect of administration of the popular recreational drug 3,4-methylene-dioxymethamphetamine (MDMA), ecstasy) on this response.
Male NIH-Swiss mice [Harlan Olac, UK] weighing 25-30g were used. They were placed individually in a novel cage (42 x 25 x 12cm) containing 14 glass marbles evenly spaced about 10 cm from the walls. Bedding was 10 cm deep sawdust. The number of marbles at least 2/3 buried was counted 30 min later. MDMA was dissolved in saline and injected i.p. at a volume of 10 ml kg-1, control animals were injected with saline.
MDMA administration produced a dose-dependent inhibition of marble burying behaviour 30 min later (Fig). An half maximal dose of MDMA (2.5 mg kg-1) produces a maximum inhibition of burying at 30 min, the attenuation at 90 min not being statistically significant. There was no effect at 180 min [30 min: control, 73±6; MDMA, 34±5, p<0.001; 90 min: control 65±7; MDMA, 45±9, N.S.; 180 min: control 57±6, MDMA, 49±6, N.S., Results reported as % marbles buried (n = 8), 't' test following arc-sin transformation].
It has been suggested that defensive burying may reflect a fear or anxiety state since anxiolytic drugs can attenuate the response. However, the fact that it is a normal response means that it is not a model of pathological anxiety (De Boer & Koolhaas, 2003). Attenuation of the response by low doses of MDMA indicates that the compound may be producing a decrease in the normal anxiety or fear status of the animal, thereby reflecting the reported human response to MDMA of "friendliness, calmness and relaxation" (Davison and Parrott, 1997). Consequently this model may be more appropriate for further investigation on the behavioural effects of MDMA in mice than models such as the plus maze or social interaction in which MDMA has been reported to be anxiogenic (Lin et al., 1999; Maldonado and Navarro, 2001).
Fig.
The effect of MDMA administration on the marble burying behaviour of mice
30 min later. Response shown as % marbles buried. Differences in experimental
group from control: 
,
P< 0.05,
, P<0.01,
p<0.001; ANOVA followed by Bonferroni post-hoc analysis.
Davison,
D. & Parrott, A.C. Human Psychopharmacol. 12: 221-226.
De Boer, S.F. & Koolhaas, J.M. (2003) Eur.J.Pharmacol. 463:
145-161.
Lin, H.Q. et al (1999) Pharmacol. Biochem. Behav. 62:
403-408.
Maldonado, E. & Navarro, J.F. (2001) Pharmacol. Res. 44:
27-31.
Njung'e, K. & Handley, S.L. (1991) Br.J.Pharmacol. 104:
105-112.