Brain aromatase overexpression does not reduce ischaemic damage nor improve long term functional outcome after experimental stroke: A magnetic resonance imaging and behavioural study

Introduction

17beta-Oestradiol, the female sex hormone, which has neuroprotective properties, is synthesised in the brain by the enzyme aromatase. We have recently reported that aromatase expression is increased after experimental stroke with implications for reducing ischaemic damage and improving behavioural outcome by local synthesis of oestrogens (Carswell et al, 2004).

Aims

The present study investigates if aromatase overexpression reduces ischaemic brain damage and/or improves long term functional outcome after experimental stroke

Methods

Dax-1 (dosage-sensitive sex reversal adrenal hypoplasia congenita region on the X-chromosome, gene-1) knock out (KO) mice are a unique strain that overexpress aromatase. Stroke was induced by permanent middle cerebral artery occlusion (MCAO) in male Dax-1 KO (n=8) and wild-type (n=8) mice. Magnetic Resonance Imaging (MRI) (7 Tesla Bruker Biospec) was used to measure infarct size 48 hours post-MCAO using a RARE T2 weighted sequence (TR/TE 5086/73 msec, 117 micron in plane resolution, 600 micron slice thickness). The infarct areas were delineated and integrated to calculate the volume of infarction using Paravision software. At 8 weeks post-MCAO, animals underwent two long term functional outcome tests (Corner Test and Foot-Fault Test) to assess deficits in Dax-1 KO and wild type mice. These sensorimotor tests were chosen specifically since they are reported to be sensitive enough to pick up and evaluate chronic (e.g. 8 weeks) sensorimotor impairments post-MCAO in mice (Zhang et al, 2002). For the Foot Fault Test, the number of incorrect forepaw placements on a grid (foot fault) on impaired side were counted and presented as a % of total steps. All data are presented as mean±SD.

Results

Plasma 17beta-oestradiol levels in wild type and Dax-1 KO mice were 8.7± 4.8 and 14.8± 6.3 pg/ml respectively (p=0.037, one tailed unpaired t-test). Infarct volumes were not significantly different between Dax-1 KO and wild type mice and sensorimotor deficits were similar between the two groups for both behavioural tests (Figure 1).

Figure 1

Conclusion

The present study provides no evidence for an influence of aromatase overexpression on stroke outcome in Dax-1 KO mice. This is contrary to our hypothesis, and may be due to insufficient additional oestrogen production to exert significant neuroprotection in Dax-1 KO mice or because MCAO induces optimal aromatase overexpression in wild type mice.