Implantable telemetry devices are widely used in experimental animals. We investigated the potential for such implants to induce stress in mice. Changes in body weight and post-mortem responses of the vas deferens to noradrenaline (as a measure of sympathetic activation) were measured 28 days after transmitter implantation. We examined the influence of the anaesthetic used during implantation (pentobarbitone or fentanyl/fluanisone/midazolam), the strain (Balb/c and CBA) and the body weight at the time of implantation (small = 19–24g; large = 27–30g). A sham-implantation procedure did not significantly affect the responses to noradrenaline. When telemetry transmitters were implanted in small mice of both strains, there was a significant increase in the maximum response to noradrenaline compared to that obtained in tissues from large mice. The anaesthetic used during implantation did not affect the responses to noradrenaline obtained post mortem. Mice of both strains had a significant post-operative weight loss and this was maintained for the experimental period. The results show that implantation of telemetry transmitters has a significant impact in mice that weigh < 25g.

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