Human insulin gene insertion in mice. Effects on the sleep-wake cycle?

Recently, insulin synthesis and the presence of an insulin receptor have been demonstrated in the brain. Intracerebroventricular infusion of insulin causes a selective increase in the amount of slow-wave sleep. In the present study, the sleep-wake cycle of transgenic mice, with or without habenular neuronal expression of the human insulin gene, was studied to investigate the possible role of brain insulin as a sleep modulator. Slow-wave sleep duration was increased in those mice expressing human insulin in the habenula. However, it is possible that this effect was not due to expression of the insulin transgene, but to the genetic background of one of the parental strains (CBA) used for insertion of the transgene. Users of transgenic mice should be aware of this possibility and be cautious in interpreting results when hybrid embryos are used as transgene recipients.