Paradoxical (REM) sleep deprivation in mice using the small‐platforms‐over‐water method: polysomnographic analyses and melanin‐concentrating hormone and hypocretin/orexin neuronal activation before, during and after deprivation

Summary
Studying paradoxical sleep homeostasis requires the specific and efficient deprivation of paradoxical sleep and the evaluation of the subsequent recovery period. With this aim, the small‐platforms‐over‐water technique has been used extensively in rats, but only rare studies were conducted in mice, with no sleep data reported during deprivation. Mice are used increasingly with the emergence of transgenic mice and technologies such as optogenetics, raising the need for a reliable method to manipulate paradoxical sleep. To fulfil this need, we refined this deprivation method and analysed vigilance states thoroughly during the entire protocol. We also studied activation of hypocretin/orexin and melanin‐concentrating hormone neurones using Fos immunohistochemistry to verify whether mechanisms regulating paradoxical sleep in mice are similar to those in rats. We showed that 48 h of deprivation was highly efficient, with a residual amount of paradoxical sleep of only 2.2%. Slow wave sleep and wake quantities were similar to baseline, except during the first 4 h of deprivation, where slow wave sleep was strongly reduced. After deprivation, we observed a 124% increase in paradoxical sleep quantities during the first hour of rebound. In addition, 34% of hypocretin/orexin neurones were activated during deprivation, whereas melanin‐concentrated hormone neurones were activated only during paradoxical sleep rebound. Corticosterone level showed a twofold increase after deprivation and returned to baseline level after 4 h of recovery. In summary, a fairly selective deprivation and a significant rebound of paradoxical sleep can be obtained in mice using the small‐platforms‐over‐water method. As in rats, rebound is accompanied by a selective activation of melanin‐concentrating hormone neurones.