"Investigation on the role of Cl- homeostasis and GABAergic transmission in sleep disorders of Down syndrome and in Prader Willi syndrome: a possible contributor to cognitive impairment"

GABA is the main inhibitory neurotransmitter of the central nervous system (CNS). Recently, GABAergic transmission has been reported to be depolarizing and possibly excitatory rather than inhibitory in a number of neurodevelopmental disorders both in patients and mouse models. In particular, the Ts65Dn mouse model of Down syndrome (DS) exhibits depolarizing GABA due to upregulation of the Cl- importer NKCC1 both in the hippocampus and in the cortex. Moreover, NKCC1 inhibition by the FDA-approved diuretic bumetanide is able to rescue inhibitory GABAergic transmission, synaptic plasticity and cognitive functions in Ts65Dn mice. Beside cognitive impairment, DS mice and people with DS show sleep disturbaces. Since sleep pattern is regulated by GABAergc transmission, we reasoned that the alteration of GABAergic transmission due to upregulation of NKCC1 might be underlying at least some of the sleep disturbances in DS mice. So, we characterized sleep in Ts65Dn mice and investigated the effects of a chronic treatment with bumetanide. We found that bumetanide ameliorates the quality of sleep in NREM and REM sleep phases before and after sleep deprivation and decreases abnormal wakefulness during light phase at baseline in Ts65Dn mice. Moreover, we also found abnormalities in other parameters, which could contribute to sleep abnormalities of Ts65Dn mice: an increase of food intake and activity (partially rescued by bumetanide) with a reduction of body temperature during dark phase. Because of the association of altered GABAergic signaling by dysregulation of the expression of NKCC1 (but also of the Cl- exporter KCC2) in many neurodevelopmental disorders characterized by cognitive or social impairment, and sleep disorders, we extended our studies to Prader Willi syndrome (PWS). PWS is a neurodevelopmental disorder, caused by defects of genomic imprinting and characterized by cognitive, social and sleep abnormalities. Here, we observed that the Snord116 5 mutant mouse model of PWS, PWScrm+/p− show an increased expression of NKCC1, specifically in the hippocampus in comparison to their wild-type mice. Moreover, we report that PWS mice have altered cognition and the circadian period in free-running conditions. In particular, mutant mice present defects of long-term memory and a reduced shortening of their circadian period together with an increase of alpha activity in dark-dark (DD). Moreover, they also show alteration of pain sensitivity, that could be linked to defects in the thermoregulation. Interestingly, in constrast with PWS people, Snord116 mutant mice showed no alterations of anxiety, repetivive, obsessive and social behaviors. In an effort to rescue cognition and the circadian phenotype by rescuing NKCC1 inhibition, we treated Snord116 mutant mice with bumetanide. Remarkably, bumetanide treatment resulted in a complete rescue of the cognitive defects and circadian alteration in DD, with no effects in controls. Our results suggest an important link between GABA transmission and the regulation of cognition and the circadian clock in PWS. In addition, the current study extends the repertoire of disorders in which NKCC1 inhibition attenuates behavioural deficits and proposes a new potential mechanism for the investigation of PWS.