Sleep Neurobiology and Circuitry

70 million Americans suffer from some sort of sleep disorder. Behavior, mood and
memory deteriorate with sleep loss and it gets worse with continuing sleep deprivation. Lack of
sleep has been linked to Alzheimer's disease. There is considerable amount of data on the
neurons that wake us up (wake-active neurons) and neurons that initiate NREM (NREM-max)
and REM sleep (REM-max). However, there are also glia in the brain and they outnumber
neurons. A single astrocyte contacts hundreds of dendrites, and tens of thousands of synapses
(Bushong et al., 2002, Halassa et al., 2007). As such, astrocytes can actively control neuronal
activity and synaptic transmission. Converging evidence shows that astrocyte activity may
regulate the waxing and waning of sleep. Sleep is increased by activating astrocytes (our data,
Pelluru et al., 2016), and recent evidence shows that cortical astrocytes are active in waking
relative to NREM and REM sleep. Are glia also active during waking in other brain regions? Or,
do glia have a varied pattern of activity similar to neurons? Are there REM-max glia? It is
important to answer these questions considering that glia are now believed to clear the brain of
waste. We will use microendoscopy to image the activity of glia and local neurons in the zona
incerta, a region where 70% of the GABA neurons are most active in NREM and REM sleep.
Four specific aims will test the overall hypothesis that there is a dynamic activation of glia
during waking, NREM and REM sleep. Glia in the zona incerta will be imaged during sleep, and
in response to 6h sleep loss to test the hypothesis that fluorescence in glia increases after sleep
loss. In aim 3, the activity of local glia will be manipulated with pharmacogenetics to test the
hypothesis that activating glia also activates local excitatory (vesicular glutamate transporter
type 2; vGLUT2) and inhibitory (Lhx6-cre, a transcription factor that colocalizes in GABA
neurons) neurons. In aim 4, the activity of the excitatory and inhibitory neurons in the zona
incerta will be manipulated (optogenetics and DREDD) and fluorescence in glia will be imaged
to test the hypothesis that activity of neurons changes activity of the local glia.
The proposed aims utilize cutting-edge methodologies to test specific hypotheses in male
and female mice. It is feasible to achieve the aims during the funding period because we have
established expertise in collecting and analyzing microendoscopy data. The overall impact of
this project is that it mechanistically identifies activity in local circuits that precedes the
emergence of sleep. Inclusion of astrocytes in circuit models will lead to a better understanding
of sleep homeostasis and unihemispheric sleep, which is something that current “neuron-
centric” models have failed to do.

Grant Number: 5I01BX000798-16
NIH Institute/Center: VA
Principal Investigator: HOWARD BECKER