Periodic Reporting for period 4 - Opto-Sleep (All-optical deconstruction of thalamic control of sleep-wake states.)
Okres sprawozdawczy: 2021-12-01 do 2022-11-30
While the functions of sleep are still a matter of debate and may include memory consolidation, brain clearance, anabolism and plasticity, the neural substrates of sleep and wake states are the subject of intense study. Successive sleep-wake cycles rely on an appropriate balance between sleep-promoting nuclei of the brain located in the anterior hypothalamus and, arousal-promoting nuclei from the posterior hypothalamus and the brainstem. My laboratory previously identified different subsets of hypothalamic cells that control wakefulness and rapid-eye movement (REM) sleep using optogenetics in combination with high-density electrophysiology in freely-behaving mice. Although we and others have dissected important subcortical and cortical sleep-wake circuits in the brain, the precise mechanism bridging sub-cortical circuits to thalamic and cortical networks remains unclear. The Opto-Sleep project aims at testing the hypothesis that the thalamus represents a hub that integrates sleep-wake inputs of both subcortical and cortical origin into stable sleep-wake states, through topographically distinct sub-cortical inputs and temporally precise circuit dynamics.
In a previous study, we identified a monosynaptic pathway between GABA neurons of the lateral hypothalamus (LH) and GABA neurons from the thalamic reticular nuclei (TRN) (i.e. LHVGAT-TRNGABA; Gutierrez Herrera et al 2016), a key structure in sensory integration and the generation of NREM sleep spindles. We showed that LHVGAT neurons exert a strong inhibition onto TRN neurons that ultimately results in a feedforward disinhibition of thalamo-cortical networks and a rapid arousal transition from NREM (but not REM) sleep to wakefulness, and facilitates emergence form anaesthesia. In contrast, acute silencing of the LHGABA-TRNGABA circuit increased the duration of NREM sleep episodes and the depth of sleep.
In a first published study, we showed that spontaneous firing of centromedial thalamus (CMT) neurons is phase-advanced to global cortical UP-states and NREM–wake transitions, and oscillates independently from somato-sensory thalamo-cortical oscillations. Importantly, we showed that tonic optogenetic activation of CMT neurons induces NREM–wake transitions, whereas burst activation mimics UP-states in the cingulate cortex (CING) and enhances brain-wide synchrony of cortical slow waves during sleep.
Our current Opto-Sleep investigations focus on the connectivity, dynamics and functions of synaptic circuits linking the medio-dorsal thalamic neurons to the prefrontal cortex across sleep-wake states (see specific aim #2). We found that amongst cortical microcircuits, CMT projections contact Parvalbumin (PV)-positive inhibitory neurons. 2-photon somatic calcium imaging reveals that the activity of GCaMP6-expressing PV inhibitory neurons is significantly increased during REM. Conversely, the activity of GCaMP6-expressing layer II/III pyramidal neurons is significantly decreased during REM sleep. Our results suggest a tight modulation of the neuronal thalamo-cortical circuits during sleep-wake transitions. This modulation is likely to be exerted by thalamic projections controlling the activity of local inhibitory neurons, which, in turn, modulate principal neuron excitability.
In a first published study, we showed that spontaneous firing of centromedial thalamus (CMT) neurons is phase-advanced to global cortical UP-states and NREM–wake transitions, and oscillates independently from somato-sensory thalamo-cortical oscillations. Importantly, we showed that tonic optogenetic activation of CMT neurons induces NREM–wake transitions, whereas burst activation mimics UP-states in the cingulate cortex (CING) and enhances brain-wide synchrony of cortical slow waves during sleep.
Our current Opto-Sleep investigations focus on the connectivity, dynamics and functions of synaptic circuits linking the medio-dorsal thalamic neurons to the prefrontal cortex across sleep-wake states (see specific aim #2). We found that amongst cortical microcircuits, CMT projections contact Parvalbumin (PV)-positive inhibitory neurons. 2-photon somatic calcium imaging reveals that the activity of GCaMP6-expressing PV inhibitory neurons is significantly increased during REM. Conversely, the activity of GCaMP6-expressing layer II/III pyramidal neurons is significantly decreased during REM sleep. Our results suggest a tight modulation of the neuronal thalamo-cortical circuits during sleep-wake transitions. This modulation is likely to be exerted by thalamic projections controlling the activity of local inhibitory neurons, which, in turn, modulate principal neuron excitability.
To our knowledge, we have described, for the first time, a neuronal circuit mechanism by which high order nuclei of the midline thalamus drive cortical activity across sleep-wake cycle in behaving mice. Our results are of great interest not only for the sleep field, but also for the field of cognitive neuroscience. Indeed, there is an increasing number of studies investigating the role of the medio-dorsal thalamus in reward processing (food intake), attention, working memory and consciousness both in animal models and human. Thus, our work aims at a better understanding of the connectivity, dynamics and functions of distinct thalamo-cortical, and sub-cortical circuits and their implications in higher brain functions.