Homeostatic Changes in GABA and Glutamate Receptors on Excitatory Cortical Neurons during Sleep Deprivation and Recovery

Abstract

Neuronal activity is regulated in a homeostatic manner through changes in inhibitory GABA and excitatory glutamate (Glu) AMPA (A) receptors (GluARs). Using immunofluorescent staining, we examined whether calcium/calmodulin-dependent protein kinase IIα (CaMKIIα)-labeled (+) excitatory neurons in the barrel cortex undergo such homeostatic regulation following enforced waking with associated cortical activation during the day when mice normally sleep the majority of the time. Sleep deprived mice were prevented from falling asleep by unilateral whisker stimulation and sleep recovery (SR) mice allowed to sleep freely following deprivation. In parallel with changes in c-Fos reflecting changes in activity, (β2-3 subunits of) GABAA Rs were increased on the membrane of CaMKIIα+ neurons with enforced waking and returned to baseline levels with SR in barrel cortex on sides both contra- and ipsilateral to the whisker stimulation. The GABAAR increase was correlated with increased gamma electroencephalographic (EEG) activity across conditions. On the other hand, (GluA1 subunits of) AMPA Rs were progressively removed from the membrane of CaMKIIα+ neurons by (Rab5+) early endosomes during enforced waking and returned to the membrane by (Rab11+) recycling endosomes during SR. The internalization of the GluA1Rs paralleled the expression of Arc, which mediates homeostatic regulation of AMPA receptors through an endocytic pathway. The reciprocal changes in GluA1Rs relative to GABAARs suggest homeostatic down-scaling during enforced waking and sensory stimulation and restorative up-scaling during recovery sleep. Such homeostatic changes with sleep-wake states and their associated cortical activities could stabilize excitability and activity in excitatory cortical neurons.

Linking Network Activity to Synaptic Plasticity during Sleep: Hypotheses and Recent Data

“…Whether these pathways are evoked in vivo as a consequence of learning-associated synaptic potentiation is unknown. However, sleep-associated changes in the number of inhibitory synapses have been observed in the cortex, as described above (Del Cid-Pellitero et al, 2017 ). Taken together, there are numerous alternate pathways by which sleep could regulate homeostatic changes in neural circuits in response to augmented network activity.…”

“…Following periods of overactivity, inhibitory synapses on pyramidal neurons have been shown to undergo presynaptic and post-synaptic enhancements, including increases in presynaptic GAD65 and GABAA receptor surface expression (Peng et al, 2010 ; Rannals and Kapur, 2011 ). Recent data suggest that GABAA receptor surface expression is increased on cortical pyramidal neurons in vivo in response to brief SD (Del Cid-Pellitero et al, 2017 ). Homeostatic increases in GABAA receptor expression have recently been linked to changes in the localization of gephyrin, a scaffolding protein that anchors GABAA receptors to the inhibitory PSD (Flores et al, 2015 ).…”

Sleep and synaptic down‐selection

“…There are several markers of synaptic strength, some more direct than others (Cirelli, ), but the overall emerging picture is consistent with SHY's prediction. For instance, the expression of excitatory glutamatergic AMPA (Alpha‐Amino‐3‐Hydroxy‐5‐Methyl‐4‐Isoxazole Propionic Acid) receptors, when measured at the synaptic level in the rat cerebral cortex and hippocampus of adult rats (Vyazovskiy, Cirelli, Pfister‐Genskow, Faraguna, & Tononi, ) and in the postsynaptic densities taken from the whole forebrain of post‐adolescence mice (Diering et al., ), is higher after wakefulness than after sleep (cytoplasmic presence/absence of immunoreactivity for these receptors, as reported in (Del Cid‐Pellitero, Plavski, Mainville, & Jones, ), is not a measure of synaptic strength). Evoked responses and field excitatory postsynaptic potentials (fEPSPs) recorded in vivo also increase with wake duration and decrease during sleep in cortex and hippocampus of adult rodents and humans (Huber et al., ; Norimoto et al., ; Vyazovskiy et al., ), although cortical evoked responses are also modulated by circadian time (Ly et al., ).…”

Plasticity during Sleep Is Linked to Specific Regulation of Cortical Circuit Activity

“…This view would be also in line with monocular deprivation experiments which showed upregulation of the phosphorylation levels within the visual cortex of the AMPA receptor subunit GluR1 during subsequent sleep (Aton et al, 2009 ). There is also evidence suggesting that sleep-dependent regulation of AMPA receptors differentially affects AMPA receptor subtypes, with the elimination and upregulation of receptor levels mainly pertaining to calcium permeable AMPA receptors which do not contain the GluR2 subunit and keep the circuit in a labile state (Lanté et al, 2011 ; Shepherd, 2012 ; Del Cid-Pellitero et al, 2017 ).…”