Histological and functional characterization of sleep-active cortical neurons in rats
Final Report Abstract
Sleep is highly conserved throughout the animal kingdom and serves several vital functions, such as cellular repair and synaptic plasticity. Sleep is dually regulated by a circadian process on the one hand and a homeostatic process (“Process S”) on the other hand. In the course of this fellowship, I conducted a series of experiments that indicate that a recently discovered population of sleep-active interneurons is the neural substrate of homeostatic sleep regulation in the cortex. These neurons were previously described in my host lab and can be identified by immunoreactivity for neuronal nitric oxide synthase (nNOS). I found that these neurons coexpress the Substance P receptor NK1 in mice, rats, and primates, and are highly activated by Substance P. Experimental dissociation of sleep from sleep pressure using hypnotics revealed that cortical nNOS/NK1 neurons are activated by sleep pressure and inhibited by wakefulness. Activation of nNOS/NK1 neurons was accompanied by elevated NREM delta power. Systematic manipulation of sleep deprivation and recovery sleep followed by Fos histochemistry showed strong correlation of nNOS/NK1 neuron activation with NREM time, NREM bout duration, and NREM delta power. Conversely, nNOS KO mice showed decreased NREM time, NREM bout duration, and NREM delta power, despite constitutively elevated sleep pressure. The newly established use of NK1 as an alternative marker for cortical sleep-active neurons enabled me to demonstrate that these neurons are still activated during recovery sleep after sleep deprivation in the absence of nNOS, although the accompanying upregulation in NREM delta power was strongly diminished. Targeted activation of cortical nNOS/NK1 neurons using pharmacogenetics (DREADD) caused an increase in NREM time and particularly NREM delta in a pilot study. Combined, these results indicate that cortical nNOS/NK1 neurons integrate sleep pressure and transform it to an output signal in the form of NO and possibly other transmitters. This output signal plays a critical role in the consolidation of NREM sleep and the production of NREM delta activity, which are both implicated in sleep-related recovery.
Publications
- (2012). Commentary on Vyazovskiy et al., Local sleep in awake rats. SRS Bulletin 18 (2)
J.E. Heiss, L. Dittrich, T.S. Kilduff
- (2012). Cortical nNOS neurons coexpress the NK1 receptor and are depolarized by Substance P in multiple mammalian species. Front. Neural Circuits 6:31
L. Dittrich, J.E. Heiss, D.R. Warrier, X.A. Perez, M. Quik, T.S. Kilduff
(See online at https://doi.org/10.3389/fncir.2012.00031)
