Endocannabinoid signaling modulates neurons of the pedunculopontine nucleus (PPN) via astrocytes

Abstract

The pedunculopontine nucleus (PPN) is known as the cholinergic part of the reticular activating system (RAS) and it plays an important role in transitions of slow-wave sleep to REM sleep and wakefulness. Although both exogenous and endocannabinoids affect sleep, the mechanism of endocannabinoid neuromodulation has not been characterized at cellular level in the PPN. In this paper, we demonstrate that both neurons and glial cells from the PPN respond to cannabinoid type 1 (CB1) receptor agonists. The neuronal response can be depolarization or hyperpolarization, while astrocytes exhibit more frequent calcium waves. All these effects are absent in CB1 gene-deficient mice. Blockade of the fast synaptic neurotransmission or neuronal action potential firing does not change the effect on the neuronal membrane potential significantly, while inhibition of astrocytic calcium waves by thapsigargin diminishes the response. Inhibition of group I metabotropic glutamate receptors (mGluRs) abolishes hyperpolarization, whereas blockade of group II mGluRs prevents depolarization. Initially active neurons and glial cells display weaker responses partially due to the increased endocannabinoid tone in their environment. Taken together, we propose that cannabinoid receptor stimulation modulates PPN neuronal activity in the following manner: active neurons may elicit calcium waves in astrocytes via endogenous CB1 receptor agonists. Astrocytes in turn release glutamate that activates different metabotropic glutamate receptors of neurons and modulate PPN neuronal activity.

Revealing the role of the endocannabinoid system modulators, SR141716A, URB597 and VDM-11, in sleep homeostasis

“…Thus, for all data combined, the presumably role of the endocannabinoid system in the modulation of the sleep homeostasis after sleep deprivation is highlighted. To add pieces to the puzzle of the putative mechanism of action of SR141716A, URB597 and VDM-11 in sleep homeostasis regulation, it is worthy to note that the endocannabinoid system has been described in astrocytes (Stella, 2010;Bosier et al, 2013;K} oszeghy et al, 2015;Oliveira da Cruz et al, 2016). Astrocytes have an important role in sleep homeostasis (Frank, 2011(Frank, , 2013 with relevant functions by releasing AD as gliotransmitter (Schmitt et al, 2012;Nadjar et al, 2013;Hines and Haydon, 2014;O'Donnell et al, 2015).…”

“…Astrocytes have an important role in sleep homeostasis (Frank, 2011(Frank, , 2013 with relevant functions by releasing AD as gliotransmitter (Schmitt et al, 2012;Nadjar et al, 2013;Hines and Haydon, 2014;O'Donnell et al, 2015). Thus, taking into account all these findings, CB 1 cannabinoid receptor, FAAH or VDM-11 located in astrocytes in sleep-related structures (K} oszeghy et al, 2015;Kova´cs et al, 2016) might be playing an undescribed role in sleep homeostasis. Indeed, the interactions between the CB 1 cannabinoid receptor, FAAH and AMT placed in neurons and astrocytes during sleep homeostasis remain to be described.…”

Cholinergic and endocannabinoid neuromodulatory effects overlap on neurons of the pedunculopontine nucleus of mice

“…For the slice preparation, 100 mM NaCl was replaced by sucrose (130 mM) and glycerol (60 mM; low Na aCSF). All chemicals were purchased from Sigma, unless Histograms of the membrane potential values were constructed from these periods and the value corresponding to the largest bin was considered as resting membrane potential [11].…”

“…These effects are largely due to activation and glutamate release of astrocytes; which, in turn activates different 5 subgroups of metabotropic glutamate receptors [11]. The effects of CB1 receptor stimulation resembled the ones elicited by carbachol, where neurons responded with inward or outward currents, or lacked response [4].…”

“…Muscarinic and nicotinic cholinergic [3,4,5] serotonergic [6,7], GABAergic [8] effects have been already described, as well as modulatory effects by orexin, ghrelin [9] or endocannabinoids [10,11]. These effects overlap in certain cases: neurons hyperpolarized by serotonin are hyperpolarized by stimulation of muscarinic acetylcholine receptors (mAChR) as well [6], and orexin and ghrelin depolarizes the same neuronal population [9].…”