Direct presynaptic and indirect astrocyte-mediated mechanisms both contribute to endocannabinoid signaling in the pedunculopontine nucleus of mice
- 512 Downloads
The pedunculopontine nucleus (PPN), a cholinergic nucleus of the reticular activating system, is known to be involved in the regulation of sleep and wakefulness. Endogenous and exogenous cannabinoids, by systemic or local administration to the pedunculopontine nucleus, can both influence sleep. We previously demonstrated that activation of astrocytes by cannabinoid type 1 (CB1) receptor agonists was able to modulate the membrane potential of PPN neurons, even in the presence of blockers of fast synaptic neurotransmission. In the present work, we provide evidence that synaptic inputs of PPN neurons are also affected by activation of presynaptic and astrocytic CB1 receptors. Using slice electrophysiology combined with calcium imaging, optogenetics and immunohistochemistry, we revealed a direct presynaptic inhibitory action on inhibitory postsynaptic currents, along with a mild increase of excitatory postsynaptic currents during CB1 receptor stimulation. Besides inhibition of excitatory and inhibitory neurotransmission through stimulation of presynaptic CB1 receptors, astrocyte- and mGluR-dependent tonic inhibition and excitation also developed. The mild stimulatory action of CB1 receptor activation on excitatory neurotransmission is the combination of astrocyte-dependent tonic excitation on excitatory neurons and the canonical presynaptic CB1 receptor activation and consequential inhibition of excitatory synaptic neurotransmission, whereas the astrocyte-dependent stimulatory action was not observed in inhibitory neurotransmission within the PPN. Our findings demonstrate that endocannabinoids act in the PPN via a dual pathway, consisting of a direct presynaptic and an indirect, astrocyte-mediated component, regulating synaptic strength and neuronal activity via independent mechanisms.
KeywordsPedunculopontine nucleus CB1 receptor Optogenetics Astrocyte Neuromodulation
This work was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences, the Szodoray Fellowship of the University of Debrecen, the Hungarian National Brain Research Program (KTIA_13_NAP-A-I/10 to BP; KTIA_NAP_13-1-2013-0001 to MA; KTIA_NAP_13-2-2014-0005 to PS) and the Hungarian Academy of Sciences (MTA-TKI 242; MA), and TÁMOP-4.2.2.B-15/1/KONV-2015-0001 (AK, CB). The authors are indebted to Professor Andreas Zimmer for providing us the CB1 knockout mouse strain and to Professor László Csernoch and Dr. Péter Szentesi for providing Rhod-2 fluorescent dye and for the valuable discussion of the results of this project.
Compliance with ethical standards
Conflict of interest
The authors declare no competing financial interest.
- Han J, Kesner P, Metna-Laurent M, Duan T, Xu L, Georges F, Koehl M, Abrous DN, Mendizabal-Zubiaga J, Grandes P, Liu Q, Bai G, Wang W, Xiong L, Ren W, Marsicano G, Zhang X (2012) Acute cannabinoids impair working memory through astroglial CB1 receptor modulation of hippocampal LTD. Cell 148(5):1039–1050CrossRefPubMedGoogle Scholar
- Soni N, Kohlmeier KA (2015) Endocannabinoid CB1 receptor-mediated rises in Ca2+ and depolarization-induced suppression of inhibition within the laterodorsal tegmental nucleus. Brain Struct FunctGoogle Scholar