Cannabinoid type 2 receptors inhibit GABAA receptor-mediated currents in cerebellar Purkinje cells of juvenile mice.

Sriity Melley Sadanandan,Jason R Pugh,Tabita Kreko-Pierce,Shailesh N Khatri,Sang H Lee

doi:10.1371/journal.pone.0233020

Sriity Melley Sadanandan, Jason R Pugh + Show 3 more

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https://doi.org/10.1371/journal.pone.0233020

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Abstract

Signaling through the endocannabinoid system is critical to proper functioning of the cerebellar circuit. However, most studies have focused on signaling through cannabinoid type 1 (CB1) receptors, while relatively little is known about signaling through type 2 (CB2) receptors. We show that functional CB2 receptors are expressed in Purkinje cells using a combination of immunohistochemistry and patch-clamp electrophysiology in juvenile mice. Pharmacological activation of CB2 receptors significantly reduces inhibitory synaptic responses and currents mediated by photolytic uncaging of RuBi-GABA in Purkinje cells. CB2 receptor activation does not change the paired-pulse ratio of inhibitory responses and its effects are blocked by inclusion of GDP-β-S in the internal solution, indicating a postsynaptic mechanism of action. However, CB2 receptors do not contribute to depolarization induced suppression of inhibition (DSI), indicating they are not activated by endocannabinoids synthesized and released from Purkinje cells using this protocol. This work demonstrates that CB2 receptors inhibit postsynaptic GABAA receptors by a postsynaptic mechanism in Purkinje cells. This represents a novel mechanism by which CB2 receptors may modulate neuronal and circuit function in the central nervous system.

Highlights

Many studies have demonstrated that synaptic transmission and plasticity in the cerebellar circuit depends on proper functioning of the endocannabinoid system [1]
We found that labelling in the Purkinje cell layer was 44.7±12.3% greater than background in wild-type tissue and only 12.4±4.2% greater than background in cannabinoid type2 (CB2) KO tissue (p = 0.044; n = 8 slices, 3 mice; 7 slices, 2 mice (KO); Fig 1B, top), an approximately 3.5 fold increase in wild-type tissue
We find that juvenile mice express functional CB2 receptors in Purkinje cells of the cerebellum

Summary

Introduction

Many studies have demonstrated that synaptic transmission and plasticity in the cerebellar circuit depends on proper functioning of the endocannabinoid system [1]. CB1 receptors are primarily expressed in the presynaptic terminals of granule cells, molecular layer interneurons, and climbing fibers, all of which synapses onto Purkinje cells [2,3,4]. Purkinje cells synthesize and release endocannabinoids, which travel retrogradely to activate presynaptic CB1 receptors and inhibit transmitter release [5,6,7,8]. CB1 receptor activity is required for long-term plasticity at parallel fiber-Purkinje cells synapses [9,10,11], widely thought to be a critical site of plasticity for cerebellar learning [12,13,14].

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