Endocannabinoids produced upon action potential firing evoke a Cl− current via type-2 cannabinoid receptors in the medial prefrontal cortex

Abstract

The functional presence of type-2 cannabinoid receptors (CB2Rs) in layer II/III pyramidal neurons of the rat medial prefrontal cortex (mPFC) was recently demonstrated. In the present study, we show that the application of the endocannabinoids (eCBs) 2-arachidonoylglycerol (2-AG) and methanandamide [a stable analog of the eCB anandamide (AEA)] can activate CB2Rs of mPFC layer II/III pyramidal neurons, which subsequently induces a Cl(-) current. In addition, we show that action potential (AP) firing evoked by 20-Hz current injections results in an eCB-mediated opening of Cl(-) channels via CB2R activation. This AP-evoked synthesis of eCBs is dependent on the Ca(2+) influx through N-type voltage-gated calcium channels. Our results indicate that 2-AG is the main eCB involved in this process. Finally, we demonstrate that under physiologically relevant intracellular Cl(-) conditions, 20-Hz AP firing leads to a CB2R-dependent reduction in neuronal excitability. Altogether, our data indicate that eCBs released upon action potential firing can modulate, through CB2R activation, neuronal activity in the mPFC. We discuss how this may be a mechanism to prevent excessive neuronal firing.

CB2 receptor antibody signal specificity: correlations with the use of partial CB2-knockout mice and anti-rat CB2 receptor antibodies

“…Extensive research over the past decade indicates that functional CB 2 Rs are expressed in glial cells and neurons in the brain [1,43,44], and evidence from qRT-PCR and ISH assays in our present study and previous reports strongly support this expression [9,26,28]. Electrophysiological evidence of brain CB 2 R modulation of neuronal activity in the cortex [31][32][33], hippocampus [22,25,30], striatum [29], and midbrain [9,26] further support the presence of functional CB 2 Rs in the brain. We recently reported that systemic or local administration of the selective CB 2 R agonist JWH133 or GW405833 into the nucleus accumbens significantly inhibited DA release in this region and attenuated intravenous cocaine self-administration, cocaine-enhanced locomotion, and cocaine-enhanced extracellular DA in the nucleus accumbens.…”

“…In situ hybridization (ISH) assays revealed CB 2 R mRNA expression in several neuronal phenotypes, including glutamatergic neurons in the cortex and hippocampus [22,24,25] and dopaminergic (DA) neurons in the midbrain [9,[26][27][28][29]. Electrophysiological assays confirmed the presence of functional CB 2 Rs in brain glutamatergic neurons [22,[30][31][32], GABAergic neurons [33], and DA neurons [9,22,26,29]. However, the specificity of the detected CB 2 R signals was questioned because CB 2 -knockout (CB 2 -KO) mice were not used as controls in many early studies [34].…”

Cell-Autonomous Excitation of Midbrain Dopamine Neurons by Endocannabinoid-Dependent Lipid Signaling

“…However in brain slice experiments, mimicking CB-R-mediated synaptic plasticity induced by endogenous 2-AG requires 10–30 μM exogenous 2-AG (e.g. Bacci et al, 2004; den Boon et al, 2014; Marinelli et al, 2008 and 2009; Wilson and Nicoll, 2001). This discrepancy is likely due to the difficulty of applying such hydrophobic compounds that readily partition non-specifically into membranes on the entire brain slice.…”

“…Indeed, in some neurons, production of 2-AG reduces excitability in an autocrine manner, mediated by CB receptors in the postsynaptic membrane (Bacci et al, 2004; den Boon et al, 2014; Marinelli et al, 2008; 2009; Stempel et al, 2016). Our study utilized three, separate G q/11 receptors known to produce 2-AG-dependent effects on synaptic plasticity in dopamine neurons and the results demonstrate that endogenously mobilizing 2-AG reduced I A .…”

“…In the brain, 2-AG is the dominant endocannabinoid (Alger and Kim, 201), and its best-known actions are as a retrograde messenger, traversing the postsynaptic cell membrane to activate G i/o protein-coupled cannabinoid type 1 (CB 1 ) receptors at presynaptic terminals and produce suppression of neurotransmitter release (Kreitzer and Regehr, 2001; Ohno-Shosaku et al, 2001; Wilson and Nicoll, 2001). In some neurons, 2-AG can reduce excitability by cell-autonomous actions mediated by receptors in the postsynaptic membrane, via CB 1 (Bacci et al, 2004; Marinelli et al, 2008; 2009), or CB 2 receptors (den Boon et al, 2014, Stempel et al, 2016). Most neuronal actions of 2-AG require CB receptors, with CB 1 receptors mediating the vast majority of actions in the brain (Lu and Mackie, 2016).…”