Endocannabinoid 2-Arachidonoylglycerol Suppresses LPS-Induced Inhibition of A-Type Potassium Channel Currents in Caudate Nucleus Neurons Through CB1 Receptor

Prenatal Δ9-Tetrahydrocannabinol Exposure in Males Leads to Motivational Disturbances Related to Striatal Epigenetic Dysregulation

BACKGROUND

Cannabis remains one of the most widely abused drugs during pregnancy. In utero exposure to its principal psychoactive component, Δ⁹-tetrahydrocannabinol (THC), can result in long-term neuropsychiatric risk for the progeny. This study investigated epigenetic signatures underlying these enduring consequences.

METHODS

Rat dams were exposed daily to THC (0.15 mg/kg) during pregnancy, and adult male offspring were examined for reward and depressive-like behavioral endophenotypes. Using unbiased sequencing approaches, we explored transcriptional and epigenetic profiles in the nucleus accumbens (NAc), a brain area central to reward and emotional processing. An in vitro CRISPR (clustered regularly interspaced short palindromic repeats) activation model coupled with RNA sequencing was also applied to study specific consequences of epigenetic dysregulation, and altered molecular signatures were compared with human major depressive disorder transcriptome datasets.

RESULTS

Prenatal THC exposure induced increased motivation for food, heightened learned helplessness and anhedonia, and altered stress sensitivity. We identified a robust increase specific to males in the expression of Kmt2a (histone-lysine N-methyltransferase 2A) that targets H3K4 (lysine 4 on histone H3) in cellular chromatin. Normalizing Kmt2a in the NAc rescued the motivational phenotype of prenatally THC-exposed animals. Comparison of RNA- and H3K4me3-sequencing datasets from the NAc of rat offspring with the in vitro model of Kmt2a upregulation revealed overlapping, significant disturbances in pathways that mediate synaptic plasticity. Similar transcriptional alterations were detected in human major depressive disorder.

CONCLUSIONS

These studies provide direct evidence for the persistent effects of prenatal cannabis exposure on transcriptional and epigenetic deviations in the NAc via Kmt2a dysregulation and associated psychiatric vulnerability.

Transduction of inflammation from peripheral immune cells to the hippocampus induces neuronal hyperexcitability mediated by Caspase-1 activation

BACKGROUND

Recent studies report infiltration of peripheral blood mononuclear cells (PBMCs) into the central nervous system (CNS) in epileptic disorders, suggestive of a potential contribution of PBMC extravasation to the generation of seizures. Nevertheless, the underlying mechanisms involved in PBMC infiltrates promoting neuronal predisposition to ictogenesis remain unclear. Therefore, we developed an in vitro model mimicking infiltration of activated PBMCs into the brain in order to investigate potential transduction of inflammatory signals from PBMCs to the CNS.

METHODS

To establish our model, we first extracted PBMCs from rat spleen, then, immunologically primed PBMCs with lipopolysaccharide (LPS), followed by further activation with nigericin. Thereafter, we co-cultured these activated PBMCs with organotypic cortico-hippocampal brain slice cultures (OCHSCs) derived from the same rat, and compared PBMC-OCHSC co-cultures to OCHSCs exposed to PBMCs in the culture media. We further targeted a potential molecular pathway underlying transduction of peripheral inflammation to OCHSCs by incubating OCHSCs with the Caspase-1 inhibitor VX-765 prior to co-culturing PBMCs with OCHSCs. After 24 h, we analyzed inflammation markers in the cortex and the hippocampus using semiquantitative immunofluorescence. In addition, we analyzed neuronal activity by whole-cell patch-clamp recordings in cortical layer II/III and hippocampal CA1 pyramidal neurons.

RESULTS

In the cortex, co-culturing immunoreactive PBMCs treated with LPS + nigericin on top of OCHSCs upregulated inflammatory markers and enhanced neuronal excitation. In contrast, no excitability changes were detected after adding primed PBMCs (i.e. treated with LPS only), to OCHSCs. Strikingly, in the hippocampus, both immunoreactive and primed PBMCs elicited similar pro-inflammatory and pro-excitatory effects. However, when immunoreactive and primed PBMCs were cultured in the media separately from OCHSCs, only immunoreactive PBMCs gave rise to neuroinflammation and hyperexcitability in the hippocampus, whereas primed PBMCs failed to produce any significant changes. Finally, VX-765 application to OCHSCs, co-cultured with either immunoreactive or primed PBMCs, prevented neuroinflammation and hippocampal hyperexcitability in OCHSCs.

CONCLUSIONS

Our study shows a higher susceptibility of the hippocampus to peripheral inflammation as compared to the cortex, mediated via Caspase-1-dependent signaling pathways. Thus, our findings suggest that Caspase-1 inhibition may potentially provide therapeutic benefits during hippocampal neuroinflammation and hyperexcitability secondary to peripheral innate immunity.

[Modulatory effect of 2-arachidonoylglycerol on voltage-gated sodium currents in rat caudate nucleus neurons with kainic acid-induced injury]

OBJECTIVE

To investigate the modulatory effect of 2-arachidonoylglycerol (2-AG) on voltage-gated sodium currents(VGSCs) in rat caudate nucleus (CN) neurons with kainic acid (KA)-induced injury and explore the molecular mechanism underlying the neuroprotective effect of 2-AG.

METHODS

Primary cultures of CN neurons isolated from neonatal SD rats were treated with KA, 2-AG+KA, RIM (a CB1 receptor antagonist) +2-AG+KA, or vehicle only (as control).After 7 days in primary culture, the neurons were treated with corresponding agents for 12 h (RIM and 2-AG were added at the same time; KA was added 30 min later) before recording of current density changes, current-voltage characteristics, activation and inactivation kinetics of VGSCs (I_Na) using whole-cell patch clamp technique.

RESULTS

In cultured CN neurons, KA significantly increased current density of VGSCs (P=0.009) as compared with vehicle treatment.KA also produced a hyperpolarizing shift in the activation curve of I_Na and significantly increased the absolute value of V_1/2 for activation (P=0.008).Addition of 2-AG in the culture medium obviously prevented KA-induced increase of I_Na (P=0.009) and hyperpolarizing shift in the activation curve of I_Na, and significantly reduced the value of V_1/2 for activation(P=0.009)in a CB1 receptor-dependent manner.2-AG alone did not affect the density, activation or deactivation of VGSCs in rat CN neurons.

CONCLUSION

In excitotoxic events, endogenous 2-AG can offer neuroprotection by modulating VGSCs in the CN neurons through a CB1 receptor-dependent pathway.

The Endocannabinoid System in Pediatric Inflammatory and Immune Diseases

Endocannabinoid system consists of cannabinoid type 1 (CB1) and cannabinoid type 2 (CB2) receptors, their endogenous ligands, and the enzymes responsible for their synthesis and degradation. CB2, to a great extent, and CB1, to a lesser extent, are involved in regulating the immune response. They also regulate the inflammatory processes by inhibiting pro-inflammatory mediator release and immune cell proliferation. This review provides an overview on the role of the endocannabinoid system with a major focus on cannabinoid receptors in the pathogenesis and onset of inflammatory and autoimmune pediatric diseases, such as immune thrombocytopenia, juvenile idiopathic arthritis, inflammatory bowel disease, celiac disease, obesity, neuroinflammatory diseases, and type 1 diabetes mellitus. These disorders have a high social impact and represent a burden for the healthcare system, hence the importance of individuating more innovative and effective treatments. The endocannabinoid system could address this need, representing a possible new diagnostic marker and therapeutic target.

[Effect of cinobufagin on transient outward potassium current in dorsal root ganglion cells of rats with cancer-induced bone pain]

OBJECTIVE

To observe the effect of cinobufagin on transient outward potassium current (IA) in rat dorsal root ganglion cells of cancer-induced bone pain (CIBP) and explore the possible analgesic mechanism of cinobufagin.

METHODS

Whole cell patch clamp technique was used to examine the effect of cionbufagin on IA in acutely isolated dorsal root ganglion (DRG) cells from normal SD rats and rats with bone cancer pain.

RESULTS

The DRG cells from rats with CIBP showed obviously decreased IA current density, an activation curve shift to the right, and an inactivation curve shift to the left. Cinobufagin treatment significantly increased the IA current density and reversed the changes in the activation and inactivation curves in the DRG cells.

CONCLUSIONS

IA current is decreased in DRG neurons from rats with CIBP. Cinobufagin can regulate the activation and inactivation of IA current in the DRG cells, which may be related to its analgesic mechanism.

Neuregulin-1 protects mouse cerebellum against oxidative stress and neuroinflammation

Cerebellum undergoes degenerative changes in neurodegenerative diseases. Two main factors including oxidative stress and neuroinflammation mediate neurodegeneration. Neuregulin-1 (Nrg1) has been implicated in many neurodegenerative diseases, while the underlying mechanisms are unknown. We hypothesized that Nrg1 prevents oxidative stress and neuroinflammation in neurodegeneration. We found a positive correlation between Nrg1 protein levels and ErbB4 and ErbB2 receptor phosphorylation in microarrays of normal human cerebellar tissue. In addition, Nrg1 was also co-localized with pErbB4 and pErbB2. Primary mouse cerebellar granule neurons (CGNs) were treated with H₂O₂ or LPS combined with recombinant Nrg1β (rNrg1β). Western blot analysis and immunofluorescence revealed that H₂O₂ and LPS-induced neuronal toxicity down-regulated the activation of ErbB receptors and Akt1, and the ratio of Bcl2/Bax, which was reversed by rNrg1β. In vivo studies showed that LPS-induced neuroinflammation in mouse cerebellum down-regulated pErbB4, pErbB2, pAkt1/Akt1 and Bcl2/Bax levels, whereas rNrg1β treatment reversed the changes. Immunohistochemistry and Western blot analysis showed that rNrg1β alleviates neuroinflammation by reducing the number of microglial cells and astrocytes and the expression of IL1β. Our results indicate that Nrg1 protects against oxidative stress and neuroinflammation in mouse cerebellum, suggesting potential therapeutic application in neuroinflammation associated with neurodegenerative diseases.

Cannabinoid CB1 and CB2 receptors differentially modulate L- and T-type Ca2+ channels in rat retinal ganglion cells

Endocannabinoid signaling system is involved in regulating multiple neuronal functions in the central nervous system by activating G-protein coupled cannabinoid CB1 and CB2 receptors (CB1Rs and CB2Rs). Growing evidence has shown that CB1Rs and CB2Rs are extensively expressed in retinal ganglion cells (RGCs). Here, modulation of L- and T-types Ca²⁺ channels by activating CB1Rs and CB2Rs in RGCs was investigated. Triple immunofluorescent staining showed that L-type subunit Ca_V1.2 was co-localized with T-type subunits (Ca_V3.1, Ca_V3.2 and Ca_V3.3) in rat RGCs. In acutely isolated rat RGCs, the CB1R agonist WIN55212-2 suppressed both peak and steady-state Ca²⁺ currents in a dose-dependent manner, with IC₅₀ being 9.6 μM and 8.4 μM, respectively. It was further shown that activation of CB1Rs by WIN55212-2 or ACEA, another CB1R agonist, significantly suppressed both L- and T-type Ca²⁺ currents, and shifted inactivation curve of T-type one toward hyperpolarization direction. While the effect on L-type Ca²⁺ channels was mediated by intracellular cAMP/protein kinase A (PKA), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and calcium/calmodulin-dependent protein kinase II (CaMKII) signaling pathways, only CaMKII signaling pathway was involved in the effect on T-type Ca²⁺ channels. Furthermore, CB65 and HU308, two specific CB2R agonists, significantly suppressed T-type Ca²⁺ channels, which was mediated by intracellular cAMP/PKA and CaMKII signaling pathways, but had no effect on L-type channels. These results imply that endogenous cannabinoids may modulate the excitability and the output of RGCs by differentially suppressing the activity of L- and T-type Ca²⁺ channels through activation of CB1Rs and CB2Rs. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

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

The major endocannabinoid in the mammalian brain is the bioactive lipid 2-arachidonoylglycerol (2-AG). The best-known effects of 2-AG are mediated by G-protein-coupled cannabinoid receptors. In principle, 2-AG could modify neuronal excitability by acting directly on ion channels, but such mechanisms are poorly understood. Using a preparation of dissociated mouse midbrain dopamine neurons to isolate effects on intrinsic excitability, we found that 100 nM 2-AG accelerated pacemaking and steepened the frequency-current relationship for burst-like firing. In voltage-clamp experiments, 2-AG reduced A-type potassium current (I_A) through a cannabinoid receptor-independent mechanism mimicked by arachidonic acid, which has no activity on cannabinoid receptors. Activation of orexin, neurotensin, and metabotropic glutamate G_q/11-linked receptors mimicked the effects of exogenous 2-AG and their actions were prevented by inhibiting the 2-AG-synthesizing enzyme diacylglycerol lipase α. The results show that 2-AG and related lipid signaling molecules can directly tune neuronal excitability in a cell-autonomous manner by modulating I_A.