Cannabis sativa (marijuana) is a fibrous flowering plant that produces an abundant variety of molecules, some with psychoactive effects. At least 4% of the world's adult population uses cannabis annually, making it one of the most frequently used illicit drugs in the world. The psychoactive effects of cannabis are mediated primarily through cannabinoid receptor (CBR) subtypes. The prevailing view is that CB1Rs are mainly expressed in the central neurons, whereas CBRs are predominantly expressed in peripheral immune cells. However, this traditional view has been challenged by emerging strong evidence that shows CBRs are moderately expressed and function in specific brain areas. New evidence has demonstrated that brain CBRs modulate animal drug-seeking behaviors, suggesting that these receptors may exist in brain regions that regulate drug addiction. Recently, we further confirmed that functional CBRs are expressed in mouse ventral tegmental area (VTA) dopamine (DA) neurons and that the activation of VTA CBRs reduces neuronal excitability and cocaine-seeking behavior. In addition, CBR-mediated modulation of hippocampal CA3 neuronal excitability and network synchronization has been reported. Here, we briefly summarize recent lines of evidence showing how CBRs modulate function and pathophysiology in the CNS.

Objective: To investigate whether a super-high dose (SHD) of methylprednisolone (MP) improves its efficacy or induces glucocorticoid (GC) resistance, and to explore the potential mechanisms of GC resistance in experimental allergic encephalomyelitis (EAE). Methods: The therapeutic effects of SHD and low-dose MP were evaluated in EAE by analyzing clinical scores, pathological changes and cytokine production. Immunohistochemistry and RT-PCR were used to investigate the expression of GC receptor (GR) isoforms and splicing factor SRp30c. Results: Both MP doses had similar therapeutic effects. The ratio of GRα to GRβ was positively correlated with clinical score changes. However, there was no difference in the GRα/GRβ ratio between SHD and low-dose MP groups. SRp30c mRNA was correlated with GRβ expression. Conclusion: This study indicates that the GRα/GRβ ratio is associated with GC sensitivity, and SRp30c may play an important role in promoting alternative splicing of GR pre-mRNA to generate GRβ in EAE rats. Compared with low-dose MP, SHD MP does not improve efficacy or induce GC resistance.

Alpha6-containing nicotinic acetylcholine receptors are primarily found in neurons of the midbrain dopaminergic (DA) system, suggesting these receptors are potentially involved in drug reward and dependence. Here, we report a novel effect that cocaine directly inhibits α6N/α3Cβ2β3-nAChR (α6*-nAChRs) function. Human α6*-nAChRs were heterologously expressed within cells of the SH-EP1 cell line for functional characterization. Mechanically dissociated DA neurons from mouse ventral tegmental area (VTA) were used as a model of presynaptic α6*-nAChR activation since this method preserves terminal boutons. Patch-clamp recordings in whole-cell configuration were used to measure α6*-nAChR function as well as evaluate the effects of cocaine. In SH-EP1 cells containing heterologously expressed human α6*-nAChRs, cocaine inhibits nicotine-induced inward currents in a concentration-dependent manner with an IC 50 value of 30 μM. Interestingly, in the presence of 30 μM cocaine, the maximal current response of the nicotine concentration-response curve is reduced without changing nicotine’s EC 50 value, suggesting a noncompetitive mechanism. Furthermore, analysis of whole-cell current kinetics demonstrated that cocaine slows nAChR channel activation but accelerates whole-cell current decay time. Our findings demonstrate that cocaine-induced inhibition occurs solely with bath application, but not during intracellular administration, and this inhibition is not use-dependent. Additionally, in Xenopus oocytes, cocaine inhibits both α6N/α3Cβ2β3-nAChRs and α6M211L/α3ICβ2β3-nCAhRs similarly, suggesting that cocaine may not act on the α3 transmembrane domain of chimeric α6N/α3Cβ2β3-nAChR. In mechanically isolated VTA DA neurons, cocaine abolishes α6*-nAChR-mediated enhancement of spontaneous inhibitory postsynaptic currents (sIPSCs). Collectively, these studies provide the first evidence that cocaine directly inhibits the function of both heterologously and naturally expressed α6*-nAChRs. These findings suggest that α6*-nAChRs may provide a novel pharmacological target mediating the effects of cocaine and may underlie a novel mechanism of cocaine reward and dependence.

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