Cannabinoid Receptor 1 Expression in Human Dorsal Root Ganglia and CB13-Induced Bidirectional Modulation of Sensory Neuron Activity

Cannabinoid receptors have been identified as potential targets for analgesia from studies on animal physiology and behavior, and from human clinical trials. Here, we sought to improve translational understanding of the mechanisms of cannabinoid-mediated peripheral analgesia. Human lumbar dorsal root ganglia were rapidly recovered from organ donors to perform physiological and anatomical investigations into the potential for cannabinoids to mediate analgesia at the level of the peripheral nervous system. Anatomical characterization of in situ gene expression and immunoreactivity showed that 61 and 53% of human sensory neurons express the CB1 gene and receptor, respectively. Calcium influx evoked by the algogen capsaicin was measured by Fura-2AM in dissociated human sensory neurons pre-exposed to the inflammatory mediator prostaglandin E2 (PGE2) alone or together with CB13 (1 μM), a cannabinoid agonist with limited blood–brain barrier permeability. Both a higher proportion of neurons and a greater magnitude of response to capsaicin were observed after exposure to CB13, indicating cannabinoid-mediated sensitization. In contrast, membrane properties measured by patch-clamp electrophysiology demonstrated that CB13 suppressed excitability and reduced action potential discharge in PGE2-pre-incubated sensory neurons, suggesting the suppression of sensitization. This bidirectional modulation of sensory neuron activity suggests that cannabinoids may suppress overall membrane excitability while simultaneously enhancing responsivity to TRPV1-mediated stimuli. We conclude that peripherally restricted cannabinoids may have both pro- and anti-nociceptive effects in human sensory neurons.

Extrasynaptic NMDA receptors bidirectionally modulate intrinsic excitability of inhibitory neurons

The NMDA subtype glutamate receptors (NMDARs) play important roles in both physiological and pathological processes in the brain. Comparing to their critical roles in synaptic modifications and excitotoxicity in the excitatory neurons, much less is understood about the functional contributions of NMDARs to the inhibitory/GABAergic neurons. By using selective NMDAR inhibitors and potentiators, we here show that NMDARs bi-directionally modulate the intrinsic excitability (defined as spontaneous/evoked spiking activity and EPSP-spike coupling) in the inhibitory/GABAergic neurons. This modulation depends on GluN2C/2D- but not GluN2A/2B-containing NMDARs. We further show that NMDAR modulator EU1794-4 mostly enhances extrasynaptic NMDAR activity, and by using it we demonstrate a significant contribution of extrasynaptic NMDARs to the modulation of intrinsic excitability in the inhibitory neurons. Altogether, this bidirectional modulation of intrinsic excitability reveals a previously less appreciated importance of NMDARs in the second-to-second functioning of inhibitory/GABAergic neurons.

Bidirectional modulation of pain-related behaviors in the zona incerta

Central amygdala neurons expressing protein kinase C-delta (CeA-PKCδ) are sensitized following nerve injury and promote pain-related responses in mice. The neural circuits underlying modulation of pain-related behaviors by CeA-PKCδ neurons, however, remain unknown. In this study, we identified a functional monosynaptic inhibitory neural circuit that originates in CeA-PKCδ neurons and terminates in the ventral region of the zona incerta (ZI), a subthalamic structure previously linked to pain processing. Behavioral experiments further show that chemogenetic inhibition of GABAergic ZI neurons is sufficient to induce bilateral hypersensitivity in uninjured mice as well as contralateral hypersensitivity after nerve injury. In contrast, chemogenetic activation of GABAergic ZI neurons reverses nerve injury-induced hypersensitivity, demonstrating that silencing of the ZI is required for injury-induced behavioral hypersensitivity. Our results identify a previously unrecognized inhibitory efferent pathway from CeA-PKCδ neurons to the ZI and demonstrate that ZI-GABAergic neurons can bidirectionally modulate pain-related behaviors in mice.

Bidirectional modulation of microRNA with clamp-like triplex switch for enhanced and programmed gene therapy

A clamp-like triplex switch (CTS) that could simultaneously down-regulate the over-expressed onco-miRNA and replenish the lost tumor suppressive miRNA in controllable manner was developed for enhanced gene therapy. Compared to...

Divergent projections of the prelimbic cortex bidirectionally regulate active avoidance

The prefrontal cortex (PFC) integrates incoming information to guide our actions. When motivation for food-seeking competes with avoidance of danger, the PFC likely plays a role in selecting the optimal choice. In platform-mediated active avoidance, rats avoid a tone-signaled footshock by stepping onto a nearby platform, delaying access to sucrose pellets. This avoidance requires prelimbic (PL) PFC, basolateral amygdala (BLA), and ventral striatum (VS). We previously showed that inhibitory tone responses of PL neurons correlate with avoidability of shock (Diehl et al., 2018). Here, we optogenetically modulated PL terminals in VS and BLA to identify PL outputs regulating avoidance. Photoactivating PL-VS projections reduced avoidance, whereas photoactivating PL-BLA projections increased avoidance. Moreover, photosilencing PL-BLA or BLA-VS projections reduced avoidance, suggesting that VS receives opposing inputs from PL and BLA. Bidirectional modulation of avoidance by PL projections to VS and BLA enables the animal to make appropriate decisions when faced with competing drives.