Experimental colitis-induced visceral hypersensitivity is attenuated by GABA treatment in mice.

Ulcerative colitis (UC) is linked with inflammation of the large intestine due to an overactive response of the colon-immune system. UC is associated with weight loss, rectal bleeding, diarrhea, and abdominal pain. Given that γ-amino butyric acid (GABA) suppresses immune cell activity and the excitability of colonic afferents, and that there is a decrease in colonic GABA during UC, we hypothesized that UC pain is due to a decrease in the inhibition of colonic afferents. Thus, restoring GABA in the colon will attenuate inflammatory hypersensitivity. We tested this hypothesis in a mouse model of colitis. Colon inflammation was induced with seven days of dextran sodium sulfate (DSS, 3%) in the drinking water. GABA (40 mg/kg) was administered orally for the same period as DSS, and body weight, colon length, colon permeability, clinical progression of colitis (disease activity index or DAI), and colon histological score (HS) were assessed to determine the effects of GABA on colitis. A day after the end of GABA treatment, visceral sensitivity was assessed with balloon distention (of the colon)-evoked visceromotor response and colon samples were collected for the measurement of GABA and cytokines. Treatment with GABA reduced the DSS-induced increase in the colon permeability, DAI, HS, and decrease in body weight and colon length. Furthermore, GABA inhibited the DSS-induced increase in the proinflammatory cytokines tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-12 (IL-12), and increased the expression of the anti-inflammatory cytokine IL-10 in the colon tissue. Importantly, GABA reduced DSS-induced visceral hypersensitivity. These data suggest that increasing gastrointestinal levels of GABA may be useful for the treatment of colitis.NEW & NOTEWORTHY GABA treatment reduces the severity of colitis and inflammation and produces inhibition of visceral hypersensitivity in colon-inflamed mice. These results raise the promising possibility that GABA treatment may be an effective therapeutic strategy for the management of symptoms associated with colitis. However, clinical studies are required to corroborate whether this mouse-model data translates to human colon.

In-Vivo Calcium Imaging of Sensory Neurons in the Rat Trigeminal Ganglion.

Genetically encoded calcium indicators (GECIs) enable imaging techniques to monitor changes in intracellular calcium in targeted cell populations. Their large signal-to-noise ratio makes GECIs a powerful tool for detecting stimulus-evoked activity in sensory neurons. GECIs facilitate population-level analysis of stimulus encoding with the number of neurons that can be studied simultaneously. This population encoding is most appropriately done in vivo. Dorsal root ganglia (DRG), which house the soma of sensory neurons innervating somatic and visceral structures below the neck, are used most extensively for in vivo imaging because these structures are accessed relatively easily. More recently, this technique was used in mice to study sensory neurons in the trigeminal ganglion (TG) that innervate oral and craniofacial structures. There are many reasons to study TG in addition to DRG, including the long list of pain syndromes specific to oral and craniofacial structures that appear to reflect changes in sensory neuron activity, such as trigeminal neuralgia. Mice are used most extensively in the study of DRG and TG neurons because of the availability of genetic tools. However, with differences in size, ease of handling, and potentially important species differences, there are reasons to study rat rather than mouse TG neurons. Thus, we developed an approach for imaging rat TG neurons in vivo. We injected neonatal pups (p2) intraperitoneally with an AAV encoding GCaMP6s, resulting in >90% infection of both TG and DRG neurons. TG was visualized in the adult following craniotomy and decortication, and changes in GCaMP6s fluorescence were monitored in TG neurons following stimulation of mandibular and maxillary regions of the face. We confirmed that increases in fluorescence were stimulus-evoked with peripheral nerve block. While this approach has many potential uses, we are using it to characterize the subpopulation(s) of TG neurons changed following peripheral nerve injury.

Subcutaneous administration of a novel TRPM8 antagonist reverses cold hypersensitivity while attenuating the drop in core body temperature.

BACKGROUND AND PURPOSE: We extend the characterization of the TRPM8 antagonist VBJ103 with tests of selectivity, specificity and distribution, therapeutic efficacy of systemic administration against oxaliplatin-induced cold hyperalgesia and the impact of systemic administration on core body temperature (CBT). EXPERIMENTAL APPROACH: Selectivity at human TRPA1 and TRPV1 as well as in vitro safety profiling was determined. Effects of systemic administration of VBJ103 were evaluated in a model of oxaliplatin-induced cold hyperalgesia. Both peripheral and centrally mediated effects of VBJ103 on CBT were assessed with radiotelemetry. KEY RESULTS: VBJ103 had no antagonist activity at TRPV1 and TRPA1, but low potency TRPA1 activation. The only safety liability detected was partial inhibition of the dopamine transporter (DAT). VBJ103 delivered subcutaneously dose-dependently attenuated cold hypersensitivity in oxaliplatin-treated mice at 3, 10 and 30 mg·kg-1 (n = 7, P < 0.05). VBJ103 (30 mg·kg-1) antinociception was influenced by neither the TRPA1 antagonist HC-030031 nor the DAT antagonist GBR12909. Subcutaneous administration of VBJ103 (3, 10 and 30 mg·kg-1, but not 100 or 300 mg·kg-1, n = 7) decreased CBT (2°C). Intraperitoneal (i.p.) administration of VBJ103 (3, 10 and 30 mg·kg-1) dose-dependently decreased CBT to an extent larger than that detected with subcutaneous administration. Intracerebroventricular (i.c.v.) administration (306 nmol/1 µL; n = 5) did not alter CBT. CONCLUSIONS AND IMPLICATIONS: We achieve therapeutic efficacy with subcutaneous administration of a novel TRPM8 antagonist that attenuates deleterious influences on CBT, a side effect that has largely prevented the translation of TRPM8 as a target.

Ribosome-Associated Vesicles promote activity-dependent local translation.

Local protein synthesis in axons and dendrites underpins synaptic plasticity. However, the composition of the protein synthesis machinery in distal neuronal processes and the mechanisms for its activity-driven deployment to local translation sites remain unclear. Here, we employed cryo-electron tomography, volume electron microscopy, and live-cell imaging to identify Ribosome-Associated Vesicles (RAVs) as a dynamic platform for moving ribosomes to distal processes. Stimulation via chemically-induced long-term potentiation causes RAV accumulation in distal sites to drive local translation. We also demonstrate activity-driven changes in RAV generation and dynamics in vivo, identifying tubular ER shaping proteins in RAV biogenesis. Together, our work identifies a mechanism for ribosomal delivery to distal sites in neurons to promote activity-dependent local translation.