Background & Aims
Chronic pain is a serious debilitating condition affecting around one-tenth of the worldwide population with an increasing incidence due to the population aging. Unfortunately the options for analgesic therapy are still limited and new treatments with improved efficacy and reduced level of unwanted side effects are needed. GABA is the main inhibitory neurotransmitter acting directly on the ionotropic (GABAA) and the metabotropic (GABAB) receptors. Reduction of GABAergic inhibition during pathological states is one of the underlying mechanisms of chronic pain. GABAB receptors are heterodimers composed of GABAB1 and GABAB2 subunits and upon its activation start a downstream cascade of events leading to reduced neuronal excitability (1,2,3). GABAB function is modulated by their auxiliary the potassium channel tetramerization domain (KCTD) clade F proteins (KCTD16; KCTD12 and KCTD8) (4,5,6,7). In this work we explored the role of KCTD16 in modulation of nociceptive synaptic transmission.
Methods
The role of GABAB auxiliary KCTD16 protein was tested in naïve mice and after induction of peripheral inflammation (carrageenan 1%) using WT and KO model of the KCTD16 (obtained from B. Bettler, Uni Basel) and the transgenic mutant mice (VGAT-ChR2-EYFP crossed with KCTD16 KO). Thermal and mechanical sensitivity was accessed in behavioral experiments with von Frey fibers and hot plate. Baclofen (3mg/kg i.p.) was used as GABAB agonist. Miniature postsynaptic excitatory currents (mEPSC) and light-evoked inhibitory currents leIPSC were recorded with whole-cell patch clamp from spinal cord dorsal horn superficial neurons in acute spinal cord slices. Immunohistochemical methods were used to study KCTD16 expression in dorsal root ganglion neurons and the spinal cord.
Results
Our data show that KCTD16-/- and WT animals have the same thermal sensitivity threshold, while the mechanical sensitivity threshold is higher in the KCTD16-/- mice under control and inflammatory conditions. Acute treatment with GABAB agonist (Baclofen) produced a stronger analgesic effect in WT mice compared to the KCTD16-/- littermates, resulting in higher thermal and mechanical thresholds in control and after inflammation. Baclofen application had a significantly higher inhibitory effect on mEPSC frequency in the WT animals, especially in the peripheral inflammation model. Interestingly, the inhibitory effect of baclofen on leIPSC was highly reduced after inflammation in the WT animals, but was minimally changed in neurons from the KCTD16-/- mice.
Conclusions
Altogether, our data suggest that the KCTD16 protein modulation of nociceptive synaptic transmission could play an important modulatory role especially during pathological conditions, when GABABR are activated. Activation of the GABAB metabotropic receptors by baclofen has an inhibitory/analgesic effect present both in behavioral tests and electrophysiological recordings from spinal cord dorsal horn neurons. This inhibitory effect seems to be seriously attenuated in the KCTD16-/- animals where the disruption of the GABAB-KCTD16 complex possibly affects also the forward signaling by GIRK, VGCC, HCN channels and adenylyl cyclase. The role of the GABABR regulatory protein KCTD16 in nociception modulation and specifically the significance for possible pain treatments needs further experiments. Supported by Grant Agency of the Czech Republic GACR 21-17085S and GAUK 198923.
References
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Presenting Author
Daniel Vasconcelos
Poster Authors
Carlos Daniel Vasconcelos
MSc
Institute of Physiology, CAS
Lead Author
Mario Heles
PhD
Institute of Physiology, CAS
Lead Author
Pavel Adamek
PhD
Institute of Physiology, CAS
Lead Author
Anirban Bhattacharyya
PhD
Institute of Physiology, CAS
Lead Author
Jiri Palecek
MD
Institute of Physiology, CAS
Lead Author
Topics
- Models: Chronic Pain - Inflammatory