SUMMARY α2δ-1, commonly known as a voltage-activated Ca2+ channel subunit, is a binding site of gabapentinoids used to treat neuropathic pain and epilepsy. However, it is unclear how α2δ-1 contributes to neuropathic pain and gabapentinoid actions. Here, we show that Cacna2d1 overexpression potentiates presynaptic and postsynaptic NMDAR activity of spinal dorsal horn neurons to cause pain hypersensitivity. Conversely, Cacna2d1 knockdown or ablation normalizes synaptic NMDAR activity increased by nerve injury. α2δ-1 forms a heteromeric complex with NMDARs in rodent and human spinal cords. The α2δ-1-NMDAR interaction predominantly occurs through the C terminus of α2δ-1 and promotes surface trafficking and synaptic targeting of NMDARs. Gabapentin or an α2δ-1 C terminus-interfering peptide normalizes NMDAR synaptic targeting and activity increased by nerve injury. Thus, α2δ-1 is an NMDAR-interacting protein that increases NMDAR synaptic delivery in neuropathic pain. Gabapentinoids reduce neuropathic pain by inhibiting forward trafficking of α2δ-1-NMDAR complexes.

Paraventricular nucleus (PVN) neurons that project to the spinal cord are important in the control of sympathetic outflow. Angiotensin II (Ang II) can stimulate PVN neurons, but its cellular mechanisms are not clear. In this study, we determined the effect of Ang II on the excitatory and inhibitory synaptic inputs to spinally projecting PVN neurons. Whole-cell patch-clamp recordings were performed on PVN neurons labeled by a retrograde fluorescence tracer injected into the thoracic spinal cord of rats. Immunocytochemistry labeling revealed that the immunoreactivity of angiotensin type 1 (AT1) receptors was colocalized with a presynaptic marker, synaptophysin, in the PVN. Application of 0.1-5 microm Ang II significantly decreased the amplitude of evoked GABAergic IPSCs in a concentration-dependent manner. Also, Ang II decreased the frequency of miniature IPSCs from 2.56 +/- 0.45 to 1.05 +/- 0.20 Hz (p < 0.05; n = 12), without affecting the amplitude and the decay time constant. The effect of Ang II on miniature IPSCs was blocked by losartan but not PD123319. However, Ang II had no effect on the evoked glutamatergic EPSCs and did not alter the frequency and amplitude of miniature EPSCs at concentrations that attenuated IPSCs. Furthermore, Ang II increased the firing rate of PVN neurons from 3.75 +/- 0.36 to 7.89 +/- 0.85 Hz (p < 0.05; n = 9), and such an effect was abolished by losartan. In addition, Ang II failed to excite PVN neurons in the presence of bicuculline. Thus, this study provides substantial new evidence that Ang II excites spinally projecting PVN neurons by attenuation of GABAergic synaptic inputs through activation of presynaptic AT1 receptors.

Systemic and intrathecal administration of derivatives of a nonpsychoactive component of marijuana significantly suppresses chronic inflammatory and neuropathic pain, without causing analgesic tolerance, in several rodent models.

Myocardial ischaemia causes the release of metabolites such as bradykinin, which stimulates cardiac sensory receptors to evoke a sympathoexcitatory reflex. However, the molecular identity of the afferent neurons and fibres mediating this reflex response is not clear. In this study, we tested the hypothesis that the cardiogenic sympathoexcitatory reflex is mediated by capsaicin‐sensitive afferent fibres. Enhanced immunofluorescence labelling revealed that vanilloid receptor 1 (VR1)‐containing afferent nerve fibres were present on the epicardial surface of the rat heart. Resiniferatoxin (RTX), a potent analogue of capsaicin, was used to deplete capsaicin‐sensitive afferent fibres in rats. Depletion of these fibres was confirmed by a substantial reduction of VR1 immunoreactivity in the epicardium and dorsal root ganglia. The thermal sensitivity was also diminished in RTX‐treated rats. Renal sympathetic nerve activity (RSNA) and blood pressure were recorded in anaesthetized rats during epicardial application of bradykinin or capsaicin. In vehicle‐treated rats, epicardial bradykinin (10 μg ml−1) or capsaicin (10 μg ml−1) application produced a significant increase in RSNA and arterial blood pressure. The RSNA and blood pressure responses caused by bradykinin and capsaicin were completely abolished in RTX‐treated rats. Furthermore, epicardial application of iodo‐RTX, a highly specific antagonist of VR1 receptors, blocked capsaicin‐ but not bradykinin‐induced sympathoexcitatory responses. Thus, these data provide important histological and functional evidence that the heart is innervated by VR1‐expressing afferent nerves and these afferent nerves are essential for the cardiogenic sympathoexcitatory reflex during myocardial ischaemia.