Background: Vagus nerve stimulation (VNS) is currently used to treat refractory

The ionotropic ATP receptor subunits P2X(1-6) receptors play important roles in synaptic transmission, yet the P2X(7) receptor has been reported as absent from neurons in the normal adult brain. Here we use RT-PCR to demonstrate that transcripts for the P2X(7) receptor are present in extracts from the medulla oblongata, spinal cord, and nodose ganglion. Using in situ hybridization mRNA encoding, the P2X(7) receptor was detected in numerous neurons throughout the medulla oblongata and spinal cord. Localizing the P2X(7) receptor protein with immunohistochemistry and electron microscopy revealed that it is targeted to presynaptic terminals in the CNS. Anterograde labeling of vagal afferent terminals before immunohistochemistry confirmed the presence of the receptor in excitatory terminals. Pharmacological activation of the receptor in spinal cord slices by addition of 2'- and 3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP; 30 microm) resulted in glutamate mediated excitation of recorded neurons, blocked by P2X(7) receptor antagonists oxidized ATP (100 microm) and Brilliant Blue G (2 microm). At the neuromuscular junction (NMJ) immunohistochemistry revealed that the P2X(7) receptor was present in motor nerve terminals. Furthermore, motor nerve terminals loaded with the vital dye FM1-43 in isolated NMJ preparations destained after application of BzATP (30 microm). This BzATP evoked destaining is blocked by oxidized ATP (100 microm) and Brilliant Blue G (1 microm). This indicates that activation of the P2X(7) receptor promotes release of vesicular contents from presynaptic terminals. Such a widespread distribution and functional role suggests that the receptor may be involved in the fundamental regulation of synaptic transmission at the presynaptic site.

Given its non-invasive nature, there is increasing interest in the use of transcutaneous vagus nerve stimulation (tVNS) across basic, translational and clinical research. Contemporaneously, tVNS can be achieved by stimulating either the auricular branch or the cervical bundle of the vagus nerve, referred to as transcutaneous auricular vagus nerve stimulation(VNS) and transcutaneous cervical VNS, respectively. In order to advance the field in a systematic manner, studies using these technologies need to adequately report sufficient methodological detail to enable comparison of results between studies, replication of studies, as well as enhancing study participant safety. We systematically reviewed the existing tVNS literature to evaluate current reporting practices. Based on this review, and consensus among participating authors, we propose a set of minimal reporting items to guide future tVNS studies. The suggested items address specific technical aspects of the device and stimulation parameters. We also cover general recommendations including inclusion and exclusion criteria for participants, outcome parameters and the detailed reporting of side effects. Furthermore, we review strategies used to identify the optimal stimulation parameters for a given research setting and summarize ongoing developments in animal research with potential implications for the application of tVNS in humans. Finally, we discuss the potential of tVNS in future research as well as the associated challenges across several disciplines in research and clinical practice.

Ageing is associated with attenuated autonomic function. Transcutaneous vagal nerve stimulation (tVNS) improved autonomic function in healthy young participants. We therefore investigated the effects of a single session of tVNS (studies 1 and 2) and tVNS administered daily for two weeks (study 3) in volunteers aged ≥ 55 years. tVNS was performed using modified surface electrodes on the tragus and connected to a transcutaneous electrical nerve stimulation (TENS) machine. Study 1: participants (n=14) received a single session of tVNS and sham. Study 2: all participants (n=51) underwent a single session of tVNS. Study 3: participants (n=29) received daily tVNS for two weeks. Heart rate variability and baroreflex sensitivity were derived. Quality of life (QoL), mood and sleep were assessed in study 3. tVNS promoted increases in measures of vagal tone and was associated with greater increases in baroreflex sensitivity than sham. Two weeks of daily tVNS improved measures of autonomic function, and some aspects of QoL, mood and sleep. Importantly, findings showed that improvements in measures of autonomic balance were more pronounced in participants with greater baseline sympathetic prevalence. This suggests it may be possible to identify individuals who are likely to encounter significant benefits from tVNS.

Fast inhibition in the nervous system is commonly mediated by GABA A receptors comprised of 2␣/2␤/1␥ subunits. In contrast, GABA C receptors containing only subunits (1-3) have been predominantly detected in the retina. However, here using reverse transcription-PCR and in situ hybridization we show that mRNA encoding the 1 subunit is highly expressed in brainstem neurons. Immunohistochemistry localized the 1 subunit to neurons at light and electron microscopic levels, where it was detected at synaptic junctions. Application of the GABA C receptor agonist cis-4-aminocrotonic acid (100 -800 M) requires the 1 subunit to elicit responses, which surprisingly are blocked independently by antagonists to GABA A (bicuculline, 10 M) and GABA C [(1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA); 40 -160 M] receptors. Responses to GABA C agonists were also enhanced by the GABA A receptor modulator pentobarbitone (300 M). Spontaneous and evoked IPSPs were reduced in amplitude but never abolished by TPMPA, but were completely blocked by bicuculline. We therefore tested the hypothesis that GABA A and GABA C subunits formed a heteromeric receptor. Immunohistochemistry indicated that 1 and ␣1 subunits were colocalized at light and electron microscopic levels. Electrophysiology revealed that responses to GABA C receptor agonists were enhanced by the GABA A receptor modulator zolpidem (500 nM), which acts on the ␣1 subunit when the ␥2 subunit is also present. Finally, coimmunoprecipitation indicated that the 1 subunit formed complexes that also contained ␣1 and ␥2 subunits. Taken together these separate lines of evidence suggest that the effects of GABA in central neurons can be mediated by heteromeric complexes of GABA A and GABA C receptor subunits.