Vascular cognitive impairment (VCI) is a common sequela of cerebrovascular disorders. Although transcutaneous auricular vagus nerve stimulation (taVNS) has been considered a complementary treatment for various cognitive disorders, preclinical data on the effect of taVNS on VCI and its mechanism remain ambiguous. To measure cerebrospinal fluid (CSF) circulation during taVNS, we used in vivo two-photon microscopy with CSF and vasculature tracers. VCI was induced by transient bilateral common carotid artery occlusion (tBCCAO) surgery in mice. The animals underwent anesthesia, off-site stimulation, or taVNS for 20 min. Cognitive tests, including the novel object recognition and the Y-maze tests, were performed 24 h after the last treatment. The long-term treatment group received 6 days of treatment and was tested on day 7; the short-term treatment group received 2 days of treatment and was tested 3 days after tBCCAO surgery. CSF circulation increased remarkably in the taVNS group, but not in the anesthesia-control or off-site-stimulation-control groups. The cognitive impairment induced by tBCCAO was significantly restored after both long- and short-term taVNS. In terms of effects, both long- and short-term stimulations showed similar recovery effects. Our findings provide evidence that taVNS can facilitate CSF circulation and that repetitive taVNS can ameliorate VCI symptoms.

Oxaliplatin is a chemotherapeutic agent used for metastatic colon and other advanced cancers. Most common side effect of oxaliplatin is peripheral neuropathy, manifested in mechanical and cold allodynia. Although the analgesic effect of bee venom has been proven to be effective against oxaliplatin-induced peripheral neuropathy, the effect of its major component; melittin has not been studied yet. Thus, in this study, we investigated whether melittin has an analgesic effect on oxaliplatin-induced allodynia. Intraperitoneal single injection of oxaliplatin (6 mg/kg) induced mechanical and cold allodynia, resulting in increased withdrawal behavior in response to von Frey filaments and acetone drop on hind paw. Subcutaneous melittin injection on acupoint ST36 (0.5 mg/kg) alleviated oxaliplatin-induced mechanical and cold allodynia. In electrophysiological study, using spinal in vivo extracellular recording, it was shown that oxaliplatin-induced hyperexcitation of spinal wide dynamic range neurons in response to peripheral stimuli, and melittin administration inhibited this neuronal activity. In behavioral assessment, analgesic effect of melittin was blocked by intrathecal α1- and α2- adrenergic receptor antagonists administration. Based on these results, we suggest that melittin could be used as an analgesic on oxaliplatin-induced peripheral neuropathy, and that its effect is mediated by activating the spinal α1- and α2-adrenergic receptors.

Cerebrospinal fluid (CSF) flow is crucial for brain homeostasis and its dysfunction is highly associated with neurodegenerative diseases. Restoring CSF circulation is proposed as a key strategy for the treatment of the diseases. Among the methods to improve CSF circulation, focused ultrasound (FUS) stimulation has emerged as a promising non-invasive brain stimulation technique, with effectiveness evidenced by ex vivo studies. However, due to technical disturbances in in vivo imaging combined with FUS, direct evidence of real-time in vivo CSF flow enhancement by FUS remains elusive. To investigate whether FUS administered through the skull base can enhance CSF influx in living animals with various real-time imaging techniques. We demonstrate a novel method of applying FUS through the skull base, facilitating cortical CSF influx, evidenced by diverse in vivo imaging techniques. Acoustic simulation confirmed effective sonication of our approach through the skull base. After injecting fluorescent CSF tracers into cisterna magna, FUS was administered at the midline of the jaw through the skull base for 30 minutes, during which imaging was performed concurrently. Enhanced CSF influx was observed in macroscopic imaging, demonstrated by the influx area and intensity of the fluorescent dyes after FUS. In two-photon imaging, increased fluorescence was observed in the perivascular space (PVS) after stimulation. Moreover, particle tracking of microspheres showed more microspheres entering the imaging field, with increased mean speed after FUS. Our findings provide direct real-time in vivo imaging evidence that FUS promotes CSF influx and flow in the PVS.