The influence of acute vagus nerve stimulation on regional brain perfusion in the normal dog, a micro-SPECT study

Vagus nerve stimulation (VNS) is an effective adjunctive treatment for refractory epilepsy, but its mechanism of action is still unknown. Functional neuroimaging studies can provide better insight into possible brain circuitry changes caused by VNS. This µ-SPECT study investigated the effects of two acute VNS paradigms on regional brain perfusion in normal dogs. A Cyberonics® pulse generator and helical electrodes were implanted in 10 Beagle dogs in the left cervical region. A cross-over study started 1 month after implantation. 99mTechnetium-ECD µ-SPECT was performed after 3 different paradigms (1 hour of sham, rapid-cycling and microburst VNS) with a wash out period of at least 1 week between different paradigms. VNS started 45 minutes before tracer injection and was continued for 10 more minutes after tracer injection. Acquisition was performed using a triple head gamma camera equipped with ultra high resolution multi pinhole collimators. Nineteen volumes of interest (VOIs) were evaluated by semi-quantitative analysis using BRASS software and for every VOI a regional perfusion index was calculated. Statistical analysis was performed using an F-test (mixed-effects model) to compare the regional perfusion indices for the 3 different conditions within each dog. One dog was excluded because of the development of Horner’s syndrome after implantation. Acute rapid-cycling VNS did not cause significant regional brain perfusion alterations. Acute microburst VNS caused a significant hypoperfusion in the left frontal lobe (p= 0.031) and in the right parietal lobe (p=0.047). In conclusion, acute microburst VNS modulates frontal and parietal cortical perfusion in the normal dog