Tonic, Burst, and Burst-Cycle Spinal Cord Stimulation Lead to Differential Brain Activation Patterns as Detected by Functional Magnetic Resonance Imaging.

OBJECTIVE: The objective of this preclinical study was to examine the responses of the brain to noxious stimulation in the presence and absence of different modes of spinal cord stimulation (SCS) using blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD-fMRI). MATERIALS AND METHODS: Sprague-Dawley rats were randomized to groups based on the mode of SCS delivered which included tonic stimulation (n = 27), burst stimulation (n = 30), and burst-cycle stimulation (n = 29). The control (sham) group (n = 28) received no SCS. The SCS electrode was inserted between T10 and T12 spinal levels prior to fMRI session. The experimental protocol for fMRI acquisition consisted of an initial noxious stimulation phase, a treatment phase wherein the SCS was turned on concurrently with noxious stimulation, and a residual effect phase wherein the noxious stimulation alone was turned on. The responses were statistically analyzed through paired t-test and the results were presented as z-scores for the quantitative analysis of the fMRI data. RESULTS: The treatment with different SCS modes attenuated the BOLD brain responses to noxious hindlimb stimulation. The tonic, burst, and burst-cycle SCS treatment attenuated BOLD responses in the caudate putamen (CPu), insula (In), and secondary somatosensory cortex (S2). There was little to no corresponding change in sham control in these three regions. The burst and burst-cycle SCS demonstrated greater attenuation of BOLD signals in CPu, In, and S2 compared to tonic stimulation. CONCLUSION: The high-resolution fMRI study using a rat model demonstrated the potential of different SCS modes to act on several pain-matrix-related regions of the brain in response to noxious stimulation. The burst and burst-cycle SCS exhibited greater brain activity reduction in response to noxious hindlimb stimulation in the caudate putamen, insula, and secondary somatosensory cortex compared to tonic stimulation.

Extracellular signal-regulated kinases trigger isoflurane preconditioning concomitant with upregulation of hypoxia-inducible factor-1alpha and vascular endothelial growth factor expression in rats.

INTRODUCTION: Extracellular signal-related kinases 1 and 2 (Erk1/2) are mitogen-activated protein kinases that have been implicated in anesthetic preconditioning; but whether Erk1/2 triggers or mediates this beneficial effect and the mechanisms by which Erk1/2 produces cardioprotection are unknown. We tested the hypothesis that isoflurane preconditioning is triggered by Erk1/2 concomitant with upregulation of hypoxia-inducible factor 1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) expression in rats instrumented for hemodynamic measurement and subjected to a 30-min coronary artery occlusion and 2-h reperfusion. METHODS: Rats randomly received IV 0.9% saline (control) or isoflurane (1.0 minimum alveolar concentration administered for 30 min and discontinued 15 min [memory period] before coronary occlusion) in the absence or presence of the selective Erk1/2 inhibitor PD 098059 (1 mg/kg in dimethylsulfoxide administered IV either 3 min before exposure to isoflurane [trigger] or 3 min after discontinuation of the drug [mediator]). Additional rabbits were pretreated with dimethylsulfoxide alone. Left ventricular tissue samples were obtained at selected intervals from additional groups of rats for Western immunoblot analysis of phospho-Erk1/2, HIF-1alpha, and VEGF protein expression. RESULTS: Isoflurane significantly (P < 0.05) reduced infarct size (41% +/- 8% of the left ventricular area at risk; triphenyltetrazolium chloride staining) as compared with control (59% +/- 4%). PD 098059 administered before, but not after, isoflurane abolished this cardioprotection (61% +/- 5% and 42% +/- 9%, respectively). Isoflurane-induced increases in phospho-Erk1/2, HIF-1alpha, and VEGF expression were also inhibited by PD 098059 pretreatment. CONCLUSIONS: The results indicate that Erk1/2 triggers isoflurane preconditioning concomitant with HIF-1alpha and VEGF upregulation in vivo.