Metabolic demands of neural-hemodynamic associated and disassociated areas in brain

Interpretation of regional blood oxygenation level-dependent (BOLD) responses in functional magnetic resonance imaging (fMRI) is contingent on whether local field potential (LFP) and multi-unit activity (MUA) is either dissociated or associated. To examine whether neural-hemodynamic associated and dissociated areas have different metabolic demands, we recorded sensory-evoked responses of BOLD signal, blood flow (CBF), and blood volume (CBV), which with calibrated fMRI provided oxidative metabolism (CMRO2) from rat’s ventral posterolateral thalamic nucleus (VPL) and somatosensory forelimb cortex (S1FL) and compared these neuroimaging signals to neurophysiological recordings. MUA faithfully recorded evoked latency differences between VPL and S1FL because evoked MUA in these regions were similar in magnitude. Since evoked LFP was significantly attenuated in VPL, we extracted the time courses of the weaker thalamic LFP to compare with the stronger cortical LFP using wavelet transform. BOLD and CBV responses were greater in S1FL than in VPL, similar to LFP regional differences. CBF and CMRO2 responses were both comparably larger in S1FL and VPL. Despite different levels of CBF-CMRO2 and LFP-MUA couplings in VPL and S1FL, the CMRO2 was well matched with MUA in both regions. These results suggest that neural-hemodynamic associated and dissociated areas in VPL and S1FL can have similar metabolic demands.

NOCICEPTIVE RESPONSES OF THE LATERAL THALAMIC NUCLEUS EVOKED BY PINCH IN ANESTHETIZED RATS

Pinch was used as a noxious stimulus and applied to the tail and hindlimbs of rats to investigate the nociceptive responsiveness of neurons in the lateral thalamus. Pinch stimuli were applied with calibrated pincher, and glass micropipettes filled with 3 M NaCl served as recording electrodes. The lateral thalamus of six rats under ketamine anesthesia was probed, including the ventrobasal (VB) complex and the posterior thalamic nucleus ( Po ), while the noxious stimulus was applied. Neuronal responses in the lateral thalamus were identified with the aid of an audio monitoring device and an oscilloscope, and several inclusion criteria had to be met. A total of 168 neurons were studied across the ventral posterolateral thalamic nucleus (VPL), ventral posteromedial thalamic nucleus (VPM), and Po of the thalamus. Of the neurons assessed in the lateral thalamus, 38 responded to the nociceptive stimuli, and most were located within the Po region of the thalamus. Very few were located in the VB. The number of responsive neurons in the anterior region of the lateral thalamus was significantly greater than the number of responsive neurons in the posterior region of the lateral thalamus. This finding indicates that the anterior region of the lateral thalamus, especially the Po area, may respond more vigorously to noxious stimuli than the posterior region.

Thalamic Stimulation as a Treatment for Primary Erythromelalgia: Technical Case Report

OBJECTIVE AND IMPORTANCE: We report the use of bilateral thalamic stimulation in a case of primary erythromelalgia with immediate and important pain relief for 3 years. CLINICAL PRESENTATION: A 12-year-old boy experiencing primary erythromelalgia had a 4-year history of recurrent attacks of severe burning pain in both feet, accompanied by local reddening, swelling, and heating of the skin. The attacks were triggered by warmth and exercise. The pain was relieved only by elevation and cooling of the lower limbs, which he achieved by immersing his legs in a bucket of ice water, resulting in severe ulceration of the skin. INTERVENTION: Because of the gradual aggravation of the signs and symptoms and resistance of the patient's condition to several medical therapies, the patient received spinal cord stimulation. The implants were removed twice because of recurrent infection. Finally, the patient was treated with bilateral electrical stimulation of the ventral posterolateral thalamic nucleus, which resulted in important pain control until 3 years later. The patient was able to avoid water immersions, and all ulcerations disappeared. CONCLUSION: We conclude that thalamic stimulation was successful in this case of primary erythromelalgia.