Thalamic Glucose Metabolism Research Articles

Whisker stimulation metabolically activates thalamus following cortical transplantation but not following cortical ablation

Local cerebral glucose utilization was assessed during whisker stimulation by 2-deoxyglucose autoradiography. Whisker stimulation increased local cerebral glucose utilization in brainstem, thalamus and whisker sensory cortex in normal rats. Whereas whisker stimulation increased glucose metabolism in brainstem, whisker stimulation failed to increase glucose metabolism in thalamus of rats that had whisker sensory cortex ablated 5 h to five weeks previously. The failure of whisker stimulation to activate thalamus after cortical ablations was probably not due to decreased cortical input to thalamus because whisker stimulation activated thalamus after large cortical tetrodotoxin injections. Failure of whisker stimulation to activate thalamus at early times (5 h and one day) after cortical ablations was not due to thalamic neuronal death, since it takes days to weeks for axotomized thalamic neurons to die. The failure of whisker stimulation to activate thalamus at early times after cortical ablations was likely due to the failure of trigeminal brainstem neurons that project to thalamus to activate axotomized thalamic neurons. This might occur because of synaptic retraction, glial stripping or inhibition of trigeminal brainstem synapses onto thalamic neurons. The thalamic neuronal death that occurs over the days and weeks following cortical ablations was associated with thalamic hypometabolism. This is consistent with the idea that the thalamic neurons die because of the absence of a cortically derived trophic factor, since the excitotoxic thalamic cell death that occurs following cortical kainate injections is associated with thalamic hypermetabolism. The glucose metabolism of parts of the host thalamus was higher and the glucose metabolism in surrounding nuclei lower than the normal side of thalamus in rats that sat quietly and had fetal cortex transplants placed into cavities in whisker sensory cortex five to 16 weeks previously. Whisker stimulation in these subjects activated the contralateral host thalamus and fetal cortical transplants. This was accomplished using a double-label 2-deoxyglucose method to assess brain glucose metabolism in the same rat while it was resting and during whisker stimulation. The high glucose metabolism of parts of host thalamus ipsilateral to the fetal cortical transplants is consistent with prolonged survival of some axotomized thalamic neurons. The finding that whisker stimulation activates portions of host thalamus further suggests that the cortical transplants maintained survival of the host thalamic neurons and that synaptic connections between whisker brainstem and thalamic neurons were functional.

Cerebral glucose utilization during stage 2 sleep in man

Using [ 18F]fluorodeoxyglucose method and positron emission tomography, we performed paired determinations of the cerebral glucose utilization at one week intervals during sleep and wakefulness, in 12 young normal subjects. During 6 of 28 sleep runs, a stable stage 2 SWS was observed that fulfilled the steady-state conditions of the model. The cerebral glucose utilization during stage 2 SWS was lower than during wakefulness, but the variation did not significantly differ from zero (mean variation: −11.5 ± 25.57%, P = 0.28). The analysis of 89 regions of interest showed that glucose metabolism differed significantly from that observed at wake in 6 brain regions, among them both thalamic nuclei. We conclude that the brain energy metabolism is not homogeneous throughout all the stages of non-REMS but decreases from stage 2 SWS to deep SWS; we suggest that a low thalamic glucose metabolism is a metabolic feature common to both stage 2 and deep SWS, reflecting the inhibitory processes observed in the thalamus during these stages of sleep. Stage 2 SWS might protect the stability of sleep by insulating the subject from the environment and might be a prerequisite to the full development of other phases of sleep, especially deep SWS.

Regional cerebral glucose metabolism differs in adult and rigid juvenile forms of Huntington disease

A 7-year-old girl with the juvenile form of Huntington disease is described. She had personality changes, speech and gait disturbances, diffuse rigidity, dementia, and a well-documented family history of Huntington disease. Electroencephalography revealed bilateral epileptic foci; however, she had no seizures. Positron emission tomography using [ 18F]-2-fluoro-2-deoxy- d-glucose with an improved method for quantification of glucose metabolism in anatomically defined regions of interest demonstrated marked hypometabolism in the caudate nuclei and putamen, as is observed in adults with the disease. Glucose metabolism was also reduced in the posterior nuclei of the thalamus. Adults with Huntington disease have consistently demonstrated normal or increased rates of thalamic glucose metabolism. The findings suggest that brain metabolic alterations of Huntington disease in children differ from those in adults which is consistent with the postmortem pathologic differences previously recognized.

Decreases of cortical and thalamic glucose metabolism produced by parietal cortex stimulation in the rat

Parietal cortex stimulation elicited focal decreases as well as increases of brain glucose metabolism in ipsilateral cortex, ipsilateral thalamus, and contralateral cortex of rats in a pattern resembling ‘surround inhibition’. It is proposed that parietal stimulation activated inhibitory circuits which decreased cortical and thalamic glucose metabolism. This decrease of cerebral glucose metabolism is important for interpreting brain glucose metabolic studies particularly when metabolic changes do not correlate with changes of neuronal activity.