Hippocampal cell density and subcortical metabolism in temporal lobe epilepsy

PURPOSE

Correlations between hippocampal cell density and subcortical metabolism in patients with temporal lobe epilepsy (TLE) were studied to explore possible links between subcortical function and the regulation of hippocampal excitability.

METHODS

Resected hippocampal cell densities were correlated with cortical and subcortical regional cerebral metabolic rate for glucose (CMRglu), as measured by [18F]-fluorodeoxyglucose positron emission tomography (18-FDG-PET), in 39 patients with intractable TLE who underwent anterior temporal lobectomy (ATL). CMRglu was measured ipsilateral and contralateral to the resected temporal lobe. Linear regression techniques were used for statistical analysis.

RESULTS

Hilar cell densities correlated positively and significantly with CMRglu in the bilateral thalamus, putamen and globus pallidus, and the ipsilateral caudate. Dentate granule cell densities correlated positively and significantly with CMRglu in the bilateral thalamus and putamen. There was no significant correlation between cell densities and CMRglu in any cortical region, including the hippocampus.

CONCLUSIONS

We postulate that hippocampal cell loss results in decreased efferent synaptic activity to the thalamus and basal ganglia, causing decreased neuronal activity in these structures with consequent hypometabolism. This synaptic activity has a significant bilateral component. Subcortical hypometabolism in patients with TLE may reinforce the epileptogenic potential of mesial temporal lobe discharges.

Effects of the submarine environment on renal-stone risk factors and vitamin D metabolism

The effects of total sunlight deprivation on urinary risk factors for nephrolithiasis and vitamin D metabolism were studied in 20 healthy male subjects. Blood and 24-h urine samples were collected before submarine deployment and 68 days later while still at sea. No subject received sunlight exposure during the test interval. Significant decreases in daily urinary excretion of calcium, uric acid, sodium, sulfate, and phosphorus were found. The relative supersaturation ratio of monosodium urate also fell. There was no change in urinary citrate or urine volume. Mean serum levels of 25-hydroxyvitamin D [25(OH)D] declined from 31 to 19 pg/ml (P < 0.0001), parathyroid hormone increased from 22 to 30 pg/ml (P < 0.0001), and osteocalcin (GLA) increased from 2.7 to 3.3 ng/ml (P = 0.005). Mean serum levels of 1,25 dihydroxy-vitamin D were unchanged. Four subjects had 25(OH)D levels below 10 ng/ml by the end of the submarine patrol. These findings suggest that exposure to the submarine environment produces physiologic changes that decrease the risk for renal stone formation. The data are consistent with the role of vitamin D metabolism in sunlight deprivation and demonstrate that compensatory mechanisms are well established within 68 days.