Immunohistochemical estimation of rat brain somatostatin on avoidance learning impairment induced by thiamine deficiency

In rats, on the 25th day after the start of a thiamine-deficient (TD) diet, impairment of avoidance learning was significantly induced in proportion t o the decrease somatostatin (SST) fluorescence intensity in the cortex, amy gdala, thalamus, hypothalamus, and hippocampus, including the CA1, CA2, and dentate gyrus (DG). Only a single injection of thiamine HCl (0.5 mg/rat, s ubcutaneous) on the 14th day after the start of a TD diet improved the amne sia to the level of the pair-fed control and prevented the decrease in the SST level. Whereas these reversal effects of thiamine treatment were not fo und when the treatment was given on the 21st day after the start of a TD di et. These results indicate that, after a certain degree of thiamine deficie ncy, TD-induced behavioral effects might be reversible, but some neuronal f ibers might be irreversibly damaged, probably due to the reduction of thiam ine-dependent enzymes in brain mitochondria. The results also suggest the p ossibility that SST in the brain may be closely related to the avoidance le arning impairment induced by TD, (C) 2000 Elsevier Science Inc.