The aim of this study was to explore the relationship between Consumption of large doses of lactic acid bacteria (LAB) and the behaviour and brain morphobiochemistry of normal growing rats. Four groups of rats were treated with LAB Cultures twice daily for 6 months. The control group received 1 ml of saline per treatment, while two experimental groups received I nil of living bacteria (Lactobacillus plantarum and Lactobacillus fermentum, respectively) and the remaining group received a heat-treated (inactivated) L. fermentum culture. After 2 and 6 months of treatment, respectively, eight animals from each group were sacrificed, and specimens were taken for further analyses. The behaviour of the rats was evaluated five times in an open-field test at monthly intervals throughout the study. Lactobacilli treatment for 2 months induced changes in the motoric behaviour of the rats. The concentration of the astrocytesoluble and filament glial fibrillary acidic protein (GFAP) decreased in the posterior part of the hemispheres, including the thalamus, hippocampus and cortex of the rats treated with L.fermentum. A greater decrease in filament GFAP (up to 50%) was shown in the group receiving the live from of L. fermentum. In contrast, the GFAP in the live L. plantarum-treated group increased, showing elevated levels of the Soluble and filament forms of GFAP in the posterior part of the hemispheres. A 60-66% decrease in the amount of the astrocyte-specific Ca-binding protein S-100b was shown in the posterior parts of the hemispheres and in the hindbrain of rats given LAB for 2 months. Prolonged feeding with LAB for 4 months up to full adulthood led to a further decrease in astrocytc reaction, reflected as all additional decrease in the amount Of Soluble GEAP and locomotor activity in all experimental groups. The changes in filament GFAP and S-100b appeared to disappear after prolonged feeding (total of 6 months) with LAB. In summary, LAB dietary treatment affected the ontogenetic development of the astrocytes, with the highest intensity observed in the early stages of rat development. It can be postulated that LAB treatment may play a preventive role in neurological diseases by decreasing astrocyte reaction and, consequently, lowering locomotor activity. (C) 2009 Elsevier Inc. All rights reserved.