Impairment of spatial memory and changes in astroglial responsiveness following loss of molar teeth in aged SAMP8 mice

In order to evaluate the mechanism(s) responsible for senile impairment of cognitive function as a result of reduced mastication, the effects of the l oss of the molar teeth (molarless condition) on the hippocampal expression of glial fibrous acidic protein (GFAP) and on spatial memory in young adult and aged SAMP8 mice were studied using immunohistochemical and behavioral techniques. Aged molarless mice showed a significantly reduced learning abi lity in a water maze test compared with age-matched control mice, while the re was no difference between control and molarless young adult mice. Immuno histochemical analysis showed that the molarless condition enhanced the age -dependent increase in the density and hypertrophy of GFAP-labeled astrocyt es in the CA1 region of the hippocampus. These effects increased the longer the molarless condition persisted. When the extracellular K+ concentration ([K+](o)) was increased from 4 to 40 mM for hippocampal slices in vitro, t he mean increase in the membrane potential was about 57 mV for fine, delica te astrocytes, the most frequently observed type of GFAP-positive cell in t he young adult mice, and about 44 mV for the hypertrophic astrocytes of age d mice. However, there was no significant difference in resting membrane po tential between these cell types. The data suggest that an impairment of sp atial memory and changes in astroglial responsiveness occur following the l oss of molar teeth in aged SAMP8 mice. (C) 2000 Elsevier Science B.V. All r ights reserved.