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A brief review of the recent publications on long-term trends of atmospheric and ionospheric parameters in the mesosphere and lower thermosphere is presented. The rocket measurements of the ion composition in the ionospheric E region are analyzed. A systematic decrease of the ratio of two principal molecular ions NO + and O 2+ from the sixties to the end of the eighties is detected. It is shown that the derived trends of the ion composition may be important in linking the temperature trends around the mesopause and the electron concentration trends in the E region.