The objective of the present project is to determine the possible changes in the subunit composition of the two major neurotransmitter systems in rat hippocam- pus during aging. The interest of this study is based on hypothesis that modifica- tions observed in some pharmacological properties of GABAA and Glutamate receptors during aging, could be explained by aged-related modifications in the molecular composition of these receptors. In turn, this potential alterations could explain, in part, the aged-related modifications in the learning capacity, memory and sensitivity to benzodiazepines. The different subunits corresponding to the GABAA and Glutamate receptors will be quantified by competitive polymerase chain reaction (c-PCR) with the inclusion of internal standars. Aged-related increase in the ex- pression of the alpha-1 subunit, in combination with a switch in the expression of the gamma subunits of the GABAA receptor in rat hippocampus are expected. As a se- cond goal, the potential aged-related modification of RNA editing in the GluR2, GluR5 and GluR6 glutamate receptor subunits will be analyzed. The RNA editing has been proposed to control the calcium permeability and the rectification properties of the channels.