Baclofen is a selective gamma-aminobutyric acid (GABA) type B agonist that may have important medicinal uses,such as in analgesics and drug addiction treatment.In addition,evidence is accumulating that suggests GABAergic-mediated neurotransmission is altered during aging.This study investigated whether baclofen administration (5 mg kg 1) induces differential effects on cortical electrical activity with age.Electroencephalograms (EEGs) were recorded from young (3-4 months) and aged (15-17 months) rats,and both the absolute and relative powers in five frequency bands (delta:2-4 Hz;theta:4-8 Hz;alpha:8-12 Hz;beta:12-20 Hz;gamma:20-100 Hz) were analyzed.Before administration of baclofen,we found that the EEG relative power in the beta band was higher in the aged than that in the young rats.After administration of baclofen,there was a slower increase in the relative power in the delta band in the aged than that in the young rats.Moreover,there was no significant difference between the two age groups in absolute power in any frequency band.These findings indicate that baclofen treatment appears to differentially modify cortical EEG activity as a function of age.Our data further elucidate the relationship between GABA B receptor-mediated neurotransmission and aging. Baclofen is a selective gamma-aminobutyric acid (GABA) type B agonist that may have important medicinal uses, such as in analgesics and drug addiction treatment. In addition, evidence is accumulating that suggests GABAergic-mediated neurotransmission is altered during aging. This study investigated whether baclofen administration (5 mg kg 1) induces differential effects on cortical electrical activity with age. Electroencephalograms (EEGs) were recorded from young (3-4 months) and aged (15-17 months) rats, and both the absolute and relative powers in five frequency bands (delta: 2-4 Hz; theta: 4-8 Hz; alpha: 8-12 Hz; beta: 12-20 Hz; gamma: 20-100 Hz) were analyzed. Before administration of baclofen, we found that the EEG relative power in the beta band was higher in the aged than that in the young rats. After administration of baclofen, there was a slower increase in the relative power in the delta band in the aged than that in the young rats. Moreover there was no significant difference between the two a ge groups in absolute power in any frequency band. These findings of that baclofen treatment appears to differentially modify cortical EEG activity as a function of age. Our data further elucidate the relationship between GABA B receptor-mediated neurotransmission and aging.