Increase in AMPA receptors in aged memory-impaired rats is not associated with increase in monoamine oxidase B levels

Aged rats may be behaviorally classified as either cognitively impaired or unimpaired based upon their performance in the Morris water maze task. In a ged Long-Evans rats, emergence of functional deficits has been related to t he increase in the alpha -amino-3-hydroxy-5-methyl-4-isoxazole propionic ac id (AMPA) receptor subtype in most hippocampal subfields, not observed in o ther brain structures. As AMPA receptors expressed in astrocytes may partic ipate in the delayed and long-term glial response to injury, we investigate d whether astrocytes participate in the increase of AMPA receptor observed in these aged rats. To this end, distribution of monoamine oxidase B, used as an astroglial marker, was characterized by quantitative autoradiography in the hippocampus and septum of young adults (six months) and aged (24-25 months) rats using [H-3]lazabemide. Specific binding to brain sections of y oung, aged unimpaired, and aged impaired animals were calculated densitomet rically, Compared to young animals, all hippocampal subfields in the aged u nimpaired group showed a significant age-related increased labeling, which was not present in the aged impaired group. This contrasts with the increas ed glial transcription described in this last group. We propose that increa se in AMPA receptors in the aged memory-impaired animals may be related to an atypic astrocytic reactivity. (C) 2000 IBRO. Published by Elsevier Scien ce Ltd. All rights reserved.