Aging affects transcranial magnetic modulation of hippocampal evoked potentials

Transcranial magnetic stimulation (TMS) is being proposed as a method of ch oice for the treatment of clinical depression, yet its action in the brain is still not well understood. In previous studies we found that TMS has a l ong-term effect on reactivity of the hippocampus to perforant path stimulat ion. Since the efficacy of antidepressants is highly age-dependent, we stud ied possible age-related effects of TMS on hippocampal evoked responses. Yo ung adult (3 months), aging (10 months) and aged (24-26 months) awake rats were subjected to daily TMS for one week, followed by measurements of sever al parameters of reactivity to perforant path stimulation in the anesthetiz ed rat. TMS did not affect responses of the hippocampus to single perforant path stimulation, but reduced drastically paired-pulse and frequency depen dent depression in the young and aging but not the old rats. Likewise, TMS increased LTP expression in the young but not the old rats, and reduced the efficacy of serotonin modulation of reactivity of the hippocampus, in the young but not the old rats. Thus, long term effects of chronic TMS on local GABAergic inhibition are highly age dependent. (C) 2001 Elsevier Science I nc. All rights reserved.