AGE-DEPENDENT LOCAL MODULATION OF HIPPOCAMPAL-EVOKED RESPONSES TO PERFORANT PATH STIMULATION

Local modulation of hippocampal-evoked responses to perforant path sti mulation was studied by leaking drugs from the recording pipette place d in the dentate gyrus of anesthetized young (3 months old), aging (17 months old) and old (28 months old) rats. In old rats, the excitatory postsynaptic potential (EPSP) slope was much reduced compared to youn g: and aging rats. The population spike (PS) size was similar in all a ge groups. Bicuculline caused a marked increase in PS size relative to population EPSP, and reversed the response to the second pulse in a p aired-pulse paradigm from inhibition to facilitation. The effect of bi cuculline was only slightly reduced in old rats. The 5-HT1a agonist 8- OH-DPAT potentiated PSs in the dentate gyrus, while not affecting pair ed-pulse inhibition. The effect of 8-OH-DPAT was slightly reduced in o ld rats. Carbachol, a cholinergic agonist, reversed paired-pulse inhib ition into facilitation in the young brain, but not in aging and old r ats. These results demonstrate that age affects differentially the act ion of biogenic amines on hippocampal reactivity to efferent stimulati on. (C) 1998 Elsevier Science Inc.