STIMULATION AT 1-5 HZ DOES NOT PRODUCE LONG-TERM DEPRESSION OR DEPOTENTIATION IN THE HIPPOCAMPUS OF THE ADULT-RAT IN-VIVO

1. We examined the efficacy of low-frequency trains (1-5 Hz) in produc ing long-term depression (LTD) or depotentiation in the hippocampus of the awake adult rat and in anesthetized rats aged from 10 days to 3 m o. 2. In the dentate gyrus we found no evidence that low-frequency tra ins produce either depotentiation or LTD in the awake, adult animal or in the anesthetized animal at any age tested (10 days-adult). 3. In a rea CA1 of both awake and anesthetized adult rats, we also found no ev idence that low-frequency trains induced either LTD or depotentiation. Only in area CA1 of very young rats (10-11 days) was clear evidence f or LTD and depotentiation obtained; at this age experiments were only possible in anesthetized animals. By 16 days, the ability to display b oth LTD and depotentiation was lost. 4. These experiments suggest that repetitive low-frequency stimulation evokes a developmentally regulat ed form of activity-dependent depression that in the hippocampus is li mited to specific pathways in the young animal. Our results leave open the question of whether alternative patterns of activity can induce L TD and/or depotentiation in the adult awake rat.