Developmental onset of long‐term potentiation in area CA1 of the rat hippocampus.

Abstract

SUMMARY1. Long-term potentiation (l.t.p.) was studied in area CAl of rat hippocampal slices during development at post-natal days 1-8, 15 and 60. Tetanic stimulation at 100 Hz for 1 s was delivered to the fibres in stratum radiatum and the time course of potentiation was recorded in stratum pyramidale for 20 min after tetanus. L.t.p. was measured at 20 min post-tetanus as an increase in the amplitude of the population spike.2. The time course and magnitude ofpost-tetanic potentiation (p.t.p.) differed with age. For 60-day-old animals p.t.p. was seen as a maximally potentiated response immediately post-tetanus that declined to a smaller potentiated response by 5 min post-tetanus. For animals younger than 15 days the response was also maximally potentiated immediately post-tetanus with subsequent decline. However, the duration of maximal potentiation was shorter and the magnitude was less. A different time course ofp.t.p. was observed at 15 days. The maximal potentiation was approximately equal to that seen at 60 days, but instead of declining, the response remained maximally potentiated throughout the entire post-tetanus monitoring period.3. L.t.p. was first observed at post-natal day 5, and by post-natal days 7 and 8 substantial levels of l.t.p. were seen consistently. The greatest magnitude of l.t.p. was found at 15 days, and was considerably more than that produced at 60 days.4. When the duration of l.t.p. was monitored for longer than 20 min the response declined back to pretetanus levels by 1-11 h for animals younger than 15 days. In 15-day-old rats the response remained maximally potentiated for the full 72 min that it was monitored, with no decline.5. In control experiments of low-frequency stimulation (l.f.s.) at 1/15 s for 100 stimuli, hippocampal slices from 60-day-old animals showed response elevation. In contrast, l.f.s. resulted in response decrement over time for slices from 5-15-day-old animals.6. Three measures ofpretetanus excitability in area CAI suggested an increase with age. The stimulus intensity required for field excitatory post-synaptic potential (e.p.s.p.) threshold declined, the magnitude ofthe maximal population spike amplitude increased, and the population spike latency decreased. These results suggest that the magnitude of l.t.p. is not strictly related to the pretetanus excitability of CAl cells.

Postnatal Inflammation Increases Seizure Susceptibility in Adult Rats

“…This time window is similar to the period we previously observed for other physiological changes caused by postnatal LPS (Spencer et al, 2006b). Interestingly, this is also the time when long-term potentiation-induced plasticity first becomes apparent (e.g., P7) and shows maximum responsivity (e.g., P15) (Harris and Teyler, 1984). Thus, we may suspect that some permanent change has taken place during this relatively sensitive period of development in which the effects of LPS (and TNF␣) can modify synapses.…”

Carbonic Anhydrase Isoform VII Acts as a Molecular Switch in the Development of Synchronous Gamma-Frequency Firing of Hippocampal CA1 Pyramidal Cells

“…In addition, this is the critical postnatal time window for the developmental appearance of HFS-induced long-term potentiation (LTP) in CA1 (Harris and Teyler, 1984;Chabot et al, 1996). In this study, we demonstrate an abrupt expression of hippocampal intrapyramidal carbonic anhydrase activity at the end of the second postnatal week.…”

Eyeblink conditioning in 12-day-old rats using pontine stimulation as the conditioned stimulus

“…Other brain systems involved in learning and memory also show neuronal plasticity in vitro early in postnatal development (21). The neuronal plasticity mechanisms underlying learning may be the same as or derived from mechanisms underlying early activity-dependent connectivity in the nervous system (22).…”