Figure 3. Rapid decrease followed by transient increase of arc mRNA level after induction of LTD in area CA1 in vivo.

A1) Means ± s.e.m.s of the amplitude of the population spike, expressed as a percent of baseline, evoked by commissural stimulation before and after paired-pulse stimulation (PPS; wide down-ward arrow) recorded from animals decapitated either 20 min (filled squares; n = 7), 40 min (filled circles; n = 2), 70 min (filled upward triangles; n = 5), or 130 min (filled down-ward triangles; n = 5) after the onset of PPS, or after either 20 min (open squares; n = 3) or 120 min (open down-ward triangles; n = 2) of only test pulse stimulation after the initial baseline stimulation period. Inserts above show representative waveforms (average of 10 recordings) recorded from an animal 5 min before (stippled line) and 127 min after PPS (solid line). Scale: 2 mV, 2 msec. A2) Similar data as shown above for the initial slope of the population EPSP evoked by commissural stimulation before and after PPS. (n = 3 for baseline, n = 5 for 40 min, n = 5 for 70 min, n = 5 for 130 min). Scale for the insert is identical. B) Means ± s.e.m.s of arc mRNA level in dorsal area CA1 (experimental), relative to ventral area CA1 (control), detected in tissue samples harvested after either baseline stimulation (Base) or either 20 min, 40 min, 70 min, or 130 min after PPS. Arc expression levels were normalized by gapdh expression in the respective tissue samples and, to approximate a normal distribution of the data, log₂ –transformed. Fold differences (FD) can be calculated from log₂(RQ) by the formula FD= 2^log2(RQ). (n = 8 for baseline, n = 7 for 20 min, n = 7 for 40 min, n = 10 for 70 min, n = 10 for 130 min). Determined Ct values for each of these groups are shown in Table 1 in the Supplementary Information. Two-tailed t-tests indicate a significant decrease in arc mRNA level 20 min after PPS followed by a significant increase in arc mRNA level 70 min after PPS (** p < 0.01).