Fig 1.
Acquisition of IA learning during the estrous cycle.
Latency before entering the dark side of the box was consistently longer in IA-conditioned rats. (A) Rats successfully acquired IA memory throughout the estrous cycle. ProE (proestrous), n = 4; E (estrous), n = 6; D1 (diestrous day 1), n = 5; D2 (diestrous day 2), n = 6. (B) OVX rats successfully acquired IA memory with (n = 5) or without (n = 5) estrogen (E2) priming. *P < 0.05, unpaired Student’s t test. Error bars represent SEM.
Fig 2.
Changes in learning-driven synaptic delivery of CP-AMPARs in CA1 pyramidal neurons during the estrous cycle.
(A) There was no difference in rectification in between untrained (n = 13) and IA-trained (n = 32) ProE rats. However, rectification increased notably after IA conditioning during other periods of the estrous cycle (untrained/ IA-trained: E, n = 11/ 32; D1, n = 7/ 16; D2, n = 9/ 28). (D) Rectification increased after IA conditioning in OVX rats that were not primed with E2 (untrained, n = 19; IA-trained, n = 16), but rectification did not change after IA conditioning in the presence of E2 (untrained, n = 13; IA-trained, n = 11). Scale bars: vertical, 20 pA; horizontal, 20 ms. (B, E) GluA1 and (C, F) GluA2 content in the synaptoneurosome fraction obtained from the rat dorsal hippocampus in ProE (untrained, n = 6; IA-trained, n = 6), D2 (untrained, n = 11; IA-trained, n = 16), and OVX rats with (untrained, n = 7; IA-trained, n = 7) or without E2 priming (untrained, n = 7; IA-trained, n = 7). *P < 0.05; Mann-Whitney U test (A, D) or unpaired Student’s t test (B-F). Error bars represent SEM.
Fig 3.
LTP was attenuated after IA task in ProE rats.
(A, B) LTP was induced at hippocampal CA3-CA1 synapses from untrained ProE (n = 8) and D2 (n = 6) rats, and from (C, D) IA-trained D2 rats (n = 6), but not in synapses from IA-trained ProE rats (n = 6). The mean amplitude 30–40 min after LTP induction was normalized to the baseline amplitude. *P < 0.05, unpaired Student’s t test. Error bars represent SEM.
Fig 4.
E2 priming prevented LTP after IA task in OVX rats.
(A, B) LTP was induced at hippocampal CA3-CA1 synapses from untrained OVX rats with (n = 8) or without (n = 6) E2 priming. (C, D) LTP was also induced in IA-trained OVX rats without E2 (n = 8), but not in IA-trained OVX rats primed with E2 (n = 7). The mean amplitude 30–40 min after LTP induction was normalized to the baseline amplitude. *P < 0.05, unpaired Student’s t test. Error bars represent SEM.
Fig 5.
Reduced IA-induced mushroom-spine formation in CA1 pyramidal neurons in ProE rats and E2-primed OVX rats.
(A, B) The number of each type of dendritic spine in untrained and IA-trained rats during different periods of the estrous cycle. IA-learning tasks significantly increased the number of mushroom-shaped spines on CA1 pyramidal neurons of D2 rat dendrites (untrained, n = 27; IA-trained, n = 25) but not in ProE rat dendrites (untrained, n = 17; IA-trained, n = 15). (C, D) The number of each type of dendritic spine in untrained and IA-trained rats with or without E2 priming. IA-learning tasks significantly increased the number of mushroom-shaped spines on the dendrites of unprimed OVX rats (untrained, n = 31; IA-trained, n = 44), but not on those of E2-primed OVX rats (untrained, n = 18; IA-trained, n = 20). *P < 0.05, unpaired Student’s t test. Error bars represent SEM. (Bottom) Representative photomicrographs (×400) of tertiary apical dendrites of CA1 pyramidal neurons. Black arrowheads indicate mushroom-shaped spines; white arrowheads indicate filopodial spines. Scale bar: 3 μm.
Fig 6.
Prior IA-task experience impaired hippocampus-dependent learning in ProE rats.
(A) Percentage of spontaneous alternation in the Y-maze task before and after IA training. The alternation rate did not change after IA learning in the D2 period (untrained, n = 8; IA-trained, n = 8), but the alternation rate was reduced after IA learning during the ProE period (untrained, n = 6; IA-trained, n = 10). (B) Latency in the second IA learning session after the initial IA training. The latency to re-enter the dark box in the second IA task was shorter during the ProE period (n = 5) than in the D1 period (n = 4). *P < 0.05, unpaired Student’s t test. Error bars represent SEM.