title: Hippocampal homosynaptic long-term depression/depotentiation induced by adrenal steroids.
abstract: The effects of adrenal steroids on synaptic plasticity were investigated in the dentate gyrus of the hippocampus. Experiments were performed in either adrenalectomized or intact (non-adrenalectomized), anesthetized rats. High-frequency stimulation was applied to the medial perforant pathway at three different frequencies; 100, 200 or 400 Hz, either post- or pre- and post-administration of the specific Type-II adrenal steroid receptor agonist RU 28362. High-frequency stimulation prior to RU 28362 administration produced a frequency-dependent long-term potentiation of the population spike, with 100 Hz showing no long-term potentiation and 400 Hz the highest degree of potentiation. In contrast, following administration of RU 28362, high-frequency stimulation produced a long-term depression (in comparison to baseline). In the experiments in which high-frequency stimulation was applied both pre- and post-RU 28362 administration, the size of the population spike was initially potentiated and then depotentiated after the RU 28362 injection. This effect was also frequency dependent, although opposite to the long-term potentiation effect. That is, 400 Hz was the least effective frequency for inducing long-term depression/depotentiation, while 100 Hz was the most effective. Long-term depression/depotentiation was immediate following high-frequency stimulation and lasted for the extent of the recording session, in some cases longer than 1 h. Similar to the finding reported in the accompanying paper, induction of long-term potentiation was substantially suppressed by RU 28362. However, in a number of experiments long-term potentiation could still be induced after RU 28362 administration, even after long-term depression/depotentiation had been established. In these cases, stimulation at the higher frequencies was necessary.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000305:Adrenal Cortex Hormones / Q000494:pharmacology*; D000732:Androstanols / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D003345:Corticosterone / Q000097:blood; D018891:Dentate Gyrus / Q000187:drug effects / Q000502:physiology; D003864:Depression, Chemical; D004558:Electric Stimulation; D004594:Electrophysiology; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects*; D007267:Injections; D008297:Male; D009473:Neuronal Plasticity / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011987:Receptors, Steroid / Q000819:agonists / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects*
chemical_list: D000305:Adrenal Cortex Hormones; D000732:Androstanols; D011987:Receptors, Steroid; C049154:11,17-dihydroxy-6-methyl-17-(1-propynyl)androsta-1,4,6-triene-3-one; D003345:Corticosterone