These experiments examined the involvement of glucocorticoid receptors (GRs or type II) located in the A2-noradrenergic cell group of the rat nucleus of the solitary tract (NTS) in modulating memory storage. Bilateral intra-NTS infusions (0.5 μL) of the specific GR agonist RU 28362 (11β,17β-dihydroxy-6,21-dimethyl-17α-pregna-4,6-trien-20yn-3-one), in doses ranging from 0.01 to 10.0 ng, immediately after inhibitory avoidance training produced a dose-dependent enhancement of 48 h retention performance. Infusions of 0.1 or 1.0 ng of the agonist enhanced retention, whereas lower or higher doses were ineffective. Post-training infusions of the GR antagonist RU 38486 [17β-hydroxy-11β-(4-dimethylaminophenyl)-17α-(1-propynyl)-oestra-4,9-dien-3 -one, 0.01-10.0 ng] into the NTS did not significantly affect retention performance, but shifted the dose-response effects of post-training systemic injections of the synthetic glucocorticoid dexamethasone to the right. These results indicate that activation of GRs in the NTS can influence memory formation for inhibitory avoidance training, and suggest that the effects of circulating glucocorticoids on memory are mediated, in part, by an activation of GRs in the NTS. Additionally, pretraining infusions of the β1-adrenergic antagonist atenolol (0.5 μg in 0.2 μL) into the basolateral nucleus of the amygdala (BLA), a brain structure which receives noradrenergic projections from the NTS and is implicated in memory storage modulation, blocked the memory-enhancing effects of the GR agonist (1.0 ng) infused into the NTS. These findings provide evidence that memory storage is modulated by glucocorticoid binding to GRs in noradrenergic cell bodies in the NTS and suggest that these modulatory effects are conveyed by ascending projections to the BLA.
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