Differential Phosphorylation of the Glucocorticoid Receptor in Hippocampal Subregions Induced by Contextual Fear Conditioning Training

Abstract

Aversive events induce the release of glucocorticoid stress hormones that facilitate long-term memory consolidation, an effect that depends on the activation of glucocorticoid receptors (GRs). GRs are distributed widely in the hippocampus. The dorsal region of the hippocampus has been related to cognitive functions and the ventral region to stress and emotion. GR acts as a transcription factor which after hormone binding becomes phosphorylated, affecting its cellular distribution and transcriptional activity. Two functionally well-described GR phosphorylation sites are serine 232 (pSer232), which enhances gene expression, and serine 246 (pSer246), having the opposite effect. Since gene expression is one of the plastic mechanisms needed for memory consolidation, we investigated if an aversive learning task would induce GR phosphorylation in the dorsal (DH) and the ventral (VH) hippocampus. We trained rats in contextual fear conditioning (CFC) using different foot-shock intensities (0.0, 0.5, or 1.5 mA). One subgroup of animals trained with each intensity was sacrificed 15 min after training and blood was collected to quantify corticosterone (CORT) levels in serum. Another subgroup was sacrificed 1 h after training and brains were collected to evaluate the immunoreactivity (IR) to GR, pSer232 and pSer246 by SDS-PAGE/Western blot in DH and VH, and by immunohistochemistry in dorsal and ventral CA1, CA2, CA3, and dentate gyrus (DG) hippocampal regions. The conditioned freezing response increased in animals trained with 0.5 and 1.5 mA during training and extinction sessions. The degree of retention and CORT levels were directly related to the intensity of the foot-shock. Although total GR-IR remained unaffected after conditioning, we observed a significant increase of pSer246-IR in the dorsal region of CA1 and in both dorsal and ventral DG. The only region in which pSer232-IR was significantly elevated was ventral CA3. Our results indicate that fear conditioning training is related to GR phosphorylation in specific

Behavioral tagging as a mechanism for aversive‐memory formation under acute stress

“…Recently, it was reported that plasmatic glucocorticoids levels increase after a CFC task and also does the Ser246 phosphorylation of GR in the dorsal hippocampus, which is associated with binding to co‐repressors inside the nucleus and transcription‐silencing (Ponce‐Lina et al., 2020). Although this fact is opposed to the stress‐induced gene transcription, this work proposes that an increase in pSer246 could inhibit the expression of genes that are not required for memory acquisition.…”

Isoxazole‐9 reduces enhanced fear responses and retrieval in ethanol‐dependent male rats

“…For example, the dorsal hippocampus is vital for spatial learning, and is particularly critical in mediating contextual discrimination (Fanselow & Dong, 2010;Wells et al, 2011). However, the ventral hippocampus is strongly associated with negative affective symptoms (Felix-Ortiz et al, 2013;Jimenez et al, 2020;Kaouane et al, 2020;Kim et al, 2020;Pinizzotto et al, 2020;Ponce-Lina et al, 2020). Similar functional differences along the septo-temporal axis of the hippocampus have been noted in humans, with ventral hippocampus demonstrating greater activity in response to negative affective symptoms (Lau et al, 2010;Strange et al, 2014).…”

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“…SDS-PAGE and Western blot were performed as previously described ( Ponce-Lina et al, 2020 ). Membranes were incubated with a goat anti-rabbit secondary antibody conjugated to horseradish peroxidase (1:3,000; Invitrogen, United States, #ab6721) for 2 h at room temperature.…”