Novel mechanism for non‐genomic action of 17β‐oestradiol on kainate‐induced currents in isolated rat CA1 hippocampal neurones

Abstract

Using whole‐cell voltage‐clamp recordings of dissociated hippocampal CA1 neurones, we demonstrated that 17β‐oestradiol rapidly potentiates kainate‐induced currents when applied either to the outside or the inside of the neurone. However, when the steroid was conjugated to bovine serum albumin (E2‐BSA), application to either the extracellular plasma membrane (E2‐BSAout) or the cytosolic side of the cell (E2‐BSAin) had no observable effect on kainate‐induced currents. However, when applied stimultaneously to both sides of the plasma membrane, E2‐BSA potentiated kainate‐induced currents. Application of E2‐BSAout and GTPγSin potentiated kainate‐induced currents. The potentiation of kainate‐induced currents by 17β‐oestradiol was occluded by cholera toxin pretreatment and appeared to be pertussis toxin insensitive. E2‐BSAin prolonged the effect of 8‐bromoadenosine 3′,5′ cyclic monophosphate (8‐bromo‐cAMP) on kainate‐induced currents. The recovery from the 8‐bromo‐cAMP response was found to be a function of the concentration of E2‐BSAin. The application of ATPγSin occluded the effect of 17β‐oestradiol. These results suggest that the non‐genomic action of 17β‐oestradiol in the potentiation of kainate‐induced currents is mediated via an action on Gs protein‐coupled receptors. This operates in concert with an internal action of 17β‐oestradiol on a cAMP‐dependent phosphorylation.

Functional significance of the rapid regulation of brain estrogen action: Where do the estrogens come from?

“…1), including the modulation of intracellular calcium [44,55,122,165,175,209] and protein kinase C (PKC; [266,276]). There is also evidence that membrane effects of estrogens can activate intracellular signaling pathways involving cyclic AMP (cAMP; [103,170,254]), protein kinase A (PKA; [104,141,266]), the "mitogen activated protein kinases" (or MAP kinases; [39,122,153,205,260,269,276]), and the tyrosine kinases [39]. The activation of these intracellular signaling pathways results primarily in phosphorylations/dephosphorylations producing different kinds of physiological responses such as the decoupling of a receptor from its effector system [141,[171][172][173] or the modulation of the catalytic activity of an enzyme [191].…”

“…Estrogen modulates electrical activity of neurons within a few seconds in some experiments [165,190,277,278] but with relatively longer latencies of up to 3-5 minutes in other biological systems [103,104,137,141,202,284]. The fastest of these effects appear to be associated with the allosteric modulations of ionotropic receptors [190,277,278], but most effects on electrical activity result from a modulation of ion channel activity through G protein linkage (for review see [132,176]).…”

Membrane-initiated estrogen signaling in hypothalamic neurons

“…Also, E2 potentiates non-NMDA (kainate)-mediated excitation of hippocampal CA1 pyramidal neurons via activation of a cAMP/PKA pathway Moss, 1996, Gu andMoss, 1998). Based on the findings from the hippocampal slice, it was hypothesized that E2 activates a Gs-coupled receptor on the extracellular surface of hippocampal neurons, which operates in concert with an internal action of E2 on cAMP-dependent phosphorylation (Gu and Moss, 1998). Importantly, these rapid actions of E2 on kainate-induced currents in hippocampal neurons are suggesting a novel mechanism (receptor) for the rapid actions of E2 in the hippocampus (Gu et al, 1999).…”

Cyclic changes in estradiol regulate synaptic plasticity through the MAP kinase pathway

“…In particular, estrogens have been shown to increase the density of dendritic spines on CA1 pyramidal neurons (7). In hippocampal slices, 17␤-estradiol increases electrophysiological responses elicited by activation of both ␣-amino-3-hydroxy-5-methylisoxazole propionic acid and N-methyl-Daspartate (NMDA) receptors and the magnitude of long-term potentiation (LTP) in field CA1 (8,9). At the cellular level, numerous laboratories have shown that, in addition to direct genomic effects, 17␤-estradiol activates the extracellular regulated kinase͞mitogen-activated protein (ERK͞MAP) kinase pathway (10)(11)(12), an effect associated with the neurotrophic͞ neuroprotective actions of estrogen (13,14).…”