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Here, we investigated kinases and calcium sources required for acute E2-induced synaptic potentiation in the hippocampus of each sex and tested whether sex differences in kinase aling extend to LTP. We recorded EPSCs from CA1 pyramidal cells in hippocampal slices from adult rats and used specific inhibitors of kinases and calcium sources.
This revealed that, although E2 potentiates synapses to the same degree in each sex, cAMP-activated protein kinase PKA is required to initiate potentiation only in Women woolley and fuck. Calcium source experiments showed that L-type calcium channels and calcium release from internal stores are both required for E2-induced potentiation in females, whereas in males, either L-type calcium channel activation or calcium release from stores is sufficient to permit potentiation. This showed that, although the magnitude of both high-frequency stimulation-induced and pairing-induced LTP is the same between sexes, PKA is required for LTP in females but not males.
These demonstrate latent sex differences in mechanisms of synaptic potentiation in which distinct molecular aling converges to common functional endpoints in males and females. Here, we studied molecular aling that underlies estrogen-induced and activity-dependent potentiation of excitatory synapses in the hippocampus.
We found that, despite similar magnitude increases in synaptic strength in males and females, the roles of cAMP-regulated protein kinase, internal calcium stores, and L-type calcium channels differ between the sexes. Therefore, latent sex differences in which the same outcome is achieved through distinct underlying mechanisms in males and females include kinase and calcium aling involved in synaptic potentiation, demonstrating that sex is an important factor in identification of molecular targets for therapeutic development based on mechanisms of neuromodulation. There is compelling evidence that the Women woolley and fuck can synthesize estrogens as neurosteroids.
More recently, studies from our lab Sato and Woolley, and others Tuscher et al. These observations motivate efforts to understand the mechanisms by which E2 synthesized in the hippocampus could influence hippocampal neurophysiology. One likely action of neurosteroid E2 is to acutely modulate synaptic transmission. It has been known for decades that E2 can potentiate excitatory synapses in the hippocampus on a time scale of minutes and in both sexes Teyler et al. E2 has also been shown to suppress perisomatic inhibitory synapses on a similar acute time scale, although this occurs only in females Huang and Woolley, The possibility that acute E2-induced excitatory synaptic potentiation shares underlying mechanisms with other forms of synaptic plasticity such as long-term potentiation LTP suggests molecular aling that could be involved in E2-induced synaptic potentiation.
In addition, acute E2 potentiation of kainate-evoked currents in female hippocampal neurons depends on cAMP-activated protein kinase PKA Gu and Moss,which is implicated in some Blitzer et al. Despite this extensive literature, however, no study has directly compared the involvement of specific kinases in E2-induced synaptic potentiation in males versus females to investigate the possibility of sex differences.
Further, whereas most of the kinases tested were similarly required in males and females, we found that PKA plays a sex-specific role in initiation, being required only in females. Given this sex difference, we then investigated whether mechanisms that underlie E2-induced synaptic potentiation also involve distinct sources of increased intracellular calcium in males and females, namely L-type calcium channels and calcium release from internal stores.
These experiments showed that, whereas both L-type calcium channels and calcium release from stores are required for E2-induced potentiation in females, in males, either of these calcium sources appears to be able to compensate for the other.
Therefore, sex differences in molecular aling that underlies synaptic plasticity Women woolley and fuck beyond neurosteroid estrogen actions and may be broadly relevant for the translation of basic mechanisms of neuromodulation to the development of therapeutics appropriate for each sex. All rats were gonadectomized 3—8 d before being used for experiments. Data were acquired with a Multiclamp B amplifier and pClamp To investigate the roles of specific kinases in E2-induced synaptic potentiation, two types of protocols were used. In the second protocol, kinase inhibitors were applied after E2-induced potentiation was established to determine the requirement of each Women woolley and fuck in the maintenance of potentiation.
In extracellular recordings, baseline fEPSPs were recorded for 15—20 min until stable. In whole-cell recordings, baseline EPSCs were recorded for 10—12 min and Women woolley and fuck LTP was induced by pairing postsynaptic depolarization to 0 mV with presynaptic stimulations delivered at 1.
Chemicals were purchased from Tocris Bioscience unless otherwise specified. The bath contained an equivalent concentration of DMSO 0. Clampfit IGOR version 6. To determine the E2 responsiveness of each recording individually, unpaired, two-tailed t tests were used to compare EPSC amplitude during 2 min immediately before E2 application to 2 min beginning 4 min after E2 was removed from the bath. Two-tailed Fisher's exact tests were used to compare the proportions of cells that responded to E2 between sexes within an experiment and within-sex between different experiments.
Unpaired, two-tailed t tests were used to compare the magnitude of E2-induced potentiation between sexes. To determine whether pharmacological inhibitors affected EPSC amplitude in E2-responsive experiments, unpaired, two-tailed t tests were performed within cell to compare EPSCs recorded during 2 min immediately before application of the inhibitor to EPSCs recorded during 2 min beginning 10 min after the inhibitor was applied.
Paired, two-tailed t tests were used to determine whether each LTP induction protocol produced ificant potentiation within each group male control, male mPKI, female control, female mPKI. All statistics were calculated with n as the of cells for whole-cell recordings or of slices for fEPSP recordings. We recorded one to four cells or slices per animal with four to eight animals per experiment, except for one control tatCN21 experiment in which two cells from two animals were used.
Full of all statistically ificant comparisons are included in the text. To determine whether this effect of E2 is similar between the sexes, we performed whole-cell recordings from CA1 neurons and recorded EPSCs evoked by Schaffer collateral stimulation before, during, and after 10 min exposure to E2 n m in acute hippocampal slices from males and females. In both sexes, EPSC amplitude began to increase within 5—8 min of E2 application and remained elevated following E2 washout. E2 potentiates excitatory synaptic transmission in both females and males.
AIndividual traces and time course of synaptic potentiation in a representative experiment in females in which E2 n m was applied for 10 min. CNormalized group EPSC amplitude data for E2 experiments in females where the magnitude of potentiation is shown separately for E2-responsive R, red and nonresponsive NR, white experiments. DIndividual traces and time course of synaptic potentiation in a representative experiment in males in which E2 was applied for 10 min.
Scale bars, 50 pA, 25 ms. Within-cell t tests were used to evaluate ificant differences between each condition. Identical experiments were done in females and males. PKA is required for initiation of E2-induced synaptic potentiation in females but not in males. AIndividual traces and time course of synaptic potentiation in a representative experiment in females in which mPKI 0. DIndividual traces and time course of synaptic potentiation in a representative experiment in males in which mPKI 0.
GIndividual traces and time course of E2-induced synaptic potentiation in a representative experiment in males in which H89 was applied until the end of the recording. Scale bars, 25 pA, 25 ms. First, to test whether the apparent E2-induced increase in EPSC amplitude in males was related to washout of the PKA inhibitor, we extended H89 application for the duration of an experiment Fig. Therefore, we tested whether each of these kinases is required for acute E2 potentiation of synaptic transmission and we investigated sex differences.
Within-cell t tests were used to determine whether a recording was E2-responsive. PD blocked E2-induced potentiation in both sexes. SU blocked E2-induced potentiation in both sexes. Y blocked E2-induced potentiation in both sexes. In separate experiments, we applied the same kinase inhibitors as above following stabilization of E2-induced potentiation in responsive cells from both sexes.
H89 had no effect on potentiated EPSCs in either sex. Y27 had no effect on potentiated EPSCs in either sex. CaMKII is one of the most extensively studied kinases in the context of synaptic potentiation. In other experiments, tatCN21 was applied after E2-induced potentiation was established.
Identical experiments were performed in males and females. Identical experiments with KN93 confirmed tatCN21 .
JIndividual traces and time course of synaptic potentiation in a representative experiment in males in which mPKI 0. To rule out alternative possibilities, we did three additional experiments. First, we modified the protocol to extend tatCN21 for an additional 10 min after washing out E2.
Consistent withEPSC amplitude increased only 10—15 min after washing out tatCN21, in both females three of five recordings and males three of five recordings data not shown. In Women woolley and fuck second set of experiments, we continued KN93 application after E2 for up to 40 min and never observed EPSC potentiation in either females six recordings or males six recordings data not shown.
In the last of these control experiments, we applied tatCN21 alone for 20—25 min and then washed it out, which had no effect on EPSC amplitude two recordings in males, data not shown. These showed that, in both sexes, CaMKII activity is required not only for initial expression but also ongoing maintenance of E2-induced synaptic potentiation. In contrast to the obtained with mPKI or tatCN21 alone, each of which failed to block E2-induced synaptic potentiation in males Figs. Coapplication of H89 and KN93 in males also blocked E2-induced potentiation in the 6 E2-responsive cells of 8 recordings Fig.
These experiments indicate that, whereas PKA is not absolutely required for E2-induced synaptic potentiation in males, it does play a role in cooperation with, and possibly by facilitating activity of, CaMKII. CaMKII activation likely requires an increase in intracellular calcium. Because NMDA receptors were blocked in our experiments, we focused on two alternative calcium sources: internal stores and L-type calcium channels.
E2 was applied in the continued presence of thapsigargin after EPSCs returned to baseline. Nifedipine by itself had no effect on baseline EPSCs and E2 was also applied in the presence of the inhibitor. Experiments with thapsigargin showed that, in females but not in males, depletion of internal calcium stores blocked the initiation of E2-induced synaptic potentiation.
Similarly, inhibition of L-type calcium channels blocked E2-induced potentiation in females but not in males.
Sex differences in the requirement of calcium release from internal stores and L-type calcium channels during E2-induced synaptic potentiation. CIndividual traces and time course of synaptic potentiation in a representative experiment in which TG was applied before E2 in males. GIndividual traces and time course of synaptic potentiation in a representative experiment in which NF was applied before E2 in males.
IIndividual traces and time course of synaptic potentiation in a representative experiment in males where NF and TG were applied together before E2. To test this possibility, we blocked both calcium release from internal stores and L-type calcium channels simultaneously.
Although neither depleting internal calcium stores nor blocking L-type calcium channels alone was sufficient to inhibit E2 potentiation of EPSCs in males, inhibiting both together did block potentiation. E2 failed to potentiate EPSCs in any of 9 recordings in which thapsigargin and nifedipine were applied together Fig. Therefore, in contrast to females, in which both calcium release from internal stores and L-type calcium channels are required for E2-induced synaptic potentiation, these two calcium sources may be able to compensate for each other in E2-induced potentiation in males.
Together with a similar result in experiments using PKA and CaMKII inhibitors, this suggests a pattern of parallel aling leading to synaptic potentiation in males that is distinct from aling leading to the Women woolley and fuck outcome in females. This raises the question of whether a sex difference in involvement of PKA is specific to E2 potentiation or if it could generalize to other forms of synaptic plasticity. However, no studies have compared the role of PKA in both sexes.
Identical experiments were performed in both sexes with or without mPKI 0. Sex differences in the requirement for PKA in long term potentiation. Scale bars, 0. Scale bars, 50 pA, 25 ms also in H. These experiments showed that whereas pairing-induced LTP was modestly attenuated by PKA inhibition in males, consistent with reports, it was abolished by PKA inhibition in females.
In this study, we found that multiple aspects of the molecular aling that underlies potentiation of excitatory synapses in the hippocampus differ between the sexes. Specifically, PKA is required for initiation of E2-induced synaptic potentiation in females but not males and both L-type calcium channels and calcium release from internal stores are required for E2-induced potentiation in females, whereas in males, either of these calcium sources is sufficient. In addition, the sex difference in PKA requirement extends to multiple forms of LTP, suggesting that this difference may be generalizable in mechanisms of synaptic potentiation.
In contrast, other aspects of molecular aling involved in E2-induced synaptic potentiation are similar between the sexes. Interestingly, despite sex differences in molecular aling, the degree of potentiation achieved in LTP or after E2 is Women woolley and fuck identical between the sexes. Therefore, these findings extend the concept of latent sex differences Oberlander and Woolley, in which distinct underlying mechanisms converge to common functional endpoints in males and females. Considering parallels between E2-induced potentiation and LTP may give insight into intracellular aling that le to synaptic potentiation.
In this regard, it is important to note that the male-female differences we observed were specific to synaptic potentiation. None of the kinase inhibitors that we used nor nifedipine altered baseline synaptic transmission in either sex. Depleting internal calcium stores with thapsigargin transiently increased EPSC amplitude similarly in both sexes. However, we found that, although E2-induced potentiation was not apparent in the presence of CaMKII inhibitors, EPSC amplitude began to increase shortly after inhibitor washout, indicating that potentiation had been initiated but could not be expressed.
Most of these studies either used males or sex was not noted, raising the possibility that some discrepancies in the literature are related to sex differences. One potential explanation for the sex differences in PKA requirement that we found derives from the idea that PKA inhibits phosphatases that normally constrain the activity of other kinases such as CaMKII and thereby permits LTP but does not directly cause it Blitzer et al.
For example, higher basal PKA activity in males might permit activity of other kinases that are essential for potentiation without E2 modulation of PKA. In females, lower basal PKA activity might fail to establish this permissive state and require stimulation by E2 to achieve it.Women woolley and fuck
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Sex Differences in Synaptic Plasticity: Hormones and Beyond