Modulation by norepinephrine of neural responses to estradiol

Beta estradiol and norepinephrine treatment of differentiated SH-SY5Y cells enhances tau phosphorylation at (Ser396) and (Ser262) via AMPK but not mTOR signaling pathway

Hyperphosphorylation of tau is one of the main hallmarks for Alzheimer's disease (AD) and many other tauopathies. Norepinephrine (NE), a stress-related hormone and 17-β-estradiol (E2) thought to influence tau phosphorylation (p-tau) and AD pathology. The controversy around the impact of NE and E2 requires further clarification. Moreover, the combination effect of physiological and psychological stress and estrogen alteration during menopause, which affect p-tau, has not been addressed. Exposure to E2 is believed to reduce NE release, however, the link between these two hormones and AD at cellular level was also remained unknown. Here, we examined whether NE and E2 treatment of differentiated SH-SY5Y cells affected tau phosphorylation. The involvement of adenosine monophosphate kinase protein kinase (AMPK) and target of Rapamycin (mTOR) as the possible mechanisms, underlying this effect was also investigated. Subsequent to SH-SY5Y differentiation to mature neurons, we treated the cells with NE, E2 and NE plus E2 in presence and absence of Compound C and Rapamycin. Cell viability was not affected by our treatment while our Western blot and immunofluorescent findings showed that exposure to NE and E2 separately, and in combination enhanced p-tau (Ser³⁹⁶) and (Ser²⁶²)/tau but not (Ser²⁰²/Thr²⁰⁵)/tau. Blocking AMPK by Compound C reduced p-tau (Ser³⁹⁶) and (Ser²⁶²), while GSK-3β and PP2A activities were remained unchanged. We also found that blocking mTOR by Rapamycin did not change increased p-tau (Ser³⁹⁶) and (Ser²⁶²) due to NE + E2 treatment. Collectively, our results suggested that tau hyperphosphorylation due to exposure to NE/E2 was mediated by AMPK, the main energy regulator of cells during stress with no significant involvement of mTOR, GSK-3β and PP2A.

Alpha1 adrenoreceptors mediate the stimulatory effects of oestrogen on stress-related hypothalamic-pituitary-adrenal activity in the female rat

Variation in challenge-induced adrenocorticotropin hormone (ACTH) release over the oestrous cycle occurs in response to fluctuations in circulating concentrations of oestrogen and progesterone. However, how these ovarian steroids interact to regulate the principal ACTH cosecretagogues, corticotropin-releasing hormone (CRH) and arginine vasopressin is not understood. Here, we measured median eminence CRH and vasopressin content in intact cycling female rats, and in ovariectomized (OVX) females steroid-replaced in a manner that approximates the relative release patterns of oestrogen and progesterone seen over the oestrous cycle. Intact cycling females showed significantly higher median eminence CRH and vasopressin concentrations during proestrous and oestrous compared to the diestrous phase. In OVX rats, a single 10 micro g injection of oestrogen failed to mimic this increase in median eminence CRH and vasopressin. However, this dose significantly elevated CRH and vasopressin content in OVX rats previously exposed to diestrous concentrations of oestrogen and progesterone. Moreover, oestrogen priming enhanced restraint-induced depletion of CRH and vasopressin from the median eminence, but only against a background of low oestrogen and progesterone replacement. Oestrogen-induced elevations in median eminence vasopressin (but not CRH) content were reduced by peripheral administration of the alpha1 adrenoreceptor antagonist prazosin. Finally, plasma ACTH concentrations following central injection of the alpha1 receptor agonist, phenylephrine, were significantly higher in rats during proestrous compared to diestrous. These results indicate that the stimulatory effect of oestrogen on both the expression and stress-induced release of ACTH cosecretagogues is exerted only against a background of low oestrogen and progesterone levels, and is mediated, in part, via the alpha1 adrenoreceptor.

Effect of delequamine (RS15385) on female sexual behaviour in the rat

The role of alpha 2-adrenoceptors in mediating the noradrenergic control of female sexual behaviour was investigated employing a selective alpha 2-adrenoceptor antagonist, delequamine (RS15385). The drug was given in graded doses of 0.01-30 mg/kg p.o. to ovariectomised plus adrenalectomised rats primed with either 2 micrograms oestradiol benzoate which yielded mainly non-receptive animals or 5 micrograms oestradiol benzoate followed 48 h later by 0.5 mg progesterone, which stimulated a high level of receptivity. Doses between 0.1 and 30 mg/kg significantly increased lordotic activity (receptivity) with an ED50 of 0.32 mg/kg, but had no effect on ear-wiggling or hopping-and-darting (proceptivity). Delequamine had no inhibitory effect in animals displaying high levels of receptivity. Thus we have shown a selective alpha 2-adrenoceptor antagonist, given orally, can stimulate female receptivity in a dose-dependent manner. Bilateral administration into the ventromedial nucleus, but not medial preoptic area, of delequamine (10 micrograms/side/rat) stimulated receptivity and it is suggested that the alpha 2-adrenoceptor may exert its effect by enhancing endogenous noradrenaline release at its active sites.

Effects of alpha-2 adrenoceptor antagonists on rough-and-tumble play in juvenile rats: evidence for a site of action independent of non-adrenoceptor imidazoline binding sites

The pharmacological specificity of alpha-2 adrenoceptor involvement in the modulation of rough-and-tumble play behavior was assessed in juvenile rats. The alpha-2 adrenoceptor antagonists idazoxan and RX821002 both increased the frequency of pinning in individually housed rats that were given a brief opportunity to play. Dorsal contacts, a measure of play solicitation, were not consistently affected by these compounds. Since RX821002 shows little affinity for non-adrenoceptor imidazoline binding sites, it is likely that the facilitation of play following administration of these two compounds is due to blockade of alpha-2 receptors. The effect of RX821002 and idazoxan is unlikely to be an artifact associated with using rats that are reared in isolation, as RX821002 also increased pinning, as well as dorsal contacts, in group-housed rats that were isolated for a short period (4h) before the play session. The alpha-1 adrenoceptor antagonist prazosin, which also binds to alpha-2B receptors, reduced the frequency of both pinning and dorsal contacts. There was a strong trend for St 587, a centrally active alpha-1 agonist, to attenuate the effect of prazosin on play. While this leaves open the possibility that prazosin may be reducing play through alpha-1 blockade, antagonist activity at alpha-2B receptors cannot be ruled out. From these data, we conclude that the facilitation of play following idazoxan and RX821002 is likely due to blockade of alpha-2A adrenoceptors. These findings add further support for a specific role of alpha-adrenoceptors in the modulation of playfulness in the juvenile rat.

Estrogen receptor immunostaining in the preoptic area and medial basal hypothalamus of estradiol benzoate- and prazosin-treated female guinea-pigs

Evidence has accumulated showing that the alpha 1-adrenergic antagonist prazosin decreases nuclear estrogen binding in the hypothalamus of the guinea-pig. In this study we asked if prazosin treatment alters estrogen receptor (ER) protein content as reflected by changes in ER-immunoreactivity. The monoclonal rat antibody H222 directed against ER was used to detect ER-immunoreactive (ER-ir) cells in eight specific preoptic and hypothalamic brain regions of ovariectomized Hartley strain guinea-pigs treated with estradiol benzoate and 1.0 mg/kg prazosin or vehicle. Immunocytochemical parameters which provided optimum conditions for detection of even modest changes in ER-immunoreactivity were first established. Then, using these optimum conditions, we compared 1) the mean number of ER-ir profiles, 2) the mean density of ER-ir staining, and 3) the distribution of ER-ir staining density readings, between conditions within each of the eight brain regions. No differences in any of these measures were found between prazosin- and vehicle-treated females. We also compared the percentage of ER-ir nuclear profiles across the eight cell groups investigated in estradiol benzoate- and vehicle-treated females. The medial preoptic area had by far the highest percentage (48%) of ER-ir profiles (P < 0.05) compared to all seven other brain regions (23% to 32% ER-ir cells). Our data, showing that ER-immunoreactivity is not reduced (6h) after prazosin treatment, suggests that mechanisms other than alterations in ER protein should be considered when interpreting the effects of prazosin on the retention of estradiol by nuclear or cytosolic extracts of hypothalamic lysates.

Norepinephrine inhibits vasopressin-stimulated flank marking in the Syrian hamster by acting within the medial preoptic-anterior hypothalamus

Syrian hamsters exhibit a form of scent marking behavior called flank marking. Flank marking, which is elicited during social contact with other hamsters and by the odors of other hamsters, communicates socially important information such as mate choice and dominance status. Vasopressinergic activity within the medial preoptic-anterior hypothalamic continuum (MPOA-AH) is essential for the expression of flank marking. In female hamsters, an inverse relationship exists between the expression of flank marking and sexual receptivity during the 4-day estrous cycle. Since norepinephrine (NE) appears to facilitate sexual receptivity, the present study investigated whether NE might have an inhibitory effect on flank marking by acting on Vasopressinergic activity within the MPOA-AH. Microinjection of 9.0 μM arginine vasopressin (AVP) into the MPOA-AH stimulated high levels of flank marking. Microinjection of 9.0 μM AVP combined with NE in concentrations of 4.0, 0.4 or 0.2 nM, drastically reduced or eliminated flank marking. In contrast, AVP in combination with 0.09, 0.04 or 0.004 nM NE produced no significant reductions in flank marking. In addition, microinjection of 9.0 μM AVP, in combination with epinephrine (4.0 nM), but not dopamine (4.0 nM), serotonin (4.0 nM) or neuropeptide Y (900 μM), significantly reduced AVP-induced flank marking. In male hamsters, microinjection of NE (4.0 nM) combined with AVP (9.0 μM) into the MPOA-AH was not found to inhibit AVP-stimulated flank marking. These results suggest that NE is involved in regulating the expression of flank marking during the estrous cycle by acting on Vasopressinergic activity within the MPOA-AH.

Estrogen receptor binding in regions of the rat hypothalamus and preoptic area after inhibition of dopamine-beta-hydroxylase

Previous studies have shown that administration of diethyldithiocarbamate (DDC), a dopamine-beta-hydroxylase inhibitor, results in a decreased concentration of estrogen receptors measured in the rodent hypothalamus and preoptic area. To determine if this modulation of receptor content is region-specific, in vitro estrogen binding assays were performed on cytosol and cell nuclear extracts of microdissected brain regions from female rats treated with DDC. For cytosol binding comparisons, ovariectomized (OVX) rats were treated with 550 mg DDC/kg b. wt. or the saline vehicle 12 h before sacrifice. For cell nuclear binding comparisons, OVX rats received a maximal dose of estradiol 12 h after DDC or saline treatment and 1 h before sacrifice. No region-specific decreases in estrogen binding were observed in either cytosol or nuclear extracts. To further examine possible regional specificity, quantitative autoradiographic analysis of the in vivo hypothalamic uptake of an iodinated analog of estradiol, 11 beta-methoxy-16 alpha-[125I]iodoestradiol (MIE2), in OVX rats treated with DDC was conducted. Animals received a saturating dose of [125I]MIE2 12 h after DDC or saline treatment and 1 h before sacrifice. DDC treatment resulted in higher background levels of radioactivity and a trend toward higher uptake levels in all brain regions, but with no evidence of marked regional specific effects in any area of the brain. In tissue uptake studies, DDC treatment resulted in higher levels of radioactivity recovered from serum and neural tissues of [125I]MIE2-injected rats, suggesting that DDC slows the clearance of MIE2.(ABSTRACT TRUNCATED AT 250 WORDS)