Effects of Ovarian Hormones on Norepinephrine and Dopamine Turnover in Individual Hypothalamic and Extrahypothalamic Nuclei

Crowley, William R.

doi:10.1159/000123333

Cited by 107 publications

(34 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The decrease in T H activity observed within I h of E, injection precedes and accompanies a rise in serum PRL. Such a decrease in TIDA neuronal function in response to acute estrogen treatment is in good agreement with previous results from Crowley (9) who showed a decrease in the turnover of DA in the ME 3 h after E, administration. In this study, plasma PRL concentrations were also determined and found to be slightly elevated.…”

Section: Discussionsupporting

confidence: 92%

Inhibitory Actions of Acute Estradiol Treatment on the Activity and Quantity of Tyrosine Hydroxylase in the Median Eminence of Ovariectomized Rats

Pasqualini

Leviel

Guibert

et al. 1991

J Neuroendocrinology

View full text Add to dashboard Cite

The effects of acute estradiol (E2) treatment on both t h e activity of tyrosine hydroxylase (TH) in t h e median eminence and t h e serum level of prolactin (PRL) were investigated. Twelve-day-ovariectornized rats were injected with li'P-E, (25 pg sc) a t 1100 h and sacrificed hourly from 1200 to 2300 h. TH activity was quantified by measuring the amount of exogenous tyrosine converted to L-DOPA in vitro by aliquots of median eminence homogenates. Serum PRL levels were evaluated by radioimmunoassay. A biphasic response of TH activity to treatment was observed: an immediate decrease occurred-preceding and accompanying a rise in serum PRL-followed by an increase beyond control levels 2 h after the maximal release of PRL. The increase in TH activity could be prevented by the pretreatment of rats with a specific rat PRL antiserum, suggesting it was not due to E, per se but rather mediated by the E,-induced PRL elevation. To pin-point the process underlying the E,-induced decrease in TH activity, we evaluated the kinetic parameters of TH in t h e median eminence as well as its quantity (by Western blot analysis) in t h e median eminence and arcuate nucleus. Finally, we used a sensitive dot-blot assay to quantify specific TH messenger ribonucleic acid in the arcuate nucleus. The decrease in TH activity after E, treatment paralleled an immediate decrease in t h e affinity of TH for its pterin cofactor (6-MPH4), while V , , , remained unchanged. A decrease in the amount of TH protein in the arcuate nucleus and median eminence as well as in the TH messenger ribonucleic acid level in the arcuate nucleus was also observed, but the latency of these effects precluded a major involvement in the immediate decline of TH activity. Therefore, when observed separately from those of PRL, E, effects on TH in tuberoinfundibular dopaminergic neurons are clearly inhibitory consisting of a 'deactivation' of the enzyme together with a reduction of its synthesis. Tuberoinfundibular dopaminergic (TIDA) neurons with cell bodies in the arcuate nucleus (AN) and nerve terminals in the median eminence (ME) exert a tonic inhibitory influence on pituitary prolactin (PRL) secretion. It is known that these cells are estradiol (E2) targets (I), however the nature and mechanism(s) of the steroid actions on TIDA neurons are still controversial: long-term ( 2 to 3 weeks) treatment with E2 is invariably reported to result in a decrease in the concentration and synthesis of dopamine (DA) in the M E (2-7). In contrast, 'intermediateterm' (3 to 5 days) treatment has been reported to increase the activity of TIDA neurons, as revealed by an increase in the rate of synthesis (8) and turnover (9-12) of DA in the M E and a rise in its concentration in hypophysial portal blood (1 3). However, the activation of TIDA neurons seems not to be due to a direct action of the steroid per se but rather to be mediated by PRL whose secretion is increased by E2 (8, 10). On the other hand, recent studies (14) showed that 3 days of estrogen treatment had no effect in...

show abstract

Section: Discussionsupporting

confidence: 92%

Inhibitory Actions of Acute Estradiol Treatment on the Activity and Quantity of Tyrosine Hydroxylase in the Median Eminence of Ovariectomized Rats

Pasqualini

Leviel

Guibert

et al. 1991

J Neuroendocrinology

View full text Add to dashboard Cite

show abstract

“…Whereas single injections of estradiol benzoate (EB) will stimulate LH surges in rats ovariectomized for 2 weeks [25], supplemental injections of EB or P are necessary to do so in rats ovariectomized for 4 weeks or longer [8,9,14], and the ability of E2-capsu!es to induce an LH surge decreases with time following OVX [34], Similarly, Dockeet al [15] reported a diminished nega tive feedback of EB on LH secretion when implanted into the medial preoptic area (MPOA) of long-term versus short-term ovariectomized rats, and suggested that this could be due to the longer interval between gonadectomy and treatment. This is of interest since the MPOA has been suggested, albeit in studies employing pharmacological lev els of E2 implanted into this region, to be involved in medi ating the suppressive influence of E2 on LH pulse fre quency but not pulse amplitude [2,3], and the effect of D2-proestrous levels of E2 on pulse frequency but not pulse amplitude is lost by I week after OVX.…”

Section: Discussionmentioning

confidence: 99%

Influence of Estradiol and Progesterone on Pulsatile LH Secretion in 8-Day Ovariectomized Rats

Leipheimer¹,

Bona‐Gallo²,

Gallo³

1986

Neuroendocrinology

View full text Add to dashboard Cite

Previous studies in our laboratory [Endocrinology 114:1605–1612 (1984); Neuroendocrinology 41:252–257 (1985)] examined the influence of ovarian steroids on pulsatile luteinizing hormone (LH) release, and involved immediate replacement following ovariectomy (OVX) of estradiol (E2) and progesterone (P) for a 24-hour period within the physiological context of the estrous cycle. The present study investigated the effects of replacing E₂ and/or P 1 week after OVX, and therefore examined whether the time elapsed following OVX influences the effects of ovarian steroids on pulsatile LH release. Immediately after jugular venous cannulation, rats were implanted with either empty silastic capsules or capsules capable of restoring physiological levels of E₂ and/or P comparable to those found in intact rats between the intervals of diestrus 1 (Dl) and diestrus 2 (D2), or D2 and proestrous morning. 24 h later, these rats were bled continuously at a rate of 50 µl whole blood/6 min for 3 h for analysis of pulsatile LH secretion. Rats with empty capsules had decreased levels of E₂ and P and elevated mean blood LH levels, pulse amplitudes and frequencies. Two groups of animals with E₂ capsules had plasma E₂ levels comparable to those seen either in the D1-D2 or D2-proestrous intervals, decreased levels of P, and in both cases significant decreases in LH pulse amplitude, but no change in LH pulse frequency or basal LH secretion. Since mean blood LH levels in 8-day ovariectomized rats are determined by LH pulse amplitude, frequency and basal LH secretion [Neuroendocrinology 37:421–426 (1983)], the E₂-induced effects on LH pulse amplitude were not sufficient to decrease mean blood LH levels. Rats with P capsules had physiological D1-D2 plasma levels of P and decreased levels of E₂, but no change in any parameter of pulsatile LH release. Rats implanted with both E₂ and P capsules had physiological D1-D2 levels of both steroids which caused a significant decrease in mean blood LH levels, due to decreases in LH pulse amplitude and pulse frequency. There was no significant difference in the extent of the decrease in pulse amplitude produced by E₂ (low) or E₂ (low) + P. This indicates that the decreased LH pulse amplitude following E₂ (low) + P is due to the E₂ (low) alone. The suppressive effects on LH pulse amplitude produced by E₂ (low or high) were mediated centrally, since the in vitro responses to LHRH of anterior pituitary (AP) fragments from E₂-implanted rats were greater than those of AP fragments from rats implanted with empty capsules. When compared with our previous studies, the present results demonstrate that some of the responses of the pulsatile LH secretory system to the negative feedback effects of ovarian steroids remain the same, while others are altered when these same levels of steroids are replaced for 24 h 1 week after OVX rather than immediately after OVX. D2-pro...

show abstract

“…Adminis tration of estradiol to ovariectomized rats acutely decreases LH and elevates PRL [7,9,28], These effects may result from direct actions on the anterior pituitary to antagonize LH-releasing hormone (LH-RH) [7,9] and dopamine released from tuberoinfundibular neurons [10], respectively, but es tradiol may also alter release of these hypophysiotropic factors [3,27], These latter effects may be mediated by changes in cen tral monoaminergic activity [4], Recently this laboratory Received: June 24,1983 Accepted after revision: October4, 1983 observed that a 3-hour exposure to estradiol benzoate (EB) in ovariectomized rats, which increases PRL and decreases LH, potentiated the accumulation of serotonin (5-hydroxytryptamine, 5-HT) after monoamine oxidase inhibition in the medial preoptic and ventromedial hypothalamic nuclei, suggesting increased turnover [16]. In addition, discrete de pletion of preoptic 5-HT with the neurotoxic indoleamine.…”

mentioning

confidence: 99%

Effects of Opiate Antagonists on Serotonin Turnover and on Luteinizing Hormone and Prolactin Secretion in Estrogen- or Morphine-Treated Rats

Johnson¹,

Crowley

1984

Neuroendocrinology

Self Cite

View full text Add to dashboard Cite

Previous findings indicate that estradiol benzoate (EB) acutely activates serotonergic projections in the medial preoptic area that are stimulatory to prolactin (PRL) secretion. Because opioid agonists also stimulate both PRL release and serotonin (5-HT) turnover, the present experiments tested whether endogenous opioid neurons may mediate estrogen feedback effects. In experiment 1, ovariectomized rats received either 50 µg EB or oil vehicle, and either saline or a long-acting opiate receptor blocker, nalmetrene (10 mg/kg), simultaneously, 3 h prior to decapitation. The pargyline method was used to determine 5-HT turnover; hence members of each treatment group received either saline or pargyline (75 mg/kg i.p.) 30 min prior to decapitation. Plasma PRL and luteineizing hormone (LH) concentrations were determined by radioimmunoassays, and 5-HT concentrations from microdissected, individual brain nuclei were measured by liquid chromatography with electrochemical detection. Nalmetrene blocked both the acute elevation of PRL and the increase in 5-HT turnover in the medial preoptic nucleus and ventromedial nucleus induced by EB. Nalmetrene alone also enhanced LH release and 5-HT turnover in the bed nucleus of the stria terminalis, and these effects were prevented by EB. A second study tested whether the opioid agonist, morphine, mimics estrogen effects on PRL and preoptic 5-HT turnover. Animals received saline, morphine (10 mg/kg i.p.) and/or naloxone (5 mg/kg i.p.) 30 min prior to decapitation. Simultaneously, half in each group received pargyline as above. Morphine stimulated both PRL release and medial preoptic 5-HT turnover, and naloxone prevented both effects. In addition, morphine enhanced 5-HT turnover in the central amygdala, and naloxone increased 5-HT turnover in the bed nucleus of the stria terminalis, and these changes appeared to be related to opioid-induced alterations in LH.

show abstract

Effects of Ovarian Hormones on Norepinephrine and Dopamine Turnover in Individual Hypothalamic and Extrahypothalamic Nuclei

Cited by 107 publications

References 17 publications

Inhibitory Actions of Acute Estradiol Treatment on the Activity and Quantity of Tyrosine Hydroxylase in the Median Eminence of Ovariectomized Rats

Inhibitory Actions of Acute Estradiol Treatment on the Activity and Quantity of Tyrosine Hydroxylase in the Median Eminence of Ovariectomized Rats

Influence of Estradiol and Progesterone on Pulsatile LH Secretion in 8-Day Ovariectomized Rats

Effects of Opiate Antagonists on Serotonin Turnover and on Luteinizing Hormone and Prolactin Secretion in Estrogen- or Morphine-Treated Rats

Contact Info

Product

Resources

About