Ovarian steroids but not the locus coeruleus regulate stress-induced prolactin secretion in female rats

The role of prolactin in the suppression of the response to restraint stress in the lactating mouse

Suppression of the hypothalamic-pituitary-adrenal (HPA) axis is a well-characterised maternal adaptation that limits the exposure of the offspring to maternally-derived stress hormones. This current study has investigated the possible involvement of the lactogenic hormone, prolactin, in this physiologically important adaptation. As expected, circulating prolactin levels were higher in unstressed lactating mice compared to their virgin counterparts. Interestingly however, the ability of an acute period of restraint stress to further elevate prolactin levels was diminished in the former group. The stress-induced rise in prolactin levels in the virgin animals was concurrent with an increase in prolactin receptor activation within the adrenal cortical cells. This adrenal response was not seen in either the stressed or control lactation group, an observation that may be in part explained by the observed downregulation of prolactin receptor mRNA expression within this tissue. Further evidence of suppression of the HPA axis during lactation was revealed using in situ hybridisation to demonstrate that while acute restraint stress increased corticotrophin releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus in both virgin and lactating mice, the magnitude of this response was reduced in the latter group. This potentially adaptive response did not, however, appear to result from the altered prolactin profile during lactation because it was not affected by the pharmacological suppression of prolactin secretion from the pituitary. This study therefore suggests that during lactation the response of the HPA axis to stress is suppressed at multiple physiological levels which are mediated by both prolactin-dependent and prolactin-independent mechanisms.

Estrogen and psychosis - a review and future directions

The link between sex hormones and schizophrenia has been suspected for over a century; however, scientific evidence supporting the pharmacotherapeutic effects of exogenous estrogen has only started to emerge during the past three decades. Accumulating evidence from epidemiological and basic research suggests that estrogen has a protective effect in women vulnerable to schizophrenia. Such evidence has led multiple researchers to investigate the role of estrogen in schizophrenia and its use in treatment. This narrative review provides an overview of the effects of estrogen as well as summarizes the recent work regarding estrogen as a treatment for schizophrenia, particularly the use of new-generation selective estrogen receptor modulators.

Hormonal and neural responses to restraint stress in an animal model of perimenopause in female rats

The present study investigated the hormonal and neural responses to stress in a perimenopause animal model induced by 4-vinylcyclohexene diepoxide (VCD), which induces progressive follicular depletion in rodents, allowing studies on the transition to ovarian failure. Female rats, aged 28 days old, were s.c. injected for 15 consecutive days with corn oil or VCD. At 85 ± 5 days after the onset of treatment, the jugular vein was cannulated in the afternoon of metoestrus and in next morning (dioestrus) at 10.00 am, rats were subjected to 30 minutes of restraint stress. Blood samples were withdrawn before (-5 minutes), during (2, 5, 15 and 30 minutes) and after (45, 60 and 90 minutes) stress and plasma prolactin, progesterone and corticosterone levels were measured. Animals were perfused, brains processed for c-Fos/tyrosine hydroxylase (TH) in the locus coeruleus (LC) and c-Fos/corticotrophin-releasing factor (CRF) in the paraventricular nucleus (PVN). In unstressed rats the density of β-endorphin fibres was assessed in LC and PVN. In VCD-treated rats, stress-induced prolactin peak was higher, basal and peak progesterone levels were lower, and both levels of corticosterone were similar to controls. However, the recovery period was longer for both adrenal hormones. In VCD-treated rats the number of c-Fos/TH and c-Fos/CRF-immunoreactive neurones was higher whereas the density of β-endorphin fibres was lower in LC and PVN. We surmise that the hyperactivity of the LC and PVN neurones in VCD-treated rats may be a result of the lower progesterone levels that resulted in the decrease of β-endorphin content in both nuclei, thus impairing the negative-feedback mechanism in the recovery period.

Potential mechanisms linking psychological stress to bone health

Chronic psychological stress affects many body systems, including the skeleton, through various mechanisms. This review aims to provide an overview of the factors mediating the relationship between psychological stress and bone health. These factors can be divided into physiological and behavioural changes induced by psychological stress. The physiological factors involve endocrinological changes, such as increased glucocorticoids, prolactin, leptin and parathyroid hormone levels and reduced gonadal hormones. Low-grade inflammation and hyperactivation of the sympathetic nervous system during psychological stress are also physiological changes detrimental to bone health. The behavioural changes during mental stress, such as altered dietary pattern, cigarette smoking, alcoholism and physical inactivity, also threaten the skeletal system. Psychological stress may be partly responsible for epigenetic regulation of skeletal development. It may also mediate the relationship between socioeconomic status and bone health. However, more direct evidence is required to prove these hypotheses. In conclusion, chronic psychological stress should be recognised as a risk factor of osteoporosis and stress-coping methods should be incorporated as part of the comprehensive osteoporosis-preventing strategy.

Reduced dopaminergic tone during lactation is permissive to the hypothalamic stimulus for suckling-induced prolactin release

Dopamine from tuberoinfundibular dopaminergic (TIDA) neurones tonically inhibits prolactin (PRL) secretion. Lactational hyperprolactinaemia is associated with a reduced activity of TIDA neurones. However, it remains controversial whether the suckling-induced PRL surge is driven by an additional decrease in dopamine release or by stimulation from a PRL-releasing factor. In the present study, we further investigated the role of dopamine in the PRL response to suckling. Non-lactating (N-Lac), lactating 4 hour apart from pups (Lac), Lac with pups return and suckling (Lac+S), and post-lactating (P-Lac) rats were evaluated. PRL levels were elevated in Lac rats and increased linearly within 30 minutes of suckling in Lac+S rats. During the rise in PRL levels, dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence (ME) and neurointermediate lobe of the pituitary did not differ between Lac+S and Lac rats. However, dopamine and DOPAC were equally decreased in Lac and Lac+S compared to N-Lac and P-Lac rats. Suckling, in turn, reduced phosphorylation of tyrosine hydroxylase in the ME of Lac+S. Domperidone and bromocriptine were used to block and activate pituitary dopamine D2 receptors, respectively. Domperidone increased PRL secretion in both N-Lac and Lac rats, and suckling elicited a robust surge of PRL over the high basal levels in domperidone-treated Lac+S rats. Conversely, bromocriptine blocked the PRL response to suckling. The findings obtained in the present study provide evidence that dopamine synthesis and release are tonically reduced during lactation, whereas dopamine is still functional with respect to inhibiting PRL secretion. However, there appears to be no further reduction in dopamine release associated with the suckling-induced rise in PRL. Instead, the lower dopaminergic tone during lactation appears to be required to sensitise the pituitary to a suckling-induced PRL-releasing factor.

The role of prolactin in co-ordinating fertility and metabolic adaptations during reproduction

Mammalian pregnancy and lactation is accompanied by a period of infertility that takes place in the midst of a sustained increase in food intake. Indeed, successful reproduction in females is dependent on co-ordination of the distinct systems that regulate reproduction and metabolism. Rather than arising from different mechanisms during pregnancy and lactation, we propose that elevations in lactogenic hormones (predominant among these being prolactin and the placental lactogens), are ideally placed to influence both of these systems at the appropriate time. We review the literature examining the impacts of lactogens on fertility and energy homeostasis in the virgin state, during pregnancy and lactation and potential long-term impacts of reproductive experience. Taken together, the literature indicates that duration and pattern of lactogen exposure is a vital factor in the ability of these hormones to alter reproduction and food intake. Transient increases in prolactin, as typically seen in healthy virgin females and males, are unable to exert lasting impacts. Importantly, both suppression of fertility and increased food intake are only observed following exposure to chronically-elevated levels of lactogens. Physiologically, the only time this pattern of lactogenic secretion is maintained in the healthy female is during pregnancy and lactation, when co-ordination between these regulatory systems emerges. This article is part of the special issue on 'Neuropeptides'.

Restraint stress increases prolactin-mediated phosphorylation of signal transducer and activator of transcription 5 in the hypothalamus and adrenal cortex in the male mouse

Prolactin is a pleiotropic peptide hormone produced by the lactotrophs in the anterior pituitary. Its rate of secretion is primarily regulated by a negative-feedback mechanism where prolactin stimulates the activity of the tuberoinfundibular dopaminergic (TIDA) neurones, increasing their release of dopamine, which accesses the pituitary via the median eminence to suppress further prolactin secretion. In addition to its well established role in lactation, circulating prolactin is secreted in response to stress, although the mechanism by which this is achieved or its cellular targets remains unknown. In the present study, we show that 15 minutes of restraint stress causes an approximately seven-fold increase in circulating prolactin concentration in male mice. Monitoring prolactin receptor activation, using immunohistochemistry to determine the level and distribution of tyrosine phosphorylated signal transducer and activator of transcription 5 (pSTAT5), we show that this stress-induced increase in prolactin interacts with both central and peripheral targets. Restraint stress for 15 minutes significantly increased pSTAT5 staining in the arcuate nucleus, median eminence and the zona fasciculata of the adrenal cortex. In each case, this response was prevented by pretreating the animals with bromocriptine to block prolactin secretion from the pituitary. Interestingly, in contrast to many cells in the arcuate nucleus, stress reduced pSTAT5 staining of the TIDA neurones (identified by dual-labelling for tyrosine hydroxylase). This suggests that there is reduced prolactin signalling in these cells and thus potentially a decline in their inhibitory influence on prolactin secretion. These results provide evidence that prolactin secreted in response to acute stress is sufficient to activate prolactin receptors in selected target tissues known to be involved in the physiological adaptation to stress.

Opioid modulation of prolactin secretion induced by stress during late pregnancy. Role of ovarian steroids

BACKGROUND

The opioid system modulates prolactin release during late pregnancy. Its role and the participation of ovarian hormones in this modulation are explored in ether stress-induced prolactin release.

METHODS/RESULTS

Estrous, 3-day and 19-day pregnant rats were used. We administered the antagonist mifepristone (Mp) and tamoxifen to evaluate progesterone and estradiol action in naloxone (NAL, opioid antagonist) or saline treated rats. Ether stress had no effect on serum prolactin levels in controls but increased prolactin release in NAL-treated rats. Prolactin response to stress in NAL-treated rats was blocked by l-DOPA administration. Mp treatment on day 18 of pregnancy increased prolactin levels after stress without alterations by NAL. Tamoxifen on days 14 and 15 of pregnancy completely blocked Mp and NAL effects on prolactin release at late pregnancy. In contrast, stress significantly increased prolactin levels in estrous rats and pretreatment with NAL prevented this. On day 3 of pregnancy, at 6.00 p.m., stress and NAL treatment inhibited prolactin levels in saline-treated rat. No effect of stress or NAL administration was detected on day 3 of pregnancy at 9.00 a.m. icv administration of specific opioids antagonist, B-Funaltrexamine but not Nor-Binaltorphimine or Naltrindole, caused a significant increase in stress-induced prolactin release.

CONCLUSIONS

Opioid system suppression of prolactin stress response during late pregnancy was observed only after progesterone withdrawal, involving a different opioid mechanism from its well-established stimulatory role. This mechanism acts through a mu opioid receptor and requires estrogen participation. The opioid system and progesterone may modulate stress-induced prolactin release, probably involving a putative prolactin-releasing factor.

Prevention of metabolic disorders and reproductive performance deficits by the blockade of Angiotensin II AT1 receptor in female rats fed with cafeteria diet

Besides the well-known detrimental effects of obesity on cardiovascular and metabolic function, studies have shown that obesity is also associated with impaired reproductive function in women. Alterations in Angiotensin II (Ang II) have been associated with obesity and with female reproduction. The aim of the present study was to evaluate the reproductive and metabolic effects of Ang II AT1 receptor blockade with losartan in an animal model of obesity, in which female rats were offered a palatable, high calorie diet from weaning to adulthood. Sexual behavior, ovulation rates and preovulatory levels of the hormones estradiol, progesterone, LH and prolactin were analyzed. Retroperitoneal and perigonadal fat pads, triglycerides and cholesterol (total, HDL and LDL), and insulin resistance were analyzed. Losartan prevented increases in fat pad storage, insulin resistance, as well as triglycerides and LDL levels induced by cafeteria diet intake. Losartan also prevented ovulatory deficits and loss of preovulatory surges of progesterone and LH in cafeteria-fed female rats probably through the prevention of the increase in body weight and body fat. No alterations in sexual behavior were observed. These results suggest, for the first time, that Ang II contributes to the development of the deleterious effects of obesity on preovulatory surges of LH and progesterone and on the reduction of ovulation in obese female rats.

Lactation deficit in OFA hr/hr rats may be caused by differential sensitivity to stress compared with Wistar and Sprague Dawley rats

OFA hr/hr (OFA) rats present a major lactation deficit that impairs offspring survival. To explore whether abnormal stress responsiveness causes this deficit, we compared their hormonal (prolactin, progesterone, and corticosterone) responses to stress (room change and 2-min ether exposure) with those of Wistar and Sprague Dawley (SD) rats. We tested responses during the estrous cycle, pregnancy, lactation, after ovariectomy, and ovarian steroid hormone priming, and responses to suckling. We evaluated hypothalamic expression of receptors for prolactin (PRLRlong) and the isoforms of receptors for progesterone (PRA and B) and estrogen (ERα and β) in late pregnancy. We tested whether administration of an anxiolytic (diazepam) improved lactation. Ether exposure increased circulating levels of the three hormones in the three strains of rats, cycling and ovariectomized, but was less effective in pregnancy and lactation. Elevated estrogen level (estrus and estradiol-treated ovariectomized rats) potentiated the prolactin response more in SD and OFA rats than in Wistar rats. Elevated progesterone level (late pregnancy, lactation, progesterone-treated ovariectomized rats) inhibited the prolactin response less in OFA than in SD or Wistar rats. Ether exposure inhibited the prolactin and oxytocin responses to suckling only in OFA rats. Diazepam treatment increased pup survival rate and the prolactin response to suckling. Hypothalamic total PR mRNA content, assayed by RT-PCR, was higher in pregnant OFA rats compared with SD and Wistar rats, but the PRB/PRA protein ratio determined by Western blot was lowest in Wistar rats, intermediate in OFA rats, and highest in SD rats. The heightened sensitivity to stress of lactating OFA rats may contribute to their lactational deficit and be caused by a combination of hypoprolactinemia and reduced inhibitory capacity of progesterone.

Prolactin in response to acute psychosocial stress in healthy men and women

BACKGROUND

Serum levels of the anterior pituitary hormone prolactin have been reported to increase in response to different types of psychological stressors in humans. However, experimental laboratory stress studies investigating the acute response of prolactin to psychological stress show inconsistent results as increased, as well as decreased or unchanged levels of prolactin have been reported.

OBJECTIVE

The aim of this study was to investigate the effect of acute psychosocial stress on serum concentrations of prolactin in healthy men and women and possible sex differences.

METHOD

Thirty men and 15 women (age 30-50 years) underwent Trier Social Stress Test (TSST), a tool for investigating psychobiological stress responses in a laboratory setting. Blood samples were collected before and directly after the stress test and after 30 min of recovery.

RESULTS

We observed significantly elevated prolactin levels - along with significantly increased plasma adrenocorticotropic hormone (ACTH), serum cortisol, heart rate, systolic blood pressure (SBP), and diastolic blood pressure (DBP) - in response to the stressor. The prolactin response pattern did not differ between men and women, but there was some indication that women might have higher magnitude of response. Large individual differences regarding the magnitude of response were seen in general. The magnitude of the prolactin response was significantly related to the magnitude of the response of the hypothalamic-pituitary-adrenal (HPA) axis and, to some extent, the cardiovascular responses, indicating that individual differences in prolactin response in healthy men and women are dependent on the general physiological stress activation. In women, the magnitude of response was also related to estradiol level.

CONCLUSION

Prolactin does increase in response to psychosocial stress, however, with large individual variation in magnitude of response. The pattern of prolactin response does not differ between men and women. However, there was some indication that women might have higher magnitude of increase than men, and that the magnitude of response in women was dependent on estradiol levels, and this needs to be further studied.

Differential changes in the hypothalamic-pituitary-adrenal axis and prolactin responses to stress in early pregnant mice

Stress can cause pregnancy failure but it is unclear how the mother's neuroendocrine system responds to stress to impair mechanisms establishing implantation. We analysed stress-evoked hypothalamic-pituitary-adrenal (HPA) axis responses in early pregnant mice. HPA axis secretory responses to immune stress in early-mid pregnancy were strong and similar to that in virgins, although activation of hypothalamic vasopressin neurones, rather than corticotrophin-releasing hormone neurones, may be more important in the stress response in pregnancy. The site and mode of detrimental glucocorticoid action in pregnancy is not established. Because circulating prolactin is important for progesterone secretion and pregnancy establishment, we also hypothesised that stress negatively impacts on prolactin and its neuroendocrine control systems in early pregnant mice. Basal prolactin secretion was profoundly inhibited by either immune or fasting stress in early pregnancy. Prolactin release is inhibited by tonic dopamine release from tuberoinfundibular (TIDA) neurones. However, immune stress did not increase TIDA neurone activity in the median eminence in pregnant mice [measured by 3,4-dihydroxyphenylacetic acid (DOPAC) content and the DOPAC:dopamine ratio]. By contrast, both immune stress and fasting caused weak induction of Fos in TIDA neurones. However, Fos induction does not always reflect dopamine secretion. Taken together, the data suggest that the stress-evoked profound reduction in prolactin secretion does not involve substantially increased dopamine activity as anticipated. In pregnancy, there was also attenuated recruitment of parvocellular paraventricular nucleus neurones and increased activation of brainstem noradrenergic nuclei after immune stress, indicating that other mechanisms may be involved in the suppression of prolactin secretion. In summary, low prolactin and increased circulating glucocorticoids together may partly explain how a mother's endocrine system mediates stress-induced pregnancy failure.

Neuroendocrine control of maternal stress responses and fetal programming by stress in pregnancy

The major changes in highly dynamic neuroendocrine systems that are essential for establishing and maintaining pregnancy are outlined from studies on rodents. These changes optimise the internal environment to provide the life support system for the placenta, embryo and fetus. These include automatic prevention of further pregnancy, blood volume expansion, increased appetite and energy storage. The brain regulates these changes, in response to steroid (estrogens, progesterone) and peptide (lactogens, relaxin) hormone signals. Activation of inhibitory endogenous opioid mechanisms in the brain in late pregnancy restrains premature secretion of oxytocin, and attenuates hypothalamo-pituitary-adrenal (HPA) responses to stress. This opioid mechanism is activated by allopregnanolone, a neuroactive progesterone metabolite. The significance of reduced HPA axis responses in shifting maternal metabolic balance, and in protecting the fetuses from adverse programming of HPA axis stress responsiveness and anxious behaviour in later life is critically discussed. Experimental studies showing sex-dependent fetal programming by maternal stress or glucocorticoid exposure in late pregnancy are reviewed. The possibility of over-writing programming in offspring through neurosteroid administration is discussed. The impact of maternal stress on placental function is considered in the context of reconciling studies that show offspring programming by stress in very early or late pregnancy produce similar phenotypes in the offspring.

Baby on board: do responses to stress in the maternal brain mediate adverse pregnancy outcome?

Stress and adverse environmental surroundings result in suboptimal conditions in a pregnant mother such that she may experience poor pregnancy outcome including complete pregnancy failure and preterm labor. Furthermore her developing baby is at risk of adverse programming, which confers susceptibility to long term ill health. While some mechanisms at the feto-maternal interface underlying these conditions are understood, the underlying cause for their adverse adaptation is often not clear. Progesterone plays a key role at many levels, including control of neuroendocrine responses to stress, procuring the required immune balance and controlling placental and decidual function, and lack of progesterone can explain many of the unwanted consequences of stress. How stress that is perceived by the mother inhibits progesterone secretion and action is beginning to be investigated. This overview of maternal neuroendocrine responses to stress throughout pregnancy analyses how they interact to compromise progesterone secretion and precipitate undesirable effects in mother and offspring.

Ovarian-steroid modulation of locus coeruleus activity in female rats: involvement in luteinising hormone regulation

The noradrenergic nucleus locus coeruleus (LC) has been reported to regulate luteinising hormone (LH) secretion in female rats. Both oestrogen and progestin receptors have been demonstrated in LC neurones, suggesting that these cells are possibly responsive to variations in circulating levels of ovarian steroids. We therefore evaluated changes in the activity of LC neurones during the oestrous cycle and after ovarian-steroid treatment in ovariectomised (OVX) rats, as determined by immunoreactivity to Fos-related antigens (FRA), which comprises all of the known members of the Fos family. Effects of ovarian steroids on the firing rate of LC neurones were also determined in a slice preparation. The number of FRA/tyrosine hydroxylase (TH)-immunoreactive (ir) neurones in the LC increased from 14.00-16.00 h on pro-oestrus, coinciding with the onset of the LH surge and rise in plasma progesterone. FRA immunoreactivity was unaltered during dioestrus. Oestradiol-treated OVX rats (OVX+E) displayed marked reduction in FRA/TH-ir neurones in LC compared to oil-treated OVX rats. Accordingly, oestradiol superfusion significantly reduced the spontaneous firing rate of LC neurones in slices from OVX rats. Compared to OVX+E, oestradiol-treated rats injected with progesterone at 08.00 h (OVX+EP) exhibited higher number of FRA/TH-ir neurones in the LC at 10.00 h and 16.00 h, and great amplification of the LH surge. Bath application of progesterone significantly increased the spontaneous firing rate of OVX+E LC neurones. Our data suggest that ovarian steroids may physiologically modulate the activity of LC neurones in females, with possible implications for LH secretion. Moreover, oestradiol and progesterone appear to exert opposite and complementary effects (i.e. whereas oestradiol inhibits, progesterone, after oestradiol priming, stimulates LC activity).

Modulatory role of locus coeruleus and estradiol on the stress response of female rats

The activity of the hypothalamic-pituitary-adrenal axis is modulated by the norepinephrinergic system and, in females, also by the ovarian hormones. We investigated the role of ovarian steroids and the locus coeruleus (LC) on stress-induced corticosterone secretion in female rats. Ovariectomized rats without hormonal replacement (OVX) or treated with estradiol (OVE) or estradiol plus progesterone (OVEP) were subjected to jugular cannulation. Immediately after that, each hormonal treatment group was subjected to LC lesion or sham surgery or no brain surgery. After 24 h, blood samples of all 9 groups were collected before and after ether inhalation. Other four groups (OVX control, sham and lesioned, and OVE) were perfused for glucocorticoid receptor (GR) immunocytochemistry in hippocampal CA1 neurons and paraventricular nucleus (PVN). Estradiol replacement decreased while LC lesions increased stress-induced corticosterone secretion. The effect of LC lesion was potentiated with the removal of ovarian steroids. Since GR expression of lesioned animals decreased in the hippocampus, but not in PVN, we suggest that the effect of LC lesion on corticosterone secretion could be due to a reduction in the efficiency of the negative feedback system in the CA1 neurons. However, this mechanism is not involved in the estradiol modulation on corticosteroid secretion, as no change in GR expression was observed in estradiol-treated animals.

GABAergic mediation of stress-induced secretion of corticosterone and oxytocin, but not prolactin, by the hypothalamic paraventricular nucleus

The hypothalamus-pituitary-adrenal axis (HPA) participates in mediating the response to stressful stimuli. Within the HPA, neurons in the medial parvocellular region of paraventricular nucleus (PVN) of the hypothalamus integrate excitatory and inhibitory signals triggering secretion of corticotropin-releasing hormone (CRH), the main secretagogue of adrenocorticotropic hormone (ACTH). Stressful situations alter CRH secretion as well as other hormones, including prolactin and oxytocin. Most inputs to the PVN are of local origin, half of which are GABAergic neurons, and both GABA-A and GABA-B receptors are present in the PVN. The objective of the present study was to investigate the role of GABA-A and GABA-B receptors in the PVN's control of stress-induced corticosterone, oxytocin and prolactin secretion. Rats were microinjected with saline or different doses (0.5, 5 and 50 pmol) of GABA-A (bicuculine) or GABA-B (phaclofen) antagonists in the PVN. Ten minutes later, they were subjected to a stressor (ether inhalation) and blood samples were collected 30 min before and 10, 30, 60, 90 and 120 min after the stressful stimulus to measure hormone levels by radioimmunoassay. Our results indicate that GABA acts in the PVN to inhibit stress-induced corticosterone secretion via both its receptor subtypes, especially GABA-B. In contrast, GABA in the PVN stimulates oxytocin secretion through GABA-B receptors and does not alter prolactin secretion.

Locus coeruleus mediates cold stress-induced polycystic ovary in rats

Previous reports about the rat ovary have shown that cold stress promotes ovarian morphological alterations related to a polycystic ovary (PCO) condition through activation of the ovarian sympathetic nerves. Because the noradrenergic nucleus locus coeruleus (LC) is activated by cold stress and synaptically connected to the preganglionic cell bodies of the ovarian sympathetic pathway, this study aimed to evaluate the LC's role in cold stress-induced PCO in rats. Ovarian morphology and endocrine and sympathetic functions were evaluated after 8 wk of chronic intermittent cold stress (4 C, 3 h/d) in rats with or without LC lesion. The effect of acute and chronic cold stress upon the LC neuron activity was confirmed by Fos protein expression in tyrosine hydroxylase-immunoreactive neurons. Cold stress induced the formation of follicular cysts, type III follicles, and follicles with hyperthecosis alongside increased plasma estradiol and testosterone levels, irregular estrous cyclicity, and reduced ovulation. Considering estradiol release in vitro, cold stress potentiated the ovarian response to human chorionic gonadotropin. Ovarian norepinephrine (NE) was not altered after 8 wk of stress. However, LC lesion reduced NE activity in the ovary of cold-stressed rats, but not in controls, and prevented all the cold stress effects evaluated. Cold stress increased the number of Fos/tyrosine hydroxylase-immunoreactive neurons in the LC, but this effect was more pronounced for acute stress as compared with chronic stress. These results show that cold stress promotes PCO in rats, which apparently depends on ovarian NE activity that, under this condition, is regulated by the noradrenergic nucleus LC.