Catecholamine turnover rates in discrete hypothalamic areas and associated changes in median eminence luteinizing hormone-releasing hormone and serum gonadotropins on proestrus and diestrous day 1

Brainstem Noradrenergic Neuronal Populations: Dual Effects on Regulating GnRH and LH Secretion

Noradrenergic neurons are a brain network that integrate viscero-sensorial signals to modulate neural and neuroendocrine function. Although it has been known for decades that noradrenergic neural circuits influence neuroendocrine and reproductive function, the cellular and molecular players involved remain largely unknown. The objective of this review is to summarize past and current knowledge regarding the influence of brainstem noradrenergic systems on GnRH and gonadotrophin secretion. The main noradrenergic cell groups A1, A2, and A6, known as the ventrolateral medulla, nucleus of the solitary tract, and locus coeruleus, respectively, are involved in the control of reproductive neuroendocrine secretion. Current evidence suggests that brainstem noradrenergic circuits promote the generation and maintenance of the LH surge in both spontaneous (rats, sheep) and induced (rabbit, ferret) ovulators. In contrast, recent studies have established that LH pulsatile secretion is suppressed by specific activation of brainstem noradrenergic cell groups. The duality of the GnRH/LH response to noradrenaline reflects the inherent complexity of hindbrain noradrenaline neurons, which are responsive to stressors and gonadal steroids (ie, estradiol) and coexpress a variety of neurotransmitters and neuropeptides. Therefore, elucidating the organization and functionality of brainstem noradrenergic systems will provide targets for controlling reproduction and understanding the interconnection with stress.

Estrous cycle influences excitatory amino acid transport and visceral pain sensitivity in the rat: effects of early-life stress

Background

Early-life stress (ELS) is a recognized risk factor for chronic pain disorders, and females appear to be more sensitive to the negative effects of stress. Moreover, estrous cycle-related fluctuations in estrogen levels have been linked with alternating pain sensitivity. Aberrant central circuitry involving both the anterior cingulate cortex (ACC) and the lumbosacral spinal cord has also been implicated in the modulation of visceral pain in clinical and preclinical studies. Here we further investigate changes in visceral pain sensitivity and central glutamatergic systems in rats with respect to estrous cycle and ELS.

Methods

We investigated visceral sensitivity in adult female Sprague-Dawley rats, which had undergone maternal separation (MS) in early life or remained non-separated (NS), by performing colorectal distension (CRD). We also assessed excitatory amino acid uptake through excitatory amino acid transporters (EAATs) in the lumbosacral spinal cord and ACC.

Results

NS animals in proestrus and estrus exhibited reduced EAAT uptake and decreased threshold to CRD. Moreover, total pain behaviors were increased in these stages. MS rats exhibited lower pain thresholds and higher total pain behaviors to CRD across all stages of the estrous cycle. Interestingly, cortical EAAT function in MS rats was inhibited in the low estrogen state—an effect completely opposite to that seen in NS rats.

Conclusions

This data confirms that estrous cycle and ELS are significant factors in visceral sensitivity and fluctuations in EAAT function may be a perpetuating factor mediating central sensitization.

Sexual differentiation of the gonadotropin surge release mechanism: a new role for the canonical NfκB signaling pathway

Sex differences in luteinizing hormone (LH) release patterns are controlled by the hypothalamus, established during the perinatal period and required for fertility. Female mammals exhibit a cyclic surge pattern of LH release, while males show a tonic release pattern. In rodents, the LH surge pattern is dictated by the anteroventral periventricular nucleus (AVPV), an estrogen receptor-rich structure that is larger and more cell-dense in females. Sex differences result from mitochondrial cell death triggered in perinatal males by estradiol derived from aromatization of testosterone. Herein we provide an historical perspective and an update describing evidence that molecules important for cell survival and cell death in the immune system also control these processes in the developing AVPV. We conclude with a new model proposing that development of the female AVPV requires constitutive activation of the Tnfα, Tnf receptor 2, NfκB and Bcl2 pathway that is blocked by induction of Tnf receptor-associated factor 2-inhibiting protein (Traip) in the male.

Noradrenergic nuclei that receive sensory input during mating and project to the ventromedial hypothalamus play a role in mating-induced pseudopregnancy in the female rat

In female rats, vaginal-cervical stimulation (VCS) received during mating induces bicircadian prolactin surges that are required for the maintenance of pregnancy or pseudopregnancy (PSP). The neural circuits that transmit VCS inputs to the brain have not been fully described, although mating stimulation is known to activate medullary noradrenergic cell groups that project to the forebrain. In response to VCS, these neurones release noradrenaline within the ventrolateral division of the ventromedial hypothalamus (VMHvl) and the posterodorsal medial amygdala (MePD), two forebrain sites that are implicated in the initiation of PSP. Noradrenaline receptor activation within the VMHvl is both necessary and sufficient for PSP induction, suggesting that noradrenaline acting within the VMHvl is particularly important in mediating the effects of VCS towards the establishment of PSP. We therefore investigated whether or not endogenous, VCS-induced noradrenaline release within the VMHvl is involved in PSP induction in the rat. Before the receipt of sufficient mating stimulation to induce PSP, a retrograde neurotoxin, dopamine-β-hydroxylase-saporin (DBH-SAP), was infused bilaterally into the either the VMHvl or the MePD to selectively destroy afferent noradrenergic nuclei in the brainstem. DBH-SAP infusions into the VMHvl lesioned mating-responsive noradrenergic neurones in A1 and A2 medullary nuclei and reduced the incidence of PSP by 50%. Infusions of DBH-SAP into the MePD had no effect on the subsequent induction of PSP. These results suggest that VCS is conveyed to mating-responsive forebrain areas by brainstem noradrenergic neurones, and that the activity of noradrenergic cells projecting to the VMHvl is involved in the induction of PSP.

Noradrenaline involvement in the negative-feedback effects of ovarian steroids on luteinising hormone secretion

Noradrenaline has been shown to modulate the ovarian-steroid feedback on luteinising-hormone (LH) release. However, despite the high amount of evidence accumulated over many years, the role of noradrenaline in LH regulation is still not clearly understood. The present study aimed to further investigate the involvement of noradrenaline in the negative-feedback effect of oestradiol and progesterone on basal LH secretion. In experiment 1, ovariectomised (OVX) rats received a single injection of oil, oestradiol, or progesterone at 09.00-10.00 h and were decapitated 30 or 60 min later. Levels of noradrenaline and its metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), were determined in microdissections of the preoptic area (POA) and medial basal hypothalamus-median eminence (MBH-ME) and correlated with LH secretion. Basal LH levels were decreased 30 and 60 min after oestradiol or progesterone injection, and this hormonal response was significantly correlated with a reduction in POA MHPG levels, which reflect noradrenaline release. In addition, noradrenaline levels in the POA were increased, whereas noradrenaline turnover (MHPG/noradrenaline ratio) was decreased 60 min after the injection of both hormones. No effect was found in the MBH-ME. In experiment 2, i.c.v. administration of noradrenaline (60 nmol), performed 15 min before oestradiol or progesterone injection in jugular vein-cannulated OVX rats, completely prevented the ovarian steroid-induced inhibition of LH secretion. The data obtained provide direct evidence that LH secretion in OVX rats is positively regulated by basal noradrenergic activity in the POA, and its reduction appears to play a role in the negative-feedback effect of ovarian steroids on LH secretion in vivo.

Intravenous luteinizing hormone-releasing hormone has no effect on serum N-terminal pro-brain natriuretic peptide in children and adolescents

BACKGROUND

Little is known about the acute effects of i.v. luteinizing hormone-releasing hormone (LHRH) on the heart function, therefore the aim of the present study was to measure N-terminal pro-brain natriuretic peptide (N-BNP) in children, who underwent a diagnostic work up for short stature or delayed puberty.

METHODS

N-BNP was measured in 52 children before and after administration of LHRH. Serum N-BNP obtained from 255 healthy children and adolescents (aged birth-18.3 years) served as a reference.

RESULTS

There was no significant difference between baseline N-BNP of children who underwent the LHRH diagnostic test and their healthy peers. There was no significant serum N-BNP level change before or after administration of LHRH (59 +/- 36 pg/mL vs 58 +/- 34 pg/mL). N-BNP fell from 399 +/- 425 pg/mL in newborns and reached 44 +/- 36 pg/mL in children aged 12-18 years.

CONCLUSION

Short stature or delayed puberty had no effect on heart function determined by serum N-BNP; i.v. LHRH does not acutely influence the level of serum N-BNP.

The role of the brain in female reproductive aging

In middle-aged women, follicular depletion is a critical factor mediating the menopausal transition; however, all levels of the hypothalamic-pituitary-gonadal (HPG) axis contribute to the age-related decline in reproductive function. To help elucidate the complex interactions between the ovary and brain during middle-age that lead to the onset of the menopause, we utilize animal models which share striking similarities in reproductive physiology. Our results show that during middle-age, prior to any overt irregularities in estrous cyclicity, the ability of 17beta-estradiol (E(2)) to modulate the cascade of neurochemical events required for preovulatory gonadotropin-releasing hormone (GnRH) release and a luteinizing hormone (LH) surge is diminished. Middle-aged female rats experience a delay in and an attenuation of LH release in response to E(2). Additionally, although we do not observe a decrease in GnRH neuron number until a very advanced age, E(2)-mediated GnRH neuronal activation declines during the earliest stages of age-related reproductive decline. Numerous hypothalamic neuropeptides and neurochemical stimulatory inputs (i.e., glutamate, norepinephrine (NE), and vasoactive intestinal peptide (VIP)) that drive the E(2)-mediated GnRH/LH surge appear to dampen with age or lack the precise temporal coordination required for a specific pattern of GnRH secretion, while inhibitory signals such as gamma-aminobutyric acid (GABA) and opioid peptides remain unchanged or elevated during the afternoon of proestrus. These changes, occurring at the level of the hypothalamus, lead to irregular estrous cycles and, ultimately, the cessation of reproductive function. Taken together, our studies indicate that the hypothalamus is an important contributor to age-related female reproductive decline.

Phosphorylation state of tyrosine hydroxylase in the stalk-median eminence is decreased by progesterone in cycling female rats

Progesterone has the capacity to suppress hypothalamic dopaminergic neuronal activity on proestrous afternoon and prolong or amplify the preovulatory prolactin surge in rats. In the present study, we examined enzyme activity and phosphorylation state of tyrosine hydroxylase (TH) in the stalk-median eminence of cycling female rats on proestrus and estrus and related these to circulating progesterone levels. Phospho-TH levels were evaluated by Western blot analysis. TH activity was determined from the rate of 3,4-dihydroxyphenylalanine (DOPA) accumulation. Phospho-TH levels at Ser-19, Ser-31, and Ser-40 were similar at 1100, 1300, and 1500 h on proestrus but declined at 1700, 1900, and 2200 h, coincident with rising serum progesterone levels. Similarly, DOPA accumulation was 30-50% lower at 1700, 1900, and 2200 h as compared with 1100-1500 h on proestrus. Ser-31 and Ser-40 phosphorylation states were increased by 1100 h on estrus to a level similar to 1100 h on proestrus, whereas DOPA accumulation was 30% greater on estrous as compared with proestrous morning. There were no significant differences among the several time points on proestrus and estrus with regard to TH protein or beta-tubulin levels. Exogenous progesterone administration (7.5 mg/kg, sc) before the preovulatory progesterone surge decreased TH activity and phospho-TH at Ser-19, Ser-31, and Ser-40, accompanied by premature increased serum prolactin. Our study suggests that decreased TH phosphorylation at Ser-19, Ser-31, and Ser-40 contributes to the decline in TH activity in the stalk-median eminence on proestrous afternoon and that progesterone may cause this initial cytoplasmic response of TH dephosphorylation.

Knockdown of clock genes in the suprachiasmatic nucleus blocks prolactin surges and alters FRA expression in the locus coeruleus of female rats

The nature of the circadian signal from the suprachiasmatic nucleus (SCN) required for prolactin (PRL) surges is unknown. Because the SCN neuronal circadian rhythm is determined by a feedback loop of Period (Per) 1, Per2, and circadian locomotor output cycles kaput (Clock) gene expressions, we investigated the effect of SCN rhythmicity on PRL surges by disrupting this loop. Because lesion of the locus coeruleus (LC) abolishes PRL surges and these neurons receive SCN projections, we investigated the role of SCN rhythmicity in the LC neuronal circadian rhythm as a possible component of the circadian mechanism regulating PRL surges. Cycling rats on proestrous day and estradiol-treated ovariectomized rats received injections of antisense or random-sequence deoxyoligonucleotide cocktails for clock genes (Per1, Per2, and Clock) in the SCN, and blood samples were taken for PRL measurements. The percentage of tyrosine hydroxylase-positive neurons immunoreactive to Fos-related antigen (FRA) was determined in ovariectomized rats submitted to the cocktail injections and in a 12:12-h light:dark (LD) or constant dark (DD) environment. The antisense cocktail abolished both the proestrous and the estradiol-induced PRL surges observed in the afternoon and the increase of FRA expression in the LC neurons at Zeitgeber time 14 in LD and at circadian time 14 in DD. Because SCN afferents and efferents were probably preserved, the SCN rhythmicity is essential for the magnitude of daily PRL surges in female rats as well as for LC neuronal circadian rhythm. SCN neurons therefore determine PRL secretory surges, possibly by modulating LC circadian neuronal activity.

Neural control of the synthesis and release of luteinizing hormone-releasing hormone

Preovulatory surges of luteinizing hormone (LH) depend upon neurotransmitter activation of neurons that secrete LH-releasing hormone (LHRH, gonadotropin-releasing hormone GnRH) and noradrenaline plays a pivotal role in this critical event. The interaction is amongst noradrenaline and other neurotransmitters such as GABA (gamma-aminobutyric acid), opiates, serotonin and excitatory amino acids (N-methyl-D-aspartate, NMDA) on LHRH neuronal activity are complex. GABA and opiates suppress the presynaptic release of noradrenaline but only GABA also directly affects the responsiveness of LHRH neurons to noradrenaline. Morphine induces the release of serotonin which either directly or indirectly via other neurotransmitters (e.g. dopamine) sensitizes LHRH neurons to the stimulatory effects of noradrenaline. NMDA rapidly induces LH release but whether this drug directly affects the activity of LHRH neurons is not known. The neuronal release of LHRH is modulated by the action of oestrogen on these various neurotransmitter systems. Antioestrogens, when placed into the medial preoptic area of otherwise completely oestrogenized rats, block LH surges; LHRH mRNA levels in such animals resemble those in 9-day castrated rats. Normally, LHRH message levels increase about the time of increased noradrenaline secretion just before the LH surge. NMDA rapidly releases LH and LHRH mRNA levels are significantly raised within 15 minutes and remain so over the next 45 minutes. Thus, it seems that stimuli which evoke LHRH release also increase LHRH mRNA transcription to replenish the hormone released during the LH surge.

Noradrenaline release in the medial preoptic area during the rat oestrous cycle: temporal relationship with plasma secretory surges of prolactin and luteinising hormone

During the rat oestrous cycle, the afternoon of pro-oestrous is characterised by preovulatory surges of luteinising hormone (LH) and prolactin. On the afternoon of oestrous, a secretory surge of prolactin has also been reported. Because the medial preoptic area (MPOA) is known to regulate prolactin and LH secretory surges and noradrenaline has been demonstrated to stimulate these hormones release, we evaluated whether noradrenaline release in the MPOA was temporally associated with plasma prolactin and LH surges in cycling rats. During the 4 days of oestrous cycle, noradrenaline concentrations were determined in microdialysates from the MPOA, collected at 30-min intervals from 10.30 h to 19.00 h. Plasma prolactin and LH levels were measured in blood samples withdrawn hourly from 14.00 h to 19.00 h on pro-oestrous and from 13.00 h to 18.00 h on the other days of the cycle. On the afternoons of both pro-oestrous and oestrous, noradrenaline levels increased at 14.00 h and remained elevated until 16.30 h. Conversely, they were low and constant throughout metoestrous and dioestrous. Correlating with noradrenaline release in the MPOA, plasma prolactin surges occurred during the afternoons of both pro-oestrous and oestrous. On pro-oestrous, the afternoon LH surge was also preceded by the increase in MPOA noradrenaline whereas, during oestrous, LH secretion was low and unaltered. A temporal association between noradrenaline release and prolactin secretion suggests that noradrenergic neurotransmission in the MPOA regulates prolactin surges in female rats. Moreover, our data also suggest that MPOA noradrenaline requires specific conditions to physiologically regulate LH secretion, which seems to occur during the afternoon of pro-oestrous.

HPA function in adolescence: Role of sex hormones in its regulation and the enduring consequences of exposure to stressors

The hypothalamic-pituitary-adrenal (HPA) axis is one of the physiological systems involved in coping with stressors. There are functional shifts in the HPA axis and its regulation by sex hormones over the lifespan that allow the animal to meet the challenges of the internal and external environment that are specific to each stage of development. Sex differences in HPA function emerge over adolescence, a phenomenon reflecting the concomitant initiation of regulatory effects of sex hormones. The focus of this review is recent research on differences between adolescents and adults in HPA function and the enduring effects of exposure to stressors in adolescence. During adolescence, HPA function is characterized by a prolonged activation in response to stressors compared to adulthood, which may render ongoing development of the brain vulnerable. Although research has been scarce, there is a growing evidence that exposure to stressors in adolescence may alter behavioural responses to drugs and cognitive performance in adulthood. However, the effects reported appear to be stressor-specific and sex-specific. Such research may contribute toward understanding the increased risk for drug abuse and psychopathology that occurs over adolescence in people.

Locus coeruleus norepinephrine regulates the surge of prolactin during oestrus

A secondary surge of prolactin has been recently characterised on the afternoon of oestrus. Because the noradrenergic nucleus locus coeruleus participates in the genesis of the pro-oestrous and steroid-induced surges of prolactin, the aim of the present study was to investigate the importance of locus coeruleus norepinephrine in the generation of the prolactin surge of oestrus. For this purpose, we initially re-evaluated the profile of prolactin secretion during the oestrous cycle to verify whether this surge of prolactin was physiological and specific to the day of oestrus. Thereafter, the following were evaluated: (i) the effect of locus coeruleus lesion on the secondary surge of prolactin and on norepinephrine concentration in the medial preoptic area (MPOA), medial basal hypothalamus (MBH) and paraventricular nucleus (PVN) during the day of oestrus and (ii) locus coeruleus neurones activity during the same day by Fos immunoreactivity. Locus coeruleus lesion completely blocked the prolactin surge of oestrus in all rats studied and also significantly reduced norepinephrine concentration in the MPOA, MBH and PVN during the day of oestrus. The number of double-labelled tyrosine hydroxylase/Fos immunoreactive neurones in locus coeruleus was significantly higher at 14.00 h of oestrus, suggesting an increase in its activity preceding the prolactin surge that generally occurs at 15.00 h. Therefore, the increase in locus coeruleus activity on the afternoon of oestrus supports the data obtained with bilateral lesion of this nucleus, suggesting a stimulatory role of locus coeruleus norepinephrine in the genesis of the secondary surge of prolactin.

Evidence that projections from the bed nucleus of the stria terminalis and from the lateral and medial regions of the preoptic area provide input to gonadotropin releasing hormone (GNRH) neurons in the female sheep brain

The arcuate nucleus/ventromedial hypothalamic nucleus (ARC/VMH) region is thought to relay estrogen feedback signals to gonadotropin-releasing hormone (GnRH) cells in the sheep brain. This region sends major projections to the lateral preoptic area (lPOA), ventral bed nucleus of the stria terminals (vBnST) and the ventro-caudal division of the median preoptic nucleus (vcMePON) with little direct input to GnRH cell bodies, suggesting interneuronal relay to GnRH neurons. The brain stem also provides input to the POA. The present study aimed to identify possible relay circuits in the POA and BnST to GnRH neurons. Biotinylated dextran amine (BDA) was injected into lPOA (n=6), vBnST (n=2), vcMePON (n=3) and periventricular nucleus (PeriV; n=1) of ewes for anterograde tracing. GnRH immunoreactive (IR) perikarya appearing to receive input from BDA-containing varicosities were identified by fluorescence microscopy, with further analysis by confocal microscopy. When BDA was injected into rostral and caudal regions of lPOA (n=3), no tracer-filled varicose fibers were found in contact with GnRH-IR perikarya. Injections into the center of the lPOA (n=3) indicated direct projections to GnRH-IR cells. Injections into the vBnST, vcMePON and PeriV indicated that cells of these regions also provide input to GnRH cells. BDA-containing varicosities found in the MPOA were immunoreactive for NPY or were GABAergic or glutamatergic when the tracer was injected into vBnST and lPOA, but not when injections were placed in the vcMePON. With injection into the PeriV, tracer-filled varicosities in the MPOA were not immunoreactive for somatostatin or enkephalin. Injection of FluoroGold into ventral POA retrogradely labeled cells in the above mentioned areas, but few were also immunoreactive for estrogen receptor-alpha. Thus, cells of the vBnST, lPOA, vcMePON and PeriV project to GnRH neurons. These cells may provide an interneuronal route to GnRH neurons from the ARC/VMH, the brain stem and other regions of the brain.

Role of the locus coeruleus in the prolactin secretion of female rats

Since locus coeruleus (LC) lesion blocks preovulatory prolactin surge, the aim of this study was to determine if this lesion would also block prolactin surges induced by steroids in ovariectomized rats and would modify basal prolactin secretion. To determine the time of the steroid-induced prolactin surges, ovariectomized rats treated with estradiol (OVE) or estradiol and progesterone (OVEP) were cannulated at 08:00 h and blood samples were collected hourly between 14:00 and 18:00 h. Ovariectomized rats treated with oil (OV-Oil) were used as control. Prolactin peaked at 16:00 h in OVE rats and at 15:00 h in OVEP. In a second experiment, male rats, cycling rats, OVE, OVEP, and OV-Oil groups were cannulated at 08:00 h, followed by LC lesion or sham-surgery. Blood samples were withdrawn at times of basal and peak prolactin levels. LC lesion blocked afternoon prolactin surges of OVE, OVEP and proestrus rats. However, the low levels observed at 16:00 h in OV-Oil, diestrus and male rats as well as at 11:00 h in OVE, OVEP, estrus, and proestrus rats were not modified by LC lesion. The high prolactin levels observed on estrus afternoon were dramatically reduced by LC lesion. Data suggest that LC neurons are important for steroid-induced prolactin surge genesis, but not for prolactin basal secretion.

LHRH release depends on Locus Coeruleus noradrenergic inputs to the medial preoptic area and median eminence

We tested the hypothesis that Locus Coeruleus (LC) inputs to the medial preoptic area (MPOA) and median eminence (ME) are essential for gonadotropin release. Proestrus and ovariectomized (OVX) rats were decapitated at 16:00 h. LC electrolytic lesion was performed at 11:00 h during proestrus and 24h before decapitation in OVX rats. Plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured and MPOA and ME were microdissected for LHRH content measurement. In addition, FOS protein in LC and MPOA were studied in proestrus and OVX rats at 12:00, 15:00, and 17:00 h. On proestrus, LC lesion blocked the LH surge and only decreased plasma FSH; in OVX rats the lesion induced only a slight decrease on plasma LH without affecting FSH secretion. An increased content of LHRH in the MPOA and ME of both groups accompanied the decreases of plasma LH. In proestrus, the number of FOS-immunoreactive (FOS-ir) neurons increased from 12:00 to 17:00 h in the LC and MPOA. In OVX rats, there was an increase at 15:00 h in the LC and a decrease at 17:00 h in both areas. The number of FOS-ir neurons was lower in OVX than in proestrus animals. Thus, LC (1) is responsible, at least in part, for gonadotropin release through the activation of LHRH neurons, (2) is more closely related to the positive than the negative feedback, and (3) seems to show an intrinsic cyclic activity which is amplified by ovarian steroids.

Effects of interleukin-1 beta on the steroid-induced luteinizing hormone surge: role of norepinephrine in the medial preoptic area

Interleukin-1beta (IL-1beta), a cytokine, is known to inhibit the preovulatory surge of luteinizing hormone (LH); however, the mechanism by which it does so is unclear. This study was done to see if this effect is mediated through hypothalamic catecholamines. Adult female Sprague-Dawley rats were ovariectomized and implanted with a push-pull cannula in the medial preoptic area (MPA) of the hypothalamus. They were injected subcutaneously with 30 microg of Estradiol on the day 8 after surgery and with 2mg of Progesterone on day 10 at 1000 h. On the day of perfusion (day 10), the rats were injected with IL-1beta or its vehicle at 1300 h. Perfusate samples from the MPA and blood samples from a jugular catheter were collected from 1300 to 1800 h. Catecholamine concentrations in the perfusate were measured using high performance liquid chromatography (HPLC)-EC and LH levels in the serum using RIA. Norepinephrine release in the MPA of control rats increased significantly at 1530, 1600, and 1630 h paralelling an increase in LH at 1600 h. In contrast, IL-1beta treatment blocked the LH surge and the rise in norepinephrine release in the MPA. No changes were observed in dopamine release, both in control and IL-treated animals. These results demonstrate for the first time that IL-induced suppression of the LH surge is probably mediated through inhibition of norepinephrine release in the MPA.

Lack of effects of acute estradiol on mood in postmenopausal women

Chronic treatment with estrogen is believed to improve mood in postmenopausal women, and recent preclinical evidence suggests that estradiol may also affect mood and behavior through acute neuronal membrane-mediated effects on the central nervous system. This study was designed to characterize potential mood effects of single doses of transdermal estradiol in healthy postmenopausal women who were not taking hormone replacement therapy (HRT). Twelve women participated in a five-session, within-subjects, double-blind study, in which they received placebo, transdermal estradiol (0.2, 0.4, and 0.8 mg), or D-amphetamine (15 mg, oral) in a randomized order. Amphetamine was included as a positive control. Dependent measures included self-report measures of mood, physiological measures, and plasma hormone levels. Despite dose-dependent increases in plasma estradiol levels, and despite the fact that D-amphetamine produced its prototypic stimulant-like effects in these postmenopausal women, estradiol did not produce effects on mood. The finding that acute administration of exogenous estradiol did not alter mood suggests that more chronic exposure to estradiol is needed to produce mood-enhancing effects.

Catecholaminergic axons innervate LH-releasing hormone immunoreactive neurons of the human diencephalon

Catecholamines have been shown to modulate gonadal functions via interactions with hypothalamic LH-releasing hormone (LHRH)-synthesizing neurons. To reveal the morphological background of this phenomenon, the distribution of LHRH neurons and tyrosine hydroxylase (TH)-immunoreactive (IR), catecholaminergic structures were mapped in the human diencephalon. First, the location of LHRH and TH-IR neuronal elements was analyzed, and then the relationship between the two different systems was examined. The LHRH-IR cell bodies were mainly present in the medial preoptic and infundibular areas. The TH-IR perikarya were located in the periventricular, paraventricular, and supraoptic hypothalamic nuclei and also in the median eminence. The TH-IR fibers were numerous in septal, infundibular, periventricular, and lateral hypothalamic regions. The brown, diaminobenzidine-labeled LHRH-containing perikarya were found to receive black, silver-intensified, TH-positive axon terminals in the infundibular and medial preoptic areas. However, in the preoptic and caudal parts of the diencephalon, only a few juxtapositions were noted. The present results indicate that hormone released from diencephalic LHRH-IR neurons in humans may be influenced by the central catecholaminergic system via direct synaptic mechanisms.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

Aproteic diet decreases hypothalamic catecholamine turnover in adult male rats

Previous reports indicate that malnutrition reduces reproductive functions. We have demonstrated that protein deprivation in the diet also causes reproductive dysfunction by reducing hypothalamic GnRH secretion. Noradrenaline and nitric oxide are modulators of GnRH secretion. Noradrenaline stimulates GnRH secretion and nitric oxide inhibits catecholamine release. This work studies the hypothalamic catecholaminergic and nitrergic neuron activity in Wistar adult male rats fed on an aproteic diet (AP) during 21 days; this treatment was started when rats were 70 days old. Our first experiment studied catecholamine turnover rate after inhibition of tyrosine hydroxylase activity by injecting (i.p.) 400 mg/kg alpha-methyl-p-tyrosine. Our second experiment studied in vitro hypothalamic nitric oxide synthase (NOS) activity in animals under the same diet. AP diet significantly decreased both noradrenaline (P<0.05) and dopamine (P<0.05) hypothalamic turnover rate. Noradrenaline turnover in cerebral cortex was not altered by the aproteic diet. However, hypothalamic NOS activity was not affected in animals fed on an AP diet. These results indicate that the lack of protein in the diet reduces catecholaminergic neuron activity in adult male rats by a NO-independent mechanism, thus suggesting that a decrease in noradrenergic activity may be involved in the reduction of GnRH secretion induced by an AP diet.

Acute effects of d-amphetamine during the early and late follicular phases of the menstrual cycle in women

Recent preclinical evidence indicates that ovarian hormones, such as estrogen and progesterone, may influence the behavioral effects of psychoactive drugs by interacting directly with neurotransmitter systems in the central nervous system. However, few studies have examined the effects of ovarian hormones on subjective or behavioral responses to psychoactive drugs in humans. In the present study, we assessed the subjective and physiological effects of d-amphetamine during the early and late follicular phases of the menstrual cycle. Nineteen healthy, regularly-cycling women participated in four sessions receiving doses of d-amphetamine (AMPH; 15 mg oral) or placebo during the early and late follicular phases of two menstrual cycles. During the early follicular phase levels of both estrogen and progesterone are low, whereas during the late follicular phase estrogen levels are higher while progesterone remains low. Dependent measures included self-report questionnaires, physiological measures and plasma hormone levels. Most of the subjective and physiological effects of AMPH were not affected by menstrual cycle phase. However, subjects reported greater Unpleasant Stimulation after AMPH, and less Unpleasant Sedation, during the late follicular phase than during the early follicular phase. These results provide limited evidence that higher levels of estrogen during the late follicular phase alter the subjective effects of AMPH in normal, healthy women.

GABA levels within the medial preoptic area: effects of chronic administration of sodium valproic acid

Sodium valproic acid (VPA) is a widely prescribed anticonvulsant medication that has been shown to interfere with pubertal maturation of the reproductive system, and induce endocrine abnormalities in adults, within a subset of the clinical population. While VPA's mechanism of action is still poorly understood, it may exert its anti-reproductive effects by enhancing GABAergic inhibition of the GnRH neuronal population within the medial preoptic area (mPOA). The purpose of this study was to determine if chronic administration of VPA alters GABA levels within the mPOA region. In Experiment 1, the mPOA, caudate, and arcuate nucleus regions were harvested from VPA-treated and control mice. Analysis of whole tissue content of GABA revealed that levels were lower in the caudate and arcuate nucleus regions of VPA-treated animals, whereas there were no group differences for the mPOA region. Collapsing across drug group, there was also a trend for males having overall higher levels of GABA as compared to females. In Experiments 2 and 3, mice were implanted with microdialysis probes within the mPOA region and sampled for extracellular GABA levels. Females (Exp. 3) were sampled either on diestrous, proestrous, or estrous. Results from males (Exp. 2) revealed that VPA enhanced extracellular GABA levels in the mPOA region compared with controls. However, GABA levels for both groups remained stable across the sampling period. Conversely, in Exp. 3, females showed cyclical release of GABA across the sampling period. For control females, GABA levels increased during the afternoon on all cycle days, but the rise on proestrus was smaller than on other cycle days. VPA-treated animals showed an overall reduction in GABA levels compared with controls. Furthermore, while GABA increased over sampling time on estrus and diestrus days of the cycle, there was not a significant rise in GABA on proestrus. These data indicate: (1) regional specificity in VPA effects upon GABA levels, (2) a sex difference in the effects of VPA on GABA levels within the mPOA, and (3) GABA levels increase on the afternoon of all days of the estrous cycle with VPA attenuating the rise seen on the afternoon of proestrus. These results provide evidence that VPA effects upon the reproductive axis may involve changes in GABA release, and that males and females show different patterns of neurochemical response to the drug.

Levels of dopamine beta hydroxylase immunoreactivity in the preoptic hypothalamus of the ovariectomised ewe following injection of oestrogen: evidence for increased noradrenaline release around the time of the oestrogen-induced surge in luteinizing hormone

We have measured dopamine beta hydroxylase (DBH) immunoreactivity in the preoptic hypothalamus as an index of release of noradrenaline in the ovariectomised (OVX) ewe at the time of an oestrogen-induced surge in luteinizing hormone (LH) release. OVX ewes (n=5) were given an injection of 50 microg oestradiol benzoate (or oil), which causes a surge in the secretion of LH. Blood samples were taken and sheep were killed 16 h later. Other groups (n=3) were given oil or oestrogen and killed 6 h later. Brains were collected for immunohistochemistry and image analysis. The number of DBH-stained cells and the integrated optical density of the cells was measured throughout the A1 field of the brainstem. The DBH staining was measured in the terminal beds of the hypothalamus. There was no difference between the controls and the EB-treated OVX ewes in the number of DBH positive cells or the optical density of DBH-staining cells in the A1 field. Within the preoptic area, there was reduced (P<0.02) DBH staining in the 16 h EB-treated ewes. There was no change in the DBH staining in the paraventricular nucleus or the arcuate nucleus of the hypothalamus. These data suggest that there is release of noradrenaline in the preoptic area at the time of the E-induced GnRH/LH surge in the OVX ewe.

Changes in the pituitary metabolism of monoamines (dopamine, norepinephrine, and serotonin) in female and male rainbow trout (Oncorhynchus mykiss) during gonadal recrudescence

The dynamics of the levels and metabolism of dopamine, norepinephrine, and serotonin were studied in pituitaries of male and female rainbow trout at different stages of gonadal development. In female rainbow trout, the turnover of dopamine (calculated using the inhibitor of tyrosine hydroxylase alpha-methyl-p-tyrosine methyl-ester HCl), serotonin metabolism, and norepinephrine levels decreased in the advanced stage of exogenous vitellogenesis with respect to the initial stage. However, data obtained in males did not show changes in either serotonergic or noradrenergic metabolism during the last stages of gonadal development. However, an increase of dopaminergic turnover was noticed in the male fish at the end of spermiation. Finally, pituitary dopaminergic activity was significantly higher in immature (prepubescent stage) than in adult fish.

Identification of alpha1B adrenergic receptor protein in gonadotropin releasing hormone neurones of the female rat

Noradrenaline is an important neurotransmitter which regulates GnRH release from the median eminence in the female rat during both basal GnRH secretion and the preovulatory or steroid hormone-induced GnRH-mediated LH surge. However, it is not clear at which sites in the brain this predominantly stimulatory influence is exerted nor is it known which adrenergic receptor subtype(s) mediate(s) the effects of noradrenaline. In order to determine if the GnRH neurones in the septum-diagonal band-preoptic area and/or their axon terminals in the median eminence are direct targets for noradrenaline, immunohistochemical triple-labelling studies were conducted to localize simultaneously GnRH peptide, dopamine-beta-hydroxylase and alpha1B adrenergic receptor protein. The results show that about 80% of all GnRH neurones examined contained patches of immunoreactive alpha1B adrenergic receptor protein at or near the plasma membrane and that some of these alpha1B adrenergic receptors were adjacent to dopamine-beta-hydroxylase containing axons. The GnRH neurones which did not contain alpha1B adrenergic receptors were preferentially located in the rostral portion of the septum and diagonal band while all GnRH neurones in the caudal septum, diagonal band and in the preoptic area expressed alpha1B adrenergic receptors. In the median eminence, a few alpha1B adrenergic receptor patches were seen in the external layer and these receptors were only rarely observed to be associated with GnRH containing axon terminals. The results suggest that the effects of noradrenaline on GnRH release are, at least in part, mediated by the activation of alpha1B adrenergic receptors which are located on most GnRH perikarya while the median eminence is not a likely site at which GnRH release is regulated by alpha1B adrenergic receptors.

The higher the dose, the greater the sex differences in escape-avoidance response in mice after acute administration of haloperidol

Sex differences in the effects of haloperidol in the escape-avoidance response have previously been found in various studies carried out in our laboratory in which mice were used as experimental subjects. Males were more affected than females by the disruptive effects of this neuroleptic of frequent clinical use. In the present work these sex differences were evaluated in a unique training session using several doses of the drug (0.075, 0.25, and 0.75 mg/kg i.p.). The number of avoidances, escapes, nonresponses, crossings during the adaptation period, crossings during intertrial intervals, and response latencies were analyzed. Statistically significant sex differences were found in the number of escapes and nonresponses: males showed fewer escape responses and more nonresponses than females. These sex differences were dose dependent: a positive correlation was obtained between doses of haloperidol and sex differences observed in the number of escapes and nonresponses. The higher the dose, the greater the sex differences. These are related not only to the impairment of motor activity, because no sex differences were found in the number of crossings during the adaptation period and intertrial intervals.

The effect of blockade of kappa-opioid receptors in the medial preoptic area on the luteinizing hormone surge in the proestrous rat

The present study examined whether blockade of kappa-opioid receptors in the medial preoptic area (MPOA) prior to the critical period on the afternoon of proestrus could prematurely evoke an ovulatory luteinizing hormone (LH) surge, and if so, whether norepinephrine (NE) is involved in mediating this response. In the first experiment, push-pull perfusion of the MPOA with nor-binaltorphimine (nor-BNI), a specific kappa-opioid receptor antagonist, was done in rats between 10.30 and 13.50 h on proestrus. To determine whether any resulting ovulation was due to a nor-BNI-induced increase in LH release, rats were injected with pentobarbital at 13.55 h to block the afternoon LH surge. In 7 of 10 rats, nor-BNI in the MPOA produced a large increase in LH release beginning between 12.30 and 13.30 h, and 5 of 7 ovulated. During MPOA perfusion with cerebrospinal fluid in our normal colony between 14.00 and 17.00 h, surges of LH release began in the majority of rats between 15.30 and 16.30 h. Thus blockade of MPOA kappa-opioid receptors advanced the LH surge by 3 h. The next experiment examined the effect of NE synthesis inhibition with bis(4-methyl-1-homopiperazinylthiocarbonyl) disulfide (FLA-63), or alpha-adrenergic receptor blockade with phenoxybenzamine (PBZ), on the nor-BNI-induced LH response. In 5 of 6 vehicle-treated rats, blockade of MPOA kappa-opioid receptors elicited a large increase in LH release and all 5 ovulated. In contrast, only 3 of 8 rats pretreated with FLA-63 had a large increase in LH release and ovulated, and PBZ prevented the nor-BNI-induced LH increase and ovulation in 4 of 4 rats. PBZ also prevented the afternoon LH surge and ovulation in 4 of 4 rats in our normal colony. Finally, HPLC measurement of NE levels in MPOA push-pull perfusate indicated no increase in NE release during the nor-BNI-induced or normal afternoon LH surges. These results indicate that antagonism of kappa-opioid receptors in the MPOA can prematurely evoke an ovulatory LH surge prior to the critical period on the afternoon of proestrus. Furthermore, the nor-BNI-induced as well as the normal afternoon LH surges are dependent on the proper functioning of central noradrenergic neurons, but do not involve increased NE release within the MPOA.

Locus coeruleus lesions decrease norepinephrine input into the medial preoptic area and medial basal hypothalamus and block the LH, FSH and prolactin preovulatory surge

The aim of this work was to study the role of the dorsal noradrenergic ascending pathway (DNAP), which originates in the locus coeruleus (LC) on the preovulatory surge of luteinizing hormone (LH) follicle-stimulating hormone (FSH) and prolactin (PRL) by producing bilateral electrolytic lesions (cathodal or anodal) in this nucleus. LC lesions were placed at 11.00 h on proestrus in female rats with regular 4-day estrous cycles. Intact rats, sham-operated as well as animals with missed lesions served as controls. In Experiment I, anodal current was applied and hourly blood samples were withdrawn (from 13.00 to 17.00 h) via a jugular catheter from conscious, freely moving rats for determination of plasma LH, FSH and PRL concentrations. In Expt. II, Expt. I was repeated using cathodal current and collecting blood samples hourly from 13.00 to 18.00 h. In both experiments the animals were sacrificed on the next morning when the occurrence of ovulation was checked. The medial septal area (MSA), medial preoptic area (MPOA), and medial basal hypothalamus (MBH) were dissected and assayed for norepinephrine (NE), dopamine (DA) and 5-hydroxyindoleacetic acid (5-HIAA) content. Experiment III was performed in order to test if a hormonal discharge occurred immediately after lesion placement. Blood samples were collected immediately before and 15, 30, 60 and 90 min postoperatively (from 11.00 to 12.30 h). Either anodal or cathodal lesions blocked the proestrous surge of LH, FSH and PRL. The hypothesis that the lesions advanced or delayed these hormonal surges was rejected since we found no increases in the hormonal levels from 11.00 to 12.30 or from 13.00 to 18.00 h, and ovulation was not observed on the following morning in the lesioned animals. Since control, sham-operated and missed-lesion groups exhibited LH, FSH and PRL surges and ovulation, this blockage appears to be caused by the destruction of the LC neurons. Also, this blockade was correlated with a decrease in the NA content in the MPOA and MBH, but not in the MSA, whereas the DA and 5-HIAA content were not changed in all groups examined. The results lead us to suggest that the integrity of noradrenergic afferent input from the LC to luteinizing hormone-releasing hormone neurons in the MPOA and MBH is essential for triggering the preovulatory surge mechanisms for gonadotrophins and PRL.

Prostaglandin fever in rats throughout the estrous cycle late pregnancy and post parturition

We have examined the influence of natural variations in endocrine status on the ability to generate a prostaglandin-induced fever in virgin female, pregnant and lactating rats and compared responses to those in male rats. Endocrine status of virgin female rats was assessed from examination of vaginal smears and time of parturition noted to enable accurate dating of pre- and postparturient fevers. Unanesthetized rats, previously prepared with intraventricular guide cannulas and intraperitoneal telemetry thermistors, were given intraventricular injections of prostaglandin E1 (2-100 ng/5 microliters) and temperatures monitored for 3 h after injection. Virgin females developed significantly larger fevers than did males at higher doses. There were no significant alterations in either fever height or duration as a function of the phase of the reproductive cycle in the females. Both pregnant and postparturient rats within the several days around birth displayed significantly lower fevers than did virgin females, but there was no further reduction in the immediate periparturient period. These data indicate that there are sex-, and possibly hormone-dependent differences in the central mechanisms involved in fever generation and antipyresis.

Cyclic and age-related changes in norepinephrine concentrations in the medial preoptic area and arcuate nucleus

High-performance liquid chromatography with electrochemical detection (HPLC-EC) and Palkovits' microdissection technique were used to measure norepinephrine (NE) concentrations in the medial preoptic area (MPA) and arcuate nucleus (AN) during various stages of the estrous cycle. NE was measured seven times at 2-h intervals between 1000 h and 2200 h on the days of proestrus and diestrus in young (4-month-old) rats and four times at 2-h intervals between 1400 h and 2000 h in old (20-22-month-old) persistently diestrous rats. On the day of proestrus in young animals, NE increased progressively from low levels at 1000 h to peak levels at 2000 h, followed by a sharp decline at 2200 h. In contrast, no changes in NE occurred on the day of diestrus. Unlike the young proestrous rats, but similar to the young diestrous rats, no changes in NE concentrations either in the MPA or in the AN occurred in the old persistently diestrous rats. These data demonstrate that NE concentrations in the MPA and AN change during the estrous cycle. We believe the increase in NE on the afternoon of proestrus is related to the surge in serum luteinizing hormone (LH) that occurs simultaneously in this stage of the estrous cycle. The lack of change in NE concentrations in the young diestrous and persistently diestrous old animals is consistent with the well-established absence of changes in serum LH in these animals.

Neonatal exposure to estradiol prevents the expression of ovarian hormone-induced luteinizing hormone and prolactin surges in adulthood but not antecedent changes in neuropeptide Y or adrenergic transmitter activity: implications for sexual differentiation of gonadotropin secretion

Sex differences in adult patterns of mating behavior and gonadotropin secretion in rats are determined in part by the presence or absence of gonadal steroids during a perinatal critical period. For example, male rats and female rats exposed neonatally to androgen do not exhibit LH surge patterns when treated appropriately with ovarian hormones in adulthood, and there is evidence that this may be due to a failure of ovarian hormones to activate the hypothalamic neuronal systems that stimulate LH secretion in such animals. Because considerable evidence suggests that estradiol formed centrally from testosterone is responsible for the permanent defeminization of mating behavior and gonadotropin secretion, the present studies compared normal females with normal males and with females treated neonatally with estradiol on the ability of ovarian hormones to induce several important neurochemical changes antecedent to the LH surge, including changes in neuropeptide Y (NPY) and LH-releasing hormone (LHRH) concentrations in the median eminence, as well as changes in turnover rates for catecholamine transmitters in the medial basal hypothalamus and medial preoptic area. Normal ovariectomized female rats responded to sequential treatment with estradiol followed by progesterone with afternoon LH and prolactin (PRL) surges, and with sequential accumulation followed by decline in concentrations of LHRH and NPY in the median eminence prior to the LH surge. In addition, administration of progesterone increased the turnover rates of norepinephrine (NE) and epinephrine (EPI) in the arcuate-median eminence region of normal females.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that amplification of norepinephrine-induced LH release by morphine is indirectly due to suppression of tuberoinfundibular dopamine secretion

We previously observed that morphine markedly amplifies LH secretion following intracerebroventricular (i.c.v.) norepinephrine (NE) infusions. Based on additional evidence, we hypothesized that perhaps these morphine effects were due to suppression of tuberoinfundibular dopamine (TIDA) secretion thus allowing NE to evoke a greater release of LHRH from axon terminals in the median eminence than would otherwise occur. In the present studies, we examined whether apomorphine (a DA receptor agonist) would suppress and haloperidol (a DA receptor antagonist) would mimic these enhancing effects of morphine on NE-induced LH secretion. Estrogen-treated ovariectomized rats were used in these studies. NE, when infused i.c.v. (45 micrograms) evoked a modest increase in plasma LH (1.1 +/- 0.2 to 2.2 +/- 0.2 ng/ml) within 15 min. When morphine sulfate (10 mg/kg s.c.) was given 15 min prior to NE, LH peak values of 11 +/- 2 ng/ml were obtained by 60 min. Treatment of rats with apomorphine (1.5 mg/kg s.c.) at -15 min, morphine at 0 min and i.c.v. NE at 15 min resulted in a significant blunting of morphine's effect on NE-induced LH release. Moreover, in all morphine-treated rats, plasma prolactin (PRL) increased significantly within 10 min, peaked at 30 min and declined towards basal values by 90 min. Apomorphine completely blocked this morphine effect of PRL release. Haloperidol (HAL; 2.5 mg/kg s.c.) treatment had no effect on basal LH release but resulted in a significant increase in PRL which remained elevated up to 180 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroendocrine concomitants of reproductive aging

Depletion of ovarian follicles is often thought to be the determining factor in female reproductive aging. However, increasing evidence suggests that neural and neuroendocrine changes play important causative roles in the decline of regular reproductive cycles leading to the menopause. A blunting or suppression in the daily pattern of secretion of several neuroendocrine hormones has been documented in aging laboratory animals and humans. Investigators have designed experiments to test whether these changes reflect multiple unrelated changes in the regulation of each of these hormones, or whether these alterations result from a fundamental change in the time-keeping mechanism that underlie these patterns of hormone secretion. Oscillations that occur approximately every 24 h are a hallmark of most living organisms. These cycles provide the organism with the capability of coordinating events that occur at higher (hourly) and lower (weekly or monthly) frequencies within an individual organism, and with the capability of synchronizing these events with the external environment. In mammals, the hypothalamic suprachiasmatic nucleus is thought to be a master oscillator that regulates most circadian rhythms in mammals. Perturbations in temporal organization occur during aging and influence multiple physiological systems, including reproductive cyclicity in females. Thus, the question for neuroendocrinologists is: Do changes in the cyclic pattern of hormone secretion reflect a change in the master oscillator, and do these changes play a role in female reproductive aging? Data from our laboratory demonstrate that the timing of the preovulatory and steroid-induced luteinizing hormone (LH) surge changes during middle-age in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of morphine on hypothalamic tyrosine hydroxylase mRNA levels in dopaminergic neurons and on preoptic DOPAC levels measured by microdialysis

Morphine not only suppresses norepinephrine-induced increases in LHRH mRNA levels but, in these same animals, it simultaneously amplifies norepinephrine (NE)-induced LH release. These observations suggest that NE may activate parallel mechanisms which independently increase LHRH mRNA levels and LHRH release and suggest that some of these effects could be mediated indirectly via morphine's action on different components of the hypothalamic dopamine (DA) system. Accordingly, in the present studies we examined the effects of morphine on various components of this dopamine system using as our index of altered DA neuronal activity, the changes which occur in tyrosine hydroxylase (TH) mRNA levels following morphine. As an ancillary index of changes which occur in dopamine neuronal activity, we measured, by microdialysis, the changes which occur in preoptic dihydroxyphenylacetic acid (DOPAC) levels after either subcutaneous injections or following microinfusions of morphine into the zona incerta (ZI). In a final study, we evaluated whether DA when given alone (icv infusion) or prior to icv NE would altered LH release. Single cell levels of TH mRNA in preoptic A15 and periventricular anterior hypothalamic A14 DA neurons were not affected by morphine 1, 5 and 24 h later. In contrast, within 1 h after morphine, TH mRNA levels in ZI A13 neurons were significantly elevated and they remained high at 5 nd 24 h compared to controls. Morphine also resulted in a significant rise in TH mRNA levels in tuberoinfundibular DA neurons (TIDA) (A12) within 1 h and these levels remained high to 5 h. Thereafter, by 24 h, message levels had returned to control values. Morphine also resulted in a rapid rise in plasma prolactin (Prl) with peak values occurring at 20 min and then returning to baseline by 90 min. When morphine was given sc it resulted, within 15 min, in a rapid rise in preoptic DOPAC levels and these levels continued to rise such that they were 217% higher than pretreatment values by 105 min. Preoptic 5-hydroxyindoleacetic acid (5-HIAA) levels also increased by 25-75% after sc morphine. The microinfusion of morphine into ZI also resulted in elevated preoptic DOPAC but not 5-HIAA levels within 15 min. The icv infusion of DA alone had no effect on plasma LH whereas, NE (icv) produced a modest but significant increase in plasma LH. When DA was given 15 min prior to the infusion of NE, neither amplification nor inhibition of NE-induced LH release occurred. From these and other studies we conclude that the morphine-induced suppression of TIDA neuronal activity may allow NE to release greater amounts of LHRH from axon terminals in the median eminence.(ABSTRACT TRUNCATED AT 400 WORDS)

Norepinephrine turnover in the goldfish brain is modulated by sex steroids and GABA

It is known that norepinephrine (NE) is important in the neuroendocrine control of pituitary gonadotropin II (GTH-II) and growth hormone (GH) release but very little is known about the factors regulating NE neurons in the goldfish brain. Female gonad-intact goldfish were implanted intraperitoneally (100 micrograms/g) with testosterone (T) or estradiol (E2) to elevate serum steroid levels. High-performance liquid chromatography measurements showed that steroid implantation had no effect on NE content in the telencephalon, including preoptic area (TEL-POA), or the hypothalamus (HYP). The turnover rate of NE was estimated from the rate of depletion of NE content from tissues following inhibition of tyrosine hydroxylase by alpha-methyl-p-tyrosine (240 micrograms/g). The present study demonstrates that E2 can decrease NE turnover rates in TEL-POA and HYP of sexually regressed goldfish (August). The results in recrudescent fish (November), however, indicate a more complex interaction of E2 with NE neurons since E2 increased NE turnover in TEL-POA and HYP in these animals. Testosterone (T) has less prominent effects on NE turnover rates in TEL-POA and HYP; the only significant effect of T-implantation was a small reduction of NE turnover in the TEL-POA of sexually recrudescent fish. Elevation of endogenous brain GABA concentrations by injection of the GABA transaminase inhibitor, gamma-vinyl-GABA (300 micrograms/g), significantly reduced NE turnover in TEL-POA. These data demonstrate that goldfish NE neurons in the TEL-POA are sensitive to regulation by changes in circulating sex steroids and by increases in brain GABA.

Morphine amplifies norepinephrine (NE)-induced LH release but blocks NE-stimulated increases in LHRH mRNA levels: comparison of responses obtained in ovariectomized, estrogen-treated normal and androgen-sterilized rats

In these studies we examined the temporal effects of intracerebroventricular (i.c.v.) infusions of norepinephrine (NE) on plasma LH and on LHRH mRNA levels in the organum vasculosum of the lamina terminalis (OVLT) and in neurons located in the rostral (r), middle (m) and caudal (c) preoptic areas (POA) of ovariectomized, estrogen-treated rats. Thereafter, we compared these responses to those which occur in androgen-sterilized rats (ASR). NE infusions not only increased plasma LH concentrations but within 1 h after NE, LHRH mRNA levels also were increased significantly in the OVLT and rPOA but not in the mPOA or cPOA. By 4 h, these message levels still were elevated in the OVLT and rPOA and they now also were significantly higher than control values in the mPOA and cPOA. While NE also increased LH secretion in ASR, the plasma LH concentrations obtained were markedly blunted compared to control values. Moreover, NE infusions did not alter single cell levels of LHRH mRNA in any region of the rostral hypothalamus. Previously, we have reported that morphine (s.c.) markedly amplifies NE-induced LH release and questioned whether these responses are accompanied by concomitant augmented increases in LHRH mRNA levels. Morphine alone did not affect basal LHRH mRNA or plasma LH levels. However, when rats were pretreated with morphine (-15 min) and NE was infused i.c.v. at 0 time, significant amplification of LH release occurred but, unexpectedly, morphine completely blocked NE-induced increases in LHRH mRNA levels in all of the neurons we examined. Morphine also amplified LH release in ASR but these responses were significantly less than those obtained in control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Origin of noradrenergic projections to GnRH perikarya-containing areas in the medial septum-diagonal band and preoptic area

The purpose of the present study was to identify the sites of origin of the noradrenergic fibers that project to areas containing gonadotropin-releasing hormone (GnRH) perikarya since norepinephrine (NE) is known to influence the activity of GnRH neurons. Fluorescent retrograde tracers were used in combination with immunohistochemistry for dopamine-beta-hydroxylase (DBH) and GnRH. Small volumes of either Fluoro-gold (FG) or Fluoro-Ruby (FR) were pressure injected into areas that contain the largest number of GnRH cell bodies, i.e., the medical septum-diagonal band complex or preoptic area. Retrogradely labeled neurons were observed ipsilaterally in the following noradrenergic cell groups: A2 (in the nucleus tractus solitarii), A1 (in the ventrolateral medulla) and locus coeruleus. Approximately 8% of all DBH-positive neurons within the A2-cell group were retrogradely labeled, while 12% of DBH-ir neurons in the A1-group were double-labeled. Only a few retrogradely labeled DBH-ir neurons were observed in the locus coeruleus (< 1%). Double-labeled neurons were not organized into discrete cell groups, but were dispersed among other NE-neurons within the A2- and A1-cell groups. The highest concentrations of double-labeled neurons were located in the central one-third of both the A2 and A1 cell groups. The results suggest that most noradrenergic terminals in the region of the GnRH perikarya in the medial septum-diagonal band/rostral preoptic area originate from ipsilateral neurons in areas A1 and A2.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary gland responsiveness to LHRH and LHRH neuronal responsiveness to excitatory stimuli are severely impaired in female rats treated neonatally with high doses of androgen

Treatment of neonatal female rats with androgen renders these animals permanently sterile as adults. Previously, we reported that these androgen-sterilized rats (ASR) do not respond to the positive feedback effects of estrogen by having LH surges. We also reported that this defect might be due to the failure of these animals to show increased hypothalamic norepinephrine turnovers (an index of secretion) in response to steroid treatment. Although LHRH-catecholamine synapses are established before or at birth, whether such synapses are functional remains to be resolved. Accordingly, in the present studies, female rats were given 1.25 mg of testosterone propionate at 5 days of age and, at 100 days of age, these ASR and controls were ovariectomized and treated with estradiol. In these animals, we examined whether activation of medullary A1 noradrenergic neurons would amplify LH release following preliminary depolarization of LHRH neurons with an electrochemical stimulus (ECS). As well, we reexamined whether LHRH neuronal responsiveness to exogenous NE and pituitary responsiveness to LHRH differ in controls versus ASR. In controls, two pulses of LHRH given 60 min apart elicited increases in plasma LH with the second pulse inducing greater LH release than the first pulse. In ASR, significantly less LH was released after either LHRH pulse and particularly after the second pulse. When the spacing between the two LHRH pulses was reduced to 25 min, equivalent levels of LH release occurred in controls and ASR after the second pulse.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteinizing hormone-releasing hormone and gamma-aminobutyric acid neurons in the medial preoptic area are synaptic targets of dopamine axons originating in anterior periventricular areas

The aim of this study was to characterize further the transmitter content and the location of the parent cells of tyrosine hydroxylase-immunoreactive boutons terminating on luteinizing hormone-releasing hormone- and glutamic acid decarboxylase-immunoreactive neurons in the rat medial preoptic area. Electron microscopic immunostaining for luteinizing hormone-releasing hormone, tyrosine hydroxylase or glutamic acid decarboxylase was performed on desipramine-pretreated (to protect norepinephrine and epinephrine axons) rats which received a stereotaxic injection of 6-hydroxydopamine into the medial preoptic area anteroventral periventricular nucleus 48 h prior to sacrifice. This treatment induced acute degeneration of dopamine axon terminals characterized by the development of autophagous cytolysosomes, an early morphological sign of catecholamine axon degeneration. To further define the cells of origin of these dopamine boutons, the anterograde marker Phaseolus vulgaris leucoagglutinin was iontophoretically applied to the zona incerta. Six days later, rats received a 6-hydroxydopamine injection into the zona incerta or the lateral ventricle, and 48 h later, double immunostaining was performed for Phaseolus vulgaris leucoagglutinin and tyrosine hydroxylase, luteinizing hormone-releasing hormone, or glutamic acid decarboxylase on preoptic area vibratome sections. Following the 6-hydroxydopamine injection into the anteroventral periventricular nucleus, autophagous cytolysosome-containing degenerated axons were found in synaptic contact with both luteinizing hormone-releasing hormone and GABA neurons in the medial preoptic area, confirming that these are dopaminergic connections. Following the double injection treatment, 6-hydroxydopamine-induced degenerated, Phaseolus vulgaris leucoagglutinin-labeled dopamine axons originating in the zona incerta were not found to contact luteinizing hormone-releasing hormone-containing or GABA cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 1 adrenergic regulation of estrogen-induced increases in luteinizing hormone-releasing hormone mRNA levels and release

Prazosin, an alpha 1 adrenergic antagonist, was used to examine the relationship between adrenergic inputs and the stimulatory effects of estrogen on LHRH mRNA and release. Bilateral cannulae were implanted just dorsal to the preoptic area (POA). Estrous cycles were monitored daily by vaginal smears. On the morning of diestrus, each rat was ovariectomized and assigned to one of three treatment groups: Control--injected with sesame oil (n = 5); Surge--injected with estradiol benzoate (EB, 10 micrograms) to produce an LH surge (n = 5); or, Surge+Prazosin--injected with EB and a prazosin-filled inner cannula was put into the POA (n = 6). Between 4-6 pm of the following day, rats were anesthetized, decapitated, trunk blood collected, and brains were stored in liquid nitrogen. In situ hybridization was performed using a 32P end-labelled 59-mer complementary to LHRH mRNA. Reduced silver grains, proportional to LHRH mRNA content, were quantified. Treatment with estrogen alone resulted in an LH surge and a 50% increase (P < 0.05) in numbers of cells expressing LHRH. This estrogen-induced increase and the LH surge were completely blocked (P < 0.01) by prazosin. Prazosin also decreased (P < 0.01) the median number of grains per cell from 81 (Surge) to 65 grains per cell (Surge+Prazosin). When the number of grains in LHRH-expressing neurons were totalled, EB increased (P < 0.05) LHRH gene expression by 53%, and local administration of prazosin completely blocked (P < 0.01) this increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Gender differences in escape-avoidance behavior of mice after haloperidol administration

Gender differences in the disruptive effects of haloperidol on some reinforced behaviors have been observed in different species. However, the inhibitory action of haloperidol on the acquisition and performance of escape-avoidance behavior has only been investigated in male subjects. The present experiment was designed to investigate possible gender differences in the effects of haloperidol on the initial phase of an escape-avoidance learning task. Male and female mice of the OF1 strain were given a single training session in a shuttle-box. Thirty minutes prior to the behavioral test, mice were injected IP with haloperidol (0.25 mg/kg) or physiological saline (10 ml/kg). Latencies of escape and avoidance responses and the number of nonresponses, escapes, avoidances, pseudoavoidances, crossings during the adaptation period, and crossings during intertrial intervals (ITIs) were evaluated. The disruptive action of haloperidol on the escape-avoidance behavior of the mice was greater in males than in females. The number of nonresponses were higher and the number of escapes lower in treated males than in their female counterparts. These gender differences were not found in control subjects. Activity measures of spontaneous motor behavior (crossings in the adaptation period and during ITIs) did not present gender differences either. Several possible mechanisms responsible for this greater susceptibility of males to the inhibitory effects of haloperidol on escape-avoidance learning are discussed, especially the modulating role of female hormones on dopaminergic activity.

Tyrosine Hydroxylase Messenger Ribonucleic Acid Levels Increase in A1 but not Locus Ceruleus Noradrenergic Neurons in Proestrous Rats but not in Diestrous or Androgen-Sterilized Animals

Norepinephrine (NE) turnovers (an index of secretion) increase in the hypothalamus of proestrous rats concomitant with luteinizing hormone surges, whereas, neither of these events are observed in diestrous nor in androgen-sterilized rats. Increased hypothalamic NE release may occur as a consequence of the withdrawal of local inhibitory γ-aminobutyric acid and opiate controls on specific presynaptic NE terminals and/or as a result of an increase in activity within noradrenergic neurons. Tyrosine hydroxylase (TH) is the rate-limiting enzyme for the synthesis of NE and our earlier studies revealed that increases in TH mRNA in A1 and locus ceruleus (LC) neurons can serve as an index of increased activity within these cells. In the present study, we evaluated whether TH message levels change in A1 and LC neurons prior to and during the hours when luteinizing hormone surges and increased NE turnovers are observed. As controls, TH mRNA levels in A1 and LC neurons were evaluated at the same hours of day in diestrous day 2 and in androgen-sterilized rats. In situ hybridization histochemistry and quantitative image analysis methods were used to measure changes in TH mRNA levels. Luteinizing hormone surges in proestrous rats began at 1500 h, peaked between 1600 and 1700 h and declined, thereafter, to 2000 h. In contrast, plasma luteinizing hormone remained basal throughout the day in diestrous and androgen-sterilized rats. While A1 neuronal TH mRNA levels did not differ in the three groups of rats during the morning (0930 to 1030 h), these message levels were significantly elevated in proestrous rats during the afternoon (1645 to 1715 h) and remained high at 2000 to 2030 h. In contrast, no changes in TH mRNA levels were observed in A1 neurons throughout the afternoon in diestrous animals or androgen-sterilized rats. TH mRNA levels in the LC did not differ in the three groups of rats and they remained unchanged throughout the afternoon hours we examined. From these observations we conclude that concomitant with afternoon proestrous luteinizing hormone surges and the accompanying increase in hypothalamic NE secretion, there is an increase in activity within A1 but not LC neurons. These data suggest that the proestrous increase in hypothalamic NE turnover we previously observed is not due solely to withdrawal of local inhibitory controls of presynaptic NE release but it also involves an increase in activity within A1 but not LC neurons.

Temporal changes in tyrosine hydroxylase mRNA levels in A1, A2 and locus ceruleus neurons following electrical stimulation of A1 noradrenergic neurons

We examined the effects of electrical stimulation (ES) of right A1 noradrenergic cells on temporal changes in tyrosine hydroxylase (TH) mRNA levels in A1, A2 and locus ceruleus (LC) neurons by in situ hybridization histochemistry and quantitative image analysis methods. The stimulation parameters used previously have been shown to increase hypothalamic norepinephrine (NE) release. Within 1 h after beginning A1 stimulation, TH mRNA levels were significantly increased and they continued to rise to reach plateau by 6 h. TH message levels at 12 h were not difference from 6 h values. A1-ES did not affect TH mRNA levels in contralateral A1 or in A2 or locus ceruleus neurons. These data suggest that changes in TH mRNA levels may serve as an index of increased A1 neuronal activity in circumstances when increases in hypothalamic NE secretion occur.

Morphine but not Naloxone Enhances Luteinizing Hormone-Releasing Hormone Neuronal Responsiveness to Norepinephrine

Some axon terminals of hypothalamic opiate neurons directly synapse on luteinizing hormone-releasing hormone (LHRH) neurons. To determine whether such synaptic connections affect LHRH neuronal activity, we have examined the profiles and concentrations of LH released in response to intracerebroventricular (icv) norepinephrine (NE, 45 μg) infusions alone or following medial preoptic area (MPOA) electrochemical stimulation (ECS) in estrogen-treated ovariectomized rats. Similar studies were performed in rats treated with naloxone (5 mg/kg ip) or morphine (20 mg/kg sc) given 15 min prior to MPOA-ECS or 30 min prior to icv NE. Naloxone neither augmented nor suppressed the LH response obtained with NE alone. MPOA-ECS evoked a significant increase in plasma LH. When the preoptic area was stimulated (0 min) and NE was infused at 30 min, a significant amplification of LH release occurred. Prior treatment of rats (-15 min) with naloxone had no effect on LH responses elicited by either preoptic stimulation alone or combined with icv NE. In the second study, morphine was given sc and had no effect on basal plasma LH levels. However, when morphine was given (-15 min) and icv NE infusions were made (30 min), the rise in plasma LH induced by NE was significantly enhanced. Preoptic ECS (0 min) evoked a rise in plasma LH and this response was also enhanced by morphine pretreatment. The major effect on LH release occurred when sc morphine injections (-15 min) were combined with MPOA-ECS (0 min) followed by icv NE (30 min). In these rats, a remarkable and highly significant release of LH occurred which reached peak levels even greater than those observed during spontaneous LH surges (2,392 versus 16 to 1,800 ng/ml). Since morphine has profound effects on the serotonergic system, in the third series of studies, morphine was infused into the dorsal raphe nucleus (DRN) and LH responses to MPOA-ECS or icv NE alone or following combined ECS + NE were examined. DRN morphine did not affect basal LH release but it produced a rapid and highly significant rise in plasma prolactin. When DRN morphine was given (-15 min) and NE was infused icv (30 min), there was marked amplification in LH release compared to those values observed after only NE. However, there were no appreciable differences in LH values obtained after sc versus DRN morphine injections in response to NE. Similarly, the amplification of LH release which occurred following DRN morphine (-15 min) + MPOA-ECS (0 min) was not different from that obtained after sc morphine. In the final group of rats, DRN morphine was given (-15 min), the preoptic area was stimulated (0 min) and NE was infused (30 min). Following this treatment, plasma LH release was also markedly enhanced and did not differ appreciably (except at 60 and 120 min) from the levels of LH released after sc morphine. Prolactin concentrations rose slowly after icv NE to reach peak levels 75 min after treatment. Combinations of morphine + MPOA-ECS without or with NE neither augmented nor suppressed the high prolactin concentrations achieved after only DRN morphine infusions. We conclude from these data that: 1) those opiate neuronal terminals which synapse directly on LHRH neurons do not affect LHRH neuronal responsiveness to either NE, to MPOA-ECS or to combined preoptic stimulation+ NE, and 2) morphine has profound effects on LHRH neuronal responsiveness to both NE, to MPOA-ECS and, in particular, to combined ECS + NE. Since amplification of LH release occurs after treatment of rats with morphine either by sc injections or DRN infusions, the augmented LH and prolactin responses observed are most likely due to the morphine-induced release of serotonin and not to direct morphine effects on LHRH neurons.

Hormonal influences on morphology and neuropeptide gene expression in the infundibular nucleus of postmenopausal women

Neuronal hypertrophy occurs in a subpopulation of neurons in the infundibular nucleus of post-menopausal women. The hypertrophied neurons contain NKB, SP and estrogen receptor gene transcripts. Although associated with reproductive aging, post-menopausal neuronal hypertrophy is not a sign of central nervous system degeneration. Quite the opposite, because the hypertrophy is accompanied by marked increases in tachykinin gene expression, reflecting increased neuronal activity. We have proposed that infundibular neurons containing NKB, SP and estrogen receptor mRNAs participate in the hypothalamic circuitry regulating estrogen negative feedback on gonadotropin release in the human. In addition, there is evidence to suggest that the hypertrophied tachykinin neurons may be involved in the initiation of menopausal flushes. Because menopause affects a well characterized system, and has consistent and substantial changes in hormone levels, we have had the rare opportunity to correlate changes in hormone secretion with structural and neurochemical changes in the human hypothalamus. We suspect that future studies of the hypothalami of post-menopausal women will continue to be a fruitful avenue for investigating neuroendocrine regulation in the human.