Insulin-induced hypoglycemia does not impair the surge of luteinizing hormone secretion in the proestrous rat

Dopamine (DA) neurons in the ventral tegmental area and substantia nigra pars compacta were induced to fire in bursts with application of N-methyl-D-aspartate (NMDA, 20 microM) and apamin (100 nM) while recording intracellularly in the rat brain slice. L-Arginine (300 microM), a substrate for nitric oxide (NO) production, increased both the number of spikes per burst and the magnitude of interburst hyperpolarizations. Nitric oxide synthase inhibitors N-nitro-L-arginine methyl ester (L-NAME, 100 microM), N-nitro-L-arginine, and 7-nitroindazole inhibited NMDA-induced burst firing by reducing the number of spikes per burst. Moreover, L-arginine (100 microM) reversed the inhibition of burst firing produced by L-NAME. These findings suggest that NO facilitates NMDA-induced burst firing in DA neurons.     

Mating activates NMDA receptors in the medial preoptic area of male rats.

Studies have emphasized the role of the medial preoptic area (MPOA) as an important site for the regulation of male sexual behavior. Indeed, ablations of the MPOA impair sexual behavior, whereas stimulation of the MPOA enhances behavior. Furthermore, neural activity in the MPOA increases with mating. The current study tested the hypothesis that activation of N-methyl-D-aspartate (NMDA) receptors occurs in MPOA neurons and is essential for the expression of male sexual behavior in rats. Results indicate that nearly all MPOA neurons that expressed Fos following mating also contained the NR1 subunit of NMDA receptors. Furthermore, mating increased phosphorylation, thus activation, of NR1 in the MPOA. Additionally, blocking NMDA receptors significantly decreased mating-induced Fos expression and mating-induced phosphorylation of NMDA receptors and impaired male sexual behavior. These results provide evidence that mating activates NMDA receptors in the MPOA and that this activation is important for the expression of male sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of alpha-2 receptors in the medial preoptic area in the regulation of sleep-wakefulness and body temperature

The study was conducted on 48 free-moving male rats to find out the role of the medial preoptic alpha2 receptors in the regulation of sleep and body temperature. Recording electrodes for assessment of sleep-wakefulness, and injector cannulae for injection of drugs in the medial preoptic area were chronically fixed on the skulls of the animals. The noradrenergic fibres projecting to the medial preoptic area were destroyed in 24 rats by administration of 6-hydroxydopamine at the ventral noradrenergic bundle. Though arousal was produced in normal rats by the injection of the alpha2 adrenergic agonist, clonidine, at the medial preoptic area, it induced sedation in rats with noradrenergic fibre lesion. Clonidine did not alter the rectal temperature in normal rats but it induced hypothermia in lesioned rats. Injection of alpha2 antagonist, yohimbine, at the medial preoptic area induced sleep in rats with intact noradrenergic fibres. However, the sleep inducing effect of this drug was very much attenuated in the lesioned animals. There was no significant change in body temperature, in both these groups of animals, after yohimbine administration. The study indicates the role of presynaptic alpha2 adrenergic receptors in arousal response and indirectly supports the contention that the alpha1 postsynaptic receptors at the medial preoptic area are involved in hypnogenesis. It also suggests that the thermal changes induced by adrenergic system are mediated through alpha1 postsynaptic receptors. But the thermal changes do not contribute towards the induced alterations in sleep-wakefulness. It is proposed that there should be separate sets of noradrenergic terminals for regulation of sleep and body temperature.     

Fos expression in rat pontine tegmental neurons following activation of the medial preoptic area

Because murine myeloma plasma cells and normal human lymph node plasma cells express BCL-X, we evaluated BCL-X expression in malignant human plasma cells. BCL-X expression was detected in several human myeloma cell lines, as well as in CD38-sorted bone marrow cells obtained from some patients. Only the antiapoptotic long form of BCL-X (BCL-X-L), was detected. Because BCL-X-L expression can protect tumor cells from apoptotic death induced by chemotherapeutic agents, we tested the clinical relevance of expression in 55 archival bone marrow biopsies. The biopsies were stained by immunohistochemistry, and BCL-X expression was correlated with the subsequent response to treatment. BCL-X expression in malignant plasma cells strongly correlated with decreased response rates in patient groups treated with either melphalan and prednisone or vincristine, Adriamycin, and dexamethasone. Response rates were 83-87% in non-BCL-X-expressing cases and 20-31% in BCL-X-expressing cases. In addition, BCL-X expression was more frequent in specimens taken from patients at relapse (77%), when compared to those at initial diagnosis (29%). Further support for the association of drug resistance with BCL-X-L expression came from studies of the 8226 dox-40 cell line. This line, which expresses p-glycoprotein and serves as a model of multidrug resistance in multiple myeloma cells, demonstrated an up-regulated expression of BCL-X-L, which was relatively specific, in that BCL-2 or BAX expression was not altered. In addition, dox-40 cells demonstrated a generalized resistance to apoptosis that was induced by several different agents. These results indicate that malignant plasma cells can express BCL-X-L and that such expression may be a marker of chemoresistant disease.     

Differential effects of intraventricular luteinizing hormone releasing hormone (LH-RH) and norepinephrine on electrical activity of the arcuate nucleus in the proestrous rat

Effects of intraventricular infusions of LH-RH and norepinephrine (NE) on the electrical activity of the arcuate nucleus were investigated in normally cycling proestrous rats. Under urethane anesthesia, recordings were made of amplitude-discriminated multiple unit spike activity and integated multiunit activity (MUA) in parallel with cortical EEG. Control infusions of saline (2 microliter, isotonic, pH 5.5) were ineffectual, but LH-RH (0.5 microgram) induced a significant increase in both multiunit spike activity and integrated MUA. While the response appeared to be continuous, statistical analysis revealed 2 phases: a quick rise which persisted for approximately 5 min, followed 15 min later by a longer-lasting elevation in activity. The onset of the 2nd increase corresponded with the attainment of peak values of pituitary LH output. Subsequent treatment with 20 microgram NE, on the other hand, resulted in a marked depression of activity. The fact that NE depresses arcuate neuronal activity at dose levels which cause the release of LH and that LH-RH increases activity within the same population of neurons, while possibly mediating an 'ultrashort-loop' negative feedback effect, suggest that this responsive component of the arcuate nucleus, perphaps the tuberoinfundibular dopaminergic system of neurons, is inhibitory to LH release.     

The effect of chronic luteinizing hormone treatment on adult rat Leydig cells

OBJECTIVES: In a preliminary pilot study of 30 treatments in 26 patients with osteonecrosis of the jaws and chronic disabling facial pain, our specific aim was to determine whether, to what degree, and how safely therapy of hypofibrinolysis and thrombophilia would ameliorate the chronic pain associated with osteonecrosis of the mandible and maxilla. STUDY DESIGN: Thrombophilia was treated with Coumadin (DuPont) in 10 patients; hypofibrinolysis was treated with Winstrol (Sanofi-Winthrop) in 20 patients, including 4 who had mixed thrombophilia and hypofibrinolysis and had previously been treated with Coumadin. The initial treatment period was targeted to be 4 months. Each patient was asked to keep a daily written pain-relief numeric rating score and side-effects diary and to provide a summary pain-relief numeric rating score and side effects compilation for the total treatment period. RESULTS: There were 4 men and 22 women in the study group; their mean age was 49 +/- 11 years. The mean onset of their osteonecrosis pain was at age 45 +/- 12 years, and the mean duration of their facial pain prior to therapy was 4.5 +/- 4.2 years. Ten patients had one or more thrombophilic traits (there were two patients with protein C deficiency, five with resistance to activated protein C and/or the mutant Factor V Leiden gene, and four with high anticardiolipin antibodies). The 10 patients who were thrombophilic were treated with Coumadin (the international normalized ratio was targeted to 2.5-3.0) for 22 +/- 9 weeks. By self-reported pain-relief numeric rating scores, 6 of the 10 patients with thrombophilia (60%) had > or = 40% pain relief, 2 (20%) had no change, and 2 (20%) had increased pain (30% and 80% worse). Nine of the 10 patients with thrombophilia (90%) had no Coumadin-related side effects; 1 patient (10%) stopped Coumadin therapy (after 28 weeks) because of nosebleeds. Winstrol (6 mg per day) was used for 16 +/- 9 weeks in 20 patients with hypofibrinolysis, some of whom had one or more hypofibrinolytic traits (10 had high levels of plasminogen activator/inhibitor activity, usually accompanied by low stimulated tissue plasminogen activator activity; 13 had high Lp[a] lipoprotein). Of these 20 patients with hypofibrinolysis, 9 patients (45%) had > or = 40% pain relief, 3 patients (15%) had 20% to 30% relief, 5 patients (25%) had no improvement, and 3 patients (15%) had increased pain (30% worse, 60% worse, and 70% worse). Six of the 20 patients with hypofibrinolysis (30%) had no Winstrol-related side effects, while 14 (70%) had side effects that could be attributed to Winstrol, including weight gain, peripheral edema, increased facial and body hair, and acne--all of which were reversed within 6 weeks of stopping Winstrol therapy. CONCLUSIONS: We postulate that thrombophilia and hypofibrinolysis lead to impaired venous circulation and venous hypertension of the mandible/maxilla with subsequent development of osteonecrosis and chronic facial pain. In many patients, facial pain can be ameliorated by treating the pathogenetic coagulation defects with Coumadin or Winstrol. Large, double-blind, placebo-controlled crossover studies will be required in the future to validate these preliminary results and to determine whether pain relief with Coumadin or Winstrol justifies the risks and side effects associated with these medications, especially for long-term use, in osteonecrosis of the jaws.     

Effects of morphiceptin in the medial preoptic area on male sexual behavior

Morphiceptin, a selective mu opioid agonist, injected into the medial preoptic area (MPOA), delayed the onset of copulation in male rats, but did not affect genital reflexes, sexual motivation or general motor activity. In a dose-dependent manner, morphiceptin (100 ng and 1000 ng) injected into the MPOA increased mount and intromission latencies. Similar injections of morphiceptin into the ventromedial hypothalamus had no effect on any parameter of copulation. The increase in copulatory latencies following the injection of the highest dose of morphiceptin was blocked by pretreatment with the opioid antagonist naloxone. In the X-maze task, morphiceptin had no effect on sexual motivation, as measured by the percentage of trials on which the male chose the female's chamber, but it increased the number of trials in which the subject did not select a chamber within 60 s and the latency to the female the first time he chose her chamber. Similar to the copulation task, the mount and intromission latencies were also increased in the X-maze, after the male reached the female. Morphiceptin in the MPOA had no effect on ex copula genital reflexes, tested in restrained supine males, or on motor activity, tested in a grid box. These results suggest that morphiceptin disrupts either the specific copulatory somatomotor pattern or a more general motivational component.     

Effects of dialyzing gamma-aminobutyric acid receptor antagonists into the medial preoptic and arcuate ventromedial region on luteinizing hormone release in male sheep

We investigated the effects of microdialyzing alpha-aminobutyric acid (GABA) receptor antagonists into either the medial preoptic area (mPOA) or the arcuate-ventromedial region (ARC-VMR) on LH secretion. Bicuculline methiodide (BMI, GABA(A) receptor antagonist), and either 2-hydroxysaclofen (SAC) or CGP 55845A (CGP, GABA(B) receptor antagonists) were used. In experiment 1, castrated rams received 4-h dialysis into either the mPOA (n = 5) or ARC-VMR (n = 4) of artificial cerebrospinal fluid (aCSF) followed by 4 h of either BMI (aCSF-BMI, 375 microM in mPOA, 1 mM in the ARC-VMR for 2-1/2 h), or aCSF-SAC (5 mM). In experiment 2, castrated rams received dialysis only in the ARC-VMR (n = 5) of aCSF-aCSF, aCSF-BMI (375 microM), or aCSF-CGP (50 microM). In experiment 3, untreated or testosterone (T)-treated castrated rams (n = 6/group) received dialysis only in the ARC-VMR of aCSF-aCSF, aCSF-BMI (375 microM), or aCSF-CGP (500 microM). Jugular blood was collected at 10-min intervals. In experiment 1, BMI suppressed mean plasma LH (p < 0.05) and increased interpulse interval (IPI, p < 0.05) at both sites. In experiment 2, BMI significantly reduced mean LH and increased IPI (p < 0.01). In experiment 3, BMI reduced mean LH in both the presence (p < 0.05) and absence of T (p < 0.01) and increased IPI (p < 0.01) in the absence of T. SAC, CGP, and aCSF did not affect LH in any experiment. These results show that dialysis of BMI, into either the mPOA or the ARC-VMR of either castrated or T-treated castrated rams decreased LH release, whereas dialysis of GABA(B) antagonists at these sites was without detectable effect.     

Luteinizing hormone requirements for ovulation in the pentobarbital-treated proestrous rat

The LH requirements for ovulation in the pentobarbital-blocked proestrous CD rat have been studied by increasing serum gonadotropin levels through electrical stimulation of the brain and subsequently comparing the effects of timed hypophysectomy on ovulation and serum LH concentrations. The arcuate nucleus (ARC) or the medial preoptic area (POA) was stimulated unilaterally for 45 min with matched pairs of biphasic rectangular pulses through a coaxial platinum electrode. Serum LH was significantly elevated above basal values at the end of stimulation, but not in sham-stimulated controls. The results of both hormone measurement and hypophysectomy showed that the pituitary continued to release LH after extrinsic stimulation of the hypothalamus had ceased. Animals did not ovulate if they had been hypophysectomized at the end of the 45 min stimulation whereas nearly all ovulated if hypophysectomy was delayed for an additional 20 min. Some evidence suggested that the pituitary could be removed earlier without affecting ovulation if the rate of LH release was increased. The minimum peak LH concentration measured in rats that subsequently ovulated fully was 187 ng/ml, substantially lower than concentrations ordinarily attained in the spontaneous proestrous surge. When serum LH was insufficiently high to cause follicle rupture, there was nevertheless the resumption of meiosis and luteinization of the large ovarian follicles. Attempts were made to restore ovulability in animals presumed to have released a subovulatory quota of gonadotropin. Ovulation was obtained when such animals, prepared by hypophysectomy after the 45 min stimulation, had been bilaterally nephrectomized prior to stimulation. However, multiple injections of progesterone after hypophysectomy were without effect. The results are discussed in relation to variables that affect minimum requirements of LH for ovulation.     

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

Phagocytosis is a fundamental process in innate resistance to infection. We have used the pathogenic yeast Cryptococcus neoformans to study the interaction of this encapsulated organism with murine macrophages in vitro. In the absence of exogenous opsonins the encapsulated yeast is almost totally resistant to ingestion by murine macrophages. Owing to its ability to activate the alternative complement pathway, the anti-phagocytic properties of the polysaccharide capsule can be partially overcome following opsonization in vitro with non-immune mouse serum and subsequent phagocytosis via complement receptors. Here, we demonstrate the importance of the complement receptor type 3 (CR3) in in vitro phagocytosis of the yeast and in in vivo resistance to infection. In vitro, 70% of a population of resident murine macrophages are able to ingest C. neoformans and then only inefficiently (1-2 organisms per cell). Previously we have shown that tumour necrosis factor-alpha (TNF-alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF) efficiently enhance ingestion of serum-opsonized encapsulated C. neoformans, and we now show that the cytokines convert a population of resident macrophages to a state where all the cells are competent for ingestion of large numbers of yeasts (6-8 per cell). We also show that these cytokines have a direct effect on CR3, as enhanced levels of complement-opsonized sheep red blood cells (EIgMC) bind to macrophages activated in this way. However, cytokines that have previously been shown to enhance phagocytosis of EIgMC have no effect on ingestion of encapsulated C. neoformans. These results demonstrate that the cytokines regulating CR3-dependent ingestion of C. neoformans are different to those regulating ingestion of EIgMC and reinforce the importance of studying pathogens rather than inert ligands in understanding the regulation of phagocytosis.     

Estrogen increases affinity of oxytocin receptors in the medial preoptic area-anterior hypothalamus

Analysis of binding data from saturation experiments using a radiolabeled oxytocin antagonist ([125I]OTA) demonstrated an increase in binding affinity after treatment with 5 micrograms estradiol benzoate (EB) for 3 days in membrane fractions from the medial preoptic area-anterior hypothalamus (MPOA-AH) of ovariectomized (OVX) rats. Analysis of data from competition experiments revealed high- and low-affinity [125I]OTA binding sites in the MPOA-AH, the medial basal hypothalamus (MBH), and hippocampus of OVX controls. Three days of EB treatment reduced low-affinity binding sites in the MPOA-AH and MBH, but not in the hippocampus. Treatment of membrane fractions from the MPOA-AH of oil-treated OVX rats in vitro with 100 nM OT or with estrogen or progesterone conjugated to bovine serum albumin (E-BSA and P-BSA) also reduced low-affinity [125I]OTA binding sites but BSA alone did not.     

Glucose availability modulates the timing of the luteinizing hormone surge in the ewe

To determine if glucose availability modulates the timing of the positive feedback action of oestrogen on gonadotropin secretion, we monitored the estradiol-induced luteinizing hormone (LH) surge in sheep (n = 5/group) made transiently hypoglycemic by insulin. Experiment 1 determined an effective insulin treatment, one which would depress tonic LH secretion. Two injections of insulin (5 IU/kg iv) 4 h apart were found to induce extended hypoglycemia (10-13 h) and to decrease the LH pulse frequency for 8 h (5.0 +/-0.32 pulses/4 h before versus 2.5+/-0.34 pulses/4 h after insulin; P<0.05; mean +/- SEM). Using this same paradigm, experiment 2 determined the influence of the transient hypoglycemia on the LH surge mechanism. In control sheep, estradiol (subcutaneous implants at hour 0) evoked an LH surge with a latency period of 12.4+/-0.5 h. When insulin was administered either before (hours -4 and 0) or after the estradiol stimulus (hours 4 and 8, or 12 and 16), the onset of the LH surge was delayed to 29.0+/-2.4 h (average of all three time groups, P <0.05). Infusion of glucose from hours 12-30, along with insulin, prevented hypoglycemia and restored the normal timing of the oestrogen-induced LH surge to that of controls (15.4+/-0.93 h, P>0.05). These findings suggest that not only is the tonic mode of LH secretion sensitive to metabolic fuel availability, but the surge mode of LH secretion is as well.     

Evidence for a luteinizing hormone surge center in the hypothalamus of the pig

Lipoprotein-X (Lp-X) is an abnormal low-density lipoprotein frequently found in liver disease. It is regarded as the most sensitive and specific biochemical parameter for the diagnosis of intra- and extrahepatic cholestasis. Moreover, Lp-X is supposed to contribute to the development of hypercholesterolemia in cholestatic liver disease, because it fails to inhibit de novo cholesterol synthesis. This investigation will focus on the relationship between the presence of Lp-X and serum lipid concentrations in cirrhosis. The significance of Lp-X in the diagnosis of cholestasis, compared with alkaline phosphatase (AP), gamma-glutamyl transferase (GGT), and bilirubin levels, will be assessed as well. The present cross-sectional study includes 212 patients with histopathologically proven cirrhosis. The detection of Lp-X and the quantification of -, beta-, and pre-beta-cholesterol was based on agar gel electrophoresis and polyanion precipitation. For the characterization of liver function, the concentrations of albumin and bilirubin, the activities of liver enzymes, and coagulation times were assessed. In a subgroup of 40 individuals, liver biopsies were re-evaluated to confirm or exclude intrahepatic cholestasis. As a result, there was no association between the appearance of Lp-X and total cholesterol concentrations. While all patients with Lp-X showed intrahepatic cholestasis (predictive value of the positive test = 1), only 16 of 28 patients with cholestasis formed Lp-X (sensitivity = 0.57). The activities of AP and of GGT, as well as the concentrations of bilirubin, were strongly elevated in most patients, with and without cholestasis. The predictive values of AP, GGT, and bilirubin were 0.77, 0.69, and 0.74 for the positive test and 0.5, 0, and 0.6 for the negative test, respectively. We conclude that Lp-X is not related to hypercholesterolemia in cirrhosis. The positive, but not the negative, Lp-X test has high predictive value for the diagnosis of cholestasis in cirrhosis. The biochemical parameters traditionally used for the assessment of extrahepatic cholestasis, AP, GGT, and bilirubin, do not support the diagnosis of intrahepatic cholestasis caused by cirrhosis.     

Vasopressin receptors in the mouse (Mus musculus) brain: sex-related expression in the medial preoptic area and hypothalamus

We have investigated the distribution of vasopressin binding sites in the brain of male and female adult mice using a radio-iodinated ligand and film autoradiography. Vasopressin receptors were uncovered in various regions of the brain including the basal nucleus of Meynert, the substantia innominata, the hypothalamic paraventricular nucleus, the substantia nigra pars compacta and the hypoglossal nucleus. A sex-related difference in the expression of vasopressin receptors was seen in the medial preoptic area/anterior hypothalamus corresponding to the rat sexually dimorphic nucleus in the rat and in the hypothalamic mammillary nuclei. In both structures the autoradiographic labeling is more intense in females than in males. These observations confirm that vasopressin binding sites are present in the hypothalamic preoptic area of most species examined so far and that sex-related expression of neuropeptide receptors could trigger sex-related behavioral differences.     

Synaptic connections between substance P-containing axons and estrogen receptor-synthesizing neurons in the medial preoptic area of the rat brain

Dual-label immunocytochemical procedures were employed to provide ultrastructural evidence for the presence of substance P (SP) in afferents to estrogen-receptive neurons in the medial preoptic area (MPO) of the female rat. SP-immunoreactive axon terminals were observed to innervate the periventricular (PvPO) and medial (MPN) preoptic nuclei of the MPO densely, and to form synaptic connections at these sites with neurons which contain estrogen receptors in their nucleus. These results indicate that estrogen-receptive preoptic neurons may be regulated by SP-containing neuronal pathways via synaptic mechanisms.     

Microinfusion of cocaine into the medial preoptic area or nucleus accumbens transiently impairs maternal behavior in the rat.

Cocaine was microinfused bilaterally (50 μg/0.5 μl/side) into the medial preoptic area (MPOA) or nucleus accumbens (NA), 2 regions within the rat brain neural circuit known to mediate maternal behavior (MB). Additionally, 2 sites not involved in this neural circuit, the dorsal striatum and dorsal medial hippocampus, were used as control sites. Microinfusion of cocaine into the MPOA or NA impaired MB, whereas infusion into the control sites did not. MB impairment was not temporally coincident with the increased locomotor activity, also documented after cocaine infusion into the MPOA or NA, arguing strongly that impaired MB is a direct, specific effect of cocaine in these areas, not a derivative of increased motor activity. This is the first demonstration that cocaine action on single central nervous system (CNS) sites can impair MB to the same extent as systemic injections. Thus, cocaine's simultaneous effect on multiple CNS sites is not required for MB impairment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)