Brain-periphery connections: do they play a role in mediating the effect of centrally injected interleukin-1 beta on gonadal function?

Endotoxin rapidly desensitizes the gonads to kisspeptin-induced luteinizing hormone release in male Siberian hamsters (Phodopus sungorus)

Activation of the immune system induces rapid reductions in hypothalamic-pituitary-gonadal (HPG) axis activity, which in turn decreases secretion of sex steroids. This response is likely adaptive for survival by temporarily inhibiting reproduction to conserve energy; however, the physiological mechanisms controlling this response remain unclear. The neuropeptide kisspeptin is a candidate to mediate the decrease in sex hormones seen during sickness through its key regulation of the HPG axis. In this study, the effects of acute immune activation on the response to kisspeptin were assessed in male Siberian hamsters (Phodopus sungorus). Specifically, an immune response was induced in animals by a single treatment of lipopolysaccharide (LPS), and reproductive hormone concentrations were determined in response to subsequent injections of exogenous kisspeptin. Saline-treated controls showed a robust increase in circulating testosterone in response to kisspeptin; however, this response was blocked in LPS-treated animals. Circulating luteinizing hormone (LH) levels were elevated in response to kisspeptin in both LPS- and saline-treated groups and, thus, were unaffected by LPS treatment, suggesting gonad-level inhibition of testosterone release despite central HPG activation. In addition, blockade of glucocorticoid receptors by mifepristone did not attenuate the LPS-induced inhibition of testosterone release, suggesting that circulating glucocorticoids do not mediate this phenomenon. Collectively, these findings reveal that acute endotoxin exposure rapidly renders the gonads less sensitive to HPG stimulation, thus effectively inhibiting sex hormone release. More broadly, these results shed light on the effects of immune activation on the HPG axis and help elucidate the mechanisms controlling energy allocation and reproduction.

Pituitary-gonadal hormones and interleukin patterns in leprosy

The functional status of pituitary-gonadal hormones and their relationship to the pattern of inflammatory cytokines in the lepromatous (LL/BL) and tuberculoid (TT/BT) poles of leprosy were investigated. Gonadotropins [luteinizing hormone (LH) and follicle-stimulating hormone (FSH)], interleukin (IL)-1beta, IL-6, tumour necrosis factor (TNF)-alpha and C-reactive protein (CRP) concentrations and erythrocyte sedimentation rate (ESR) were significantly higher in LL/BL leprosy patients than in controls and were not different from controls in TT/BT patients. LH and FSH were positively correlated with IL-1beta, IL-6 and TNF-alpha, and CRP concentrations and ESR. Testosterone plasma levels were significantly decreased in LL/BL patients and not different in TT/BT patients compared with controls. In addition, testosterone levels were inversely correlated with IL-6 and TNF-alpha. Prolactin plasma levels of both LL/BL and TT/BT patients were not different when compared with those of controls. There was a significant positive correlation between IL-6 and TNF-alpha plasma levels and ESR and CRP concentrations. IL-1beta was positively correlated with ESR but not with CRP. The significant correlations between gonadotropins and testosterone and cytokines in leprosy patients suggest that cytokines may have a direct influence at testicular level and may be of pathogenetic significance in leprosy and in other inflammatory states involving reproductive dysfunction.

Immune-endocrine interactions and Leydig cell function: the role of cytokines

Inflammatory disease is known to affect male reproductive function and fertility. Male accessory gland infections (MAGI) account for almost 15% of all cases of male infertility seen in infertility clinics. Infections of the male accessory glands are associated with increased counts of white blood cells in semen and elevated levels of pro-inflammatory cytokines in the semen and the testis. Numerous studies have underscored the importance of cytokines in the regulation of testicular and glandular function during pathophysiological events as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this paper is to particularly review the role of cytokines in the regulation of Leydig cell function in the testis primarily under pathophysiological conditions, and also considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Importance of the paraventricular nucleus of the hypothalamus as a component of a neural pathway between the brain and the testes that modulates testosterone secretion independently of the pituitary

We previously reported that in adult male rats, the intracerebroventricular (icv) injection of corticotropin-releasing factor (CRF) or the beta-adrenergic agonist isoproterenol (ISO) significantly inhibited the ability of human chorionic gonadotropin (hCG) to stimulate testosterone (T) secretion. The finding that this phenomenon also took place when LH release had been blocked with an LHRH antagonist suggested that icv CRF and ISO did not alter Leydig cell function by influencing the activity of pituitary gonadotrophs. We therefore proposed the existence of a neural pathway connecting the brain to the testes, whose activation by icv CRF or ISO interfered with T secretion. Based on the intratesticular injection of the transganglionic tracer pseudorabies virus, we recently identified the paraventricular nucleus (PVN) of the hypothalamus as a component of this neural link. The aim of the present work was to investigate the functional role of this brain area in mediating the ability of CRF and ISO to inhibit the ability of hCG to stimulate T secretion. We first demonstrated that local microinfusion of CRF or ISO directly into the PVN mimicked the effect of their icv injection, suggesting that the PVN does indeed represent a site of action of ISO and CRF in altering Leydig cell responsiveness to gonadotropin. In contrast, neither CRF nor ISO microinfusion into the central amygdala or the frontal cortex influenced hCG-stimulated T secretion. To further investigate the role of the PVN in ISO- and CRF-induced blunting of hCG stimulation of T, we determined the effect of icv CRF or ISO on testicular activity of rats with electrolytic lesions of the PVN. These lesions, which did not in themselves influence Leydig cell responsiveness to hCG, blocked the effect of both icv ISO and CRF on hCG-induced T release. Collectively, these results support the hypothesis that CRF- and ISO-induced activation of cells in the area of the PVN decreases the ability of gonadotropin to release T and suggests that this nucleus represents an important site of the proposed neural connection between the brain and the testes.

Anatomical and functional evidence for a neural hypothalamic-testicular pathway that is independent of the pituitary

Testosterone (T) secretion is classically considered to be under the primary control of pituitary LH, itself regulated by the hypothalamic peptide LH-releasing hormone. Secretagogues present in the general circulation and/or manufactured in the testis can also alter Leydig cell activity independently of the pituitary. Finally, spanchnic innervation regulates testicular LH receptors and blood flow. In the present work, we provide evidence that, in addition, there may be a neural brain-testicular circuit that regulates T release function independently of LH release. We had recently reported that the intracerebroventricular injection of IL-1beta, corticotropin-releasing factor, or beta-adrenergic agonists significantly interfered with the T response to human chorionic gonadotropin through mechanisms that did not involve LH. Here, we show that the injection of the transganglionic retrograde tracer pseudorabies virus into the testes caused viral staining in the spinal cord, the brain stem, and the hypothalamus. This observation indicates the presence of a neural pathway between the central nervous system and the testis. We then demonstrated that spinal cord injury significantly interfered with this staining, thus supporting the hypothesis that the proposed circuit travels through the cord. Finally, we showed that spinal cord injury completely abolished the ability of intracerebroventricularly injected IL-1beta or corticotropin-releasing factor to blunt the T response to human chorionic gonadotropin, which suggests that these two secretagogues act within the brain to stimulate a neural pathway that interferes with Leydig cell function independently of the pituitary. The hitherto unsuspected brain-testicular circuit that these experiments have uncovered may play a role in pathologies, so far unexplained, that are characterized by decreased T levels despite normal LH production.

Testicular macrophage modulation of Leydig cell steroidogenesis

This review will highlight recent advances in the study of the immuno-endocrinology of the testis, in particular how macrophage-derived inflammatory mediators affect Leydig cell functions. Both the beneficial and deleterious outcomes resulting from macrophage-Leydig cell interactions are discussed. A brief overview of testicular physiology is provided that discusses the functional and anatomical compartmentalization of the testis into the gamete and endocrine compartments where spermatogenesis and testosterone biosynthesis take place, respectively. The process of steroidogenesis including the activities of the steroidogenic enzymes and the role of steroidogenic acute regulatory protein (StAR) are described. The close physical association between Leydig cells and interstitial testicular macrophages suggests that these cells are functionally related. Under normal physiological and non-inflammatory conditions macrophages play an important role in Leydig cell development. If macrophages are absent from the testicular interstitium, Leydig cells fail to develop normally, which suggest that macrophages provide essential growth and differentiation factors for Leydig cells. In contrast, when macrophages are activated and elaborate inflammatory mediators, Leydig cell steroidogenesis is inhibited. Activated macrophages produce pro-inflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor (TNF) that are profoundly inhibitory to Leydig cells and appear to act as transcriptional repressors of steroidogenic enzyme gene expression. Macrophages also produce reactive oxygen species (ROS) such as hydrogen peroxide, which also inhibits Leydig cell functions. ROS appear to act acutely by perturbing Leydig cell mitochondria resulting in the inhibition of StAR protein expression. One important consequence of this immune modulation of Leydig cell function may be manifest behaviorally by switching the affected animal from 'testosterone' behavior, to 'sickness' behavior. Increased interest in immune-endocrine control of reproductive function over the past decade has stimulated research into the molecular and biochemical immunopathophysiology of the reproductive system. As investigations unravel mechanisms underlying reproductive dysfunction caused by inflammation and infection, an understanding of the role that immune-endocrine interactions play in the normal physiology of the reproductive system has emerged.

In vitro cytokine secretion in individuals with schizophrenia: results, confounding factors, and implications for further research

The present paper reviews the results of all publications on in vitro cytokine secretion in patients with schizophrenia, as published by March 2001. The authors supply easy to read tables with respect to the individual cytokines and soluble cytokine receptors investigated, the in vitro methodology used, characterization of the patient samples, and the results on cytokine secretion as stated in these studies. Inconsistent results, e.g., regarding in vitro secretion of IL-2 with 11/18 studies finding decreased secretion, 5/18 finding no change, and 2/18 finding increases, cannot systematically be correlated with any methodological procedures nor any diagnostic subtypes, per se. However, factors such as medication and cigarette smoking are likely to play a role. The authors suggest that more hypothesis-driven research, together with more carefully designed studies, as well as better communication between basic or animal researchers and clinicians might help to answer the question of whether there are meaningful peripheral changes in the immune system related to schizophrenia.

Diametric effects of bacterial endotoxin lipopolysaccharide on adrenal and Leydig cell steroidogenic acute regulatory protein

Immune activation results in the activation of adrenal steroidogenesis and inhibition of gonadal steroidogenesis. Previous studies indicated that these effects were caused primarily by activation and suppression of the secretion of ACTH and LH, respectively. However, other evidence indicated a direct effect of the immune system on the gonads. In this study, serum testosterone, quantitated by RIA after lipopolysaccharide injection, showed a significant decrease within 2 h. Parallel measurement of serum LH showed no change. There were no differences in LH receptor or cAMP produced in Leydig cells between vehicle- and lipopolysaccharide-injected mice. The 30-kDa form of the steroidogenic acute regulatory (StAR) protein was quantitated, by Western blot, in Leydig cells and was found to decrease in a time-dependent manner. No change in StAR protein messenger RNA (mRNA) was detected by Northern analysis during this time, nor were any changes found in the levels of mRNA for the steroidogenic enzymes P450scc, 3beta-hydroxysteroid dehydrogenase delta4-delta5-isomerase, or P450c17. In the adrenal, StAR protein was increased, as was StAR protein mRNA. No changes were observed in the levels of mRNA for P450scc, 3beta-hydroxysteroid dehydrogenase delta4-delta5-isomerase, or P450c21. Thus, although the mechanisms of regulation differ, changes in the levels of StAR protein are a sensitive indicator of the steroidogenic capacity of these two tissues.

Role of cytokines in testicular function

Inflammatory disease has been established to affect male reproductive function and fertility. Relevant inflammatory diseases include general and chronic infectious diseases as well as localized acute or chronic infections of the male genitourinary tract. Male accessory gland infections account for almost 15% of all cases of male infertility seen in infertility clinics while fertility usually is not a clinical objective among patients with acute systemic infections such as Gram-negative sepsis. Infections of the male accessory glands frequently are associated with increased counts of white blood cells in semen and elevated levels of proinflammatory cytokines in semen and the testis. There is a mounting body of evidence that demonstrates the importance of cytokines and chemokines in the regulation of testicular and glandular function during pathophysiological states as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this review is to examine the role of cytokines in the regulation of steroidogenesis and spermatogenesis in the testis under physiological and pathophysiological conditions and considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Differential effects of superior and inferior spermatic nerves on testosterone secretion and spermatic blood flow in cats

It has been postulated that testosterone secretion is partially regulated by signals from the spermatic nerves. To further examine this hypothesis in vivo, the superior (SSN) or the inferior (ISN) spermatic nerves were stimulated electrically (varying intensity, 25 Hz, 0.2 msec, 10 min) in anesthetized cats, determining the testosterone concentration and the blood flow in the spermatic vein. In some additional experiments arterial blood was sampled, and norepinephrine (NE) output was calculated. Stimulation of the SSN (25-35 V) increased the testosterone concentration in spermatic vein blood (P < 0.01 compared with prestimulation levels). The response varied among animals, reaching a 50-100% increase in some animals, whereas in others it ranged from almost undetectable to more than 10 ng/100 g x min. Under the same experimental conditions, the NE output increased from 135.4 +/- 99 to 1614.2 +/- 347 pg/ml (P < 0.01), and spermatic blood flow decreased from 24.1 +/- 1.42 to 20.2 +/- 1.65 ml/min x 100 g (P < 0.05) during nerve stimulation. By contrast, stimulation of the ISN (25-35 V) modified neither the testosterone concentration, the NE output, nor the blood flow in the spermatic vein. High intensity stimulation (36-70 V) of each spermatic nerve evoked different vascular and hormonal effects. SSN activation induced a marked decrease in spermatic blood flow during stimulation and an increase in the testosterone response, whereas ISN activation resulted only in an enhanced spermatic blood flow. Our results suggest that testosterone secretion, although mainly dependent on gonadotropin secretion, could be further regulated by neural inputs from the SSN acting directly or alternatively through changes in blood flow. It would appear that the SSN mainly supplies the vasoconstrictor fibers to the testis, whereas the ISN provides vasodilator fibers.

The inhibitory effect of intracerebroventricularly injected interleukin 1beta on testosterone secretion in the rat: role of steroidogenic acute regulatory protein

Exposure to disease or injury often results in impaired reproductive activity accompanied by decreased testosterone levels. After immune activation, the cytokine interleukin 1-beta (IL-1beta) circulates in high concentrations, and its exogenous administration evokes many of the sequelae of immune activation. Previously, we have shown that the administration of this cytokine into the cerebral ventricles blunts hCG-stimulated testosterone secretion. This effect, though time-dependent, occurs before significant elevation of interleukin 6 in the peripheral bloodstream, does not depend on adrenal activation, and/or changes in LH concentrations, leading us to hypothesize a direct connection between the brain and testis. To explore this mechanism further, we isolated testicular tissue from rats treated intracerebroventricularly (icv) with vehicle or IL-1beta 30 or 90 min before they were killed. We found that in vivo cytokine treatment blunted ex vivo testosterone secretion in response to hCG, showing that the mechanism is independent of circulating cytokines. Though hCG binding was moderately reduced by icv IL-1beta in these preparations, the extent of this inhibition did not explain our observations. As the first acutely and hormonally regulated step in the biosynthesis of testosterone is the transfer of cholesterol into the inner mitochondrial membrane, which is mediated by steroidogenic acute regulatory (StAR) protein, we hypothesized that the rapid effects of icv IL-1beta on testicular responsiveness to hCG might be due to reduced levels of StAR. We report here that StAR protein was indeed reduced in Leydig cells isolated from rats treated in vivo with IL-1beta. Furthermore, treatment with a water-permeable form of cholesterol that bypasses the requirement for StAR partially restored hCG-stimulated testosterone secretion from testes isolated from rats treated icv with IL-1beta. Taken together, our data indicate that StAR plays a role in the suppression of testicular function evoked by central administration of IL-1beta.

Cytokines in the neuroendocrine system

Cytokines are important partners in the bidirectional network interrelating the immune and the neuroendocrine systems. These substances and their specific receptors, initially thought to be exclusively present in the immune system, have recently been shown to be also expressed in the neuroendocrine system. Cytokines can modulate the responses of all endocrine axes by acting at both the central and the peripheral levels. To explain how systemic cytokines may gain access to the brain, several mechanisms have been proposed, including an active transport through the blood-brain barrier, a passage at the circumventricular organ level, as well as a neuronal pathway through the vagal nerve. The immune-neuroendocrine interactions are involved in numerous physiological and pathophysiological conditions and seem to play an important role to maintain homeostasis.

Alcohol rapidly lowers plasma testosterone levels in the rat: evidence that a neural brain-gonadal pathway may be important for decreased testicular responsiveness to gonadotropin

Alcohol is reported to suppress testosterone (T) secretion in the adult male rat. Decreases in the circulating levels of luteinizing hormone (LH) and/or the activity of testicular steroidogenic enzymes have been proposed as putative mechanisms underlying this inhibitory effect. We have recently provided functional evidence for a neural pathway between the brain and the male gonads that plays an important role in the ability of brain proinflammatory cytokines to blunt testicular responsiveness to human chorionic gonadotropin (hCG). The present work was designed to test the hypothesis that a similar pathway might be implicated in the inhibitory influence of alcohol on T secretion. Alcohol, administered intraperitoneally or intragastrically, significantly prevented the T response to the gonadotropin. This effect was significant within 15 min of drug treatment. In the intragastric model (the only one used for this type of experiment), the effect of alcohol was not altered by prior blockade of LH release, which suggests that it is independent of changes in the activity of the pituitary gonadotrophs. The lowest effective dose of alcohol, delivered intraperitoneally, was 2.0 g/kg. The intracerebroventricular injection of the alpha- and beta-adrenergic receptor antagonists phentolamine and propranolol significantly reversed the inhibitory influence of alcohol when it was administered 15 min, but not 60 min, before hCG. Collectively, our results indicate that (1) alcohol induces a rapid and profound decrease in plasma T levels that is secondary to decreased testicular responsiveness to hCG; and (2) at least part of this acute inhibitory action of alcohol may depend on the activation of a neural, adrenergic-dependent pathway between the brain and the testes.

The intracerebroventricular injection of interleukin-1beta blunts the testosterone response to human chorionic gonadotropin: role of prostaglandin- and adrenergic-dependent pathways

The present work extends our previous report that the intracerebroventricular (i.c.v.) injection of interleukin-1beta(IL-1beta, 80 ng) significantly blunted the testosterone response to 1 U/kg human CG (hCG), an effect that we attributed to the stimulation of inhibitory pathways connecting the hypothalamus to the testes. Systemic blockade of prostaglandin-dependent pathways with ibuprofen (alpha-methyl-4-[2-methylpropyl]benzeneacetic acid; sodium salt), which did not, in itself, alter the stimulatory effect of hCG on testosterone release in control rats, modestly, but significantly (P < 0.05) reversed the inhibitory influence of IL-1beta. In contrast, blockade of brain receptors for CRF was unable to alter the effect of IL-1beta, as were lesions of the ventromedial hypothalamic nucleus, a brain area implicated in the control of ovarian function. Blockade of beta-adrenergic receptors significantly prevented the decrease in testicular responsiveness induced by the i.c.v. injection of IL-1beta. Finally, the central injection of the beta-adrenergic agonist isoproterenol, as well as that of norepinephrine, mimicked the ability of icv IL-1beta to blunt testicular secretory activity and produced a marked (P < 0.01) decrease in the response to hCG within 5 min of their administration. We propose that the explanation that best fits our findings is that the i.c.v. injection of IL-1beta activates a neural, catecholamine-dependent pathway that connects the brain and the testes independently of the pituitary.

Inhibition of gonadotropin-induced testosterone secretion by the intracerebroventricular injection of interleukin-1 beta in the male rat

The intracerebroventricular (icv) injection of the proinflammatory cytokine interleukin (IL)-1 beta is known to significantly decrease plasma LH levels in the male rat, thereby lowering testosterone (T) secretion. We show here that central administration of this cytokine (20-80 ng) also inhibits T secretion in response to human CG (hCG), an effect that is apparent already when IL-1 beta is injected 15 min before hCG. This phenomenon is independent of LH secretion because lowering LH levels with the potent GnRH antagonist Azaline B neither mimics nor affects the suppressive influence of icv IL-1 beta on the hCG-induced T secretory response. Elevations in plasma corticosterone levels do not seem to play a role either, because icv IL-1 beta is able to blunt hCG-induced T secretion in animals whose corticosterone has been removed by adrenalectomy or reduced by the administration of antibodies to CRF. Furthermore, the observation that icv IL-1 beta inhibits the T response to hCG before elevations in plasma IL-6 concentrations are detectable, and that central treatment with the cytokine is more effective than iv treatment, indicates that circulating levels of neither IL-1 beta nor IL-6 are important mediators of this effect. Collectively, these results lead us to propose that IL-1 beta of central origin influences neural pathways linking the brain and the testes, resulting in decreased testicular responses to hCG.

Lipopolysaccharide-induced suppression of the hypothalamic gonadotropin-releasing hormone pulse generator in ovariectomized goats

Ovariectomized goats were implanted with the electrode arrays for monitoring the electrophysiological manifestation of the activity of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator, namely multiple-unit activity (MUA) volleys associated with pulsatile luteinizing hormone secretion. They were then subjected to i.v. challenges of lipopolysaccharide (LPS) at the dose of 200 or 400 ng/kg. The interval between the MUA volleys was significantly prolonged by higher dose of LPS whereas neither amplitude nor duration of the MUA volleys was altered. These results suggest that immunological disturbance as evoked by LPS administration directly affects the hypothalamic GnRH pulse generator by slowing down the pulse frequency, and thereby lowers gonadotropin secretion from the anterior pituitary gland, which would culminate in gonadal suppression.