Morphine-3-glucuronide: hyperglycemic and neuroendocrine potentiating effects

The greater potency of morphine-6-glucuronide (M6G) as well as the inactivity of morphine-3-glucuronide (M3G) with respect to the antinociceptive effects of the parent molecule, morphine (MOR), have been well established. It has been suggested that M3G is an antagonist of MOR's antinociceptive and respiratory depressive effects. The present study addressed the central nervous system (CNS) interaction of these opiate metabolites on their metabolic and hormonal effects. Whole body glucose kinetics were assessed on conscious, chronically catheterized, unrestrained rats. M3G (5 μg) or H₂O (5 μl) was injected intracerebroventricularly (i.c.v.) 15 min prior to the bolus administration of H₂O (5 μl), M6G (1 μg), or MOR (80 μg). i.c.v. M3G (5 μg) resulted in behavioral excitation, hyperglycemia (+50%), stimulation of glucose rate of appearance (R_a; +100%), glucose rate of disappeaance (R_d; +70%), and metabolic clearance rate (MCR; +33%) within 30 min after injection with no alterations in hormone concentrations. i.c.v. M6G and MOR produced progressive hyperglycemia with significantly high catecholamine and corticosterone levels. M3G pretreatment resulted in enhanced elevations in plasma glucose levels (+52% and +18%), plasma lactate (+138% and +108%), norepinephrine (+96% and +30%), and epinephrine (+62% and +67%) in response to both i.c.v. MOR and M6G administration. These findings suggest a non-opiate and non-hormonal mechanism for M3G-induced hyperglycemia. In contrast, the metabolic and hormonal responses to i.c.v. M6G and MOR are associated with elevations in catecholamine and corticosterone levels, which are remarkably enhanced by M3G pretreatment, most likely through accelerated catecholamine release. Our findings suggest a modulatory role for MOR glucuronidation, not only by rendering it inactive, as in the case of M3G, but by an interplay of the metabolic effects of the parent molecule and its metabolite     

Differential effects of IL-1ra on sickness behavior and weight loss induced by IL-1 in rats

Peripheral and central injections of recombinant human interleukin-1β (IL-1β) have been shown to decrease social exploration and to induce body weight loss in rats. To characterize the receptor mechanisms of these effects, we used as a tool a specific antagonist of the receptors of IL-1, IL-1ra. Intraperitoneal (i.p.) administration of IL-1ra (8 mg/kg) blocked the effect of i.p. injection of IL-1β (4 μg/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 μg/rat, i.c.v.) abrogated the effects of centrally administered IL-1β (30 ngn/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 μg/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1β (4 μg/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1β on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.     

Differential hemodynamic, metabolic and hormonal effects of morphine and morphine-6-glucuronide

Although the hyperglycemic effect of morphine has been previously described, it is not clear whether this is the result of increased glucose production and/or decreased glucose utilization and if this metabolic effect is lost with glucuronidation. This study assessed the hemodynamic (heart rate; HR and mean arterial blood pressure; MABP), hormonal and whole body glucose metabolic effects of morphine (MOR) and its metabolite morphine 6-glucuronide (MOR-6G) in conscious unrestrained chronically catheterized rats. Whole body glucose kinetics were assessed with a primed constant intravenous infusion of [3-³H]gluccose in rats infused i.c.v. with H₂O (Con; 5 μl/h), MOR (80 μg/h) or MOR-6G (1 μg/h) for a total of 4 h. MOR administration resulted in a significant 20% elevation in HR and no change in MABP. MOR-6G produced a 14% increase in HR and no change in MABP. A significant rise in plasma glucose (+23%), hepatic glucose production (R_a; +27–61%) and whole body glucose utilization (R_d; +31–61%) was also observed within 60 min of MOR administration. I.c.v. MOR-6G resulted in hemodynamic, metabolic and hormonal parameters of H₂O infused rats. I.c.v. MOR resulted in a significant increases in epinephrine (2-fold), norepinephrine (50%), corticosterone (97%) with no alterations in plasma insulin and glucagon. I.c.v. MOR-6G resulted in more marked elevations in norepinephrine (5-fold), epinephrine (7-fold) and similar elevation in corticosterone (99%) and modest elevation of glucagon (40%). These results indicate that (i) MOR-induced hyperglycemia is the result of direct central (CNS) mechanisms that result in increased hepatic glucose production, (ii) MOR-induced stress response is enhanced at least 80-fold with glucuronidation, and (iii) MOR inhibits the pancreatic glucose-stimulated insulin release.     

Brain interleukin-1β and tumor necrosis factor-α are involved in lipopolysaccharide-induced delayed rectal allodynia in awake rats

Recently, we have developped a model of delayed (12 h) increase in sensitivity (allodynia) to rectal distension (RD) induced by intraperitoneal lipopolysaccharide (LPS) in awake rats. Thus, we examined whether central interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are involved in LPS response. Abdominal contractions (criterion of visceral pain) were recorded in rats equipped with intramuscular electrodes. RDs were performed at various times after pharmacological treatments. RD induced abdominal contractions from a threshold volume of distension of 0.8 ml. At lowest volume (0.4 ml), this number was significantly increased 12 h after LPS. Intracerebroventricular (i.c.v.) injection of IL-1 receptor antagonist, IL-1β converting enzyme inhibitor or recombinant human TNF-α soluble receptor reduced LPS-induced increase of abdominal contractions at 0.4 ml volume of distension. When injected i.c.v., recombinant human IL-1β and recombinant bovine TNF-α reproduced LPS response at 9 and 12 h and at 6 and 9 h, respectively. These data suggest that IL-1β and TNF-α act centrally to induce delayed rectal hypersensitivity and that central release of these cytokines is responsible of LPS-induced delayed (12 h) rectal allodynia.     

Differential effects of central and peripheral injection of interleukin-1β on brain c-fos expression and neuroendocrine functions

Cytokines such as interleukin-1β (IL-1β) alter the activity of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes in the rat. However, the brain sites at which IL-1β exerts these effects have not been well identified. The present study sought to identify some of these sites, using c-fos protein expression as an index of cellular activation. We also attempted to determine possible differences between the effects of peripheral and central injection of IL-1β on the activation of specific brain areas. Castrated male rats received intravenous (i.v.) or intracerebroventricular (i.c.v.) injections of IL-1β through a jugular catheter or a permanent cannula implanted in the right lateral ventricle, respectively. Blood samples were taken before, as well as 30 and 120 min after i.v. or i.c.v. IL-1β infusion in order to measure plasma ACTH and LH levels. Immediately thereafter, the rats were anesthetized with pentobarbital, then perfused. Their brains were removed and postfixed for one hour. Thirty-μm frozen sections were cut and approximately every fourth tissue section was processed for c-fos expression by an avidin-biotin-peroxidase method. Both i.v. (1 μg) and i.c.v. (100 ng) injection of IL-1β significantly increased plasma ACTH levels, but only i.c.v. treatment measurably inhibited LH secretion. I.c.v. infusion of the cytokine markedly augmented c-fos expression in the paraventricular nucleus (PVN) and the arcuate nucleus (ARC) of the hypothalamus. A large amount of CRF cells in the PVN contained labelled c-fos protein (as measured by a double labelling technique), which indicates that CRF perikarya in this hypothalamic region are activated by the central administration of IL-1β. In contrast, i.v. injection of IL-1β did not significantly alter c-fos expression in the PVN or the ARC of the hypothalamus. These results suggest that the increased HPA axis activity which follows the peripheral IL-1β administration, a phenomenon previously shown to depend on endogenous CRF, does not require immediate activation of hypothalamic CRF perikarya. Thus our results indicate that the stimulatory effect of blood-born cytokine may be exerted at the level of nerve terminals in the median eminence. In contrast, i.c.v.-injected IL-1β appears to activate the HPA axis through a stimulation of CRF neurons within the parvocellular part of PVN. Finally, we postulate that the increase in cellular activity observed in the ARC of the hypothalamus may be involved in the decrease in LH secretion observed after i.c.v. infusion of IL-1β.     

Contribution of excitatory amino acids to morphine-induced metabolic alterations

Previous studies have indicated that excitatory amino acids are involved in the analgesic and addictive properties of morphine. However, their role in the morphine-induced alterations in glucose metabolism is not known. This study assessed the contribution of NMDA receptor activation to the morphine-induced hormonal and metabolic alterations in conscious unrestrained chronically catheterized rats. Whole body glucose flux was assessed with a primed constant intravenous infusion of [3-³H]glucose in rats pretreated with the NMDA-receptor antagonist MK-801 (0.25 mg/kg, intraarterial) or an equal volume (1.5 ml) of sterile saline (0.9% ) administered 15 min prior to i.c.v. injection of H₂O (Con; 5 μl) or morphine sulfate (80 μg). No significant alterations were noted in metabolic and hormonal parameters of H₂O injected rats. i.c.v. morphine increased the plasma glucose concentration (60%), hepatic glucose production (R_a; 60%) and whole body glucose utilization (R_d; 53%), but did not alter the glucose metabolic clearance rate (MCR). MK-801 alone resulted in transient hyperglycemia (25%), stimulation of glucose R_a (60%) and glucose R_d (53%), and a significant (30%) increase in MCR. MK-801 pretreatment blunted the morphine-induced hyperglycemia and the increased glucose R_a and R_d. Morphine increased the plasma concentration of epinephrine (4-fold), norepinephrine (2-fold) and corticosterone (67%); however, no alterations in plasma insulin and glucagon were detected. MK-801 pretreatment, blunted the morphine-induced increase in corticosterone and norepinephrine, and elicited a significant rise in insulin concentrations. These results indicate that activation of the NMDA receptors contributes to the morphine-induced hyperglycemia and hormonal alterations. Furthermore, this response appears partially mediated by activation of sympathetic outflow and suppression of insulin release, which is blunted by inhibition of NMDA receptors.     

Permissive role of glucocorticoids on interleukin-1 activation of the hypothalamic serotonergic system

The present study analyses the effect of IL-1β (10 ng i.c.v.) on the hypothalamic serotonergic system and the modulatory role of glucocorticoids. Changes in the serotonin metabolite 5-hydroxyindolacetic acid (5-HIAA) were recorded in freely moving rats by in vivo voltammetry using chronically implanted carbon fiber electrodes (8 μm) in the medial preoptic area. IL-1β induced a dual increase in 5HIAA levels: a rapid, short-term rise was followed by a lasting increase possibly due to newly synthesized IL-1. The synthetic glucocorticoid dexamethasone (DEX, 3 mg/kg i.p., 30 min before IL-1β), prevented the effect of IL-1β starting from 150 min, suggesting that it only inhibited the second increase. In adrenalectomized rats IL-1β had no effect but when these rats were given DEX (40 μg/kg a day for 3 days) the short-term increase was restored. The glucocorticoid receptor antagonist RU38486 (25 mg/kg s.c., 60 min before IL-1β) completely prevented IL-1β activation of the serotonergic system. The results indicate that the glucocorticoids are effective inhibitors of IL-1 synthesis but that they play a permissive role on IL-1β induced activation of the serotonergic system.     

Role of theα1-andα2-adrenoceptors of the lateral hypothalamus in the dipsogenic response to central angiotensin II in rats

The present experiments were conducted to investigate the role of theα₁-andα₂-adrenergic receptors of the lateral hypothalamus (LH) on the drinking response elicited by intracerebroventricular (i.c.v) injections of carbachol and angiotensin II (AII) in rats. Clonidine (anα₂-adrenergic agonist) injected into the LH produced a dose-dependent reduction of the drinking responses elicited by i.c.v. administration of carbachol and AII. Theα₁-adrenergic agonist phenylephrine injected into the LH reduced the dipsogenic response to i.c.v. AII, but not to carbachol. Injection of yohimbine (anα₂-adrenergic antagonist) and prazosin (anα₁-adrenergic antagonist) into the LH also reduced the water intake produced by i.c.v. injection of AII. Previous injection ofα₁-orα₂-adrenergic antagonists into the LH increased the antidipsogenic effect of clonidine or phenylephrine injected into the same area on the water intake induced by i.c.v. AII. These results show that theα₁-andα₂-adrenergic receptors of the LH are involved in the control of drinking responses elicited by i.c.v. injection of AII in rats. They also show that clonidine, but not phenylephrine, suppresses the drinking induced by i.c.v. carbachol. The data suggest that the discharge of central α-adrenergic receptors has a dual (inhibitory and excitatory) effect on water intake induced by central AII.     

Hormonal and metabolic effects of neuroglucopenia

We examined the role of central neuroglucopenia, induced by intracerebroventricular (i.c.v.) administration of 2-deoxyglucose (2-DG), on glucose and amino acid kinetics in conscious dogs. Group 1 received i.c.v. 2-DG at 2.5 mg·kg⁻¹·min⁻¹ for 15 min. Group 2 received an equal intravenous (i.v.) amount of 2-DG. In the i.c.v. group, plasma glucose levels rose from 106 ± 4 mg/dl to a peak of 204 ±12 mg/dl by 90 min. Blood lactate increased from 689 ± 1 to 2,812 ± 5 μ mol/1 and blood alanine did not change from basal (256 ± 41 μ mol/1). The rate of hepatic glucose production, determined isotopically, was increased 2-fold over basal (P < 0.01). Significant increases (P < 0.001) over basal were also noted in plasma epinephrine, norepinephrine, insulin, glucagon and cortisol. Leucine rate of appearance (Ra) showed a 30% decrease from basal to2.4 ± 0.05 μmol·kg⁻¹ ·min⁻¹ (P < 0.01). In group 2 plasma glucose levels were not altered but plasma cortisol and glucagon showed a modest transient increase above basal (P < 0.05). No significant changes were noted in amino acid kinetics. These findings suggest that periventricular neuroglucopenia, in the absence of peripheral glucose deprivation, is accompanied by hyperglycemia secondary to enhanced hepatic glucose production with decreased glucose utilization and by increased hepatic uptake of gluconeogenic precursors. These, however, were not accompanied by increased whole body proteolysis as was previously seen with generalized glucopenia resulting from insulin-induced hypoglycemia.     

Effects of central injection of glucose on thermogenesis in normal, VMH-lesioned and genetically obese rats

Intra-cerebroventricular (i.c.v.) injection of glucose (0.1–1.0 μmol) caused dose-dependent increases in resting oxygen consumption (V_O2) of conscious rats (maximum increase of 15.4 ± 2% at 0.5 μmol). These effects were significantly attenuated by peripheral (i.p.) pretreatment with the β-adrenoceptor antagonist propranolol, indicating the importance of the sympathetic nervous system (SNS) in the response. Plasma glucose concentrations were elevated (11%) 30 min after central injection of glucose, but intravenous glucose (0.5 μmol) did not affect resting V_O2. Animals which had been fasted for 12 h prior to V_O2 measurements exhibited reduced basal V_O2 values, but the nutritional state of the animal did not affect the metabolic response to central injections of glucose (0.5 μmol). Rats exhibiting genetic (fa/fa Zucker rats) and hypothalamic (VMH-lesioned) obesity showed similar thermogenic responses to centrally administered glucose, to their lean counterparts. These data suggest a dual action of central glucose in the regulation of energy balance, involving stimulation of energy expenditure in addition to its reported inhibition of energy intake. The defective diet-induced thermogenesis associated with VMH and genetic obesities does not appear to result from an inability to respond to changes in intracerebroventricular glucose concentrations.     

Interleukin-1β System (Ligand, Receptor Type I, Receptor Accessory Protein and Receptor Antagonist), TNF-α, TGF-β1 and Neuropeptide Y mRNAs in Specific Brain Regions During Bacterial LPS-Induced Anorexia

Bacterial lipopolysaccharide (LPS) or endotoxin induces neurological manifestations including anorexia. It is proposed that LPS-induced cytokine production is involved in the generation of neurological manifestations and in neuroinflammatory/immunological responses during Gram-negative infections. For example, LPS-induced effects can be blocked or ameliorated by the interleukin-1 receptor antagonist (IL-1Ra). Here, sensitive and specific RNase protection assays were used to investigate the effects of the intracerebroventricular (i.c.v.) administration of LPS on mRNA levels of interleukin-1β (IL-1β) system components, tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β1, and neuropeptide Y (NPY) in the cerebellum, hippocampus, and hypothalamus. The same brain region sample was analyzed with all of the antisense probes. The data show simultaneous local induction of multiple cytokine components messenger ribonucleic acids (mRNAs) within specific brain regions in anorectic rats responding to i.c.v. administered LPS (500 ng/rat). Interleukin-1β and IL-1Ra had a similar mRNA induction profile (hypothalamus > cerebellum > hippocampus). Interleukin-1 receptor type I (IL-1RI) mRNA also increased in all three brain regions examined, and the soluble form of IL-1 receptor accessory protein (IL-1R AcP II) mRNA was induced in the hypothalamus. Tumor necrosis factor-α mRNA levels increased in the hypothalamus > hippocampus > cerebellum. Levels of membrane bound IL-1R AcP, TGF-β1, and NPY mRNAs did not change significantly in any brain region. The results suggest that: (1) endogenous up-regulation of IL-1β and TNF-α in the hypothalamus contribute to LPS-induced anorexia; and (2) the ratio IL-1Ra/IL-1β, and IL-1β ↔ TNF-α interactions may have implications for Gram-negative infections associated with high levels of LPS in the brain-cerebrospinal fluid.     

Circadian rhythms and energy metabolism with special reference to the suprachiasmatic nucleus

The role of the hypothalamic suprachiasmatic nucleus (SCN) was examined in rats and obtained following results: (a) The time-dependent (light > dark) hyperglycemic response to intracranial injection of 2-deoxy-d-glucose (2DG) disappeared in rats with bilateral lesions of the SCN, in rats on weeks 4–6 after surgical blinding, and in congenitally blind (hereditary microphthalmic) rats; (b) The hyperglycemia induced by electrical stimulation of the SCN was not observed in weeks 4–8 after surgical blinding; (c) Change in the blood glucose concentration after insulin injection into the SCN was eliminated by SCN lesions; (d) Alterations in activity of autonomic efferents to peripheral organs on light exposure disappeared after SCN lesions; (e) SCN lesions decreased the blood glucagon level and increased the blood insulin level; (f) SCN lesions decreased protein intake, and glucagon increased it; (g) Increases in the plasma renin activity and vasopressin concentration after water-deprivation were suppressed in hereditary microphthalmic rats with abnormal SCN. These findings suggest that the SCN is involved in the mechanism of blood glucose and body fluid intake as well as that of circadian rhythm.     

Indications of pre- and post-synaptic 5-HT1A receptor interactions in feeding behavior and neuroendocrine regulation

This bipartite study uses behavioral and biochemical means to explore the involvement of both pre- and post-synaptic 5-HT_1A receptors in the control of food intake and neuroendocrine regulation. In the pharmacological study, the administration of the 5-HT_1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; 60 μg/kg b.wt., i.p.) to rats caused a significant increase in 2 h intake of a high carbohydrate (CARB)/sugar diet (P < 0.05) during the relatively inactive feeding period of the late light cycle. No significant change was detected in the intake of Purina laboratory chow at 2 h, or of the intake of either diet at 4 h and 24 h after 8-OH-DPAT administration. Injection of 8-OH-DPAT induced a drop in insulin levels in rats maintained on high CARB/sugar diets only (−90%; P<0.05). It also caused an increase in circulating glucose levels in both high CARB/sugar (240%; P<0.01) and chow fed (123%; P<0.05) rats; it did so more intensely in high CARB/sugar-fed rats. In the biochemical study, radioligand binding techniques were used to assess 5-HT_1A receptor density in the hypothalamus, as well as the relationship between 5-HT_1A receptors and circulating levels of insulin and glucose. Chronic and acute administration (25 mg/kg b.wt./5 injections, and 50 mg/kg b.wt., respectively, i.p.) of the potent hypoglyce mic agent tolbutamide (TOL) caused a significant increase in 5-HT_1A receptor density (+243% and +132.6%, respectively; P<0.05) in the medial hypothalamus but not in the lateral hypothalamus, as compared to vehicle-treated rats. Chronic glucose replacement therapy showed a trend towards reversing the depressed circulating glucose levels as well as the medial hypothalamic 5-HT_1A receptor density to control levels. These studies indicate that the pre-synaptic mechanism of 8-OH-DPAT-induced hyperphagia may require specific circulating levels of insulin and glucose, which are regulated via post-synaptic 5-HT_1A receptors.     

Palmitate incorporation into different brain regions in the awake rat

A quantitative method is presented to examine palmitate flux into a stable metabolic compartment in individual brain regions of awake rats. Following the i.v. injection of [¹⁴C]palmitate, brain radioactivity rose and then fell until, at 4 h, a stable concentration was reached that was maintained for up to 24 h. The flux of plasma palmitate into this 4 h compartment was calculated by dividing regional brain radioactivity at 4 h, as determined by quantitative autoradiography, by the integral of the plasma palmitate specific activity. Palmitate flux varied from 2.0 × 10⁻⁵ μmol/g·s into the internal capsule to 9.3 × 10⁻⁵ μmol/g·s into the arcuate nucleus, and generally was proportional to the regional cerebral metabolic rate for glucose, as measured with 2-deoxy-d-[1-¹⁴C]glucose. The results demonstrate that it is possible to determine unidirectional palmitate flux into a stable metabolic compartment in individual brain regions of awake rats, that flux into gray matter regions generally exceeds flux into white matter, and that palmitate flux is proportional to published values for regional brain oxidative metabolism.     

Murine tumor necrosis factor alpha is transported from blood to brain in the mouse

The cytokines are important components of the brain-immune axis. Recent work has shown thet [¹²⁵I]IL-1α and [¹²⁵I]IL-1β are transported from the blood into the brain by a saturable system. Here we show that murine tumor necrosis factor alpha (mTNFα)_ labeled with ¹²⁵I (I-mTNFα) crosses the blood-brain barrier (BBB) after i.v. injection by a transport system different from that for the interleukins. Self inhibition with mTNFα showed that this transport system was saturable, and lack of inhibition by IL-1β, IL-6, or MIP-1α showed selectivity of the system. High performance liquid chromatography (HPLC) of the radioactivity recovered from brain and from cerebrospinal fluid after the i.v. injection of I-mTNFα showed that the cytokine crossed the BBB largely in intact form. Capillary depletion showed that the accumulation of I-mTNFα in the cerebral cortex was due to passage across the BBB rather than to sequestration by capillaries. Transport rate was not changed by acute treatment with the neurotoxin aluminium or by acute and chronic treatment with the cationic chelator deferoxamine, but it was more than three times faster in neonatal rats. Efflux of I-mTNFα from the brain was slower than would have been predicted based on reabsorption of cerebrospinal fluid, suggesting that TNFα is sequestered by the brain. The BBB was not disrupted by up to 50 μg kg⁻¹ of mTNFα i.v. in either adult mice or neonatal rats as assessed by the BBB's impermeability to radioactively labeled albumin. The saturable transport of mTNFα across the BBB supports the concept of direct blood to brain transport of cytokines as a mechanism by which the peripheral immune system can affect brain function.     

Different receptor mechanisms mediate the effects of endotoxin and interleukin-1 on female sexual behavior

Activation of the immune system by lipopolysaccharide (LPS) produces physiological, neuroendocrine and behavioral effects, some of which are mediated by cytokine production. We have previously shown that the cytokine interleukin-1 (IL-1) inhibits sexual behavior in female, but not male rats, while producing a comparable suppression of locomotion in both sexes. The present study examined the effects of LPS on sexual behavior and locomotion of male and female rats, and the involvement of IL-1 receptors in mediating the effects of IL-1 and LPS on females' behavior. Peripheral (i.p.) administration of LPS (50 or 250 μg/kg) significantly decreased sexual behavior in females, up to 6 h after administration, while it had no effect on male sexual behavior. However, locomotor activity, measured in the open-field test, was similarly reduced by LPS in both males and females. Pretreatment with the IL-1 receptor antagonist (IL-1ra) either i.p. (10 mg/kg) or intracerebroventricularly (i.c.v.) (50 μg/rat) did not prevent the inhibition of female sexual behavior and locomotion induced by either i.p. (50 μg/kg) or i.c.v. (200 or 400 ng/rat) administration of LPS, respectively. However, identical doses of IL-1ra significantly reversed the effects of IL-1β, administered either i.p. (5 μg/kg) or i.c.v. (50 ng/rat), respectively. These results demonstrate that both LPS and IL-1β produce marked inhibition of sexual behavior in female, but not in male rats. However, IL-1 receptors are not required for the effects of LPS on sexual behavior in female rats.     

Brain-IL-1β induces local inflammation but systemic anti-inflammatory response through stimulation of both hypothalamic–pituitary–adrenal axis and sympathetic nervous system

It is well established that systemic inflammation induces a counter-regulatory anti-inflammatory response particularly resulting in deactivation of monocytes/macrophages. However, recently we demonstrated a systemic anti-inflammatory response without preceding signs of systemic inflammation in patients with brain injury/surgery and release of cytokines into the cerebrospinal fluid (CSF). In order to analyze the mechanisms and pathways of systemic immunodepression resulting from sterile cerebral inflammation we established an animal model using continuous intra-cerebroventricular (i.c.v.) or intra-hypothalamic (i.h.) infusion of rat recombinant (rr) tumor necrosis factor (TNF)-α and interleukin (IL)-1β for 48 h. Controls received intra-venous (i.v.) cytokine administration. Interestingly, i.c.v. and i.h. infusion of IL-1β but not TNF-α produced distinct signs of central nervous system (CNS) inflammation. Correspondingly, i.c.v. infusion of IL-1β particularly diminished the TNF-α but increased the IL-10 concentration in whole blood cultures after endotoxin stimulation. All parameters normalized within 48 h after termination of the infusion. Blocking the hypothalamic–pituitary–adrenal (HPA) axis by hypophysectomy (HPX) led to complete recovery of the diminished TNF-α concentration and temporarily inhibited the IL-10 increase. Blocking the sympathetic nervous system (SNS) transmission by application of the β₂-adrenoreceptor antagonist propranolol not only inhibited the increase but further downregulated the endotoxin induced IL-10 concentration in the media of whole blood cell cultures, whereas the TNF-α decrease was only partially prevented. Interestingly, HPX and propranolol also diminished the cell invasion into the CSF. In summary, activation of both the HPA axis and the SNS plays an important role in systemic anti-inflammatory response resulting from cytokines in brain and cerebral inflammation.     

Inhibition of central GABAA receptors enhances hepatic glucose production and peripheral glucose uptake

Previous studies have demonstrated that intracerebroventricular (ICV) injection of bicuculline methiodide (BMI), a gamma-amkrobutyric acid receptor antagonist, increases plasma glucose concentrations. The purpose of the present study was to determine whether the hyperglycemic response was due to an increased rate of hepatic glucose production (HGP) or a change in the rate of glucose utilization. In vivo glucose flux was assessed in catheterized, conscious overnight fasted rats using [3-³H]glucose. ICV injection of BMI (10 nmol) increased glucose levels 60% after 30 min. This hyperglycemia resulted from a rapid increase in HGP that exceeded an increased rate of glucose utilization. No alteration in the glucose metabolic clearance rate, an index of the avidity of the body's tissues for glucose, was detected in BMI-Injected rats. BMI enhanced both hepatic gluconeogermals and glycogenolysis, since the reduction in War glycogen (19 μmol/g liver) could not totally account for all of the increased HGP. These metabolic alterations were associated with sustained increases in circulating concentrations of corticosterone, giucagon and catecholamines. Prior adrenalectomy completely abolished the BMI-induced increase in glucose flux and the reduction in tissue glycogen, despite the persistent hyperglucagonemia. These data indicate that, in the fasted condition, the hyperglycemia produced by central administration of BMI results from an increased rate of HGP (both gluconeogenesis and glycogenolysis) and not a reduction in the ability of tissues to use glucose. The concomitant elevation in glucose disposal was the result of an increased mass action effect. The enhanced glucose metabolic response to BMI appears mediated exclusively by an increased secretion of epinephrine from the adrenal medulla.     

Intracerebroventricular injection of choline increases plasma oxytocin levels in conscious rats

In the present study, we examined the effect of intracerebroventricularly (i.c.v.) injected choline on both basal and stimulated oxytocin release in conscious rats. I.c.v. injection of choline (50–150 μg) caused time- and dose-dependent increases in plasma oxytocin levels under normal conditions. The increase in plasma oxytocin levels in response to i.c.v. choline (150 μg) was greatly attenuated by the pretreatment of rats with atropine (10 μg; i.c.v.), muscarinic receptor antagonist. Mecamylamine (50 μg; i.c.v.), a nicotinic receptor antagonist, failed to suppress the effect of 150 μg choline on oxytocin levels. Pretreatment of rats with 20 μg of hemicholinium-3 (HC-3), a specific inhibitor of choline uptake into nerve terminals, greatly attenuated the increase in plasma oxytocin levels in response to i.c.v. choline injection. Osmotic stimuli induced by either oral administration of 1 ml hypertonic saline (3 M) following 24-h dehydration of rats (type 1) or an i.c.v. injection of hypertonic saline (1 M) (type 2) increased plasma oxytocin levels significantly, but hemorrhage did not alter basal oxytocin concentrations. The i.c.v. injection of choline (50, 150 μg) under these conditions caused an additional and significant increase in plasma oxytocin concentrations beyond that produced by choline in normal conditions. These data show that choline can increase plasma oxytocin concentrations through the stimulation of central cholinergic muscarinic receptors by presynaptic mechanisms and enhance the stimulated oxytocin release.