Developmental changes in hypothalamic toll-like-receptor 4 mRNA expression and the effects of lipopolysaccharide on such changes in female rats

Hypothalamic pro-inflammatory cytokine expression exhibits a weaker response to lipopolysaccharides (LPS) during the early neonatal period than during the later developmental period. Although toll-like receptor 4 (TLR4), which recognizes bacterial molecules, activates pro-inflammatory cytokine responses, the developmental changes in hypothalamic TLR4 expression have not been evaluated. In this study, the hypothalamic TLR4 mRNA levels of saline-injected and LPS-injected rats were measured during the neonatal, pre-pubertal, and post-pubertal periods. The rats’ hypothalamic TLR4 mRNA levels gradually increased from the neonatal to pubertal period and were altered by the injection of LPS at all examined ages (postnatal day (PND) 5, 15, 25, and 42). LPS injection resulted in decreased hypothalamic TLR4 mRNA expression at PND5, whereas it increased hypothalamic TLR4 mRNA expression at PND15, 25, and 42. After the injection of LPS, the hypothalamic mRNA levels of the pro-inflammatory cytokines interleukin (IL)-1β, tumor necrosis factor α, and IL-6 were attenuated during the early developmental period and increased acutely on PND42. The expression profiles of these pro-inflammatory cytokines exhibited similar, but not entirely consistent, changes to those displayed by TLR4 during the developmental period. Hypothalamic TLR4 mRNA expression gradually increased throughout the developmental period, whereas the mRNA expression levels of the pro-inflammatory cytokines increased acutely at PND42. Thus, it is assumed that hypothalamic TLR4 hypoactivity contributes to the low sensitivity of pro-inflammatory cytokines to LPS during the early developmental period.     

Long term alterations in neuroimmune responses of female rats after neonatal exposure to lipopolysaccharide

Male and female rats display significant gender-associated differences in their responses to an immune challenge, and gender-specific alterations in many aspects of physiology are seen after a variety of interventions during the neonatal period. It is well-established that neonatal exposure to an immune challenge can alter centrally mediated inflammatory responses in adult male rats and yet little is known about female responses after a similar challenge. We therefore asked if neonatal exposure to lipopolysaccharide (LPS) would alter febrile and hypothalamic cyclooxygenase (COX)-2 responses to an adult immune challenge in female rats. Female Sprague-Dawley rats were administered a single injection of the bacterial endotoxin LPS at postnatal day 14 and were examined as adults for febrile, COX-2 and activity changes to LPS, as well as responses to interleukin (IL)-1beta. Adult female rat responses were similar to those we have seen previously for the males in that febrile and hypothalamic COX-2 responses to adult LPS were attenuated in neonatally LPS-treated animals. Responses to adult IL-1beta were unaffected. Interestingly, females did not display the elevated basal hypothalamic COX-2 that was previously seen in males. Thus we demonstrate that, like in the males, neonatal exposure to LPS has a powerful effect on adult responses to further LPS challenge in the female rats.     

Changes in responsiveness of appetite, leptin and hypothalamic IL-1β and TNF-α to lipopolysaccharide in developing rats

In addition to its role as a regulator of energy homeostasis, leptin plays a pivotal role in some immune/inflammatory responses. Synthesis and secretion of leptin are increased under immune stress conditions, and increased leptin may participate in the development of anorexia and fever. These actions are partially mediated by up-regulation of hypothalamic IL-1β. Leptin also protects against immune stress-induced lethality. On the other hand, the response and roles of leptin to immune stress conditions in the neonatal period have scarcely been examined. We hypothesized that 1. the response of leptin to immune stress would be suppressed in the early neonatal period, 2. hyporesponse of leptin in the early neonatal period would attenuate the anorectic response and increase the lethal rate under immune stress conditions and 3. supplementation of leptin in the early neonatal period would increase the anorectic response, whereas it would decrease the lethal rate under immune stress conditions. To test these hypotheses, we first examined the developmental changes in the responses of leptin and hypothalamic proinflammatory cytokines, i.e., IL-1β and TNF-α, to LPS-induced immune stress in female rats. We also examined the developmental changes in the anorectic response and lethality rate under LPS-induced immune stress conditions. Five- and 15-day-old rats showed no leptin response and a weak hypothalamic IL-1β response to LPS when compared with 25- and 42-day-old rats. Fifteen-day-old rats showed low anorectic responses and high lethality rates when compared with 25- and 42-day-old rats under LPS-induced immune stress conditions. We then examined whether administration of leptin affected the response to the anorectic and lethal effects of LPS in 15-day-old rats. Administration of leptin further attenuated body weight after LPS injection, but not after saline injection. On the other hand, administration of leptin did not affect survival rate. In addition, hypothalamic IL-1β mRNA levels were not affected by leptin administration. In conclusion, the absence of a leptin response may act to prevent immune stress-induced anorexia during the early neonatal period.     

The effects of prenatal undernutrition and postnatal high-fat diet on hypothalamic Kiss1 mRNA and serum leptin levels

Prenatal undernutrition and postnatal overnutrition increase the risk of some metabolic disorders in adulthood, and hypothalamic leptin resistance makes an important contribution to these effects. Leptin plays important roles in the maintenance of reproductive function, and its actions might be partially mediated by kisspeptin, which is a potent positive regulator of gonadotropin-releasing hormone. In this study, the effects of prenatal undernutrition and postnatal overnutrition on reproductive parameters and sexual maturation during the peripubertal period were evaluated. Rats subjected to prenatal undernutrition (IUGR) and fed a postnatal high-fat diet (HFD) (n = 7) exhibited 40% higher serum leptin levels and 30% lower hypothalamic Kiss1 (the gene encoding kisspeptin) mRNA levels than those subjected to prenatal undernutrition (IUGR) and fed a normal diet (n = 7). No such HFD-induced postnatal alterations were observed in the rats fed a normal diet during the prenatal period (control) (n = 7 per group). Although the consumption of the HFD did not affect the serum luteinizing hormone levels or body weight of the IUGR or control rats, it did promote vaginal opening in both groups (evaluated in 14 rats per group). These findings indicate that hypothalamic leptin resistance might occur in IUGR-HFD rats, but these changes do not influence downstream effectors of the reproductive endocrinological system. They also suggest that the relationships between nutritional conditions, body weight, reproductive factors, and sexual maturation are complex.     

Decreased NPY innervation of the hypothalamic nuclei in rats with cancer anorexia

Whether the decrease in food intake that occurs at the onset of anorexia in tumor bearing (TB) rats is related to a change in the hypothalamic neuropeptide Y (NPY) system was tested by comparing NPY expression in sham operated Fischer Control and anorectic TB rats. Coronal cryocut sections of their fixed brain were processed by the peroxidase-antiperoxidase method with NPY polyclonal antibodies. NPY-immunoreactive fibers were widely distributed throughout the forebrain, but were most prominent in the hypothalamic paraventricular, suprachiasmatic, arcuate and periventricular nuclei. NPY-immunoreactive neurons were visualized in Control and anorectic TB rats in the preoptic region, the arcuate nucleus, and occasionally in the lateral hypothalamus. Semiquantitative image analysis showed a significant decrease in the NPY immunostaining in some hypothalamic nuclei of the anorectic TB rats, most prominently in the supraoptic nucleus, the parvocellular portion of the paraventricular nucleus, and, to a lesser extent, the suprachiasmatic and arcuate nuclei. No changes in NPY innervation were seen in the ventromedial nucleus and the lateral hypothalamus. The data support the hypothesis of an altered hypothalamic NPY system at the onset of anorexia in TB rats and also reveal the hypothalamic nuclei through which NPY influences food intake.     

The melanocortin agonist Melanotan-II reduces the orexigenic and adipogenic effects of neuropeptide Y (NPY) but does not affect the NPY-driven suppressive effects on the gonadotropic and somatotropic axes in the male rat

Neuropeptide Y (NPY) is a strong orexigenic neurotransmitter also known to modulate several neuroendocrine axes. alpha-Melanocyte-stimulating hormone (MSH) is an essential anorectic neuropeptide, acting on hypothalamic MC3/4 receptor subtypes. When given as an intracerebroventricular bolus injection, Melanotan-II (MT-II), a non selective MC receptor agonist, inhibits feeding, suppresses the NPY orexigenic action, and reduces basal insulinaemia. We evaluated the effects of a 7-day central infusion of MT-II (15 nmol/day) given either alone or in association with NPY (5 nmol/day) in male Sprague-Dawley rats. MT-II produced almost full anorexia for 1-2 days but then feeding gradually returned to normal despite continued MT-II infusion. When coinfused with NPY, MT-II also produced the same initial anorectic episode but then maintained feeding to upper normal levels, thus cancelling the hyperphagia driven by NPY. Whereas NPY infusion produced a doubling of fat pad weight, MT-II reduced adiposity by a factor of two compared to pair-fed rats, and vastly curtailed the NPY-driven increase in fat pad weight. MT-II infusion also significantly curtailed the NPY-induced rise in insulin and leptin secretions. NPY infusion significantly inhibited hypothalamic pro-opiomelanocortin mRNA expression, most likely cancelling the alpha-MSH anorectic activity. As expected from previous studies, chronic NPY infusion strongly inhibited both the gonadotropic and somatotropic axes, and coinfusion of MT-II did not reverse these NPY-driven effects, in sharp contrast with that seen for the metabolic data. MT-II infusion alone had little effect on these axes. In conclusion, chronic MT-II infusion generated a severe but transient reduction in feeding, suggesting an escape phenomenon, and clearly reduced fat pad size. When coinfused with NPY, MT-II was able to cancel most of the NPY effects on feeding, but not those on the neuroendocrine axes. It appears therefore that, as expected, NPY and alpha-MSH closely interact in the control of feeding, whereas the neural pathways by which NPY affects growth and reproduction are distinct and not sensitive to MC peptide modulation.     

Enhanced inhibitory feeding response to alpha-melanocyte stimulating hormone in the diet-induced obese rat

A dysregulation in the hypothalamic neuropeptide systems involved in the control of appetite has previously been shown in models of diet-induced obesity. In the present study, male Sprague-Dawley rats were rendered obese by a highly palatable cafeteria-style diet over 20 weeks, while control rats had access to standard laboratory chow. Feeding responses to alpha-melanocyte stimulating hormone (alpha-MSH), an anorectic peptide and neuropeptide Y (NPY), a potent orexigenic agent were investigated in diet-induced obese and control animals. In addition, endogenous hypothalamic peptide levels were determined in these animals. Intracerebroventricular injections of either 4 nmol alpha-MSH or saline vehicle were given 10 min prior to the onset of the dark phase. Diet-induced obese rats had significantly enhanced nocturnal inhibitory feeding responses to alpha-MSH (P<0.05). The orexigenic feeding response induced by 1 nmol NPY was similar for both groups. At sacrifice, both alpha-MSH and NPY peptide content were selectively reduced in the paraventricular nucleus (PVN) of these animals (P<0.05). Although diet-induced obesity had no effect on responses to NPY, the significantly greater inhibition of nocturnal feeding by alpha-MSH and reduction in PVN alpha-MSH peptide level, suggests melanocortinergic signalling may be reduced in obesity which may account for the hyperphagia of these animals when presented with a palatable diet.     

Metabolic, neuroendocrine and immune functions in basal conditions and during the acute-phase response to endotoxic shock in undernourished rats

Chronic malnutrition is one of the most important causes of several metabolic, immune and neuroendocrine dysfunctions. The aim of the present study was to determine the influence of chronic food restriction on basal neuroendocrine, immune and adipocyte functions and during the acute-phase response to endotoxic shock in female rats. The effect of refeeding of undernourished rats on the above-mentioned functions was also investigated. For these purposes, plasma total protein, glucose, triglycerides, ACTH, corticosterone, tumor necrosis factor-alpha (TNF) and leptin (LEP) levels were determined in basal condition and 2 h after endotoxin (LPS; 180 microgram/kg body weight, i.p.) administration in 3 different groups: (1) well-nourished (WN) controls; (2) undernourished (UN) rats as a consequence of chronic food restriction, and (3) UN rats re-fed to restoration of their body weights in the WN rat range. The results indicate that UN rats, in comparison with WN controls, developed an arrest in body weight gain as well as in basal hypoglycemia, hypotriglyceridemia, hypoleptinemia, hypercorticosteronemia and enhanced adrenal glucocorticoid content; however, no changes in basal total protein, ACTH and TNF plasma levels and in anterior pituitary ACTH concentrations were found. When endotoxic shock was induced, the LPS-induced hypoglycemia developed in WN rats was abolished in UN animals, and both ACTH and TNF plasma concentrations after endotoxin, albeit significantly (p < 0.05) higher than the respective basal values, were significantly (p < 0.05) lower in UN than in WN control rats. Despite the high basal plasma corticosterone concentration in UN vs. WN rats, the LPS-induced glucocorticoid release was similar in WN and UN rats. Additionally, LPS treatment did not modify basal plasma LEP levels, regardless of the group. Interestingly, UN rats fed ad libitum for 15 days restored their body weight to WN rat range values, and the various metabolic dysfunctions seen in UN rats in both basal and post-LPS conditions were fully normalized. Our results clearly indicate that chronic undernutrition not only affects, as earlier described, reproductive function but also metabolic, neuroendocrine, immune and adipocyte functions, and that the effects induced by undernutrition can be fully reversed after recovery of normal body weight. The present study strongly supports the involvement of the metabolic status in the effectiveness of the defense mechanisms developed in patients in inflammatory stress conditions.     

Postnatal overfeeding leads to obesity and exacerbated febrile responses to lipopolysaccharide throughout life

The perinatal environment can be crucial for programming long-term physiology, including the mechanisms regulating body weight, and postnatal overfeeding can lead to obesity throughout life. Inflammation-related complications are of particular concern in the obese. However, little is known about how postnatal overfeeding contributes to changes in the ability to respond to inflammation. In the present study, we investigate changes in the febrile and neurochemical response to immune challenge with lipopolysaccharide (LPS), in juvenile and adult, male and female Wistar rats made obese by overfeeding during the postnatal period. We demonstrate that febrile responses to LPS are exacerbated in these rats, with peak core temperatures being up to 0.5 °C higher compared to those in controls, and this is associated with an enhanced pro-inflammatory cytokine profile and enhanced hypothalamic-pituitary-adrenal (HPA) axis activation. Plasma pro-inflammatory cytokines concentrations were approximately three-fold greater in neonatally overfed rats after LPS and there were approximately twice as many neurones activated in the paraventricular nucleus of the hypothalamus as in controls, with a prolonged corticosterone response. We also observed elevated expression of toll-like receptors (TLR) 2 and 4 in adipose tissue and greater inhibitory factor κB phosphorylation in these obese animals. Despite similar changes in expression of adipose TLR3, there was no corresponding alteration in the response to a viral mimetic that acts at this receptor. We suggest that an elevated febrile response to LPS therefore occurs in cases of obesity and this is associated with altered HPA axis function and enhanced TLR2/4 expression in adipose tissue and an up-regulated downstream pro-inflammatory cascade.     

Prenatal exposure to glucocorticoids affects body weight,serum leptin levels,and hypothalamic neuropeptide-Y expression in pre-pubertal female rat offspring

Glucocorticoid secretion is a key endocrine response to stress. It has been reported that prenatal stress induces long-lasting alterations in body weight regulation systems, which persist after the stress has ceased. In this study, the long-term effects of prenatal glucocorticoid exposure on body weight changes and the expression of appetite-regulating factors were examined in female rats. Pregnant rats were given normal drinking water (control) or dexamethasone (1 μg/mL) dissolved in drinking water (DEX) from day 13 of pregnancy until delivery. Then, the body weight change, serum leptin levels, and hypothalamic NPY mRNA levels of their offspring were examined. The DEX dams gained significantly less body weight during pregnancy than the control dams. The DEX dams’ offspring exhibited a significantly lower birth weight than the offspring of the control dams, and the same was true for body weight at postnatal days 20 and 28. The offspring of the DEX dams displayed significantly higher serum leptin levels and significantly lower hypothalamic NPY mRNA levels compared with the offspring of the control dams. Significant inverse correlations were detected between body weight and the serum leptin level, and between the serum leptin level and the hypothalamic NPY mRNA level. On the other hand, a significant positive correlation was detected between body weight and the hypothalamic NPY mRNA level. These results indicate that leptin production is increased in a long-lasting manner in offspring exposed to glucocorticoids during the prenatal period and that this results in attenuated body weight gain and hypothalamic NPY expression during the pre-pubertal period.     

Effect of d-fenfluramine on neuropeptide Y concentration and release in the paraventricular nucleus of food-deprived rats.

Recent evidence indicates that Neuropeptide Y (NPY) is an important signal in the hypothalamic neural circuitry that stimulates feeding in the rat. Administration of d-fenfluramine (FEN) has been shown to rapidly inhibit feeding in the rat. Because food deprivation increases the levels and release of NPY in the paraventricular nucleus (PVN) of the hypothalamus, the aim of this study was to investigate whether the rapid anorectic effects of FEN in food-deprived (FD) rats are associated with alterations in the hypothalamic NPYergic system. In the first experiment, the effect of FEN (10 mg/kg) on NPY concentrations in nine microdissected hypothalamic sites was assessed by radioimmunoassay (RIA) in rats either food deprived for 3 days or fed ad lib during the experimental period. In response to food deprivation, NPY concentrations increased significantly in the PVN and arcuate nucleus, but NPY levels remained unchanged in the remaining seven hypothalamic sites. In control rats maintained on ad lib food supply, FEN injection produced little effect on NPY concentration in hypothalamic sites. However, FEN suppressed NPY levels selectively in the PVN of FD rats, so that NPY concentrations measured in the nucleus were within the range found in satiated control rats. In the second experiment, the effect of FEN on NPY release in the PVN was examined in FD rats by the push-pull cannula (PPC) technique. NPY levels in the PPC perfusate were unchanged in FD rats during the period 30-120 min after saline or FEN injection. Also, the mean rate of NPY release was similar in vehicle- and FEN-treated FD rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuropeptide Y counteracts the anorectic and weight reducing effects of ciliary neurotropic factor

Ciliary neurotrophic factor (CNTF), a cytokine of the interleukin-6 superfamily, has been shown to induce hypophagia and weight loss. Neuropeptide Y (NPY) and orexin are potent orexigenic signals in the hypothalamus. Anorexia, normally seen in response to infection, injury and inflammation, may result from diminished hypothalamic orexigenic signalling caused by persistently elevated cytokines, including CNTF. To test this hypothesis, we first examined the effects of chronic intracerebroventricular (i.c.v.) infusion of CNTF for 6-7 days on food intake and body weight as well as hypothalamic NPY and orexin gene expression in male rats. Subsequently, the effectiveness of NPY replacement to counteract the effects of CNTF by coinfusion of NPY and CNTF was evaluated. Chronic i.c.v. infusion of CNTF (2.5 microg/day) reduced body weight (14.3% vs control) at the end of 7 days. Food intake remained suppressed for 5 days postinfusion and subsequently gradually returned to the control range by day 7. Serum leptin concentrations in these rats were in the same range seen in control rats. Chronic i.c.v. infusion of higher doses of CNTF (5.0 microg/day) produced sustained anorexia and body weight loss (29% vs controls) through the entire duration of the experiment. This severe anorexia was accompanied by markedly suppressed serum leptin concentrations. Furthermore, CNTF infusion alone significantly reduced hypothalamic NPY gene expression (P < 0. 05) without affecting orexin gene expression. As expected, in fusion of NPY alone (18 microg/day) augmented food intake (191.6% over the initial control, P < 0.05) and produced a 25.1% weight gain in conjunction with a 10-fold increase in serum leptin concentrations at the end of the 7-day period. Interestingly, coinfusion of this regimen of NPY with the highly effective anorectic and body reducing effects of CNTF (5.0 microg/day) not only prevented the CNTF-induced anorexia and weight loss, but also normalized serum leptin concentrations and hypothalamic NPY gene expression. These results demonstrate that chronic central infusion to produce a persistent elevation of the cytokine at pathophysiological levels (a situation that may normally manifest during infection, injury and inflammation) produced severe anorexia and weight loss in conjunction with reduction in both serum leptin concentrations and hypothalamic NPY gene expression. Reinstatement of hypothalamic NPY signalling by coinfusion of NPY counteracted these CNTF-induced responses.     

Observations on the Orexigenic Hypothalamic Neuropeptide Y-System in Neonatally Overfed Weanling Rats

Early postnatal overnutrition is a risk factor for obesity in juvenile and adult life. Underlying pathophysiological mechanisms are still unclear. Hypothalamic neuropeptides are decisively involved in the regulation of body weight and food intake. In this study, we investigated consequences of early postnatal overnutrition, as compared to normo-and undernutrition, on NPY within the arcuate nucleus and paraventricular nucleus (PVN). The normal litter size of Wistar rats was adjusted on the third day of life from 10 pups (normal litters, NL; normonutrition) to only three newborns (small litters, SL; overnutrition) or 18 pups per mother (large litters, LL; undernutrition). SL rats developed clear overweight until the day 21 of life (P<0.0001), as well as hyperleptinaemia (P<0.001), and hyperinsulinaemia (P<0.01). LL rats were underweight and had decreased leptin and insulin concentrations. Using radioimmunoassay, NPY contents were determined in hypothalamic micropunches, and immunocytochemistry for NPY was performed in serial hypothalamic sections on day 21 of life. While in the underweight, hypoleptinaemic, and hypoinsulinaemic LL rats increased concentrations of NPY in the arcuate nucleus and PVN were observed, no decrease in NPY content was found in the overweight, hyperleptinaemic, and hyperinsulinaemic SL rats. Moreover, the percentage of NPY-immunopositive neurones per total number of neurones was increased not only in the LL rats, but also in the SL rats. Since the NPY system is functionally mature already at this age, these findings might indicate an acquired resistance of the hypothalamic NPY system to increased levels of insulin and/or leptin in early postnatally overfed SL rats.     

Neuropeptide Y and lipid increase apolipoprotein AIV gene expression in rat hypothalamus

Apolipoprotein AIV (apo AIV) is a circulating signal released from intestinal cells in response to lipid feeding and contributes to the anorectic effect of a lipid meal. We have demonstrated that apo AIV is also synthesized in the hypothalamus, and that hypothalamic apo AIV gene expression is regulated physiologically. Neuropeptide Y (NPY) is a hypothalamic neuropeptide with broad regulatory actions in the central nervous system. In the present studies, the effects of intracerebroventricular (i.v.t.) administration of NPY and of intraduodenal lipid infusion on hypothalamic apo AIV gene expression were determined using competitive RT-PCR in fasted rats. I.v.t. injection of NPY alone significantly increased apo AIV mRNA levels in the hypothalamus in a dose-dependent manner. Intraduodenal infusion of lipid also stimulated the gene expression of hypothalamic apo AIV, but no further significant increment occurred when i.v.t. injection of NPY was combined with lipid infusion. These results suggest that NPY and lipid may regulate apo AIV gene expression in the rat hypothalamus.     

Neonatal LPS injection alters the body weight regulation systems of rats under non-stress and immune stress conditions

It has been reported that prenatal immune stress induced by lipopolysaccharides or cytokines increases food intake and leads to obesity and other features of metabolic syndrome in adulthood. Using Sprague–Dawley rats, we evaluated whether neonatal LPS injection altered their body weight regulation systems under non-stress and immune stress conditions. On Day 10 after birth, all pups were injected with LPS (100 μg/kg, i.p.) (PND₁₀LPS) or saline (PND₁₀Saline). After weaning, body weight was significantly elevated in PND₁₀LPS compared with PND₁₀Saline. Thereafter, the rats were injected with LPS (100 μg/kg, i.p.) or saline (used as a basal condition) from 7 to 8 weeks of age. Under basal conditions, cumulative food intake were significantly higher, serum leptin concentration was significantly increased, and hypothalamic NPY mRNA expression was significantly decreased in PND₁₀LPS compared with PND₁₀Saline. Under adult LPS injected conditions, body weight gain and cumulative food intake were suppressed in both the PND₁₀LPS and PND₁₀Saline groups compared with those observed under basal adult saline-injected conditions. The suppressive effects induced by adult LPS injection were less evident in the PND₁₀LPS group than in the PND₁₀Saline group. Adult LPS injection increased the serum leptin concentration in the PND₁₀Saline rats, but not in the PND₁₀LPS rats. In addition, adult LPS injection increased the mRNA expression of anorexinergic factors (IL-1β, and TNF-α), and decreased that of the orexinergic factor NPY in both groups. However, the influence of adult LPS injection upon these factors was less evident in the PND₁₀LPS group than in the PND₁₀Saline group. These results suggest that neonatal LPS injection alters body weight regulation under both non-stress and immune stress conditions in male rats. Changes in the endocrine, neuropeptide, and cytokine regulation systems might be involved in these alterations.     

Transcriptional involvement of protein kinase C-alpha isozyme in amphetamine-mediated appetite suppression

Amphetamine (AMPH) is known as an anorectic agent. The anorectic action of AMPH has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an appetite stimulant in the brain. The molecular mechanisms behind this anorectic action of AMPH are still unclear. This study investigated the possible role of protein kinase C (PKC) isotypes in this anorectic action. Results revealed that most PKC isotypes (alpha, betaII, gamma, delta, eta, lambda and zeta), except betaI and epsilon isotypes, were stimulated during a repeated treatment of AMPH. Among these stimulated isotypes, three isotypes (alpha, delta, lambda) were activated and expressed in a similar manner, while the other isotypes were expressed differently and specifically. To determine if PKCalpha was involved in the anorectic response of AMPH, the infusions of antisense oligonucleotide into the brain were performed 1 h before daily AMPH treatment in freely moving rats, and the results showed that PKCalpha knock down could block the anorectic response and restore NPY mRNA levels in AMPH-treated rats. These results suggest that PKC isotypes- (at least the alpha isotype), related modification of NPY gene expression in hypothalamus might play an essential role in the central regulation of AMPH-mediated feeding suppression.     

Refractory hypothalamic adenylate cyclase in anorectic tumor-bearing rats: implications for NPY-induced feeding

Although isoproterenol stimulated adenylate cyclase activity in hypothalamic membranes taken from freely-feeding, food-restricted or nonanorectic tumor-bearing rats, the response was greatly reduced in anorectic tumor-bearing rats. The addition of NPY to the membrane preparation inhibited adenylate cyclase activity in hypothalamus taken from freely-feeding and food-restricted rats, but NPY-inhibitory activity was significantly reduced in both groups of tumor-bearing rats. These results suggest that cyclic AMP formation is refractory in anorectic tumor-bearing rats, and that NPY-induced inhibition of hypothalamic adenylate cyclase is reduced in tumor-bearing rats prior to the onset of significant anorexia. Therefore, NPY-induced feeding may be reduced in tumor-bearing organisms due to a dysfunction in the cyclic AMP second messenger system.     

Maternal undernutrition induces neuroendocrine immune dysfunction in male pups at weaning.

The present study was designed to assess the effect of maternal undernutrition, during gestation and lactation, on the neuroendocrine [hypothalamo-pituitary-adrenal (HPA)]-immune axis response to endotoxin (LPS) administration. For this purpose, 21-day-old male rats from both well-nourished (WN) and undernourished (UN) mothers were examined 2 h after injection (i.p.) of vehicle alone (VEH) or containing LPS (130 microg/kg BW). Circulating levels of glucose (GLU), ACTH, corticosterone (B), tumor necrosis factor-alpha (TNFalpha) and leptin were explored. The results indicate that: (a) mother body weight was significantly (p < 0.05) reduced, as a consequence of UN, at the second and third weeks of pregnancy; (b) no differences in basal glycemia were found in the two groups of pups, and LPS treatment did not induce hypoglycemia, in either group; (c) basal plasma ACTH, B and TNFalpha levels were similar in the two groups, and LPS-induced ACTH, B and TNFalpha secretions, although severalfold higher than respective VEH values (p < 0.05) in pups from WN mothers, were fully (ACTH and B) and partially (TNFalpha) abolished in products from UN mothers; (d) both mean body weights and basal plasma leptin levels were significantly (p < 0.05) lower in pups from UN than from WN mothers, and LPS administration did not modify plasma leptin values in products from both groups. In addition, results of dispersed total adrenal cells incubated in vitro indicate that: (a) both basal and ACTH (22 pM)-induced B secretion were significantly (p < 0.05) lower in cells from UN than WN pups, and (b) leptin (100 nM) was able to inhibit partially ACTH-stimulated B output by adrenal gland (AG) cells from WN pups; however, it failed to inhibit ACTH-stimulated glucocorticoid release by AG cells from UN pups. The present results indicate that undernutrition in mothers, during the very critical periods of gestation and lactation, induces in their male pups at weaning: (a) reduced circulating leptin levels and body weight values; (b) metabolic adaptation to normal carbohydrate metabolism; (c) hyporesponsiveness of the HPA and immune (TNFalpha) axes during endotoxemia, and (d) leptin resistance at the adrenocortical level. This study strongly supports that undernutrition of mothers results in neuroendocrine immune dysfunction of their pups; however, adrenal resistance to the inhibitory effect of leptin on glucocorticoid output is developed, probably as an adaptive mechanism to counteract unfavorable metabolic conditions.     

The febrile response to intraperitoneal lipopolysaccharide: strain and gender differences in rats

The acute-phase febrile responses of the inbred Lewis (LEW) and Fischer 344 (F344) rat strains and their parent Sprague-Dawley (S-D) strain to immune challenge with lipopolysaccharide (LPS) were compared. LEW and S-D males and females displayed a biphasic febrile response with a markedly attenuated second phase in F344 rats. At 2 h after LPS (50 microg/kg), corticosterone was significantly higher in F344 than in LEW rats, but serum interleukin-1beta was higher only in F344 than LEW males. These data suggest that the greater LPS-induced corticosterone response of F344 rats mediates differences between febrile responses of F344 and LEW males and females.