Macrophage inflammatory protein-1: unique action on the hypothalamus to evoke fever

Macrophage inflammatory protein (MIP-1) administered systemically causes a fever not blocked by a prostaglandin (PGE) synthesis inhibitor. The purpose of this study was to examine the central mechanism of pyrexic action of this cytokine in the unrestrained rat. After guide cannulae for microinjection were implanted stereotaxically just above the anterior hypothalamic preoptic area (AH/POA), the body temperature of each rat was monitored by a colonic thermistor probe. Saline control vehicle or MIP-1 was microinjected into the AH/POA in one of eight concentrations ranging from 0.0028-9.0 ng per 0.5 mu 1 volume. MIP-1 induced a biphasic or monophasic fever of short latency characterized by an inverse dose-response curve. The potency of MIP-1 was in the femtomolar (10(-15)) range with the lowest dose of 0.028 ng producing a fever of over 2.0 degrees C with a latency of 15 min or less. To determine whether a PGE mediates MIP-1 fever, indomethacin was administered either intraperitoneally in a dose of 5.0 mg/kg or directly into the MIP-1 injection site in a dose of 0.5 microgram/0.5 mu 1, both injected 15 min before MIP-1. Pretreatment of the injection site in the AH/POA with indomethacin failed to prevent the febrile response evoked by MIP-1 injected at the same locus. Further, the dose of systemic indomethacin, which blocks PGE-induced fever in the rat, attenuated only partially the MIP-1 fever. The results demonstrate that MIP-1 is the most potent endopyrogen discovered thus far, and that its action is directly in the region of the hypothalamus which contains both thermosensitive and pyrogen-sensitive neurons. The local action of MIP-1 on cells of the AH/POA in evoking fever is unaffected by the PGE inhibitor which indicates, therefore, that a cellular mechanism operates in the hypothalamus to evoke fever independently of the central synthesis of a PGE.     

Fever induced by macrophage inflammatory protein-1 (MIP-1) in rats: hypothalamic sites of action.

The purpose of this study was to clarify the central site of action as well as functional characteristics of the febrile response of the cytokine, macrophage inflammatory protein-1 (MIP-1). Guide cannulae for microinjection were implanted stereotaxically in the rat just above the pyrogen and thermosensitive area of the anterior hypothalamic, preoptic area (AH/POA). Following postoperative recovery, the body temperature of each rat (Tbo) was monitored during an experiment by a colonic thermistor probe at 0.5-1.0-h intervals. When MIP-1 was microinjected in a 0.5-microliter volume into the AH/POA in one of eight concentrations ranging from 0.0028 nanograms (ng) to 9.0 ng, an intense monophasic or biphasic fever was evoked. The MIP-1-induced increase in the Tbo of the rat was characterized by its short latency of 15 to 30 min and an inverse dose-response curve. Measures of mean latency and maximal rise in Tbo following MIP-1 confirmed the potency of this dose. Although the dose of 0.028 ng produced a fever of over 2.0 degrees C with a latency of only 15 min or less, the hyperthermic response became less intense as the dose of MIP-1 was increased. An anatomical mapping of sites of microinjection which reacted to MIP-1 in mediating fever revealed that the medial portion of the POA of the rat just rostral to the border of the AH was the region of maximum sensitivity to the cytokine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fever evoked by macrophage inflammatory protein-1 (MIP-1) injected into preoptic or ventral septal area of rats depends on intermediary protein synthesis

Macrophage inflammatory protein-1 (MIP-1), a novel cytokine composed of α/β subunits, is released from macrophages during infection, MIP-1 injected intravenously in the rabbit or into the anterior hypothalamic, preoptic area (AH/POA) of the rat causes an intense fever, which is not blocked by prostaglandin synthesis inhibitors, ibuprofin or indomethacin, respectively. The purpose of this study was to determine the role of de novo protein synthesis on the fever evoked by MIP-1 applied to thermosensitive cells of the AH/POA. Guide cannulae were implanted bilaterally above the AH/POA or ventral septal area (VSA) and medially above the third cerebral ventricle in each of 11 male Sprague-Dawley rats. Following postoperative recovery, body temperature (T_b) was monitored by a colonic thermistor probe. The bilateral microinjection of MIP-1 in a dose of 14 pg per 0.5 μ1 into the AH/POA caused a biphasic elevation in T_b to 0.9 ± 0.2 °C within 3.0 h, and persisted for over 6.0 h. An identical injection of MIP-1 into the VSA increased T_b biphasically to 0.1 ± 0.1 °C within 1.0 h and to 0.8 ± 0.3 °C within 3.0 h. The infusion into the third ventricle of 80 μg/10 μ1 of the inhibitor of protein synthesis, anisomycin, either 10 or 30 min before the microinjection of MIP-1 into the AH/POA, attenuated significantly the rise in T_b for 1.0 to 3.0 h or 2.5 to 3.0 h, respectively. These results coincide with the earlier finding that anisomycin inhibits both endotoxin- and IL-1β-induced fevers. Further, the synthesis of a new protein factor may be required functionally for the initiation and maintenance of a fever whose mechanism of induction apparently is metabolically independent of the cyclooxygenase pathway.     

Fever and feeding in the rat: Actions of intrahypothalamic interleukin-6 compared to macrophage inflammatory protein-1β (MIP-1β)

The chemokines, macrophage inflammatory protein-1 (MIP-1) and its subunit MIP-1β, induce an intense fever in the rat when they are injected directly into the anterior hypothalamic, pre-optic area (AH/POA), a region containing thermosensitive neurons. The purpose of this study was to compare the central action on body temperature (T_b) of MIP-1β with that of interleukin-6 (IL-6), which also has been implicated in the cerebral mechanism underlying the pathogenesis of fever. Following the stereotaxic implantation in the AH/POA of guide cannulae for repeated micro-injections, radio transmitters which monitor T_b continuously were inserted intraperitoneally in each of 15 male Sprague-Dawley rats. Each micro-injection was made in a site in the AH/POA in a volume of 1.0 μl of pyrogen-free artificial CSF, recombinant murine MIP-1β, or recombinant human IL-6. MIP-1β in a dose of 25 pg evoked an intense fever characterized by a short latency, a mean maximum rise in T_b of 2.4 ± 0.21°C reached by 3.7 ± 0.42 hr, and a duration exceeding 6.5 hr. Injected into homologous sites in the AH/POA, IL-6 induced a dose dependent fever of similar latency and a mean maximal increase in T_b of 1.2 ± 0.25°C, 1.8 ± 0.15°C, and 2.1 ± 0.22°C and duration of 6.2 ± 1.28 hr, 6.7 ± 0.49 hr, and 6.8 ± 0.65 hr when given in doses of 25, 50, and 100 ng, respectively. These results show that MIP-1β and the highest dose of IL-6 induce a fever of comparable intensity, but MIP-1β exerts its action in a much lower concentration. Thus, the de novo synthesis and subsequent action of the MIP-1 family of cytokines on neurons of the AH/POA in response to a pyrogen challenge apparently play a functional role in the pathogenesis of fever. Further, the endogenous activity of IL-6 in the hypothalamus which is enhanced in response to a lipopolysaccharide also may reflect its essential part in the acute phase response to a bacterial challenge. Copyright © 1994 Wiley-Liss, Inc.     

Cytokines and Thermoregulation: Interleukin-9 Injected in preoptic area fails to evoke fever in rats

A number of the members of the family of cytokines including IL-1, IL-2, IL-6, and IL-11 act directly in the brain to induce a febrile response in the rat and other species. The purpose of this study was to examine the effect of interleukin-9 (IL9) when this cytokine is applied directly to the thermosensitive and pyrogen reactive region of the anterior hypothalamic, preoptic area (AH/POA). In male Sprague-Dawley rats, guide cannulae for microinjection into the AH/POA were implanted stereotaxically, and radio transmitters for monitoring body temperature (T_b) were placed intraperitoneally. Following postoperative recovery, recombinant murine macrophage inflammatory protein (MIP)-1β was microinjected in the AH/POA of each rat in a dose of 28 pg/1μl to identify pyrogen reactive sites in the AH/POA. Then recombinant human IL-9 was suspended in pyrogen-free CSF vehicle and microinjected in the same sites in concentrations of 2.4, 24, and 240 U/μl. In contrast to the pyrexic action of MIP-1β, IL-9 failed to elicit a significant alteration in the T_b of the rats at any of the doses tested. IL-9 was also without effect on the intakes of either water or food. These results demonstrate that IL-9 applied to the region of the diencephalon in which other cytokines act to evoke fever may not play a direct role in the thermogenic component underlying the acute phase response. However, as demonstrated in several different cell systems, IL-9 may require a cofactor related to pyrogen for a febrile response to develop.     

Urocortin in the ventromedial hypothalamic nucleus acts as an inhibitor of feeding behavior in rats

Urocortin (UCN), a member of the corticotropin-releasing factor (CRF) family, inhibits food intake when it is injected intracerebroventricularly in rats. To explore the site of action of UCN in feeding behavior, we examined the effects of injection of UCN into various hypothalamic nuclei on food and water intake in 24-h fasted rats. Injection of UCN into the ventromedial hypothalamic nucleus (VMH) significantly inhibited food and water intake over 3 h without sedative effect, but no significant effect was observed following injection either into the lateral hypothalamic area, or the paraventricular nucleus of the hypothalamus. To further explore the physiological significance of endogenous UCN of the VMH in feeding behavior, the effect of immunoneutralization of hypothalamic UCN on food intake was examined. Injection of anti-rat UCN rabbit gamma-globulin into the bilateral VMH in freely fed rats significantly potentiated food and water intake compared with rats that received normal rabbit gamma-globulin. These results suggest that endogenous UCN in the VMH exert inhibitory control on ingestive behavior.     

GABA-related feeding control in genetically obese rats

Feeding in response to glucoprivation induced by 2-deoxy-D-glucose (2-DG) is impaired in genetically obese (Zucker) rats. Muscimol, a GABAA-agonist (0.5 nmol/0.5 microliter in each area) increased food intake in lean rats over 3 h but in fatty rats only at 30 min after infusion into the VMH. Injection of muscimol into the DMH and PVN increased feeding of both phenotypes. Picrotoxin, a non-competitive GABAA-antagonist (0.1 nmol/0.5 microliter) increased food intake after infusion into the LH of both phenotypes and decreased food intake over a 3 h period when infused into the VMH. DMH and PVN of fatty rats. In the lean littermates, picrotoxin was only effective in reducing food intake at 30 min after infusion into the VMH and PVN but not the DMH. The present results suggest that the fatty Zucker rat has a disturbance in the GABA-related regulatory mechanism of feeding behavior in the ventromedial hypothalamus, which may be responsible for the impaired response to glucoprivation found in these rats.     

Changes in extracellular hypothalamic glucose in relation to feeding

The aim of the present in vivo microdialysis study was to investigate the relation between feeding and changes in glucose concentrations in the rat ventromedial hypothalamus (VMH). Absolute ambient glucose concentrations in VMH were 1.43 mm in non-deprived rats as compared to 0.94 mm after 24-h food deprivation. To examine whether feeding influences hypothalamic glucose, changes of glucose concentration over time were determined relative to a baseline. Experiments were conducted in relation to both, nutritional state (food-deprived rats vs. non-deprived rats) and feeding conditions throughout the experiment (freely feeding rats vs. rats without access to food). The results of this microdialysis study show clearly that glucose concentration in the VMH of rats increases significantly in relation to food intake. The data demonstrate that a 24-h food deprivation before the experiment further augments this increase (up to 350% from baseline) as compared to non-deprived conditions (up to 60% from baseline). However, the magnitude of food related increase in VMH glucose does not correlate with the individual amount of food eaten. In conclusion, the present study shows for the first time that VMH glucose concentrations increase with food intake in the early dark phase, indicating that such changes do not only occur after pharmacological treatment, but also under physiological feeding conditions. The results further indicate that the feeding related increase in VMH glucose depends on the nutritional state of the organism.     

Organization of central hyperthermic mechanisms in helium-cold hypothermic hamsters

We have investigated the ability of three hyperthermic stimuli (PGE2, 5-HT and ACh) to elicit hyperthermia in the Helium-Cold (He-Cold) hypothermic hamster. Hamsters in these conditions are poikilothermic and will passively follow room temperature in a regulated cold room. Animals were injected centrally at AH/POA sites via an indwelling guide tube at body temperatures maintained between 9-12 degrees C. Active sites in the AH/POA were determined prior to the experiment by PGE2 injection. PGE2 injection at an effective AH/POA site immediately reversed the anesthetic induced hypothermia in warm air. Hamsters were induced into hypothermia by the He-Cold induction method and body temperatures were maintained in a 9 degrees C cold room. Colonic temperatures were monitored at 5 minute intervals by a YSI thermistor probe and telethermometer. Central injections of 5-HT (2 micrograms/microliter) and ACh (50 micrograms/microliter) at effective AH/POA sites evoked significant increases in colonic temperature in He-Cold hamsters. PGE2 injections were not different from saline control injections and did not elicit pronounced temperature changes in these animals. Specific blockade of the 5-HT and ACh temperature increases was demonstrated with specific antagonist injections. The results suggest that the central organization of heat-gain mechanisms in the AH/POA is the same as normothermic animals even at temperatures well below those previously investigated.     

Anorexic action of a new potential neuropeptide Y antagonist [ -Tyr, -Thr]-NPY (27–36) infused into the hypothalamus of the rat

Neuropeptide Y (NPY) produces a vigorous feeding response in several species when it is injected into hypothalamic structures involved in eating behavior. The purpose of this study was to determine whether a unique carboxy terminal fragment of NPY would alter the pattern of eating induced in the rat either by NPY injected into the hypothalamus or by a 24-h period of food deprivation. In this case, two -tyrosine residues and one t.-threonine residue of the NPY_27–36 fragment were transformed to their D-conformation to produce [ -Tyr^27,36, -Thr³²]-NPY (27–36), i.e., D-NPY_27–36. Guide cannulae for microinjection were implanted stereotaxically just dorsal to the paraventricular nucleus (PVN) or ventromedial hypothalamus (VMH) of 24 adult male Sprague-Dawley rats. Following postoperative recovery, a microinjection of artificial CSF or 1.1 jig or 3.3 μg of a peptide was made directly into the PVN or VMH as follows; native NPY; D-NPY_27–36; or [L-Tyr^27,36 L-Thr³²]-NPY (27–36), i.e., L-NPY_27–36. Food intakes were measured at intervals of 0.25, 0.5, 1.1, 2.0, 4.0, and 24 h. When D-NPY_27–36 was microinjected at NPY reactive sites in the PVN or VMH of the rat 15 min before a similar microinjection of NPY, the intense eating response induced by the peptide was reduced significantly. Not only was the effect dose dependent, but D-NPY_27–36 also augmented the latency to feed. A mixture of the two doses of NPY and DNPY_27–36 injected at the same hypothalamic loci did not attenuate the intake of food but tended to enhance the feeding response in the rats. After the rats were deprived of food for 24 h, D-NPY_27–36 microinjected in the same hypothalamic sites similarly caused a dose-dependent suppression of normal feeding behavior. However, the CSF control vehicle and L-NPY_27–36 microinjected in the PVN or VMH were without effect on the pattern of eating. Further, D-NPY_27–38 injected in the same hypothalamic sites affected neither body temperature nor water intakes of the rats significantly. These results demonstrate that the D substitution of this C-fragment of the NPY molecule, i.e., D-NPY_27–36, serves to inhibit feeding evoked in the rat by hypothalamic NPY as well as the natural eating response to food deprivation. Thus, the D-NPY_27–36 molecule may act as an antagonist at one or more subtypes of the NPY receptor in the brain of the rat.     

Anorexic action of a new potential neuropeptide Y antagonist [d-Tyr, d-Thr]-NPY (27–36) infused into the hypothalamus of the rat

Neuropeptide Y (NPY) produces a vigorous feeding response in several species when it is injected into hypothalamic structures involved in eating behavior. The purpose of this study was to determine whether a unique carboxy terminal fragment of NPY would alter the pattern of eating induced in the rat either by NPY injected into the hypothalamus or by a 24-h period of food deprivation. In this case, two l-tyrosine residues and one t.-threonine residue of the NPY_27–36 fragment were transformed to their D-conformation to produce [d-Tyr^27,36,d-Thr³²]-NPY (27–36), i.e., D-NPY_27–36. Guide cannulae for microinjection were implanted stereotaxically just dorsal to the paraventricular nucleus (PVN) or ventromedial hypothalamus (VMH) of 24 adult male Sprague-Dawley rats. Following postoperative recovery, a microinjection of artificial CSF or 1.1 jig or 3.3 μg of a peptide was made directly into the PVN or VMH as follows; native NPY; D-NPY_27–36; or [L-Tyr^27,36 L-Thr³²]-NPY (27–36), i.e., L-NPY_27–36. Food intakes were measured at intervals of 0.25, 0.5, 1.1, 2.0, 4.0, and 24 h. When D-NPY_27–36 was microinjected at NPY reactive sites in the PVN or VMH of the rat 15 min before a similar microinjection of NPY, the intense eating response induced by the peptide was reduced significantly. Not only was the effect dose dependent, but D-NPY_27–36 also augmented the latency to feed. A mixture of the two doses of NPY and DNPY_27–36 injected at the same hypothalamic loci did not attenuate the intake of food but tended to enhance the feeding response in the rats. After the rats were deprived of food for 24 h, D-NPY_27–36 microinjected in the same hypothalamic sites similarly caused a dose-dependent suppression of normal feeding behavior. However, the CSF control vehicle and L-NPY_27–36 microinjected in the PVN or VMH were without effect on the pattern of eating. Further, D-NPY_27–38 injected in the same hypothalamic sites affected neither body temperature nor water intakes of the rats significantly. These results demonstrate that the D substitution of this C-fragment of the NPY molecule, i.e., D-NPY_27–36, serves to inhibit feeding evoked in the rat by hypothalamic NPY as well as the natural eating response to food deprivation. Thus, the D-NPY_27–36 molecule may act as an antagonist at one or more subtypes of the NPY receptor in the brain of the rat.     

Effect of food deprivation and leptin repletion on the plasma levels of estrogen (E2) and NADPH-d reactivity in the ventromedial and arcuate nuclei of the hypothalamus in the female rats

The exact role of leptin in fasting has not been completely elucidated. To determine whether leptin can act in fasting to influence plasma estrogen levels and nitric oxide synthase reactivity in food regulating centers of the brain, we fasted female rats for 4 days and treated them i.p. with vehicle or 100 microg of recombinant mouse leptin as 1 ml on the 3rd and 4th day twice daily (10.00 and 17.00 h). Proestrus blood was collected at 10.00, 14.00, 18.00 and at 22.00 h, plasma obtained and assayed for estrogen (E2) and leptin levels. Verification of ovulation occurrence was by examining the oviduct for extruded ovum. The rat brains were removed and processed for nitric oxide synthase reactivity in the ventromedial hypothalamus (VMH) and arcuate nucleus (ARC) using NADPH-diaphorase histochemistry, a marker for neurons expressing NOS enzyme. Leptin effect on dependable variables such as food intake, water intake and body weight gain was also investigated. Four days fasting significantly decreased body weight, estrogen and postfast leptin levels, nitric oxide reactivity in the VMH and ARC nucleus and stopped ovulation in many (4 out of 5) rats fasted and given vehicle. Leptin treatment significantly increased plasma estrogen and postfast leptin levels, restored ovulation in many (4 out of 5) rats and increased nitric oxide reactivity in the VMH and ARC. Leptin significantly inhibited food intake, water intake and gain in body weight during recommenced feeding. These observations suggest that leptin could act in the pituitary-ovarian axis during fasting to improve reproductive function by partly stimulating estrogen secretion.     

Components of hypothalamic obesity: bipiperidyl-mustard lesions add hyperphagia to monosodium glutamate-induced hyperinsulinemia

Rats with bilateral electrolytic lesions in the general region of the ventromedial hypothalamic (VMH) nucleus develop hyperinsulinemia, excessive food intake and obesity. Monosodium glutamate (MSG) destroys neurons of the arcuate hypothalamic (AH) nucleus and produces hyperinsulinemic but hypophagic obesity. Bipiperidyl mustard (BPM) primarily destroys VMH neurons, but has produced only a slight obesity even when rats were maintained on high-fat diets. In the present study, rats treated with MSG (AH lesion) were hyperinsulinemic, moderately obese and hypophagic; BPM rats (primarily VMH lesion) were not different from controls when fed standard chow diets. However, MSG/BPM rats (AH+VMH lesion) were hyperinsulinemic, massively obese and hyperphagic. Thus, two components of the electrolytic lesion syndrome previously attributed to VMH damage (hyperinsulinemia and obesity) were reproduced simply by MSG treatment alone. The third component (hyperphagia) occurred only when both AH and VMH were lesioned, suggesting that neurons in both nuclei may perform a satiety function and may be able to substitute for one another in this respect. Since MSG treatment is required for all components of both obesity syndromes described here, this underscores the importance of MSG-sensitive neurons in mechanisms of obesity. The combined treatment approach also represents the first rat model of hyperinsulinemic, hyperphagic obesity that can be entirely produced by systemic administration of neurotoxins.     

Role of preoptic and anterior hypothalamic cholinergic input on water intake and body temperature

To elucidate the role played by cholinergic mechanism in the preoptic area (POA) and anterior hypothalamus (AH) in the control of body temperature and water intake of rats, we used microdialysis without disturbing the behavior of unanesthetized animals. After microdialysis, we also investigated immunoreactivity for c-Fos protein in the hypothalamus. Stimulation with neostigmine, an acetylcholine esterase inhibitor, through microdialysis probe increased extracellular concentration of acetylcholine (ACh) in the POA and AH, and was accompanied by a dose-dependent fall in body temperature and increased water intake. Addition of atropine, a muscarinic receptor antagonist, to the dialysis medium containing neostigmine suppressed the neostigmine-induced changes in rectal temperature and water intake. Neostignime markedly increased c-Fos-like immunoreactivity (Fos-IR) in certain hypothalamic areas, including the paraventricular nucleus, supraoptic nucleus and median preoptic nucleus. This increase was also attenuated by atropine. These results suggest that cholinergic inputs and activation of muscarinic processes in POA and AH induced a decline in body temperature and increased water intake.     

Macrophage Inflammatory Protein-1β (MIP-1β) Produced Endogenously in Brain During E. coli Fever in Rats

Macrophage inflammatory protein-1 (MIP-1) evokes an intense fever, independent of a prostaglandin mechanism, and is now thought to play an important role in the defence response to bacterial pyrogens. The purpose of this study was 2-fold: (i) to determine whether the potent doublet of this cytokine, MIP-1β, is actually produced in the brain in response to a pyrogenic dose of a lipopolysaccharide of Escherichia coli and (ii) to determine the anatomical site of synthesis of this cytokine in the brain. Following the intense fever produced by intraperitoneal administration of lipopolysaccharide in the unrestrained rat, MIP-1β immunoreactivity was identified post mortem in two regions of the brain implicated in fever: the organum vasculosum laminae terminalis (OVLT) and the anterior hypothalamic, preoptic area (AH/POA). Microinjection of goat anti-mouse MIP-1β antibody (anti-MIP-1β) directly into the AH/POA markedly suppressed fever in rats in response to lipopolysaccharide. Further, anti-MIP-1β administered 180 min after the injection of lipopolysaccharide acted as an antipyretic and reversed the fever induced by the endotoxin. Anti-MIP-1β or control immunoglobulin G antibody microinjected into the hypothalamus immediately before the intraperitoneal injection of the control saline did not alter the temperature of the rats. Taken together, the present results demonstrate that MIP-1β is produced in the brain in response to a bacterial endotoxin. These observations, in the light of earlier data on fever induced by MIP-1β, further support the hypothesis that endogenously synthesized MIP-1β acts as an intermediary factor in the evocation of fever by acting on the thermosensitive cells of the brain.     

Reversible hyperphagia and obesity following intracerebral microinjections of colchicine into the ventromedial hypothalamus of the rat

Colchicine, a drug which produces a reversible inhibition of intraaxonal transport and synaptic transmission, was used as a reversible neural blocker to investigate the role of the ventromedial hypothalamus (VMH) in the control of ingestive behavior and body weight regulation. Male Sprague-Dawley rats received intracranial microinjections of colchicine into the VMH. Volume and concentration of the colchicine solution were varied to assess specificity of action and dose-response relationship. When colchicine (2 and 4 μg) was microinjected bilaterally into the VMH, there was a dose-dependent increase in food and water intakes and body weight gain which lasted several days. The acute period of hyperphagia was followed by a marked depression in feeding which persisted until body weight was lowered to control levels. This suppression of feeding appeared to be a consequence of the preceding period of hyperphagia and obesity, since colchicine-treated rats which were pair-fed with controls to prevent obesity continued to maintain normal food intake and body weight gain when later fed ad libitum. The results of this study confirm the importance of the VMH in the long term regulation of feeding, and indicate that reversible neuronal blocking with colchicine is a useful technique for investigating the neural substrates of feeding and other behaviors.     

Differential sensitivities of pyrogenic chemokine fevers to cyclooxygenase isozymes antibodies

It has been proposed that prostaglandin (PG)E(2) production via a process catalyzed by the inducible isoform of cyclooxygenase (COX)-2 and activation of specific PGE(2) receptor subtypes within the preoptic/anterior hypothalamus (AH/POA) is the last step and unique pathway in the induction of a fever. However, many data support the existence of a PG-independent pathway. That is, other more rapid mechanisms, which involve the constitutive COX-1 isozyme, may be more critical for a PG-dependent fever. Thus, we examined the role of both COX isoforms in the AH/POA in fevers induced by macrophage inflammatory protein (MIP)-1beta, a PG-independent pyrogen, and RANTES (regulated on activation, normal T-cells expressed and secreted), a PG-dependent pyrogen. In freely moving rats, two independent polyclonal antibodies were used which neutralize COX-1 and COX-2. The microinjection of either MIP-1beta or RANTES into the pyrogen-sensitive region of the AH/POA induced an intense fever of rapid onset. Peripheral pretreatment with an antipyretic dose of dexamethasone which prevents COX-2 expression, or the microinjections into the AH/POA of either anti-COX-1 or anti-COX-2, blocked the febrile response induced by RANTES but not that induced by MIP-1beta. These results provide strong evidence for the existence of rapid mechanisms in the AH/POA which involve both COX isozymes during the fever induced by RANTES, and further support the existence of an alternative PG-independent pathway in the febrile response.     

Mapping of hypothalamic sites involved in the effects of NPY on body temperature and food intake

The objective of the present study was to identify hypothalamic sites that might be implicated in the effects of neuropeptide Y (NPY) on both body temperature and food intake. For this purpose, the effects of direct microinjections of NPY in several doses (0.156–20 μg) into discrete hypothalamic nuclei on body temperature were examined in rats. To examine specificity of effects, food consumption of animals following injections was also measured. Results indicate that the influence of NPY on body temperature varies with the hypothalamic region where the peptide is administered. NPY had no effect on temperature after administration into the ventromedial (VMH) and the perifornical hypothalamus (PeF). However, a significant hypothermia was seen following administration into the preoptic (POA) and arcuate nucleus (Arc), and hyperthermia was seen after injection into the paraventricular nucleus (PVN). Finally, a biphasic effect was observed after injection into the lateral hypothalamus (LH): hyperthermia with relatively small doses and hypothermia with higher doses. Similar effects were obtained when administred into the third ventricle (3V) but in an inverted dose-related fashion: hypothermia at low and hyperthermia at higher doses. For feeding, NPY consistently increased food intake in all regions examined, with the strongest effect obtained after administration into the PeF. The present results clearly dissociate the effects of NPY on food intake and body temperature, and demonstrate that these effects are related to specific hypothalamic nuclei.     

Opioid-induced feeding: Localization of sensitive brain sites

These experiments were designed to identify brain sites at which opioids might act to influence ingestive behavior and to determine which opioid receptor types are involved. After food deprivation, rats were given microinjections of naloxone into several brain regions and food intake was measured. Injections into or near the paraventricular (PVN) or ventromedial (VMH) hypothalamic nuclei or the globus pallidus (GP) reduced food intake; injections into the striatum or lateral hypothalamus (LH) were ineffective. A second study examined the ingestive effects of roughly equimolar doses (1.43-1.75 nmol) of dynorphin A (DYN), beta-endorphin (beta-END), and D-Ala2,D-Leu5-enkephalin (DADLE) when injected into 4 different brain regions. Only DYN significantly increased food intake, and this effect was seen only with injections into the PVN and VMH. Beta-END stimulated water intake when injected into the PVN, VMH and GP but not the LH. Further studies indicated that with PVN injections, DYN was effective at a dose as low as 0.47 nmol, and that a higher dose of DADLE (4.39 nmol) did stimulate food intake. These studies support an important role for dynorphin and the kappa opioid receptor in the regulation of feeding and suggest that the opioid regulation of food and water intake can be differentiated both by sites of action and by effective agonists.     

2,5-Anhydro-D-mannitol: its unique central action on food intake and blood glucose in rats.

Peripheral administration of D-fructose has been reported to decrease food intake, and its 2-deoxy analogue, 2,5-anhydro-D-mannitol (2,5-AM), increased food intake and decreased blood glucose in rats. In the present study, 2,5-AM was selected for comparison with well-known 2-deoxy analogues of glucose. Infusion of 2,5-AM into the rat third cerebroventricle at 11.00 h induced feeding dose dependently (Y = 0.63 logX-1.20, r = 0.95, P less than 0.05). Rats treated with 2,5-AM at a maximal effective dose of 24 mumol/rat ate meals most persistently (P less than 0.05). No periprandial drinking was observed. Ambulatory activity increased concomitantly with feeding, but did not exceed the activity normally associated with a meal. Infusion of 24 mumol 2,5-AM into the third cerebroventricle induced no substantial change in plasma glucose or insulin in any 60-min experimental period. Unilateral microinfusion of 1.2 mumol 2,5-AM induced feeding in all 6 rats (P less than 0.01) when a cannula tip was located in the ventromedial hypothalamic nucleus (VMH), but not in the lateral hypothalamic area (LHA). These findings indicate that feeding elicitation may be due to disinhibition by 2,5-AM through the VMH. This is quite unique compared to the action mechanisms of hexose, pentose and their analogues, except 2,5-AM.