Experimental sepsis induces sustained inflammation and acetylcholinesterase activity impairment in the hypothalamus.

Sepsis is one of the leading causes of mortality in intensive care units besides causing profound alterations in the brain. One of the structures notably affected during sepsis is the hypothalamus, resulting in important physiopathological consequences. Recently, we provided evidence that the presence of neuroinflammation, oxidative stress, and apoptosis in the hypothalamus of septic rats, is accompanied by impairment of arginine vasopressin (AVP) secretion. We had also demonstrated that sepsis survivor animals present attenuated AVP secretion after osmotic challenge, suggesting a persistent inflammation in the hypothalamus. However, the long-term course of inflammation in the hypothalamus remains unclear. Thus, we induced sepsis by cecal ligation and puncture (CLP) in Wistar rats and, five days after sepsis induction, the hypothalamus of each animal was collected for analysis. Nonmanipulated animals (naive) were used as controls. We found that CLP-induced morphological alterations in microglial cells are accompanied by an increase in Iba-1 immunoreactivity. Moreover, we observed enhanced expression of NF-κB and CREB transcription factors, which are well known to modulate the immune response. Additionally, we found that phosphorylation of GSK3α/ß (a kinase upstream to the CREB signaling pathway) was increased, as well as COX-2, iNOS, and IL-6 that are canonic inflammatory proteins. Thus, our results indicated the presence of sustained activation of resident glial cells that may result in neuroinflammation and cholinergic neurotransmission disruptions in the hypothalamus.

Impact of systemic lupus erythematosus on oral health-related quality of life.

Oral symptoms in systemic lupus erythematosus (SLE) patients are often unexplored and affect the health-related quality of life. The aims of this study were: (a) to evaluate the oral health condition of SLE patients compared to control subjects without rheumatic diseases; (b) to determine the consequences of oral health condition in the quality of life of these two groups. Individuals with SLE ( n = 75) and without SLE ( n = 78) (control group), paired for gender and age, underwent complete oral examination. Sociodemographic and clinical information was obtained, and interviews were conducted using the Brazilian version of the oral health impact profile. The activity and damage of SLE disease were assessed, respectively, by the systemic lupus erythematosus disease activity index 2000 and the Systemic Lupus International Collaborating Clinics/American College of Rheumatology damage index for systemic lupus erythematosus. When we analysed the oral health condition and hygiene habits of the participants, SLE patients exhibited an increased number of missing teeth despite their higher frequency of tooth brushing. No significant differences were verified in other habits and clinical parameters evaluated such as smoking, flossing, salivary flux, periodontitis, decayed and filled teeth. Patients with SLE presented with worse oral health-related quality of life than controls ( P = 0.011). The significant difference was on individuals' physical disability ( P = 0.002). The determinant of the negative impact on the oral health-related quality of life was prosthesis wearing ( P < 0.05). Overall, the oral health impact profile score was higher in individuals with moderate SLE damage compared to SLE individuals with no damage ( P = 0.043). Patients with SLE had a negative impact of oral condition on their quality of life. The evaluation of the oral health-related quality of life might be useful to monitor the effects of SLE on oral condition.

Activation of locus coeruleus heme oxygenase-carbon monoxide pathway promoted an anxiolytic-like effect in rats.

The heme oxygenase-carbon monoxide pathway has been shown to play an important role in many physiological processes and is capable of altering nociception modulation in the nervous system by stimulating soluble guanylate cyclase (sGC). In the central nervous system, the locus coeruleus (LC) is known to be a region that expresses the heme oxygenase enzyme (HO), which catalyzes the metabolism of heme to carbon monoxide (CO). Additionally, several lines of evidence have suggested that the LC can be involved in the modulation of emotional states such as fear and anxiety. The purpose of this investigation was to evaluate the activation of the heme oxygenase-carbon monoxide pathway in the LC in the modulation of anxiety by using the elevated plus maze test (EPM) and light-dark box test (LDB) in rats. Experiments were performed on adult male Wistar rats weighing 250-300 g (n=182). The results showed that the intra-LC microinjection of heme-lysinate (600 nmol), a substrate for the enzyme HO, increased the number of entries into the open arms and the percentage of time spent in open arms in the elevated plus maze test, indicating a decrease in anxiety. Additionally, in the LDB test, intra-LC administration of heme-lysinate promoted an increase on time spent in the light compartment of the box. The intracerebroventricular microinjection of guanylate cyclase, an sGC inhibitor followed by the intra-LC microinjection of the heme-lysinate blocked the anxiolytic-like reaction on the EPM test and LDB test. It can therefore be concluded that CO in the LC produced by the HO pathway and acting via cGMP plays an anxiolytic-like role in the LC of rats.

Activation of locus coeruleus heme oxygenase-carbon monoxide pathway promoted an anxiolytic-like effect in rats

The heme oxygenase-carbon monoxide pathway has been shown to play an important role in many physiological processes and is capable of altering nociception modulation in the nervous system by stimulating soluble guanylate cyclase (sGC). In the central nervous system, the locus coeruleus (LC) is known to be a region that expresses the heme oxygenase enzyme (HO), which catalyzes the metabolism of heme to carbon monoxide (CO). Additionally, several lines of evidence have suggested that the LC can be involved in the modulation of emotional states such as fear and anxiety. The purpose of this investigation was to evaluate the activation of the heme oxygenase-carbon monoxide pathway in the LC in the modulation of anxiety by using the elevated plus maze test (EPM) and light-dark box test (LDB) in rats. Experiments were performed on adult male Wistar rats weighing 250-300 g (n=182). The results showed that the intra-LC microinjection of heme-lysinate (600 nmol), a substrate for the enzyme HO, increased the number of entries into the open arms and the percentage of time spent in open arms in the elevated plus maze test, indicating a decrease in anxiety. Additionally, in the LDB test, intra-LC administration of heme-lysinate promoted an increase on time spent in the light compartment of the box. The intracerebroventricular microinjection of guanylate cyclase, an sGC inhibitor followed by the intra-LC microinjection of the heme-lysinate blocked the anxiolytic-like reaction on the EPM test and LDB test. It can therefore be concluded that CO in the LC produced by the HO pathway and acting via cGMP plays an anxiolytic-like role in the LC of rats.

Acute stress-induced antinociception is cGMP-dependent but heme oxygenase-independent

Endogenous carbon monoxide (CO), which is produced by the enzyme heme oxygenase (HO), participates as a neuromodulator in physiological processes such as thermoregulation and nociception by stimulating the formation of 3′,5′-cyclic guanosine monophosphate (cGMP). In particular, the acute physical restraint-induced fever of rats can be blocked by inhibiting the enzyme HO. A previous study reported that the HO-CO-cGMP pathway plays a key phasic antinociceptive role in modulating noninflammatory acute pain. Thus, this study evaluated the involvement of the HO-CO-cGMP pathway in antinociception induced by acute stress in male Wistar rats (250-300 g; n=8/group) using the analgesia index (AI) in the tail flick test. The results showed that antinociception induced by acute stress was not dependent on the HO-CO-cGMP pathway, as neither treatment with the HO inhibitor ZnDBPG nor heme-lysinate altered the AI. However, antinociception was dependent on cGMP activity because pretreatment with the guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxaline-1-one (ODQ) blocked the increase in the AI induced by acute stress.

Acute stress-induced antinociception is cGMP-dependent but heme oxygenase-independent.

Endogenous carbon monoxide (CO), which is produced by the enzyme heme oxygenase (HO), participates as a neuromodulator in physiological processes such as thermoregulation and nociception by stimulating the formation of 3',5'-cyclic guanosine monophosphate (cGMP). In particular, the acute physical restraint-induced fever of rats can be blocked by inhibiting the enzyme HO. A previous study reported that the HO-CO-cGMP pathway plays a key phasic antinociceptive role in modulating noninflammatory acute pain. Thus, this study evaluated the involvement of the HO-CO-cGMP pathway in antinociception induced by acute stress in male Wistar rats (250-300 g; n=8/group) using the analgesia index (AI) in the tail flick test. The results showed that antinociception induced by acute stress was not dependent on the HO-CO-cGMP pathway, as neither treatment with the HO inhibitor ZnDBPG nor heme-lysinate altered the AI. However, antinociception was dependent on cGMP activity because pretreatment with the guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxaline-1-one (ODQ) blocked the increase in the AI induced by acute stress.

Central hydrogen sulphide mediates ventilatory responses to hypercapnia in adult conscious rats.

AIM: Hydrogen sulphide (H2S) is endogenously produced and plays an important role as a modulator of neuronal functions; however, its modulatory role in the central CO2 chemoreception is unknown. The aim of the present study was to assess the role of endogenously produced H2S in the ventilatory response to hypercapnia in adult conscious rats. METHODS: Cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CSE) inhibitors (aminooxyacetate: AOA and propargylglycine: PAG respectively) and a H2S donor (sodium sulphide: Na2S) were microinjected into the fourth ventricle (4V). Ventilation (V̇(E)), oxygen consumption (V̇O2) and body temperature were recorded before (room air) and during a 30-min CO2 exposure (hypercapnia, 7% CO2). Endogenous H2S levels were measured in the nucleus tractus solitarius (NTS). RESULTS: Microinjection of Na2S (H2S donor), AOA (CBS inhibitor) or PAG (CSE inhibitor) did not affect baseline of the measured variables compared to control group (vehicle). In all experimental groups, hypercapnia elicited an increase in V̇(E). However, AOA microinjection, but not PAG, attenuated the ventilatory response to hypercapnia (P < 0.05), whereas Na2S elicited a slight, not significant, enhancement. Moreover, endogenous H2S levels were found higher in the NTS after hypercapnia (P < 0.05) compared to room air (normoxia) condition. CONCLUSION: There are a few reports on the role of gaseous transmitters in the control of breathing. Importantly, the present data suggest that endogenous H2S via the CBS-H2S pathway mediates the ventilatory response to hypercapnia playing an excitatory role.

Activity of megestrol acetate in postmenopausal women with advanced breast cancer after nonsteroidal aromatase inhibitor failure: a phase II trial.

BACKGROUND: As novel treatments carry substantial price tags and are mostly cost-prohibitive in low- and middle-income countries, there is an urgent need to develop alternatives, such as off-patent drugs. Megestrol acetate (MA) has a longstanding history in the treatment of breast cancer, but recently it is being used less often due to the advent of newer agents. PATIENTS AND METHODS: This two-stage phase II trial evaluated the antitumor activity and toxicity of MA in postmenopausal women with hormone-sensitive advanced breast cancer who had experienced disease progression on a third-generation nonsteroidal aromatase inhibitor (NSAI). Eligible patients had metastatic breast cancer treated with a NSAI with at least 6-month progression-free survival (PFS), or relapse after ≥1 year on adjuvant NSAI. Patients received MA at a single daily oral dose of 160 mg. Primary end point was clinical benefit rate (CBR). RESULTS: Forty-eight patients were enrolled. The CBR was 40% [95% confidence interval (CI) 25% to 55%], and the median duration of clinical benefit was 10.0 (95% CI 8.0-14.2) months. The median PFS was 3.9 (95% CI 3.0-4.8) months. The most common grade 3 adverse events were anemia (2%), dyspnea (2%), fatigue (2%), musculoskeletal pain (4%), deep vein thrombosis (10%), and weight gain (2%). CONCLUSIONS: This is the first study to prospectively evaluate the efficacy and safety of MA in postmenopausal women with hormone-sensitive disease progressing on a NSAI. MA has demonstrated activity and acceptable tolerability in this setting, and therefore remains a reasonable treatment option in a cost-sensitive environment. These results also provide the background for further evaluation of progestins in the treatment of breast cancer. CLINICAL TRIALS: local trial number, related to the approval by the IRB: CEP 108/06.

Endogenous preoptic hydrogen sulphide attenuates hypoxia-induced hyperventilation.

AIM: We hypothesized that hydrogen sulphide (H2 S), acting specifically in the anteroventral preoptic region (AVPO - an important integrating site of thermal and cardiorespiratory responses to hypoxia in which H2 S synthesis has been shown to be increased under hypoxic conditions), modulates the hypoxic ventilatory response. METHODS: To test this hypothesis, we measured pulmonary ventilation (V˙E) and deep body temperature of rats before and after intracerebroventricular (icv) or intra-AVPO microinjection of aminooxyacetate (AOA; CBS inhibitor) or Na2 S (H2 S donor) followed by 60 min of hypoxia exposure (7% O2 ). Furthermore, we assessed the AVPO levels of H2 S of rats exposed to hypoxia. Control rats were kept under normoxia. RESULTS: Microinjection of vehicle, AOA or Na2 S did not change V˙E under normoxic conditions. Hypoxia caused an increase in ventilation, which was potentiated by microinjection of AOA because of a further augmented tidal volume. Conversely, treatment with Na2 S significantly attenuated this response. The in vivo H2 S data indicated that during hypoxia the lower the deep body temperature the smaller the degree of hyperventilation. Under hypoxia, H2 S production was found to be increased in the AVPO, indicating that its production is responsive to hypoxia. The CBS inhibitor attenuated the hypoxia-induced increase in the H2 S synthesis, suggesting an endogenous synthesis of the gas. CONCLUSION: These data provide solid evidence that AVPO H2 S production is stimulated by hypoxia, and this gaseous messenger exerts an inhibitory modulation of the hypoxic ventilatory response. It is probable that the H2 S modulation of hypoxia-induced hyperventilation is at least in part in proportion to metabolism.

Interaction between the carbon monoxide and nitric oxide pathways in the locus coeruleus during fever.

We have documented that the locus coeruleus (LC), the main noradrenergic nucleus in the brain, is part of a thermoeffector neuronal pathway in fever induced by lipopolysaccharide (LPS). Following this pioneering study, we have investigated the role of the LC carbon monoxide (CO) and nitric oxide (NO) pathways in fever. Interestingly, despite both CO and NO are capable of activating the same intracellular target, soluble guanylate cyclase (sGC), our data have shown that LC CO is an antipyretic molecule, whereas LC NO is propyretic. Thus, aiming at further exploring the mechanisms underlying their anti- and propyretic properties, we investigated the putative interplay between the LC CO and NO pathways. Male Wistar rats were implanted with a guide cannula in the fourth ventricle (4V) and a temperature datalogger capsule in the peritoneal cavity. The animals were microinjected into the 4V with an inhibitor of heme oxygenase (HO) (ZnDPBG [zinc(II)deuteroporphyrin IX 2,4 bis ethylene glycol]), or a CO donor (CORM-2 [tricarbonyldichlororuthenium-(II)-dimer]), or an inhibitor of nitric oxide synthase (NOS) (l-NMMA [N(G)-monomethyl-L-arginine acetate]), or an NO donor (NOC12 [3-ethyl-3-(ethylaminoethyl)-1-hydroxy-2-oxo-1-triazene]), and injected with LPS (100 µg/kg i.p.). Two hours later, the rats were decapitated, and the brains were frozen and cut in a cryostat. LC punches were processed to assess LC bilirubin and nitrite/nitrate (NOx) levels. Microinjection of ZnDPBG reduced LC bilirubin and increased LC NOx, whereas l-NMMA diminished LC NOx and reduced LC bilirubin. Furthermore, NOC12 caused an increase in LC bilirubin, whereas CORM-2 caused a reduction in LC NOx. These findings are consistent with the notion that in the LC during LPS fever the CO pathway downmodulates NOS activity and the NO pathway upmodulates HO activity, and, together with previous data, allow us to conjecture that LC CO blunts fever by downmodulating NOS (antipyretic property), LC NO upmodulates HO and sGC activities favoring the development of LPS fever (propyretic effect).

Opioid µ-receptors in the rostral medullary raphe modulate hypoxia-induced hyperpnea in unanesthetized rats.

AIM: It has been suggested that the medullary raphe (MR) plays a key role in the physiological responses to hypoxia. As opioid µ-receptors have been found in the MR, we studied the putative role of opioid µ-receptors in the rostral MR (rMR) region on ventilation in normal and 7% hypoxic conditions. METHODS: We measured pulmonary ventilation (VE) and the body temperatures (Tb) of male Wistar rats before and after the selective opioid µ-receptor antagonist CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, cyclic, 0.1 µg per 0.1 µL) was microinjected into the rMR during normoxia or after 60 min of hypoxia. RESULTS: The animals treated with intra-rMR CTAP exhibited an attenuation of the ventilatory response to hypoxia (430 ± 86 mL kg(-1) min(-1)) compared with the control group (790 ± 82 mL kg(-1) min(-1) ) (P < 0.05). No differences in the Tb were observed between groups during hypoxia. CONCLUSION: These data suggest that opioids acting on µ-receptors in the rMR exert an excitatory modulation of hyperventilation induced by hypoxia.

Hydrogen sulfide as a cryogenic mediator of hypoxia-induced anapyrexia.

Hypoxia causes a regulated decrease in body temperature (Tb), a response that has been aptly called anapyrexia, but the mechanisms involved are not completely understood. The roles played by nitric oxide (NO) and other neurotransmitters have been documented during hypoxia-induced anapyrexia, but no information exists with respect to hydrogen sulfide (H(2)S), a gaseous molecule endogenously produced by cystathionine ß-synthase (CBS). We tested the hypothesis that H(2)S production is enhanced during hypoxia and that the gas acts in the anteroventral preoptic region (AVPO; the most important thermosensitive and thermointegrative region of the CNS) modulating hypoxia-induced anapyrexia. Thus, we assessed CBS and nitric oxide synthase (NOS) activities [by means of H(2)S and nitrite/nitrate (NO(x)) production, respectively] as well as cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) levels in the anteroventral third ventricle region (AV3V; where the AVPO is located) during normoxia and hypoxia. Furthermore, we evaluated the effects of pharmacological modifiers of the H(2)S pathway given i.c.v. or intra-AVPO. I.c.v. or intra-AVPO microinjection of CBS inhibitor caused no change in Tb under normoxia but significantly attenuated hypoxia-induced anapyrexia. During hypoxia there were concurrent increases in H(2)S production, which could be prevented by CBS inhibitor, indicating the endogenous source of the gas. cAMP concentration, but not cGMP and NO(x), correlated with CBS activity. CBS inhibition increased NOS activity, whereas H(2)S donor decreased NO(x) production. In conclusion, hypoxia activates H(2)S endogenous production through the CBS-H(2)S pathway in the AVPO, having a cryogenic effect. Moreover, the present data are consistent with the notion that the two gaseous molecules, H(2)S and NO, play a key role in mediating the drop in Tb caused by hypoxia and that a fine-balanced interplay between NOS-NO and CBS-H(2)S pathways takes place in the AVPO of rats exposed to hypoxia.

Central NO-cGMP pathway in thermoregulation and survival rate during polymicrobial sepsis.

Sepsis induces production of inflammatory mediators such as nitric oxide (NO) and causes physiological alterations, including changes in body temperature (Tb). We evaluated the involvement of the central NO-cGMP pathway in thermoregulation during sepsis induced by cecal ligation and puncture (CLP), and analyzed its effect on survival rate. Male Wistar rats with a Tb probe inserted in their abdomen were intracerebroventricularly injected with 1 microL NG-nitro-L-arginine methyl ester (L-NAME, 250 microg), a nonselective NO synthase (NOS) inhibitor; or aminoguanidine (250 microg), an inducible NOS inhibitor; or 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 0.25 microg), a guanylate cyclase inhibitor. Thirty minutes after injection, sepsis was induced by cecal ligation and puncture (CLP), or the rats were sham operated. The animals were divided into 2 groups for determination of Tb for 24 h and assessment of survival during 3 days. The drop in Tb seen in the CLP group was attenuated by pretreatment with the NOS inhibitors (p < 0.05) and blocked with ODQ. CLP rats pretreated with either of the inhibitors showed higher survival rates than vehicle injected groups (p < 0.05), and were even higher in the ODQ pretreated group. Our results showed that the effect of NOS inhibition on the hypothermic response to CLP is consistent with the role of nitrergic pathways in thermoregulation.

Antinociception synergy between the peripheral and spinal sites of the heme oxygenase-carbon monoxide pathway.

We have shown that the peripheral and spinal cord heme oxygenase (HO)-carbon monoxide (CO)-soluble guanylate cyclase-cGMP pathways play an important role in antinociception in the rat experimental formalin model. Our objective was to determine if there is synergism between peripheral (paw) and spinal HO-CO pathways in nociception. Rats were handled and adapted to the experimental environment for a few days before the formalin test, in which 50 microL of a 1% formalin was injected subcutaneously into the dorsal surface of the right hind paw. The animals were then observed for 1 h and the frequency of flinching behavior was taken to represent the nociceptive response. Thirty minutes before the test, rats were pretreated with intrathecal injections of the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) or heme-lysinate, which is a substrate of the HO pathway. The paw treatments took place 20 min before the test. Low doses of ZnDPBG did not increase nociception, while a low heme-lysinate dose did not change flinching behavior after paw or spinal injections. Combined subactive spinal (50 nmol) and peripheral (40 nmol) low doses of ZnDPBG induced hypernociception (increase of 80% in the first and 25% in the second phase flinching), whereas combined spinal-peripheral heme-lysinate (50 and 30 nmol) led to second phase antinociception (40% reduction in flinching). These findings suggest a synergy between the peripheral and spinal HO-CO pathways. Local activation of the HO system probably regulates the nociception initiation in peripheral tissue and participates in buffering the emerging nociceptive signals at the peripheral and spinal sites of action. In short, an antinociceptive synergy exists between peripheral and spinal HO pathways, which may reduce the doses required and side effects.

Antinociception synergy between the peripheral and spinal sites of the heme oxygenase-carbon monoxide pathway

We have shown that the peripheral and spinal cord heme oxygenase (HO)-carbon monoxide (CO)-soluble guanylate cyclase-cGMP pathways play an important role in antinociception in the rat experimental formalin model. Our objective was to determine if there is synergism between peripheral (paw) and spinal HO-CO pathways in nociception. Rats were handled and adapted to the experimental environment for a few days before the formalin test, in which 50 µL of a 1 percent formalin was injected subcutaneously into the dorsal surface of the right hind paw. The animals were then observed for 1 h and the frequency of flinching behavior was taken to represent the nociceptive response. Thirty minutes before the test, rats were pretreated with intrathecal injections of the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) or heme-lysinate, which is a substrate of the HO pathway. The paw treatments took place 20 min before the test. Low doses of ZnDPBG did not increase nociception, while a low heme-lysinate dose did not change flinching behavior after paw or spinal injections. Combined subactive spinal (50 nmol) and peripheral (40 nmol) low doses of ZnDPBG induced hypernociception (increase of 80 percent in the first and 25 percent in the second phase flinching), whereas combined spinal-peripheral heme-lysinate (50 and 30 nmol) led to second phase antinociception (40 percent reduction in flinching). These findings suggest a synergy between the peripheral and spinal HO-CO pathways. Local activation of the HO system probably regulates the nociception initiation in peripheral tissue and participates in buffering the emerging nociceptive signals at the peripheral and spinal sites of action. In short, an antinociceptive synergy exists between peripheral and spinal HO pathways, which may reduce the doses required and side effects.

5-HT1A, but not 5-HT2 and 5-HT7, receptors in the nucleus raphe magnus modulate hypoxia-induced hyperpnoea.

AIM: In the present study, we assessed the role of 5-hydroxytryptamine (5-HT) receptors (5-HT(1A), 5-HT(2) and 5-HT(7)) in the nucleus raphe magnus (NRM) on the ventilatory and thermoregulatory responses to hypoxia. METHODS: To this end, pulmonary ventilation (V(E)) and body temperature (T(b)) of male Wistar rats were measured in conscious rats, before and after a 0.1 microL microinjection of WAY-100635 (5-HT(1A) receptor antagonist, 3 microg 0.1 microL(-1), 56 mm), ketanserin (5-HT(2) receptor antagonist, 2 microg 0.1 microL(-1), 36 mm) and SB269970 (5-HT(7) receptor antagonist, 4 microg 0.1 microL(-1), 103 mm) into the NRM, followed by 60 min of severe hypoxia exposure (7% O(2)). RESULTS: Intra-NMR microinjection of vehicle (control rats) or 5-HT antagonists did not affect V(E) or T(b) during normoxic conditions. Exposure of rats to 7% O(2) evoked a typical hypoxia-induced anapyrexia after vehicle microinjections, which was not affected by microinjection of WAY-100635, SB269970 or ketanserin. The hypoxia-induced hyperpnoea was not affected by SB269970 and ketanserin intra-NMR. However, the treatment with WAY-100635 intra-NRM attenuated the hypoxia-induced hyperpnoea. CONCLUSION: These data suggest that 5-HT acting on 5-HT(1A) receptors in the NRM increases the hypoxic ventilatory response.

Glutamatergic neurotransmission modulates hypoxia-induced hyperventilation but not anapyrexia

The interaction between pulmonary ventilation (V E) and body temperature (Tb) is essential for O2 delivery to match metabolic rate under varying states of metabolic demand. Hypoxia causes hyperventilation and anapyrexia (a regulated drop in Tb), but the neurotransmitters responsible for this interaction are not well known. Since L-glutamate is released centrally in response to peripheral chemoreceptor stimulation and glutamatergic receptors are spread in the central nervous system we tested the hypothesis that central L-glutamate mediates the ventilatory and thermal responses to hypoxia. We measured V E and Tb in 40 adult male Wistar rats (270 to 300 g) before and after intracerebroventricular injection of kynurenic acid (KYN, an ionotropic glutamatergic receptor antagonist), alpha-methyl-4-carboxyphenylglycine (MCPG, a metabotropic glutamatergic receptor antagonist) or vehicle (saline), followed by a 1-h period of hypoxia (7 percent inspired O2) or normoxia (humidified room air). Under normoxia, KYN (N = 5) or MCPG (N = 8) treatment did not affect V E or Tb compared to saline (N = 6). KYN and MCPG injection caused a decrease in hypoxia-induced hyperventilation (595 ± 49 for KYN, N = 7 and 525 ± 84 ml kg-1 min-1 for MCPG, N = 6; P < 0.05) but did not affect anapyrexia (35.3 ± 0.2 for KYN and 34.7 ± 0.4ºC for MCPG) compared to saline (912 ± 110 ml kg-1 min-1 and 34.8 ± 0.2ºC, N = 8). We conclude that glutamatergic receptors are involved in hypoxic hyperventilation but do not affect anapyrexia, indicating that L-glutamate is not a common mediator of this interaction.

Glutamatergic neurotransmission modulates hypoxia-induced hyperventilation but not anapyrexia.

The interaction between pulmonary ventilation (V E) and body temperature (Tb) is essential for O2 delivery to match metabolic rate under varying states of metabolic demand. Hypoxia causes hyperventilation and anapyrexia (a regulated drop in Tb), but the neurotransmitters responsible for this interaction are not well known. Since L-glutamate is released centrally in response to peripheral chemoreceptor stimulation and glutamatergic receptors are spread in the central nervous system we tested the hypothesis that central L-glutamate mediates the ventilatory and thermal responses to hypoxia. We measured V E and Tb in 40 adult male Wistar rats (270 to 300 g) before and after intracerebroventricular injection of kynurenic acid (KYN, an ionotropic glutamatergic receptor antagonist), alpha-methyl-4-carboxyphenylglycine (MCPG, a metabotropic glutamatergic receptor antagonist) or vehicle (saline), followed by a 1-h period of hypoxia (7% inspired O2) or normoxia (humidified room air). Under normoxia, KYN (N = 5) or MCPG (N = 8) treatment did not affect V E or Tb compared to saline (N = 6). KYN and MCPG injection caused a decrease in hypoxia-induced hyperventilation (595 +/- 49 for KYN, N = 7 and 525 +/- 84 ml kg-1 min-1 for MCPG, N = 6; P < 0.05) but did not affect anapyrexia (35.3 +/- 0.2 for KYN and 34.7 +/- 0.4 masculine C for MCPG) compared to saline (912 +/- 110 ml kg-1 min-1 and 34.8 +/- 0.2 masculine C, N = 8). We conclude that glutamatergic receptors are involved in hypoxic hyperventilation but do not affect anapyrexia, indicating that L-glutamate is not a common mediator of this interaction.

The ventilatory response to environmental hypercarbia in the South American rattlesnake, Crotalus durissus.

To study the effects of environmental hypercarbia on ventilation in snakes, particularly the anomalous hyperpnea that is seen when CO(2) is removed from inspired gas mixtures (post-hypercapnic hyperpnea), gas mixtures of varying concentrations of CO(2) were administered to South American rattlesnakes, Crotalus durissus, breathing through an intact respiratory system or via a tracheal cannula by-passing the upper airways. Exposure to environmental hypercarbia at increasing levels, up to 7% CO(2), produced a progressive decrease in breathing frequency and increase in tidal volume. The net result was that total ventilation increased modestly, up to 5% CO(2) and then declined slightly on 7% CO(2). On return to breathing air there was an immediate but transient increase in breathing frequency and a further increase in tidal volume that produced a marked overshoot in ventilation. The magnitude of this post-hypercapnic hyperpnea was proportional to the level of previously inspired CO(2). Administration of CO(2) to the lungs alone produced effects that were identical to administration to both lungs and upper airways and this effect was removed by vagotomy. Administration of CO(2) to the upper airways alone was without effect. Systemic injection of boluses of CO(2)-rich blood produced an immediate increase in both breathing frequency and tidal volume. These data indicate that the post-hypercapnic hyperpnea resulted from the removal of inhibitory inputs from pulmonary receptors and suggest that while the ventilatory response to environmental hypercarbia in this species is a result of conflicting inputs from different receptor groups, this does not include input from upper airway receptors.

Chemical lesions of the nucleus isthmi increase the hypoxic and hypercarbic drive to breathing of toads.

The nucleus isthmi (NI) is a mesencephalic structure of the amphibian brain that has recently been reported to participate in the hypoxic and hypercarbic drive to breathing. However, previous studies used electrolytic and kainic lesions, which causes diffuse and nonspecific destruction. Thus, in the present study, we assessed the participation of NI in the respiratory response to hypoxia and hypercarbia using lesions produced with ibotenic acid (a substance that selectively destroys cell bodies but spares fibers of passage) into the NI of toads (Bufo paracnemis). Our results demonstrated that, under resting breathing, NI plays no role in pulmonary ventilation. Hypoxia and hypercarbia caused hyperventilation in all groups. Chemical lesions in the NI elicited an increase in ventilatory response to hypoxia and hypercarbia, due to a higher tidal volume. We conclude that NI cell bodies do not participate in the control of pulmonary ventilation under resting conditions, but exert an inhibitory modulation of hypoxic and hypercarbic drive to breathing, acting on tidal volume.