Evidence that brain nitric oxide inhibition increases metabolic cost of exercise, reducing running performance in rats

To assess the role of nitric oxide (NO) in the metabolic rate and running performance of rats submitted to exercise on a treadmill, 1.43 micromol (2 microL) of Nomega-nitro-L-arginine methyl ester (L-NAME, n=6), a NO synthase inhibitor, or 2 microL of 0.15M NaCl (SAL, n=6) was injected into the lateral cerebral ventricle of male Wistar rats immediately before the animals started running (18m min(-1), 5% inclination). Oxygen consumption (VO2) was measured at rest, during the exercise until fatigue and thereafter during the 30 min of recovery using the indirect calorimetry system. Mechanical efficiency (ME) was also calculated during the running period. During the first 11 min of exercise, there was a similar increase in VO2 while ME remained the same in both groups. Thereafter, VO2 remained stable in the SAL group but continued to increase and remained higher in the L-NAME group until fatigue. The L-NAME-treated rats also showed a sharper decrease in ME than controls. In addition, there was a significant reduction in workload performance by L-NAME-treated animals compared to SAL-treated animals. This suggests that central blockage of nitric oxide increases metabolic cost during exercise, reduces mechanical efficiency and decreases running performance in rats.     

Central nitric oxide inhibition modifies metabolic adjustments induced by exercise in rats

The influence of the central nervous system on metabolic function is of interest in situations deviating from basal states, such as during exercise. Our previous study in rats demonstrated that central nitric oxide (NO) blockade increases metabolic rate, reducing mechanical efficiency during exercise. To assess the role of brain nitric oxide in the plasma glucose, lactate and free fatty acids (FFAs) concentrations of rats submitted to an incremental exercise protocol on a treadmill until fatigue, 1.43 micromol (2 microl) of N(omega)-nitro-l-arginine methyl ester (L-NAME, n=6), a NO synthase inhibitor, or 2 microl of 0.15M NaCl (SAL, n=6) was injected into the lateral cerebral ventricle (icv) of male Wistar rats immediately before exercise (starting at 10 m/min, with increments of 1m/min every 3 min until fatigue, 10% inclination). Blood samples were collected through a chronic jugular catheter at rest and during exercise until fatigue. During exercise, the L-NAME-treated animals had the following metabolic response compared to controls: (1) an increased hyperglycemic response during the first 60% of time to fatigue; (2) higher plasma lactate levels; and (3) a significant transitory increase in plasma free fatty acids during the dynamic phase of exercise that returned to basal levels earlier than controls during the steady state phase of exercise. In addition L-NAME-treated rats fatigued earlier than controls. The data indicate that the inhibition of the brain nitrergic system induced by icv L-NAME treatment disrupted the accuracy of the neural mechanism that regulates plasma glucose and free fatty acids mobilization during exercise in rats.     

Alteration in hypothalamic monoamine metabolism of freely moving diabetic rat.

Changes in hypothalamic monoamine metabolism were investigated in freely moving streptozotocin (STZ)-induced diabetic rats by using in vivo microdialysis technique. Six weeks later, the animals were implanted with microdialysis probe (molecular weight cut-off index: 12,000-14,000) into the ventromedial portion of the hypothalamus (VMH). The dialysate was collected and loaded onto HPLC to be assayed for norepinephrine (NE), dopamine (DA), serotonin (5-HT) and their metabolites (MHPG, DOPAC and 5-HIAA). The concentration of NE was decreased in the dialysate from the VMH of diabetic rats, whereas there was no significant change in MHPG level. The concentrations of 5-HT and 5-HIAA were reduced in diabetic rats. The DA concentration was obviously increased accompanied by the reduction of DOPAC level. The observed changes in hypothalamic monoamine metabolism, especially the reduced NE release, may play an important role in the induction of hyperphagia in freely moving STZ-induced diabetic rats.     

Role of the ventromedial nucleus of hypothalamus in the male-induced enhancement of lordosis in female rats.

The involvement of the ventromedial nucleus of the hypothalamus (VMH) in the mating-induced enhancement of lordosis in ovariectomized estrogen-primed rats was investigated. In the first experiment, females with bilateral VMH or sham lesions were primed with 2 micrograms estradiol benzoate, and 48 h later they were subjected to repeated-mating tests. The VMH-lesioned rats failed to exhibit lordosis during the tests; however, the sham-operated females exhibited a gradual increase in lordosis quotient (LQ) with repetitive matings. In the second experiment, ovariectomized females were bilaterally implanted with estradiol (E2) or cholesterol (C) in the VMH, 48 h prior to behavioral testing. Repeated-mating-induced elevation in LQ was observed in the females when they were bilaterally implanted with E2 in the VMH; C was ineffective. To exclude the possibility of the spread of E2 to areas adjacent to VMH, plasma-luteinizing hormone (LH) was measured. Elevation in the circulating LH levels following ovariectomy was not suppressed in the females following bilateral E2 implants in the VMH, suggesting that the effect of estrogen is localized within or immediately around the VMH. The results suggest that the integrity of the VMH is critical for the potentiation of lordosis behavior in ovariectomized estrogen-primed females by male-originating sensory cues, and that selective priming of the VMH with estrogen is sufficient for the male-induced enhancement of lordosis.     

Effect of pedalling rates on physiological response during endurance cycling

This study was undertaken to examine the effect of different pedalling cadences upon various physiological responses during endurance cycling exercise. Eight well-trained triathletes cycled three times for 30 min each at an intensity corresponding to 80% of their maximal aerobic power output. The first test was performed at a freely chosen cadence (FCC); two others at FCC - 20% and FCC + 20%, which corresponded approximately to the range of cadences habitually used by road racing cyclists. The mean (SD) FCC, FCC - 20% and FCC + 20% were equal to 86 (4), 69 (3) and 103 (5) rpm respectively. Heart rate (HR), oxygen uptake (VO2), minute ventilation (VE) and respiratory exchange ratio (R) were analysed during three periods: between the 4th and 5th, 14th and 15th, and 29th and 30th min. A significant effect of time (P < 0.01) was found at the three cadences for HR, VO2. The VE and R were significantly (P < 0.05) greater at FCC + 20% compared to FCC - 20% at the 5th and 15th min but not at the 30th min. Nevertheless, no significant effect of cadence was observed in HR and VO2. These results suggest that, during high intensity exercise such as that encountered during a time-trial race, well-trained triathletes can easily adapt to the changes in cadence allowed by the classical gear ratios used in practice.     

Rhythmical slow wave electroencephalographic activity elicited by hippocampal injection of muscarinic agents in the rat

In freely moving male Wistar rats the hippocampal EEG was recorded by using chemitrodes (combinations of guide cannulas with bipolar recording electrodes) chronically implanted into the dorsal hippocampus (CA1).The muscarinic agents oxotremorine and arecoline applied intrahippocampally caused a long-lasting increase in the amount of rhythmical slow wave activity (RSA) of the hippocampal EEG accompanied by a decrease of the dominating frequency. At the same time, the well-known relationship between defined behavioral states and EEG patterns was abolished. The effect of oxotremorine could be blocked by subsequent application of the muscarinic antagonist scopolamine.The results support the hypothesis that a non-rhythmic activation of hippocampal muscarinic receptors may result in the generation of RSA within the hippocampal formation.     

运动后过量氧耗与血乳酸血糖及丙氨酸代谢的关系

目的 探讨最大运动负荷后的运动后过量氧耗与血乳酸、血糖及氨基酸代谢的变化关系。方法 １０名男子健康大学生,通过活动跑台Ｂｒｕｃｅ的方法进行渐增负荷跑,至力竭为止。并测定气体代谢和血液中血乳酸、血糖及丙氨酸各指标。结果：运动结束３０分钟恢复后,ＶＯ２恢复到安静时水平,但血Ｌａ浓度仍然比安静时水平高,丙氨酸在运动中上升,运动结束３０分钟恢复后减少,但并未恢复到安静时的水平。结论 运动后过量氧耗与用于Ｌ     

Role of Cholinergic Structures in Individual Resistance of Rat Circulatory System to Posthemorrhagic Hypoxia

Experiments employing ultrasound technique showed that nonselective blockade of central muscarinic cholinoceptors with amizyl significantly increases the number and lifespan of rats highly resistant to acute massive blood loss. This pretreatment increased individual resistance of the circulatory system to posthemorrhagic hypoxia (blood pressure and portal blood flow rate). Preliminary blockade of central nicotinic cholinoceptors and peripheral muscarinic cholinoceptors with cyclodol and methacin, respectively, had no effect on the percentage of rats highly and low resistant to acute blood loss. Preliminary blockade of peripheral muscarinic cholinoceptors with methacin prevented the decrease in the cardiac output in low resistant animals during the posthemorrhagic period. __________ Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 140, No. 8, pp. 142–145, August, 2005     

Independence of exercise-induced diaphragmatic fatigue from ventilatory demands

Exercise-induced diaphragmatic fatigue (DF) manifests after - rather than during - exercise. This suggests that DF reflects post-exercise diaphragm-shielding. This study tested the physiological hypothesis that diaphragmatic force-generation undergoes similar regulations during either whole-body-exercise or controlled hyperventilation, but differs during recovery. Ten trained subjects (VO2(max) 60.3+/-6.4 ml/kg/min) performed: I, cycling exercise (maximal workload: 85% VO2(max)); II, controlled hyperventilation (exercise breathing pattern) followed by recovery. Ergospirometric data and twitch transdiaphragmatic pressure (TwPdi) were consecutively assessed. DF occurred following exercise, while hyperventilation enhanced diaphragmatic force-generation (TwPdi-rest 2.28+/-0.58 vs. 2.52+/-0.54, TwPdi-end-recovery: 1.94+/-0.32 kPa vs. 2.81+/-0.49 kPa, both p<0.05). TwPdi was comparable between the two protocols until recovery (p>0.05, RM-ANOVA) whereby it underwent a progressive increase. In conclusion, TwPdi progressively increases and is subject to similar regulations during exercise versus controlled hyperventilation, but differs markedly during recovery. Here, DF occurred after exercise while TwPdi increased subsequent to hyperventilation. Therefore, ventilatory demands regulate diaphragmatic force-generation during exercise, whereas DF must be attributed to non-ventilatory controlled feedback mechanisms.     

Involvement of muscarinic cholinergic and alpha2-adrenergic mechanisms in growth hormone secretion during exercise in humans

The purpose of this study was to examine the role of muscarinic cholinergic and alpha2-adrenergic mechanisms in growth hormone (GH) secretion during exercise in humans. The GH responses induced during moderate-intensity exercise (using a cycle ergometer at 60% maximal oxygen uptake, VO2max, for 30 min) without treatment (control) and after the administration of a muscarinic cholinergic antagonist (atropine 1 mg) or after an alpha2-adrenergic antagonist (yohimbine 15 mg) were compared in seven healthy men. Although, serum GH concentration had increased significantly after exercise in the control experiment [mean peak GH concentration 52.64 (SEM 18.60) ng x ml(-1)], the increase was suppressed by the administration of either atropine [mean peak GH concentration 8.64 (SEM 7.47) ng x ml(-1)] or yohimbine [mean peak GH concentration 17.50 (SEM 7.89) ng x ml(-1)]. The area under the curve of serum GH concentration against time was significantly lower in the experiment using these drugs [with atropine, mean area 458 (SEM 409) ng x ml(-1) min], with yohimbine mean area 946 (SEM 435) ng x ml(-1) min] than in the control experiment [mean area 3135 (SEM 1098) ng x ml(-1) x min]. These results suggest that muscarinic cholinergic and alpha2-adrenergic mechanisms are involved in GH secretion during exercise in humans.     

Role of hippocampal M2 muscarinic receptors in the estrogen-induced enhancement of working memory

We have previously demonstrated that acetylcholine, acting at M2 muscarinic receptors, mediates the estradiol-induced increase in hippocampal N-methyl-d-aspartate receptor binding and the associated enhancement in working memory. The goal of present experiment was to investigate the role of hippocampal M2 receptors in the behavioral aspects of these effects. Ovariectomized rats were trained to locate a hidden escape platform on a matching-to-place version of the water maze in which the platform was moved to a new location for each session of four daily trials. Following 18 days of training, rats were randomly assigned to receive one of the following treatments: 1) injections of oil vehicle delivered 72 and 48 h before testing and continuous delivery of vehicle into the dorsal hippocampus via bilateral cannulae implants connected to osmotic minipumps; 2) injections of estradiol benzoate (EB) delivered 72 and 48 h before testing and continuous delivery of vehicle into the hippocampus; 3) injections of EB delivered 72 and 48 h before testing and continuous delivery of the M2 muscarinic receptor antagonist, AFDX 116, into the hippocampus; and 4) injections of EB delivered 72 and 48 h before testing and continuous delivery of AFDX 116 into a control site in the cortex. Chronic administration of AFDX 116 into the hippocampus, but not the cortex, significantly attenuated an estrogen-induced enhancement in performance on a working memory task in the water maze as indicated by increased latency and increased path length to locate an escape platform during a test trial when a 90 min delay was imposed between the first and second trials. These results indicate that acetylcholine acts at M2 muscarinic receptors located in the hippocampus to mediate the positive effects exerted by estrogen on working memory.     

Neuronal activation in the CNS during different forms of acute renal failure in rats

The effect of experimentally induced acute renal failure (ARF) on neuronal cell activation was investigated by immunohistochemistry for Fos and Fra-2 in the rat brain. ARF in rats was induced by bilateral nephrectomy (BNX), bilateral ureter ligature (BUL) and uranyl acetate injection with proper controls (sham-operation or saline injections, respectively). To follow the effect of the development of ARF, rats were killed 30 and 60 min, and 3, 12, 24 and 72 h after surgery, or 3 h to 12 days after uranyl acetate injections. In the BUL and BNX rats, urea and creatinine rose markedly in the plasma within 72 h, while in the uranyl acetate—injected rats the highest levels were observed on the 7th day, followed by a marked decline.     

Comparison of objective methods for determining ventilatory threshold

This study was undertaken to compare and re-examine the relation of lactate threshold (LT) and ventilatory threshold (VT), using six objective determination methods proposed previously. Twenty-one young male subjects performed a cycle exercise test in which the work rate was increased by 150 kg.m every 2 min up to his limit of volitional fatigue. Through each test, gas exchange parameter measurements were made every 1 min (every 30 s at nearly maximal level), and the venous blood samples were taken from a warmed ear lobe at each work rate for determining blood lactate concentration. LT and its variance were determined by the intersecting straight lines regression. LT ranged from 0.72 to 1.40 l/min in terms of VO2, and the mean value of S.D. for each LT was about 0.1 l/min. Each objective method for determining VT used in this study was based on the simple modelling of the criterion for visual detection of VT, that is the non-linear increase in VE or the systematic increase in VE/VO2. When the relationship between LT and VT was examined, VT by the objective methods based on determining minimum value of VE/VO2 showed relatively high consistency with LT. Of 16-20 individuals out of all 21 subjects, there were VT within LT +/- 0.2 in VO2. It is concluded that VE/VO2 is a more sensitive index for detecting VT than VE in the gas exchange parameters, and the objective VT determination method based on minimum value of VE/VO2 could facilitate estimation of LT within an error of +/- 0.2 l/min VO2 in most normal individuals.     

Patterns of weaning and adult response to stress

We have previously shown that excitation of certain neurons in the ventromedial nucleus of the hypothalamus (VMH) of rats induces hyperrunning activity. The present study investigated the involvement of these VMH neurons in inducing excessive running under the activity-stress paradigm. The VMH of 6-week-old male rats was bilaterally lesioned by administration of kainic acid. Control animals received saline in the VMH. They were housed in running-wheel activity cages with free access to food for 6 days of the recovering period, and then fed 1 h each day for 6 days. Control animals exhibited marked increases in both running activity and its light/dark ratio, and developed stomach ulcers. In contrast, animals with bilateral VMH lesions showed a significantly attenuated increase in running activity and no change in light/dark ratio. VMH lesions also suppressed stomach ulceration. These results suggest that VMH neurons play a crucial role in inducing excessive running and stomach ulceration during exposure to the activity-stress paradigm.     

Infant rats: VMH damage and the ontogeny of obesity and neuroendocrine dysfunction

The VMH was bilaterally destroyed in preweanling (Day 10) or postweanling (Day 40) male and female rats. Growth parameters (body weight, body length, Lee indices) were measured until 200 days of age, nutrient intake was measured during maturity, and an analysis of endocrine gland weights and adenohypophyseal morphology was performed on preweanling rats. When compared with controls, growth was abnormal for VMH rats after 50–80 days of age. Bilateral preweanling females displayed elevated body weights, normal body lengths, and elevated Lee indices, while bilateral preweanling males had normal body weights, stunted linear growth, and elevated Lee indices. Postweanling VMH rats exhibited elevated body weights and elevated Lee indices; however, postweanling VMH males displayed augmented linear growth. VMH rats were normophagic and demonstrated finickiness to taste-aversive fluids. Endocrine gland analysis revealed that preweanling VMH males had neuroendocrine deficits related to somatotrophic hormone (low pituitary weight, decreased adenohypophyseal acidophils), while female VMH rats had neuroendocrine pathology related to metabolic dysfunction (all gland weights were low, decreased adenohypophyseal basophil size).     

Lesions in ventromedial hypothalamus or amygdala do not affect naloxone's suppression of water consumption

Rats received lesions in the ventromedial hypothalamus (VMH) or amygdala, or were sham operated, and then were tested for two-hour intake of water after injections of naloxone (2 mg/kg), MIF-1 (2, 4, or 8 mg/kg), or diluent. There was a significant effect of test compound, with naloxone reducing consumption relative to the diluent control and the largest dose of MIF-1. Although MIF-1 tended to suppress drinking, the effect did not reach significance. There was no main effect for lesions, indicating that the amygdala and the VMH do not play a critical role in the effect of naloxone or MIF-1 on water consumption. A significant lesion by time interaction occurred, however, with amygdala-lesioned rats drinking the most in the first 30 min but much less after that. The VMH rats drank the most in the 30-60 min interval, but there were no differences in groups after 60 min. Thus, it appears that the intact VMH and basolateral amygdala are not necessary for naloxone's suppression of water consumption in the rat.     

Development of VMH obesity in vagotomized rats.

In 3 different experiments, vagotomy failed to reverse or prevent the development of hyperphagia and obesity following VMH lesions. In the first experiment, previously vagotomized male rats were given bilateral VMH lesions after testing for completeness of vagotomy. In a second experiment on male rats, vagotomy preceded or followed VMH lesions, and testing for completeness of vagotomy was not carried out until the end of the experiment. In a third experiment obese VMH female rats were vagotomized before or after VMH lesions, and completeness of vagotomy was assessed histologically. In each experiment, vagotomized VMH rats displayed hyperphagia and became obese. Discrepancies between these results and those reported by others are discussed in terms of diet offered, surgical procedures, and the possibility of continuing malaise after vagotomy.     

Development of amygdaloid cholinergic mediation of passive avoidance learning in the rat

Summary Passive avoidance learning was studied in young rats 13–30 days of age following bilateral injections of saline or antimuscarinic and/or muscarinic agents into three amygdaloid nuclei — lateral (L), basolateral (BL), and cortical (CO). While acquisition was not influenced by saline injections into various other cerebral structures, it was significantly altered by similar injections into these amygdaloid nuclei, especially by those into the BL nucleus, suggesting that this nucleus is particularly involved in passive avoidance learning. Atropine induced significant deficits from as early as 13 days on. These deficits increased and were of similar strength after injections into any of the three studied nuclei until day 16; after that age, they diminished slightly following CO and L nuclei administration, while remaining substantial after BL nucleus injections at all ages, even at 30 days. No facilitatory effects could be elicited by arecoline injected alone, while arecoline could antagonize the disturbing effect of atropine, when given in combination, from day 13 on. These results suggest a muscarinic cholinergic mediation of passive avoidance learning through the synaptic elements located in the basal lateral part of the amygdala in the young rat.     

Voltammetry in unanesthetized rat: Increases of striatal dopamine turnover after unilateral haloperidol injection into the substantia nigra

In freely moving rats, effects of unilateral haloperidol injection into the substantia nigra were monitored with in vivo voltammetry in the bilateral striata. The electrochemical responses at 120 mV versus Ag-AgCl, reflecting mainly a level of 3,4-dihydroxyphenylacetic acid (DOPAC), increased both in the striata within 1.5 h after 5 μg of haloperidol treatment. In the experiments of high-performance liquid chromatography with electrochemical detection, the ratio of DOPAC to dopamine in the striata significantly increased at 2.75 h after drug treatment. These data support the idea that unilateral injection of haloperidol into the substantia nigra in freely moving rats increases dopamine turnover in the bilateral striata.     

Contractile properties of the human triceps surae following prolonged exercise and beta-blockade

Sixteen healthy males volunteered to perform both an incremental maximal and prolonged submaximal treadmill test with beta-blockade (2 X 80 mg oral propranolol per day) or matched placebo in a blind crossover design. Prior to and following the prolonged exercise, electrical stimulation of the triceps surae was performed to examine contractile properties. During the maximal test, the heart rate (HR) was reduced at all times by beta-blockade. The time to exhaustion in this test was significantly reduced by beta-blockade (P less than 0.03), while the maximal oxygen uptake (VO2 max) was not significantly lower (P = 0.06). In response to prolonged treadmill walking at 60% of VO2 max, the HR was reduced but VO2, respiratory quotient and ventilation were not affected by beta-blockade relative to placebo. Plasma concentrations of free fatty acids increased during exercise in the placebo but not beta-blocked treatment (P less than 0.0001). Plasma noradrenalin and adrenalin increased with exercise; the increase in adrenalin with beta-blockade was greater than that with placebo (P less than 0.0001). The RPE obtained at intervals during the prolonged exercise were greater for beta-blockades than placebo. Eight of 16 subjects were unable to complete full 90 min with beta-blockade; but all 16 completed the test with placebo. The electrically evoked twitches in the triceps surae muscle group after exercise did not differ in peak torque or one-half relaxation time compared to pre-exercise. The time to peak twitch torque was significantly shorter after exercise. No differences in twitch were observed due to beta-blockade. The tetanic responses at 10, 20, 50 and 100 Hz were not affected by either exercise or the beta-blockade. In conclusion, an increased subjective estimate of fatigue (RPE) was observed during prolonged exercise with beta-blockade. This subjective fatigue did not relate to altered peripheral muscle force production during electrical stimulation. The results suggest either a central rather than peripheral origin of fatigue, or fatigue in a muscle group not examined by stimulation of the triceps surae.