Tryptophan-induced central fatigue in exercising rats is related to serotonin content in preoptic area

To assess the effects of increased hypothalamic tryptophan (TRP) availability on 5-HT content in preoptic area on thermoregulation and work production during exercise on treadmill, 20.3 μM of L-TRP (n = 7) or 0.15 M NaCl (n = 6) was injected into the lateral cerebral ventricle of male Wistar rats immediately before the animals started running (18 m min⁻¹ 5% inclination). Exercise time to fatigue (min), and workload (kgm) were analysed. Core temperature was measured by telemetry. At fatigue, brains were quickly removed and preoptic area (POA), hypothalamus (HP), frontal cortex (FC), hippocampi (HC) were rapidly dissected and frozen immediately in dry ice. Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured by HPLC. TRP-exercised rats showed the highest content of 5-HT in the POA and the lowest in the hippocampi compared to the rested and SAL-exercised rats. An inverse relationship between TF and a direct correlation with body temperature changes and POA-5HT levels were observed. A correlation between HC 5-HT content and TF was also found. However, there was no correlation between HC 5-HT content and changes in Tb at fatigue. Finally, our results bring further evidences that increased 5-HT content in POA is involved with an increase in heat production during exercise. In addition, the direct correlation of 5-HT level in hippocampi and TF of TRP-exercised rats suggests that this brain area is also related to motor activity control during exercise. In conclusion, our data indicated that tryptophan-induced central fatigue in exercising rats is related to serotonin content in preoptic area.     

不同剂量碘化钾对大鼠子代脑发育的影响

目的：观察不同剂量碘化钾对仔鼠神经元特异性烯醇化酶（NSE）表达的影响。方法：断乳后1个月大鼠饮用不同浓度的碘水,饲养3个月后雌雄合笼,取第2代60日龄仔鼠,测量血清甲状腺激素值,以NSE为观察指标,采用光镜观察免疫组织化学染色的标本结合图像分析的方法,研究仔鼠大脑的发育情况。结果：各碘过量组甲状腺激素水平呈下降趋势,100HI组呈明显甲低状态;海马CA3区NSE阳性细胞的NA、Vv和灰度值随碘过量的严重程度而呈下降趋势,在100HI组呈明显的统计学差异。结论：大鼠对碘摄入量的增高有较强的耐受性,在100HI组可以观察到以NSE表达降低为主要特点的脑发育障碍,其发病机理可能与碘过量所致的甲状腺功能低下有关。     

The cardiovascular challenge of exercising in the heat

Exercise in the heat can pose a severe challenge to human cardiovascular control, and thus the provision of oxygen to exercising muscles and vital organs, because of enhanced thermoregulatory demand for skin blood flow coupled with dehydration and hyperthermia. Cardiovascular strain, typified by reductions in cardiac output, skin and locomotor muscle blood flow and systemic and muscle oxygen delivery accompanies marked dehydration and hyperthermia during prolonged and intense exercise characteristic of many summer Olympic events. This review focuses on how the cardiovascular system is regulated when exercising in the heat and how restrictions in locomotor skeletal muscle and/or skin perfusion might limit athletic performance in hot environments.     

Elevated catecholamines in thirty-day-old chicken brain after depletion during development

The effects of prenatal reserpine administration upon uptake of tritiated norepinephrine (H³-NE) by newly hatched chick brain suggests an interference of catecholamine (CA) uptake and/or binding. The relationship between fluorescence from CA and the radioactivity from H³-NE approached unity in the control group where no such relation was seen in the reserpine treated group. Moreover, 30 days after hatching, CA levels in whole brain of chicks hatched from drug-injected eggs were significantly higher than vehicle-injected controls. However, reserpine did cause a slight but significant elevation of total protein in 14-day-old embryo brain. These data support the hypothesis that ontogenetic alteration of systems exhibiting end-product inhibition can be of a long-lasting, perhaps permanent nature. The direction of change in CA 30 days after hatching, opposite to the change induced pharmacologically during development, is additional support for the concept of ?thermostat”? type regulation of enzyme activity being determined by product concentration at critical periods during development.     

Influence of the myopia gene on brain development

Evaluation of the performance of 17-18-year-old high school students on standard intelligence tests confirms previous reports that nearsighted persons consistently achieve scores approximately eight I.O. points higher than non-myopes. Comparison of tests administered to the same students 10 years earlier suggests that the intellectual gain precedes the development of nearsightedness. Since there is convincing evidence from genetic studies that myopia is an inherited condition, probably transmitted as a recessive characteristic, it is concluded that the myopia gene has a stimulant action on the brain in addition to its effect on the eye. The high frequency of myopia in urbanized societies is explained in terms of an evolutionary adjustment, myopes probably having a survival advantage under conditions of industrialization.     

Influence of magnesium on the beta-inhibition of catecholamines in the uterine circular muscle of estrogen-treated rats

The effects of Mg and isoprenaline on the uterine circular muscle of ovariectomized rats which were injected with estradiol for 2--6 days were investigated. The muscle strip exhibited an action potential that was composed of a spike and a plateau, and also exhibited a twitch-like contraction due to electrical stimulation. The duration of the action potential became longer when the treatment with estrogen was applied until the maximal effect was built up in 4--5 days. Both the duration of the action potential and the amplitude of contraction were reduced when isoprenaline was applied. When Mg (0.5 mM) was added to the bathing solution these beta-effects were progressively potentiated and the maximal effect was obtained in about 1 hr. An increase in membrane conductance was induced by the application of isoprenaline in a control Locke solution and it was further accelerated by exposure to Mg-containing solution. The possibility that the beta-action is potentiated by Mg ions which penetrated into the membrane is concluded.     

Influence of pinealectomy on the amygdala kindling development in rats

A considerable number of studies have demonstrated the anticonvulsant effect of melatonin. The present study examines the influence of pinealectomy on the amygdala kindling development in rats. Animals were divided into three groups: Pinealectomized rats (PNT) Sham rats (SHAM) and Control rats (CTL). The mean number of stimulations and the afterdischarge (AD) duration for each stage of kindling were similar among CTL and SHAM animals. Conversely, PNT animals showed particular characteristics during kindling development. They did not present stage 1 and spent a shorter time in stage 2 in relation to the CTL and SHAM animals. Consequently, the number of stimulations required to reach stage 5 was lower for the PNT group when compared to the CTL and SHAM groups. Besides, a longer AD duration during stage 5 in the PNT group was also observed. The present findings indicate that the pineal gland removal exert a significant influence on amygdala kindling development suggesting that melatonin holds potential interest in experimental therapy for epilepsy.     

Voluntary drinking and hydration in non-acclimatized girls exercising in the heat

The intent of this study was to assess the influence of drink flavor and composition on voluntary drinking and hydration status in girls exercising intermittently in the heat (35 ± 1°C, 45–50% relative humidity). Twelve physically active, nonacclimatized girls (9–12 years) performed three 3 h identical sessions, each consisting of four 20 min cycling bouts at 50% separated by 25 min of rest. One of the three beverages (chilled to 8–10°C) was assigned to each session: unflavored water (W), grape-flavored water (FW) and grape-flavored water plus 6% carbohydrate and 18 mmol l⁻¹ NaCl (CNa). Drinking was ad libitum. Body weight (BW), drink intake (DI), heart rate, rectal and skin temperatures, and perceptions of thirst and stomach fullness were monitored periodically. Total DI was 759, 940, 1,045 g in W, FW and CNa, respectively (P < 0.05 for CNa–W and FW–W). BW changes were −0.15, 0.16, and 0.45% in W, FW and CNa, respectively, but only the difference between CNa and W was significant (P < 0.05). Other physiological and perceptual variables were not different between trials. In conclusion, beverage flavoring regardless if its combination with carbohydrate and NaCl, mildly enhanced voluntary drinking in young non-acclimatized girls. In contrast to previous research in young boys, euhydration was maintained in the girls by an adequate intake of unflavored water.     

Effects on brain cholecystokinin-8-sulfate and serotonin in adult rats after neonatal reduction of catecholamines

Depletion of dopamine (DA) in neonatal rats by cerebroventricular infusion of 6-hydroxydopamine with desmethylimipramine resulted in a significant decrease in mesolimbic immunoreactive cholecystokinin-8-sulfate (CCK-8SI) and a marked increase in striatal serotonin in 10-week-old rats. In contrast, neonatal norepinephrine (NE) depletion did not affect either CCK-8SI or serotonin in the frontal cortex, anterior cingulate cortex or hippocampus. Neonatal DA and NE depletion did not induce an increase in striatal serotonin.     

Effects of catecholamines on water intake in rats

It is known that intraperitoneally (IP) injected adrenaline (A) inhibits food intake in otherwise hungry animals. In a recent work, Hinton et al. (6) showed that IP A also inhibits water intake in thirsty rats, concluding that A's effect is unspecific. We administered A IP or intramuscularly (IM) in different doses in rats made thirsty either by 18-h water deprivation or by subcutaneous injection of hypertonic saline or polyethylene glycol. IP A reduced water intake in all experimental conditions. A dose-related inhibition was observed in water-deprived animals. On the other hand, IM A showed a small effect only at the highest dose (50 micrograms/100 g body weight). When some of these experiments were repeated using noradrenaline (NA) and isoproterenol (IS), IM administration of either substance showed no effect. IP administration reduced water intake significantly only at the highest dose of NA (50 micrograms/100 g). It is concluded that water intake inhibition by catecholamines in rats made thirsty either by osmotic or by volumetric challenges is of porto-hepatic origin and, in contrast with food intake inhibition, has no beta-adrenergic component.     

Effects of infusion of corticotropin-releasing factor antagonist into the locus coeruleus on freezing behavior and brain catecholamines in rats

Administration of 0.2 microg of alpha-helical CRF(9-41) (corticotropin-releasing factor receptor antagonist, ahCRF(9-41)) into the locus coeruleus (LC) region significantly reduced footshock-induced freezing behavior in adult male rats. Changes in the concentrations of noradrenaline (NA), dopamine and their catabolites in cortex, hippocampus and hypothalamus of footshocked rats were reminiscent of those observed in stressed animals. Rats injected with ahCRF prior to footshock displayed cerebral catecholamine responses that were not different from controls injected with vehicle. The results confirm earlier findings that CRF receptors at the LC region may mediate freezing and behavioral expression of fear. However, the results also suggest that though CRF receptors within the LC region mediate footshock-induced behavior, they are not necessarily involved in the short-term catecholamine response to footshock.     

The influence of glucagon on hepatic glycogen mobilization in exercising rats

Summary The significance of glucagon for the alterations in carbohydrate and fat metabolism during swimming has been evaluated. Fed, male rats were used. Blood was drawn by cardiac puncture for glucose analysis and either rabbit-antiglucagonserum (A-rats) or normal rabbitserum (N-rats) injected. Twentynine rats were then forced to swim (S-rats) with a tail weight for 60 min, while 16 rats were resting controls (C-rats). Subsequently blood was drawn and samples of liver and muscle tissue collected. In SN-rats glucagon concentrations increased from 152±18 (S.E.) pg/ml (CN-rats) to 332±61 (P<0.05), while liver glycogen decreased (P<0.001) and blood glucose increased (P<0.05). In SA-rats, however, the changes in liver glycogen and blood glucose were halved indicating that increased glucagon secretion enhances hepatic glycogen depletion during prolonged exercise. NEFA rose in SA-rats (P<0.005) as well as in SN-rats (P<0.05). Glycerol concentrations, however, only increased in SA-rats (P<0.05) indicating a shift towards lipid combustion in antibody treated rats. Muscle glycogen and plasma insulin diminished and blood lactate increased uniformly in exercised rats.     

Adrenal hormones and brain catecholamines responses to morning and afternoon immobilization stress in rats

The response of adrenal hormones and brain catecholamines to immobilization stress, applied in the morning or in the afternoon, was studied in rats. Immobilization induced greater increments in plasma corticosterone in the morning than in the afternoon; i.e. when the basal levels of this hormone were low rather than high. There was no significant difference between the plasma and adrenal corticosterone levels of the morning and those of the afternoon-stressed rats. Decreases in brain norepinephrine were observed in both groups (a.m. and p.m.) of immobilized rats, but no variations in dopamine concentration were detected. Immobilization led to a decline in the adrenal epinephrine level in the morning but no significant variation was observed in the afternoon-stressed rats.     

Effect of substance P on the content of catecholamines and on the enzymes of their synthesis in the brain of chronically alcoholized rats

The effect of a single administration of the endogenous peptide substance P on the content of dopamine (DA), and norepinephrine (NE), and on the activity of tyrosine hydroxylase (TH) and dopamine β-hydroxylase (D-β-H) is studied in the hypothalamus and midbrain of rats after a 6-month alcoholization. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 7, pp. 46–48, July, 1994     

Effects of oral N-acetylcysteine on fatigue, critical power, and W' in exercising humans

The accumulation of reactive oxygen species (ROS) is associated with muscular fatigue. The antioxidant N-acetylcysteine (NAC) can extend time to fatigue (TTF), but the effect appears to be exercise intensity dependent. The purpose of this study was to determine the effects of an acute oral dose of NAC on time to fatigue (TTF), critical power (CP), W' (curvature constant), V(O2) kinetics and muscle EMG during cycling exercise. Male (n=7) subjects performed four tests at power outputs corresponding to 80, 90, 100, and 110% of the peak power output achieved during the incremental test (Pmax) under NAC and placebo (PLA) conditions. TTF was increased only in the 80% Pmax trial (p=0.033). CP was higher with NAC (NAC: 232±28 W versus PLA: 226±31 W; p=0.032), but W' tended to decrease (NAC: 15.5±3.8 kJ versus W': 16.4±4.5 kJ; p=0.10). The change in W' was negatively related to the change in CP (r = -0.96). MdPF and RMS of EMG tended to change less with NAC. There were no significant differences in V(O2) kinetics. These results demonstrate that oral NAC was successful in extending time to fatigue at 80% Pmax but not at higher work rates.     

Influence of unilateral ovariectomy on follicular development in cycling rats

Ovarian follicular development was analyzed in intact and unilaterally ovariectomized cyclic rats. Holtzman rats, followed for three successive cycles, were classified as 4- or 5-day animals, with estrus designated as day 1. Intact 4- and 5-day animals were killed on each day of the estrous cycle and one ovary from each animal was saved for histology and examined for normal follicles larger than 352 μ. Cycling rats were unilaterally ovariectomized on day 1 and killed on each of the remaining days of the immediate estrous cycle and day 1 of the next cycle. The follicular population (normal follicles larger than 352 μ) was studied in the remaining ovary. During the estrous cycle of intact rats, there was a gradual increase in the number of follicles with a diameter of 518 to 571 μ and greater; however, the total number of follicles ranging in size from 352 to 571 μ and larger remained relatively constant. At day 5, in the 5-day cycling rat, the ovaries were depleted of follicles measuring from 395 to 570 μ. Following unilateral ovariectomy on day 1, there was a temporary decrease in the number of follicles larger than 448 μ. This agreed with the finding that animals semi-spayed on day 1 and injected with 20 I.U. human chorionic gonadotropin on day 2 (PM) did not ovulate, whereas intact animals ovulated an average of seven eggs after the same treatment. The remaining ovary of animals unilaterally ovariectomized on day 1 showed a significant increase by the next estrus in the number of follicles larger than 448 μ. The method of compensatory ovulation in the rat involved doubling the number of large follicles which ultimately matured during the estrous cycle. This resulted from increased proliferation of smaller follicles in the course of the cycle rather than from decreased follicular atresia.     

Effect of catecholamines on the activity of rat brain dipeptidyl aminopeptidase

The inhibitory effect of catecholamines, their metabolic intermediates and derivatives on the activity of rat brain dipeptidyl aminopeptidase was studied. The enzyme was extracted from a crude mitochondrial fraction containing lysosomes (and also synaptosomes) and purified by three-step column chromatography. The activity of the purified enzyme was inhibited by a low concentration (IC50 2 approximately 5 mM) of dopamine, norepinephrine and epinephrine. Dihydroxyphenylalanine or dihydroxyphenylacetic acid, each having a carboxyl group, showed only a weak inhibitory effect (IC50 greater than 10 mM). These results suggest the possibility that brain dipeptidyl aminopeptidase activity may be regulated by the changing of the concentration of catecholamines in the central nervous system.