Influence of increased catecholamine levels in blood plasma during cold-adaptation and intramuscular infusion on thresholds of thermoregulatory reactions in guinea-pigs

Summary Catecholamines and some of their metabolites were determined in urine and blood plasma of guinea-pigs before, during and after acclimation to a cold or warm environment. During adaptation to 5°C the amounts of noradrenaline in plasma and 24-h urine samples continuously increased up to 600% compared with values obtained at an ambient temperature of 22°C. Higher levels of dihydroxyphenylglycol and 3-methoxy-4-hydroxyphenylglycol further indicated an increased turnover of noradrenaline during cold adaptation. Acclimation to an ambient temperature of 28°C reduced the peripheral release of noradrenaline in comparison to the release observed at 22°C. Cold-induced increases in metabolic rate and electrical muscle activity both occur at a considerably lower mean body temperature in cold-than in warm-adapted guinea-pigs. The shift of thermoregulatory cold defence reactions to a lower mean body temperature could also be observed in warm-adapted animals after intramuscular infusion of noradrenaline in amounts comparable to those released during cold adaptation.It is concluded that high peripheral sympathetic activity directly or indirectly inhibits noradrenergic neurons in the lower brain stem that modulate the thermoregulatory control system by means of their afferents to the hypothalamus. As a consequence of this peripheral influence the thermoregulatory set point is shifted to a lower mean body temperature.Abbreviations A adrenaline - CA cold adapted - CNS central nervous system - DHPG dihydroxyphenylglycol - EMA electrical muscle activity - HPLC high performance liquid chromatography - 5-HT 5-hydroxytryptamine (serotonine) - MHPG 3-methoxy-4-hydroxypheyylglycol - MR metabolic rate - NA noradrenaline - T _b mean body temperature - WA warm adapted     

Effects of cold adaptation and noradrenaline on thermosensitivity of rat hypothalamic neurons studiedin vitro

The experiments performed on rat brain slices have shown that cold adaptation of an animal influences the thermosensitivity of hypothalamic medial preoptical neurons. The adaptation is followed by an increase in the proportion of 38–41°C-thermoresponsive neurons and by a decrease in the proportion of 35–38°C-thermoresponsive units. In control animals, noradrenaline (NA) increased the responses of hypothalamic neurons to the action of 35–38°C temperature and decreased them to the action of 38–41°C temperature. Cold adaptation prevented the effects of NA on neuronal thermosensitivity, which suggests that their NA sensitivity is modified by cold adaptation.Neirofiziologiya/Neurophysiology, Vol. 26, No. 3, pp. 171–176, May–June, 1994.     

Effect of unilateral surgical denervation of brown adipose tissue on uncoupling protein mRNA level and cytochrom-c-oxidase activity in the Djungarian hamster

The bilateral lobe of interscapular brown adipose tissue of the Djungarian hamster was unilaterally denervated in order to study the role of the sympathetic innervation for maintenance and cold-induced increase of non-shivering thermogenesis. Denervation decreased the noradrenaline content of brown adipose tissue to less than 9% of the intact contralateral pad. This low noradrenaline level was maintained for 1–14 days after denervation. First, to study the role of the sympathetic innervation of brown adipose tissue in the maintenance of the high thermogenic capacity characteristic of the cold acclimated state, brown adipose tissue was denervated in hamsters either kept at thermoneutrality or acclimated to 5°C ambient temperature for 4 weeks. Cold-acclimated hamsters had elevated levels of uncoupling protein messenger ribonucleic acid (8.1-fold) and cytochrom-c oxidase-activity (3-fold). Denervation of brown adipose tissue decreased uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity as compared to the intact pad in thermoneutral and in cold-acclimated hamsters. However, in cold-acclimated hamsters uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity in denervated brown adipose tissue both were maintained on an elevated 6-fold higher levels as compared to thermoneutral controls. Second, to study the role of the sympathetic innervation of brown adipose tissue in the cold-induced increase in thermogenic capacity, hamsters were denervated prior to cold acclimation and responses were measured after 3 and 14 days of cold exposure. Uncoupling protein-messenger ribonucleic acid level and cytochrom-c-oxidase-activity of intact brown adipose tissue increased after 14 days cold acclimation. Denervation did not completely prevent a cold-induced 1.5-fold increase of cytochrom-c-oxidase-activity and a 3.2-fold increase of the uncoupling protein-messenger ribonucleic acid level in denervated brown adipose tissue after 14 days of cold acclimation. In conclusion, high levels of uncoupling protein-messenger ribonucleic acid and cytochrom-c-oxidase activity in brown adipose tissue of cold-acclimated hamsters can partially be maintained without intact sympathetic innervation, suggesting a considerable contribution of trophic factors not requiring sympathetic innervation for maintenance. The cold-induced increase of cytochrom-c-oxidase activity and expression of uncoupling protein-messenger ribonucleic acid largely depends upon sympathetic innervation of brown adipose tissue.Abbreviations ANOVA analysis of variance - BAT brown adipose tissue - COX cytochrom-c-oxidase - HPLC high performance liquid chromatography - mRNA messenger ribonucleie acid - NA noradrenaline - T _a ambient temperature - UCP uncoupling protein     

Sources of heat during nonshivering thermogenesis in Djungarian hamsters: a dominant role of brown adipose tissue during cold adaptation

Summary To assess the thermogenic importance of BAT in Djungarian hamsters we removed about 40% of their BAT and compared their thermogenic abilities before and after the operation. BAT was weighed and assayed for its respiratory properties (Cox, mitochondria). Following removal of BAT we observed considerable reductions of NST. The comparison of NST with BAT weight and with respiratory properties of BAT following partial removal of BAT revealed that at least three different pathways for heat production were involved in NST. In cold-adapted hamsters (values for warm-adapted hamsters in parentheses) we estimated that 66.2% (37.0%) of all NST was produced by mitochondrial respiration in BAT; 16.3% (38.4%) was produced in other organ sites but required the presence of BAT, i.e. there was a mediatory action of BAT on thermogenesis in other organ sites. A further 11.5% (23%) of NST occurred outside of and independent of BAT. Mitochondrial respiration in BAT was the only compartment of NST which increased its contribution during cold adaptation (238 mW to 1,062 mW), whereas the other sources of heat remained largely unchanged.Abbreviations BAT brown adipose tissue - BATex partial removal of brown adipose tissue - BMR basal metabolic rate at thermoneutrality - Cox cytochrome c oxidase - NA noradrenaline - NST nonshivering thermogenesis     

Influence of amygdala catecholamines on ovarian and adrenal medullary secretion.

The amygdaloid complex participates in the modulation of endocrine functions, and contains measurable amounts of noradrenaline (NA) and dopamine (DA). This study examined the contribution of the amygdaloid catecholaminergic systems to the regulation of the adrenal medulla and the ovary. To accomplish this the neurotoxin 6-hydroxydopamine (6-OHDA) was bilaterally injected into the basolateral nucleus of the amygdala (ABL) in cycling rats. The contents of NA and DA in right and left amygdala decreased significantly in lesioned animals with respect to sham lesioned animals, but hypothalamic levels were not different between groups. Administration of 6-OHDA to rats increased the NA, DA and adrenaline (A) contents of the adrenals compared to vehicle treated rats. In addition, lesioned animals showed a significant increase of NA and DA contents in the ovary, although A levels did not differ between groups. Serum oestradiol (O) concentrations were significantly lower in lesioned animals than in controls. These data suggest that the amygdaloid catecholaminergic systems exert an inhibitory effect on catecholamine content of the adrenals and the ovary, and influence the ovarian oestradiol secretion mechanism.     

Interaction of arginine vasopressin and corticotropin releasing factor demonstrated with an improved bioassay

We developed an improved in vivo bioassay for corticotropin releasing factor (CRF) by modifying the injection schedule in the standard chlorpromazine-morphine-pentobarbital assay procedure. A combined injection of chlorpromazine and morphine followed 75 min later by injection of pentobarbital produced low basal levels of corticosterone and rendered the animals highly sensitive to synthetic CRF but insensitive to the stress of ether or histamine. The lowest dose of CRF that significantly elevated plasma corticosterone levels was 0.01 micrograms/kg. Using this assay, we studied CRF-arginine vasopressin (AVP) interactions at doses that were expected to raise systemic peptide concentrations to levels measured in hypophysial portal blood. The threshold for a significant corticosterone response was found to be at least 250-fold lower for CRF-41 than for AVP. The order in which CRF and AVP are injected was also found to be important, potentiation being greater if CRF was given first. In addition, rats deprived of water for 24 hr were more sensitive to CRF than normally hydrated animals.     

Changes in hypothalamic noradrenaline and 5-hydroxytryptamine levels during the development of warm- and cold-adaptation in the rat

Hypothalamic 5-hydroxytryptamine (5-HT) and noradrenaline (NA) as well as plasma corticosterone levels were studied in male rats after 1, 2, 4 and 6 weeks of exposure to 4--7 or 30--31 degrees C. An increase of the NA concentration and a decrease of the 5-HT level was observed after the first week in both cold and warm environment together with an increase of plasma corticosterone levels in both groups. NA, 5-HT and plasma corticosterone levels returned to normal in cold-exposed animals by the 6th week whereas in warm-acclimated rats NA and corticosterone levels regained their initial values and 5-HT concentrations remained low. Changes by the end of the first week of exposure may result from the thermal stress. The low 5-HT levels of warm-adapted animals at the end of the 6th week were probably secondary to the process of adaptation.     

Role of Corticotropin-Releasing Factor (CRF) Receptor-1 on the Catecholaminergic Response to Morphine Withdrawal in the Nucleus Accumbens (NAc)

Stress induces the release of the peptide corticotropin-releasing factor (CRF) into the ventral tegmental area (VTA), and also increases dopamine (DA) levels in brain regions receiving dense VTA input. Since the role of stress in drug addiction is well established, the present study examined the possible involvement of CRF1 receptor in the interaction between morphine withdrawal and catecholaminergic pathways in the reward system. The effects of naloxone-precipitated morphine withdrawal on signs of withdrawal, hypothalamo-pituitary-adrenocortical (HPA) axis activity, dopamine (DA) and noradrenaline (NA) turnover in the nucleus accumbens (NAc) and activation of VTA dopaminergic neurons, were investigated in rats pretreated with vehicle or CP-154,526 (selective CRF1R antagonist). CP-154,526 attenuated the increases in body weight loss and suppressed some of withdrawal signs. Pretreatment with CRF1 receptor antagonist resulted in no significant modification of the increased NA turnover at NAc or plasma corticosterone levels that were seen during morphine withdrawal. However, blockade of CRF1 receptor significantly reduced morphine withdrawal-induced increases in plasma adrenocorticotropin (ACTH) levels, DA turnover and TH phosphorylation at Ser40 in the NAc. In addition, CP-154,526 reduced the number of TH containing neurons expressing c-Fos in the VTA after naloxone-precipitated morphine withdrawal. Altogether, these results support the idea that VTA dopaminergic neurons are activated in response to naloxone-precipitated morphine withdrawal and suggest that CRF1 receptors are involved in the activation of dopaminergic pathways which project to NAc.     

Synaptosomal and brain mitochondrial lipids in hibernating and cold-acclimated golden hamsters

Synaptosomes and mitochondria were isolated from the brains of warm-adapted, hibernating, and cold-acclimated golden hamsters (Mesocricetus auratus). Lipid extracts of these subcellular fractions were prepared and assayed for plasmenylethanolamine (ethanolamine plasmalogen) and cholesterol levels. The ganglioside composition of synaptosomes was also determined. Samples from the hibernating animals showed characteristic changes in lipid composition. These changes include decreases in plasmenylethanolamine levels and a shift in the ganglioside composition toward a higher percentage of the more polar gangliosides. Those animals which were exposed to cold and did not hibernate (cold-acclimated) showed no such changes. Fatty acid analyses of synaptosomal and mitochondrial ethanolamine glycerophospholipids demonstrated a similar trend. Samples from hibernators showed decreases in 16:0, 18:0, and 22:6 (n-3), and increases in 16:1, 18:1, and 20:4 (n-6) fatty acids. No changes were detectable in samples from cold-acclimated animals, indicating that hibernating and cold-acclimated hamsters represent chemically distinct populations.     

Estrogen and androgen influence hypothalamic AVP and CRF concentrations in fetal and adult sheep

The present study tested the hypothesis that action of sex steroids on the hypothalamus-pituitary-adrenal (HPA) axis is measurable in the hypothalamus. Late-gestation fetal sheep were treated (5 mg/21 days) with either estradiol, androstenedione, or tamoxifen and compared to age-matched control fetuses. Tamoxifen significantly increased hypothalamic corticotropin releasing factor (CRF) and arginine vasopressin (AVP) concentrations, and androstenedione significantly decreased hypothalamic CRF concentration. Adult sheep were treated with estrone (10 mg/21 days), and responded with significant increases in hypothalamic AVP concentration, but not in immunoreactive ACTH concentration or processing within the pituitary. The results demonstrate that the effect of estrogen on the HPA axis is measurable in the hypothalamus, and is therefore not primarily at the anterior pituitary.     

Disturbances in catecholamine metabolism during formation and development of chronic alcoholism]

There has been carried out an investigation dealing with catecholamines metabolism in the patients suffering from alcoholism in the first, second and third stage at the short-term remission. The first developed alcoholism stage was determined as a typical one for increasing the excretion with urine of DOPA, dopamine (DA), noradrenaline (NA) and adrenaline (A), as well as the blood levels of DA, NA and A. DA/NA rate evidences about an increased synthesis of NA with DA. The marked second alcoholism stage is characterized by an acute decrease of excreting with urine and blood levels of NA. Alongside with the latter. DA excretion with urine and its blood levels remained high. DA/NA rate indicates to the considerably low relative activity of NA with DA synthesis, both in relation to the control and to the developed first alcoholism stage. In the third alcoholism stage NA excretion with urine and its blood levels become lower relatively to the marked second stage. Simultaneously DA excretion with urine and its blood levels are lower than in the developed second stage, hower exceed the control values. DA/NA rate testifies the slight activation of NA and DA synthesis. The results obtained in the work indicate to the significant role of CA metabolism disturbances in the alcoholic dependence formation.     

In vivo and in vitro release of ACTH by synthetic CRF

The 41-residue corticotropin releasing factor (CRF) was synthesized by the solid phase method. The synthetic CRF and arginine vasopressin (AVP) were examined for ACTH releasing activity and effects on the release of 5 other pituitary hormones in vivo and in vitro. Injection of the CRF into pharmacologically blocked rats increased plasma corticosterone levels in a dose-related manner. The minimum effective dose was 1.6 x 10(-12) mol/100 g body weight. CRF also significantly stimulated release of ACTH-like immunoreactivity in a dose-related manner from rat pituitary quarters beginning at a concentration of 10(-9) M. AVP, a peptide known to have CRF activity, exhibited slightly lower corticotropin releasing activity than the CRF at equimolar dose levels. Secretion of other pituitary hormones was not appreciably altered by either the CRF or AVP.     

Pineal melatonin in hibernating and aroused golden hamsters (Mesocricetus auratus)

Daily changes of pineal melatonin content were determined in warm-adapted nonhibernating and cold-adapted hibernating golden hamsters (Mesocricetus auratus). Pineal melatonin in nonhibernating golden hamsters showed marked daily rhythm with the night values about 20 times higher than the daytime ones. In hamsters hibernating for 2 and 3 days the melatonin rhythm was abolished, since no increase of pineal melatonin over basal levels occurred throughout 24 hr period. After arousal from hibernation melatonin increased rapidly regardless whether the hamsters were provoked to arousal during day or night.     

新生大鼠下丘脑CRF和AVP神经元对急性低氧的应答

目的:观察肾上腺摘除新生大鼠下丘脑促肾上腺皮质激素释放激素(CRF)和精氨酸加压素(AVP)神经元对急性低氧的应答.方法:在低压氧舱中模拟高海拔低氧,用放免法测定AVP和CRP含量.结果:新生大鼠暴露于急性低氧环境下(模拟5 000 m和7 000 m海拔高度,24 h),其下丘脑CRP在3 d和7 d龄大鼠中无明显变化,但14d、21 d和28 d时低于对照;下丘脑AVP在3 d大鼠中亦无变化,但14 d时低于对照,7 d、21 d及28 d时高于对照.两者对低氧的应答模式随日龄而变化.摘除肾上腺后,14 d、21 d及28 d大鼠下丘脑CRF和AVP含量均显著低于同龄完整大鼠,此时暴露于急性低氧环境下,CRF和AVP无进一步的变化.结论:摘除肾上腺抑制下丘脑CRF和AVP的发育,影响它们对低氧应激的正常应答.     

Tissue catecholamine concentrations in spontaneously hypertensive rats

Tissue concentrations of noradrenaline (NA), dopamine (DA) and adrenaline (A) were compared in spontaneously hypertensive (SHR) and normotensive (NCR) rats, aged 1, 3, 8, 14 and 24 weeks The organs analyzed included the brain, subdivided into prosencephalon and rhombencephalon, heart, adrenal glands and kidney. Brain catecholamines were significantly lower in SHR than in NCR, and the difference appeared already at the age of 3 weeks. Concomitant increase was found in the adrenal NA and A concentrations of the SHR. Concentration of NA in the heart decreased in the SHR following onset of hypertension. It is concluded that the diminished NA, DA and A concentrations in the brain as well as the augmented adrenal NA and A levels in the SHR may be causally related to the development of hypertension, while the heart NA level reflects the secondary, hypertension -- related changes.     

Golden hamsters are nocturnal in captivity but diurnal in nature

Daily activity rhythms are nearly universal among animals and their specific pattern is an adaptation of each species to its ecological niche. Owing to the extremely consistent nocturnal patterns of activity shown by golden hamsters (Mesocricetus auratus) in the laboratory, this species is a prime model for studying the mechanisms controlling circadian rhythms. In contrast to laboratory data, we discovered that female hamsters in the wild were almost exclusively diurnal. These results raise many questions about the ecological variables that shape the activity patterns in golden hamsters and the differences between laboratory and field results.     

Comparative thermoregulatory adaptations of field mice of the genus Apodemus to habitat challenges

Thermoregulatory abilities, which may play a role in physiological adaptations, were compared between two field mouse species (Apodemus mystacinus and A. hermonensis) from Mount Hermon. While A. hermonensis is common at altitudes above 2100 m, A. mystacinus is common at 1650 m. The following variables were compared in mice acclimated to an ambient temperature of 24°C with a photoperiod of 12L:12D, body temperature during exposure to 4°C for 6 h, O₂ consumption and body temperature at various ambient temperature, non-shivering thermogenesis measured as a response to a noradrenaline injection, and the daily rhythm of body temperature. Both species could regulate their body temperature at ambient temperatures between 6 and 34°C. The thermoneutral zone for A. mystacinus lies between 28 and 32°C, while for A. hermonensis a thermoneutral point is noted at 28°C. Both species increased O₂ consumption and body temperature as a response to noradrenalin. However, maximal VO ₂ consumption as an response to noradrenaline and non-shivering thermogenesis capacity were higher in A. mystacinus, even though A. hermonensis is half the size of A. mystacinus. The body temperature rhythm in A. hermonensis has a clear daily pattern, while A. mystacinus can be considered arhythmic. The results suggest that A. hermonensis is adapted to its environment by an increase in resting metabolic rate but also depends on behavioural thermoregulation. A. mystacinus depends more on an increased non-shivering thermogenesis capacity.Abbreviations C thermal conductance - NA noradrenaline - NST non-shivering thermogenesis - OTC overall thermal conductance - RMR resting metabolic rate - STPD standard temperature and pressure dry - T _a ambient temperature - T _b body temperature - I _b Min minimal T _b , measured before NA iniection - T _b NA maximal - T _b as a response to NA injection - T _lc lower critical point - TNP thermoneutral point - TNZ thermoneutral zone - VO₂ O₂ consumption - VO₂ Min minimal VO₂ measured before NA injection - VO₂NA maximal VO₂, as a response to NA injection     

The effects of ghrelin/GHSs on AVP mRNA expression and release in cultured hypothalamic cells in rats

Ghrelin, the endogenous ligand for growth hormone secretagogues (GHSs) receptor (GHS-R), increases adrenocorticotropin (ACTH) and cortisol (corticosterone) as well as GH secretion in humans and animals. However, the site of GHSs action to induce ACTH secretion is not fully understood. To clarify the mechanisms of the action of ghrelin/GHSs on ACTH secretion, we analyzed the effects of KP-102 and ghrelin on the mRNA expression and release of corticotropin releasing factor (CRF) and arginine vasopressin (AVP), ACTH secretagogues, in monolayer-cultured hypothalamic cells of rats. Incubation of cells with KP-102 for 4 h and 8 h and with ghrelin for 4 h significantly increased AVP mRNA expression and release without changing CRF mRNA expression. CRF levels in culture media were undetectable. Suppression of GHS-R expression by siRNA blocked ghrelin- and KP-102-induced AVP mRNA expression and release. NPY significantly increased AVP mRNA expression and release. Furthermore, treatment of cells with anti-NPY IgG blocked KP-102-induced AVP mRNA expression and release. We previously reported that KP-102 significantly increases NPY mRNA expression in cultured hypothalamic cells. Taken together, these results suggest that ACTH secretion by ghrelin/GHSs is induced mainly through hypothalamic AVP, and that NPY mediates the action of ghrelin/GHSs.     

Effects of chlorpromazine on hypothalamic aminergic neurons and stress responses in moderate cold

Guinea-pigs were treated with chlorpromazine or 0.9% NaCl and exposed to +4 degrees C or +23 degrees C for 2 h. Hypothalamic noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), 3-methoxy-4-hydroxyphenylethylene-glycol (MHPG), homovanillinic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were determined by high-performance liquid chromatography. Serum and urinary catecholamines, muscle and liver glycogen and blood glucose were also measured. Chlorpromazine caused deep hypothermia at this moderately cold temperature and slight hypothermia at room temperature. Cold increased the activity of noradrenergic and serotonergic neurons, as indicated by the increase in hypothalamic MHPG and 5-HIAA and also the MHPG:NA and 5-HIAA:5-HT ratios. A tendency towards drug-induced inhibition of hypothalamic serotonergic neurons was seen, although this was not significant. A drug-induced inhibition of noradrenergic neurons could not be ruled out. Increased drug-induced turnover of DA was observed in the cold, and a tendency in the same direction was seen at room temperature. Excretion of DA into the urine was induced by chlorpromazine. The hypothermic guinea-pigs had low serum catecholamines, indicating diminished sympathetic activity, but high urinary catechols, a sign of cold stress.