Differential sensitivity to neurotensin-induced hypothermia, but not analgesia, in Fischer and Lewis rats

Neurotensin (NT) produces behavioral and physiological effects, including analgesia and hypotheria, when administered into the CNS. Fischer and Lewis rats exhibit differential behavioral responses to central NT receptor activation. To further characterize these differences, we assessed central NT-induced analgesia and hypothermia in independent groups of rats from each strain. Fischer and Lewis rats showed a similar dose-orderly analgesic response in a hot-plate test. Such an isosensitivity was not observed for NT-induced hypothermia. Although NT produced a dose-orderly decrease in mean rectal temperature in both strains, the magnitude of the hypothermic response was significantly smaller in Fischer than in Lewis rats. These findings provide further evidence of genetic differences in central neurotensinergeric neurotransmission in these two strains.     

Response acquisition with delayed reinforcement in Lewis and Fischer 344 rats

Previous work has shown neurochemical and behavioral differences between Lewis rats and Fischer 344 rats. Some of this work suggests that there might be differential sensitivity to delayed reinforcement between the two strains. To further explore this possibility, Lewis (n=8) and Fischer 344 (n=8) rats were exposed to a response-acquisition task with a non-resetting 20s delay to reinforcement. A tandem fixed-ratio 1, fixed-time 20s schedule of reinforcement was programmed for one of two levers; presses on the alternate lever had no programmed consequences. A greater number of Lewis rats (5/8) acquired lever pressing compared to the Fischer 344 rats (2/8). Future work with these strains may lead to a better understanding of the genetic and/or neurochemical factors involved in temporal control of behavior.     

Features of oxidative phosphorylation in brain mitochondria of rats with different sensitivity to oxygen insufficiency]

Oxidative phosphorylation parameters have been investigated in the isolated brain mitochondria of rats preliminary divided into non-resistant (NR) and high-resistant (HR) animals by their sensitivity to hypobaric hypoxia. During the NAD-dependent substrates oxidation it was shown that the identical effectiveness of the respiratory chain function in both groups of animals was reached at more tension of the oxidative processes. It has been established that at the identical effectiveness of the succinate oxidation by the brain mitochondria in both groups of animals compensatory potentialities of the succinate-oxidase pathway of oxidation is higher in the brain of the NR to hypoxia animals. It has been shown the regulated influence of the NAD-dependent pathway of oxidation activity on the succinate-oxidase site of respiratory chain. This influence is more expressed in the brain mitochondria of the NR animals that in the HR animals.     

Effects of S-petasin on corticosterone release in rats

Petasites hybridus is used in Chinese herbal medicine. S-petasin is a bioactive compound isolated from leaves or roots of Petasites hybridus. S-petasin has been used to relieve gastrointestinal pain, lung disease, and spasms of the urogenital tract. However, the side effect of S-petasin on endocrine systems are still not clear. This study explored the effects of S-petasin on the release of corticosterone in vivo and in vitro. An intravenous injection of S-petasin (10 microg/kg) decreased both basal and adrenocorticotropin (ACTH)-induced plasma corticosterone concentration in male rats. In vitro, S-petasin (3 x 10(-6) - 10(-4) M) caused a significant reduction of basal and ACTH-stimulated release of corticosterone from the enzymatically dispersed rat zona fasciculata-reticularis (ZFR) cells in a dose-dependent manner. In order to study possible mechanisms, ZFR cells were incubated with S-petasin (10(-5) M) in the presence or absence of forskolin (adenylate cyclase activator, 10(-6) - 10(-4) M), 8-Br-cAMP (a cAMP analogue, 10(-6) 10(-4) M), 25-OH-cholesterol (pregnenolone biosynthesis precursor, 10(-5) M) combined with trilostane (a blocker of 3beta-hydroxysteriod dehydrogenase, 3beta-HSD, 10(-6) M) and deoxycorticosterone (corticosterone biosynthesis precursor, 10(-9) - 10(-6) M) at 37 degrees C for 1h. The concentration of pregnenolone and corticosterone in media were measured by radioimmunoassay. The stimulatory effects of corticosterone secretion induced by forskolin (10(-5) - 10(-4) M), 8-Br-cAMP (10(-5) - 10(-4) M) and deoxycorticosterone (10(-7) - 10(-6) M) were reduced by S-petasin at 10(-5) M. The stimulatory effects of pregnenolone secretion induced by 25-OH-cholesterol combined with or without trilostane was reduced by S-petasin at 10(-5) M. These results suggest that S-petasin inhibits the production of corticosterone from rat ZFR cells in part through decreasing the activities of adenylyl cyclase, P450scc and 11beta-hydroxylase.     

Effects of estradiol on corticosterone secretion in ovariectomized rats

The effects of estradiol benzoate (EB) on steroidogenesis in rat zona fasciculata-reticularis (ZFR) cells were studied. Female rats were ovariectomized (Ovx) for 2 weeks and then injected subcutaneously with oil or EB for 3 days before decapitation. ZFR cells were isolated and incubated with adrenocorticotropin (ACTH) or prolactin (PRL) for 1 h. Corticosterone concentrations in plasma and cell media, and adenosine 3',5'-cyclic monophosphate (cAMP) production in ZFR cells were determined by radioimmunoassay. The effects of EB replacement in vivo on the activities of steroidogenic enzymes in ZFR cells were measured by the amounts of intermediate steroidal products separated by thin-layer chromatography. Replacement of EB in vivo resulted in a dose-dependent increase of plasma PRL and corticosterone in Ovx rats. The basal, ACTH-, and PRL-stimulated release of corticosterone by ZFR cells was greater in EB- than in oil-treated animals. Forskolin-induced production of cAMP was greater in the EB-replaced rats than in oil-treated animals, which correlated with the increase of corticosterone production. The 3-isobutyl-l-methylxanthine (IBMX) plus ACTH-, IBMX plus PRL-, and forskolin plus PRL-stimulated productions of cAMP were higher in EB- than in oil-treated rats. The enzyme activities of postpregnenolone were not affected by EB replacement in Ovx rats. These results suggest that the EB-related increase of corticosterone production in Ovx rats is associated with an increase of cAMP generation and the stimulatory effect of PRL on ZFR cells.     

慢性应激不同方式对大鼠血清皮质酮的影响

目的：比较慢性应激不同方式对生理状态大鼠血清皮质酮水平的影响,研究机体慢性应激反应的整体性适应特征。方法：采用连续4周的适宜游泳、束缚和二者复合的三种应激方式后,测定大鼠血清皮质酮基础含量,分析不同慢性应激方式对皮质酮水平的影响。结果：血清皮质酮水平与对照组比较,复合组无显著性差异;游泳组虽升高但无显著性;束缚组升高有显著性意义。结论：束缚可致大鼠血清皮质酮水平增高;初步认定游泳与束缚复合慢性应激方式可能对机体的整体适应性能具有积极意义。     

Photoperiod regulates corticosterone rhythms by altered adrenal sensitivity via melatonin-independent mechanisms in Fischer 344 rats and C57BL/6J mice

Most species living in temperate zones adapt their physiology and behavior to seasonal changes in the environment by using the photoperiod as a primary cue. The mechanisms underlying photoperiodic regulation of stress-related functions are not well understood. In this study, we analyzed the effects of photoperiod on the hypothalamic-pituitary-adrenal axis in photoperiod-sensitive Fischer 344 rats. We first examined how photoperiod affects diurnal variations in plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone. ACTH levels did not exhibit diurnal variations under long- and short-day conditions. On the other hand, corticosterone levels exhibited a clear rhythm under short-day condition with a peak during dark phase. This peak was not observed under long-day condition in which a significant rhythm was not detected. To analyze the mechanisms responsible for the photoperiodic regulation of corticosterone rhythms, ACTH was intraperitoneally injected at the onset of the light or dark phase in dexamethasone-treated rats maintained under long- and short-day conditions. ACTH induced higher corticosterone levels in rats examined at dark onset under short-day condition than those maintained under long-day condition. Next, we asked whether melatonin signals are involved in photoperiodic regulation of corticosterone rhythms, and rats were intraperitoneally injected with melatonin at late afternoon under long-day condition for 3 weeks. However, melatonin injections did not affect the corticosterone rhythms. In addition, photoperiodic changes in the amplitude of corticosterone rhythms were also observed in melatonin-deficient C57BL/6J mice, in which expression profiles of several clock genes and steroidgenesis genes in adrenal gland were modified by the photoperiod. Our data suggest that photoperiod regulates corticosterone rhythms by altered adrenal sensitivity through melatonin-independent mechanisms that may involve the adrenal clock.     

Neurotensin modulation of spontaneous EPSCs in the nucleus accumbens of Lewis and Fischer 344 rats

Fischer 344 (F344) and Lewis (LEW) rats are inbred strains that are differentially sensitive to drugs of abuse and that respond differently to the endogenous neuropeptide neurotensin (NT). To understand the mechanisms involved we used whole cell patch clamp recording technique to study the effects of an equimolar concentration of NT and its active analog, d-Tyr[11]neurotensin (d-NT), on the amplitude and frequency of spontaneous excitatory postsynaptic currents (sEPSCs) in nucleus accumbens medium spiny (MS) neurons in brain slices. NT and d-NT produced an increase in the amplitude but not in the frequency of sEPSCs in all neurons tested in both F344 and LEW rats. In LEW rats, NT and d-NT produced an increase in sEPSCs of the same magnitude. In contrast, in F344 rats, d-NT produced an increase in sEPSCs that was 2.4 times larger than that of NT. Moreover, the effect of d-NT in F344 rats was also significantly larger than that measured in LEW rats whereas NT produced an effect of the same magnitude in both strains. These results demonstrate that MS neurons in F344 rats are more responsive to the activation of NT receptors sensitive to d-NT than LEW animals. This finding parallels previous behavioral data and provides additional evidence that the NT circuitry differs in the two strains, in a brain region known to play a key role in the rewarding effects of drugs of abuse.     

Effect of corticosterone treatment on muscle protein turnover in adrenalectomized rats and diabetic rats maintained on insulin

The effect of corticosterone on protein turnover in skeletal muscle was investigated in growing rats. Protein synthesis was measured in vivo by the constant infusion of [(14)C]tyrosine. The extent to which any effect of corticosterone is modulated by the hyperinsulinaemia induced by steroid treatment was examined by giving the hormone not only to adrenalectomized rats but also to streptozotocin-induced diabetic rats maintained throughout the treatment period on two dosages of insulin by an implanted osmotic minipump. Approximate rates of protein degradation were also estimated in some cases as the difference between synthesis and net change in muscle protein mass. Measurements were also made of free 3-methylhistidine concentration in muscle and plasma. At 10mg of corticosterone/100g body wt. per day, growth stopped and muscle wasting occurred, whereas at 5 mg of corticosterone/100g body wt. per day no net loss of protein occurred. However, this low dose did induce muscle wasting when insulin concentration was regulated by a dose of 1.2 units/day. Protein synthesis was markedly depressed in all treated groups, the depression in the insulin-maintained rats being marginally more than in the hyperinsulinaemic adrenalectomized rats. The oxidative soleus muscle appeared to be less susceptible to the effect of the corticosterone than was the more glycolytic plantaris or gastrocnemius muscle. Any effect of the corticosterone on protein degradation was much less than its effects on protein synthesis. Where increases in the degradation rates appeared to occur in the rats treated with 10mg of corticosterone/100g body wt. per day, the increases were less than 20%. The free intracellular 3-methylhistidine concentrations were doubled in all groups treated with 5 mg of corticosterone/100g body wt. per day and increased 5-fold in the adrenalectomized rats treated with 10mg of corticosterone/100g body wt. per day, with no change in plasma concentration in any of the groups. It is therefore concluded that: (a) the suppression of protein synthesis is the main effect of glucocorticoids in muscle; (b) marked increases in insulin afford only minor protection against this effect; (c) stimulation of protein degradation may occur, but to a much lesser extent.     

Effects of corticosterone on connectin content and protein breakdown in rat skeletal muscle

We examined the effects of a glucocorticoid, corticosterone, on calpain activity, connectin content and protein breakdown in rat muscle. The results indicated that calpain activity was increased by corticosterone and thus breakdown of connectin was stimulated followed by increased breakdown of skeletal muscle protein.     

Differences in dopamine responsiveness to drugs of abuse in the nucleus accumbens shell and core of Lewis and Fischer 344 rats

The use of inbred rat strains provides a tool to investigate the role of genetic factors in drug abuse. Two such strains are Lewis and Fischer 344 rats. Although several biochemical and hormonal differences have been observed between Lewis and Fischer 344 strains, a systematic comparison of the effect of different drugs of abuse on dopamine (DA) transmission in the shell and core of the nucleus accumbens of these strains is lacking. We therefore investigated, by means of dual probe microdialysis, the effect of different doses of morphine (1.0, 2.5, and 5.0 mg/kg), amphetamine (0.25, 0.5, and 1.0 mg/kg) and cocaine (5, 10, and 20 mg/kg) on DA transmission in the shell and in the core of nucleus accumbens. Behavior was monitored during microdialysis. In general, Lewis rats showed greater DA responsiveness in the NAc core compared to F344 rats except after 2.5 mg/kg of morphine and 20 mg/kg of cocaine. In the NAc shell, different effects were obtained depending on drug and dose: after 1.0 mg/kg of morphine no strain differences were observed, at 2.5 and 5.0 mg/kg Lewis rats showed greater increase in DA in the NAc shell. Following amphetamine and cocaine challenge, Lewis rats showed greater DA increase in the shell after 0.25 mg/kg of amphetamine and 20 mg/kg of cocaine. Behavioral activation was greater in Lewis rats in response to the lowest dose of morphine (1.0 mg/kg), to the highest dose of amphetamine (1.0 mg/kg) and to all doses of cocaine. These differences might be the basis for the different behavioral responses of these strains to drugs of abuse.     

Effects of housing density on Long Evans and Fischer 344 rats

At many breeding facilities, rats are housed at relatively high densities until they are 5 weeks old, at which point they are either shipped for research or rehoused at standard cage densities according to weight. The authors carried out a pilot study in Long Evans and in Fischer 344 rats to investigate whether continuing to house rats at high densities (24 in(2) floor space per rat) past the age of 5 weeks, through puberty and into adulthood would alter behavioral or physiological parameters compared with raising rats at standard densities (about 72 in(2) floor space per rat). After rats reached puberty, the authors rehoused them with unfamiliar cagemates. The researchers evaluated clinical and behavioral signs of stress, weight, blood glucose concentration, white blood cell count and serum corticosterone concentration. Overall, cage density had little effect on the parameters measured, though gender seemed to affect stress in Long Evans rats. The results suggest that rats of these strains can be raised at the higher densities tested until any age and regrouped with unfamiliar cagemates without compromising rats' welfare or subsequent experimental data.     

Effects of anterior pituitary hormones on hepatic corticosterone metabolism in rats

Experiments were conducted to determine the effects of anterior pituitary hormones on hepatic corticosterone metabolism in rats. Hypophysectomy lowered A-ring reduction but did not affect sidechain metabolism. Administration of prolactin, FSH, LH or FSH + LH to hypophysectomized rats affected neither process. Similarly, ACTH or growth hormone, when given alone, did not affect corticosterone metabolism. However, combined treatment with ACTH and growth hormone significantly reduced the rate of ring A metabolism, suggesting that hormonal interactions may be important in the control of hepatic steroid metabolism.     

Effect of cold environment on skeletal muscle mitochondria in growing rats

Summary Growing rats (4 weeks old) were kept for 3 weeks at 11° C and 24° C respectively. The cold-adapted animals showed a significantly higher oxygen consumption (64%). Volume density of subsarcolemmal and interfibrillar mitochondria as well as volume density of fat droplets were estimated in M. soleus and the diaphragm of both groups. In cold-adapted animals, the total volume of mitochondria was significantly increased by 24% in diaphragm and 37% in M. soleus. The volume of subsarcolemmal mitochondria was almost doubled in each muscle, but the volume of interfibrillar mitochondria did not change significantly. The surface of the inner mitochondrial membranes per unit volume of mitochondrion in M. soleus was significantly increased both in interfibrillar and subsarcolemmal mitochondria, whereas the surface of the outer mitochondrial membranes per unit volume of mitochondrion was increased only in the subsarcolemmal mitochondria. The volume of fat droplets in the diaphragm and M. soleus of cold adapted animals increased significantly by 62% and 150% respectively.     

Reduced sensitivity of peripheral cells to glucocorticoids in hypercholesterolemia

It has been found that lymphocytes of hypercholesterolemic (HCh) subjects are characterized by a reduced number of glucocorticoid receptors (GcR) as compared with the cells of normolipidemics (N). Addition of HCh-sera or very low density lipoproteins, or low density lipoproteins isolated both from HCh-sera and N-sera to cultured human skin fibroblasts brought about a fall in the number of GcR in the cells. High density lipoproteins had no effect on GcR level. Dexamethasone was less effective in inhibiting cholesterol synthesis from [14C]acetate in the lymphocytes and fibroblasts with a reduced number of GcR. In the presence of dexamethasone (I x 10(-8)M) in fibroblast growth medium, reduced number of GcR (due to preincubation with very low density lipoproteins) led to a substantial increase in cholesterol synthesis. These findings indicate that the sensitivity of peripheral cells to glucocorticoids is decreased in HCh which might be one of the trigger mechanisms of atherogenesis.     

Effects of paraquat on mitochondria of rat skeletal muscle

The effect of the herbicide paraquat (N,N'-dimethyl 4,4'-bipyridium), known to damage the lipid cellular membrane by peroxidation with superoxide radicals and a singlet oxygen, was investigated on skeletal muscle mitochondria. Minced rat gastrocnemius muscles were incubated in 8 mM paraquat solution. Mitochondrial fractions prepared from the incubated muscles were examined with respect to respiratory function and the enzyme activity of cytochrome c oxidase and succinate-cytochrome c reductase in the electron transport chain. The ADP/O ratio, RCR, and state 3 rates (= oxygen consumption in state 3) decreased gradually. State 4 rates (= oxygen consumption in state 4) increased in the initial stages and decreased after longer incubations. Enzyme activities gradually increased. These results suggested that paraquat damaged the mitochondrial membrane and disrupted oxidative phosphorylation in the early stage of incubation. Also, the electron transport chain was accelerated in the earlier stage and broken following a longer incubation. The inhibitory modality of paraquat on mitochondrial respiration was shown to be different from that of other known inhibitors.     

Biochemical criteria of mammalian cell sensitivity to glucocorticoids

The resistance of Morris hepatoma cells strain 8994 to glucocorticoids which lack hormonal induction of tyrosine aminotransferase synthesis was studied. The cells of Morris hepatoma 7777 were used as a sensitive strain by a criterion of the enzyme synthesis. Using two-dimensional polyacrylamide gel electrophoresis, it was demonstrated that, i) in the cells of the "resistant" Morris hepatoma strain 8994 glucocorticoids change the rate of synthesis of at least five proteins, ii) two of these proteins are common for both cell strains, while the other ones are individual for each line, iii) in the cells of Morris hepatoma 8994 tyrosine aminotransferase is not controlled by glucocorticoids, iiii) glucocorticoids may not only control the activated genes but also the genes whose expression is suppressed. It was assumed that in the absence of disturbances in the receptor apparatus the resistance of any cell population to glucocorticoids can only be established by the use of a great variety of experimental approaches. The resistance of a cell population to the hormones cannot be judged upon by an analysis of the intensity of synthesis of one or even several proteins.     

Predictable adaptations by skeletal muscle mitochondria to different exercise training workloads

1. Mitochondria were isolated according to their cellular location within the fibers of pooled gastrocnemius and plantaris muscle of the rat. This procedure yields two populations of mitochondria which display different biochemical properties. 2. The adaptive response of these mitochondria populations to the chronic exposure to different elevated energy demands (different modes of exercise training) was investigated. 3. The observed changes in mitochondrial protein content and cytochrome oxidase activity in the respective mitochondria population suggests that each population is capable of independent adaptations. 4. The adaptive response of each mitochondria population, furthermore, was predictable with respect to the metabolic energy demand of the exercise training workload.     

Description and analysis of differential sensitivity to glucocorticoids in Fao cells

This study shows that the derived hepatoma cell line Fao displays different sensitivities for glucocorticoid induction of tyrosine aminotransferase (TAT), alanine aminotransferase (AAT) and gamma-glutamyltransferase (GGT). This was seen in the different behaviors of nine steroids with respect to these three effects: (1) in the presence of full agonists (dexamethasone or deacylcortivazol), half-maximal induction of GGT occurred at approx 5- to 6-fold higher agonist concentrations than those required for half-maximal induction of AAT and TAT; (2) in the presence of full antagonists (RU 486, R5020, or progesterone) the GGT response induced by an equal agonist concentration was inhibited at concentrations approx 4- to 5-fold lower than those required for an equivalent inhibition of TAT response; (3) in the presence of cortexolone, deoxycorticosterone, 11 beta-hydroxyprogesterone and dexamethasone-3'-oxetanone, there was a partial agonistic effect (30-50%) on TAT and AAT responses, whereas there was a mainly antagonistic effect (very weak agonistic effect: 0-10%) on GGT response; (4) regardless of the steroid or its full or partial agonist activity, a given TAT induction level (50%, for example) always corresponded to the same AAT and GGT induction levels (50 and 10% respectively). We provide evidence showing that the three above-mentioned biological responses are mediated via the same type of glucocorticoid receptor binding site. Consequently, this differential behavior probably originates from a phenomenon occurring after the common steps (activation, translocation) that follow the formation of the steroid-receptor complex. This leads us to propose a model in which this phenomenon is assumed to originate from a difference in the affinities of the activated receptor for the nuclear acceptor sites of the TAT and GGT genes.