A Rat Model of Alzheimer's Disease Based on Abeta42 and Pro-oxidative Substances Exhibits Cognitive Deficit and Alterations in Glutamatergic and Cholinergic Neurotransmitter Systems.

Alzheimer's disease (AD) is one of the most serious human, medical, and socioeconomic burdens. Here we tested the hypothesis that a rat model of AD (Samaritan; Taconic Pharmaceuticals, USA) based on the application of amyloid beta42 (Abeta42) and the pro-oxidative substances ferrous sulfate heptahydrate and L-buthionine-(S, R)-sulfoximine, will exhibit cognitive deficits and disruption of the glutamatergic and cholinergic systems in the brain. Behavioral methods included the Morris water maze (MWM; long-term memory version) and the active allothetic place avoidance (AAPA) task (acquisition and reversal), testing spatial memory and different aspects of hippocampal function. Neurochemical methods included testing of the NR1/NR2A/NR2B subunits of NMDA receptors in the frontal cortex and CHT1 transporters in the hippocampus, in both cases in the right and left hemisphere separately. Our results show that Samaritan rats(™) exhibit marked impairment in both the MWM and active place avoidance tasks, suggesting a deficit of spatial learning and memory. Moreover, Samaritan rats exhibited significant changes in NR2A expression and CHT1 activity compared to controls rats, mimicking the situation in patients with early stage AD. Taken together, our results corroborate the hypothesis that Samaritan rats are a promising model of AD in its early stages.

Rapamycin blocks the antidepressant effect of ketamine in task-dependent manner.

OBJECTIVE: The aim of our study was to test whether ketamine produces an antidepressant effect in animal model of olfactory bulbectomy and assess the role of mammalian target of rapamycin (mTOR) pathway in ketamine's antidepressant effect. METHODS: Bulbectomized (OBX) rats and sham controls were assigned to four subgroups according to the treatment they received (ketamine, saline, ketamine + rapamycin, and saline + rapamycin). The animals were subjected to open field (OF), elevated plus maze (EPM), passive avoidance (PA), Morris water maze (MWM), and Carousel maze (CM) tests. Blood samples were collected before and after drug administration for analysis of phosphorylated mTOR level. After behavioral testing, brains were removed for evaluation of brain-derived neurotrophic factor (BDNF) in prefrontal cortex (PFC) and hippocampus. RESULTS: Ketamine normalized hyperactivity of OBX animals in EPM and increased the time spent in open arms. Rapamycin pretreatment resulted in elimination of ketamine effect in EPM test. In CM test, ketamine + rapamycin administration led to cognitive impairment not observed in saline-, ketamine-, or saline + rapamycin-treated OBX rats. Prefrontal BDNF content was significantly decreased, and level of mTOR was significantly elevated in OBX groups. CONCLUSIONS: OBX animals significantly differed from sham controls in most of the tests used. Treatment had more profound effect on OBX phenotype than controls. Pretreatment with rapamycin eliminated the anxiolytic and antidepressant effects of ketamine in task-dependent manner. The results indicate that ketamine + rapamycin application resulted in impaired stress responses manifested by cognitive deficits in active place avoidance (CM) test. Intensity of stressor (mild vs. severe) used in the behavioral tests had opposite effect on controls and on OBX animals.

Anxiety-like behavior in the elevated-plus maze tests and enhanced IL-1ß, IL-6, NADPH oxidase-1, and iNOS mRNAs in the hippocampus during early stage of adjuvant arthritis in rats.

We studied anxiety-like behavior in the elevated plus-maze (EPM) tests in male Lewis rats on days 2 and 4 of adjuvant arthritis (AA). In plasma we analyzed C-reactive protein (CRP), albumin, ACTH, corticosterone, in the hippocampus the mRNA expression of interleukin-1ß (IL-1ß), interleukin-6 (IL-6), corticotrophin releasing factor (CRH), NADPH oxidases NOX1 and NOX2, and inducible NO-synthase (iNOS). EPM tests showed a higher anxiety index in AA rats on days 2 and 4 and reduction of total entries. On days 2 and 4 we found reduced plasma albumin, enhanced CRP, ACTH and corticosterone, and in the hippocampus enhanced mRNA for NOX1 and IL-1ß in AA rats, on day 4 we found enhanced mRNAs for iNOS and IL-6, and reduced mRNA for CRH. The mRNA for NOX2 did not change on any experimental day. These results suggest enhanced anxiety, as well as locomotor impairment during the early phase of AA that correlate with enhanced mRNA expressions of parameters of oxidative stress NOX1, iNOS, and inflammatory cytokines IL-1ß and IL-6 in the hippocampus.

Effect of feeding status on adjuvant arthritis severity, cachexia, and insulin sensitivity in male Lewis rats.

We studied the effect of food restriction, overfeeding, and normofeeding on cachexia, inflammatory and metabolic parameters, and insulin sensitivity in chronic adjuvant arthritis (AA) in rats. Food restriction during AA increased circulating ghrelin, corticosterone, decreased leptin, and ameliorated arthrogram score and systemic inflammation compared to normofeeding. Overfeeding worsened arthrogram score and systemic inflammation, and led to lipid accumulation in the liver, but not to alterations of adipokine and ghrelin plasma levels relative to normofeeding. Independently of feeding status, AA induced cachexia, in which modulation of mRNA expressions for appetite-regulating neuropeptides (NPY, AgRP, POMC, CART) in the arcuate nucleus (ARC) does not play a primary role. The overexpression of IL-1ß mRNA in the ARC suggests its role in the mechanisms of impaired energy balance during AA under all feeding conditions. Normal HOMA index in all arthritic groups does not indicate the development of insulin resistance by feeding interventions in these rats.

Alterations in adipocyte glucose transporter GLUT4 and circulating adiponectin and visfatin in rat adjuvant induced arthritis.

UNLABELLED: Rheumatoid arthritis in humans brings about impaired insulin sensitivity and glucose tolerance. Since adipose tissue plays a role in glucose homeostasis, we evaluated the size of adipocytes, the amount of glucose transporter type 4 (GLUT4) in adipocyte plasma membranes, and circulating insulin, glucose, and adipokines affecting glucose metabolism, resistin, adiponectin and visfatin during experimental adjuvant arthritis (AA) in male Lewis rats. AA was induced by a single injection of complete Freund's adjuvans. Adipocyte diameter was assessed microscopically, GLUT4 was measured by Western blotting. Plasma insulin, adiponectin, visfatin were quantitated by RIA, and resistin by ELISA. Arthritic rats showed cachexia, reduced adipocyte size, and downregulated membrane GLUT4 (4065 +/- 962 vs. 9911 +/- 680 arb. units of optic density, p < 0.01), reduced plasma adiponectin (1.956 +/- 0.10 vs. 3.16 +/- 0.22 microg/ml, p < 0.001), and enhanced visfatin (1.84 +/- 1.05 vs. 1.24 +/- 0.1 ng/ml, p < 0.01). Plasma glucose and insulin were unaltered, as were the resistin levels. CONCLUSION: AA induced cachexia results in reduction of adipocyte size, and paradoxically also in downregulation of GLUT4 in adipocyte membranes. This is supposed to be functionally related to the reduced adiponectin levels. The upregulated visfatin in rat arthritis is a novel finding, and it confirms its role in autoimmunity across the species.

Enhanced expressions of mRNA for neuropeptide Y and interleukin 1 beta in hypothalamic arcuate nuclei during adjuvant arthritis-induced anorexia in Lewis rats.

OBJECTIVE: Food intake is activated by hypothalamic orexigenic neuropeptide Y (NPY), which is mainly under the dual control of leptin and ghrelin. Rat adjuvant arthritis (AA), similarly as human rheumatoid arthritis, is associated with cachexia caused by yet unknown mechanisms. The aim of our study was to evaluate NPY expression in hypothalamic arcuate nuclei (nARC) under the conditions of AA-induced changes in leptin, ghrelin and adiponectin. Since IL-1beta is involved in the central induction of anorexia, we studied its expression in the nARC as well. METHODS: AA was induced to Lewis rats using complete Freund's adjuvant. On days 12, 15 and 18 after complete Freund's adjuvant injection, the levels of leptin, adiponectin, ghrelin and IL-1beta were determined by RIA or ELISA. The mRNA expressions for NPY, leptin receptor (OB-R), ghrelin receptor (Ghsr) and IL-1beta were determined by TaqMan RT-PCR from isolated nARC. RESULTS: In AA rats, decreased appetite, body mass and epididymal fat stores positively correlated with reduced circulating and epididymal fat leptin and adiponectin. Ghrelin plasma levels were increased. In nARC, mRNA for OB-R, Ghsr and NPY were overexpressed in AA rats. AA rats showed overexpression of mRNA for IL-1beta in nARC while circulating, and spleen IL-1beta was unaltered. CONCLUSION: During AA, overexpression of orexigenic NPY mRNA in nARC along with enhanced plasma ghrelin and lowered leptin levels occur. Decreased food intake indicates a predominant effect of the anorexigenic pathway. Activated expression of IL-1beta in nARC suggests its role in keeping AA-induced anorexia in progress. The reduction in adiponectin may also contribute to AA-induced anorexia.

Early stage of adjuvant arthritis alters behavioral responses in male but not female rats.

Anxiety and depression commonly occur in the pathology of rheumatic diseases. Little is known about how inflammatory disease in its early stage, before any clinical manifestation, may affect general activity. The aim of this study was to compare the anxiety-like behaviour in the early stage of adjuvant arthritis (AA), and the paw edema, and corticosterone (CORT) levels in the developed stage of AA among male and female Long Evans rats. The behavioural activity was evaluated by elevated plus maze tests. These revealed significantly reduced number of entries into the open arm of the maze in arthritic males compared to controls or to females 4 days after AA induction. Arthrihtic and control females did not differ. The number of entries into the closed arm of the maze was the same across the genders and studied intervals. Time spent in the open arm was significantly lower in arthritic males against controls or arthitic females. Time spent in the closed arm showed inverse picture to the time spent in the open arm. Hind paw swelling measured on day 23 of AA was the same in males and females, as was the elevation of CORT levels in plasma. Male rats showed anxiety-like behaviour on day 4 of AA, while female rats did not show any change, indicating different brain sensitivity to early inflammation among the genders.

Relationship among nitric oxide, leptin, ACTH, corticosterone, and IL-1beta, in the early and late phases of adjuvant arthritis in male Long Evans rats.

Leptin, a hormone regulating body weight, food intake, and metabolism, is associated with activation of immune cells and inflammation. In this study we analyzed levels of leptin, adrenocorticotropic hormone (ACTH), corticosterone, interleukin 1beta (IL-1beta), and nitric oxide (NO) production on days 10 and 22 of adjuvant arthritis (AA) in male Long Evans rats to ascertain possible relationship of leptin with its modulators during the early and late phases of chronic inflammation. The circulating leptin levels were significantly reduced already on day 10 of AA compared to controls (1.97+/-0.22 ng/ml vs. 3.08+/-0.25 ng/ml, p<0.05); on day 22 no significant further drop was observed (1.06+/-0.21 ng/ml). Leptin mRNA in epididymal fat tissue was reduced in arthritic animals compared to controls on day 22 (0.61+/-0.09 vs. 1.30+/-0.1 arbU/GAPDH (p<0.01). IL-1beta concentration in spleen was enhanced on day 10 of AA (24.55+/-4.67 pg/100 microg protein vs. 14.33+/-1.71 pg/100 microg protein; p<0.05); on day 22 it did not differ from controls. ACTH and corticosterone levels were significantly elevated only on day 22 of AA (ACTH: 306.17+/-42.22 pg/ml vs. 157.61+/-23.94 pg/ml; p<0.05; corticosterone: 5.24+/-1.38 microg/100 ml vs. 1.05+/-0.23 microg/100 ml; p<0.01). Nitrate levels were enhanced similarly on days 10 (49.86+/-1.83 microM) and 22 of AA (43.58+/-2.17 microM), compared to controls (23.42+/-1.39 microM, p<0.001). These results show that corticosterone does not stimulate leptin production during AA. The suppression of leptin may be a consequence of permanent activation of NO, IL-1beta, and of lower weight gain. Circulating leptin does not seem to play a key role in the progression of chronic arthritis.

Exogenous IL-1beta induces its own expression, but not that of IL-6 in the hypothalamus and activates HPA axis and prolactin release.

OBJECTIVE: Proinflammatory cytokines IL-1beta, and IL-6 are synthesized in the brain, where they exert local regulatory functions. Our aim was to find out whether, along with the activation of hypothalamo-pituitary-adrenocortical (HPA) axis and prolactin (PRL), the acute systemic enhancement of IL-1beta affects its own production in the hypothalamus as well as that of IL-6. METHOD: Forty five minutes after a single i.p. administration of recombinant rat IL-1beta (5 microg/kg) to male Long Evans rats we estimated the expression of IL-1beta and IL-6 mRNA in the hypothalamus by real time PCR, ACTH, corticosterone (CORT), and PRL by RIA RESULTS: IL-1beta administration stimulated the expression of IL-1beta mRNA in the hypothalamus by 99 %, but not that of IL-6. It also significantly activated plasma levels of ACTH, PRL, CORT, and CORT production in adrenal gland. CONCLUSION: These results indicate that acute peripheral enhancement of IL-1beta may induce neuroendocrine changes also via the immediate activation of its own expression in the hypothalamus, but not that of IL-6 expression in the hypothalamus was found.