Calcium uptake in brain synaptosomes from rats exposed to daily toluene for up to 80 weeks

Rats were exposed to toluene, 500 p.p.m., for 12 hrs/day for up to 80 weeks. The brains were removed and the synaptosomes were prepared. Potassium-stimulated and unstimulated synaptosomes were incubated with 45Ca2+ for 1/2, 2, 4, 8, and 16 min. Toluene exposure for 4 and 12 weeks caused a significant, approximately 20%, increase in 45Ca2+ uptake into unstimulated synaptosomes. The effect was of moderate quantity and transient, since it was not significant after 30 and 80 weeks of exposure. It seems doubtful whether the demonstrated change in calcium uptake should have any relevance in connection with the "organic solvent neurotoxicity syndrome".     

Self-injurious behavior produced in rats by daily caffeine and continuous amphetamine

Self-biting (SB) is an unusual behavioral effect of high doses of certain amphetamine-like drugs in rats. This bizarre behavior has received little attention, perhaps because the high doses of drug required and the dramatic disturbance of the animals' behavioral repertoire have raised the possibility that SB is a high dose phenomenon. However, we have found that continuous administration of very low amounts of amphetamine reliably produces SB in rats, and that this behavioral change can be very selective. We compared SB produced by continuous amphetamine to SB produced by daily caffeine; the latter has been proposed as an animal model for self-injurious behavior (SIB) in the Lesch-Nyhan syndrome. Subcutaneous silicone pellets containing amphetamine base were implanted for 4.5 days; caffeine was administered daily for 10 days. The amphetamine pellets produced the highest rate of SB (75% vs 40%) with the least toxic effects (no deaths vs three deaths). Neither drug produced stereotypy. The dopamine antagonist haloperidol was only marginally effective in controlling SB produced by daily caffeine but the dopamine antagonist pimozide (which has a longer duration of action) prevented SB by amphetamine pellet rats. Continuous release amphetamine pellets may provide an alternative to the caffeine model of SIB in humans, particularly for the Lesch-Nyhan syndrome.     

Selenium in the anterior pituitary of rats exposed to sodium selenite: light and electron microscopic localization

Metal selenide accumulations were demonstrated in the anterior pituitary of the rat by a histochemical technique at light and electron microscopic levels. After administration of sodium selenite either by drinking water (2.5 to 15 ppm) or by ip injection (5 to 20 mg/kg body wt), intracellular accumulations were found in secretory granules and lysosomes of the somatotrophs, thyrotrophs, corticotrophs, and the gonadotrophs. The amount of countable deposits increased with increasing doses, whether selenite was given in drinking water or by ip injection. Localization of deposits was independent of route of administration. Following a single ip injection of 5 mg sodium selenite/kg, a steadily increasing amount of visible deposits was seen throughout the first week. After this peak the deposits started to decrease but could still be found after 2 weeks. Selenium may possibly create bonds to endogenous zinc in the anterior pituitary as has been suggested for the brain.     

Biphasic effects of chronic nicotine treatment on hypothalamic immunoreactive beta-endorphin in the mouse

Hypothalamic but not pituitary immunoreactive beta-endorphin (beta-E) was significantly reduced (37%) in mice 24 hr following 30 daily doses of nicotine (1200 micrograms/kg, SC). Hypothalamic beta-E returned towards normal levels within 7 days and was observed to rise 50% above normal 14 days after the cessation of nicotine treatment. None of the other neuropeptides measure, substance P, neurotensin, or [met5]-enkephalin was altered by nicotine treatment. The data suggest that the hypothalamic beta-E containing neurons were unable to adapt to nicotine's repeated effects on this system.     

A comparison of hypothalamic cell numbers in dwarf and normal weight rats exposed prenatally to methylazoxymethanol (MAM)

Growth deficiencies follow MAM exposure during the period when the growth hormone releasing factor (GRF) cells of the hypothalamus form, while animals exposed slightly later in gestation when the inhibitors of growth hormone release are forming, exhibit giantism. Counts of sample regions of the hypothalamus have shown that rats treated in utero on the 14th day of gestation have reductions in the number of GRF cells, increases in the number of SRIF (somatotropin release inhibiting factor) cells, and alterations of pituitary structure. These effects occurred in all treated subjects, even though obvious effects on body size were present in a small fraction of the treated animals. The present study was designed to examine the effect of 20 mg/kg MAM on the 13th day of gestation (a peak period for production of GRF cells) on GRF and SRIF cell numbers, in a large sample of dwarf-treated rats, normal weight-treated rats, and controls. The results of total counts of hypothalamic cells identified by immunocytochemistry demonstrated significant reductions in GRF cells in both dwarf and normal weight rats exposed to MAM, compared to controls, with no difference between the two treated groups. Like pituitary weights, the neuron counts were significantly correlated with body weight only in dwarf animals. SRIF cell numbers were equivalent to those in controls, suggesting that the increase reported earlier may have been due to a rebound effect in proliferation rather than some response of SRIF cells to GRF cell reduction. Despite the close relationship between GRF cell number and body weight in dwarfs, the fact that the neuron deficiency was just as great in normal weight treated rats indicates that the change in GRF neuron number does not, in and of itself, account for the growth deficiencies observed in treated animals.     

Influence of testosterone on some behavioral reactions of male immature rats exposed to continual light

Neurosteroids are a perspective group of effectors that can be used to uncover the mechanisms of neurohumoral control underlying behavioral activity and the biological influence of the photoperiodic stimuli that regulate a number of physiological and metabolic processes of most organisms. At present, the achievements made in this area are the beginnings of elucidation of the complex organization of the circaoscillatory systems and signify progress towards an effective hormonal chronotherapy for the future. The present study shows that infusion of testosterone (40 micrograms/100 b.w.) in male immature white rats subject to continual light leads to an increase in horizontal and vertical locomotor activity in an open field study and to weak prolongation of the latency of thermic pain reaction in the tail flick test. The effect of this steroid was studied at 4 and 24 h after infusion. Testosterone stimulates the exploratory motivation and the emotional state of rats adaptive behavior is modulated by altering exogenic photoperiocity thus increasing the entropy of the behavior. The effects of testosterone differ in that they depend on the biorhythmic activity of the organism. This is in agreement with the belief that there is a connection between steroids and the structural and functional plasticity of the central nervous system.     

Formation of methemoglobin by photoactivation of nitrofurantoin or of 5-nitrofurfural in rats exposed to UV-A light

The antibacterial drug nitrofurantoin (NFT) is notorious for causing hemolytic anemia, which may be related to the methemoglobinemia, another side-effect of NFT. As NFT is photolabile, and nitrite, well known as a MetHb generator, is an important photoproduct of NFT, it seems not unlikely that light is a cause of NFT-induced MetHb formation. When rats were irradiated with UV-A immediately after oral NFT administration, the amount of MetHb significantly increased: 0.97 +/- 0.37% n = 36 (P less than 0.001 Student's t-test, control value: 0.5%). An increase in MetHb was also observed with rats simultaneously exposed to UV-A and the major photodecomposition product of NFT, viz. 5-nitrofurfural. In addition in vitro experiments proved the formation of MetHb as a result of photoactivation of NFT. Nitrite, photochemically formed from nitrofurfural and from the metabolite nitrofuroic acid, plays an important role. A dark reaction of the other photoproduct, nitrofurfural, with hemoglobin also appeared to cause a considerable amount of MetHb in vitro. However, because of rapid deactivation of nitrofurfural by either photodecomposition or metabolism, this dark reaction is not expected to contribute to the in vivo MetHb formation.     

Induction of oxidative stress in liver and kidney of rats exposed to Nigerian bonny light crude oil

The local population of Niger‐Delta in the Southern part of Nigeria have used bonny light crude oil (BLCO) as a remedy for various ailments and are exposed to some extent to this widespread environmental contaminant or its metabolites through the food chain. BLCO's hepatorenal toxicity was studied using oxidative stress indices to elucidate the precise nature and mechanism of action. BLCO was orally administered at concentrations of 0, 200, 400, and 800 mg kg^?1 to adult male rats for 7 days. After exposure, kidney weight was unaffected, but liver weight decreased significantly at 800 mg kg^?1 only compared with control. BLCO exposure resulted in dose‐dependent elevation of serum aminotransferases, total bilirubin, urea, and creatinine. Activities of superoxide dismutase and catalase decreased significantly, whereas γ‐glutamyltransferase activity and the level of glutathione increased significantly in BLCO‐treated animals compared with control in both liver and kidney of rat. Renal activities of glucose‐6‐phosphatase and 5′‐nucleotidase markedly decreased in a dose‐dependent manner in BLCO‐exposed rats. In addition, the levels of hydrogen peroxide and lipid peroxidation significantly increased, dose dependently, in liver and kidney of BLCO‐treated rats compared with control. BLCO‐treated rats showed marked degeneration of kidney evident in cortical hemorrhages, tubular necrosis, protein casts, and cellular infiltration. However, no treatment‐related liver histopathology was observed. The results suggested that BLCO elicits disruption of antioxidant status and concomitant elevation of hydrogen peroxide and lipid peroxidation differentially in liver and kidney of rats. The hepatorenal toxicity of BLCO could be due to induction of oxidative stress in liver and kidney. © 2011 Wiley Periodicals, Inc. Environ Toxicol, 2012.     

Elevation of Met5-enkephalin and beta-endorphin hypothalamic content in rats receiving anorectic drugs: differences between D-fenfluramine and D-amphetamine

D-Fenfluramine, an anorectic that releases serotonin (5-HT), repeatedly injected in rats (15 mg/kg per day) enhanced the met5-enkephalin and beta-endorphin content of the hyhpothalamus. The onset of this effect was slow, reaching a peak at 5 days; the increase in beta-endorphin gradually declined toward control level while the drug was still being administered although that of met-enkephalin persisted for 15 days. The elevation of the opioid peptide content of the hypothalamus was temporally associated with a slowing in the rate of body weight increase. A transient, small, increase in striatal met-enkephalin content was also induced by repeated D-fenfluramine injections; however the met-enkephalin content of frontal cortex, hippocampus and brainstem was not affected. A modification of the beta-endorphin content of hypothalamus was not seen after acute injection of D-fenfluramine or D-amphetamine but an increase was observed during repeated treatment with D-fenfluramine. Repeated injections of D-amphetamine for 5 days (4.5 mg/kg per day) failed to increase either the met-enkephalin or the beta-endorphin content of the hypothalamus. These data suggest that the anorexia elicited by repeated injections of D-fenfluramine but not that elicited by D-amphetamine, includes a participation by hypothalamic and beta-endorphin stores.     

NOS II inhibition restores attenuation of endothelium-dependent hyperpolarization in rat mesenteric artery exposed to lipopolysaccharide

The aim of this study was to assess the effects of lipopolysaccharide (LPS) exposure on the endothelium-dependent hyperpolarization in the rat mesenteric artery using isometric tension recordings and electrophysiological studies. Mesenteric arterial rings of male Sprague-Dawley rats were incubated with LPS for 6 hours. All experiments were performed in the presence of indomethacin to inhibit the formation of vasoactive prostanoids. Contraction to phenylephrine was significantly reduced in rings incubated with LPS, which was restored in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME). L-NAME resistant relaxation to acetylcholine was attenuated in LPS-treated rings. LPS exposure hyperpolarized resting membrane potentials of arterial smooth muscle cells, which was repolarized by incubation with either L-NAME or 1400W, a selective inhibitor of nitric oxide synthase II (NOS II). Endothelium-dependent hyperpolarization to acetylcholine was attenuated in arteries incubated with LPS, while incubation with LPS and 1400W restored EDHF-mediated hyperpolarization. LPS-induced membrane potential change was mimicked by incubation with either SIN-1 or diethylamine NONOate, a donor of nitric oxide. These data suggest that LPS exposure attenuates EDHF-mediated both relaxation and hyperpolarization in the rat mesenteric artery. The possible mechanisms underlying decreased EDHF-mediated responses might be due to, at least in some part, massive nitric oxide induced by NOS II.     

Effects of electroacupuncture on beta-endorphin contents in rats

Effects of electroacupuncture (EA) on pain threshold and beta-endorphin (beta-End) contents in plasma, pituitary (Pit), hypothalamus (Hyp) and cerebrospinal fluid (CSF) were studied in nontreated, dexamethasone (Dex) treated and adrenalectomized (Adrex) male SD rats by the use of specific determination of rat beta-End (combination of HPLC and RIA). EA increased pain threshold and plasma beta-End with no effect on beta-End contents in Pit, Hyp and CSF. Dex did not affect control pain threshold, but tended to reduce EA-induced increase in pain threshold (EA-analgesia, EAA) and EA-induced increase in plasma beta-End. Adrex increased plasma beta-End without change in control pain threshold. Adrex tended to reduce EAA, but a tendency of further increase in plasma beta-End was observed after addition of EA. Adrex increased Pit beta-End, but no further change in Pit beta-End was observed after addition of EA. A positive correlation between plasma beta-End and plasma ACTH was observed in nontreated, Dex treated and Adrex rats. No correlation between plasma beta-End and potency of EAA was observed in nontreated, Dex treated and Adrex rats. The hind-paw pressure test without EA increased plasma beta-End to the same degree as that produced by EA, and it produced no analgesia. These results suggest that Pit beta-End may not be mainly involved in the development of EAA.     

Different pattern of changes in calcium binding proteins immunoreactivity in the medial prefrontal cortex of rats exposed to stress models of depression

Reductions in the number and size of neurons in the medial prefrontal cortex (mPFC) have been documented in many post-mortem studies of depressed patients and animals exposed to stress. Here, we examined the effect of chronic unpredictable stress (CUS) and chronic mild stress (CMS) on specific populations of neurons in the rat mPFC. Antibodies directed against parvalbumin (PV), calbindin D-28K (CB) and active caspase-3 have been used to quantify the numerical density of PV-immunoreactive (PV-ir), CB-ir and active caspase-3-ir cells, and to measure the relative optical density of neuropil. CUS decreased the density of CB-ir neurons and the optical density of CB-ir neuropil. In turn, CMS increased the densities of both CB-ir neurons and neuropil, while PV-ir neurons and PV-ir neuropil were not changed. The frequency distribution of neuronal surface areas was significantly different only for PV-ir neurons, and only between the control and CUS group. CMS reduced the density of active caspase-3-ir cells while CUS did not. We concluded that the mPFC reveals a different pattern of changes in neurons containing calcium binding proteins and active caspase-3 immunoreactivity in response to CUS and CMS.     

Delayed response to 2-deoxy-D-glucose in hypothalamic obese rats

A dose-response relationship for the effects of 2-deoxy-D-glucose (2-DG) (0-400 mg/kg) on food intake was established in normal and obese ventromedial hypothalamic lesioned rats. In normal animals the lowest dose that produced a statistically signififant increase over baseline food intake was 100 mg/kg 2-DG. Larger doses produced a progressively greater effect. Most of the increase in food intake occurred during the first hour after the injection of 2-DG, the latency of the first feeding bout being shorter for higher doses of the compound. Obese VMH rats significantly increased their 4-hr food intake after 150, 200, and 250, and 400 mg/kg 2-DG, but the increase in feeding was delayed compared to control animals. During the first hour after the injection, the food intake of obese rats was unaffected by doses of 2-DG up to 250 mg/kg, and inhibited by higher doses (300 and 400 mg/kg). The effects of VMH lesions on 2-DG-induced eating are attributed to the elimination of afferents from peripheral glucoreceptors.     

Desenkephalin-gamma-endorphin restores the impaired sensitivity of hypophysectomized rats to small doses of apomorphine

Hypophysectomized male rats, tested 7 days after removal of the pituitary, showed a reduced sensitivity to small doses of apomorphine. In these rats, subcutaneous (s.c.) treatment with apomorphine (25, 100 or 250 micrograms/kg) did not elicit any reduction in locomotor activity measured 5 min after injection in contrast to that observed in sham-operated control rats. The enhancement of locomotor activity and stereotyped behavior, 20 min after the s.c. administration of apomorphine, was similar in hypophysectomized rats and in control animals. Prolactin does not seem to be implicated in this altered sensitivity, since hyperprolactinaemia induced by pituitary homografts under the kidney capsule did not change the response to apomorphine in hypophysectomized rats. Chronic treatment with desenkephalin-gamma-endorphin (DE gamma E), a beta-endorphin fragment with neuroleptic-like properties, administered s.c. twice a day for 7 days at the dose of 10 micrograms/rat, restored the sensitivity to small doses of apomorphine in the hypophysectomized rats. The data suggest that removal of the pituitary leads to impaired sensitivity of presumably presynaptically located dopamine receptors mediating the effects of small doses of apomorphine without altering the sensitivity of postsynaptically located dopamine receptors that mediate the hypermotility and stereotypy induced by apomorphine. This impaired sensitivity to low doses of apomorphine could be restored by DE gamma E but not by prolactin, supporting the conclusions from previous experiments that DE gamma E and prolactin may selectively interfere with pre- and postsynaptic dopamine receptors respectively.     

Mediation of beta-endorphin by the isoflavone puerarin to lower plasma glucose in streptozotocin-induced diabetic rats

We investigate the mechanism(s) of plasma glucose lowering action of puerarin in streptozotocin-induced diabetic rats (STZ-diabetic rats). Puerarin at the effective dosage to lower higher plasma glucose increased plasma beta-endorphin-like immunoreactivity (BER) in STZ-diabetic rats. Both effects of puerarin were abolished by the pretreatment with prazosin. Also, puerarin enhanced BER release from isolated rat adrenal medulla in a concentration-dependent manner that can be abolished by prazosin. Moreover, bilateral adrenalectomy in STZ-diabetic rats eliminated the actions of puerarin including the plasma glucose lowering effect and plasma BER elevating effect. In addition, naloxone and naloxonazine inhibited the plasma glucose lowering action of puerarin. Unlike in wild-type diabetic mice, puerarin failed to lower the plasma glucose in opioid micro-receptor knockout diabetic mice. In conclusion, our results suggest that puerarin may activate alpha (1)-adrenoceptors on the adrenal gland to enhance the secretion of beta-endorphin to result in a decrease of plasma glucose in STZ-diabetic rats.     

Maze learning in rats exposed to xylene intoxication

Summary In their neurotropic intoxication research work the authors made an application of maze technique so as to complement other test procedures. Rats were given small doses of xylene to bring about a subacute intoxication. When established, this intoxication was found to cause a set-back in learning and a lability in realizing skill acquired under developing xylene effect while it did not interfere with crystallized, well-trained stereotypes of behaviour.     

Nitrate formation in rats exposed to nitrogen dioxide

Sprague-Dawley rats exposed to atmospheres containing low levels of nitrogen dioxide (NO₂) for 24 hr had increased levels of nitrate in their urine on the day of exposure and on the 3 subsequent days. The total increase in urinary nitrate was linearly related to the nitrogen dioxide concentration administered. We recovered in urine 8.4 ± 1.1 μmol nitrate/ppm $\text{NO}{}_2\text{24}\text{-hr}$ exposure (slope ± 95% confidence limits) for 185-g rats. Both the linearity and magnitude of this effect imply that reaction with respiratory tract water is not a major pathway of NO₂ absorption in the lung. Instead, our observations support the hypothesis that the major interaction of NO₂ in the lung is with readily oxidizable tissue components to form nitrite. We estimate that 9.6 μmol of nitrite is formed in the respiratory tract of the rat per ppm NO₂ per 24-hr exposure. We also estimate that humans breathing air containing 0.1 ppm NO₂ have about 3.6 mg of nitrite formed in their respiratory tract per day.     

Neurofunctional effects in rats prenatally exposed to fluoxetine

In the treatment of depression fluoxetine [a selective serotonine reuptake inhibitor (SSRIs)] is a widely used drug in humans. The selectivity, efficacy, side effects and simplicity of dosage contributed to fluoxetine's clinical acceptance. Several psychiatric disorders (many of them responsive to SSRIs) are present during pregnancy; up to 10% of pregnant women fulfill diagnostic criteria for major or minor depression with an even higher percentage developing postpartum depression. Therefore, significant numbers of women may be taking SSRIs while pregnant. Since fluoxetine's safe use during pregnancy is not yet established and experimental studies inconclusive, we performed the present research in order to investigate the neurobehavioral effects produced in rats by prenatal exposure to fluoxetine (5 and 10 mg/kg/sc from day 13 to 20 of gestation) on cognitive functions, emotional reactivity and sexual performance.