Effects of Aging and Amyloid-β Peptides on Choline Acetyltransferase Activity in Rat Brain

Choline acetyltransferase (ChAT, acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6), involved in the learning and memory processes is responsible for the synthesis of acetylcholine. There are many discrepancies in literature concerning ChAT activity during brain aging and the role of amyloid beta peptides in modulation of this enzyme. The aim of the study was to investigate the mechanism of ChAT regulation and age-related alteration of ChAT activity in different parts of the brain. Moreover the effect of A peptides on ChAT activity in adult and aged brain was investigated. The enzyme activity was determined in the brain cortex, hippocampus and striatum in adult (4-months-old), adult-aged (14-months-old) and aged (24-months-old) animals. The highest ChAT activity was observed in the striatum. We found that inhibitors of protein kinase C, A, G and phosphatase A2 have no effect on ChAT activity and that this enzyme is not dependent on calcium ions. About 70% of the total ChAT activity is present in the cytosol. Arachidonic acid significantly inhibited cytosolic form of this enzyme. In the brain cortex and striatum from aged brain ChAT activity is inhibited by 50% and 37%, respectively. The aggregated form of A 25-35 decreased significantly ChAT activity only in the aged striatum and exerted inhibitory effect on this enzyme in adult, however, statistically insignificant. ChAT activity in the striatum was diminished after exposure to 1 mM H₂O₂. The results from our study indicate that aging processes play a major role in inhibition of ChAT activity and that this enzyme in striatum is selectively sensitive for amyloid beta peptides.     

Effects of Starvation on Normal Development of β-Hydroxybutyrate Dehydrogenase Activity in Foetal and Newborn Rat Brain

THE mitochondrial enzyme β-hydroxybutyrate dehydrogenase (BDH) catalyses the conversion of β-hydroxybutyrate to acetoacetate, with the subsequent production of three molecules of adenosine triphosphate for every molecule of β-hydroxybutyrate oxidized. Recent evidence suggests that this energy-yielding reaction is important for maintaining the metabolism of the brain when the supply of glucose is chronically depleted. Owen et al.¹ demonstrated that β-hydroxybutyrate and acetoacetate become the principal sources of energy for the brain in humans subjected to prolonged starvation. The transition from glucose to ketones as the primary substrate for oxidative metabolism in the central nervous system occurs without demonstrable cerebral dysfunction¹.     

Effects of Sulpiride on Prolactin and mRNA Levels of Steroid 5α-reductase Isozymes in Adult Rat Brain

Prolactin (PRL) promotes maternal behavior (MB), a complex pattern of behavior aimed at maximizing offspring survival. 3α,5α-reduced neurosteroids may also regulate MB. Indeed, PRL, 3α,5α-reduced neurosteroids, and 5α-reductase (5α-R), the key enzyme in the biosynthesis of these neuroactive steroids, are all increased in stress situations These facts led us to hypothesize a possible interrelation between PRL levels and 5α-R. In the present study we quantified mRNA levels of both 5α-R isozymes in prefrontal cortex of male and female rats after administration of sulpiride, an inductor of PRL secretion. Our results demonstrated that mRNA levels of both 5α-R isozymes were significantly increased in male and female rats by sulpiride, directly or via sulpiride-induced hyperprolactinemia. Since 3α,5α-reduced neurosteroids and PRL exert anxiolytic effects in response to stress, these molecules and 5α-R may possibly participate in a common pathway of significant adaptation to stress situations.     

Effects of Dihydrotestosterone on Brain mRNA Levels of Steroid 5α-Reductase Isozymes in Early Postnatal Life of Rat

We studied the expression of type 1 (5α-R1) and type 2 (5α-R2) 5α-reductase isozymes (5α-R) and their regulation by dihydrotestosterone (DHT) in the prefrontal cortex of male and female rats during postnatal sexual differentiation of the central nervous system (CNS), using one-step quantitative RT-PCR coupled with laser-induced fluorescence capillary electrophoresis. We found a higher expression of 5α-R2, which is considered a masculinizing enzyme, in the female versus male CNS, and observed sexual dimorphism in the regulation of both 5α-R isozymes by DHT. These results open up a new research line that could improve understanding of the role of 5α-R isozymes in the physiology of the CNS.     

Steroid 5α-Reductase in Adult Rat Brain After Neonatal Dihydrotestosterone Administration

Testosterone (T) is known to play an important masculinizing role in the developing brain of rat, including the regulation of 5α-reductase (5α-R) isozymes. However, the effects of dihydrotesterone (DHT), a more potent androgen than T, have not been elucidated. In this study, DHT was administered from day 5 through day 20 of postnatal life (period of postnatal sexual differentiation of the central nervous system) at doses of: 12 mg/kg/d on days 5, 6, 7, 8, 19, and 20; 15 mg/kg/d on days 9, 10, 11, 12, 16, 17, and 18; and 18 mg/kg/d on days 13, 14, and 15. In adulthood, quantitative RT-PCR was used to measure mRNA levels of 5α-R1 and 5α-R2 isozymes in the prefrontal cortex (PFC) of male and female rats with varied androgenic status. Under our study conditions, neonatal DHT administration influenced on adult PFC 5α-R isozymes levels and their regulation pattern by androgens, and this pattern was the inverse of that reported in adult neonatally T-treated rats.     

Fast Pseudo-Periodic Oscillation in the Rat Brain Voltage-gated Sodium Channel α Subunit

In the work reported here, we have investigated the changes in the activation and fast inactivation properties of the rat brain voltage-gated sodium channel (rNa_v 1.2a) α subunit, expressed heterologously in the Chinese Hamster Ovary (CHO) cells, by short depolarizing prepulses (10 – 1000 ms). The time constant of recovery from fast inactivation (τ_fast) and steady-state parameters for activation and inactivation varied in a pseudo-oscillatory fashion with the duration and amplitude of a sustained prepulse. A consistent oscillation was observed in most of the steady-state and non-inactivating current parameters with a time period close to 225 ms, although a faster oscillation of time period 125 ms was observed in the τ_fast. The studies on the non-inactivating current and steady-state activation indicate that the phase of oscillation varies from cell to cell. Co-expression of the β1 subunit with the α subunit channel suppressed the oscillation in the charge movement per single channel and free energy of steady-state inactivation, although the oscillation in the half steady-state inactivation potential remained unaltered. Incidentally, the frequencies of oscillation in the sodium channel parameters (4–8 Hz) correspond to the theta component of network oscillation. This fast pseudo-oscillatory mechanism, together with the slow pseudo-oscillatory mechanism found in these channels earlier, may contribute to the oscillations in the firing properties observed in various neuronal subtypes and many pathological conditions.     

Effects of (−)-Sesamin on Chronic Stress-Induced Anxiety Disorders in Mice

This study investigated the effects of (?)-sesamin on chronic electric footshock (EF) stress-induced anxiety disorders in mice. Mice were treated with (?)-sesamin (25 and 50 mg/kg) orally once a day for 21 days prior to exposure to EF stress (0.6 mA, 1 s every 5 s, 3 min). Mice treated with (?)-sesamin (25 and 50 mg/kg) exhibited less severe decreases in the number of open arm entries and time spent on open arms in the elevated plus-maze test and the distance traveled in the open field test following exposure to chronic EF stress. Similarly, mice treated with (?)-sesamin exhibited significantly less severe decreases in brain levels of dopamine, norepinephrine, and serotonin following exposure to chronic EF stress. Increases in serum levels of corticosterone and expression of c-Fos were also less pronounced in mice treated with (?)-sesamin (25 and 50 mg/kg). These results suggest that (?)-sesamin may protect against the effects of chronic EF stress-induced anxiety disorders by modulating dopamine, norepinephrine, and serotonin levels, c-Fos expression, and corticosterone levels.     

Effects of Chronic Stress and Phenytoin on the Long-term Potentiation （LTP） in Rat Hippocampal CA1 Region

Stress is the response to stimulation from inside andoutside with complicated effects on organisms. Appropri-ate stressful reactions are helpful in resisting diseases byactivating unspecific modulation system, while severe orprolonged stresses are harmful and even induce mentaland physical disorders such as recurrent depression, post-traumatic stress disorder (PTSD), Alzheimer’s disease andepilepsy [1]. Hippocampus, a main brain region of keyimportance for learning, memory and emotion, is t…     

Effects of α-Tocopherol on Carbon Tetrachloride Metabolism in Rat Liver Microsomes

α-tocopherol is the major lipid-soluble radical-scavenging antioxidant in rat liver. It has long been used as a putative protective agent in CC1₄ induced liver injury but with variable results. We have used a-tocopherol loaded rat liver microsomes to study the effect of this vitamin on CC1₄ metabolism in vitro. As expected, a-tocopherol inhibits CC1₄-dependent microsomal lipid peroxidation and, at a very high concentration, will inhibit the covalent binding of CC1,- to microsomal protein by up to 50%. No inhibitory effect was observed towards CC1₃ production as measured by the electron spin resonance technique of spin-trapping but this apparent discrepancy may represent a limitation of the technique. The high levels required to inhibit covalent binding probably preclude the likelihood of a-tocopherol significantly affecting that phenomenon at endogenous concentrations but may be relevant to other experiments employing high doses of a-tocopherol as an experimental hepatoprotective agent.     

Effects of Aluminium on β-Amyloid (1–42) and Secretases (APP-Cleaving Enzymes) in Rat Brain

Chronic administration of aluminium has been proposed as an environmental factor that may affect some pathological changes related to neurotoxicity and Alzheimer’s disease (AD). The abnormal generation and deposition of β-amyloid (Aβ) in senile plaques are hallmark features in the brains of AD patients. Furthermore, Aβ is generated by the sequential cleavage of the amyloid precursor protein (APP) via the APP cleaving enzyme (α-secretase, or β-secretase) and γ-secretase. In the present study, we investigated the modulation of Aβ deposition and neurotoxicity in aluminium-maltolate-treated (0, 15, 30, 45 mmol/kg body weight via intraperitoneal injection) in experimental rats. We measured Aβ1–40 and Aβ1–42 in the cortex and hippocampus in rat brains using ELISA. Subtypes of α-secretase, β-secretase, and γ-secretase, including ADAM9, ADAM10, ADAM17 (TACE), BACE1, presenilin 1 (PS1) and nicastrin (NCT), were determined using western blotting analyses. These results indicated that aluminium-maltolate induced an AD-like behavioural deficit in rats at 30 and 45 mmol/kg body weight. Moreover, the Aβ1–42 content increased significantly, both in the cortex and hippocampus, although no changes were observed in Aβ1–40. Furthermore, ADAM9, ADAM10, and ADAM17 decreased significantly; in contrast, BACE1, PS1, and NCT showed significant increase. Taken together, these results suggest that the changes in secretases may correlate to the abnormal deposition of Aβ by aluminium in rat brains.     

Effects of α lipoic acid on noise induced oxidative stress in rats

This study was conducted to identify how exposure to ambient noise that is over 75 dB affects the oxidant-antioxidant profile using hematological and biochemical indicators, and to investigate the effects of a strong and current antioxidant, $\alpha$ lipoic acid, on rats that were subjected to noise stress. For this purpose, five groups of eight rats were formed as follows: Control (K), Noise Exposure (GK), Lipoic Acid (LA), Noise Pollution + $\alpha$Lipoic Acid (GK + LA) and Oil (Y). The blood samples collected from rats were analyzed and MDA (malondialdehyde), GSH (glutathione), SOD (superoxide dismutase), CAT (catalase), NO (nitrit oxide), GPx (glutathione peroxidase), leukocytes, monocytes, lymphocytes, erythrocytes, hemoglobin, hematocrit, glucose, cholesterol, total protein, triglycerides, HDL (high density lipoprotein), LDL (low density lipoprotein), and urea-N levels were measured. The physical factory environment in a textile factory was preferred to simulate the noise exposure. Ambient noise was measured to be 75 dB. Exposure to physical ambient noise was sustained for 30 days. MDA level was measured at the lowest level in the LA and GKLA groups while it was statistically significantly higher in other groups than it was in the control group. It was observed that GSH reached its lowest level in the group that was exposed to noisy environment, the 100 mg/kg/day $\alpha$lipoic acid administered on the experimental model increased this level to that of the control group and this change was statistically significant (p < 0.05). Considering the urea levels, the increases in GK and GKLA groups and the decreases in LA and Y groups were observed to be statistically significant. When glucose levels were compared to the control group, they were found to be statistically significantly lower in all groups. As a result, it was observed that exposure to noise for 30 days was likely to lead to leukocyte-based immune deficiency and using $\alpha$ lipoic acid as an antioxidant might provide a significant protection against the noise stress.     

The Effects of Chromium Picolinate and Chromium Histidinate Administration on NF-κB and Nrf2/HO-1 Pathway in the Brain of Diabetic Rats

The objective of this experiment was to investigate the effects of supplemental chromium picolinate (CrPic) and chromium histidinate (CrHis) on nuclear factor-kappa B (NF-??B p65) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway in diabetic rat brain. Nondiabetic (n?=?45) and diabetic (n?=?45) male Wistar rats were either not supplemented or supplemented with CrPic or CrHis via drinking water to consume 8???g elemental chromium (Cr) per day for 12?weeks. Diabetes was induced by streptozotocin injection (40?mg/kg i.p., for 2?weeks) and maintained by high-fat feeding (40?%). Diabetes was associated with increases in cerebral NF-??B and 4-hydroxynonenal (4-HNE) protein adducts and decreased in cerebral nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha (I??B??) and Nrf2 levels. Both Cr chelates were effective to decrease levels of NF-??B and 4-HNE protein adducts and to increase levels of I??B?? and Nrf2 in the brain of diabetic rats. However, responses of these increases and decreases were more notable when Cr was supplemented as CrHis than as CrPic. In conclusion, Cr may play a protective role in cerebral antioxidant defense system in diabetic subjects via the Nrf2 pathway by reducing inflammation through NF-??B p65 inhibition. Histidinate form of Cr was superior to picolinate form of Cr in reducing NF-??B expression and increasing Nrf2 expression in the brain of diabetic rats.     

Time-Course of Brain Oxidative Damage Caused by Intrastriatal Administration of 6-Hydroxydopamine in a Rat Model of Parkinson’s Disease

The unilateral and intrastriatal injection of 6-hydroxydopamine is commonly used to provide a partial lesion model of Parkinson’s disease in the investigation of the molecular mechanisms involved in its pathogenesis and to assess new neuroprotective treatments. Its capacity to induce neurodegeneration has been related to its ability to undergo autoxidation in the presence of oxygen and consequently to generate oxidative stress. The aim of the present study was to investigate the time course of brain oxidative damage induced by 6-hydroxydopamine (6 μg in 5 μl of sterile saline containing 0.2% ascorbic acid) injection in the right striatum of the rat. The results of this study show that the indices of both lipid peroxidation (TBARS) and protein oxidation (carbonyl and free thiol contents) increase simultaneously in the ipsilateral striatum and ventral midbrain, reaching a peak value at 48-h post-injection for both TBARS and protein carbonyl content, and at 24 h for protein free thiol content. A lower but significant increase was also observed in the contralateral side (striatum and ventral midbrain). The indices of oxidative stress returned to values close to those found in controls at 7-day post-injection. These data show that the oxidative stress is a possible triggering factor for the neurodegenerative process and the retrograde neurodegeneration observed after 1-week post-injection is a consequence of the cell damage caused during the first days post-injection. The optimal time to assess brain indices of oxidative stress in this model is 48-h post-injection.     

Excitotoxicity in Rat’s Brain Induced by Exposure of Manganese and Neuroprotective Effects of Pinacidil and Nimodipine

Manganese (Mn) is an essential trace element for humans. However, manganism would be caused by excessive Mn. The mechanisms underlying excitotoxicity induced by manganism are poorly understood. As it is known to us, glutamate (Glu) is the most prevalent excitatory neurotransmitter. To determine the possible role of dysfunction of Glu transportation and metabolism in Mn-induced excitotoxicity, the rats were ip injected with different dose of MnCl₂ (0, 50, 100, and 200 μmol/kg), the levels of Mn and activities of GS, PAG, Na⁺-K⁺-ATPase, and Ca²⁺-ATPase in striatum were investigated. In addition, effect of 20.38 μmol/kg pinacidil (K⁺ channel opener) or 2.4 μmol/kg nimodipine (Ca²⁺ channel blocker) were studied at 200 μmol/kg MnCl₂. With dose-dependent inhibition of GS, Na⁺-K⁺-ATPase, and Ca²⁺-ATPase activities, increase of Mn levels and PAG activity were observed. Further investigation indicated that pre-treatment of pinacidil or nimodipine reversed toxic effect of MnCl₂ significantly. These results suggested that MnCl₂ could induce dysfunction of Glu transportation and metabolism by augmenting the excitotoxicity dose-dependently; pinacidil and nimodipine might antagonize manganese neurotoxicity.     

In Vitro Effects of Environmentally Relevant Polybrominated Diphenyl Ether (PBDE) Congeners on Calcium Buffering Mechanisms in Rat Brain

Polybrominated diphenyl ethers (PBDEs) are widely used as additive flame-retardants and have been detected in human blood, adipose tissue, and breast milk. Developmental and long-term exposures to these chemicals may pose a human health risk, especially to children. We have previously demonstrated that polychlorinated biphenyls (PCBs), which are structurally similar to PBDEs and cause neurotoxicity, perturb intracellular signaling events including calcium homeostasis and protein kinase C translocation, which are critical for neuronal function and development of the nervous system. The objective of the present study was to test whether environmentally relevant PBDE congeners 47 and 99 are also capable of disrupting Ca^{2 +} homeostasis. Calcium buffering was determined by measuring ⁴⁵Ca^{2 +} -uptake by microsomes and mitochondria, isolated from adult male rat brain (frontal cortex, cerebellum, hippocampus, and hypothalamus). Results show that PBDEs 47 and 99 inhibit both microsomal and mitochondrial ⁴⁵Ca^{2 +} -uptake in a concentration-dependent manner. The effect of these congeners on ⁴⁵Ca^{2 +} -uptake is similar in all four brain regions though the hypothalamus seems to be slightly more sensitive. Among the two preparations, the congeners inhibited ⁴⁵Ca^{2 +} -uptake in mitochondria to a greater extent than in microsomes. These results indicate that PBDE 47 and PBDE 99 congeners perturb calcium signaling in rat brain in a manner similar to PCB congeners, suggesting a common mode of action of these persistent organic pollutants. The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory of the US Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use. These results will be presented at the 21th Biennial Meeting of International Society for Neurochemistry and American Society for Neurochemistry in Cancun, Mexico (August 19–24, 2007). Special issue article in honor of Dr. Frode Fonnum.     

Effects of Glucose, Insulin, and Supernatant from Pancreatic β-cells on Brain–Pancreas Relative Protein in Rat Hippocampus

Brain–pancreas relative protein (BPRP) is a novel protein that mainly expresses in brain and pancreas. In our previous study, we found that various stressors significantly decreased the expression of BPRP in pancreas in vivo, accompanied by changes in insulin and glucose levels, and that expression of BPRP in pancreas also decreased significantly in diabetic rats induced by Streptozocin (STZ). All these findings suggest that BPRP may be a glucose or insulin-sensitive protein. However, how the changes in insulin or glucose levels influence the expression of BPRP in hippocampus requires further study. Here, we investigated the effects of insulin or glucose on the expression of BPRP in primary cultured hippocampal neurons. We supplied hippocampal neurons with glucose, insulin, or supernatant from pancreatic β-cells, which secrete insulin into the supernatant. Our data showed that insulin had beneficial effect on the viability while no significant effect on the expression of BPRP in hippocampal neurons. On the contrary, 40 mM glucose or free glucose culture significantly decreased the expression of BPRP, while had no significant effect on the viability and apoptosis of hippocampal neurons. Further study showed that levels of insulin in the supernatant collected from pancreatic β-cells medium changed over days, and that supernatant increased the viability of hippocampal neurons, while it had no obvious effect on the expression of BPRP in hippocampal neurons. These results suggest that BPRP may be a glucose-sensitive protein.