Improving effect of acetylcholine receptor agonists on a deficit of 2-deoxyglucose uptake in cerebral cortical and hippocampal slices in aged and AF64A-treated rats

Therapeutic Value ofHippophae rhamnoidesL. Against Subchronic Arsenic Toxicity in Mice

The present study was planned to investigate the therapeutic efficacy of Hippophae rhamnoides L. against the toxic effects of arsenic in mice. H. rhamnoides L. is used as an herbal remedy for gastric ulcers, burns, and some skin and allergic diseases. Twenty-five Swiss albino mice were exposed to arsenic (25 ppm) in drinking water for 3 months. After 3 months different fruit extracts of H. rhamnoides L. (500 mg/kg for 10 days) were administered, the animals were sacrificed, and blood and tissues were assayed for various biochemical indicators of oxidative stress and whether arsenic was removed from tissues. Treatment with different fruit extracts of H. rhamnoides L. showed significant protection from arsenic inhibition of blood delta-aminolevulinic acid dehydratase activity and restored blood reduced glutathione levels. Other hematologic variables like white blood cell counts, hemoglobin, and hematocrit were partially protected by supplementation with a water extract of H. rhamnoides L. (HF-WRT). Significant protection was also observed in altered hepatic, renal, and brain reduced/ oxidized glutathione ratio and thiobarbituric acid-reactive substances levels. The aqueous extract of H. rhamnoides L. (HF-WRT) also provided protection against parameters indicative of liver injury such as aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities. There was also no effect on blood and tissue arsenic concentrations observed except some moderate depletion of blood arsenic concentrations, suggesting that the drug has no ability to chelate intracellular arsenic. It can be concluded from these results that post-treatment with an aqueous extract of H. rhamnoides L. (HF-WRT) significantly protects against arsenic-induced oxidative stress but does not chelate arsenic, suggesting it may have a beneficial role as a supplementing agent during chelation of arsenic by other means.

In vitro and in vivo studies investigating possible antioxidant actions of nicotine: relevance to Parkinson's and Alzheimer's diseases

An inverse relationship appears to exist between cigarette smoking and the risk of Parkinson's and Alzheimer's diseases. Since both diseases are characterized by enhanced oxidative stress, we investigated the antioxidant potential of nicotine, a primary component of cigarette smoke. Initial chromatographic studies suggest that nicotine can affect the formation of the neurotoxin 6-hydroxydopamine resulting from the addition of dopamine to Fenton's reagent (i.e., Fe2+ and H2O2). Thus, under certain circumstances, nicotine can strongly affect the course of the Fenton reaction. In in vivo studies, adult male rats being treated with nicotine showed greater memory retention than controls in a water maze task. However, neurochemical analysis of neocortex, hippocampus, and neostriatum from these same animals revealed that nicotine treatment had no effect on the formation of reactive oxygen species or on lipid peroxidation for any brain region studied. In an in vitro study, addition of various concentrations of nicotine to rat neocortical homogenates had no effect on lipid peroxidation compared to saline controls. The results of these studies suggest that the beneficial/protective effects of nicotine in both Parkinson's disease and Alzheimer's disease may be, at least partly, due to antioxidant mechanisms.

M1 muscarinic receptor stimulation decreases aspartate release in the rat neostriatum

This study investigates the effects of different muscarinic receptor agonists on extracellular glutamate and aspartate concentrations in the rat neostriatum. In vivo intracerebral perfusions were undertaken in the conscious rat using a concentric push-pull cannulae system. Amino acid concentrations in samples were determined by HPLC with fluorometric detection. The intrastriatal perfusion of arecoline, a M1-M2 muscarinic receptor agonist, produced a significant decrease in extracellular [ASP] (45% of decrease) but not in extracellular [GLU]. These effects were blocked by scopolamine, a M1-M2 muscarinic receptor antagonist. McN-A-343, a M1 muscarinic receptor agonist, but not the M2 muscarinic receptor agonist, oxotremorine, produced a significant decrease in extracellular [ASP] (40% of decrease) but not in extracellular [GLU]. The effects of McN-A-343 on extracellular [ASP] were blocked by pirenzepine, a M1 muscarinic receptor antagonist. These results suggest that the decrease in extracellular [ASP] could be mediated, at least in part, by M1 muscarinic receptor activation in the rat neostriatum.

M1 acetylcholine receptor stimulation increases the extracellular concentrations of glutamate and GABA in the medial prefrontal cortex of the rat

The present study was undertaken to examine the effects of different muscarinic receptor agonists on glutamate and GABA concentrations in the medial prefrontal cortex of the rat. In vivo perfusions were made in the conscious rat using a concentric push-pull cannulae system. Amino acid concentrations in samples were determined by HPLC with fluorometric detection. The intracortical perfusion of arecoline, a M1-M2 muscarinic receptor agonist, produced a significant increase in extracellular [GLU] and [GABA]. McN-A-343, a M1 muscarinic receptor agonist, but not the M2 muscarinic receptor agonist, oxotremorine, produced a significant increase in extracellular [GLU] and [GABA]. The effects of McN-A-343 on extracellular [GLU] and [GABA] were blocked by pirenzepine, a M1 muscarinic receptor antagonist. These results suggest that M1 muscarinic receptor stimulation increases the extracellular concentrations of GLU and GABA in the medial prefrontal cortex of the rat.

Chronic nicotine treatment prevents neuronal loss in neocortex resulting from nucleus basalis lesions in young adult and aged rats

In both young adult and aged rats, we tested the ability of chronically administered nicotine to rescue neocortical neurons from transneuronal degeneration resulting 5 mo after ibotenic acid (IBO) lesioning of the nucleus basalis magnocellularis (NBM). Young adult (2-3 mo-old) and aged (20-22-mo-old) rats were given unilateral infusions of IBO (5 mu g/1 mu L) at two sites within the NBM. Following surgery, animals began receiving either daily ip injections of nicotine (0.2 mg/kg) or saline vehicle. Treatment continued for 5 mo, at which time all animals were sacrificed and their brains processed histologically. For each brain, computer-assisted image analysis was then used to analyze the unlesioned (left) and lesioned (right) side of five non-consecutive brain sections from parietal cortex Layers II-IV and V. NBM lesioning in both young adult and aged vehicle-treated rats resulted in a significant 16-21% neuronal loss ipsilateral to NBM lesioning in neocortical Layers II-IV. Aged NBM-lesioned rats also exhibited a significant 12% neuronal loss in neocortical Layer V ipsilaterally. By contrast, those NBM-lesioned young adult and aged rats that received daily nicotine treatment postsurgery did not show any ipsilateral neuronal loss in the same parietal cortex areas, indicating that chronic nicotine treatment prevented the transneuronal degeneration of neocortical neurons resulting 5 mo afer NBM lesioning.

Nicotine enhances Morris water maze performance of young and aged rats

We have recently demonstrated that nicotine administration improves the acquisition and/or memory retention of aged rats in 17-arm radial maze, Lashley III maze, and one-way active avoidance testing. The present study extends our evaluation of nicotine's cognition-enhancing potential by determining the effect of nicotine on acquisition and retention of the Morris water maze in young adult (2 to 3 months old) and aged (25 to 26 months old) Sprague-Dawley rats. For 3 days prior to the onset of testing, and 15 min prior to daily testing, rats were treated IP with 0.2 mg/kg nicotine or saline vehicle. Compared to the performance of young adults, vehicle-treated aged rats were impaired in water maze acquisition. Nicotine substantially enhanced the acquisition of aged rats. Furthermore, nicotine significantly improved the memory retention of young adult rats. These cognitive improvements may involve a nicotine-receptor induced increase in generalized alertness and/or a facilitation of higher integrative function. The results suggest that nicotine and/or nicotinic agonists may be useful in treating age-associated memory impairment and/or Alzheimer's disease.

Facilitatory effect of olfactory bulbectomy on 2-deoxyglucose uptake in rat amygdala slices

The aim of the present study was to determine whether the 2-deoxyglucose uptake of amygdala slices was affected by olfactory bulbectomy. At 7, 14 and 21 days post-lesion, bilateral olfactory bulbectomized rats exhibited a significant increase of 2-deoxyglucose uptake in amygdala slices, but not in the cerebral cortex. In addition, unilateral olfactory bulbectomized rats showed a high uptake of 2-deoxyglucose uptake in the ipsilateral amygdala, but not in the contralateral amygdala. These results suggest that the enhancement of 2-deoxyglucose uptake is related to the hyperexcitability of amygdala neurons following bulbectomy, and that this enhancement may be responsible for the behavioral changes in olfactory bulbectomized rats.

Facilitatory effects of somatostatin on reduced uptake of 2-deoxyglucose in cerebral cortical and hippocampal slices from aged rats

The aim of the present study was to determine whether or not the reduction of 2-deoxyglucose uptake by the cerebral cortical slices in aged rats (22-23 months old) was attenuated by somatostatin or carbachol. In 8-week-old rats, somatostatin and carbachol produced concentration-dependent increases in 2-deoxyglucose uptake. 2-Deoxyglucose uptake of the cortical slices in 22-23-month-old rats was significantly facilitated by treatment with 0.1-1 microM somatostatin or 1-100 microM carbachol. Metabolic responses to somatostatin or carbachol were quite similar in young and aged rats. The present results demonstrated that 2-deoxyglucose uptake by the cerebral cortex was facilitated by somatostatin and carbachol in both young and old rats.

Age-related impairment of food anticipatory locomotor activity in rats

In rats of various ages (11 weeks to 24 months), restricted feeding was carried for 6 successive days and food was withheld completely on the 7th day to assess the effect of aging on food anticipatory activity. When feeding was restricted to a single meal at a fixed time of day (1330-1730), rats exhibited intense locomotor activity from 1-3 h before feeding time (prefeeding activity). This prefeeding activity was still detected on the fasting day. In addition, intense locomotor activity was observed for 1330-1730 even on the fasting day (mealtime-associated activity). Thus, mealtime-associated activity of the fasting day became an another good index for food anticipatory activity. These results indicate that the rats had come to anticipate the mealtime. Both prefeeding and mealtime-associated activities were similar at 11 weeks and 9 months of age, but they were impaired at 12 and 24 months of age. In 11-week-old rats, there was a negative correlation between the level of mealtime-associated activity and the daily duration of access to food, but this relationship was absent in 12-month-old rats. The present study suggests that aging strongly impairs the manifestation of food anticipatory activity in rats.

Facilitatory effect of phorbol ester on 2-deoxyglucose uptake in rat hippocampal slices

It is well known that synaptic potentiation in the hippocampus can be produced by phorbol ester, a protein kinase C activator. The 2-deoxyglucose uptake is an index of regional glucose utilization which predominantly reflects activity in the axonal terminal of neuronal pathways. In the present experiment, therefore, we examined whether application of phorbol ester produces a facilitatory effect on 2-deoxyglucose uptake by the rat hippocampus in vitro. The application of phorbol-12,13-dibutyrate (PdBU) produced an elevation of 2-deoxyglucose uptake, while pretreatment with PdBU for 60 min eliminated the pdBU-induced elevation. Pretreatment with protein kinase C inhibitors, K252a (0.1 and 1 microM) or staurosporine (0.1 and 1 microM), was found to block significantly the PdBU-induced elevation of 2-deoxyglucose uptake. In addition, the facilitatory effect of glutamate, quisqualate and carbachol on 2-deoxyglucose uptake was reduced by pretreatment with PdBU. In the present experiment, we demonstrated that application of phorbol ester caused an elevation of 2-deoxyglucose uptake, which is linked in turn to neuronal activity, suggesting a positive relationship between protein kinase C activation and energy consumption.