Heterogeneity of hepatic nicotine oxidase

When rats were pretreated with 3-methylcholanthrene or β-naphthoflavone, hepatic nicotine oxidase activity per cytochrome P-448 molecule decreased, but the specific activity of the enzyme remained unchanged. After phenobarbital pretreatment, the specific activity of nicotine oxidase increased while the activity of the enzyme per cytochrome P-450 molecule decreased. α-Naphthoflavone selectively inhibited the activities of phenobarbital-induced nicotine oxidase and constitutive form(s) of the enzyme. These results show that phenobarbital-induced cytochrome P-450 and constitutive forms(s) of the enzyme may be active in hepatic nicotine oxidation.     

Effects of prenatal administration of nicotine on amino acid pools,protein metabolism,and nicotine binding in the brain

The effects of nicotine on brain protein metabolism and on the properties of the nicotine binding site were investigated in newborn animals exposed to nicotine during gestation. Brain protein synthesis rates measured in vivo were lower by 18% in newborn of treated animals. Protein degradation rates measured in vitro in the presence of nicotine were lower by 13%. The effect was specific forl-(-) nicotine, sinced-(+)nicotine, nicotinic acid, or nicotinamide had no effect on degradation rates. Newborn brain amino acid levels, mainly nonessential amino acids and amino acids of putative neurotrans nitter function, were changed some-what; an increase in the level of taurine (13%), threonine (21%), serine (35%) and glycine (35%), and a decrease in lysine (14%) was observed in the offspring of nicotine treated animals (0.5 mg/kg, s.c., 2×daily throughout gestation). These changes could not account for the decrease in protein metabolism. Nicotine binding was higher by 25% in the offspring of animals exposed to nicotine during gestation. No such increase was found after treatment of adult rats with nicotine, indicating that the properties of the nicotine binding site change with age.     

Effects of steroids on the brain opioid system

The experiments reported here add further evidence in support of the view that sex steroids may influence the binding characteristics of brain opioid receptors. In particular, it has been shown that: (a) the number of μ-opioid receptors varies in the hypothalamus of regularly cycling female rats according to the different phases of the estrous cycle, which are characterized by fluctuations of circulating levels of sex steroids; (b) the number of μ-opioid receptors decreases in the hypothalamus and in the corpus striatum when ovariectomized rats are submitted to treatments with estradiol and progesterone able to induce a “positive” feedback effect on LH release. A treatment with estrogen alone able to induce a “negative” feedback effect on LH release brings about an increase of the number of μ-opioid receptors in the thalamus and in the hippocampus; (c) in addition to the μ-receptors, receptors of the delta type may also be involved in the control of gonadotropin secretion; recent results here presented indicate that a line of immortalized hypothalamic cells (GT1 cells), which synthesize and secrete LHRH, present δ opioid receptors on their membranes; these are apparently involved in the control of LHRH release from these cells.     

Effects of tobacco smoke constituents on MPTP-induced toxicity and monoamine oxidase activity in the mouse brain

Exposure to cigarette smoke has been found to attenuate the reduction in striatal dopamine levels caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice and to inhibit monoamine oxidase (MAO) activity in brain tissue. To confirm whether specific smoke constituents which have been reported to protect against MPTP toxicity were responsible for these effects, mice were treated chronically with nicotine, 4-phenylpyridine and hydrazine. Although all three compounds prevented the decrease in dopamine metabolite levels induced by MPTP, there was no significant effect on dopamine levels. None of the three compounds inhibited MAO activity in cerebral tissue following treatment in vivo. However, an extract of tobacco smoke particulate matter caused a marked inhibition of MAO A and MAO B activity when added in vitro. The results suggest that one or more unidentified substances in tobacco smoke are capable of inhibiting brain MAO and perhaps altering the formation of the active metabolite of MPTP.     

Effects of ammonia on monoamine oxidase and enzymes of GABA metabolism in mouse brain.

Acute and chronic ammonia toxicity was produced in the mice by intraperitoneal injection of ammonium chloride (200 mg/kg) and by exposure of mice to ammonia vapours (5% v/v) continuously for 2 days and 5 days respectively. The ammonia content was elevated in the cerebellum, cerebral cortex and brain stem and in liver. In acute ammonia intoxication there was a decrease in the monoamine oxidase (MAO) activity in all the three regions of brain. In chronic ammonia toxicity (2 days of exposure) a significant increase in the activity of MAO was observed in the cerebral cortex while in cerebellum and brain stem there was a significant decrease. In cerebral cortex and cerebellum there was a rise in the activity of MAO as a result of exposure to ammonia vapours for 5 days. A significant decrease was observed in the activity of glutamate decarboxylase (GAD) in all the three regions of the brain both in acute and chronic ammonia toxicity (2 days). There was a decrease in the activity of this enzyme only in the cerebral cortex in the animals exposed to ammonia for 5 days. The activity of GABA-aminotransferase (GABA-T) showed a significant rise in cerebellum and a fall in the brain stem in acute ammonia toxicity. In chronic ammonia toxicity GABA-T showed a rise in all the three regions of brain. Chronic ammonia toxicity produced a significant decrease in the content of glutamate in all the three regions without a significant change in the content of aspartate. GABA and glutamine. The content of alanine increased in all the three regions of brain under these experimental conditions. The ratio of glutamate + aspartate/GABA and glutamate/glutamine showed a decrease in all the three regions as a result of ammonia toxicity.     

Effects of titanium compounds on a D-glucose-D-glucose oxidase assay system.

Titanium compounds affect the measurement of D-glucose oxidase (and therefore D-glucose) by the D-glucose-D-glucose oxidase-peroxidase-2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) assay system. The validity of measurement of the activity of D-glucose oxidase immobilised on supports based on titanium oxides is affected by complexation of the intermediate hydrogen peroxide with the support, and such supports may prove to be unsuitable for the immobilisation of D-glucose oxidase. The formation of titanic peroxides is among the reasons discussed for the various interactions encountered. The use of the assay system for the determination of D-glucose oxidase contaminated with catalase and for the determination of hydrogen peroxide is also described.     

Significant modulation of mitochondrial electron transport system by nicotine in various rat brain regions

The mitochondrion is the organelle responsible for generation of most usable energy in a cell. It also plays an important role in a series of physiological processes such as apoptosis and proliferation. Although previous studies have demonstrated that nicotine modulates the morphology and function of mitochondria, the mechanism(s) underlying these effects is largely unknown. In this study, using a microarray consisting of 4793 clones derived from a mouse dopamine cDNA library, we profiled the gene expression patterns for six brain regions (amygdala, hippocampus, nucleus accumbens, prefrontal cortex, striatum and ventral tegmental area) of female Sprague-Dawley rats subjected to nicotine treatment for 7 days through osmotic minipump infusion. We identified a number of genes and pathways, including components of the electron transport system of mitochondria, such as cytochrome c oxidase subunit I (Mt-co1), Mt-co2, Mt-co3, cytochrome b (Mt-cyb), mitochondrial NADH dehydrogenase 4 (Mt-nd4), and Mt-nd6, that were significantly modulated by nicotine in multiple brain regions. Bioinformatics analysis provided evidence that Gene Ontology categories related to the electron transport system were overrepresented in each brain region. Finally, the results from the microarray analysis were verified by quantitative RT-PCR for four representative genes. Together, our findings imply that mitochondria are involved in neuronal adaptation to chronic nicotine exposure.     

Effects of inhibitors on monoamine oxidase activity in perch (Perca flavescens) brain in vitro

1. Perch brain homogenates were incubated in vitro and monoamine oxidase (MAO) activity was determined fluorometrically, using a kynuramine substrate. 2. Clorgyline, harmaline and deprenyl inhibited MAO activity in a concentration-related manner, with single sigmoid inhibition curves, and the type A inhibitors harmaline and clorgyline were more effective than the type B inhibitor deprenyl. 3. Two types of inhibition were recognized in vitro; a fast-onsetting inhibition, similar to that produced by a reversible inhibitor, and a slow-onsetting inhibition, which is time- and concentration-dependent and presumably represents inactivation of the enzyme.