Male Wistar rats were subjected to right-unilateral 6-hydroxydopamine (6-OHDA) (2 µg/µl) lesions of the ventral tegmental area (VTA) or the substantia nigra (SN), or were sham-operated, and their ability to acquire the operant task was studied by means of Y-maze and shuttle-box tasks. Lesions of both the VTA and the SN resulted in an impairment of conditioned avoidance response and increase of crossing latency tested by means of shuttle-box task, suggesting significant effects of long-term memory. 6-OHDA significantly decreased spontaneous alternation in Y-maze task, suggesting effects on spatial memory, especially on short-term memory. In addition, 6-OHDA lesions of the VTA and the SN induced reductions in superoxide dismutase (SOD), glutathione peroxidase (GPX) activities and malondialdehyde (MDA) levels in the temporal lobe rather than in the frontal lobe homogenates. Our results provide further support for the toxic effects of 6-OHDA-induced memory impairment and oxidative stress with relevance for Parkinson's disease.

New enzymes of nicotine catabolism instrumental in the detoxification of the tobacco alkaloid by Arthrobacter nicotinovorans pAO1 have been identified and characterized. Nicotine breakdown leads to the formation of nicotine blue from the hydroxylated pyridine ring and of γ‐N‐methylaminobutyrate (CH3‐4‐aminobutyrate) from the pyrrolidine ring of the molecule. Surprisingly, two alternative pathways for the final steps in the catabolism of CH3‐4‐aminobutyrate could be identified. CH3‐4‐aminobutyrate may be demethylated to γ‐N‐aminobutyrate by the recently identified γ‐N‐methylaminobutyrate oxidase [Chiribau et al. (2004) Eur J Biochem271, 4677–4684]. In an alternative pathway, an amine oxidase with noncovalently bound FAD and of novel substrate specificity removed methylamine from CH3‐4‐aminobutyrate with the formation of succinic semialdehyde. Succinic semialdehyde was converted to succinate by a NADP+‐dependent succinic semialdehyde dehydrogenase. Succinate may enter the citric acid cycle completing the catabolism of the pyrrolidine moiety of nicotine. Expression of the genes of these enzymes was dependent on the presence of nicotine in the growth medium. Thus, two enzymes of the nicotine regulon, γ‐N‐methylaminobutyrate oxidase and amine oxidase share the same substrate. The Km of 2.5 mm and kcat of 1230 s−1 for amine oxidase vs. Km of 140 µm and kcat of 800 s−1 for γ‐N‐methylaminobutyrate oxidase, determined in vitro with the purified recombinant enzymes, may suggest that demethylation predominates over deamination of CH3‐4‐aminobutyrate. However, bacteria grown on [14C]nicotine secreted [14C]methylamine into the medium, indicating that the pathway to succinate is active in vivo.

Although the ability of Bifidobacterium spp. to grow on fructose as a unique carbon source has been demonstrated, the enzyme(s) needed to incorporate fructose into a catabolic pathway has hitherto not been defined. This work demonstrates that intracellular fructose is metabolized via the fructose-6-P phosphoketolase pathway and suggests that a fructokinase (Frk; EC 2.7.1.4) is the enzyme that is necessary and sufficient for the assimilation of fructose into this catabolic route in Bifidobacterium longum. The B. longum A10C fructokinase-encoding gene (frk) was expressed in Escherichia coli from a pET28 vector with an attached N-terminal histidine tag. The expressed enzyme was purified by affinity chromatography on a Co 2؉ -based column, and the pH and temperature optima were determined. A biochemical analysis revealed that Frk displays the same affinity for fructose and ATP (K m fructose ‫؍‬ 0.739 ؎ 0.18 mM and K m ATP ‫؍‬ 0.756 ؎ 0.08 mM), is highly specific for D-fructose, and is inhibited by an excess of ATP (>12 mM). It was also found that frk is inducible by fructose and is subject to glucose-mediated repression. Consequently, this work presents the first characterization at the molecular and biochemical level of a fructokinase from a gram-positive bacterium that is highly specific for D-fructose.

Abstract:The high density of the steroid hormone receptors in the structures of temporal lobe involved in learning and memory, such as the hippocampus, perirhinal cortex, entorhinal cortex and amigdaloid complex, shows that there must be a direct relationship between gonadal hormones and organizational effects of steroid hormones in those structures during development of the nervous system. The present study was undertaken in order to investigate the effect of testosterone administration during the third week of gestation on the spatial memory formation of the offspring rats and the level of soluble proteins in the temporal lobe and frontal lobe of brain, as evidence of important organizational effects of androgens during prenatal development in brain sexual dimorphism. Animals have received testosterone undecanoate on days 14, 15, 16 and 19, 20, 21 of gestation. Learning and memory tests were started 100 days after the testosterone treatment. At the end of the experiments, the temporal and frontal lobes of brain were removed for assessing the level of soluble proteins. Testosterone treatment significantly improved spontaneous alternations percentage of male offspring in Y-maze task comparative with female offspring and reference memory in radial 8 arm-maze task (decreasing in number of reference memory errors in both male and female offspring groups), suggesting effects of both short and long-term memory. Also, testosterone significantly increased the brain soluble protein level of treated female rats in 14-16 prenatal days compared with the control group as well as the brain soluble protein level of treated male rats. These results suggest that steroid hormones play an important role in the spatial learning and memory formation by means of protein synthesis in different lobes of the brain.

No abstract