Behavioral and neurochemical effects induced by chronic L-DOPA administration

2-Arachidonoylglycerol as a possible treatment for anorexia nervosa in animal model in mice

We have investigated the effects of 0.001mg/kg 2-arachidonoylglycerol (2-AG) administered in combination with compounds present in the body alongside 2-AG like 2-palmitoylglycerol and 2-linoleylglycerol (also termed "entourage"), on cognitive function,food intake, and neurotransmitter levels in the hippocampus and hypothalamus of mice under diet restriction. Young female Sabra mice were treated with vehicle, 2-AG, 2-AG+entourage, 2-AG+entourage+5-(4-Chlorophenyl)-1-(2,4-dichloro-phenyl)- 4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide (SR141716A, a CB₁ antagonist) and SR141716A. The mice were fed for 2.5h a day for 14days. Cognitive function was evaluated by the eight arm maze test, and neurotransmitter (norepinephrine, dopamine, L-DOPA and serotonin) levels were measured in the hippocampus and hypothalamus by high-performance liquid chromatography-electrochemical detection. Food intake was increased by 2-AG and, to an even greater extent, by 2-AG+entourage. SR141716A reversed the effect of 2-AG+entourage. The administration of 2-AG+entourage improved cognitive function compared to the vehicle mice, and this improvement was blocked by SR141716A. 2-AG+entourage-treated mice showed an increase in norepinephrine (NE), dopamine and L-DOPA levels in the hippocampus. SR141716A normalized NE and L-DOPA levels. There were no significant changes in hypothalamic neurotransmitter levels. The use of very low doses of the endocannabinoid 2-AG+entourage can improve cognitive function by elevating norepinephrine and L-DOPA levels in the hippocampus, without cannabinomimetic side effects. These findings may have implications for cognitive enhancement in anorexia nervosa.

Structural, functional, and biochemical changes in the brain during modeling of dopamine system disturbances in rats

Dysfunction of the dopamine system was modeled in Wistar rats by injection of 50 mg/kg L-dopa over 4 weeks. Experimental rats demonstrated considerably decreased locomotor activity and increased emotional strain compared to the control group. Structural changes consisted in a significant decrease in the size of neuronal bodies in the sensorimotor cortex (layers III and V) and caudate nucleus together with changed variability of these parameters compared to the corresponding values in the control. The neuroglial index increased by 22% in layer V, tended to decrease in layer III, and remained unchanged in the caudate nucleus. L-Dopa changed specific activity of enzymes: tyrosine hydroxylase activity in the sensorimotor cortex decreased by 25%, while monoamine oxidase B activity in the caudate nucleus increased by 33%. Thus, dysfunction of the dopamine system resulting in changes in dopamine metabolism not only leads to structural and functional rearrangements reducing functional capacities of the cell systems, but is also associated with compensatory and repair reactions in the brain.

Long-lasting neurotoxicity of prenatal benzene acute exposure in rats

Benzene is a common element of environmental pollution. Although this substance is not recognized as a teratogenic agent, it is not known whether prenatal exposure to benzene may induce neurobehavioral changes in the progeny. Benzene 0.1mg/kg was injected subcutaneously (s.c.) acutely at day 15 of gestation into pregnant female rats of the Sprague-Dawley strain and neurotoxicity of the substance was studied in pups and male adult animals of the same progeny. No change was found in total number of neonates, body weight and eye opening time between benzene-exposed animals and controls. No malformations were observed. At birth, neonatal reflexes (cliff aversion, forelimb placing, bar holding, forelimb grasping, startle) were scored in benzene-exposed pups and their percent appearance was found to be anticipated (more benzene-exposed pups exhibited reflexes each day) in comparison to that of control animals. Also, the completion (maximum appearance, i.e. 100% of the brood was found to exhibit each reflex) of neonatal reflexes in benzene-exposed animals preceded that of controls. Starting 2 months after birth, cognitive and motor performance was assessed only in male animals of the prenatally benzene-exposed progeny. The overall evaluation of motor activity in benzene-exposed animals in the open-field test revealed reduced ambulation in these rats as compared to control animals. Acquisition of active avoidance responses in the shuttle-box test, as assessed by the number of conditioned avoidance responses and the percent of learners, was impaired in benzene-exposed rats as compared to control animals. Prenatal exposure to benzene was also followed by reduced retention latency in a step-through passive avoidance task in two retention tests. These results suggest that acute exposure to benzene during gestational organogenesis may cause long-lasting changes in motor behavior and cognitive processes. This may be relevant for the assessment of benzene toxic profile for the progeny of pregnant subjects, although teratogenic effects are not observed.

Influence of repeated levodopa administration on rabbit striatal serotonin metabolism, and comparison between striatal and CSF alterations

Parkinson's disease (PD) is characterized by decreased striatal dopamine, but serotonin (5-HT) is also reduced. Because 5-HT decreases following a single levodopa injection, levodopa has been suggested to contribute to PD's serotonergic deficits. However, in a recent study, rat striatal serotonin levels were reported to increase following 15-day levodopa administration. To address this issue, we administered levodopa (50 mg/kg) to rabbits for 5 days, then measured serotonin, its precursors tryptophan and 5-hydroxytryptophan (5-HTP), and its major metabolite 5-hydroxyindole-acetic acid (5-HIAA) in striatum and CSF. Striatal serotonin and tryptophan were unchanged, while 5-HTP and 5-HIAA increased 4- and 7-fold, respectively. CSF 5-HTP and 5-HIAA were also significantly increased. In levodopa-treated animals, 5-HTP concentrations were moderately correlated (r = 0.679) between striatum and CSF, while weak correlations were present between striatal and CSF concentrations of both serotonin and 5-HIAA. These results suggest that repeated levodopa treatment increases striatal serotonin turnover without changing serotonin content. However, levodopa-induced alterations in striatal serotonin metabolism may not be accurately reflected by measurement of serotonin and 5-HIAA in CSF.