ABSTRACT
Reactive oxygen species (ROS), formed during normal aerobic metabolism, are involved in signal transduction and cognitive functions, but highly increased ROS concentrations may also have detrimental effects. The aim of the present study was to investigate whether aging and cognitive functions are associated with ROS generation in human neocortex obtained from neurosurgical patients. ROS formation in mitochondria from fresh and re-thawed neocortical specimens was measured by monitoring ROS-mediated conversion of dihydrorhodamine 123 to fluorescent rhodamine 123. The validity of this technique was characterized in rat brain mitochondria. The increase in the concentration-response curve of the complex I inhibitor rotenone on ROS generation, as measured by rhodamine 123 (Rh123) fluorescence, was much more pronounced than that of rotenone on mitochondrial [(3)H]-choline uptake [which indicates changes in the mitochondrial membrane potential (DeltaPsi(M))]. Thus, mitochondrial ROS generation can be shown by Rh123 fluorescence although this fluorescence may also reflect changes in DeltaPsi(M) to some extent. ROS formation in human brain mitochondria positively correlated with the age of patients. Moreover, an age-corrected positive correlation of ROS formation with presurgical cognitive performance was observed. Our data suggest a mild increase in ROS formation with aging possibly reflecting a physiological compensation of mitochondrial function. Furthermore, higher cognitive performances in tests of executive functions may be paralleled by slightly increased ROS levels.
Subject(s)
Aging/metabolism , Cognition/physiology , Mitochondria/metabolism , Neocortex/metabolism , Reactive Oxygen Species/metabolism , Adolescent , Adult , Aged , Animals , Child , Child, Preschool , Electron Transport Complex I/antagonists & inhibitors , Electron Transport Complex I/metabolism , Female , Humans , Infant , Male , Middle Aged , Mitochondria/drug effects , Neocortex/drug effects , Neocortex/surgery , Rats , Rats, Wistar , Reproducibility of Results , Rotenone/pharmacology , Young AdultABSTRACT
The autoinhibitory control of electrically evoked release of [3H]-dopamine and the properties of that induced by nicotinic receptor (nAChR) stimulation were studied in slices of the human neocortex. In both models [3H]-dopamine release was action potential-induced and exocytotic. The selective dopamine D2 receptor agonist (-)-quinpirole reduced electrically evoked release of [3H]-dopamine, yielding IC50 and I(max) values of 23 nM and 76%, respectively. Also, the effects of several other subtype-selective dopamine receptor ligands confirmed that the terminal dopamine autoreceptor belongs to the D2 subtype. The autoinhibitory feedback control was slightly operative under stimulation conditions of 90 pulses and 3 Hz, with a biophase concentration of endogenous dopamine of 3.6 nM, and was enhanced under blockade of dopamine reuptake. [3H]-dopamine release evoked in an identical manner in mouse neocortical slices was not inhibited by (-)-quinpirole, suggesting the absence of dopamine autoreceptors in this tissue and underlining an important species difference. Also, nAChR stimulation-induced release of [3H]-dopamine revealed a species difference: [3H]-dopamine release was evoked in human, but not in rat neocortical slices. The nAChRs inducing [3H]-dopamine release most probably belong to the alpha3/beta2subtype, according to the potencies and efficacies of subtype-selective nAChR ligands. Part of these receptors may be located on glutamatergic neurons.
Subject(s)
Autoreceptors/physiology , Dopamine/metabolism , Neocortex/metabolism , Receptors, Nicotinic/physiology , 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine/analogs & derivatives , 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine/pharmacology , Adolescent , Adult , Aged , Alkaloids/pharmacology , Analysis of Variance , Animals , Azocines/pharmacology , Calcium/pharmacology , Child , Child, Preschool , Domperidone/pharmacology , Dopamine Antagonists/pharmacology , Dose-Response Relationship, Drug , Drug Interactions , Electric Stimulation/methods , Feedback/drug effects , Female , Fluvoxamine/pharmacology , Humans , In Vitro Techniques , Isoxazoles/pharmacology , Male , Maprotiline/analogs & derivatives , Maprotiline/pharmacology , Mice , Middle Aged , Neocortex/drug effects , Neocortex/radiation effects , Nicotine/pharmacology , Nicotinic Antagonists/pharmacology , Potassium/pharmacology , Pyrrolidines/pharmacology , Quinolizines/pharmacology , Rats , Sulpiride/pharmacology , Time Factors , Tritium/metabolismABSTRACT
Some studies have demonstrated antidepressant activity of neurokinin-1-receptor antagonists (NK-1-RA) in major depressive disorder. However, the underlying mechanisms of this antidepressant effect are largely unknown. Preclinical studies in rats and mice have suggested that NK-1-RA do increase the neuronal release of serotonin (5-HT). This, however, seems to be compensated by an increased 5-HT reuptake, indicating that NK-1-RA have no inhibitory effect on the 5-HT transporter in rodents. Given the possibility that modulation of neurotransmitter release and reuptake may differ between species, with major differences found between rodents and humans, we investigated for the first time the possible modulatory effect of NK-1-RA on 5-HT uptake in human brain synaptosomes and compared it with the situation in rat cortex. We found that the specific human NK-1-RA L-733060, in contrast to the SSRI fluvoxamine (IC50=10(-7.96)M) did not inhibit 5-HT uptake in human brain synaptosomes and did not modulate fluvoxamine-induced 5-HT uptake inhibition at 1 muM. Furthermore, substance P as well as Sar9Met(O2)11SP, as the major agonists at the NK-1-R, did not modulate 5-HT uptake in human brain synaptosomes. Similar results were found in rat cortex synaptosomes by using the rat-specific NK-1-RA WIN51708. These results show that in humans, as in rodents, inhibition of the 5-HT transporter is probably not the underlying mechanism of the assumed antidepressant activity of NK-1-RA.
