Monoamines, microdialysis

As described above, because MAO is bound to mitochondrial outer membranes, MAOIs first increase the concentration of monoamines in the neuronal cytosol, followed by a secondary increase in the vesicle-bound transmitter. The enlarged vesicular pool will increase exocytotic release of transmitter, while an increase in cytoplasmic monoamines will both reduce carrier-mediated removal of transmitter from the synapse (because the favourable concentration gradient is reduced) and could even lead to net export of transmitter by the membrane transporter. That MAOIs increase the concentration of extracellular monoamines has been confirmed using intracranial microdialysis (Ferrer and Artigas 1994). 

Crochet, S. Sakai, K. (1999b). Effects of microdialysis application of monoamines on the EEG and behavioural states in the cat mesopontine tegmentum. Eur. J. Neurosci. 11, 3738-52. 

Chen N., Reith M. Autoregulation and monoamine interactions in the ventral tegmental area in the absence and presence of cocaine a microdialysis study in freely moving rats. J. Pharmacol. Exp. Ther. 271 1597, 1994. 

Nakajima W, Ishida A, Ogasawara M, Takada G. 1998. Effect of N-methyi-D-aspartate and potassium on striatal monoamine metabolism in immature rat an in vivo microdialysis study. Neurochem Res 23(9) 1159-1165. 

Chen NH, Reith ME. Monoamine interactions measured by microdialysis in the ventral tegmental area of rats treated systemically with (+/-)-8-hydroxy-2-(di- -propylamino)tetralin. J Neurochem 1995 64 1585-1597. 

Celada P, Artigas F. Monoamine oxidase inhibitors increase preferentially extracellular 5-hydroxytryptamine in the midbrain raphe nuclei. A brain microdialysis study in the awake rat. Nanny n-Schrnicdcbcrgs Arch Pharmacol 1993 347 583-590. 

Herrera-Marschitz M, Luthman J, Ferre S (1994) Unilateral neonatal intracerebroventricular 6-hydroxydopa-mine administration in rats II. Effects on extracellular monoamine, acetylcholine and adenosine levels monitored with in vivo microdialysis. Psychopharmacology (Berl) 116 451-456. 

Becker JB, Adams F, Robinson TE (1988) Intraventricular microdialysis A new method for determining monoamine metabolite concentrations in the cerebrospinal fluid of freely moving rats. J Neurosci Methods 24 259-269. 

Somewhat different results were reported from other laboratories n-3 fatty acid deficiency in rats caused a decrease in dopamine level and D2-receptor density in the frontal cortex as well as a decrease in serotonin receptor density (Delion, 1994,1996), whereas fish oil increased the dopamine level (Chalon, 1998). A decrease in the dopamine release from the frontal cortex was also detected by the microdialysis method after thyramine stimulation but not after KCl stimulation (Zimmer, 1998, 2000). In aged rats, however, the monoamine level was not affected, whereas monoamine oxidase activity was decreased during n-3 fatty acid deficiency (Delion, 1997). 

This chapter describes two microbore LC-based methods for measurement of monoamine neurotransmitters in rat brain dialysates a method for the determination of the catecholamines (CA) noradrenaline (NAD), adrenaline (AD), and dopamine (DA) and a method for the determination of the indoleamine serotonin (5HT) and its major metabolite 5-hydroxyindoleacetic acid (SHIAA) (3). For all compounds, a limit of detection of 1 pmol or less (in an injected volume of 10 pL) can be achieved. Basal serotonin can be measured in microdialysates without including a reuptake inhibitor in the microdialysis perfusion fluid. Both of these systems are routinely used in the authors laboratory for the analysis of dialysates from striatum, hippocampus, and substantia nigra. Both methods are selective, robust, and can be automated. 

The concentration in the Ringer s solution used for perfusing the microdialysis probe can be varied according to the transmitter being studied. In normal circumstances, the concentration should mirror the concentration in the extracellular fluid i.e., 1,1 mM, However, in some cases where the analysis is more demanding, the concentration may be increased to 2.2 mM, This stimulates the release of the transmitter slightly, so that monoamine concentrations in the dialy-sate are elevated. For example, this is done m the case of the determination of 5HT and NAD in hippocampus. 

Mas, M., Fumero, B. Gonzalez-Mora, J. L. 1995. Voltammetric and microdialysis monitoring of brain monoamine neurotransmitter release during sociosexual interactions. Behav. Brain Res., 71, 69—79. 

Fig. 1 Chromatograms of a standard solution of monoamine transmitters and their metabolites at (A) a poly(para-aminobenzoic acid) modified electrode and (B) a bare glassy carbon electrode. (1) Norepinephrine, (2) epinephrine, (3) dopamine, (4) 3,4-dihydroxyphenol acetic acid, (5) serotonin, (6) 5-hydroxyindole acetic acid, and (7) homovanillic acid. Source From Study on the effect of electromagnetic impulse on neurotransmitter metabolism in nerve cells by high performance liquid chromatography-electrochemical detection coupled with microdialysis, in Anal. Biochem. ...

Over the last decade, direct detection of ACh with LC—MS/MS systems employing an electrospray-ionization (ESI) source have resulted in superior limits of detection, increased reliability, and improved temporal resolution with microdialysis sampling. Like monoamines, ACh is a small, polar, hydrophilic compound that is not readily retained on RP columns. In MS analysis, the selection criteria of LC systems. 

Chaurasia CS, Chen CE, Ashby Jr CR. In vivo on-Une HPLC—microdialysis simultaneous detection of monoamines and their metabolites in awake freely-moving rats. J Pharm Biomed Anal 1999 19 413-22. 

Zhang W, Cao X, Xie Y, Ai S, Jin L, Jin J. Simultaneous determination of the monoamine neurotransmitters and glucose in rat brain by microdialysis sampling coupled with liquid chromatography—dual electrochemical detector. J Chromatogr B Anal Tech Biomed Life Sd 2003 785(2003) 327-36. 

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