Hydrogen peroxide monitored in vivo, in situ and in real time in rat brain, is it a marker of central cholinergic dynamics?

Abstract

Acetylcholine (ACh) is a neurotransmitter acting in both the peripheral and central nervous system (CNS). Various analytical techniques have been adopted for the measurement of ACh in brain. They are complex and “off-line” methods mainly based on separation of ACh and choline and their enzymatic metabolism with detection of the hydrogen peroxide (H₂O₂) formed. Here we propose a significantly less complex methodology i.e. fast cyclic voltammetry with treated carbon fibre micro-electrodes. It allows monitoring a specific voltammetric oxidation signal [R] in vitro in the presence of H₂O₂ as well as a selective signal [R] in vivo, in situ and “in real time” following local intrastriatal injection of H₂O₂ with no change in its oxidation potential. Similarly, intrastriatal injection of acetylcholine (ACh, not electroactive chemical) produces an increase in the size of [R], while neostigmine (ACh esterase inhibitor, not active upon the sensor) significantly decreases [R]. An increase of [R] is also monitored in the striatum of conscious freely moving rats treated with ACh receptor antagonists such as scopolamine or atropine. Thus in vivo modifications of [R] may reflect central cholinergic dynamics and in particular metabolised ACh with generation of H₂O₂.