Increases in cholinergic neurotransmission measured by using choline-sensitive microelectrodes: enhanced detection by hydrolysis of acetylcholine on recording sites?
Previous experiments demonstrated that second-based transient increases in choline concentrations measured by electrodes coated with choline oxidase (ChOx) and the amperometric detection of hydrogen peroxide validly indicate the depolarization-dependent release of acetylcholine (ACh) and its hydrolysis by endogenous acetylcholinesterase (AChE). Therefore, choline-sensitive microelectrodes have become valuable tools in neuropharmacological and behavioral research. The present experiments were designed to test the possibility that co-immobilization of ChOx plus AChE on recording sites increases the level of detection for evoked ACh release in the brain. If newly released ACh is not completely hydrolyzed by endogenous AChE and capable of reaching the extracellular space, currents recorded via sites equipped with both enzymes should be greater when compared with sites coated with ChOx only. Pairs of platinum-recording sites were coated either with AChE plus ChOx or ChOx alone. Potassium or nicotine-evoked currents were recorded throughout the entire dorsal-ventral extent of the medial prefrontal cortex (mPFC). The amplitudes of evoked cholinergic signals did not differ significantly between AChE+ChOx and ChOx-only coated recording sites. Additional experiments controlling for several potential confounds suggested that, in vivo, ACh levels > or =150fmol were detected by recordings sites featuring dual enzyme coating. Collectively, these results indicate that co-coating of microelectrodes with AChE does not enhance the detection of cholinergic activity in the cortex compared with measurements via recording sites coated only with ChOx.
Giuliano
Chiara
C
Department of Psychology and Neuroscience Program, University of Michigan, Ann Arbor, MI 48109-1043, USA.
Parikh
Vinay
V
Ward
Josh R
JR
Chiamulera
Christian
C
Sarter
Martin
M
D000109:Acetylcholine / Q000737:chemistry* / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D002138:Calibration; D002794:Choline / Q000494:pharmacology*; D004800:Enzymes, Immobilized; D006868:Hydrolysis; D007150:Immunohistochemistry; D008297:Male; D008839:Microelectrodes; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D016707:Tissue Fixation
D004800:Enzymes, Immobilized; D018722:Nicotinic Agonists; D011189:Potassium Chloride; D009538:Nicotine; D000429:Alcohol Oxidoreductases; C019888:choline oxidase; D002794:Choline; D000109:Acetylcholine