title: Paradoxical lower sensitivity of Locus Coeruleus than Substantia Nigra pars compacta neurons to acute actions of rotenone.
abstract: Parkinson's disease (PD) is not only associated with degeneration of dopaminergic (DAergic) neurons in the Substantia Nigra, but also with profound loss of noradrenergic neurons in the Locus Coeruleus (LC). Remarkably, LC degeneration may exceed, or even precede the loss of nigral DAergic neurons, suggesting that LC neurons may be more susceptible to damage by various insults. Using a combination of electrophysiology, fluorescence imaging and electrochemistry, we directly compared the responses of LC, nigral DAergic and nigral non-dopaminergic (non-DAergic) neurons in rat brain slices to acute application of rotenone, a mitochondrial toxin used to create animal and in vitro models of PD. Rotenone (0.01-5.0μM) dose-dependently inhibited the firing of all three groups of neurons, primarily by activating KATPchannels. The toxin also depolarised mitochondrial potential (Ψm) and released reactive oxygen species (H2O2). When KATPchannels were blocked, rotenone (1μM) increased the firing of LC neurons by activating an inward current associated with dose-dependent increase of cytosolic free Ca2+([Ca2+]i). This effect was attenuated by blocking oxidative stress-sensitive TRPM2 channels, and by pre-treatment of slices with anti-oxidants. These results demonstrate that rotenone inhibits the activity of LC neurons mainly by activating KATPchannels, and increases [Ca2+]ivia TRPM2 channels. Since the responses of LC neurons were smaller than those of nigral DAergic neurons, our study shows that LC neurons are paradoxically less sensitive to acute effects of this parkinsonian toxin.
authors: Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
authors: Andrew G
authors: AG
authors: Yee
authors: Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
authors: Peter S
authors: PS
authors: Freestone
authors: Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
authors: Ji-Zhong
authors: JZ
authors: Bai
authors: Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand. Electronic address: j.lipski@auckland.ac.nz.
authors: Janusz
authors: J
authors: Lipski
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D000831:Animals, Newborn; D000959:Antihypertensive Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003981:Diazoxide / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D007306:Insecticides / Q000494:pharmacology*; D008125:Locus Coeruleus / Q000166:cytology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D009474:Neurons / Q000145:classification / Q000187:drug effects*; D065842:Pars Compacta / Q000166:cytology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D012402:Rotenone / Q000494:pharmacology*; D050053:TRPM Cation Channels / Q000378:metabolism; D014044:Tolbutamide / Q000494:pharmacology
chemical_list: D000959:Antihypertensive Agents; D007004:Hypoglycemic Agents; D007306:Insecticides; D017382:Reactive Oxygen Species; D050053:TRPM Cation Channels; C557080:Trpm2 protein, rat; D012402:Rotenone; D014044:Tolbutamide; D006861:Hydrogen Peroxide; D003981:Diazoxide; D002118:Calcium
keywords: Brain slice; Calcium; Electrochemistry; Electrophysiology; K(ATP); Parkinsonian toxin; TRPM2