title: Functional interactions between dopamine, serotonin and norepinephrine neurons: an in-vivo electrophysiological study in rats with monoaminergic lesions.
abstract: Anatomical studies have established the existence of reciprocal relationships between the main population of monoamine, serotonin (5-HT), norepinephrine (NE) and dopamine (DA) neurons in the brain. The present study was thus conducted to examine the firing activity of 5-HT and NE neurons in DA-depleted rats, as well as the firing activity of DA neurons in 5-HT- or NE-depleted rats. The selective lesion of DA neurons elicited by 6-hydroxydopamine (6-OHDA) decreased the spontaneous firing activity of dorsal raphe (DR) nucleus 5-HT neurons by 60%, thus revealing the excitatory effect of the DA input on these 5-HT neurons. In contrast, the selective lesion of 5-HT neurons produced by 5,7-dihydroxytryptamine (5,7-DHT) enhanced by 36% the firing activity of VTA DA neurons, thereby indicating an inhibitory effect of the 5-HT input on these DA neurons. With regard to the reciprocal interaction between DA and NE neurons, it was observed that the selective loss of DA neurons achieved by the intra-ventral tegmental area (VTA) injection of 6-OHDA increased the firing activity of a subset of locus coeruleus (LC) NE neurons by 47%. The selective loss of NE neurons in response to the intra-LC injection of 6-OHDA enhanced the firing activity of VTA DA neurons by 70%, demonstrating a net inhibitory role of the NE input on VTA DA neurons. These findings have important consequences for antidepressant treatments aimed at enhancing simultaneously 5-HT, NE and DA transmission. Indeed, based on the understanding of such interactions, it may be possible to develop strategies to improve the effectiveness of antidepressant drugs by preventing counter-productive negative feedback actions.
authors.affiliation: Institute of Mental Health Research, University of Ottawa, Ottawa, Ontario, Canada. bguiard@rohcg.on.ca
authors.forename: Bruno P
authors.initials: BP
authors.lastname: Guiard
authors.forename: Mostafa
authors.initials: M
authors.lastname: El Mansari
authors.forename: Zul
authors.initials: Z
authors.lastname: Merali
authors.forename: Pierre
authors.initials: P
authors.lastname: Blier
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D004298:Dopamine / Q000172:deficiency / Q000378:metabolism*; D004347:Drug Interactions; D008125:Locus Coeruleus / Q000166:cytology / Q000187:drug effects; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009498:Neurotoxins / Q000633:toxicity*; D009638:Norepinephrine / Q000172:deficiency / Q000378:metabolism*; D011903:Raphe Nuclei / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000172:deficiency / Q000378:metabolism*; D017557:Ventral Tegmental Area / Q000166:cytology / Q000187:drug effects
chemical_list: D009498:Neurotoxins; D012701:Serotonin; D004298:Dopamine; D009638:Norepinephrine