Effects of drugs of abuse on putative rostromedial tegmental neurons, inhibitory afferents to midbrain dopamine cells.
Recent findings have underlined the rostromedial tegmental nucleus (RMTg), a structure located caudally to the ventral tegmental area, as an important site involved in the mechanisms of aversion. RMTg contains γ-aminobutyric acid neurons responding to noxious stimuli, densely innervated by the lateral habenula and providing a major inhibitory projection to reward-encoding midbrain dopamine (DA) neurons. One of the key features of drug addiction is the perseverance of drug seeking in spite of negative and unpleasant consequences, likely mediated by response suppression within neural pathways mediating aversion. To investigate whether the RMTg has a function in the mechanisms of addicting drugs, we studied acute effects of morphine, cocaine, the cannabinoid agonist WIN55212-2 (WIN), and nicotine on putative RMTg neurons. We utilized single unit extracellular recordings in anesthetized rats and whole-cell patch-clamp recordings in brain slices to identify and characterize putative RMTg neurons and their responses to drugs of abuse. Morphine and WIN inhibited both firing rate in vivo and excitatory postsynaptic currents (EPSCs) evoked by stimulation of rostral afferents in vitro, whereas cocaine inhibited discharge activity without affecting EPSC amplitude. Conversely, nicotine robustly excited putative RMTg neurons and enhanced EPSCs, an effect mediated by α7-containing nicotinic acetylcholine receptors. Our results suggest that activity of RMTg neurons is profoundly influenced by drugs of abuse and, as important inhibitory afferents to midbrain DA neurons, they might take place in the complex interplay between the neural circuits mediating aversion and reward.
BB Brodie Department of Neuroscience, University of Cagliari, Monserrato, Italy.
Salvatore
S
Lecca
Miriam
M
Melis
Antonio
A
Luchicchi
Maria Grazia
MG
Ennas
Maria Paola
MP
Castelli
Anna Lisa
AL
Muntoni
Marco
M
Pistis
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D000831:Animals, Newborn; D001522:Behavior, Animal / Q000187:drug effects; D048588:Benzoxazines / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D013287:Illicit Drugs / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects*; D009434:Neural Pathways / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077285:Rimonabant; D013997:Time Factors; D017557:Ventral Tegmental Area / Q000166:cytology*
D048588:Benzoxazines; D013287:Illicit Drugs; D009025:Morpholines; D009281:Naphthalenes; D009292:Narcotic Antagonists; D018733:Nicotinic Antagonists; D010880:Piperidines; D011720:Pyrazoles; D009270:Naloxone; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D008464:Mecamylamine; D009020:Morphine; D003042:Cocaine; D000077285:Rimonabant; C109925:AM 281; D004298:Dopamine