Presynaptic facilitation of glutamatergic synapses to dopaminergic neurons of the rat substantia nigra by endogenous stimulation of vanilloid receptors.
Growing evidence regarding the function of vanilloid receptor-1 (VR1) in the brain suggests potential central roles of this receptor, previously described to occur primarily in peripheral sensory neurons. In the present study, we used electrophysiological and biochemical techniques to investigate the function and the endogenous stimulation of VR1 in dopaminergic neurons of the substantia nigra pars compacta (SNc). The VR1 agonist capsaicin increased the frequency of both TTX-sensitive and -insensitive spontaneous EPSCs (sEPSCs) without affecting their amplitude, suggesting a presynaptic site of action. In contrast, no effect was detected with regard to GABAergic transmission. No increase in sEPSC frequency was observed in the presence of cadmium chloride, while the voltage-dependent calcium channel antagonist omega-conotoxin MVIIC did not prevent capsaicin action. The VR1 antagonists capsazepine and iodoresiniferatoxin (IRTX) blocked the effects of capsaicin. Importantly, IRTX per se reduced sEPSC frequency, suggesting a tonic activity of VR1. The endogenous VR1 agonist anandamide (AEA) produced an IRTX-sensitive increase in the frequency of sEPSCs on dopaminergic neurons that was more pronounced when protein kinase A had been activated. Furthermore, mass spectrometric analyses and binding experiments revealed high levels of endogenous AEA and specific binding of AEA to VR1 receptors in the SNc. These data suggest a tonic facilitation of glutamate release exerted by VR1 in the SNc through a stimulation of VR1 by endovanilloids, including anandamide. The increase in sEPSC frequency by VR1 onto midbrain dopaminergic neurons suggests the involvement of these receptors in motor and cognitive functions involving the dopaminergic system.
Marinelli
Silvia
S
Istituto di Ricovero e Cura a Carattere Scientifico Fondazione Santa Lucia, University of Tor Vergata, 00179 Rome, Italy. s.marinelli@hsantalucia.it
Di Marzo
Vincenzo
V
Berretta
Nicola
N
Matias
Isabel
I
Maccarrone
Mauro
M
Bernardi
Giorgio
G
Mercuri
Nicola B
NB
D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002211:Capsaicin / Q000031:analogs & derivatives* / Q000494:pharmacology; D004224:Diterpenes / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D063388:Endocannabinoids; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D008636:Mesencephalon / Q000737:chemistry / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D053284:Polyunsaturated Alkamides; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D011955:Receptors, Drug / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D001095:Arachidonic Acids; D002121:Calcium Channel Blockers; D004224:Diterpenes; D063388:Endocannabinoids; D018756:GABA Antagonists; D053284:Polyunsaturated Alkamides; D012333:RNA, Messenger; D011955:Receptors, Drug; C468130:iodoresiniferatoxin; D018698:Glutamic Acid; D013779:Tetrodotoxin; C071423:capsazepine; D002211:Capsaicin; D002118:Calcium; C078814:anandamide; D004298:Dopamine