The activation of mu opioid receptors promotes a small modulation of calcium currents in rat pallidal neurons.
Globus pallidus receives, from dorsal neostriatum, a dense enkephalinergic innervation whose role is still uncertain. We examined the possibility that the activation of mu, delta or k opioid receptors modulate high-voltage-activated calcium currents in isolated GP neurons. Neither dynorphin nor DPEPE inhibited calcium current, whilst DAMGO produced a small (-16%) but consistent response, selectively antagonized by CTOP. The mu-mediated modulation required the activation of G-proteins but was voltage-independent. The pre-incubation in omega-conotoxinVIA abolished the response, implying the involvement of N-type calcium channels. These findings suggest that enkephalin may exert a direct influence on GP excitability also through post-synaptic effects. In degenerative conditions as Parkinsonism, an excessive stimulation of mu binding sites might induce a pathological inhibition of calcium signals, thus contributing to modify the GP firing pattern and transmitter release.
IRCCS Fondazione, S. Lucia, Italy. stefani@uniroma2.it
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A
Stefani
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Spadoni
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P
Giacomini
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F
Lavaroni
G
G
Bernardi
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000378:metabolism; D004399:Dynorphins / Q000494:pharmacology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D005917:Globus Pallidus / Q000166:cytology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D000701:Analgesics, Opioid; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016308:Enkephalin, Leucine-2-Alanine; D004399:Dynorphins; D020866:omega-Conotoxin GVIA; D002118:Calcium