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-ac tivated calcium currents in isolated GP neurons. Neither dynorphin nor DPEP E inhibited calcium current, whilst DAMGO produced a small (-16%) but consi stent response, selectively antagonized by CTOP. The mu -mediated modulatio n required the activation of G-proteins but was voltage-independent. The pr e-incubation in omega -conotoxinVIA abolished the response, implying the in volvement of N-type calcium channels. These findings suggest that enkephali n may exert a direct influence on GP excitability also through post-synapti c effects. In degenerative conditions as Parkinsonism, an excessive stimula tion of mu binding sites might induce a pathological inhibition of calcium signals, thus contributing to modify the GP firing pattern and transmitter release. (C) 2001 Elsevier Science B.V. All rights reserved.