1 The modulation of [3H]-5-hydroxytryptamine ([3H]-5-HT) e ux from superfused rat cortical synaptosomes by delta, kappa, mu and ORL1 opioid receptor agonists and antagonists was studied. 2 Spontaneous [3H]-5-HT e ux was reduced (20% inhibition) by either 0.5 mM tetrodotoxin or Ca2+-omission. Ten mM K+-evoked [3H]-5-HT over¯ow was largely Ca2+-dependent (90%) and tetrodotoxin-sensitive (50%). 3 The delta receptor agonist, deltorphin-I, failed to modulate the K+-evoked neurotransmitter e ux up to 0.3 mM. The kappa and the mu receptor agonists, U-50,488 and endomorphin-1, inhibited K+-evoked [3H]-5-HT over¯ow (EC50=112 and 7 nM, respectively; Emax=28 and 29% inhibition, respectively) in a norBinaltorphimine- (0.3 mM) and naloxone- (1 mM) sensitive manner, respectively. None of these agonists signi®cantly a ected spontaneous [3H]-5-HT e ux. 4 The ORL1 receptor agonist nociceptin inhibited both spontaneous (EC50=67 nM) and K+- evoked (EC50=13 nM; Emax=52% inhibition) [3H]-5-HT e ux. The e ect of NC was insensitive to naloxone (up to 10 mM), but was antagonized by [Nphe1]nociceptin(1-13)NH2 (a novel selective ORL1 receptor antagonist; pA2=6.7) and by naloxone benzoylhydrazone (pA2=6.3). The ORL1 ligand [Phe1c(CH2-NH)Gly2]nociceptin(1-13)NH2 also inhibited K+ stimulated [3H]-5-HT over¯ow (EC50=64 nM; Emax=31% inhibition), but its e ect was partially antagonized by 10 mM naloxone. 5 It is concluded that the ORL1 receptor is the most important presynaptic modulator of neocortical 5-HT release within the opioid receptor family. This suggests that the ORL1/nociceptin system may have a powerful role in the control of cerebral 5-HT-mediated biological functions.
Modulation of 5-hydroxytryptamine efflux from rat cortical synaptosomes by opioids and nociceptin
MARTI, Matteo;MORARI, Michele;CALO', Girolamo;GUERRINI, Remo;
2000
Abstract
1 The modulation of [3H]-5-hydroxytryptamine ([3H]-5-HT) e ux from superfused rat cortical synaptosomes by delta, kappa, mu and ORL1 opioid receptor agonists and antagonists was studied. 2 Spontaneous [3H]-5-HT e ux was reduced (20% inhibition) by either 0.5 mM tetrodotoxin or Ca2+-omission. Ten mM K+-evoked [3H]-5-HT over¯ow was largely Ca2+-dependent (90%) and tetrodotoxin-sensitive (50%). 3 The delta receptor agonist, deltorphin-I, failed to modulate the K+-evoked neurotransmitter e ux up to 0.3 mM. The kappa and the mu receptor agonists, U-50,488 and endomorphin-1, inhibited K+-evoked [3H]-5-HT over¯ow (EC50=112 and 7 nM, respectively; Emax=28 and 29% inhibition, respectively) in a norBinaltorphimine- (0.3 mM) and naloxone- (1 mM) sensitive manner, respectively. None of these agonists signi®cantly a ected spontaneous [3H]-5-HT e ux. 4 The ORL1 receptor agonist nociceptin inhibited both spontaneous (EC50=67 nM) and K+- evoked (EC50=13 nM; Emax=52% inhibition) [3H]-5-HT e ux. The e ect of NC was insensitive to naloxone (up to 10 mM), but was antagonized by [Nphe1]nociceptin(1-13)NH2 (a novel selective ORL1 receptor antagonist; pA2=6.7) and by naloxone benzoylhydrazone (pA2=6.3). The ORL1 ligand [Phe1c(CH2-NH)Gly2]nociceptin(1-13)NH2 also inhibited K+ stimulated [3H]-5-HT over¯ow (EC50=64 nM; Emax=31% inhibition), but its e ect was partially antagonized by 10 mM naloxone. 5 It is concluded that the ORL1 receptor is the most important presynaptic modulator of neocortical 5-HT release within the opioid receptor family. This suggests that the ORL1/nociceptin system may have a powerful role in the control of cerebral 5-HT-mediated biological functions.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
