Orphanin FQ/nociceptin and naloxone benzoylhydrazone activate distinct receptors in BE(2)-C human neuroblastoma cells.

kappa(3) opioid receptors have a unique binding and analgesic profile, as originally defined by naloxone benzoylhydrazone (NalBzoH). Although antisense studies demonstrated the close relationship between kappa(3) opioid and Orphan opioid receptor-like receptor (ORL1) and implied they were generated from the same gene, these studies also revealed differences in the sensitivity profiles of NalBzoH and orphanin FQ/nociceptin (OFQ/N), indicating that they were not identical. To help define the relationship between kappa(3) and ORL1 receptors, we utilized BE(2)-C human neuroblastoma cells that natively express functional ORL1 and kappa(3) opioid receptors. (125)I-[Tyr(14)]OFQ/N binds to a single population of receptors in BE(2)-C cells. Competition binding and adenylyl cyclase studies clearly illustrated marked selectivity differences between the ORL1 and the kappa(3) sites. Furthermore, antisense DNA targeting ORL1 blocked the inhibition of cAMP by OFQ/N, but not by NalBzoH. Thus, the receptor mechanisms mediating the activity of OFQ/N and NalBzoH in BE(2)-C cells are distinct.

beta-Funaltrexamine inactivates ORL1 receptors in BE(2)-C human neuroblastoma cells.

The potential interactions of natively expressed mu-opioid and opioid receptor-like (ORL1) receptors were studied by exposing intact BE(2)-C cells to agonists or antagonists for 1 h. Pretreatment with the mu-opioid receptor agonist, [D-Ala(2), N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO), or the ORL1 receptor agonist, orphanin FQ/nociceptin desensitized both mu-opioid and ORL1 receptor responses. beta-Funaltrexamine (beta-FNA) pretreatment also blocked both mu-opioid and ORL1 receptor responses, but only mu-opioid receptor binding was reduced. Moreover, beta-FNA (1 microM) failed to inhibit specific ORL1 receptor binding.

Nitric oxide is required for the maintenance but not initiation of ganglionic long-term potentiation.

The role of nitric oxide in long-term potentiation of the nicotinic pathway of synaptic transmission in the isolated superior cervical ganglia of rat was studied. Long-term potentiation was induced by a brief tetanizing pulse (tetanus, 20 Hz/20 s) to the preganglionic nerve. The amplitude of the extracellularly recorded postganglionic compound action potential was used as an index of synaptic transmission. Pretreatment with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (10 microM) or L-N(G)-nitro-arginine (10 microM) 30 min before tetanus, inhibited long-term potentiation. The inactive enantiomer of the nitric oxide synthase inhibitor, N(G)-nitro-D-arginine methyl ester (10 microM), failed to inhibit the long-term potentiation when given 30 min before the tetanus. Washout of L-N(G)-nitro-arginine, but not N(G)-nitro-L-arginine methyl ester, resulted in complete recovery of long-term potentiation. The nitric oxide synthase inhibitor had no significant effect on the basal ganglionic neurotransmission or post-tetanic potentiation. Furthermore, established long-term potentiation was blocked by superfusion of ganglia with N(G)-nitro-L-arginine methyl ester 1 h after a tetanus. Pretreatment of ganglia with the nitric oxide donor, sodium nitroprusside (100 microM), or the nitric oxide synthase substrate, L-arginine (1 mM), completely prevented the inhibitory effects of N(G)-nitro-L-arginine methyl ester on the tetanus-induced long-term potentiation. These findings present evidence for a requirement of nitric oxide for the maintenance but not induction of long-term potentiation in rat isolated superior cervical ganglia.

Nitric oxide mediates long-term potentiation in rat superior cervical ganglion.

Long-term potentiation (LTP) of the nicotinic pathway of the superior cervical ganglion (SCG) is remarkably similar to that of the hippocampus which has been shown to involve nitric oxide (NO). We investigated a similar possible involvement of NO in the LTP of the SCG of the rat. Treatment of ganglia with the NO-synthase inhibitor N(G)-nitro-L-arginine (L-NOARG, 10 microM) blocked LTP at the maintenance phase.