Effect of 1DMe, a Neuropeptide FF Analog, on Acetylcholine Release From Myenteric Plexus of Guinea Pig Ileum

Abstract

ABSTRACT-Since neuropeptide FF (NPFF) is a putative neurotransmitter to exert anti-opioid activity, we examined the effects of [D-Tyr 1 , (NMe)Phe 3]neuropeptide FF (1DMe), a stable NPFF analog, on acetylcholine (ACh) release from a longitudinal muscle-myenteric plexus (LMMP) preparation of guinea pig ileum in which opioids were known to inhibit ACh release when muscarinic autoinhibition was not fully activated. In the presence of atropine, 1DMe increased spontaneous and electrical field stimulation (EFS)-evoked ACh release in a concentration-dependent manner. Naloxone also increased ACh release. The stimulatory effects of 1DMe and naloxone were not additive. In the absence of atropine, 1DMe did not affect ACh release. Morphine decreased spontaneous and EFS-evoked ACh release in the presence of 1 mM atropine. 1DMe as well as naloxone counteracted the inhibitory effects of morphine on EFS-evoked ACh release. The combination of 1DMe and naloxone was not more inhibitory than either drug alone. 1DMe had no appreciable effect on norepinephrine-induced inhibition of spontaneous and EFS-evoked ACh release. These results first demonstrated the effects of a NPFF analog on neurotransmitter release: 1DMe had a stimulatory effect on spontaneous and EFS-induced ACh release from the LMMP preparation of guinea pig ileum, probably by counteracting the inhibitory effect of endogenous opioids on ACh release.Keywords: Neuropeptide FF, Acetylcholine release, Morphine, Muscarinic autoinhibition, Myenteric plexusThe important role of an octapeptide neuropeptide FF (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH 2; NPFF) has been demonstrated in the central nervous system (1). NPFF exerts modulatory action on morphine-induced analgesia in rodents (2, 3). Namely, the intracerebroventricular administration of NPFF reverses morphine-induced analgesia in rats (1). NPFF antagonizes the modulation of Ca 2+ channels by mu-opioids in isolated rat spinal ganglion and dorsal raphe neurons (4, 5) and by nociceptin in rat dorsal raphe neurons (5). NPFF modulates the excitatory synaptic transmission through an interaction with presynaptic delta-opioid receptors in the pontine parabrachial nucleus in vitro (6). Although these results suggest that NPFF reverses the effect of morphine or endogenous opioids, the exact mechanism of the action of NPFF at the neuronal and cellular level remains unknown.It is well known that morphine has a marked inhibitory effect on the motility of the gastrointestinal tract in the human as well as experimental animals (7). The inhibitory effect of morphine is mainly due to reduction in acetylcholine (ACh) release from enteric cholinergic neurons (8, 9). In a previous report, we demonstrated that morphine inhibited ACh release from longitudinal muscle with myenteric plexus (LMMP) preparations of the guinea pig ileum when muscarinic autoinhibition was not fully activated (10). We also demonstrated that endogenous opioids are involved in the regulation of ACh release, because naloxone increases electrical field stimulation (EFS)-evoke...

Neuropeptide FF (NPFF) Analogs Functionally Antagonize Opioid Activities in NPFF2 Receptor-Transfected SH-SY5Y Neuroblastoma Cells

“…It is identical to that demonstrated in dorsal root ganglion (Rebeyrolles et al, 1996) and dorsal raphe neurons (Roumy and Zajac, 1999). In contrast to the specificity toward opioid receptors established in neurons (Roumy and Zajac, 1999) and in in vitro models (Takeuchi et al, 2001), the activation of NPFF 2 receptors in SH 2 -D9 cells also reduces the inhibition of N-type Ca 2ϩ channels induced by NPY Y 2 and ␣ 2 -adrenergic receptors. It should be recognized, however, that the interaction of NPFF 2 receptors with other G protein-coupled receptors has not been exhaustively studied in isolated neurons and thus it cannot be entirely excluded that the activation of NPFF 2 receptors could antagonize the activity of receptors other than the opioids.…”

“…NPFF or analogs, which are inactive by themselves, reverse the opioid-induced inhibition of Ca 2ϩ conductance in NPFF 2 receptor-expressing neurons dissociated from rat dor-sal root ganglion (Rebeyrolles et al, 1996), dorsal raphe (Roumy and Zajac, 1999), and NPFF 1 -expressing neurons from the hypothalamic periventricular nucleus (Roumy et al, 2003). This functional antagonism also has been observed by others in different models such as acetylcholine release in the myenteric plexus of the guinea pig (Takeuchi et al, 2001), electrical response in hippocampus slices (Miller and Lupica, 1997), or Met-enkephalin release in the spinal cord (Ballet et al, 1999). In this latter case, blockade of presynaptic ␦-opioid autoreceptors after activation of NPFF receptors leads to enhanced release of Met-enkephalin that activates -opioid receptors (Mauborgne et al, 2001).…”

Physical Association between Neuropeptide FF and μ-Opioid Receptors as a Possible Molecular Basis for Anti-opioid Activity

“…For example, the NPFF analog 1DMe blocks presynaptic ␦-opioid auto-receptors in the spinal cord, leading to an increase in K ϩ -evoked met-enkephalin release (10). 1DMe also inhibits the reduction induced by morphine, but not by noradrenalin, of the electrically evoked acetylcholine release in the guinea pig myenteric plexus (11). Furthermore, on isolated neurons from rat periventricular and dorsal raphe nuclei, that co-express nociceptin receptors and NPFF 1 or NPFF 2 receptors, respectively, NPFF analogs inhibit the nociceptin-induced reduction of N-type Ca 2ϩ channel conductance (12,13).…”

Identification of proNeuropeptide FFA peptides processed in neuronal and non‐neuronal cells and in nervous tissue

“…Recent data provided evidence that opioid and NPFF endogenous systems exert a tonic activity, NPFF counteracting tonic opioid analgesia under resting conditions [13]. NPFF is also implicated in morphine tolerance, morphine abstinence and also in several physiological processes, such as body thermoregulation, food intake and blood pressure regulation [7,[14][15][16][17][18][19][20][21].These pharmacological effects are mediated by two G-protein-coupled receptors, NPFF 1 and NPFF 2 , cloned in human and rat [22][23][24][25]. Pharmacological characterization of these receptors in recombinant cell lines showed a better selectivity of peptides deduced from proNPFF A sequence for NPFF 2 receptors binding, whereas proN-PFF B -derived peptides displayed a greater affinity for NPFF 1 receptors [26].…”

“…Recent data provided evidence that opioid and NPFF endogenous systems exert a tonic activity, NPFF counteracting tonic opioid analgesia under resting conditions [13]. NPFF is also implicated in morphine tolerance, morphine abstinence and also in several physiological processes, such as body thermoregulation, food intake and blood pressure regulation [7,[14][15][16][17][18][19][20][21].…”