Central effects of neuropeptide FF on intestinal motility in naive and morphine-dependent rats

Central and peripheral modulation of gastrointestinal transit in mice by DN-9, a multifunctional opioid/NPFF receptor agonist

BACKGROUND

The nonapeptide DN-9 functions as a multifunctional agonist to opioid and neuropeptide FF (NPFF) receptors and exhibits antinociceptive effects at the central and peripheral levels.

METHODS

The effects of DN-9 on small and colonic intestinal transit were evaluated using the upper gastrointestinal (GI) transit test and colonic bead expulsion assay, respectively. Opioid and NPFF receptor antagonists were used to investigate the mechanisms of DN-9-induced GI inhibition. Furthermore, the agonism of the DN-9 analog [Phg⁹ ]-DN-9 to opioid and NPFF receptors was tested by the cAMP assay.

KEY RESULTS

Intracerebroventricular administration of DN-9 dose-dependently slowed upper GI transit and colonic expulsion via mu- and kappa-opioid receptors in the brain, independent of the delta-opioid receptor. Similarly, intraperitoneal injection of DN-9 dose-dependently inhibited GI propulsion via the peripheral opioid receptors. DN-9-induced GI transit inhibitions were significantly aggravated by the NPFF receptor antagonist RF9. Moreover, the DN-9 analog [Phg⁹ ]-DN-9, an agonist at mu-, delta-, and kappa-opioid receptors but not NPFF receptors, inhibited GI more potently than DN-9. In addition, intracerebroventricular NPFF significantly attenuated the central inhibitory effects induced by [Phg⁹ ]-DN-9 and morphine. However, central and peripheral injections of NPFF or RF9 almost had no significant effects on GI transit by itself.

CONCLUSION AND INFERENCES

Intracerebroventricular and intraperitoneal administrations of DN-9 inhibit GI transit via opioid receptors in mice by central and peripheral mechanisms, respectively. In addition, the NPFF agonism of DN-9 possesses antiopioid effects on GI transit, which might explain the reduced constipation at the antinociceptive doses.

Modulation of neuropeptide FF (NPFF) receptors influences the expression of amphetamine-induced conditioned place preference and amphetamine withdrawal anxiety-like behavior in rats

Many data indicate that endogenous opioid system is involved in amphetamine-induced behavior. Neuropeptide FF (NPFF) possesses opioid-modulating properties. The aim of the present study was to determine whether pharmacological modulation of NPFF receptors modify the expression of amphetamine-induced conditioned place preference (CPP) and amphetamine withdrawal anxiety-like behavior, both processes relevant to drug addiction/abuse. Intracerebroventricular (i.c.v.) injection of NPFF (5, 10, and 20 nmol) inhibited the expression of amphetamine CPP at the doses of 10 and 20 nmol. RF9, the NPFF receptors antagonist, reversed inhibitory effect of NPFF (20 nmol, i.c.v.) at the doses of 10 and 20 nmol and did not show any effect in amphetamine- and saline conditioned rats. Anxiety-like effect of amphetamine withdrawal was measured 24h after the last (14 days) amphetamine (2.5mg/kg, i.p.) treatment in the elevated plus-maze test. Amphetamine withdrawal decreased the percent of time spent by rats in the open arms and the percent of open arms entries. RF9 (5, 10, and 20 nmol, i.c.v.) significantly reversed these anxiety-like effects of amphetamine withdrawal and elevated the percent of time spent by rats in open arms at doses of 5 and 10 nmol, and the percent of open arms entries in all doses used. NPFF (20 nmol) pretreatment inhibited the effect of RF9 (10 nmol). Our results indicated that stimulation or inhibition of NPFF receptors decrease the expression of amphetamine CPP and amphetamine withdrawal anxiety, respectively. These findings may have implications for a better understanding of the processes involved in amphetamine dependence.

Opioid-modulating properties of the neuropeptide FF system

Opioid receptors are involved in the control of pain perception in the central nervous system together with endogenous neuropeptides, termed opioid-modulating peptides, participating in a homeostatic system. Neuropeptide FF (NPFF) and related peptides possess anti-opioid properties, the cellular mechanisms of which are still unclear. The purpose of this review is to detail the phenomenon of cross-talk taking place between opioid and NPFF systems at the in vivo pharmacological level and to propose cellular and molecular models of functioning. A better knowledge of the mechanisms underlying opioid-modulating properties of NPFF has potential therapeutic interest for the control of opioid functions, notably for alleviating pain and/or for the treatment of opioid abuse.

Effect of electroacupuncture at Sibai on the gastric myoelectric acitivities of denervated rats

AIM: To explore the mechanism of the exciting effects of electro-acupuncture (EA) at Sibai on the gastric myoelectric activities.

METHODS: A total of 32 rats were randomly divided into four groups. Through intraperitoneal injection with atropine (the anti-cholinergic agent by blockade of muscarinic receptors), hexamethonium (automatic nerve ganglion-blocking agent) and reserpine (anti-adrenergic agent by depleting the adrenergic nerve terminal of its norepinephrine store), effects of EA at Sibai on the gastric myoelectric activities of the denervated rats were observed.

RESULTS: After intraperitoneal injection of atropine and hexamethonium, the average amplitude and ratio of period to time in the phase of high activity of gastric myoelectric slow wave, and the average numbers of the peaks of gastric myoelectric fast wave were significantly decreased (P < 0.01, P < 0.05, P < 0.01), while after intraperitoneal injection of reserpine, the aforementioned three parameters were increased (P < 0.01, P < 0.05, P < 0.01). EA at Sibai point partially relieved the inhibitory effect of atropine and hexamethonium on the gastric myoelectric activities in the rats (P < 0.05 or P > 0.05).

CONCLUSION: Cholinergic and adrenergic nervous systems and autonomic nerve ganglion participate in the peripheral passage of the controlling effects of EA at Foot Yangming Channel on gastrointestinal tract.

Characteristics and cholinergic control of the 'minute rhythm' in ovine antrum, small bowel and gallbladder

Eight adult conscious rams were used to characterize further the minute rhythm and to determine the role of cholinergic receptors in nervous control of this event. In chronic experiments, the myoelectrical and motor activity of the gastrointestinal tract and gallbladder were recorded. Physiological experiments were performed in fasted or non-fasted rams before, during and after feeding, and the occurrence of minute rhythm during various phases of the migrating motor myoelectric complex was observed. The pattern occurred most frequently in the small intestine, where it exhibited mostly the propagating character. It was also detectable in the ileum. In the gallbladder, the minute rhythm arrived systematically and its character was irregular, propagating, retropropagating or stationary. In all episodes observed, it was well correlated with that in the small intestine. In the pyloric antrum, the minute rhythm was identified occasionally. During pharmacological experiments, 0.15 M NaCl or graded doses of hexamethonium, atropine and pirenzepine were administered intravenously during various phases of the migrating motor myoelectric complex, in fasted and non-fasted animals, before and during feeding. The drugs inhibited the minute rhythm in the small bowel for a longer period than in the gallbladder. However, the smallest dose of pirenzepine (0.02 mg/kg) exerted a non-significant effect both in the small intestine and in the gallbladder. It is concluded, that in normal conditions the minute rhythm occurs regularly in the entire small intestine and in the gallbladder. In the small intestine the pattern is organized more precisely. The minute rhythm is controlled by nicotinic receptors and by muscarinic receptor subtypes.

Anti-opioid efficacy of neuropeptide FF in morphine-tolerant mice

The modulatory effects of 1DMe (d-Tyr-Leu-(NMe)Phe-Gln-Pro-Gln-Arg-Phe-NH2), an agonist of Neuropeptide FF (NPFF) receptors, on opioid antinociceptive activity have been compared in naive and tolerant mice in the tail-flick and the hot-plate tests. In naive mice, 1DMe alone had no effect on pain threshold but decreased dose-dependently (3-22 nmol) the analgesic activity of morphine in both tests. In tolerant mice, injections of 60-fold lower doses of 1DMe (0.05-0.5 nmol) reverse morphine-induced analgesia in the tail-flick test but this anti-opioid effect was no longer observed with the highest doses of 1DMe tested (3-22 nmol). In the hot-plate test, the anti-opioid action of 1DMe was not detected, whatever doses tested. Neither the NPFF-like immunoreactivity content of spinal cord and of olfactory bulbs, nor the density of NPFF receptors in olfactory bulbs, were altered. These results indicate that a chronic morphine treatment modifies the pharmacological properties of NPFF but the type of pain test is crucial in determining NPFF effects.

Endogenous opiates: 1995

This article is the eighteenth installment of our annual review of research concerning the opiate system. It includes articles published during 1995 reporting the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects. The specific topics covered this year include stress: tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.