MIF-1 and Tyr-MIF-1 augment muscimol-stimulated chloride uptake in cerebral cortex

Effects of Tyr-MIF-1 on stress-induced analgesia and the blockade of development of morphine tolerance by stress in mice

The role of Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) in biological responses to stress exposure was examined in mice. Intraperitoneal or intracerebroventricular administration of Tyr-MIF-1 attenuated not only footshock (FS)- and forced swimming (SW)-stress-induced analgesia (SIA) but also socio-psychological (PSY)-SIA that, when using the communication box, is produced without any direct physical nociceptions. Tyr-MIF-1 also disrupted the suppressive effect of concurrent exposure to FS- and PSY-stress on the development of morphine antinociceptive tolerance. In elevated-plus-maze tests, mice treated with Tyr-MIF-1 tended to spend more time in the open arms compared with the control group, suggesting the anxiolytic properties of the peptide. Thus, the finding that Tyr-MIF-1 modulates these stress responses suggests that the peptide regulates an endogenous biological alert system responding to stress exposure, perhaps, counteracting the excessive response of the system. Furthermore, Tyr-MIF-1, in the case of PSY-stress, through the attenuation of emotional factors such as fear and anxiety, may suppress PSY-SIA and inhibition by PSY-stress of the development of morphine tolerance.

Central administration of Tyr-MIF-1 stimulates gastrointestinal motility in rats: evidence for the involvement of dopamine, sigma and CCK receptors

The effect of central administration of the endogenous peptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) on the gastrointestinal myoelectric activity and its mechanism of action were studied in rats. Tyr-MIF-1 (40 & 80 micrograms/kg i.c.v.) stimulated antral and duodenal myoelectric activity in a multiphasic manner. On the antrum it induced a primary increase of the frequency of antral spike bursts followed by a consecutive return to control value and a second rise of the frequency. Likewise duodenal migrating myoelectric complexes (MMCs) were initially disrupted and replaced by an irregular spiking activity followed by a reaparition of the phase III of the MMCs with increased amplitude and frequency. Haloperidol (1 mg/kg i.p.) blocked all the effects of Tyr-MIF-1 whereas sulpiride (5 mg/kg s.c.) blocked only the duodenal stimulation without affecting that on the antrum. Similarly BMY-14802 (0.5 mg/kg s.c.) antagonized selectively the primary antral stimulation and the initial disruption of duodenal MMC induced by Tyr-MIF-1. L365 260 (10 micrograms/kg i.c.v.) has also antagonized only the initial disruption of duodenal MMCs. DTG and JO 1784 (100 micrograms/kg i.c.v. each) reproduced fully the effect of Tyr-MIF-1 on the duodenum but not that on the antrum. Domperidone, (+)SCH 23390, devazepide, PK 11-195 and flumazenil did not have effect on the action of Tyr-MIF-1. It is concluded that Tyr-MIF-1 stimulates the antrum involving haloperidol sensitive but nondopamine, dopamine, probably sigma receptors, and the duodenum via a pathway where central D2 dopamine, sigma and CCKB receptors are implied.

Oral administration of Tyr-MIF-1 stimulates gastric emptying and gastrointestinal motility in rodents

The effects of orally administered Tyr-MIF-1, an agonist of an endogenous antiopiate system, were examined on gastric emptying in mice and gastrointestinal myoelectric activity in rats. Tyr-MIF-1 (5 mg/kg in mice, 20 mg/kg in rats) accelerated gastric emptying of a methylcellulose test meal, increased the frequency of antral spike bursts, and disrupted intestinal migrating myoelectric complexes. These effects were reproduced by a subcutaneous administration of Tyr-MIF-1 at the same dosage. They were blocked by naloxone (1 mg/kg) but not by the kappa receptor subtype antagonist MR 2266 (1 mg/kg). The GABAA antagonist bicuculline (0.5 mg/kg), but not the GABAB antagonist 2-hydroxysaclofen (4 mg/kg), also antagonized the effects of Tyr-MIF-1. These data demonstrate that oral Tyr-MIF-1 stimulates gastric emptying and gastrointestinal motility through a systemic or central action that involves opioid and GABA systems.

MIF-1 and Tyr-MIF-1 do not alter GABA binding on the GABAA receptor

The endogenous brain peptides MIF-1 and Tyr-MIF-1 have been reported to alter binding at several sites on the GABAA receptor. To determine whether these peptides affect binding at the GABA site, we assessed effects of MIF-1 and Tyr-MIF-1 on [3H]SR 95531 binding in mouse cortical synaptosomal membranes. Neither peptide altered [3H]SR 95531 binding across a wide range of concentrations (10(-12)-10(-6) M). Scatchard analysis indicated no change in either apparent affinity or receptor density at both the high-affinity and low-affinity GABA sites with MIF-1 or Tyr-MIF-1, 10(-9) M. Thus, MIF-1 and Tyr-MIF-1 do not affect binding at the GABA site on the GABAA receptor.

Chronic morphine administration augments benzodiazepine binding and GABAA receptor function

Behavioral and neurochemical evidence indicates links between the opioid and GABA neurotransmitter systems. To assess effects of chronic opiates on the major site of postsynaptic GABAergic activity, the GABAA receptor, we administered chronic morphine and naltrexone to mice and evaluated binding at the benzodiazepine and t-butylbicyclophosphorothionate (TBPS) sites and GABA-dependent chloride uptake. After morphine (3 days), benzodiazepine receptor binding in vivo but not in vitro was increased in cortex compared to placebo-treated mice. TBPS binding was unchanged in cortex, but muscimol-stimulated chloride uptake was increased at low doses of muscimol. Benzodiazepine and TBPS binding and muscimol-stimulated chloride uptake were unchanged in naltrexone-(8 days) compared to placebo-treated mice. When naltrexone was administered previously to block opiate sites, the increases in benzodiazepine binding and chloride uptake observed with chronic morphine were reversed. These results indicate that chronic morphine but not naltrexone enhances benzodiazepine binding and GABAA receptor function, perhaps by an action at opioid receptors.