Behavioral effects of melanocyte stimulating hormone release-inhibiting factor-1 (MIF-1)

Effects of melanostatine (MIF-1) on focal potentials in slices of rat brain cortex

The effects of tripeptide melanostatine (Melano-Inhibitory Factor--MIF-1) in concentrations 10(-7)-10(-5) M on parameters of focal potentials (FPs) were studied in slices of rat olfactory and parietal cortex. The addition of MIF-1 to perfusion fluid caused in olfactory cortex the primary depression of FP amplitudes evoked by stimulation of the lateral olfactory tract (LOT); this depression was replaced by restoration and prolonged (30-40 min) enhancement of FP amplitudes and by appearance of additional FP components, such as disynaptic EPSPs and IPSPs. In parietal cortex slices MIF-1 caused the elevation of FP amplitudes evoked by stimulating adjoining points. The repetitive perfusion of slices with MIF-1 potentiated the peptide effect on the increase of FP amplitudes. During excitatory period MIF-1 influenced specifically the functional plasticity in olfactory cortex, having facilitated the induction and sustaining of post-tetanic potentiation (PTP). Data observed support the idea of the activatory influence of MIF-1 on the CNS at the cellular level, which is likely to lie in the ground of antidepressant properties of this peptide.

MIF-1 potentiates the action of tricyclic antidepressants in an animal model of depression

In the present paper, the effect of simultaneous treatment of rats with low doses of MIF-1 and tricyclic antidepressants on rat behavior in the forced swim test was studied. It was found that MIF-1 stimulated in a dose-dependent manner "active" behavior of animals in this paradigm. The effect of MIF-1 appeared to be independent of changes in rats' locomotion in the open field test. The combined treatment of rats with MIF-1 (0.01 mg/kg IP) and amitriptyline (5 mg/kg IP) or desipramine (1.25 mg/kg) IP) significantly stimulated active behavior in the forced swim test above the level obtained with each of the drugs given separately. The present data suggest the potential clinical efficacy of a combined therapy of depressive patients with MIF-1 and small doses of tricyclic antidepressants.

MIF-1 is active in a chronic stress animal model of depression

MIF-1 was tested in an animal model of depression that used unpredictable chronic stress. In this paradigm, rats received either no stressors or a daily protocol of a variety of stressors for 20 days, during which time daily, intraperitoneal injections of various compounds were given. The tricyclic antidepressant imipramine (5 mg/kg) and low doses (0.1 and 1.0 mg/kg) of MIF-1 significantly increased activity and decreased defecation in an open field on day 21. No dose of naloxone (0.01-10.0 mg/kg) acted as an antidepressant. A high dose (10.0 mg/kg) of MIF-1 significantly increased the effects of chronic stress and produced hyperalgesia. Chronically-stressed rats were significantly more analgesic than controls. The results indicate that MIF-1 can act as an antidepressant in this model.

The effect of oxytocin and fragment (MIF-I) on the development of tolerance to hypothermic and hypnotic action of ethanol in the rat

The daily pretreatment of rats with oxytocin (OXY) or MIF-I prior to ethanol (Et-OH) administration markedly altered the alcohol tolerance when tested on the fifth day of treatment. OXY (800 and 2400 nmole/kg SC) and MIF (800 nmole/kg SC) inhibited the development of tolerance to the hypnotic effect of Et-OH. MIF at this dose also inhibited the tolerance to the hypothermic effect. Only OXY in the dose of 800 nmole/kg suppressed hypothermia in an acute experiment with Et-OH and produced by itself hypothermia after acute administration (2400 nmole/kg). The tolerance to this last effect developed after four days of peptide treatment. The results indicate that OXY and MIF-I can influence the processes of development of tolerance to some central depressive effects of Et-OH in rats.

MIF-1 (Pro-Leu-Gly-NH2) decreases activity in Siamese fighting fish (Betta splendens)

The effects of MIF-1 (Pro-Leu-Gly-NH2) on activity and aggression of male Siamese Fighting Fish ( Betta splendens) were considered. Animals were given intraperitoneal injections of 0.0 or 10.0 mg/kg MIF-1. After a 10-minute delay, they were placed in a 10 gallon aquarium and their activity was monitored for 60 minutes. Although aggressive responses in the presence of suitable opponents were not reliably affected, as significant decrease in general activity was produced. This is compatible with differential effects of MIF-1 across species.