MIF (Pro-Leu-Gly-NH2): failure to affect oxotremorine effects in mice and rats as well as fluphenazine catalepsy or amphetamine hyperactivity in rats

Effects of Pro-Leu-Gly-NH2 and cyclo (Leu-Gly) on the binding of 3H-quinuclidinyl benzilate to striatal cholinergic muscarinic receptors

The effects of Pro-Leu-Gly-NH2 (melanotropin release inhibiting factor, MIF) and its analog, cyclo (Leu-Gly) on the mouse and rat striatal cholinergic muscarinic receptors labeled with 3H-quinuclidinyl benzilate (QNB) were investigated. 3H-QNB bound to the rat striatal muscarinic receptors at a single high affinity site with receptor density (Bmax value) of 1200 fmol per mg protein and an apparent dissociation constant (Kd value) of 53.5 pM. At 140 pM concentration of 3H-QNB, the specific binding to the receptors was 724 fmol per mg protein. MIF in a concentration range of 10(-9) to 10(-4) M did not alter the binding of 3H-QNB but at 10(-3) M decreased the binding by 25%. Cyclo (Leu-Gly), on the other hand, in the concentration range of 10(-9) to 10(-3) M had no effect on the binding of 3H-QNB. A single injection of MIF (3 or 10 mg/kg IP) to rats did not alter the Bmax or the Kd value of 3H-QNB to bind to the striatal membranes. 3H-QNB bound to the mouse striatal muscarinic receptors at a single high affinity site with a Bmax value of 991 fmol/per mg protein and a Kd value of 21 pM. Neither acute administration of MIF (3 or 10 mg/kg IP) nor chronic treatment of the peptide (2, 8 or 32 mg/kg IP, daily for 5 days) to mice could influence the binding of 3H-QNB to the striatal muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin octapeptide (CCK-8), ceruletide and analogues of ceruletide: effects on tremors induced by oxotremorine, harmine and ibogaine. A comparison with prolyl-leucylglycine amide (MIF), anti-Parkinsonian drugs and clonazepam

Cholecystokinin octapeptide (CCK-8), ceruletide (caerulein, CER) and 10 analogues of ceruletide, were studied in mice for antagonism of the tremors induced by harmine (5 mg/kg, s.c.), ibogaine (20 mg/kg, s.c.) and oxotremorine (0.2 mg/kg, s.c.). The following reference drugs were tested for comparison: prolyl-leucylglycine amide (MIF), atropine, haloperidol, biperiden, ethopropazine, trihexyphenidyl, methixene and clonazepam. All treatments were subcutaneous, the antagonists being given 10 min (in some trials 30 min) before the tremorogen. Tremorolytic potency (ED50) was calculated from dose-response curves. Against the tremors induced by either harmine or ibogaine, CCK-8 and ceruletide, as well as many of the analogues of ceruletide had greater tremorolytic potency than the reference drugs. Against oxotremorine, however, ceruletide and its most potent analogue, Nle8-CER (other analogues were not tested) were inactive and MIF showed very little effectiveness. Additional experiments on hypothermia and sedation as well as evaluation of previous studies on other central actions suggested that the tremorolytic effect of CCK-like peptides is independent of other central effects. The CCK-like peptides may play a physiological role in the regulation of extrapyramidal motor activity.

Actions of substance P, MIF, TRH and related peptides in the substantia nigra, caudate nucleus and nucleus accumbens

Neurones in the substantia nigra were found to be sensitive to iontophoretically applied substance P, substance P 1-9 methyl ester and substance P 1-9 amide. Substance P 1-2, 4-9 and 5-9 methyl esters, thyrotropin releasing hormone (TRH), Pyroglutamyl-histidyl-2 methyl prolineamide (methyl TRH), Pyroglutamyl-histidyl-2 methyl prolineamide (methyl TRH), histidyl-proline-diketopiperazine (His-Pro) and MSH releasing inhibiting factor (MIF) were without effect on neurones in this area. Thyrotropin releasing hormone (TRH), methyl TRH, His-Pro and MIF were inactive on neurones in the caudate nucleus and nucleus accumbens. Bilateral injections of substance P and substance P 1-9 methyl ester into the ventral tegmental area (VTA) of conscious rats produced locomotor activity, while similar injections of substance P 4-9 and 5-9 methyl esters did not. The locomotor activity produced by amphetamine was prolonged by TRH, while MIF was devoid of such activity. The data suggest that substance P and substance P 1-9 have similar effects in the substantia nigra, although the mechanism of action is unclear. Thyrotropin releasing hormone and MIF probably do not have acute actions in the brain areas tested.

MIF-1: effects on norepinephrine, dopamine and serotonin metabolism in certain discrete brain regions

A single injection of melanocyte-stimulating hormone inhibitory factor (MIF-1) in a dose of 3 mg/kg IP produced no significant effect on dopamine turnover. However, a dose of 5 mg/kg increased striatal tyrosine hydroxylase activity by 25% and homovanillic acid level by 27% when compared to control values. No change in either parameter was detected in olfactory tubercles. Dopamine levels also were elevated in striatum, pons-medulla and cerebral cortex in rats receiving 5 mg/kg dose of MIF-1. In olfactory tubercles, dopamine levels were however, reduced to 71% of control values taken as 100%. The concentration of norepinephrine tended to increase in several brain areas examined but, the change was statistically significant only in olfactory tubercles and cerebral cortex. The level of norepinephrine metabolite, 3-methoxy-4-hydroxyphenylethylene glycol, was lowered to 63% in whole brain of animals given MIF-1 at the dose of 5 mg/kg. These data suggest that MIF-1 enhances the turnover of dopamine and norepinephrine in the brain. However, MIF-1 treatment seemed to produce no consistent change in brain serotonin turnover. In striatum and cortex, this neuropeptide increased serotonin but elevated the level of its metabolite, 5-hydroxyindoleacetic acid indicating that the release of this brain amine was decreased in these two brain regions. The levels of 5-hydroxyindoleacetic acid were enhanced in hypothalamus and pons-medulla regardless of the dose of MIF-1 administered.