Alpha-MSH and MIF-2 effects on serotonin levels and accumulation in various rat brain areas

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

Consideration of the isolation, structure, localization, and behavioral effects of melanocyte stimulating hormone release inhibiting factor (MIF-1) is followed by a review of its opiate antagonistic and clinical effects. Evidence pertaining to various hypotheses offered in explanation of these behavioral effects is examined and evaluated. It is concluded that MIF-1 affects behavior in many instances with possible antagonistic effects as well as clinical possibilities.

Alpha-melanocyte-stimulating hormone and behavior

Melanocyte-stimulating hormone (MSH) has putative adaptive significance in all forms of species where it is present. In mammals the polypeptide chain influences learning, memory and attention. Chemically MSH shares the first 13 (alpha-MSH) or the first 18 or 22 (beta-MSH) amino acids with adrenocorticotropic hormone (ACTH), even though the mechanisms of secretion and behavioral effects are often quite different. The still shorter peptide chain MSH/ACH4-10 demonstrates significant melanotropic and behavioral actions of alpha-MSH without showing any steroidogenic effect. Behaviorally, alpha-MSH and MSH/ACTH analogues (MSH/ACTH4-9 and MSH/ACTH4-10 influence the parameters of learning, attention and memory in both human and infrahuman subjects. Alpha-MSH has also been reported to increase sensitivity and augment arousal mechanisms in the CNS. Alpha-MSH has been observed to increase and sustain novelty-induced defecation, and this behavior was found to be accompanied by a concomitant decrease in whole brain DA and NE levels in both intact and hypophysectomized rats exposed daily to a test box. The behavioral effects of alpha-MSH may be partially modulated by the enhanced cyclic-AMP activity in the CNS observed after MSH administration. MSH also seems to be working in conjunction with the hypothalamic tripeptide MIF-1 and the pineal hormone melatonin, both of which can affect the release of MSH from the pituitary. Recent evidence suggests that MSH is counterbalancing against and complementing with the effects of endorphins, specifically beta-endorphin (61-91 chain of beta-LPH), in maintaining learning and attentive behaviors.

alpha-MSH, MIF-I and melatonin: effects on novelty-induced defecation, plasma 11-OHCS and central catecholamines in rats

The pituitary-hypothalamo-pineal complex involving MSH, MIF-I and melatonin has been strongly emphasized in the adaptive mechanism of the animal. A series of experiments was conducted to investigate the effects of alpha-MSH, MIF-I and melatonin on novelty-induced defecation, step-down activity, plasma 11-OHCS levels and whole brain DA and NE concentrations over days of novelty X drug treatment. alpha-MSH consistently enhanced and sustained novelty-induced defecation, increased plasma 11-OHCS levels in the resting intact rats and in the novelty exposed hypophysectomized (hypox) rats, and decreased brain DA and NE levels in intact, hypox and sham-hypox rats. MSH did not increase plasma 11-OHCS in intact and sham-hypox rats during exposure to novelty. MIF-I significantly habituated novelty-induced defecation and increased brain DA and NE levels over 5 days of drug X novelty treatment. Melatonin, on the other hand, inhibited novelty-induced defecation, decreased plasma 11-OHCS and increased brain DA level over 5 days of melatonin X novelty treatment. MSH, MIF-I or melatonin did not show any significant effect on the step-down activity of the rats. The results suggest the possibility that central CAs may be implicated in the behavioral changes observed after alpha-MSH, MIF-I and melatonin administration and in the interaction of the pituitary-hypothalamo-pineal complex involving MSH, MIF-I and melatonin.

alpha-MSH effects on novelty-induced defecation, plasma 11-OHCS and whole brain catecholamines in hypophysectomized rats

The effect of hypophysectomy on novelty-induced defecation was found to be inhibitory in nature, but this effect was reversed by treatment with alpha-MSH. MSH-treated hypox rats maintained, over days, novelty-induced defecation and showed a significant elevation in plasma 11-OHCS levels, compared with the levels of control-injected counterparts. MSH treatment also reduced over Days 1 to 5 the whole brain DA and whole brain NE levels in hypox animals. Control-treated hypox rats, however, showed an increase in brain NE concentration which was significantly reduced by MSH treatment. Sham-hypox animals also sustained novelty-induced defecation after MSH treatment but did not show a significant rise in plasma 11-OHCS level. Whole brain DA and whole brain NE levels in sham-hypox rats were also reduced significantly by MSH treatment. The behavioral maintenance of defecation in hypox and sham-hypox rats seem to be concomitant with significant reductions in whole brain catecholamines.

Effects of MIF-I and melatonin on novelty-induced defecation and associated plasma 11-OHCS and brain catecholamines

In two experiments the effects were investigated of MSH-inhibiting factor-I (MIF-I) and of Melatonin on step-down latencies, defection, plasma 11-OHCS levels, whole brain DA and whole brain NE concentrations on Days 1, 3 and 5 of novelty exposure. Treatment with MIF-I led to a significant habituation of novelty-induced defecation over 5 days, whereas plasma 11-OHCS level was reduced only on Day 1. The concentrations of whole brain DA and whole brain NE also showed a significant increase over days of MIF-I and novelty treatment. Melatonin treatment, on the other hand, significantly inhibited novelty-induced defecation and reduced plasma 11-OHCS level on Day 5 of novelty exposure. Melatonin treatment led to a significant increase of whole brain DA in animals exposed to novelty for 5 days. Neither MIF-I nor Melatonin was found to significantly affect the step-down activity of treated animals. The overall results suggested a possible relationship between novelty-induced defecation and brain DA levels of MIF-I and Melatonin treated animals.

Serotonin and MSH secretion: effect of parachlorophenylalanine on the pituitary cytology of the eel

Parachlorophenylalanine (pCPA), an inhibitor of tryptophan hydroxylase which depletes brain serotonin in higher vertebrates, was injected into freshwater eels. After 4 or 6 injections (200 mg/kg/day) or 10 injections (100 and 140 mg/kg/day), the animals are paler, with a low melanophore index. In the pituitary gland, granules tend to accumulate in the basal part of the MSH cells and in the perinuclear area. Cells appear smaller with a decreased nuclear area (P less than 0.001). In the neurohypophysis, the amount of neurosecretory material is often reduced. Conversely, injections of 5-hydroxytryptophan induce a strong darkening, a result similar to that previously reported in some amphibian species and in one lacertilian species. These data substantiate the hypothesis of a stimulatory influence of 5-hydroxytryptamine on MSH release and possibly its synthesis in the eel and other lower vertebrates.

Investigations on alpha-MSH and MIF-1 effects on cyclic AMP levels in rat brain

It has been suggested that the peptides alpha-metanocyte stimulating hormone (alpha-MSH) and MSH-release inhibitory factor (MIF-1) may alter adenosine-3', 5'-cyclic monophosphate (cAMP) metabolism [13,26]. Normal and hypophysectomized (hypoxed) rats were administered saline (controls IP daily X 3), alpha-MSH (80 mug/kg IP daily X 3) or MIF-1 (1 or 10 mg/kg IP daily X 3) and sacrificed 30 min after the third injection in a focused microwave oven (1.5 KW; 2-3 sec). Various brain areas were then assayed for cAMP levels after each treatment. The occipital cortex area was the only area to show consistent changes in both normal and hypoxed rats after alpha-MSH treatment. These findings were replicated for the occipital cortex in a second group of normal and hypoxed rats which were similarly treated. The results suggest a correlation between the rise in cAMP found and reported changes in visual acuity and attention in rats and human after treatment with alpha-MSH [8,14, 23].

Alpha-MSH and MIF-I effects on catecholamine levels and synthesis in various rat brain areas

Attempts were made to find a biochemical correlate with previously observed behavioral alterations after administration of alpha-melanocyte-stimulating hormone (MSH) and MSH release-inhibiting factor (MIF-I). Brains of intact and hypophysectomized (hypox) rats were analyzed for endogenous catecholamine levels and the disappearance rate of endogenous norepinephrine (NE) after treatment with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT). The studies undertaken show the following: (1) After the injection of MSH (100 mug/kg IP daily x 3) and AMPT, samples in different groups of intact and hypox rats were taken at 0, 1, 2, 4 and 6 hrs in 7 different brain areas. In the mid-brain area for the intact group of rats, the rate of disappearance of NE was faster and for the hypox rats it was slower than the rate for control rats not treated with the peptides. NE levels in the same area at time 0 were 11 percent lower than controls in hypox rats and unchanged in unoperated animals. (2) After the injection of MIF-I (20 mg/kg IP daily x 3) in similar experiments as with MSH, a reduced rate (p less than 0.05) of NE disappearance for the first 4 hr and an increased rate (p less than 0.05) of NE disappearance for the last 2 hr of the experiments occurred for both the intact and hypox rats in the mid-brain area where endogenous NE levels were lowered by 11 and 12 percent at 0 min. In no other brain areas were alterations in NE breakdown found in both the intact and hypox rat groups. Behavioral changes have been found previously under similar experimental conditions in both intact and hypox rats. (3) Rates of dopamine disappearance in experiments similar to those described for NE disappearance indicated that in the striatal brain area no change was found in the intact rats after either MSH or MIF-I, whereas a decrease in DA disappearance was found for hypox rats during the six hour experimental period only after MSH. The results indicate that a correlation between behavioral changes, rates of disappearance and endogenous levels of NE in the mid-brain area may occur after MIF-I at the times examined but that a similar correlation for MSH did not appear likely.