Effects of central alpha-MSH injections on performance in a cued discrimination task

Biphasic effect of melanocortin agonists on metabolic rate and body temperature

The melanocortin system regulates metabolic homeostasis and inflammation. Melanocortin agonists have contradictorily been reported to both increase and decrease metabolic rate and body temperature. We find two distinct physiologic responses occurring at similar doses. Intraperitoneal administration of the nonselective melanocortin agonist MTII causes a melanocortin-4 receptor (Mc4r)-mediated hypermetabolism/hyperthermia. This is preceded by a profound, transient hypometabolism/hypothermia that is preserved in mice lacking any one of Mc1r, Mc3r, Mc4r, or Mc5r. Three other melanocortin agonists also caused hypothermia, which is actively achieved via seeking a cool environment, vasodilation, and inhibition of brown adipose tissue thermogenesis. These results suggest that the hypometabolic/hypothermic effect of MTII is not due to a failure of thermoregulation. The hypometabolism/hypothermia was prevented by dopamine antagonists, and MTII selectively activated arcuate nucleus dopaminergic neurons, suggesting that these neurons may contribute to the hypometabolism/hypothermia. We propose that the hypometabolism/hypothermia is a regulated response, potentially beneficial during extreme physiologic stress.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Glycyl-L-glutamine antagonizes alpha-MSH-elicited thermogenesis

The objective of this study was to determine whether glycyl-L-glutamine [beta-endorphin(30-31)] modulates the thermoregulatory actions of alpha-MSH. Microinjection of alpha-MSH (0.06 nmol) into PGE2-responsive thermogenic sites in the medial preoptic area of rats generated a hyperthermic response, inducing a 0.85 +/- 0.19 degrees C rise in colonic temperature (Tc) within 45 min. Coadministration of glycyl-L-glutamine (3.0 nmol) completely blocked the response, maintaining Tc at baseline levels. This was not attributable to glycyl-L-glutamine hydrolysis because coadministration of glycine and glutamine had no effect on alpha-MSH-induced thermogenesis. Glycyl-L-glutamine, injected alone, was similarly without effect. These data indicate that glycyl-L-glutamine inhibits alpha-MSH-induced thermogenesis but is devoid of thermoregulatory activity itself.

Alpha-melanocyte-stimulating hormone (MSH) and [Nle4,D-Phe7]-alpha-MSH: effects on core temperature in rats

The thermoregulatory effects of alpha-melanocyte stimulating hormone (MSH), its potent analog, [Nle4,D-Phe7]-alpha-MSH (NDP-MSH), and the 1-7, 4-10, and 7-13 amino acid fragments of NDP-MSH were examined by administering these substances to the anterior hypothalamic-preoptic area (AHPOA) of rats. In Experiments 1a (MSH) and 1b (NDP-MSH), animals received 0, 0.5, 1, 5, 10, or 50 pM peptide in 0.5 microliters sterile saline (n = 6/group), with core rectal temperatures being recorded 0, 10, 20, 30, 40, 50, and 60 min after injection. In Experiment 2, subjects received 5 pM NDP-MSH1-7, NDP-MSH4-10, NDP-MSH7-13, NDP-MSH, or the vehicle, 0.5 microliters sterile saline, in a counterbalanced fashion (n = 13). Results indicated a significant effect of dose for both MSH, F(5, 30) = 2.81, p = 0.03, and NDP-MSH, F(5, 30) = 4.98, p = 0.002. A Newman-Keul's analysis indicated that mean temperatures for all groups receiving MSH or NDP-MSH were significantly greater than for the group that received saline (p < 0.05). An analysis of the data from Experiment 2 indicated a significant effect of substance, F(4, 48) = 17.31, p < 0.001. Mean temperature of animals receiving NDP-MSH, the 4-10, or the 7-13 fragments, did not differ from each other but were significantly greater than mean temperatures for animals receiving sterile saline or the 1-7 fragment of NDP-MSH (p < 0.05).