The roles of RFamide-related peptide-3 in mammalian reproductive function and behaviour.

To maximise reproductive success, organisms restrict breeding to optimal times of the day or year, when internal physiology and external environmental conditions are suitable for the survival of both parent and offspring. To appropriately coordinate reproductive activity, internal and external standing is communicated to the hypothalamic-pituitary-gonadal axis via a coordinated balance of stimulatory and inhibitory neurochemical systems. The cumulative balance of these mediators ultimately drives the pattern of gonadotrophin-releasing hormone secretion, a neurohormone that stimulates pituitary gonadotrophin secretion. Until 2000, a complementary inhibitor of pituitary gonadotrophin secretion had not been identified. At this time, a novel, avian hypothalamic peptide capable of inhibiting gonadotrophin secretion in cultured quail pituitary cells was uncovered and named gonadotrophin-inhibitory hormone (GnIH). Subsequently, the presence and functional role for the mammalian orthologue of GnIH, RFamide-related peptide, (RFRP-3), was examined, confirming a conserved role for this peptide across several rodent species. To date, a similar distribution and functional role for RFRP-3 have been observed across all mammals investigated, including humans. This overview summarises the role that RFRP-3 plays in mammals and considers the implications and opportunities for further study with respect to reproductive physiology and the neural control of sexual behaviour and motivation.

Degradation of the S. frugiperda peritrophic matrix by an inducible maize cysteine protease.

A unique 33-kDa cysteine protease (Mir1-CP) rapidly accumulates at the feeding site in the whorls of maize (Zea mays L.) lines that are resistant to herbivory by Spodoptera frugiperda and other lepidopteran species. When larvae were reared on resistant plants, larval growth was reduced due to impaired nutrient utilization. Scanning electron microscopy (SEM) indicated that the peritrophic matrix (PM) was damaged when larvae fed on resistant plants or transgenic maize callus expressing Mir1-CP. To directly determine the effects of Mir1-CP on the PM in vitro, dissected PMs were treated with purified, recombinant Mir1-CP and the movement of Blue Dextran 2000 across the PM was measured. Mir1-CP completely permeabilized the PM and the time required to reach full permeability was inversely proportional to the concentration of Mir1-CP. Inclusion of E64, a specific cysteine protease inhibitor prevented the damage. The lumen side of the PM was more vulnerable to Mir1-CP attack than the epithelial side. Mir1-CP damaged the PM at pH values as high as 8.5 and more actively permeabilized the PM than equivalent concentrations of the cysteine proteases papain, bromelain and ficin. The effect of Mir1-CP on the PMs of Helicoverpa zea, Danaus plexippus, Ostrinia nubilalis, Periplaneta americana and Tenebrio molitor also was tested, but the greatest effect was on the S. frugiperda PM. These results demonstrate that the insect-inducible Mir1-CP directly damages the PM in vitro and is critical to insect defense in maize.