Administration of a 5HT 3 receptor antagonist increases the intake of diets containing Eucalyptus secondary metabolites by marsupials

Abstract

The effect of a naturally occurring plant phenolic constituent (the acylphloroglucinol derivative, jensenone, derived from Eucalyptus jensenii) on the food intake of two folivorous marsupials, the common ringtail (Pseudocheirus peregrinus) and the common brushtail possum (Trichosurus vulpecula) was studied. When fed diets containing varying concentrations of jensenone, both species regulated their intake of jensenone so as not to exceed a ceiling intake. This ceiling was about twice as high for common ringtails as for common brushtails from northern Australia. Southern populations of common ringtails showed greatly reduced capacities to tolerate jensenone. When common brushtails were injected (0.5 mg.kg-0.75 body mass) with ondansetron (a selective antagonist of serotonin 5HT3 receptors), they ate significantly more jensenone than animals injected with physiological saline. The same pattern was observed when common ringtails were fed diets containing both jensenone and ondansetron (0.0035 mg.g-1 wet mass of diet). Ondansetron injection had no effect on food intake when the food did not contain jensenone while the addition of higher doses of ondansetron to diets of common ringtails very slightly reduced food intakes of a non-jensenone diet. When common brushtails were given 50 mg of jensenone by gastric lavage, their average subsequent intake of dietary jensenone matched the difference between the daily threshold and the dose given, although the response of individuals was highly variable. Lavage with water alone had no effect on subsequent jensenone intake compared with the pre-dose period. We interpret these results as evidence that the antifeedant effects of jensenone and related compounds are partly mediated by serotonin action on 5HT3 receptors most likely via "nausea" to condition a food aversion.

Bark salicylates and condensed tannins reduce vole browsing amongst cultivated dark-leaved willows (Salix myrsinifolia)

“…A great number of studies in which high concentrations of purified phytochemicals have been added to the diet of captive animals have demonstrated that as the concentration of harmful chemicals in the diet increases, food intake declines and the amount of the ingested chemicals remains below a certain threshold level (e.g. Lawler et al 1998;Pass and Foley 2000;Clauss et al 2003). There is however, no earlier evidence demonstrating the function of these mechanisms when the animals feed on a natural plant diet containing the same compounds.…”

The dilemma of foraging herbivores: dealing with food and fear

“…Specialists can cope with higher toxin concentrations than generalists by reducing toxin absorption (Sorensen et al 2004) or by using more efficient or less expensive metabolic pathways (Boyle et al 1999;Shipley et al 2012). These processes delay the physiological feedback affecting intake, which is instigated by the plasma concentration of the toxin or its metabolites (McLean et al 2007), the emetic system (Provenza et al 1994;Lawler et al 1998), dose-dependent inhibition of cellular function (Forbey et al 2011) or possibly acidosis (Foley 1992).…”

Chemical Defenses in Eucalyptus Species: A Sustainable Strategy Based on Antique Knowledge to Diminish Agrochemical Dependency

“…A different class of phenolic derivatives, formylated phloroglucinols, only produced by some Eucalyptus species have shown to display a wide range of ecologically significant biological activities, particularly as anti-feedant (Lawler et al 1998, Sidana et al 2010.…”