Browsing by Subject "Novel food avoidance"

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  • Mahiout, Selma; Pohjanvirta, Raimo (2016)
    The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxicity of dioxins, but also plays important physiological roles, which are only beginning to unfold. Previous studies have surprisingly unveiled that low doses of the potent AHR agonist TCDD induce a strong and persistent avoidance of novel food items in rats. Here, we further examined the involvement of the AHR in the avoidance response in Sprague-Dawley rats with three established AHRagonists: 6-formylindolo(3,2-b)carbazole (FICZ), (beta-naphthoflavone (BNF) and benzo[a]pyrene (BaP); with a novel selective AHR modulator (C2); and with an activator of another nuclear receptor, CAR: 2,4,6-tryphenyldioxane-1,3 (TPD). As sensitive indices of AHR or CAR activity, we used Cypl al and Cyp2b1 gene expression, as they are, respectively, the drug-metabolizing enzymes specifically regulated by them. We further attempted to address the roles played by enhanced neophobia and conditioned taste aversion (CTA) in the avoidance behaviour. All AHR agonists triggered practically total avoidance of novel chocolate, but the durations varied. Likewise, acutely subtoxic doses of C2, differing by 25-fold, all elicited a similar outcome. In contrast, TPD did not influence chocolate consumption at all. If rats were initially accustomed to chocolate for 6 h after single FICZ or BNF exposure, avoidance was still clearly present two weeks later when chocolate was offered again. Hence, the avoidance response appears to specifically involve the AHR instead of being triggered by induction of intestinal or hepatic nuclear receptor signalling in general. It is also shared by both endogenous and exogenous AHR activators. Moreover, this behavioural change in rats seems to contain elements of both CTA and enhanced neophobia, but further clarification of this is still required. (C) 2016 Elsevier Inc. All rights reserved.
  • Pohjanvirta, Raimo; Mahiout, Selma (2019)
    Previous studies have shown that several aryl hydrocarbon receptor (AHR) agonists, including β-naphthoflavone (BNF), elicit avoidance of novel food items in rodents, with this behavioral response displaying a similar doseresponse to hepatic induction of CYP1A1. The avoidance has been found to bear substantial similarity to conditioned taste avoidance/aversion (CTA). The present study set out to confirm the indispensability of AHR in the avoidance response, to verify whether vagal afferent fibers are involved in it, and to see if AHR signaling might interfere with the effect of the classic trigger of CTA, LiCl. To this end, globally AHR deficient (AHRKO) or vagotomized wildtype rats were treated by gavage with 60 mg/kg BNF or ip with 0.15M LiCl (4 ml/kg), and presented with chocolate which was either novel or familiar to them. Both the avoidance response and Cyp1a1 induction were missing in AHRKO rats. In contrast, Ahr+/− rats exhibited them in full, save for a single outlier. Total subdiaphragmatic vagotomy failed to interfere with the avoidance of novel or familiar chocolate or induction of Cyp1a1. After LiCl administration, male AHRKO rats showed a significantly mitigated suppression of chocolate consumption compared with wildtype animals (~60% vs. ~10% of control chocolate intake, respectively). A similar tendency was seen in females, but they were less responsive to LiCl. These findings corroborate AHR as a prerequisite of the BNF-induced novel food avoidance, prove vagal afferents unlikely mediators of this response, and imply an unforeseen involvement of AHR signaling in the thoroughly-characterized CTA instigated by LiCl.