A conspicuous but scantly studied feature of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity is avoidance of unfamiliar foodstuffs, which seems to be one of the very few exquisitely sensitive behavioural effects in adult laboratory animals. Here we characterized this peculiar response further after low doses of TCDD. The time-course of the novelty avoidance, the role of nutriment form and dependence of the aversion on the time lag between TCDD exposure and the presentation of a novel food item was determined using rats with different sensitivities to lethality of TCDD. Rats were offered chocolate, liquid nutriment or familiar feed with an unfamiliar texture and the consumptions were measured for varying periods. Aversion to a novel food item (chocolate) emerged within 5.5h after TCDD exposure. A lag of a week or more between TCDD exposure and the presentation of chocolate abolished the avoidance whereas simultaneous presentation of chocolate with TCDD treatment rendered the rats oblivious to the chocolate's presence for over 40 days. Rats avoided also liquid nutriments when these were coupled with TCDD administration but this faded much sooner than chocolate aversion. Even a change in feed texture at the exposure was able to elicit the response. However, habituation was found to interfere with the aversion. These findings indicate that temporal proximity to TCDD exposure is a requisite for the avoidance response which emerges rapidly and may linger on for extended periods, but is not strictly confined to any specific food type. The molecular mechanisms of this tantalizing behavioural alteration remain to be determined.
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