2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced appetite suppression in the Sprague-Dawley rat is not a direct effect on feed intake regulation in the brain.

The most striking sign of acute toxicity of TCDD in animals is a progressive reduction of feed intake, accompanied by loss of body weight eventually resulting in death. The mechanism(s) of this voluntary feed refusal is (are) not known but it is generally accepted that both centrally and peripherally (via feedback) acting anorectic agents exert their effect(s) in the hypothalamus. In this study direct administration into the lateral cerebral ventricle of rats resulted in much higher concentrations of TCDD in the hypothalamus and also in other regions of the brain than after a lethal intravenous (iv) injection. While rats injected iv displayed the expected cachectic syndrome, intracerebroventricularly (icv)-dosed animals ate and gained weight normally. These findings preclude the possibility of a direct effect of TCDD on appetite-regulating areas of the brain. Moreover, these results require the assumption that the appetite suppressive effect of TCDD is due to a (feedback) mechanism originating in the periphery.