2,3,7,8-Tetrachlorodibenzo-p-dioxin treatment induces c-Fos expression in the forebrain of the Long-Evans rat.
ABSTRACT 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most toxic environmental pollutants. In the present study, we examined c-Fos expression in the central nervous system (CNS) after administration of a lethal dose of TCDD to the adult Long-Evans rat to clarify if the CNS participates in TCDD-induced intoxication. A single dose of TCDD (dissolved in olive oil, 50 microg/kg) or olive oil alone was administered to the rats by gavage. Animals were allowed to survive for 1 day to 5 weeks. Three days after the administration, a significantly large number of Fos-immunopositive cells were found in the hypothalamus (i.e. dorsomedial hypothalamic nucleus, paraventricular hypothalamic nucleus, medial preoptic nucleus), central amygdaloid nucleus and bed nucleus of the stria terminalis. These results suggest that some TCDD toxicity may be induced by its direct action on the CNS.
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ABSTRACT: Many toxic environmental and food agents have been suspected to be potential risk factors in inducing memory disabilities under normal and pathological conditions. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (known as dioxin or TCDD) is a common and prototypical member of a class of noxious environmental and food contaminants called the halogenated aromatic hydrocarbons. Since the role of dioxin in memory processes has not been studied in detail, the present report aims at elucidating the role of this pollutant in the maintenance of cognitive function. We found that TCDD (50miccrog/kg) induced spatial memory deficits in the Morris water maze (MWM) task in female but not male mice. This sex-dependant effect of dioxin seems to be related to the alteration of estrogen pathways, as treatment with 17beta-estradiol-3-benzoate (E; 5microg/day) reversed memory deficits induced by TCDD. We also observed that cognitive impairments produced by dioxin, which is known to interfere with retinoid turnover and metabolism, were abolished by retinoic acid (RA) treatment (150microg/kg). The cognitive effects of E and RA treatments seem to derive from common rather than additive mechanisms since memory deficits produced by TCDD were fully reversed by these compounds when used separately or in combination. Attenuation of dioxin-induced memory deficits in mice lacking transthyretin (TTR) suggests that TCDD may be acting by affecting the major route of retinol transport involving TTR. Taken together, these results suggest that the environmental and food pollutant TCDD can induce memory deficits by altering the estrogen pathways and a main route of TTR-mediated retinol transport.NeuroToxicology 04/2008; 29(2):318-27. · 2.65 Impact Factor
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ABSTRACT: Orexins, novel neuropeptides, are exclusively localized in the hypothalamus and implicated in the regulation of a variety of activities, including food intake and energy balance. Nitric oxide (NO), an unconventional neurotransmitter, is widely present in numerous brain regions including the hypothalamus, and has similar physiological roles to those of the orexins. The present study was undertaken to examine the distribution of orexin neurons and the presence of neuronal nitric oxide synthase (nNOS) in the orexin neurons to clarify whether NO interacts with the orexins in the neuronal regulation activities in the Long-Evans rat. We used two double-labeling methods: nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry in combination with orexin immunohistochemistry, and double-labeling fluorescent immunohistochemistry for orexin and nNOS. The majority of the orexin immunoreactive neurons were localized mainly in the areas of the dorsomedial hypothalamic nucleus (DMN), the dorsal part of the perifornical nucleus (PEF) and lateral hypothalamic area. The orexin immunoreactive cell bodies were medium in size, and triangular, round, elliptic, and fusiform in shape. The sizes and shapes of orexin neurons in the different parts were similar. Cell bodies coexpressing the orexin and nNOS or NADPH-d were present in the areas of the DMN and the PEF, and the nerve fibers containing orexin and nNOS were distributed in the DMN and PEF, arcuate nucleus (ARN) and ventromedial hypothalamic nucleus (VMH). These results provide morphological evidence that there exists a population of nNOS- or NADPH-d-/orexin-coexpressing neurons in the orexinergic cell group in the hypothalamus, and taken together with previous findings, suggest that NO may play a role in the mechanisms by which orexin neurons regulate food intake and energy balance.Neuroscience Research 06/2003; 46(1):53-62. · 2.20 Impact Factor