title: Learning behavior in rat offspring after in utero and lactational exposure to either TCDD or PCB126.
abstract: OBJECTIVE
  We studied and compared the possible effects of in utero and lactational exposure to 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) or 3, 3', 4, 4', 5-pentachlorobiphenyl (PCB126) on learning behavior in offspring.
  
  
  METHODS
  Pregnant Long-Evans Hooded rats were administered either TCDD (50, 200, or 800 ng/kg) or PCB126 (500, 2,000 or 8,000 ng/kg) on gestational day 15. A procedure of schedule-controlled operant behavior was applied to examine learning behavior in the male and female offspring at 11 weeks of age for 30 days. Three indices, namely, response rates in a fixed ratio (FR) and in a differential reinforcement of low rates (DRL), and reward rate in the DRL component in multiple FR 20 DRL 20 s (mult-FR 20 DRL 20-s) test sessions, were used for the evaluation of learning behavior.
  
  
  RESULTS
  Toxic effects on learning behavior in male and female pups following in utero and lactational exposure to TCDD or PCB126 were observed mainly in the FR learning component. However, no linear dose-dependent effects of either of the two compounds were observed for the above three indices. The response rates of animals in the low-dose TCDD and PCB126 groups decreased and those in medium-dose TCDD and PCB126 groups appeared to induce hyperactive behavior. The high dose of PCB126 appeared to have a distinct toxicity from that of TCDD in terms of the acquisition of learning behavior.
  
  
  CONCLUSIONS
  Toxicities of PCB126 and TCDD in learning behavior might be similar to each other and the current toxic equivalency factor (TEF) of 0.1 for PCB126 can be considered to be appropriate for this endpoint.
authors: Research Center for Environmental Risk, National Institute for Environmental Studies, Tsukuba, 305-8506, Japan.
authors: Rieko
authors: R
authors: Hojo
authors: Masaki
authors: M
authors: Kakeyama
authors: Yoshika
authors: Y
authors: Kurokawa
authors: Yasunobu
authors: Y
authors: Aoki
authors: Junzo
authors: J
authors: Yonemoto
authors: Chiharu
authors: C
authors: Tohyama