Prenatal opiate exposure impairs radial arm maze performance and reduces levels of BDNF precursor following training

Prenatal exposure to opiates, which is invariably followed by postnatal withdrawal, can affect cognitive performance. To further characterize these effects, we examined radial 8-arm maze performance and expression of brain derived neurotrophic factor (BDNF) in male rats prenatally exposed to the opiate l-α-acetylmethadol (LAAM). Female rats received 1.0 mg/kg/day LAAM or water via daily oral gavage for 28 days prior to breeding, during breeding, and throughout pregnancy. Pups were fostered to non-treated lactating dams at birth and underwent neonatal opiate withdrawal. At 5–6 months, prenatal water- and LAAM-exposed males (n = 6 each; non-littermates) received radial arm maze training consisting of ten trials a day for five days and three retention trials on day six. Rats prenatally exposed to LAAM had poorer maze performance, decreased percent correct responding and more reference and working memory errors than prenatal water-treated controls. However, they were able to acquire the task by the end of training. There were no differences between the groups on retention 24 h after testing. Following retention testing, hippocampi were removed and protein extracted from cytosol and synaptic fractions. Western blots were used to measure levels of mature and precursor BDNF protein, as well as the BDNF receptor TrkB. BDNF precursor protein was significantly decreased in the synaptic fraction of trained prenatal LAAM-treated rats compared to prenatal water-treated trained controls. No effects were found for the full-length or truncated TrkB receptor. In untrained rats, prenatal treatment did not affect any of the measures. These data suggest that prenatal opiate exposure and/or postnatal withdrawal compromise expression of proteins involved in the neural plasticity underlying learning.