@article{teixeira_pereira_hermini_1997,  title={Effects of naltrexone and cross-tolerance to morphine in a learned helplessness paradigm},  volume={30},  ISSN={0100-879X},  url={https://doi.org/10.1590/S0100-879X1997000600012},  DOI={10.1590/S0100-879X1997000600012},  number={6},  journal={Brazilian Journal of Medical and Biological Research},  publisher={Associação Brasileira de Divulgação Científica},  author={Teixeira, N.A. and Pereira, D.G. and Hermini, A.H.},  year={1997},  month={Jun},  pages={775–782} }