TY  - JOUR 
T1  - Effects of naltrexone and cross-tolerance to morphine in a learned helplessness paradigm
JO  - Brazilian Journal of Medical and Biological Research
A1  - Teixeira, N.A.
A1  - Pereira, D.G.
A1  - Hermini, A.H.
SN  - 0100-879X
UL  - 10.1590/S0100-879X1997000600012
VL  - 30 
Y1  - 1997
PB  - Brazil 
ER  -