[1] UNIV AUTONOMA TLAXCALA, CTR INVEST REPROD ANIM, NEUROFISIOL LAB, TLAXCALA 9000, MEXICO
[2] UNIV VERACRUZ, CTR INVEST BIOL, VERACRUZ, MEXICO
[3] NATL AUTONOMOUS UNIV MEXICO, INST INVEST BIOMED, DEPT FISIOL, MEXICO CITY 04510, DF, MEXICO
[4] RUTGERS STATE UNIV, INST ANIM BEHAV, NEWARK, NJ 07102 USA