Effects of MIF-I and sex differences on tonic immobility duration in the lizard, Anolis carolinensis

In June, 36 lizards (males and females) were injected with 0.01, 0.1, 1.0, 10.0, or 100 mg/kg of MIF-I, or the diluent vehicle, and placed in a cage for ten minutes. Tonic immobility (TI) was then induced on an open lab table. All doses of MIF-I significantly reduced TI duration as compared to the duration with the diluent alone. In subsequent experiments lizards were injected with 0.1 mg/kg of MIF-I, 0.1 mg/kg of naloxone, or the diluent vehicle, and placed in small aquaria for ten minutes. TI was then induced in the small aquaria. In July, using 60 females, MIF-I and naloxone slightly reduced the duration of TI, but not significantly, and overall TI durations were reduced as compared with the first experiment possibly because the lizards could escape from the view of the experimenter in the corners of the aquaria. A third experiment was done in late September and early October with 120 males and 120 females. No drug effect was seen, but there was a significant difference between the TI durations of males and females, the females having longer durations. A relationship between the difference in response to MIF-I and the breeding seasons of the lizards could not be determined due to the possibility that the change in experimental design after the June experiments may alone have accounted for the loss of the significant response to MIF-I.