Intake of and preference for sweet solutions are attenuated in morphine-withdrawn rats.

The hypothesis that intake of sweet solutions is partially controlled by endogenous opioid peptides was tested in 2 experiments that examined the effects of repetitive morphine administration and withdrawal on subsequent intake of and preference for saccharin solutions in rats. Experiment 1 established that 17 hr after morphine withdrawal, rats consumed less saccharin, but not less water, than did controls. The groups did not differ 8 days later.

Stimulus novelty and significance as determinants of electrodermal responsivity: the serial position effect.

Three experiments examined the effects of stimulus novelty and significance on the skin conductance component of the orienting response. The test stimuli used in the different experiments involved either a neutral change in stimulation (i.e.

Reduced saccharin preference in CXBK (opioid receptor-deficient) mice.

The preference for sweet solutions in opioid receptor-deficient (CXBK) and control (C57BL/6By) mice was compared. CXBK and C57BL/6By (C57) mice were presented for 2 h/day with 2 tubes, one always containing water and the other containing either water or various concentrations of saccharin solution. Fifteen minutes before the drinking session, half of the mice in each strain were injected with naltrexone (0.