Abstract
Four non-pregnant and non-lactating ewes satiated with concentrate were intracerebroventricularly injected with70nmol and 140nmol of muscimol which is an agonist of gamma-aminobutyric acid-A receptor (experiment 1). Then three of these sheep were also intracerebroventricularly injected with 140nmol muscimol after they were satiated with concentrate or roughage (experiment 2). In experiment 1, the administration of 70nmol and 140nmol muscimol elicited feeding behavior within 15 min after the administration in sheep satiated with concentrate and the action continued for 30min. In addition, the stimulation of concentrate intake was dose dependent. In experiment 2, the administration of 140nmol muscimol stimulated not only concentrate intake as seen in experiment 1, but also roughage intake within 15 min after the administration. These results indicate that muscimol administration eliminates satiety with either roughage or concentrate. However, the stimulation of concentrate intake was prominent compared to that of roughage intake. It is likely that the suppressive action of muscimol on satiety induced by physical factors is less than that on satiety induced by metabolic factors. Otherwise, other actions of muscimol on the central nervous system might affect roughage intake. Then the rate of feed intake was reduced irrespective of the diet given and the daily intake of roughage was reduced. The rebound response might reduce feed intake after muscimol eliciting feeding behavior.
