By Brian Sheerin and Emma Berry NEWMARKET, UK -- As expected, an international cast of buyers swept into action at Park Paddocks for the opening day of the Tattersalls December Mares Sale, with some of the leading lights heading to Japan, Australia and America after more than 15 million gns was spent on breeding prospects. It was the aptly-named Callisto Star who lit up the first of two Sceptre Sessions when selling from Ballybin Stud in Ireland to Badgers Bloodstock for 675,000gns. The dam of American Oaks winner Rhea Moon...