MICROBIOTA-MEDIATED ELEVATION OF HOST 5-HT IS POSTNATALLY INDUCIBLE ns 2.0 SPF GF PO P21 P42 SPFGF PO P21 P42 PO P21P42P42 SPF+ABX VEH SPF+ABX VE D SPF GF P0... 42 P0. 21 P42 P42 SPF GF PO P21 P42 PO P21 P42 P42 GF+CONV PF+ABX VEHMICROBIOTA-MEDIATED ELEVATION OF HOST 5-HT IS POSTNATALLY INDUCIBLE