▁the ▁ret in oh yp oth al am ic ▁tract ▁( R HT ). ▁Gl ut am ate ▁has ▁an ▁exc itat ory ▁effect ▁on ▁SC N ▁neur ons , ▁and ▁P AC AP ▁appears ▁to ▁enh ance ▁the ▁effects ▁of ▁gl ut am ate ▁in ▁the ▁hypoth al am us . ▁ ▁Other ▁post ▁syn apt ic ▁targets ▁of ▁ip R GC s ▁include : ▁the ▁inter g entic ulate ▁leaf let ▁( IG L ), ▁a ▁cluster ▁of ▁neur ons ▁located ▁in ▁the ▁th al am us , ▁which ▁play ▁a ▁role ▁in ▁circ ad ian ▁ent rain ment ; ▁the ▁ol iv ary ▁pre te ct al ▁nucle us ▁( OP N ), ▁a ▁cluster ▁of ▁neur ons ▁in ▁the ▁mid bra in ▁that ▁controls ▁the ▁pup ill ary ▁light ▁ref lex ; ▁the ▁vent rol ater al ▁pre opt ic ▁nucle us ▁( V L PO ), ▁located ▁in ▁the ▁hypoth al am us ▁and ▁is ▁a ▁control ▁center ▁for ▁sleep ; ▁ ▁the ▁am yg d ala . ▁ ▁Function ▁ ▁P up ill ary ▁light ▁ref lex ▁▁ ▁Using ▁various ▁phot ore ceptor ▁knock out ▁m ice , ▁research ers ▁have ▁identified ▁the ▁role ▁of ▁ip R GC s ▁in ▁both ▁the ▁trans ient ▁and ▁sust ained ▁signal ing ▁of ▁the ▁pup ill ary ▁light ▁ref lex ▁( PL R ). ▁Trans ient ▁PL R ▁occurs ▁at ▁dim ▁to ▁moder ate ▁light ▁intens ities ▁and ▁is ▁a ▁result ▁of ▁phot otr ans du ction ▁occurr ing ▁in