The MT 1 ( or Mel 1a or MTNR1A ) and MT 2 ( or Mel 1b or MTNR1B ) receptor subtypes are present in humans and other mammals , while an additional melatonin receptor subtype Mel 1c has been identified in amphibia and birds .
The MT 1 ( or Mel 1a or MTNR1A ) and MT 2 ( or Mel 1b or MTNR1B ) receptor subtypes are present in humans and other mammals . 
 While an additional melatonin receptor subtype Mel 1c has been identified in amphibia and birds .