The trigeminal system in birds and nociception

Aim of this paper is to give a concise overview of what is known about the trigeminal nociceptive system in birds. Several types of nociceptors have been discovered, thermal nociceptors and polymodal, i.e. mechanothermal and mechanochemical receptors. Information from these receptors reaches the Laminae I and II of the caudal subnucleus of the descending trigeminal system and of the dorsal horn of the rostral spinal cord. The organization of the afferents to the avian brainstem and of the primary nociceptive centers is largely the same as that in mammals. This is also true for a number of histochemical characteristics of these primary centers. The comparability of the ascending nociceptive system in birds and mammals is more problematic. This is due to the differences in organization of the forebrain in mammals and birds. The paper concludes with a short discussion on the sense of pain and the connection with nociception.