TEMPERATURE-SENSITIVE RECEPTORS AND RESPONSE OF DORSAL HORN NEURONS TO THERMAL STIMULATION OF THE FEATHERED SKIN IN PIGEONS

Abstract

Numerous investigations exist on the temperature sensitive cutaneous receptors and of dorsal horn neurons responding to the thermal stimulation of the skin in mammals. However, in birds, only several investigations of cutaneous temperature-sensitive receptors and none of dorsal horn neurons were published. This chapter investigates the thermosensitivity of all cutaneous receptors in a feathered skin area of the pigeon and compares the response of primary afferent fibers with the responses of dorsal horn neurons to the same stimuli. The response of primary afferent fibers was recorded from a cutaneous nerve of the wig. In the investigation described in the chapter, a single unit activity of dorsal horn neurons was recorded with microelectrodes from the cervical enlargement of the spinal cord. Thermal stimulation was presented either with a thermode pressed to the skin or by radiant thermal stimulation with a heating coil or a cold metal rod, which were approached to the skin without touching it. In the dorsal horn, neurons were found and they responded to mechanical stimulation. At the dorsal border of the dorsal horn, many neurons were found that responded specifically to noxious thermal stimulation. As with primary afferent fibers, there was a strong maintained excitation at skin temperatures near or above 50˚C. The above results show that there are neurons in the dorsal horn of the pigeon having similar response characteristics to thermal stimulation of the skin as the primary afferent fibers.