Analysis of avian cold receptor function

The response characteristics of facial specific cold receptors of the pigeon were studied quantitatively by recording single unit activity from the trigeminal ganglion at various stimulus conditions and subsequent analysis of the discharge pattern. Responses to maintained temperatures as well as to cooling steps were qualitatively identical to those seen in the corresponding mammalian cold receptor populations, but avian cold receptors were generally less sensitive, particularly to dynamic stimuli. The major differences between avian and mammalian cold receptors were that avian cold units only occasionally discharged in periodic groups of impulses at constant temperatures and that there was no indication of cyclic receptor events being involved in the dynamic response to cooling, as it is the case in all mammalian cold sensors. Additionally, the temporal pattern of the grouped discharges was less regular in avian cold units. Application of calcium, EGTA and menthol revealed a comparatively low dependence of cold receptor function on external calcium. The results provide evidence that calcium-controlled processes and periodic receptor events contribute only insignificantly to the signal transduction of avian cold receptors. This indicates a different functional organization of the transducer processes of avian and mammalian cold receptors.