Warm receptors in the nasal region of cats.

1. Specific warm receptors in the nasal region of cats were studied by recording afferent impulses from single units dissected from the infraorbital nerve. In addition, a few cold fibres from the same region were examined.2. Numerous warm fibres with spot-like receptive fields were found on the back of the nose. They were not excited by mechanical stimulation.3. Multi-fibre strands serving this area responded to moderate warming with an increase of the integrated discharge.4. At constant temperatures from 30 degrees C on, single warm fibres showed a steady discharge with a regular sequence of impulses, the frequency of which rose steeply with temperature and reached a maximum between 45 and 47 degrees C. At higher temperatures the frequency fell to zero.5. Rapid warming caused a dynamic overshoot, rapid cooling a transient inhibition of the warm fibre discharge. The highest dynamic frequencies of single fibres were 200 impulses/sec.6. For a large population of single warm fibres the average maximum of static activity was 36 impulses/sec at 46 degrees C, whereas the cold fibre population had a maximum of 9 impulses/sec at 27 degrees C.