Mechanical and thermal responses of polymodal receptors recorded from the superior spermatic nerve of dogs.

1. One hundred and fifty-three units were recorded from the superior spermatic nerve of dogs and were tested with mechanical, chemical or heat stimulation. Among 104 units tested with all three methods of stimulation ninety-three units responded to all of them; thus 90% of the superior spermatic nerve units are considered to be polymodal receptors. Only mechanical and thermal responses are reported in this paper. 2. Conduction velocities measured at the nerve trunk in the abdominal cavity were mostly within the A-delta fibre range (average conduction velocity: 11.1 m.s-1, n = 63), but in the receptive region much delay was observed. In contrast to the cutaneous polymodal receptors, polymodal receptors in the superior spermatic nerve usually had multiple receptive sites, up to nine in number. 3. Mechanical responses of these polymodal receptors consisted of dynamic and steady-state responses and sometimes were followed by after-discharges. Maximum responses were obtained with a noxious intensity of stimulation, but thresholds scattered over a wide range including non-noxious intensities. 4. In response to heating, these polymodal units gave an irregular discharge that increased roughly in parallel to temperature rise with an average threshold and S.E. of mean, 42.6+/-0.4 degrees C (n = 73). They showed sensitization or deactivation or both on repetition of heating. Cooling the receptive site caused only transient and weak responses, if any.