The responses of dorsal horn neurones to controlled mechanical stimulation of the hindlimb skin in the rabbit

The functional characteristics and spatial arrangement of Type I mechanosensitive units found in the sural nerve of the anaesthetized rabbit have been investigated.There are approximately 108 Type I units innervating a skin area of about 59.1 cm² supplied by the sural nerve giving an innervation density of 1.83. This innervation density of 1.83 does not vary over the skin territory innervated by the sural. The dome/fibre ratio was 2.7.The domes were found to be distributed in a dispersed but fairly regular pattern. The average nearest neighbour distance was 5.3 mm. A stimulus of 5.5 threshold units showed the existence of a small receptive field of radius 2 mm surrounding each dome; at a 3 mm radius even the largest 2 mm indentation failed to evoke a response.The response of the Type I units exhibited 4 distinct phases:

1. (1) a dynamic phase

2. (2) a transient adaptive phase

3. (3) a highly irregular static phase

4. (4) an off phase. The impulse frequency/static displacement relationship was best fitted by a power function. The impulse frequency/velocity characteristic became horizontal at an average value of 15 μm/ms. A power function provided the best fit for this relationship.

The possible physiological significance of the differences between properties of Type I receptor populations in the rabbit and cat are discussed.