The patterns of discharge of static and dynamic gamma motoneurones in the decerebrate rabbit.

1. The effect of natural stimulation of the limbs (usually pinching the forepaws) on the discharges of muscle spindle primary and secondary afferents and gamma motoneurones of the gastrocnemius medialis muscle were examined in the precollicular decerebrate rabbit, paralysed with gallamine triethiodide to prevent extrafusal muscle contraction. 2. The afferents showed only excitation in response to natural stimulation. The same stimulus strongly inhibited some gamma motoneurones and, at the same time, predominantly excited others. 3. Since extrafusal muscle contraction was prevented using gallamine triethiodide, intrafusal contraction was responsible for the afferent excitation, and could only have been evoked by those gamma motoneurones excited by natural stimulation. The distribution of effects from gamma motoneurones that were strongly inhibited by natural stimulation could not be deduced from afferent recordings. 4. On the basis of these afferent and efferent recordings, and the known structure of the muscle spindle, gamma motoneurones were identified as static or dynamic. 5. The results are discussed in relation to the patterns of discharge of static and dynamic gamma motoneurones.