The Effect of DOPA on the Spinal Cord 7. Reflex activation of static γ‐motoneurones from the flexor reflex afferents

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Abstract
In unanaesthetized spinal cats reflex activation of γ‐motoneurones (to a flexor muscle) from the flexor reflex afferents (FRA) has been assessed from the discharge recorded in muscle spindle afferents. After injection of L‐DOPA the resting discharge frequency increases in afferents with secondary endings and volleys in the FRA evoke a longlasting acceleration of the discharge in these afferents. On the basis of previous experiments showing that spindle afferents with secondary endings are activated from static but not from dynamic γ‐motoneurones it is inferred that static γ‐motoneurones are spontaneously active and reflexly activated from the FRA after an injection of DOPA. It has been confirmed that in the acute spinal cat, not treated with DOPA, there is no or little evidence for reflex activation of static γ‐motoneurones from the FRA and it is postulated that the reflex pathway to static γ‐motoneurones is inhibited in this preparation. The results are discussed in relation to other reflex effects evoked from the FRA.