Intrathecal alpha-trinositol facilitates the flexor reflex but does not block the depressive effect of neuropeptide Y.

We have studied the effects of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate, PP56), a putative antagonist of neuropeptide Y receptors, on the nociceptive flexor reflex in decerebrate, spinalized rats after intrathecal and intravenous administration. Intrathecal alpha-trinositol caused strong and prolonged facilitation of the flexor reflex, which was usually associated with an increase in spontaneous motoneuron activity. The reflex depressive effect of intrathecal neuropeptide Y was neither blocked nor reversed by alpha-trinositol. Intravenous alpha-trinositol at low doses had no effect on the flexor reflex and at high dose, reflex facilitation was sometimes observed. It is concluded that alpha-trinositol acts as a spinal excitant and is not an antagonist of the neuropeptide Y receptor in the rat spinal cord.