2-Amino-7-phosphonoheptanoic acid depresses gamma-motoneurons and polysynaptic reflexes in the cat spinal cord.

The effects of 2-amino-7-phosphonoheptanoic acid (APH), a selective antagonist of N-methyl-D-aspartate (NMDA) receptors, were studied on spinal cord functions in unanaesthetized spinal cats. APH (10 mg/kg i.v.) depressed spontaneous activity of gamma-motoneurons and segmental polysynaptic ventral root reflexes (VRRs) without affecting monosynaptic VRRs. The NMDA-induced enhancement of polysynaptic VRRs and activation of gamma-motoneurons were antagonized by APH. The results support the hypothesis that NMDA receptors are involved in the polysynaptic excitation of motoneurons, including gamma-motoneurons, and thus participate in motor functions of the spinal cord.