Electro-myographic studies on sheep injected with the n,n-dimethylated tryptamine alkaloids of phalaris tuberosa

Abstract

The administration of N,N-dimethylated tryptamine alkaloids, toxic constituents of the pasture plant, Phalaris tuberosa, to sheep produces both convulsive and spastic activity. The convulsive activity originates in the brain, since it is interrupted by experimental procedures which block connection between the brain and motor neurones of the spinal cord. The spastic activity originates in the spinal cord, since it is not affected by section of the cord anterior to the relevant segments, but is abolished by section of efferent nerves and by “Myanesin” which blocks transmission below the cell bodies of the intemuncial neurones. Local, excessive discharge of motor neurones persists in the hind limb muscles after section of their afferent pathways or of the cord at the anterior lumbar or posterior cervical region, or of both cord and afferent nerves together. It is therefore not due to hyperexcitability of the sensory components of the cord or peripheral nervous system, nor to hypersensitivity of the gamma afferent system. The fact that the local effect in the hind limbs can be eliminated by sectioning of the ventral roots of the lumbar and anterior sacral cord shows it is not due to direct effects on transmission either at the neuromuscular junction or in nerve fibres. Barbiturates suppress the local effect in the isolated cord but more slowly and at a higher dose than is required to suppress the convulsions.