Relationships between spinocervical tract neurons and descending catecholamine-containing axons in the cat

Lumbosacral (L6-S1) spinal cord neurons in the cat were retrogradely labelled after uptake of horseradish peroxidase by their severed axons in the upper cervical (C3-C4) dorsolateral funiculus. Sections of L6-S1 containing labelled neurons were then processed immunocytochemically using antibodies against dopamine-beta-hydroxylase or tyrosine hydroxylase, two enzymes responsible for the synthesis of catecholamines. Two hundred and ninety eight retrogradely-labelled cells within laminae III-V of the dorsal horn were examined under high power (x 1000) with the light microscope. In Triton X-100-treated material, only 13% of these cells had catecholamine-containing varicosities closely apposed to their somata and proximal dendrites, which suggests that in comparison with the postsynaptic dorsal column pathway, spinocervical tract neurons are only sparsely innervated by descending catecholaminergic axons.