There are few catecholamine- or neuropeptide Y-containing synapses in the intermediolateral cell column of rat thoracic spinal cord.

1. A quantitative electron microscopic immunocytochemical technique was used to assess the number of synapses immunoreactive for tyrosine hydroxylase (TH), phenylethanolamine N-methyl-transferase (PNMT) and neuropeptide Y (NPY) in the intermediolateral cell column in segments T2 and T3 of rat thoracic spinal cord. 2. TH synapses comprised about 5%; PNMT synapses 1-2%; and NPY synapses 1-2% of the total number of synapses in the intermediolateral cell column. All three types of synapses were predominantly or exclusively on dendrites. 3. Our results suggest that catecholamine/NPY neurons may not provide a major synaptic input to sympathetic preganglionic neurons in rat upper thoracic spinal cord.