Leydig cells: octopaminergic neurons in the leech.

Leydig cells are electrically-coupled neurons in the segmental ganglia of the leech. This study reports that they stain specifically with high concentrations (0.05 mg/ml) of the dye neutral red, and that they contain octopamine, as demonstrated by radioenzymatic assay. Individual cell bodies were pooled and found to contain 0.37 pmol octopamine/cell body, giving an approximate intracellular concentration of 7.75 mM. Leydig cell bodies contain approximately 75% of the octopamine content of a segmental ganglia. Intracellular injection of large amounts of Lucifer yellow, coupled with long diffusion times, revealed a previously-undescribed Leydig cell process. The probability that Leydig cells are octopaminergic neurosecretory cells is discussed.