Localisation of substance P immunoreactivity in amacrine cells of the retina.

Since its actions on smooth muscle were first described by von Euler and Gaddum, substance P has been isolated and characterised as an undecapeptide. The distribution of substance P-like immunoreactivity in both the central and peripheral nervous systems and its reported excitatory action on neurones implicate substance P as a possible neurotransmitter and/or neuromodulator. Previous studies using bioassay and radioimmunoassay techniques have reported substance P in retinal extracts. Here we describe the specific immunohistochemical localisation of substance P-like immunoreactivity in a population of morphologically distinct amacrine cells of the pigeon retina. The localisation of substance P-like immunoreactivity and the recent localisation of enkephalin-like and somatostatin-like immunoreactivity in other types of amacrine cells suggest that the neuropeptides have a specific role in retinal function.