Substance P-immunoreactive neurons in the human retina

Area of Science:

• Neuroscience
• Ophthalmology
• Cell Biology

Background:

• Substance P (SP) is a neuropeptide functioning as a neurotransmitter or neuromodulator in the retina.
• Understanding the specific cell types expressing SP is crucial for elucidating retinal circuitry and function.

Purpose of the Study:

• To identify and characterize the types and distribution of SP-immunoreactive (SP-IR) cells in the human retina.
• To describe the morphology and stratification patterns of SP-IR neurons within the inner plexiform layer (IPL).

Main Methods:

• Immunohistochemistry using an antiserum to SP on postmortem human retinae.
• Avidin-biotin complex (ABC) method for visualization.
• Whole-mount and plastic-embedded preparations, as well as 20-micron sections for radial views.

Main Results:

• Intensely SP-IR amacrine cells of a single type were identified, characterized by large cell bodies and extensive dendritic arborization in specific IPL strata (S3, S5).
• These amacrine cells possess unique 'axon-like' processes and dendritic extensions reaching blood vessel walls and outer plexiform layer (OPL).
• A faintly SP-IR ganglion cell type, resembling Golgi type 2 amacrine cells, was also observed, with its dendrites ensheathed by SP-IR amacrine processes.

Conclusions:

• The study reveals a distinct population of SP-IR amacrine cells in the human retina with specific morphological and laminar features.
• A potential SP-IR ganglion cell type, influenced by amacrine inputs, was identified.
• These findings contribute to a deeper understanding of SP's role in human retinal function and neurotransmission.