Immunohistochemical evidence for the localization of neurons containing the putative transmitter l-proline in rat brain

We examined whether there are the neurotransmitter candidate amino acid l-proline containing neurons localized in the rat brain. Antibodies against l-proline conjugated with rabbit serum albumin were raised in a rabbit and purified with affinity chromatography. Strong l-proline-like immunoreactivity was confined to several groups of neurons in the arcuate nucleus (n) and supraoptic n in the hypothalamus and area postrema. The brainstem had markedly stained fibers in the medial longitudinal fasciculus and localized neuronal cell body labeling in the red n, mesencephalic trigeminal n, lateral reticular n, raphe obscurus n, solitary n, compact ambiguus n, motor trigeminal n and n of trapezoid body. Our findings are consistent with the hypothesis that l-proline may function as a neurotransmitter or neuromodulator in the brain.