Lumbar dorsal root ganglia of the cat: A quantitative study of peptide immunoreactivity and cell size

The purpose of the present study was to quantify the extent to which several peptides and serotonin coexist with substance P or somatostatin in selected lumbar dorsal root ganglia of the cat. The technique for the simultaneous visualization of two antigens by immunofluorescence was used to investigate the coexistence of neuropeptides in the lumbar dorsal root ganglia of colchicine‐treated cats. Perikarya immunoreactive for calcitonin gene‐related peptide, galanin, leu‐enkephalin, somatostatin, and substance P were visualized in both the lumbar 5 and 6 dorsal root ganglia. In contrast, no immunoreactivity was observed for adipokinetic hormone, bombesin, dynorphin A, met‐enkephalin, oxytocin, tyrosine hydroxylase, thyrotropin‐releasing hormone, vasopressin, vasoactive intestinal peptide, or serotonin in either ganglion examined. Substance P coexisted with calcitonin‐gene‐related peptide, somatostatin, and leu‐enkephalin. Somatostatin was colocalized with calcitonin gene‐related peptide, leu‐enkephalin, and substance P but coexisted with galanin minimally. The cell area of immunoreactive perikarya was also examined. Data concerning the cross‐sectional area of immunoreactive cells indicated that somatostatin‐immunoreactive perikarya were generally the largest population observed (up to ∼6,000 μm²). Somatostatin and calcitonin gene‐related peptide, as well as substance P and calcitonin gene‐related peptide, coexisted in populations of cell bodies that had a smaller size (less than 2,000 μm²). These results suggest that certain peptides which coexist in the dorsal root ganglia may provide histochemical markers for functional groups of primary afferent neurons.