Calretinin-immunoreactive neurons in the trigeminal and dorsal root ganglia of the rat

Abstract

The cell body size of primary neurons were measured in the trigeminal (TG) and lumbar dorsal root ganglia (DRG) monochrome-stained for calretinin (CR)-like immunoreactivity. A trichrome stain for CR, carbonic anhydrase (CA) and tachykinin (TK) was also employed to estimate possible overlap of cellular distribution of these substances. In the DRG, the cell size spectrum of CR-positive cells was clearly bimodal; a greater proportion (84.1%) of CR-positive cells was distributed in the range ≧ 800 μm 2 with a mode between 1,500–1,600 μm 2, while a smaller proportion (14.8%) < 700 μm 2 with a mode of 400–500 μm 2. They were evenly distributed throughout the DRG. Although CR-positive TG neurons were smaller than similar DRG neurons, a bimodal distribution pattern remained unchanged. 94.6% of CR-positive cells measured 100–1,400 μm 2 with peak ranges of 200–300 μm 2 and 400–500 μm 2. Most of CR-positive cells in the ophthalmic division were 400 μm 2 or larger and small CR-positive cells ( < 400 μm 2 ) were concentrated in the maxillary and mandibular divisions. Most of CR-positive DRG cells showed CA activity (76.5%), while those with TK-immunoreactivity were rare (7.2%). In the TG, 38.4% of CR-positive cells were TK-positive. They were mostly smaller than 800 μm 2. On the other hand, CA was detected in 43.4% of CR-positive TG cells. Most of the TG cells co-expressing CR and CA were 400 μm 2 or larger. Simultaneous co-expression of TK and CA by the CR-positive cells was negligible. The cell bodies co-expressing CR and TK were more or less concentrated in the maxillary and mandibular divisions of the TG. The results suggest that CR-positive DRG cells are mostly proprioceptive, whereas similar TG cells include many small primary neurons innervating the visceral mucosa.