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

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 μm² with a mode between 1,500-1,600 μm², while a smaller proportion (14.8%) < 700 μm² with a mode of 400-500 μm². 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 μm² with peak ranges of 200-300 μm² and 400-500 μm². Most of CR-positive cells in the ophthalmic division were 400 μm² or larger and small CR-positive cells (< 400 μm²) 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 μm². 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 μm² 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.