Nasal sensory nerve populations responding to histamine and capsaicin

Retrograde labeling of trigeminal nasal neurons. A, Medial portion of ganglion indicated by the dotted area. Line represents 0.5 mm. B, Two nasally labeled neurons from A. Line represents 15 μm. C, Typical distribution of nasally labeled neurons throughout trigeminal ganglion. D, Schematic distribution of nasal neurons (shaded areas) in right trigeminal ganglion (dorsal aspect). Line represents 5 mm (1-mm intervals).

Photomicrographs of trigeminal ganglion. A, DiI-labeled nasal neurons. B, Immunohistochemical staining for substance P. Note that the smaller of the 2 DiI-labeled cells (upper left corner) also contained substance P. In addition, a non–DiI-labeled substance P–positive cell can be seen in the center of B. Line represents 25 μm.

Immunohistochemical staining of substance P (SP) in nasally labeled neuron. Data are total cell counts recorded from 12-μm trigeminal slices harvested from 3 guinea pigs.

Effect of 10 μmol/L histamine (Hist) and 0.5 μmol/L capsaicin (Cap) on intracellular [Ca²⁺]_free in dissociated DiI-labeled nasal trigeminal neurons. Cell numbers for each group are shown in parentheses.

Responses of nasally labeled and unlabeled trigeminal neurons to 10 μmol/L histamine and 0.5 μmol/L capsaicin. Unlabeled data account for 59 experiments (643 neurons). Nasally labeled data account for 37 experiments (48 neurons). ^∗Significant difference in the percentage of neurons in a particular responder group between unlabeled and nasally labeled trigeminal neurons (P < .05).