Cell death of primary sensory neurons in the trigeminal ganglion of Brn-3a knockout mice

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Immunohistochemistry for parvalbumin, calbindin D-28k, calretinin and calcitonin gene-related peptide was performed on the trigeminal ganglion and oro-facial tissues in Brn-3a wildtype and knockout mice at embryonic day 18.5 and postnatal day 0. In wildtype mice, the trigeminal ganglion contained abundant parvalbumin-, calbindin D-28k- and calcitonin gene-related peptide-immunoreactive neurons while the ganglion was almost devoid of calretinin-immunoreactive neurons. In Brn-3a knockout mice, a 63% decrease of parvalbumin-immunoreactive neurons was detected. On the other hand, the absence of Brn-3a dramatically increased the number of calbindin D-28k- immunoreactive (3.5-fold increase) and calretinin-immunoreactive neurons (91-fold increase). The number of calcitonin gene-related peptide-immunoreactive neurons, however, was not altered by the Brn-3a deficiency. Cell size analysis indicated that loss of Brn-3a increased the proportions of sm all (<100 μm^2) parvalbumin-, calbindin D-28k- … More and calcitonin gene-related peptide-immunoreactive neurons while decreased those of large (>200 μm^2) immunoreactive cells. Calretinin-immunoreactive neurons were either small or medium (100-200 μm^2) in mutant mice. The oro-facial tissues contained parvalbumin-, calbindin D-28k- and calcitonin gene-related peptide-immunoreactive fibers but not calretinin-immunoreactive ones in wildtype mice. In Brn-3a knockout mice, the number of parvalbumin-immunoreactive fibers markedly decreased in the infraorbital nerve and parvalbumin-immunoreactive endings disappeared in the vibrissa. On the other hand, the number of calbindin D-28k-immunoreactive fibers increased significantly in the infraorbital and mental nerves. In addition, calbindin D-28k-immunoreactive endings appeared in the vibrissa. As well, some fibers showed calretinin-immunoreactivity In the infraorbital nerve of the mutant. However, no obvious charge of calcitonin gene-related peptide-immunoreactive fibers was observed in the oro-facial region of knockout mice. Taken together, these data suggest that Brn-3a deficiency has effects on the expression of neurochemical substances in the trigeminal ganglion. Less