Galanin immunoreactivity reveals a vibrissae-related primary afferent pattern in perinatal rats after neonatal infraorbital nerve transection

Immunocytochemistry was used to demonstrate the distribution of galanin immunoreactivity in the trigeminal (V) brainstem complex of normal rats and rats that sustained neonatal transection of the infraorbital nerve (ION, the V branch that supplies the mystacial vibrissae). In normal adult and perinatal (postnatal day [P-] 7) rats, there is very little galanin immunoreactivity in the rostral part of the V brainstem complex. However, there is dense immunoreactivity for this peptide in layers I and II of V subnucleus caudalis (SpC). There was a marked upregulation of galanin immunoreactivity at all levels of the V brainstem complex of P-7 rats that sustained ION transection on P-0. In V subnucleus interpolaris and the magnocellular part of SpC, this immunoreactivity occurred in clusters which had a pattern resembling that of the mystacial vibrissae. In animals examined at 30 days or more after ION transection, there were a few more galanin-immunoreactive fibers on the deafferented side of the brainstem than on the intact side, but there was no evidence of a vibrissae-related pattern. Our interpretation of these results is that galanin immunocytochemistry reveals a vibrissae-related pattern in the central arbors of axotomized primary afferents for at least 1 week after they have been disconnected from the periphery.