Neonatal infraorbital nerve transection in the rat: Comparison of effects on substance P immunoreactive primary afferents and those recognized by the lectinBandierea simplicifolia-I

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Abstract
Retrograde tracing, immunocytochemical, and histochemical methods were used to determine the manner in which different classes of trigeminal (V) ganglion cells respond to transection of their axons during infancy. Retrograde tracing with true blue (TB), histochemistry using the plant lectin Bandieraea simplicifolia‐I (BS‐I), and immunocytochemistry using an antiserum directed against substance P (SP) were carried out in the V ganglion and V brainstem complex of normal adult rats. In the adult V ganglion, 11.9 ± 1.9% of the cells that sent axons into the infraorbital nerve (ION) contained SP‐like immunoreactivity (SPLI) and 26.9 ± 3.6% bound the lectin BS‐I. Only 2.7 ± 1.6% of ION cells were labelled by both the SP antiserum and BS‐I. Transection of the ION on the day of birth had very different effects upon primary afferent neurons containing SPLI and those labelled by BS‐I. We have previously shown that such lesions result in a significant expansion of the portion of SpC innervated by primary afferents containing SPLI and we have also provided data consistent with the proposal that ganglion cells recognized by an antiserum directed against SP are more likely than other primary afferent neurons to survive neonatal axotomy. In the present study, combination of retrograde tracing with TB and lectin binding histochemistry showed that cells recognized by BS‐I were selectively lost after neonatal ION transection. Only 14.2 ± 4.4% of the ION ganglion cells that projected into this nerve at the time of the lesion and that survived neonatal axotomy were BS‐I positive when the animals reached adulthood. Neonatal ION transection also resulted in a permanent reduction in the density of BS‐I binding in SpC. Bandieraea simplicifolia‐I binding in the brainstem ipsilateral to the damaged nerve was almost completely gone within 1 day of the nerve transection and recovered only partially by the time the rats were 2 months of age. In alternate sections tested with the SP antiserum, there was a slight reduction in the density of SPLI in the deafferented SpC on postnatal days 4 and 5, but this change never approached that observed for BS‐I binding.

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