Long-term effects of neonatal axoplasmic transport attenuation on the organization of the rat's trigeminal system

Abstract

The current study examined the long-term effects of infraorbital nerve (ION) axoplasmic transport attenuation with vinblastine on the organization of trigeminal (V) primary afferents and central vibrissae-related patterns. Retrograde tracing and single unit recording were used to evaluate the innervation of vibrissae follicles in adult (P > 60) rats that sustained application of vinblastine to the ION at birth. Single units recorded from vinblastine-treated animals yielded responses to deflection of a single vibrissa, and a significantly (P < 0.001) higher percentage of these cells (85.7%) showed rapidly adapting responses compared with normal rats (42.2%). Retrograde tracing revealed a qualitatively and normal distribution of V ganglion cells innervating A-row and E-row vibrissae follicles in vinblastine-treated rats. Transganglionic tracing with horseradish peroxidase (HRP) demonstrated a qualitatively and quantitatively normal somatotopic organization of vibrissae follicle input to V nucleus principalis (PrV) and V subnucleus interpolaris (SpI) in the vinblastine-treated animals. Despite the nearly normal mapping of V ganglion cell axons onto the vibrissae follicles and brainstem, staining for either cytochrome oxidase (CO) or parvalbumin failed to reveal vibrissae-related patterns in PrV, SpI, or the magnocellular portion of V subnucleus caudalis in these animals. Labelling of thalamocortical afferents with HRP and staining for CO also failed to reveal a cortical vibrissae-related pattern in the vinblastine-treated rats. The present results indicate that although transient attenuation of axoplasmic transport with vinblastine has limited effects on the peripheral and central projections of surviving V primary afferents, it permanently disrupts the normal development and maintenance of central vibrissae-related patterns.