Neurotrophin receptor (p75) in the trigeminal thalamus of the rat: Development, response to injury, transient vibrissa-related patterning, and retrograde transport

We report on the transient, patterned expression of p75 in the ventrobasal (VB) thalamus, the major thalamic relay for somatosensation. We immunostain ed the brains of developing rats ranging in age from embryonic day (E) 14.5 to postnatal day (PD) 15 with an antibody against p75. To compare p75 expr ession with the developing synaptic organization within VB, we also immunol ocalized the synaptic-vesicle-associated protein, synaptophysin (SYN), on a lternate sections. p75-immunoreactivity (IR) was dense and uniform in the v entroposterior medial nucleus (VPM) in the late embryonic and early postnat al periods (E 16.5 to PD 3). In contrast, from PD 4-10, p75-IR in the VPM w as patterned, reminiscent of cytochrome-oxidase-stained barreloids, a chara cteristic feature of the VB in rodents. By PD 14, p75-IR in the VPM was no longer detectable. The ventroposterior lateral nucleus (VPL), in contrast, exhibited no p75-IR. No p75-IR was detected in the ventroposterior lateral nucleus (VPL) at any developmental stage in which VPM could be distinguishe d from VPL. Light, but clearly patterned SYN-LR, first detectable on PD 2-3 , increased in intensity in both VPL and VPM through PD 15. Sectioning the infraorbital nerve on PD 0 resulted in blurred patterns of p75- and SYN-IR within VPM in PD 7-9 rat pups. Removing large portions of the somatosensory cortex on PD 0 resulted in subsequent greatly reduced p75- and SYN-IR with in VB. To specify the source of the p75-IR terminals, we stereotaxically in jected into the VPM of PD 4-5 rats a monoclonal antibody to p75. One to 2 d ays later, IR of retrogradely transported p75 antibodies could be traced wi thin axons and cell bodies of neurons associated with the trigeminothalamic pathway through the caudal diencephalon and mesencephalon; labelling was c onfined to the contralateral trigeminal principal sensory nucleus. The obse rved, transiently patterned p75-IR in VPM the early postpartum period sugge sts a role for p75 in synaptogenesis and pattern formation. Anat Rec 259:44 6-460, 2000. (C) 2000 Wiley-Liss, Inc.