Trigeminal primary afferent neurons were labeled by injecting the rat trigeminal ganglion with either wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), cholera toxin B subunit (B)-HRP or Bandeiraea simplicifolia isolectin B4 (IB4)-HRP, B-HRP stained medium to large cells (> 600 μm2), while IB4-HRP mostly small cells (< 400 μm2). WGA-HRP labeled trigeminal ganglion neurons of all sizes. Cell bodies in the mesencephalic trigeminal tract nucleus were labeled with WGA-HRP and B-HRP but not IB4-HRP. B-HRP revealed dense projection to the entire brain stem sensory trigeminal nuclear complex (BSTC) except for lamina II of the medullary dorsal horn (MDH). Some contralateral projection was also seen in the caudal part of MDH. Non-trigeminal nuclei receiving B-HRP-labeled terminals included the paratrigeminal nucleus (paraV), solitary tract nucleus, supratrigeminal nucleus, Probst's nucleus and median accessory nucleus. Following IB4-HRP application, terminal label was found in more restricted regions within the BSTC. Modest terminal label was seen in the dorsal part of principal sensory nucleus and at the medial edge of subnucleus interpolaris, while relatively dense terminal fields were seen in the dorsal half of subnucleus oralis. The MDH laminae I and II contained dense terminal label. Non-trigeminal nuclei were almost devoid of the IB4-HRP-labeled terminals excepting the paraV that contained dense terminal label. The terminal areas revealed with WGA-HRP coincided with B-HRP-labeled and IB4-HRP-labeled areas combined.
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