LARGE CALIBER PRIMARY AFFERENT NEURONS PROJECTING TO THE GRACILE NUCLEUS EXPRESS NEUROPEPTIDE-Y AFTER SCIATIC-NERVE LESIONS - AN IMMUNOHISTOCHEMICAL AND IN-SITU HYBRIDIZATION STUDY IN RATS

Using immunohistochemistry and in situ hybridization, we studied chang es in expression of some neuropeptides in large and medium-sized neuro ns in lumbar 4 and 5 rat dorsal root ganglia projecting to the gracile nucleus, in response to peripheral axotomy. Fourteen days after unila teral sciatic nerve transection, many large neurons and some medium-si zed neurons in ipsilateral dorsal root ganglia were strongly neuropept ide Y-positive. Galanin-, vasoactive intestinal polypeptide (VIP)- and peptide histidine-isoleucine (PHI)-like immunoreactivities coexisted with neuropeptide Y-like immunoreactivity in some of these neurons. Af ter axotomy numerous large and medium-sized cells contained neuropepti de Y mRNA in the ipsilateral ganglia, whereas no hybridization was see n in the contralateral or control ganglia. Cross-sectioned, large neur opeptide Y-positive fibres were observed in a somatotopically appropri ate zone within the ipsilateral gracile fasciculus, A dense network of neuropeptide Y-immunoreactive, large nerve fibres and terminals was s een in the ipsilateral gracile nucleus. A small number of galanin- and VIP/PHI-like immunoreactive nerve fibres and terminals were also obse rved in adjacent sections. Neuropeptide Y-like immunoreactivity coloca lized with galanin- or VIP/PHI-like immunoreactivity in some nerve fib res. None of these neuropeptide immunoreactivities could be detected i n nerve fibres and terminals in the control or contralateral gracile n ucleus. These findings suggest that neuropeptides, in addition to thei r role in small dorsal root ganglion neurons, may have a function in l arge and medium-sized dorsal root ganglion neurons projecting to lamin ae III and IV in the dorsal horn as well as to the gracile nuclei, as a part of their response to peripheral axotomy.