Immunohistochemical localization of neurokinin-1 receptor in the lumbar spinal cord of young rats: morphology and distribution

The type and distribution of neurokinin-1 (NK-1) receptor-expressing neuron es were studied in young (14-day-old) rats' lumbar spinal cord using pre-em bedding immunohistochemistry. The heaviest immunoreactivity was observed in the middle part and lateral fourth of lamina I where thr great majority of immunoreactive perikarya represented fusiform and multipolar cells. In lam ina II the middle and medial part showed moderate immunoreactivity, most of the cells resembled stalked cells. In lamina III the labelled perikarya we re evenly distributed, while those in lamina IV accumulated mainly in the l ateral part. In both laminae most of the labelled neurones represented cent ral cells, the rest of them belonged to the antenna-type cells with long do rsally directed dendrites penetrating the superficial laminae. The immunore activity in laminae V-VII was uniform and relatively weak. In lamina VIII t he immunopositive perikarya were encountered only rarely while in lamina IX virtually all motoneurones showed weak immunoreactivity. Lamina X containe d small, multipolar and fusiform labelled perikarya. In conclusion, we foun d that the general appearance of the NK-1 receptor immunostaining and the m ajor type of NK-1 receptor-expressing neurones were similar to that found p reviously in adult spinal cord. Using the same method as Brown and colleagu es the number of labelled NK-1 receptor immunoreactive cells was similar in young and adult animals except lamina I where the number of immunoreactive neurones was twice that in adults.