DISTRIBUTION OF SOMATOSTATIN MESSENGER-RNA CONTAINING NEURONS IN THE PRIMARY PAIN RELAYING NUCLEI OF THE RAT

Background: The spinal trigeminal nucleus and the dorsal horn of the s pinal cord are the critical areas in relaying noxious impulses. They a lso contain large amounts of somatostatin-like immunoreactivities. Ear ly publications focussed on immunohistochemical studies and were devoi d of a detailed description of the distribution of somatostatin in the two nuclei at the molecular level. Method: Frontal tissue sections fr om the mudulla and the spinal cord of eight rats were examined and a n on-radioactive in situ hybridization histochemical procedure was adopt ed to study the distribution of somatostatin mRNA positive neurons in the two nuclei. Results: A widespread distribution of somatostatin mRN A containing neurons was shown in the two nuclei at all levels. The po sitive neuron profiles were normally round or oval in shape and small to medium in size. Three types of cells were identified, which were as sociated with the intensity of the hybridization signals. The highest density of somatostatin mRNA positive neuron profiles was found in the gelatinous subnucleus at the caudal part of the spinal trigeminal nuc leus and in the substantia gelatinosa of the dorsal horn at the levels of the cervical and lumbar cords. Most of them belonged to type I neu rons. Conclusions: The present findings are compared to reports of pre vious studies. It is suggested that somatostatin in the two nuclei may play an important role in the modulation and transmission of pain sig nals. (C) 1995 Wiley-Liss, Inc.