An electron microscopic study of somatostatin immunoreactive structures in lamina II of the rat spinal cord

We are reporting the results of a light and electron microscopic study of somatostatin (SOM) immunoreactive (I) structures in lamina II of the lumbar spinal cord of the rat. At the light microscopic level, the observed distribution and morphology of SOM-I cell bodies and fibers confirmed published studies. At the electron microscopic level, SOM immunostaining in perikarya was localized to the golgi region. Immunostaining in cell bodies could be enhanced by colchicine treatment and after such treatment, it was noticeably increased in the cytoplasm. Synaptic contacts on SOM-I cell bodies were rare and SOM-I axons contacted unlabeled somata in lamina II. Some SOM-I dendrites participate in glomerular arrangements and they exhibited postsynaptic densities adjacent to the central profile of the glomerulus. Nonglomerular SOM-I dendrites and spines were postsynaptic to vesicles containing axons. Vesicle containing SOM-I axons presynaptic to larger dendrites were also observed in the outer portion of lamina II. Somatostatin has been implicated in nociception and some of the SOM-I structures reported here may be the anatomical substrates for SOM-induced analgesia.