Central somatostatin systems revealed with monoclonal antibodies

The distribution of central neurons displaying somatostatin immunoreactivity was studied using three monoclonal antibodies to cyclic somatostatin. The sensitive ABC immunoperoxidase technique was employed. A large number of positive cell groups including many previously undescribed populations were detected throughout the brain and spinal cord. Telencephalic somatostatin neurons included periglomerular cells in the olfactory bulb, mitral cells in the accessory olfactory bulb, and multipolar cells in the anterior olfactory nuclei, neocortex, amygdala, hippocampus, lateral septum, striatum, and nucleus accumbens. Within the hypothalamus, positive neurons were found in the periventricular, suprachiasmatic, and arcuate nuclei, and throughout the anterior and lateral hypothalamus. The entopeduncular nucleus and zona incerta contained many positive neurons, and the lateral habenula had a dense terminal field suggesting a pallidohabenula somatostatin pathway. Somatostatin neurons were also found in association with many sensory systems. Positive cells were present in the superior and inferior colliculi, the ventral cochlear nuclei, the ventral nucleus of the lateral lemniscus, nucleus cuneatus, nucleus gracilus, and the substantia gelatinosa. Various cerebellar circuits also displayed somatostatin immunoreactivity. Golgi cells throughout the cerebellar cortex were intensely stained, and some Purkinje cells in the paraflocculus also showed a positive reaction. Positive fibers were present in the granular layer and large varicose fibers were present in the inferior cerebellar peduncle. Many nuclei known to project to the cerebellum, including the nucleus reticularis tegmenti pontis, the medial accessory inferior olive, the nucleus prepositus hypoglossi, and many areas of the reticular formation contained positive neurons. These studies demonstrate that these new monoclonal antibodies are of great value for the study of central somatostatin systems. Previously described somatostatin systems are readily detected with these antibodies, and in addition, many otherwise unrecognized somatostatin cell groups have been discovered.