Somatostatin-like immunoreactivity characterizes neurons of the nucleus reticularis thalami in the cat and monkey

This report presents immunohistochemical evidence for the occurrence of a somatostatin-related peptide in neurons of the thalamic reticular nucleus, a nucleus known to modulate thalamic activity by y-aminobutyric acid (GABA)-mediated inhibition. In eight cats and kittens and one rhesus monkey, sections through the nucleus reticularis thalami and adjoining regions of the thalamus, subthalamus, and mesencephalic tegmentum were incubated in anti-somatostatin antisera and processed by the Sternberger peroxidase-antiperoxidase or Coons direct immunofluorescence methods. In each brain, intense somatostatin-like immunoreactivity was found in neurons of the nucleus reticularis thalami. The immunoreactivity was localized to the perinuclear region of the neurons in both species. Somatostatin-like immunoreactivity appeared in only a sharply restricted subset of other zones thought to have an embryologic origin in the ventral thalamus (including, in the cat, two nuclei that project to the amygdala: the nucleus subparafascicularis and the peripeduncular nucleus of the mesodiencephalic tegmentum). An incidental finding was that the pars late&is of the cat's substantia nigra contains a system of fine fibers expressing somatostatin-like immunoreactivity.