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The presence of somatostatin-like (SOM) immunoreactivity within GABAergic neurons of the nucleus reticularis thalami (NRT) was demonstrated by immunocytochemical methods in the cat using a two-color, double immunoperoxidase method with antisera raised in different species. GABAergic neurons were identified by means of a sheep antiserum to glutamic acid decarboxylase, the biosynthetic enzyme for y-aminobutyric acid (GABA). SOM immunoreactivity was visualized with a rabbit antiserum to synthetic somatostatin. Vibratome sections of perfusion-fixed tissue were processed according to the pre-embedding unlabeled peroxidase antiperoxidase (PAP) method for light and electron microscopy. Single sections through the NRT were first processed for glutamic acid decarboxylase-like (GAD) or SOM immunoreactivity. With either antiserum, most neurons of the NRT were immunoreactive. The intracellular sites recognized by the two antisera had only partially overlapping distributions. SOM immunoreactivity appeared largely restricted to perinuclear structures which were identified by electron microscopy as the Golgi apparatus and multivesicular bodies. GAD immunoreactivity also appeared in the Golgi apparatus but was broadly dispersed throughout the cytoplasm of the cell body and dendrites. Intensely GAD-immunoreactive dots in the neuropil of the NRT were shown by electron microscopy to be immunoreactive boutons. Coexistence of the SOM and GAD antigens was demonstrated in sections sequentially incubated with rabbit anti-somatostatin, swine anti-rabbit IgG, rabbit PAP, and 4-chloro-1-naphthol (blue color), followed by sheep anti-rat glutamic acid decarboxylase, donkey anti-goat IgG, goat PAP, and 3,3'-diaminobenzidine (brown color). Many neurons contained blue-black perinuclear skeins (SOM and GAD immunoreactivity) and brown reaction product in the cytoplasm (GAD immunoreactivity) and were contacted by dark brown punctate profiles (GAD immunoreactivity). Control experiments showed that a weak cross-reactivity of the two linking antisera did not impair the simultaneous visualization method. This study provides direct evidence for the existence, within GABAergic neurons of the cat NRT, of a substance immunocytochemically indistinguishable from somatostatin. The data suggest that neurons of the feline NRT compromise a "SOM-positive subtype" of GABAergic neurons. Immunohistochemical evidence strongly suggests that central, peripheral, autonomic, and enteric nervous sysneuropeptides coexist with classical and nonclassical neu-tems. The production of low molecular weight polypeprotransmitters in endocrine cells and in neurons of the tides by amine-producing endocrine and enteric cells was

Creatine is a major component of energy metabolism and enzymes involved in its synthesis have therefore been of considerable interest. L-arginine-glycine amidinotransferase, commonly called transamidinase, catalyzes the first reaction in the biosynthesis of creatine. This first reaction is believed to occur in the kidney because of the high concentration of transamidinase in that tissue. Transamidinase activity is also found in many other tissues of the rat, but its role in these tissues is not known. Immunochemical studies with antisera and monoclonal antibodies were used to confirm and refine our understanding of the presence of transamidinase in rat tissues. Immunofluorescence histochemistry was performed to localize transamidinase immunoreactivity within specific tissues including cells in the proximal tubules of the kidney, hepatocytes of the liver, and alpha cells of the pancreatic islet. Immunochemical studies with monoclonal antibodies confirm localization of transamidinase immunoreactivity in the proximal tubules of the kidney. The localization of such immunoreactivity in specialized cells yields insight into possible physiological role(s) of transamidinase in the rat.

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. In the nucleus reticularis of the cat, immunoreactive neurons were observed regularly in experiments with antisera generated against somatostatin-14 and were also found in preliminary experiments with an antiserum against the "non-somatostatin" (1 to 14) sequence of somatostatin-28. These observations, together with the perinuclear location of the immunoreactivity, suggest that a somatostatin precursor molecule may be present or at least that the neurons contain both the larger and smaller somatostatin-related peptides. The neurons of the nucleus reticularis also showed moderate acetylcholinesterase activity but were negative in tests of immunoreactivity to antisera raised against avian pancreatic polypeptide and Met-enkephalin. We conclude that the presence of somatostatin-like immunoreactivity may be a defining characteristic of the nucleus reticularis thalami and suggest that the functional activity of the neurons of the nucleus reticularis may involve not only a GABA mechanism but also the action of somatostatin or a related neuropeptide.