NEUROPEPTIDE-Y AND SOMATOSTATIN-LIKE IMMUNOREACTIVITY IN NEURONS OF THE MONKEY AMYGDALA

Neurons in the monkey amygdala exhibiting neuropeptide Y-like immunore activity and somatostatin-like immunoreactivity were identified using an avidin-biotin immunohistochemical technique. Differential co-existe nce of the two peptides was demonstrated using two-color immunoperoxid ase and adjacent section methods. Numerous neuropeptide Y-positive neu rons were observed in the basolateral and superficial amygdaloid nucle i. A moderate number of neuropeptide Y-positive neurons was seen in th e medial subdivision of the central nucleus, but only a few neurons we re observed in the lateral subdivision. Numerous somatostatin-positive neurons were stained in all major amygdaloid nuclei and always outnum bered neuropeptide Y-positive cells. All amygdaloid nuclei contained n umerous peptide-positive fibers whose density varied depending on the nucleus. Approximately 90% of neuropeptide Y-positive neurons also exh ibited somatostatin-like immunoreactivity. The percentage of somatosta tin-positive neurons that exhibited neuropeptide-Y immunoreactivity va ried in different nuclei. In the superficial amygdaloid nuclei, medial subdivision of the central nucleus and most portions of the basolater al nuclei the predominant cell type stained with both the neuropeptide Y and somatostatin antibodies was a spine-sparse non-pyramidal neuron . In the dorsal portion of the lateral nucleus, however, most peptide- positive neurons had spiny dendrites. Only the cell bodies and proxima l dendrites of somatostatin-positive neurons in the lateral subdivisio n of the central nucleus were immunostained. This study demonstrates t hat specific cell populations in the primate amygdala contain neuropep tide Y, somatostatin or both peptides. Most peptide-positive neurons i n the basolateral and superficial amygdaloid nuclei appear to be local circuit neurons that contribute to the dense plexus of peptide-positi ve axons in these regions. The finding of neurons with spiny dendrites in the dorsal part of the lateral nucleus suggests that these cells m ay be functionally different from peptide-positive neurons in other po rtions of the basolateral amygdala. The lateral subdivision of the cen tral nucleus is distinguished from other amygdaloid nuclei by containi ng a large population of somatostatin-positive neurons that do not exh ibit neuropeptide Y immunoreactivity.