Morphology of peptide-immunoreactive neurons in the rat central nucleus of the amygdala.

The morphological characteristics of peptide-immunoreactive neurons in the rat central nucleus of the amygdala were examined. Observations were compared with details of neuron morphology available from Golgi-stained tissue to determine whether peptide immunoreactivity was associated with specific cell types in the central nucleus. The lateral subdivision (CL) of the central nucleus contained mainly medium-sized, densely spiny neurons. Larger, pyramiform spiny neurons; medium-sized, sparsely spinous neurons; and small, aspinous cells were also present in CL. Somatostatin-, neurotensin-, corticotropin-releasing factor (CRF)-, and enkephalin-immunoreactive neurons in CL were characterized as the medium spiny and larger, pyramiform types. No obvious morphological differences were evident among medium spiny neurons containing different peptides. In the medial subdivision, substance P, neurotensin, somatostatin, and CRF were present within pyramiform, sparsely spinous neurons with long dendrites. Galanin immunoreactivity in the medial subdivision was associated with moderately spiny, pyramiform neurons and a larger, aspinous, polygonal neuron. The ventral subdivision of the central nucleus contained neurons similar to those found in the adjacent medial and lateral subdivisions. In addition, this subdivision contained a characteristic ovoid neuron with long, sparsely spinous dendrites. Vasoactive intestinal polypeptide (VIP) and neurotensin appeared to be present within this cell type. In the lateral capsular subdivision, neurotensin and enkephalin were present in cells resembling the medium spiny neurons characteristic of this part of the central nucleus. Numbers of spindle-shaped, biopolar somatostatin, and VIP neurons were identified in the medial, lateral, and ventral subdivisions. The present results provide evidence for a heterogeneous morphology of peptide-immunoreactive neurons in the rat central nucleus that are distributed across cytoarchitectonic boundaries. Except for substance P, neuropeptides in the central nucleus appear to be expressed by a variety of neurons rather than morphologically characteristic types of cell.