Detection of vasopressin mRNA in cells of the medial amygdala but not the locus coeruleus by in situ hybridization

Vasopressin (AVP)-immunoreactive cells have been previously reported in the medial amygdala (AME) and in the locus coeruleus (LC). The present study was designed to verify the presence of AVP-synthesizing neurons in these areas using in situ hybridization histochemistry. A ³⁵S- labelled oligonucleotide probe, complementary to the glycopeptide portion of the vasopressin-encoding mRNA, was used to label cells expressing the AVP gene in brain sections from male Wistar rats. AVP mRNA-positive cells were identified in the AME and were located throughout the anterodorsal and posterodorsal aspect of the nucleus. Cells in the LC, however did not exhibit labelling for the glycopeptide portion of the AVP gene. The highest density of labelled cells in the medical amygdala occured 2.30 to 2.80 mm caudal to bregma. The labelling intensity of the cells averaged 53.8 ± 3.9 grains/cells and was constant throughout the rostro-caudal extent of the AME. These data demonstrate the presence of AVP-synthesizing cells in the AME and provide a method for quantifying their activity. In addition, these data suggest that the cells in the LC may not synthesize vasopressin.