high concentrations were found in the periaqueductal central gray matter and the dorsal raphe nucleus , and moderate levels were present in the locus coeruleus , the parabrachial nuclei , the nucleus raphe magnus and in the nucleus of the solitary tract . beta-endorphin was measurable in all 43 brainstem nuclei investigated ;
C0023951
locus coeruleus
C0006121
brainstem