Aromatic L-amino acid decarboxylase immunohistochemistry in the suprachiasmatic nucleus of the sheep. Comparison with tyrosine hydroxylase immunohistochemistry.

Using antisera against tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC), we have demonstrated the presence of numerous AADC immunoreactive neurons and a few TH immunoreactive neurons, homogeneously distributed throughout the suprachiasmatic nucleus. Similar results have been described in other species. These observations show that this nucleus is able to synthesize trace amines (such as phenylethylamine or tyramine) in addition to dopamine. It is hypothesized that these trace amines are possibly involved in the integration of day length variation in sheep, a species whose reproduction is closely related to photoperiod.