Transient coexistence of tyrosine hydroxylase and gamma-aminobutyric acid immunoreactivities in the developing anterior olfactory nucleus of the mouse

The localization of tyrosine hydroxylase (TH)-immunoreactive (IR) (TH-IR) n eurons, which are transiently observed in the anterior olfactory nucleus (A ON) of the mouse, was studied. A double-labelling method was used with anti bodies against TH, L-3,4-dihydroxyphenylalanine (DOPA), phenylethanolamine- N-methyltransferase (PNMT). aminobutyric acid (GABA), calretinin (CR) and c albindin-D28k (CB). When the total number of TH-IR neurons observed in all regions of the AON obtained from 10- to 14-day-old mice was set at 100%, 30 % of TH-IR neurons were observed in the lateral (AOL), 25% in the dorsal (A OD), 20% in the ventral (AOV), 15% in the medial (AOM) and 5% in both the p osterior (AOP) and external (AOE) regions. Approximately 40% of the TH-IR n eurons in the AOL to the AOV regions also exhibited GABA immunoreactivity. This corresponds to 20% of the total number of BH-IR neurons observed in al l regions of the AON, and also corresponds to 12% of the total number of GA BA-IR neurons observed in all regions of the AON. However, TH-IR neurons di d not exhibit concomitant PNMT, CR, and CB immunoreactivities. These findin gs suggest that the TH-IR neurons in the AON of the mouse, a proportion of which is also GABA-IR, may function as a source of neuromodulators for the postnatal growth of GABA-IR neurons.