Somatostatin (SRIF) like immunoreactivity in median eminence (ME) of female rat brain: evidence of compartmentalization in ME.

ABSTRACT

Somatostatin (SRIF) immunoreactivity was observed in rostrocaudal extent (Bregma levels-1.8 mm to -3.8 mm) of the median eminence (ME) in female rat brain using Avidin-Biotin Complex (ABC) method (Hsu et al, 1981). SRIF immunoreactivity (IR) was observed in entire-rostrocaudal extent of both internal (IZ) and external zone (EZ) of ME. Image analysis of SRIF stained sections showed that in rostral ME (Bregma -1.8 to -2.3 mm) dense immunoreactive nerve terminals were observed in EZ. In medial ME (Bregma -2.3 mm to 3.3 mm) SRIF-IR was low in IZ and dense in EZ. In this region dense immunoreactive nerve terminals were observed in lateral margin of EZ. In caudal ME (Bregma -3.3 mm to -3.8 mm) nerve terminals in lateral EZ and median IZ and EZ showed dense reactivity in nerve terminals. These results led us to hypothesize that each region-lateral IZ and EZ and medial IZ and EZ are independent functional units in ME. Six functionally independent compartments could be identified-Compartment I and III of IZ and IV in EZ (Lateral margins in ME), Compartment V (IZ) and Compartment VI (medial EZ).