BRAIN HISTAMINERGIC SYSTEM IN MAST CELL-DEFICIENT (WS WS) RATS - HISTAMINE CONTENT, HISTIDINE-DECARBOXYLASE ACTIVITY, AND EFFECTS OF (S)ALPHA-FLUOROMETHYLHISTIDINE/

The mast cell-deficient [Ws/Ws (White spotting in the skin)] rat was i nvestigated with regard to the origin of histamine in the brain. No ma st cells were detected in the pia mater and the perivascular region of the thalamus of Ws/Ws rats by Alcian Blue staining, The histamine con tents and histidine decarboxylase (HDC) activities of various brain re gions of Ws/Ws rats were similar to those of +/+ rats except the hista mine contents of the cerebral cortex and cerebellum. As the cerebral c ortex and cerebellum have meninges that are difficult to remove comple tely, the histamine contents of these two regions may be different bet ween Ws/Ws and +/+ rats, We assume that the histamine content of whole brain with meninges in Ws/Ws rats is <60% of that in +/+ rats. So we conclude that approximately half of the histamine content of rat brain is derived from mast cells. Next, the effects of (S)alpha-fluoromethy lhistidine (FMH), a specific inhibitor of HDC, on the histamine conten ts and HDC activities of various regions of the brain were examined in Ws/Ws rats. In the whole brain of Ws/Ws rats, 51 and 37% of the hista mine content of the control group remained 2 and 6 h, respectively, af ter FMH administration (100 mg/kg of body weight). Therefore, we sugge st that there might be other histamine pools including histaminergic n eurons in rat brain.