440 Y Kwak, et al FLI expression in the overall NST through rostral- caudal axis The FLI expression levels in six regions through ros- tral-caudal axis were plotted in the Fig. 3. There was strong tendency that the FLI cell number increases from r1 to i3 area and reduced toward i4 area for all stimulations. The control stimulation with DW induced maximum FLI level around i2-NST. Meanwhile, 1.0 M NaCl stimulation in- duced maximum FLI levels in i3 area. This tendency was consistent in both left and right NST. The left i1-NST showed significant difference in FLI cell numbers between 0.1 M and 1.0 M NaCl stimulation (p＜0.05). The left i2 area showed significant difference in FLI cell numbers be- tween control (DW) and 1.0 M NaCl stimulation (p＜0.05). The left i3 area showed significant difference in FLI cell numbers between control (DW) or 0.1 M NaCl and 1.0 M NaCl stimulation (p＜0.05). As shown in Fig. 3B, the right i1 area showed significant difference in FLI cell numbers between 0.1 M and 1.0 M NaCl stimulation (p＜0.05). The right i2-NST showed sig- nificant difference in FLI cell numbers between 0.1/0.3 M and 1.0 M NaCl stimulation (p＜0.05). The right i3 area showed significant difference in FLI cell numbers between control (DW) and 1.0 M NaCl stimulation (p＜0.05). Fur- thermore, there was a tendency of dose-dependent increase in FLI expression in the left/right i1, i2 and i4 areas but the differences were insignificant. FLI expression in the subregions of NST along rostral- caudal axis Fig. 4 shows the FLI expression levels in six subregions of the left NST along rostral-caudal axis. There were only two subregions that showed significantly increased FLI expression. The dorsal-middle (Fig. 4B showed increased FLI level between 0.3/0.6 M and 1.0 M NaCl (p＜0.05) in the left i1 area and between control (DW) and 1.0 M NaCl (p＜0.05) in the left i2-NST. The dorsal-medial subregions (Fig. 4C) showed increased FLI between control (DW) and 1.0 M NaCl in the left i2 area and between control (DW) and 1.0 M NaCl in the left i3 area. There were no sig- nificant increases in dorsal-lateral and ventral-lateral/mid- dle/medial subregions. The position difference of maximum FLI level between control and NaCl stimulation was clear in the subregions as in the overall NST including rostral and intermediate NST. In the control, maximum FLI level was observed around i1 area but in the NaCl stimulation it was i2 or i3 area. Therefore, the NST with maximum FLI expression in response to NaCl was located more poste- rior than control (DW). The FLI expression levels in six subregions of the right NST through rostral-caudal axis are shown in Fig. 5. The dorsal-middle subregion only showed significantly increas- ed FLI level between 0.3 M and 1.0 M NaCl in the right i2 area (p＜0.05) and between control (DW) and 1.0 M NaCl in the right i3 area (p＜0.05). The dorsal-middle i2 and i3 areas only increased FLI level significant. The FLI ex- pressions in the right NST in the subregions were different from the left NST. For cell count, Abercrombie correction factor was calcu- lated using N/n=T/(T＋H), here N is real cell number, n is estimated cell number, T is thickness of section, and H is mean height of soma. The length of NST neuron was 11.2±1.9μm and width was 6.8±1.1μm. The height of soma was not clear so we used the width instead of height. Applying Abercrombie’s calculation for 8μm section thick- ness and subtraction the result from one and multiplying by 100 for percentage value, resulted in 45.9%. DISCUSSION Salt taste perception is important to determine the in- take of food. The discrimination of salt concentration is im- plied in this perception. Therefore, dose-dependent re- sponse is expected in the NST. In this regard, a morpho- logical neural activity may provide an evidence for salt dis- crimination perception in the NST. Fig. 4. Comparison of FLI cell numbers in the subregions of the left NST. (A) dorsal-lateral, (B) dorsal-middle, (C) dorsal-medial, (D) ventral-lateral, (E) ventral-middle, (F) ventral-medial. The animal numbers are marked in parenthesis: Control (n=6), 0.1 M (n=5), 0.3 M (n=6), 0.6 M (n=6) and 1.0 M (n=4) NaCl. Error bars indicate SEM. *p ＜0.05.