Midbrain is regarded as a higher center which controls hypothalamus in general and in water and electrolytes regulations as well. The author observed the changes of urine volume by osmotic stimulations around the midbrain of rabbits.
Korean domestic white male rabbits weighing 1. 8 kg. were gavaged with 2% sodium chloride solution, 100 ml 3 times hourly for hydration before experiment. The sites of stimulation in the midbrain were deviced as illustrated in Diagram 1 and 2 and Table 1, so that each site was located 2 mm apart one another in 3 directions.
When the urine volume through the indwelling catheter exceeded 4 ml per 5 minutes after hydration, 2% sodium chloride solution 0.05 ml was injected bilaterally to the planned symmetrical areas by the aids of stereotaxic apparatus and Choi´s stereotaxic atlas, and so far urine volume was reduced in those areas, distilled water was injected to see the effects of hypotonic stimulation in the same way as mentioned above.
Thus, the following results were obtained as shown in Diagram 3 and Table 24.
1) Rapid and marked reduction of urine volume by 2% sodium chloride injection and also significant increase of its volume by distilled´ water injection were observed in the following 6 areas.
a) ⓒd´2 i.e. a part of Red nucleus.
b) ⓒd3 i.e. a part of Medial geniculate body.
c)2 i.e. between Brachium of inferior colliculus and Medial geniculate body. lateral edge of Red nucleus.
d)´2i.e.
e) gc2 i.e. inside of Brachium of inferior colliculus.
=) 3d2 i.e. inner edge of Nucleus of lateral lemniscus.
These results are considered that the above areas are related to osmoreceptors, have some connections between hypothalamus either directly or indirectly, and or might be a neurosecretory organ.
2) Rapid and marked reduction of urine volume by 2% sodium chloride injection and marked reduction or no change of its volume by distilled water injection were observed at the following 14 areas.
ⓒcl, ⓒcx, Dee, @e´2, ®ci, ®ei, I;lc2, Re´2, lei gee, ®ci, ®d,, 11.
Theses results suggest that mechanical stimulations might play some roles rather than acting as osmotic effectors.
3) No remarkble change of urine volume was observed by the osmotic stimulations in the rest of 39 areas.
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