All issues > Volume 7(4); 1964

Original Article

J Korean Pediatr Soc. 1964;7(4):113-132. Published online November 30, 1964.

Experimental studies on the effects of osmotic stimulation in the Hypothalamus, Limbic System and Midbrain upon blood pressure

Johng-Un Hahn¹

¹Department of Pediatrics, College of Medicine, Seoul National University

Abstract

The Central nervous control of cardiovascular activity shows that this control is exerted at different levels of the neuraxis. It was reported by many investigators that electrical stimulation of cerebral cortex, limbic system and hypothalamus produced changes in cardiovascular system, i. e. blood pressure. However some authers report are controversial against another auther. In another word, they did not bring us definite conclusion. In addition, all of those authors stimulated some areas of central nervous system by electrical stimulation, electrolytic lesion and so on. Homeostatic mechanism in electrolyte metabolism and influence of salts upon blood pressure are studied very much and clinician are aware of this facts. In an attempt to know the relation of central nervous system and blood pressure, auther’s attention was called to the changes of blood pressure induced by osmotic stimulation in midbrain, limbic system and hypothalamus directly. Experiments were conducted on Korean white male rabbits weighing 1.8 kg exactly. The animals were anesthetized with subcutaneous 20% urethan and the rabbits were fixed in a stereotaxic instrument carrying syringe, blood pressure manometer and monodrum of kymogram. Midbrain, Hippocampus, Amygdala, Preoptic area, Septal area, Anterior area, Medial area and Posterior area of hypothalamus were injected with 0.05 c.c. of isotonic saline hypertonic 2% NaCl solution and hypotonic aq. dest. respectively into the site according to Choi’s stereotaxic coordinates of Korean rabbit diencephalon. Blood pressure were obtained from internal carotid antery which is connected with mercury manometer through poleyethylene tube. The polyethlene tube was filled with 25% magnesium sulfate solution in order to prevent blood coagulation. At the end of the experiment the animal were perfused with 10% formaline and brain was submitted to routine histological procedures to determine the positions of injection. The results were as follows. 1. There were not any remarkable changes of blood pressure following the injection of physiologic saline, 2% NaCl solution and aq. dest. in the midbrain. 2. There were not any noticeable changes of blood pressure following the injection of physiologic saline, 2% NaCl solution and aq. dest. into the hippocampus. 3. Following the injections of physiologic saline in the amygdala there were not any changes of blood pressure. One of 2 rabbits revealed a rise of blood pressure following injection of 2% NaCl solution in the amygdala and a slight fall of blood pressure following injection of aq. dest. in the same place were observed in a rabbit of 2. 4.Following the injection nf physiologic saline in the preoptic area there were not any changes of blood pressure. But one of 2 rabbits revealed a rise of blood pressure following injection of 2% NaCl solution in the same place and also a rise of blood pressure was observed following the injection of aq. dest. in a rabbit of two. 5. Following the injection of physiologic saline in the septal area in 2 rabbits there was a slow fall of blood pressure in one of 2 rabbits and the other one revealed rapid fall of blood pressure just after injection. All of 2 rabbits revealed a rise of blood pressure following the injection of 2% NaCl solution in the same area and a slight fall of blood pressure following injection of aq. dest. was observed in a rabbit of two. 6. There were not any noticeable changes of blood pressure following the injection of physiologic saline in the anterior area of hypothalamus in 5 rabbits. Following the injection of 2% NaCl solution in the same area in 5 rabbits, there were remarkable rise of blood pressure in all cases. And following the injection of aq. dest. in the same area in 5 rabbits, there were remarkable rapid fall of blood pressurein all cases. 7.There were remarkable rise of blocxl pressure following the injection of physiologic saline and 2% NaCl solution in the medial hypothalamus in a rabbit among each of 2. Following the injection of aq. dest, in the same area in 2 rabbits, there was a fair of blood pressure in a rabbit. 8.Physiologic saline injection in the posterior area of hypothalamus revealed not any change of blood pressure among 3 rabbits. The most striking findings observed was a rise of blood pressure following the injection of 2% NaCl solution in the same area in. all of 5 rabbits and a fall of blood pressure following the injection of aq. dest. in all of 5 rabbits. The range of a rise of blood pressure was about 10 mm Hg and that of fall of blood pressure was about 20 mm Hg. The Figure of uprising curve of blood pressure were slow and showed almost bell shaped curve. The figure of fall of blood pressure were sharp and dramatic. And recovering period toward normal level were comparatively slow. The changes of blood pressure could be due either to autonomic nervous or to humoral mechanism or to both occuring simultaneously. However with the fact that the sympathetic function in posteriorior area and parasympathetic function in anterior area of hypothalamus can not be reasonably explain the mechanism of this experimental findings: Hypertonic solution brought the rise of blood pressure by the osmotic stimulation in the anterior and posterior area of hypothalamus and hypotonic solution brought the fall of blood pressure by the osmotic stimulation in the same areas. I conclude, therefore, the above experimental findings shows that the anterior and posterior hypothalamus have baroreceptic functions to the osmotic stimulation.

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