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Cardiovascular effects of hypertonic sodium chloride solutions when injected into the liquor space of anaesthetized
Insights
Injecting hypertonic solutions into a cat's brainstem or ventricles caused increased blood pressure and heart rate. This response, mediated by sympathetic nervous system discharge, was triggered by osmolarity changes or sodium ions.
Area of Science:
- Neuroscience
- Physiology
Background:
- Understanding the central nervous system's regulation of cardiovascular function is crucial.
- Investigating the role of cerebrospinal fluid (CSF) osmolarity and ionic composition in cardiovascular control.
Purpose of the Study:
- To determine the effects of injecting hypertonic and hypotonic solutions into the cisterna magna and cerebral ventricles on blood pressure and heart rate in anesthetized cats.
- To identify the specific stimuli and neural pathways involved in the observed cardiovascular responses.
Main Methods:
- Anesthetized cats underwent injections of various solutions (NaCl, glucose, sucrose, distilled water) into the cisterna magna or lateral cerebral ventricles.
- Cerebrospinal fluid flow was controlled via aqueduct cannulation.
- Arterial blood pressure and heart rate were monitored.
- Bilateral vagotomy was performed to isolate sympathetic nervous system effects.
Main Results:
- Hypertonic solutions and distilled water injected into the cisterna magna or ventricles induced a significant rise in arterial blood pressure and tachycardia.
- Isotonic solutions had no effect on cardiovascular parameters.
- The observed pressor responses and tachycardias were attributed to sympathetic nervous system discharge.
- Cisternal injections were linked to osmolarity changes, while ventricular injections were attributed to sodium ions.
Conclusions:
- Cerebrospinal fluid osmolarity and sodium ion concentration are potent regulators of cardiovascular function via sympathetic pathways.
- Specific brain regions accessible through the cisterna magna and ventricular system are involved in processing these osmotic and ionic signals.
- These findings contribute to understanding central cardiovascular regulation mechanisms.
Abstract:
1 In cats anaesthetized with chloralose, hyper- and hypotonic solutions were injected into the cisterna magna (in 0.5 ml) or into a lateral cerebral ventricle (in 0.2 to 0.3 ml), with aqueduct cannulated to prevent the injected solution from entering the subarachnoid space, and the effects on blood pressure and heart rate were examined. 2 Cisternal injections of hyper- and hypotonic solutions of NaCl (0.51 M and 0.05 M), glucose (1.03 M and 0.10 M), or sucrose (1.02 M and 0.10 M), as well as distilled water produced a rise in arterial blood pressure with tachycardias. Isotonic solutions of NaCl, glucose or sucrose were ineffective. 3 Ventricular injections of the hypertonic NaCl solution, also produced a pressor response with tachycardia effects when injected in this way. 4 The pressor responses and the tachycardias occurred after bilateral vagotomy and resulted from a sympathetic discharge which, on cisternal injection, originated from structures reached from the subarachnoid space, and on ventricular injection, from structures in the ventricular walls, probably in the hypothalamus. 5 The stimuli responsible for the discharge, were, on cisternal injection, the changes in osmolarity and on ventricular injection, the sodium ions.
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