The cerebral blood flow values used in experimental and clinical investigations as the informative criteria for brain blood supply are often misleading. The correlation between the cerebral blood supply and brain function is not proven in all cases. An increase of brain activity is known to be accompanied by a rise of blood flow in activated regions, while a decreased activity results in a decreased blood flow. This demonstrates the close correlation between the brain blood supply and its activity. Such a correlation had not been noted in the age-dependent decrease of cerebral blood flow, suggesting the existence of special age-related mechanisms that develop with age to maintain brain metabolism. The biomechanical properties are of special significance as predicted in the early 20th century. Only recently were they validated by the simultaneous recording of Transcranial Dopplerogram and Rheoencephalogram with in-depth analysis focused on single cardiac cycles. Functioning of the intracranial blood and cerebrospinal fluid dynamics was integrated with a special physiological test "Prognosis-2" to measure brain cognitive function. Correlation was demonstrated with the circulatory-metabolic state of brain activity, especially in people with changing cognitive function. The data supports a conceptual model of adequate circulatory-metabolic supply of brain activity, showing the functional unity, which follows from integration of the mentioned systems.
The present work reports studies of the quantitative spatial and temporal characteristics of changes in local blood flow in different layers of the somatosensory cortex of rats during adequate mechanical stimulation of the vibrissae. Studies were performed using 34 Wistar rats. Skull trepanning was performed under urethane (1 g/kg) anesthesia. Television-guided microscopy was used to introduce a set of three platinum electrodes (100 microns in diameter, with tip diameters of 30-40 microns) into the somatosensory cortex projection zone of the vibrissae. The first and third electrodes were positioned in cortical layers I-III and IV-VI and the central electrode was used to generate hydrogen within the tissue. Electrode positions were confirmed histologically after experiments. Animals were placed on artificial ventilation and one or all vibrissae were stimulated at a frequency of 3 Hz for 60 sec, with interstimulus intervals of 3 min. Changes in the local blood flow were measured during stimulation and for 1 min afterwards, using the hydrogen clearance method, and brain tissue impedance was also measured. There was a small (up to 5-7%) reduction in blood flow in the first seconds of stimulation, which was followed 15-25 sec later by an increase and subsequent return to initial when stimulation stopped. The increases in blood flow during stimulation of all vibrissae were by 24.2 +/- 6.7% (n = 36) in layers IV-VI and 24.5 +/- 5.6% (n = 34) in layers I-III; increases in response to stimulation of single vibrissae were by 19.4 +/- 7.4% (n = 28) and 17.8 +/- 6.4% (n = 28) respectively. The dynamics of impedance changes corresponded to those of blood flow changes. Thus, heterogeneity was found in changes of local brain blood flow in different layers of the somatosensory cortex during increases in cortical functional activity.
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