Biomedical subjects
Publications and source records attributed to V N Semernia.
Whisker stimulation in rats was found to increase the local cerebral blood flow (lCBF), its SD and to damp slow oscillations. It was established that lCBF drops slightly within a few seconds after the stimulus onset. The data obtained suggest that lCBF evoked sensory stimulation changes are distinctly localized in different layers of the somatosensory cortex.
We evaluated increases in local cerebral blood flow (LCBF) localized to single activated cortical columns by H2 clearance methods. The rat whisker-barrel cortex is a model for cortical function and neural processing in active explorative behaviors. Up to four 30-40 microns Pt wire electrodes were inserted in or near the rat whisker-barrel cortex. Electrode positions were mapped by postmortem histology. H2 was generated electrochemically by constant current from one electrode and detected by one or more other electrodes 300-500 microns away. Changes in LCBF produced inverse changes in PH2. Shifts during steady H2 generation were calibrated against standard H2 inhalation clearance curves at rest and during inhalation of 7.5% CO2 for 1 min for quantitative estimates of LCBF. Contralateral whisker stimulation at 3 Hz, 1 min duration and delivered every 2 min produced the largest increases in LCBF. LCBF responses were detected in approximately 1 s. Stimulation of single whiskers produced the largest responses when an electrode was in the corresponding barrel. These results indicate that increased neural activity in a single cortical column produces blood flow responses primarily in that column.
In patients with partial craniospinal blocks, the impedance responses to certain functional tests were by 20-30% less obvious. Osteopathic procedures normalised the impedance fluctuations. The data obtained suggest that the CSF dynamics plays an important role in genesis and changes of the head impedance.
Any single method for measuring changes in local cerebral blood flow (LCBF) or blood vessels during physiological stimuli has individual strengths and deficiencies. The coupling of multiple methods based on different physical principles permits simultaneous measurements and tests of interrelated cerebrovascular changes and mechanisms. The present paper describes combined recordings of LCBF by H2 clearance with inhalation (H2Cl-Inh) and with steady electrochemical generation (H2Cl-Gen), by laser Doppler flowmetry (LDF) and by dimensional changes in surface vessels with videomicroscopy through acute cranial windows in rats anesthetized with urethane 1g/kg or urethane (0.6 g/kg) plus chloralose (0.05 g/kg)ip. For H2Cl-Gen recordings paired or quadred Pt sharped block of electrodes (diameter 0.04-0.06 mm) with distance between single electrode 0.3-0.5 mm, was inserted to brain tissue in barrel cortex. One electrode was used for H2 generation and others for LCBF recordings and their position in brain tissue was examined morphologically. Increase local blood flow in barrel cortex and arterial dilation were stimulated by inhalation of 7% CO2 and mechanical stimulation of the contralateral whiskers. H2Cl-Inh was a "gold standard" for quantitative measurements of LCBF within a tissue radius 0.3-0.5 mm from the recording electrode during related tests during steady states at the same site. H2Cl-Gen was very sensitive to transient changes in flow and could record latencies. H2Cl-Gen was calibrated for quantitative measurements of changes in LCBF by pairing with H2Cl-Inh responses to CO2 inhalation. The laser Doppler miniature probe recorded the time course and normalized intensity changes within an approximate 1 mm3 volume of cortex but with more background noise and less sensitivity compared to H2Cl-Gen. Bright illumination of the cranial window increased LCBF by both methods in these experiments. The diameters of surface arterioles and venues were measured in single video frames with date-time markers for correlation with electrical recordings. Changes in diameter were small and were slower compared to H2Cl-Gen and LDF in the present recordings. Received data permit to conclude that there are two optimal combinations of methods were (1) H2Cl-Gen and H2Cl-Inh for both dynamic sensitivity and quantitative LCBF during systemic and neuronal stimulation, and (2) H2Cl-Gen, LDF, and videomicroscopy for multidimensional monitoring of cerebral circulation.
The goal of the present investigation was to compare data received by modifications of H2-clearance method with inhalation (H2-Inh) and electrochemical generation in brain tissue (H2-Gen) of H2 from the same recording electrodes in acute experiments (urethane 1g/kgip) with Wistar rats (n = 39). Block of three or four Pt electrochemically sharpened electrodes to tip diameters of 20-40 mu, 0.3-0.5 mm apart and 0.8-1.0 mm in length were inserted through the dura into sensorimotor cortex. One electrode was used for H2 generation (DC current 3-5 microA) and the others for PH2 recordings by polarographical method. Durations of H2 inhalation and H2 electrochemical generation were 3 or 10s with similar amplitudes of PH2. Data was recorded with a MacLab analog-digital system and Macintosh 11si computer. Recordings of resting LCBF were made with H2-Gen and H2-Inh the beginning of the experiment and after 40-60 min. LCBF was stimulated with inhalation of 7.5% CO2 for 60s. In 6 preparations LCBF was measured 10-20 min. after occlusions of two branches of the middle cerebral artery. After experiments the brain was perfused with India ink and cut in frozen sections for morphological analyses. The mean values of resting LCBF measured by H2-Inh was 1.67 +/- 0.54 ml/g/min. (+/- SD, N = 149), and by H2-Gen 3.17 +/- 0.91 (N = 147). The diffusional component was estimated as 1.2-2.5 (equivalent units, ml/g/min.) in dead cortex. The ratio of clearances in H2-Gen to H2-Inh varied in different experiments from 1.0 up to 4.0.(ABSTRACT TRUNCATED AT 250 WORDS)
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The feature of correlation between functional activity of the brain tissue and structural-functional characteristics of the vascular system after sensory deprivation by the removal of whiskers in newborn animals were studied in nembutal-anaesthetized rats in comparison to the animals under d-tubocurarine with local anesthesia. It has been shown that there are major changes of EP parameters and ECoG in the sensory-deprived brain area and diminution of brain cortex thickness. Changes in the vascular system are mainly structural, what are revealed as disorganization in angioarchitecture of radial arteries. At the same time, differences in the blood circulation intensity are found in d-tubocurarine animals only. The largest volume of the local blood circulation is observed in intact hemisphere of sensory-deprived animal. Thus, it can be concluded that sensory-deprived model is the alternative to the ischemia model. This model can be used in studies of physiology of brain blood circulation, and the "structure-function" correlation, in particular.
The local cerebral blood flow (LCBF) and cerebrovascular reactivity to CO2 inhalation test were studied in rabbits after experimental local brain lesions. A decrease of the LCBF and cerebrovascular reactivity was observed in the grey and white matter surrounding the traumatic focus at the distance of about 15 mm, being minimal on the 3rd-5th days followed by normalizing by the 10th-14th days after lesions. The cerebrovascular reactivity was found to be a valuable prognostic parameter to assess the functional restoration of the brain.
Studies in cats and in neurosurgical patients reveal that intraskull pressure, blood volume and total brain blood flow depend on the same factors, to a different extent though. This is determined by structural--functional organization of the intraskull circulation system, the analysis of which revealed a scheme of functional interrelationships among volumes and pressures of fluid media in the closed skull space. The features of interrelationships are not rigid and can have their own specifics in concrete situations.
The functional stability of cerebral circulation involves its ability to resist against external influences and is based on the cerebral vessels reactivity. Objective methods for evaluation of this reactivity are proposed using standard and specific functional loads. The indices of intracranial and systemic hemodynamics were recorded in experimental animals, healthy humans and patients with head injuries during postoperative period. The dynamics of cerebral vessel reactivity was found to depend on the body functional state.
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