Dynamic thermal mapping of rat brain during sensory stimulation and spreading depression

Using both techniques of thermovision and statistical analysis of thermal imaging, dynamics of temperature distribution over the dorsal surface of the brain were investigated through the intact skull during acute experiments on white rats. Both diffuse and regionally specific cerebral thermal reactions were observed during visual, acoustic, and somatosensory stimulation, together with multiple local thermal response, often following a specific pattern. These outline thermal effects differing from the compartment of the brain to another in degree, stability, and point of onset. Temperature waves developed together with spreading depression, produced in the cortex by injecting KC1. Once investigations had been performed this response could be divided into diffuse and spatially ordered components. The possible mechanisms of this thermal imaging of brain processes are discussed, together with how they are linked with changes in cerebral blood flow and neuronal metabolic thermal production.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Institute of Radio Engineering and Electronics, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 26–35, January–February, 1986.     

Cortical afterdischarges during Leao's cortical spreading depression.

Cortical spreading depression (CSD) has been employed in unanesthetized curarized rats, in order to analyse the role of the cerebral cortex in the generation of epileptic self-sustained parozysms produced by direct cortical electrical stimulation. CSD was preferred because it is reversible and may be repeated several times in the same animal. CSD evoked in the hemisphere contralateral to the stimulated cortex decreased the duration of the afterdischarge by 40% and modified its form and amplitude both at the cortical and reticular levels. The possible role of cortical and subcortical structures in the development of after-discharges is discussed.     

Phosphorylation of cerebral cortex proteins during spreading cortical depression

Spreading cortical depression induced by the topical application of 25 % KC1 onto on hemisphere of the rat brain produced an increase in 32P radioactivity in the proteins of the microsomal [+39 %] and membrane [+21 %] fraction of the affected hemicortex compared with the intact contralateral hemicortex; conversely, radioactivity in the cytosol fraction fell by 19 %, while in the mitochondrial fraction it remained the same. The results are evaluated from the aspects of a possible difference in the response of cAMP-dependent and cAMP-independent protein phosphorylation to the depolarization of cortical cells in vivo.     

Bicarbonate and ammonia changes in brain during spreading depression

An alkaline, followed by an acid-going transient, characterizes acid-base changes in the interstitial space during spreading depression in a variety of brain structures. In rat, such changes are associated with a significant rise in brain lactate content. How brain proton buffers behave during spreading depression is unknown. Techniques to significantly improve the response time of gas permeable membrane semimicroelectrodes for carbon dioxide and ammonia are reported. Measurements with such electrodes, when coupled to measurements of hydrogen ion concentration (from microelectrodes), permit rapid changes to be determined in bicarbonate concentration or ammonia and ammonium ion concentration, respectively. Bicarbonate concentration fell from 30 +/- 1 (n = 16) to 14 +/- 1 mM (n = 16) during spreading depression. On the other hand, ammonia concentration rose from 2.3 +/- 0.1 to 4.4 +/- 0.3 microM (n = 17) while ammonium ion concentration rose from 116 +/- 11 (n = 17) to 382 +/- 30 microM (n = 17) during spreading depression. Bicarbonate changes probably reflect titration of brain bicarbonate stores by accumulated lactic acid. Similar physicochemical changes do not explain the rise in ammonia and ammonium ion concentrations. Instead, elevation of the latter can only result from an increase in ammonia content of the interstitial space.     

Suppression of gamma EEG activity as an index of a spreading depression wave in the neocortex of a waking rabbit

A spreading depression (SD) can spontaneously develop in seizures, attacks of migraine, vascular disorders and other pathological states of the brain. However, problems in technique of recording the DC-potential in the neocortex of humans and waking animals substantially restrict the possibilities of studying functional consequences of the SD. In this article, the EEG pattern was studied in detail at the moment of the SD development. Specific features were revealed, which make it possible to detect the SD without recording shifts of the DC-potential. At the moment of the SD arrival, the interhemispheric balance drastically disturbs because of a strong decrease in the high-frequency activity. By the time indices, the course of the suppression of the gammal and gamma2 EEG frequencies is the most reliable symptom of the SD wave development. The EEG spectral power in the delta band increases with a certain delay in reference to the deep depression of the high-frequency activity and is, in essence, an SD aftereffect. The found EEG signs of an SD wave can substantially simplify the identification of this phenomenon both in experiment and clinical conditions in certain pathological states of the brain.