72 FRACTAL GEOMETRY OF BRAIN BLOOD BARRIER IN FORCED COLD ACCLIMATION, ESTIVATION AND HIBERNATION Marchenko V.S., Marchenko L.N, Lutsenko D.G., Govorukha T.P. Institute for Problems of Cryobiology and Cryomedicine of the National Academy of Sciences of Ukraine, Kharkov, Ukraine e-mail: marchik@list.ru Blood Brain Barrier (BBB) should be considered as a complex of fractal like structures, randomness of which functioning could rise under quasi-cyclic (fractal) regimens of acclimation, designating the over-robustness of regulation centers as a adaptation strategy. When processing of the electron and confocal microscopy (CM) data of hamster and rat brain we determined fractal dimension (D) as tangent of slope of linear approximation of logarithmic dependence of surface areas of image brightness difference versus dimension of the square, which limits the surface. Forced acclimation was performed by 15-minute-long rhythmic temperature exposures (RTE), the simultaneous blowing of animals by cold (10ºC) and hot (40ºC) air (6 actions per minute), in the start of each of 9 light period hours during 3 month. After that the animal were placed into the cold chamber (10ºC), herewith in rats we observed an elevated temperature stability, and the hamsters entered the torpor for 1-2 days, which is not inherent for them in summer. This approach could be the basis of experimental model of estivation (E) in the case if we could find a significant differences between CNS structure of this torpid state and hibernation (H), and this become the aim of our study. In dynamics of RTE (Fig. 1, 2), as a model of first stages of FA, we observed a rise in randomness of microhemocirculation. Biomicroscopy and electron microscopy reveal a fractal halo (D~1.7) around erythrocytes and endotheliocytes’ microvilli, that is not characteristic for H, but typical for E, although with lower area and dimensions (Fig. 3, 4). Under H and in lesser extent under E, unlike FA, there are the evident signs of reduction (D~1.2) of elements of dendritic tree (Fig. 7, top right), as well as the fragmentation of synaptic buds. Under E in most single neurons the fractal peculiarities of surface structure disturbances characteristic for an active state (D~1.4) are preserved as well as the ability to grow spinules. After FA and 1-2 bouts of E in synaptic apparatus of 25% of synapses (in 10% during H) the parasynaptic structure is formed, which consists of cisterns with various D values (during H the values of D of pre- and postsynapses are the same ~1.3), that could be the correlate of vegetative memory (Fig. 4, 6, arrows). Under FA the geometry of endotheliocytes and synapses is “synchronized”, and there is the rise in transcytosis and BBB permeability for neuromediators and, probably, torpor hormones. These structures get the same dimensions (~1.7 or ~1.3) during decreasing of BBB resistance for acetylcholine (ACh) and norepinephrine (NE), correspondingly (Fig 5); the special endothelial areas, “fractal pores” (Fig. 2, arrow), are formed, which have the characteristic alternation of persistent and anti-persistent compartments. Under H when pinocytosis and active pericytes are absent, pericapillary and arachno-endothelial macrophages are on the foreground and form the “watch station” of closed BBB (Fig. 7, arrows). Thus the D value could be the important parameter of brain functional geometry, and FA could be the basis of the primary models of estivation. Control Acclimation Estivation Hibernation 1 (P - pericytes) 2 (V - microvilli) 3 (E - erythrocyte) 4 (S - synapse) 0 1 2 К 10,00 20 40 60 80 120min 0 0,2 0,4 D of endothel. Cp3Н‐ACh Cp3Н‐NE left axis Y: Cp – coefficient of BBB permeability; left axis Y: D 5 gradation of blue – D~1.2; green – D~1.3; yellow D~1.5; red D~1.7 6 CM (DiOC2). Top right: D- analysis of neuron (beta- tubulin marker). 7 Fig. Permeability and fractal analysis of structure elements of BBB and its neuro-glial environment S E V P E V E E