The use of fluorescent-protein conjugates for staining brain capillaries in hypo- and hyperthermia (26-42 degrees)

The temperature dependency of cerebrocortical capillary diameter (CD), number perfused with fluorescent tracer (CN), and intercapillary distance (ICD) has been investigated for three body temperatures (26, 37, and 42 degrees), in order to analyze the influence of undesired cooling or warming which frequently occurs in animal experiments and humans (freezing, heat disposal, fever, etc.). The capillary bed (Wistar-Frömter rats, N = 92, ketaminxylazin anesthesia) was visualized with a double staining method using serum proteins coupled with either FITC (fluorescein isothiocyanate) or RB-200 (rhodamine-lissamin) injected ia immediately before decapitation. CD (6.1 +/- 0.3 micron, 37 degrees) increased during cooling by about 18%, during warming by about 13%. CN (313 +/- 83/mm2, 37 degrees) showed a 12% increase in response to temperature reduction and 18% after elevation. ICD was characterized by small insignificant changes of the mean values (44.2 +/- 5.5 micron, 37 degrees) at 26 degrees and 42 degrees. Mean cerebrocortical surface PO2 (sPO2) ranging between 15 and 22 mm Hg (37 degrees) increased slightly during warming or decreased during cooling. The sPO2 histogram showed a Gaussian-like shape in the range 0-40 mm Hg at low temperatures (26-34 degrees) and a left-shifted frequency distribution between 34-42 degrees. It was interesting to note that above 38 degrees sporadically high sPO2 values were registered in the range 40-80 mm Hg. Nevertheless, despite pronounced temperature variations, the net effect between O2 transport and consumption was balanced to such an extent that tissue anoxia was not detected within the rat cerebro-cortex.