ANALYZING FUNCTIONAL CONNECTIVITY IN BRAIN-SLICES BY A COMBINATION OFINFRARED VIDEO MICROSCOPY, FLASH-PHOTOLYSIS OF CAGED COMPOUNDS AND SCANNING METHODS

We evaluate a novel set-up for scanning functional connectivity in bra in slices from the somatosensory cortex of the rat. Upright infrared v ideo microscopy for targeted placement of electrodes is combined with rapid photolysis of bath-applied caged neurotransmitter induced by a x enon flash lamp. Flash photolysis of caged glutamate and electrical st imulation produce comparable field potential responses and demonstrate that the viability of the submerged slices exceeds several hours. Glu tamate release leads to field potential responses whose two phases are differentially affected by selective blockade of N-methyr-D-aspartate - and mino-3-hydroxy-5-methyl-4-isoxazolepropionate-type glutamate rec eptors with DL-2-amino-5-phosphonovaleric acid and nitro-2,3-dioxobenz o[f]quinoxaline-7-sulphonamide, respectively. Rapid computer-controlle d scanning of hundreds of distinct stimulation sites with simultaneous recordings at a fixed reference site allows construction of functiona l input maps from peak amplitudes and delays to peak of field potentia l responses. Selective laminar expansion of the functional input maps after bicuculline application demonstrates that the combination of thi s conveniently assembled set-up with pharmacological and physical mani pulations can provide insights into the determinants of functional con nectivity in brain slices. (C) 1998 IBRO. Published by Elsevier Scienc e Ltd.