SURVIVAL AND FUNCTIONAL DEMONSTRATION OF INTERREGIONAL PATHWAYS IN FORE MIDBRAIN SLICE EXPLANT CULTURES/

An important general question in neurobiology concerns the development and expression of the rich context of neuronal phenotypes, especially in relation to the diverse patterns of connectivity. Organotypic cult ures of brain slices may offer distinct advantages for such studies if such a preparation survives, maintains a wide diversity of neuronal p henotypes and displays appropriate synaptic connections between region s. To address these requirements, we utilized long-term organotypic cu ltures of intact horizontal slices of rat forebrain and midbrain and a ssessed a variety of markers of phenotype in combination with function al tests of connectivity. This explant preparation displayed a distinc t viability requirement such that the greatest explant survival was se en in slices taken from pups of less than postnatal day 7 and was inde pendent of N-methyl-D-aspartate channel blockade. The anatomical featu res of the major brain regions (e.g., neocortex, striatum, septum, hip pocampus, diencephalon and midbrain) were observed in their normal bou ndaries. The presence of cholinergic and catecholaminergic neurons was demonstrated with acetylcholinesterase histochemistry and tyrosine hy droxylase immunohistochemistry. Labelled neurons displayed multiple, r egionally-appropriate cytoarchitectures and, in some cases, could be s een to project to brain regions in a manner quite similar to that seen in vivo. Finally, the direct demonstration of spontaneous and evoked interregional excitatory synaptic transmission was made using whole-ce ll patch-clamp recordings from striatal neurons which revealed an inta ct glutamate-using corticostriatal pathway. This simple explant prepar ation appears to contain a rich diversity of neuronal types and synapt ic organization. Therefore, this preparation appears to have several d istinct advantages for basic neurobiologic research since it combines long-term culture viability and many features of mature brain includin g complex interregional neuronal systems. (C) 1998 IBRO. Published by Elsevier Science Ltd.