NEURAL DYNAMICS IN CORTEX-STRIATUM COCULTURES .1. ANATOMY AND ELECTROPHYSIOLOGY OF NEURONAL CELL-TYPES

An in vitro system was established to analyse corticostriatal processi ng. Cortical and striatal slices taken at postnatal days 0-2 were co-c ultured for three to six weeks. The anatomy of the organotypic co-cult ures was determined using immunohistochemistry. In the cortex parvalbu min-positive and calbindin-positive cells, which resembled those seen in vivo, had laminar distributions. In the striatum, strongly stained parvalbumin-positive cells resembling striatal GABAergic interneurons and cholinergic interneurons were scattered throughout the tissue. The soma area of these interneuron classes was larger than the average st riatal soma area, thus enabling visual selection of cells by class bef ore recording. Cortical neurons with projections to the striatum showe d similar morphological features to corticostriatal projection neurons in vivo. No projections from the striatum to the cortex were found. I ntracellular recordings were obtained from 94 neurons. These were firs t classified on the basis of electrophysiological characteristics and the morphologies of cells in each class were reconstructed. Two types of striatal secondary neurons with unique electrophysiological dynamic s were identified: GABAergic interneurons (n = 17) and large aspiny, p robably cholinergic, interneurons (n = 15). The electrophysiological a nd morphological characteristics of cortical pyramidal cells (n = 27), cortical interneurons (n = 1), as well as striatal principal neurons (n = 34), were identical to those reported for similar ages in vivo. O rganotypic cortex-striatum co-cultures are therefore suitable as an in vitro system in which to analyse corticostriatal processing. The netw ork dynamics, which developed spontaneously in that system, are examin ed in the companion paper.