SPATIAL PATTERN OF EVOKED SYNAPTIC EXCITATION IN THE MOUSE NEOSTRIATUM IN-VITRO

The spatial distribution of stimulus-evoked excitation in the mouse ne ostriatum was investigated in vitro by using voltage-sensitive dyes an d an optical multi-site recording system (laser scanning microscopy). The scanning area (880x830 mu m) was positioned in the center of coron al neostriatal slices and records were taken simultaneously from up to 20 detection sites. Stimulus-induced optical signals were blocked by tetrodotoxin (TTX) and disappeared following removal of Ca2+ from the extracellular medium. Furthermore, these responses were inhibited by t he glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) indicating that the evoked signals reflected mainly glutamaterg ic synaptic activity. Electrical stimulation at defined positions elic ited characteristic spatial patterns of activity within the neostriatu m. Stimulation of the medial subcortical white matter or stimulation a t the dorsomedial corner or at the midpoint of the scanning area evoke d synaptic activity at all recording sites. However, the largest respo nse amplitudes were invariably observed in the ventrolateral part of t he scanning area. In contrast, stimulation at the dorsolateral, ventro lateral or at the ventromedial corner induced synaptic reponses which remained restricted to a relatively small area in close vicinity to th e site of stimulation. The GABAA receptor antagonist bicuculline did n ot influence the pattern of activity distribution. However, in the pre sence of bicuculline, a N-methyl-D-aspartate (NMDA) receptor-mediated delayed signal component was observed which again was most pronounced in the ventrolateral part of the scanning area. These results, obtaine d in an in vitro slice preparation, demonstrate that spatially defined afferent activation of neostriatal neuronal circuits leads to a chara cteristic pattern of activity distribution within the neostriatum. Thu s, our data complement observations from morphological investigations as well as from electrophysiological studies in vivo that suggest a fu nctional compartmentalization of this brain area.