The excitability of cholinergic, glutamatergic and dopaminergic elemen
ts within the rat neostriatum was studied in both in vivo and in vitro
preparations. In vivo, the microdialysis technique was used to measur
e the release of striatal acetylcholine and dopamine under basal and e
lectrically evoked conditions. For comparison, acetylcholine, dopamine
and glutamate release was assayed in media obtained from superfused r
at striatal slices. Electrical stimulation was used to derive the stre
ngth-duration functions and their chronaxies of stimulated elements co
ntaining the three neurotransmitter types. The chonaxies for experimen
ts in vitro and in vivo were similar: the chronaxy values for elements
containing acetylcholine were the shortest, the values for glutamate
were intermediate, and the values for those containing dopamine were t
he longest. Based on the chronaxy estimates, it is proposed that the e
lements containing acetylcholine are the large cholinergic interneuron
s of striatum, and the elements containing glutamate and dopamine are
the terminals of corticostriatal and nigrostriatal neurons, respective
ly. These results indicate that electrical stimulation of neural eleme
nts surrounding a microdialysis probe can be an additional tool to exa
mine the factors that regulate neurotransmitter release. Likewise, inv
estigators can activate specific striatal elements by using pulse dura
tions that coincide with their chronaxies. (C) 1997 Elsevier Science B
.V.