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(Accepted June 19, 1999)
Cell-attached mode of patch clamp technique was employed to investigate the properties of acetylcholine (ACh)-induced ion channels in acutely dissociated neurons from the marginal division (MrD) of rat striatum. Two types of conductance states (25 pS and 60 pS) were recorded. The 25 pS channel (more than 80%) was the main type in the neurons of MrD and was described here. The amplitudes of inward currents increased with hyperpolorization and the reversing potential was about 0 mV. Both single short opening and long burst openings were observed in MrD neurons. Two time constants of these two kinds of ion channels are 0.29 ms, 1.84 ms and 1.96 ms, 18.24 ms, respectively. Average close time can be fitted with two exponential functions, the two time constants are 1.7 ms and 54 ms. Probability of channel opening is about 0.012 and no voltage-dependence was found. The properties of reversing potential, voltage-independence and the form of agonist to the ion channels indicated that the recorded channel currents flow through AChR channels. The mAChR is involved in slow synaptic transmission and Ach can not induce the opening of mAChR ion channel. The binding site of ACh to AChR and the nAChR ion channel are the same protein, ACh can only activate nAChR ion channel directly. Therefore, the recorded ion channels in the present study are nAChR ion channels. The results suggest that nAChR ion channels exist in the neurons of MrD and the MrD probably is involved in learning and memory mechanism of the brain.
KEY WORDS: Marginal division; striatum; nicotinic acetylcholine receptor; patch clamp; ion channels.
INTRODUCTION
The "marginal division" (MrD) is a new subterritory of the striatum first discovered by Siyun Shu in 1988 (1). It is located at the caudal extent of caudate putamen (CPU) and surrounds the rostral border of globus pallidus (GP) in rat striatum. MrD differs from the other areas of the striatum in morphology and chemical architecture (1). It has specific internal organization and fiber connections which are distinct from the rest of the striatum. The neurons of MrD have numerous long local collaterals running within the MrD and they send projections to the caudal-most parts of the globus pallidus and substantia nigra (1). Compared to the...