Submitted on July 24, 2008
Revised on October 20, 2008
Accepted on December 2, 2008
Presynaptic actions of D2-like receptors in the rat cortico-striato-globus pallidus disynaptic connection in vitro
Katsushige Watanabe1, Takako Kita2, and Hitoshi Kita1*
1 Univ. of Tennessee Health Science Ctr.
2 University of Tennessee
* To whom correspondence should be addressed. E-mail: hkita{at}utmem.edu.
The cerebral cortex, the neostriatum (Str), and the external segment of the globus pallidus (GPe) form a cortico-Str-GPe disynaptic connection, which is one of major connections in the basal ganglia circuitries and a target of dopamine modulation. The aim of the present study was to examine the actions of D2-like dopamine receptors (D2LRs) in this connection using rat brain slice preparations. Electrical stimulation of the frontal cortex evoked disynaptic IPSCs in cesium filled GPe neurons voltage-clamped at 0 mV. The IPSCs evoked by threshold stimulation were small, less than 10 pA. Applications of the D2LR agonist quinpirole to bath or locally to Str decreased the amplitude of the cortical stimulation-induced IPSCs. Electrical stimulation of Str evoked monosynaptic IPSCs in GPe neurons. Local application of quinpirole to GPe decreased the Str stimulation-induced IPSCs. Bath application of quinpirole decreased the frequency of large mIPSCs that were considered to be evoked by local collateral axons of GPe neurons. These results suggested that activation of D2LRs decrease the gain of cortico-Str-GPe disynaptic connection, with the decrease attributed to activation of D2LRs in Str and GPe, and that both Str-GPe and GPe-GPe GABAergic inhibitions are under the control of presynaptic D2LRs.
