Objective: To explore the effects of endogenous dopamine (DA) on striatum medium spiny neurons (MSNs) in acute brain slices by the means of electrophysiology and elucidate the impact of nigrostriatal circuit loop on the functional status of MSNs.
Methods: Various structural combinations of striatum and cortex or/and substantia nigra were used to explore the conditions with appearance of spontaneous two-state voltage oscillations. And the blockage of dopaminergic or glutamic acid receptor was employed to examine how amino glutaminic acid from cortex and dopamine from substantia nigra influenced two-state voltage oscillations.
Results: It was found that 65.2% (30/46) MSNs recorded in corticostriatonigral slices displayed spontaneous and two-state voltage oscillations.92.3% (24/26) of MSNs in dorsal striatum close to cortex. And the percentage was only 30% (6/20) in ventral striatum. The amplitude of depolarized plateau potential (up state) decreased through a blockage of dopamine receptor (P < 0.05). The potential level of up state decreased through a blockage of D1 receptor (P < 0.05) and action potentials were stopped. The results of blocking D2 receptors were the increased potentials level of two states (P < 0.05). The membrane potential of MSNs showed a stable resting level in corticostriatonigral (-67 ± 3 mV, n = 10), corticostriatal (-70 ± 3 mV, n = 10), striatal (-73 ± 3 mV, n = 10) and nigrostriatal (-71 ± 3 mV, n = 10) slices. There was no significant difference (P > 0.05) .
Conclusion: Endogenous dopamine from substantia nigra may regulate the instantaneous integration and coding of information from cortex by tonic effect on short-term plasticity of paired and short pulses in corticostriatal synapses.