Action sites of rotation and unit firing induced by l-stepholidine and DA agonists in basal ganglia of 6-OHDA-lesioned rats.

AIM

To elucidate the action sites of l-stepholidine (SPD) in the basal ganglia.

METHODS

Counting the rotations after intra-nucleus microinjection and recording the neuron firing by microiontophoresis of SPD and DA agonists in the basal ganglia of 6-hydroxydopamine (6-OHDA)-lesioned rats.

RESULTS

The DA immunoreactive substance was markedly reduced in the 6-OHDA-lesioned rats. The intra-neostriatum microinjection of apomorphine (Apo, D1/D2), SK&F 38393 (D1), and SPD elicited remarkable rotation, and the characteristics of SK&F 38393-produced rotation were of long latency and long duration. The intra-substantia nigra pars reticulata (SNR) injection of Apo, SK&F 38393, and SPD induced the rotation response, while the selective D2 agonist quinpirole hydrochloride (Ly171555) did not because of scarce D2 receptors in the SNR. The intraglobus pallidus (GP) injection of DA agonists and SPD failed to evoke rotation, but the GP nucleus still had the contribution to rotation elicited by i.p. injection of DA agonists and SPD in the 6-OHDA-lesioned rats with successive kainic acid (KA) lesion. Besides, the successive lesion of entopeduncular nucleus (EP) on rotation was less important than that of GP nucleus. The microiontophoresis of Apo and SPD into the SNR could evoke the neuron firing, but failed to activate the GP neurons, which were activated by sodium glutamate (Glu) and inhibited by gamma-aminobutyric acid (GABA).

CONCLUSION

The action sites of SPD-induced rotation and neuron firing via the D1 receptors are in the neostriatum and SNR instead of GP. The direct neurocircuit through SNR is the most important for rotation of 6-OHDA-lesioned rats.