Repeated D1 dopamine receptor agonist administration prevents the development of both D1 and D2 striatal receptor supersensitivity following denervation

Mar 1, 1992Synapse (New York, N.Y.)

Repeated stimulation of D1 dopamine receptors stops increased sensitivity of D1 and D2 receptors in movement areas after nerve loss

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Abstract

Daily administration of SKF 38393 (8.0 mg/kg) prevented the development of both D1 and D2 receptor supersensitivity in rats with 6-OHDA lesions.

6-OHDA lesions of the dopamine pathway caused rat CPu neurons to become supersensitive to D1 and D2 agonists.
D1 receptor stimulation is necessary for D2 agonist-induced inhibition, which is lost after denervation.
Quinpirole administration selectively prevented the development of D2 receptor supersensitivity.
SKF 38393 administration prevented the development of both D1 and D2 receptor supersensitivity and maintained synergistic inhibitory responses.
Behavioral tests showed SKF 38393 prevented contralateral rotations in response to apomorphine in lesioned rats.
After a 4-week withdrawal from D1 agonist treatment, supersensitivity and contralateral rotations re-emerged, indicating effects were not permanent.

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Following 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal dopamine (DA) pathway, rat caudate-putamen (CPu) neurons are supersensitive to the inhibitory effects of both D1 and D2 dopamine (DA) receptor selective agonists. In addition, both the necessity of D1 receptor stimulation for D2 agonist-induced inhibition and the synergistic inhibitory effects of D1 and D2 agonists are abolished by denervation. The present study attempted to determine the relative roles of D1 and D2 DA receptors in the development of denervation supersensitivity to DA agonists and the "uncoupling" of functional interactions between the receptors following 6-OHDA lesions of the nigrostriatal DA pathway. Beginning on the day after an intraventricular 6-OHDA (or vehicle) injection, groups of rats received daily injections of either the selective D1 receptor agonist SKF 38393 (8.0 mg/kg, s.c.), the D2 agonist quinpirole (0.5 mg/kg, s.c.), or saline for 7 days. On the day following the last agonist injection, rats were anesthetized and prepared for extracellular single cell recording with iontophoretic drug administration. Daily administration of quinpirole selectively prevented the development of D2 receptor supersensitivity, whereas daily administration of SKF 38393 prevented the development of both D1 and D2 receptor supersensitivity. In addition, D1, but not D2, agonist treatment prevented the loss of synergistic inhibitory responses typically produced by 6-OHDA lesions. Behavioral observations revealed similar effects; daily injections of SKF 38393, but not quinpirole, prevented contralateral rotational responses to the mixed D1/D2 agonist apomorphine (1.0 mg/kg, s.c.) in rats with unilateral 6-OHDA lesions of the nigrostriatal pathway. After a 4-week withdrawal from repeated D1 agonist treatment, both supersensitive inhibitory responses of CPu neurons and contralateral rotations to apomorphine were evident, indicating that the preventative effects on DA receptor supersensitivity were not permanent. These findings indicate that continued agonist occupation of striatal D1 DA receptors following DA denervation not only prevents the development of D1 DA receptor supersensitivity but also exerts a similar regulation of D2 receptor sensitivity.

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Repeated D1 dopamine receptor agonist administration prevents the development of both D1 and D2 striatal receptor supersensitivity following denervation

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