Changes in the D1 receptor-adenylate cyclase complex after priming.

Area of Science:

• Neuroscience
• Pharmacology
• Dopamine receptor signaling

Background:

• Unilateral 6-hydroxydopamine (6-OHDA) lesions induce motor asymmetry in rats.
• D1 receptor agonists are typically ineffective in inducing contralateral turning in naive lesioned rats.

Purpose of the Study:

• To investigate the effect of priming with a dopamine agonist on D1 receptor function in a rat model of Parkinson's disease.
• To determine if priming alters D1 receptor binding or downstream signaling.

Main Methods:

• Rats received unilateral 6-OHDA lesions.
• Drug-naive and primed rats (primed with D2 agonist LY 171555) were administered D1 agonist SKF 38393.
• Contralateral turning behavior was measured.
• D1 receptor binding (Bmax, Kd) and dopamine-stimulated adenylate cyclase activity were analyzed in striatal tissue.

Main Results:

• SKF 38393 failed to induce turning in drug-naive lesioned rats.
• Priming with LY 171555 rendered SKF 38393 fully effective in inducing contralateral turning.
• No significant changes in D1 receptor binding (Bmax, Kd) were observed between drug-naive and primed rats.
• Dopamine-stimulated adenylate cyclase showed a decreased Km for dopamine in the lesioned striata of primed rats compared to drug-naive rats.

Conclusions:

• Priming with a D2 agonist enhances the functional efficacy of D1 agonists in a lesioned state.
• The priming effect appears to involve alterations in the signal transduction pathway of D1 receptors, not changes in receptor number or affinity.
• These findings suggest novel therapeutic strategies targeting dopamine receptor signaling mechanisms for motor disorders.