D1 dopamine receptors intrinsic activity and functional selectivity affect working memory in prefrontal cortex

Abstract

Dopamine D₁ agonists enhance cognition, but the role of different signaling pathways (e.g., cAMP or β-arrestin) is unclear. The current study compared 2-methyldihydrexidine and CY208,243, drugs with different degrees of both D₁ intrinsic activity and functional selectivity. 2-Methyldihydrexidine is a full agonist at adenylate cyclase and a super-agonist at β-arrestin recruitment, whereas CY208,243 has relatively high intrinsic activity at adenylate cyclase, but much lower at β-arrestin recruitment. Both drugs decreased, albeit in dissimilar ways, the firing rate of neurons in prefrontal cortex sensitive to outcome-related aspects of a working memory task. 2-Methyldihydrexidine was superior to CY208,243 in prospectively enhancing similarity and retrospectively distinguishing differences between correct and error outcomes based on firing rates, enhancing the micro-network measured by oscillations of spikes and local field potentials, and improving behavioral performance. This study is the first to examine how ligand signaling bias affects both behavioral and neurophysiological endpoints in the intact animal. The data show that maximal enhancement of cognition via D₁ activation occurred with a pattern of signaling that involved full unbiased intrinsic activity, or agonists with high β-arrestin activity.

Figure 1.. D₁ intrinsic activity and functional selectivity of 2MDHX and CY208.

(a & b) Representative curves of induction of β-arrestin activation at D₁R (a) and D₁R-mediated adenylate cyclase activation (b) by 2MDHX and CY208. All data are expressed as a percentage of dopamine activity. (c & d) Population analysis showed 2MDHX and CY208 have functional selectivity at β-arrestin vs. cAMP based on E_max (c) and EC₅₀ (d). Grey lines represent mean±SEM. Star indicates the comparison between 2MDHX vs CY208. Pound indicates the comparison between β-arrestin vs cAMP. (e - g) Averaged (mean±SEM) bias scaled by (f) Δlog(RA) and (g) ΔΔlog(RA). Each individual sample was shown in (e), along with the dopamine as reference. (h & i) D₁ antagonist SCH23390 (SCH) completely blocked the increases of β-arrestin (h) and cAMP (i) induced by 2MDHX and CY208. *, # indicates P<0.05; **, ## indicates P<0.005; ***, ### indicates P<0.001.

Figure 2.. Effects of 2MDHX and CY208 on single unit activity in PFC. (a & d)

Both 2MDHX and CY208 decreased firing rate (FR) of prospective neurons (a) and retrospective neurons (d). (Upper) Normalized FR for every single unit for control vs. 2MDHX and CY208. (Lower) Averaged FR of all units. (b & e) There was a significant interaction between drug and outcome based on FR for prospective neurons (b) and retrospective neurons (e). Star indicates post hoc comparison between control vs 2MDHX (red) or between control vs CY208 (blue). Pound indicates the interaction between drugs (2MDHX vs CY208) and outcomes (correct vs error). (c & f) d’of error vs. correct based on FR was significantly decreased by 2MDHX but not CY208 for prospective neurons (c), whereas it was less decreased by 2MDHX than CY208 for retrospective neurons (f). Grey lines represent each unit. *, # indicates P<0.05; **, ## indicates P<0.005; ***, ### indicates P<0.0001.

Figure 3.. Effects of 2MDHX and CY208 on the neuronal network in PFC.

(a) 2MDHX significantly increased spike-spike synchronization between units measured by coherence. CY208 did not increase but even decreased it at beta and gamma bands (27, 35–37 Hz). Each line is averaged coherence of all paired units at each frequency. Star indicates P<0.05 for post hoc comparison between control vs 2MDHX (red) or between control vs CY208 (blue). (b) 2MDHX but not CY208 significantly increased the power density of LFP oscillation at theta and beta bands (7–9, 15–16 Hz, zoom in at top right corner). Same format as in A. (c) 2MDHX maintained whereas CY208 significantly decreased synchronization between LFP oscillation and unit spike oscillation at theta, beta, and gamma bands (6, 16–18, 35, 49–51 Hz). Same format as in (a).

Figure 4.. Effects of 2MDHX and CY208 on cognitive performance.

(a) Both 2MDHX and CY208 produced an inverted-U dose effect on DAR task whereby low doses improved but high doses had no effect or tended to impair the accuracy of performance as measured by correct rate. (b) 2MDHX but not CY208 improved decision making at a low dose as measured by duration, whereas at high dose they both tended to impair it. (c) 2MDHX and CY208 did not change motor function as measured by running speed. Star indicates the comparison between control vs 2MDHX (red) or the comparison between control vs CY208 (blue). (d) Pretreatment of D₁ antagonist SCH39166 (SCH) blocked cognitive enhancement induced by 2MDHX or CY208. * indicates P<0.05. ** indicates P<0.01.