Local Regulation of Striatal Dopamine Release Shifts from Predominantly Cholinergic in Mice to GABAergic in Macaques

Abstract

Dopamine critically regulates neuronal excitability and promotes synaptic plasticity in the striatum, thereby shaping network connectivity and influencing behavior. These functions establish dopamine as a key neuromodulator, whose release properties have been well studied in rodents but remain understudied in nonhuman primates. This study aims to close this gap by investigating the properties of dopamine release in macaque striatum and comparing/contrasting them to better-characterized mouse striatum, using ex vivo brain slices from male and female animals. Using combined electrochemical techniques and photometry with fluorescent dopamine sensors, we found that evoked dopamine signals have smaller amplitudes in macaques compared with those in mice. Interestingly, cholinergic-dependent dopamine release, which accounts for two-thirds of evoked dopamine release in mouse slices, is significantly reduced in macaques, providing a potential mechanistic underpinning for the observed species difference. In macaques, only nicotinic receptors with alpha-6 subunits contribute to evoked dopamine release, whereas in mice, both alpha-6 and non-alpha6-containing receptors are involved. We also identified robust potentiation of dopamine release in both species when GABA_A and GABA_B receptors were blocked. This potentiation was stronger in macaques, with an average increase of 50%, compared with 15% in mice. Together, these results suggest that dopamine release in macaque is under stronger GABA-mediated inhibition and that weaker cholinergic-mediated dopamine release may account for the smaller amplitude of evoked dopamine signals in macaque slices.

Keywords: acetylcholine; caudate putamen; dopamine sensor; nicotinic receptors; primates; voltammetry.

Figure 1.

Dopamine signals across the striatum are smaller in macaques compared with mice. A, Coronal section images from macaque (left) and mouse (right) delineating the striatal subregions recorded. Images adapted from Scalable Brain Atlas. NAc, nucleus accumbens; DMS, dorsomedial striatum; DLS, dorsolateral striatum. B, C, Superimposed representative dopamine transients evoked by a single-pulse electrical stimulation of increasing intensity (black tick) from (B) the putamen of monkey or (C) the DLS of mouse. D, The input–output curves show mean peak amplitude of dopamine signals evoked at each stimulation intensity in the mouse (blue) and macaque (red) striatal subregions (n = 33, 23, 31 slices/12, 6, 4 mice; n = 23, 31, 16 slices/19, 10, 5 macaques). Symbols and lines are mean ± SEM.

Figure 2.

Dopamine fluorescent sensors confirms smaller magnitude of evoked dopamine signals in macaques. A, B, Representative photometry traces obtained from macaque brain slices expressing the fluorescent dopamine sensors dLight1.3b (A) and GRAB-DA1m (B). Dopamine signals were evoked by increasing stimulation intensities. Top right corner shows fluorescence images of brain sections from macaque caudate and putamen. C, Input–output curves of photometry signals measured in macaque brain sections expressing dLight1.3b (filled symbols, n = 14 slices/3 macaques) and GRAB-DA1m (open symbols, n = 11 slices/ 2 macaques). D, E, Photometry input–output curves macaque striatum (red) and mouse striatum (blue) when using dLight1.3b (14 slices/3 macaques; 16 slices/7 mice) and GRAB-DA1m (slices n = 11 slices/2 macaque; 16 slices/6 mice). F, Voltammetry input–output curves from mouse (blue) and macaque (red) dorsal striatum expressing the fluorescent sensors (open symbols) or not expressing the sensors (filled symbols).

Figure 3.

Smaller cholinergic contribution to evoked dopamine signals in macaques compared with mice. A, Representative dopamine transients evoked by single-pulse electrical stimulation (tick) before (pale) and after 1 µM DHβE application (solid) in macaque (red) and mouse (blue). B, C, The input–output curves of dopamine amplitudes with increasing stimulation intensities in macaque (B) and mouse (C) before (pale) and after (solid) 1 µM DHβE bath application. n = 27 slices/4 macaques, n = 26 slices/9 mice. D, Proportion of dopamine peak amplitudes blocked by the nicotinic receptor blocker DHβE in macaque (red) and mouse (blue) dorsal striatum from male (white) and female (orange) animals. Bars are mean ± SEM, and symbols are individual values. E, Time course of dopamine peak amplitudes as 1 and 10 μM DHβE were bath-applied in macaque caudate and putamen slices. Data is mean ± SEM normalized to predrug application. F, Time course of the dopamine peak amplitudes during application of nicotinic blocker conotoxin-PIA (0.1 µM) followed by 1 µM DHβE. Data is mean ± SEM normalized to predrug application for macaque (red) and mouse (blue), n = 5 slices/2 macaque; 15/2 mice.

Figure 4.

Stronger inhibitory modulation by GABA over striatal dopamine signals in macaques than mice. A, Representative traces of dopamine signals (right), the current–voltage plots (left top), and the voltammograms (left middle and bottom) evoked by a single pulse of electrical stimulation (tick) in macaque (red) and mouse (blue) striatum before and after (green) bath application of the GABA receptor blockers (5 μM gabazine and 2 μM CGP55845). B, C, The input–output curves of dopamine amplitude evoked by stimulation of increasing intensity before and after (green) GABA receptor blockers in macaque (B, red) and mouse (C, blue). Symbols and lines are mean ± SEM. n = 13 slices/3 macaque; 12 slices/6 mice. D, E, Time course of the dopamine amplitudes evoked at 300 µA during application of the GABA receptor blockers when done in the (D) absence (n = 11 slices/4 macaque; 12 slices/6 mice) or (E) presence of 1 µM DHβE in macaque (red) and mouse (blue) striatum (n = 29 slices/4 macaque; 13 slices/4 mice). Amplitude is normalized to predrug application (E). Symbols and lines are mean ± SEM. F, Percent change in the dopamine peak amplitudes evoked by 300 µA after GABA receptor blockers in macaque (red) and mouse (blue) bars were plotted as bar graphs together with individual values for the two species. Bars and lines are mean ± SEM, and symbols represent data from single experiments shown in white symbols for male and orange for female. n = 13 slices/4 macaques in ACSF and 31 slices/4 macaques in DHβE; 12 slices/6 mice in ACSF and 13 slices/4 mice in DHβE.

Figure 5.

Shift from acetylcholine to GABA modulation of dopamine signals in macaque compared with mice. A, Bar plot shows the overall magnitude of the evoked dopamine signals for maximal stimulation (300 µA) across striatal subregions in macaque (red) and mouse (blue). Solid portion represents the amplitude remaining after DHβE, denoting cholinergic-independent release. Light portion represents the amplitude of cholinergic-dependent release, which was blocked by DHβE. n = 61 slices/13 macaque; n = 61 slices/11 mice. * significant difference from mouse subregion. NAc, nucleus accumbens; DMS, dorsomedial striatum; DLS, dorsolateral striatum. B, The input–output curves of the cholinergic-dependent dopamine signals in the macaque caudate (red) and the mouse DMS (blue). C, The input–output curves of the non-ACh-dependent dopamine signals in the macaque caudate (red) and the mouse DMS (blue). n = 27 slices/4 macaques, n = 26 slices/9 mice. D, Amplitude of evoked dopamine signals at maximal stimulation (300 µA) for macaque caudate (red) and mouse DMS (blue) before and after GABA receptor antagonists gabazine and CGP (green). * main effect of GABA blockers. n = 13 slices/3 macaque; 12 slices/6 mice. E, The input–output curves of the GABA-modulated dopamine signals in the macaque caudate (red) and the mouse DMS (blue). n = 12–13 slices/3–4 animals. F, Amplitude of evoked dopamine signals remaining after DHβE at maximal stimulation (at 300 µA) for macaque caudate (red) and mouse DMS (blue) before and after GABA receptor antagonists gabazine and CGP (green) in the presence of nicotinic receptor antagonist. ^# significant interaction species × GABA blocker. n = 31 slices/4 macaques; 13 slices/4 mice. For all plots, symbols and lines are mean ± SEM. G, Diagram summarizing main findings and a model for interpreting the species differences.