Regional and sex differences in spontaneous striatal dopamine transmission

Abstract

Striatal dopamine release is key for learning and motivation and is composed of subregions including the dorsal striatum (DS), nucleus accumbens core, and the nucleus accumbens shell. Spontaneously occurring dopamine release was compared across these subregions. Dopamine release/uptake dynamics differ across striatal subregions, with dopamine transient release amplitude and release frequency greatest in male mice, and the largest signals observed in the DS. Surprisingly, female mice exhibited little regional differences in dopamine release for DS and nucleus accumbens core regions, but lower release in the nucleus accumbens shell. Blocking voltage-gated K⁺ channel (Kv channels) with 4-aminopyridine enhanced dopamine detection without affecting reuptake. The 4-aminopyridine effects were greatest in ventral regions of female mice, suggesting regional differences in Kv channel expression. The dopamine transporter blocker cocaine also enhanced detection across subregions in both sexes, with greater overall increased release in females than males. Thus, sex differences in dopamine transmission are apparent and likely include differences in the Kv channel and dopamine transporter function. The lack of regional differences in dopamine release observed in females indicates differential regulation of spontaneous and evoked dopamine release.

Keywords: Kv channels; accumbens; cocaine; dopamine; sex differences; striatum.

FIGURE 1

Example dopamine (DA) transients measured across striatal subregions. (a) Timeline of experimental procedures. Spontaneous DA (sDA) was measured in mice across subregions at baseline (Figures 1–3), after 4-aminopyridine (4AP; voltage-gated K⁺ channel [Kv channels] blocker; Figures 4 and 5), and after cocaine (DAT blocker; Figures 6 and 7). Evoked DA (eDA) was measured in mice (Figure 5) in dorsal and ventral striatum and the effects of Kv channel blockers (4AP and Ba2+) on eDA clearance were tested (Figure 5). eDA release and uptake was measured in female rats across regions (Figure S1). (b) Schematic indicating the locations used to determine the regional location of DA transients in brain slices. (c) Example traces and color plots for DA transient events in the dorsal striatum (DS), nucleus accumbens core (NAcc), and nucleus accumbens shell (NAcs)

FIGURE 2

Regional and sex differences in dopamine (DA) transient amplitude. (a) Distribution of transient release amplitude under baseline (no drug) conditions. Inset (a1) represents the top 25% of amplitude values across regions. (b) Cumulative release probability distribution of DA amplitudes indicates directional trends when only region is investigated. (c) Quantification of DA release by region and sex under baseline conditions indicates clear sex differences in regional release, with no apparent regional differences for female mice. (d) 3-dimensional visualization of average amplitude by anatomical location. Bar plots indicate mean ± SEM values. *p < .05, **p < .01, ***p < .001. n = 264 release events from 60 brain slices from 23 mice

FIGURE 3

Regional and sex differences in dopamine (DA) transient frequency. (a) Regional comparison of DA transient frequency. Frequency was highest in the dorsal striatum (DS), followed by the nucleus accumbens core (NAcc) and finally the nucleus accumbens shell (NAcs). (b) Comparison of DA transient frequency between males and females. Female mice generally have a lower frequency of release. (c) Plot of the variance of the frequency between males and females and (d) across regions did not differ significantly across the sex and region variables. (e) 3-dimensional visualization of frequency by anatomical location. Bar plots indicate mean ± SEM values. *p < .05, **p < .01, ***p < .001. n = 60 brain slices from 23 mice

FIGURE 4

Voltage-gated K⁺ channel blockade increases dopamine (DA) transient amplitude and frequency, with greater increases observed in females. (a) Distribution of transient release amplitude in the presence of 4AP (30 μM). Inset (a1) represents the top 25% of amplitudes. (b) Cumulative release amplitude shows an increase in amplitude in each region following 4AP administration. 3-dimensional visualization of (c) amplitude and (d) frequency by anatomical location, (e) overall amplitude, and (f) upper quartile amplitude following 4AP administration. (g) Within-subject changes in frequency compared with baseline conditions after 4AP indicated clear increases in release frequency that were more pronounced in females. Regional and sex comparison of (h) transient frequency. Bar plots indicate mean ± SEM values. *p < .05, **p < .01, ***p < .001. n = 2,407 events from 60 brain slices from 23 mice

FIGURE 5

Clearance for dopamine (DA) transients varies by sex and is not influenced by voltage-gated K⁺ channel blockade. Example evoked DA traces and example curve fit from single exponential decay model (blue) under (a) baseline and (b) 4AP (30 μM) conditions. (c) 4AP increases evoked DA release in the nucleus accumbens core (NAcc). However, (d) 4AP has no apparent effect on DA clearance in the NAcc. The nonselective K channel blocker barium (100 μM) increased DA release (e) but had no effect on DA clearance (f) in the dorsal striatum (DS). Clearance for DA transients was measured after 4AP, and (g) females demonstrated greater variability and higher mean tau values than males in all regions. Bar plots indicate Mean ± SEM values. *p < .05, **p < .01, ***p < .001. n = 5 brain slices from mice for each evoked experiment. n = 1,111 events from 60 brain slices from 23 mice for spontaneous release experiments

FIGURE 6

Dopamine (DA) transients have reduced clearance after cocaine. (a, b) Examples of cyclic voltammograms (CV; a1), current traces (a2,3), and color plots (a4,5) of DA transients after administration of the voltage-gated K⁺ channel blocker 4AP (30 μM). These peaks are used as a baseline comparison for reuptake findings. (b) Example CV (b1), current traces (b2,3), and color plots (b4,5) for DA transients after cocaine (3 μM) administration. Arrows in a2,3 and b2,3 indicate the peak for the color-matched CVs depicted in a1 and b1

FIGURE 7

Cocaine increases dopamine (DA) transient amplitude and frequency. (a) Distribution of transient release amplitude in the presence of cocaine (3 μM). Inset (a1), the top 25% of amplitudes. (b) Cumulative release amplitude indicates increases in amplitude across regions following cocaine. 3-dimensional visualization of (c) amplitude and (d) frequency by anatomical location, (e) overall amplitude, and (f) upper quartile amplitude following 4AP administration. (g) Increases in transient frequency after cocaine indicate clear increases in release frequency across all regions. (h) Regional and sex comparison of transient frequency. In general, sex and regional relationships observed in Figure 7 were maintained with cocaine. Bar plots indicate mean ± SEM values. *p < .05, **p < .01, ***p < .001. n = 1974 events from 60 brain slices from 23 mice