Impact of Acute and Persistent Excitation of Prelimbic Pyramidal Neurons on Motor Activity and Trace Fear Learning

Abstract

Drug-induced neuroadaptations in the mPFC have been implicated in addictive behaviors. Repeated cocaine exposure has been shown to increase pyramidal neuron excitability in the prelimbic (PL) region of the mouse mPFC, an adaptation attributable to a suppression of G protein-gated inwardly rectifying K 1 (GIRK) channel activity. After establishing that this neuroadaptation is not seen in adjacent GABA neurons, we used viral GIRK channel ablation and complementary chemogenetic approaches to selectively enhance PL pyramidal neuron excitability in adult mice, to evaluate the impact of this form of plasticity on PL-dependent behaviors. GIRK channel ablation decreased somatodendritic GABA B receptor-dependent signaling and rheobase in PL pyramidal neurons. This manipulation also enhanced the motor-stimulatory effect of cocaine but did not impact baseline activity or trace fear learning. In contrast, selective chemogenetic excitation of PL pyramidal neurons, or chemogenetic inhibition of PL GABA neurons, increased baseline and cocaine-induced activity and disrupted trace fear learning. These effects were mirrored in male mice by selective excitation of PL pyramidal neurons projecting to the VTA, but not NAc or BLA. Collectively, these data show that manipulations enhancing the excitability of PL pyramidal neurons, and specifically those projecting to the VTA, recapitulate behavioral hallmarks of repeated cocaine exposure in mice.

GIRK channel activity in prelimbic pyramidal neurons regulates the extinction of cocaine conditioned place preference in male mice

“…Gabbr1 gRNA treatment abolished somatodendritic currents evoked by the GABA B R agonist baclofen in these neurons, in both male and female mice (Figure 2B,C); two-way ANOVA revealed a main effect of viral treatment (F(1,24) = 141.9, ****p < 0.0001), but there was no main effect of sex (F(1,24) = 0.57, p = 0.46) or interaction between sex and viral treatment (F(1,24) = 2.76, p = 0.11). In contrast to GIRK channel ablation in PL pyramidal neurons (Figure 1D), 16,17 In the cocaine CPP study, three-way repeated measures ANOVA revealed a main effect of sex (F(1,30) = 7.79, p = 0.009). To enhance our ability to detect viral treatment effects, we conducted sex-specific two-way repeated measures ANOVA analyses.…”

“…GIRK channels formed by GIRK1 and GIRK2 subunits mediate ~50% of the composite GABA B R‐dependent somatodendritic current in layer 5/6 PL pyramidal neurons; the GIRK channel component of the GABA B R‐dependent current is selectively suppressed by repeated cocaine 15 . To evaluate the behavioural consequences of this cocaine‐induced neuroadaptation, we used an established viral Cre ablation approach and conditional Girk1 knockout ( Girk1 fl/fl ) mice to suppress GIRK channel activity in PL pyramidal neurons in drug‐naïve subjects 16,17 . AAV8‐CaMKIIα‐Cre (mCherry) or AAV8‐CaMKIIα‐mCherry vectors were infused into the PL of Girk1 fl/fl mice (Figure 1A).…”

“…As GIRK channel ablation increased PL pyramidal neuron excitability (Figure 1D) while GABA B R ablation was without effect (Figure 2D), we hypothesized that increased PL pyramidal neuron excitability underlies the CPP extinction impairment in male mice. To test this hypothesis, we employed a neuron‐specific chemogenetic approach to acutely increase the excitability of PL pyramidal neurons in male mice 16 . AAV vectors harbouring hM3Dq (CaMKIIα‐hM3Dq(mCherry)) or control (CaMKIIα‐mCherry) were infused into the PL of male C57BL/6J mice (Figure 3A).…”

“…After surgery, animals were allowed 2–3 weeks (chemogenetic or GIRK2 overexpression studies) or 4–5 weeks (GIRK1 or GB1 ablation studies) for full recovery and gene expression before behavioural and/or electrophysiological assessments. The scope and accuracy of viral targeting were assessed using fluorescence microscopy as previously described 16 . Brightfield and fluorescent images were overlaid and evaluated using the mouse brain atlas, 22 and only data from mice in which >70% of viral‐driven bilateral fluorescence was confined to the PL were included in the final analysis.…”

“…Previously, we reported that genetic suppression of GIRK channel activity in PL pyramidal neurons of drug-naive mice potentiates the acute motor-stimulatory effect of cocaine. 16 GIRK channel ablation in PL pyramidal neurons also impacted measures of affect and impaired working memory and diminished cognitive flexibility in male, but not female, mice. 17 Because GABAergic signalling in the PL has been implicated in the expression and extinction of context-evoked cocaine memories, 12,18,19 we sought to determine the impact of PL pyramidal neuron-specific ablation of GIRK channels or GABA B R on cocaine conditioned place preference (CPP) and extinction.…”