Relapse to drug use can be initiated by drug-associated cues. The intensity of cue-induced drug seeking in rodent models correlates with the induction of transient synaptic potentiation (t-SP) at glutamatergic synapses in the nucleus accumbens core (NAcore). Matrix metalloproteinases (MMPs) are inducible endopeptidases that degrade extracellular matrix (ECM) proteins, and reveal tripeptide Arginine-Glycine-Aspartate (RGD) domains that bind and signal through integrins. Integrins are heterodimeric receptors composed of αβ subunits, and a primary signaling kinase is focal adhesion kinase (FAK). We previously showed that MMP activation is necessary for and potentiates cued reinstatement of cocaine seeking, and MMP-induced catalysis stimulates β3-integrins to induce t-SP. Here, we determined whether β3-integrin signaling through FAK and cofilin (actin depolymerization factor) is necessary to promote synaptic growth during t-SP. Using a small molecule inhibitor to prevent FAK activation, we blocked cued-induced cocaine reinstatement and increased spine head diameter (d_h). Immunohistochemistry on NAcore labeled spines with ChR2-EYFP virus, showed increased immunoreactivity of phosphorylation of FAK (p-FAK) and p-cofilin in dendrites of reinstated animals compared with extinguished and yoked saline, and the p-FAK and cofilin depended on β3-integrin signaling. Next, male and female transgenic rats were used to selectively label D1 or D2 neurons with ChR2-mCherry. We found that p-FAK was increased during drug seeking in both D1 and D2-medium spiny neurons (MSNs), but increased p-cofilin was observed only in D1-MSNs. These data indicate that β3-integrin, FAK and cofilin constitute a signaling pathway downstream of MMP activation that is involved in promoting the transient synaptic enlargement in D1-MSNs induced during reinstated cocaine by drug-paired cues.

SIGNIFICANCE STATEMENT Drug-associated cues precipitate relapse, which is correlated with transient synaptic enlargement in the accumbens core. We showed that cocaine cue-induced synaptic enlargement depends on matrix metalloprotease signaling in the extracellular matrix (ECM) through β3-integrin to activate focal adhesion kinase (FAK) and phosphorylate the actin binding protein cofilin. The nucleus accumbens core (NAcore) contains two predominate neuronal subtypes selectively expressing either D1-dopamine or D2-dopamine receptors. We used transgenic rats to study each cell type and found that cue-induced signaling through cofilin phosphorylation occurred only in D1-expressing neurons. Thus, cocaine-paired cues initiate cocaine reinstatement and synaptic enlargement through a signaling cascade selectively in D1-expressing neurons requiring ECM stimulation of β3-integrin-mediated phosphorylation of FAK (p-FAK) and cofilin.

与药物相关的线索可能会导致吸毒复发。啮齿动物模型中线索诱导的药物寻找强度与伏核核心（NAcore）谷氨酸能突触的瞬时突触增强（t-SP）的诱导相关。基质金属蛋白酶 (MMP) 是诱导型内肽酶，可降解细胞外基质 (ECM) 蛋白，并揭示通过整合素结合并发出信号的三肽精氨酸-甘氨酸-天冬氨酸 (RGD) 结构域。整合素是由αβ亚基组成的异二聚体受体，主要信号激酶是粘着斑激酶（FAK）。我们之前表明，MMP 激活对于可卡因寻求的提示恢复是必要的，并且增强了可卡因寻求的提示恢复，并且 MMP 诱导的催化作用刺激 β3-整合素诱导 t-SP。在这里，我们确定了通过 FAK 和 cofilin（肌动蛋白解聚因子）的 β3-整合素信号传导对于促进 t-SP 期间的突触生长是否是必需的。使用小分子抑制剂来防止 FAK 激活，我们阻止了提示诱导的可卡因恢复和脊柱头部直径 ( _dh ) 的增加。用 ChR2-EYFP 病毒对 NAcore 标记的树突棘进行的免疫组织化学显示，与熄灭和轭合的盐水相比，恢复动物树突中 FAK (p-FAK) 和 p-cofilin 磷酸化的免疫反应性增加，并且 p-FAK 和 cofilin 依赖于 β3-整合素信号传导。接下来，雄性和雌性转基因大鼠被用来用 ChR2-mCherry 选择性标记 D1 或 D2 神经元。我们发现在 D1 和 D2 中型多棘神经元 (MSN) 中药物寻找过程中 p-FAK 增加，但仅在 D1-MSN 中观察到 p-cofilin 增加。 这些数据表明，β3-整合素、FAK 和 cofilin 构成 MMP 激活下游的信号传导途径，参与促进药物配对线索恢复可卡因期间诱导的 D1-MSN 中短暂的突触增大。

意义声明药物相关线索会加速复发，这与伏隔核的短暂突触增大相关。我们发现可卡因诱导的突触增大依赖于细胞外基质（ECM）中的基质金属蛋白酶信号通过β3-整合素激活粘着斑激酶（FAK）并磷酸化肌动蛋白结合蛋白丝切蛋白。伏隔核核心 (NAcore) 包含两种主要的神经元亚型，选择性表达 D1-多巴胺或 D2-多巴胺受体。我们使用转基因大鼠研究每种细胞类型，发现通过丝动蛋白磷酸化诱导的信号传导仅发生在表达 D1 的神经元中。因此，可卡因配对信号通过 D1 表达神经元中选择性的信号级联启动可卡因恢复和突触扩大，需要 ECM 刺激 β3-整合素介导的 FAK (p-FAK) 和丝切蛋白磷酸化。