作为岛叶的主要输出亚区，非颗粒皮层岛叶（Agranular insular cortex,AI）与已知的介导负性戒断状态的中央杏仁核（Central Amygdala, CeA）和伏隔核（Nucleus Accumbens, NAc）之间存在神经投射。 且AI分布有大量的阿片受体，其中约 80%分布在 AI 的 γ-氨基丁酸（GABA）能神经元上。另外已有的研究发现，阿片类药物的戒断反应与多个脑区的 GABA 能神经元的适应性改变有关。这些证据提示岛叶 AI的GABA能神经元可能是介导吗啡戒断的关键靶神经元。
本研究首先通过c-fos与GABA能神经元共染的方法，探索岛叶AI的GABA能神经元是否存在纳洛酮诱导的吗啡戒断相关的神经元活性的改变。 结果发现在纳洛酮诱导的吗啡戒断过程中，岛叶AI的GABA能神经元激活的数量显著增加，提示纳洛酮诱导的吗啡戒断与 AI的GABA 能神经元的激活有关。之后，我们通过实时位置偏爱/厌恶模型探索激活 AI 的 GABA 能神经元是否能够诱导出类似吗啡戒断的回避反应。结果发现，激活岛叶 AI的 GABA能神经元能够诱导出实时位置厌恶，提示AI的GABA能神经元的激活诱发了厌恶状态进而导致回避反应。最后，我们通过调控 AI的GABA能神经元的活性，检测其对纳洛酮诱导的吗啡戒断的影响，并从对负性戒断状态的回避动机和躯体戒断症状两个方面来考察AI的GABA能神经元的作用。结果发现，抑制 AI的GABA能神经元的活性影响了纳洛酮诱导的条件性厌恶模型（Conditioned Place Aversion, CPA）的建立。而通过对 CPA 训练过程中的躯体戒断症状的分析发现，抑制 AI 的 GABA 能神经元对纳洛酮诱导的躯体戒断症状没有影响。本研究证明了岛叶 AI的GABA能神经元的激活介导了吗啡戒断的负性回避动机。
Opiate withdrawal is known to be accompanied with severe withdrawal symptoms, including somatic withdrawal symptoms and the motivation of avoidance to the negative withdrawal state. Avoidance to the negative withdrawal state is a powerful strength that motivates continued drug use and may account for the high rate of relapse during abstinence. The insular cortex has proven to be a critical area that regulates drug craving. Besides, there’s evidence that the insular cortex mediates drug withdrawal, suggesting that the insular cortex might be a key region that mediates the effects of withdrawal on drug craving. However, the underlying mechanism of how the insular cortex mediate the opiate withdrawal remains to be clarified.
As the main output sub-region of insular cortex, agranular insular cortex (AI) has abundant connections with areas such as the central amygdala（CeA）and the nucleusaccumbens (NAc), which are known to be involved in opiate withdrawal. Besides, AI was found to be distributed with a lot of -opioid receptors, and about 80% of which were expressed on GABAergic neurons. Further, opiate withdrawal has been reported to be related with adaptive changes of GABAergic neurons in several brain areas. Therefore, we hypnotize that GABAergic neurons in AI might play a crucial role in mediating opiate withdrawal.
To address this hypothesis, firstly we explored whether there were opiate withdrawal related neuronal activity changes in GABAergic neurons in AI, which were done by co-labeling the GABAergic neuron with c-fos after naloxone induced morphine withdrawal. An increased number of neurons co-labeled with c-fos and GAD67 (marker of GABAergic neurons) in AI was found in animals experienced morphine withdrawal, suggesting that naloxone induced morphine withdrawal is related with the activation of GABAergic neurons in AI. And then, a real-time place preference/avoidance model was used to characterize the effects of activating GABAergic neurons in AI. It was found that activation of GABAergic neurons in AI lead to a real-time place avoidance, suggesting that activation of GABAergic neurons in AI might mediate the avoidance to morphine withdrawal. In order to verify the deduction, we regulated the neuronal activities of GABAergic neurons in AI by optogenetics and then examined their effects on naloxone induced morphine withdrawal, including both the motivational and the physical aspects. It was found that, inhibition of GABAergic neurons in AI prevented the establishment of naloxone induced conditioned place aversion (CPA) in mice. Furthermore, analysis of somatic withdrawal symptoms during CPA training revealed that inhibition of GABAergic neurons in AI has no effect on the somatic opioid withdrawal symptoms. The present findings indicate that hyperactivity of GABAergic neurons in AI might play a causal role in mediating the avoidance to the negative withdrawal state, which may maintain the opiate use in human addicts.