Environmental cues associated with morphine modulate release of glutamate and γ-aminobutyric acid in ventral subiculum

Objective To investigate whether environmental cues associated with different properties of morphine could regulate the extracellular levels of glutamate and y-aminobutyric acid （GABA） in the hippocampal ventral subiculum, which play a critical role in the reinstatement of drug-seeking behavior induced by environmental cues. Methods Conditioning place preference （CPP） and conditioning place aversion （CPA） models were used to establish environment associated with rewarding and aversive properties of morphine respectively. Microdialysis and high performance liquid chromatography were used to measure the extracelluar level of glutamate and GABA in the ventral subiculum under these environmental cues. Results Exposure to the environmental cues associated with rewarding properties of morphine resulted in a decrease （approximately 11%） of extracellular level of GABA in ventral subiculum, and exposure to the environmental cues associated with aversive properties of morphine resulted in an increase （approximately 230%） of extracellular level of glutamate in ventral subiculum. Conclusion Environmental cues associated with different properties of morphine modulate the release of distinct neurotransmitters in the hippocampal ventral subiculum possibly through different neural circuit.

The Anterior Insula and its Projection to the Prelimbic Cortex are Involved in the Regulation of 5-HT-Induced Itch

Itch is an unpleasant sensation that urges people and animals to scratch.Neuroimaging studies on itch have yielded extensive correlations with diverse cortical and subcortical regions,including the insular lobe.However,the role and functional specificity of the insular cortex(IC)and its subdivisions in itch mediation remains unclear.Here,we demonstrated by immunohistochemistry and fiber photometry tests,that neurons in both the anterior insular cortex(AIC)and the posterior insular cortex(PIC)are activated during acute itch processes.Pharmacogenetic experiments revealed that nonselective inhibition of global AIC neurons,or selective inhibition of the activity of glutaminergic neurons in the AIC,reduced the scratching behaviors induced by intradermal injection of 5-hydroxytryptamine(5-HT),but not those induced by compound 48/80.However,both nonselective inhibition of global PIC neurons and selective inhibition of glutaminergic neurons in the PIC failed to affect the itching-scratching behaviors induced by either 5-HT or compound 48/80.In addition,pharmacogenetic inhibition of AIC glutaminergic neurons effectively blocked itch-associated conditioned place aversion behavior,and inhibition of AIC glutaminergic neurons projecting to the prelimbic cortex significantly suppressed 5-HT-evoked scratching.These findings provide preliminary evidence that the AIC is involved,at least partially via aversive emotion mediation,in the regulation of 5-HT-,but not compound 48/80-induced itch.