PET imaging on neurofunctional changes after optogenetic stimulation in a rat model of panic disorder

Chronic fluoxetine enhances extinction therapy for PTSD by evaluating brain glucose metabolism in rats: an [18F]FDG PET study

BACKGROUND

Recent studies suggest that selective serotonin reuptake inhibitors (SSRIs) and exposure therapies have been used to reduced footshock-induced posttraumatic stress disorder (PTSD) symptoms. However, the therapeutic effect of the combination of SSRIs treatment with exposure therapy remains a matter of debate. This study aimed to evaluate these therapeutic effect through the behavioural and the neuroimaging changes by positron emission tomography (PET) in model rats.

METHODS

Pavlovian fear conditioning paradigm to establish model rats, and serial PET imaging with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) was performed during the control, fear-conditioning, and extinction-retrieval phases. The expression of c-Fos was used to identify neural activity.

RESULTS

We report that fear conditioning increased glucose metabolism in the right amygdala and left primary visual cortex but decreased glucose metabolism in the left primary somatosensory cortex. After extinction retrieval, there was increased [¹⁸F]FDG uptake in the left striatum, left cochlear nucleus and right primary visual cortex but decreased uptake in the anterior cingulate cortex in the extinction group. Fluoxetine increased [¹⁸F]FDG uptake in the left hippocampus and right primary visual cortex but decreased uptake in the bilateral primary somatosensory cortex, left primary/secondary motor cortex and cuneiform nucleus. The combined therapy increased [¹⁸F]FDG uptake in the left hippocampus, left striatum, right insular cortex, left posterior parietal cortex, and right secondary visual cortex but reduced uptake in the cerebellar lobule. c-Fos expression in the hippocampal dentate gyrus and anterior cingulate cortex in the fluoxetine and combined groups was significantly higher than that in the extinction group, with no significant difference between the two groups.

CONCLUSIONS

Chronic fluoxetine enhanced the effects of extinction training in a rat model of PTSD. In vivo PET imaging may provide a promising approach for evaluation chronic fluoxetine treatment of PTSD.

Spatiotemporal dynamics of brain function during the natural course in a dental pulp injury model

Purpose

Toothache, a common disorder afflicting most people, shows distinct features at different clinical stages. This study aimed to depict metabolic changes in brain and investigate the potential mechanism involved in the aberrant affective behaviors during the natural process of toothache.

Methods

We investigated the spatiotemporal patterns of brain function during the natural course of toothache in a rat model of dental pulp injury (DPI) by using positron emission tomography (PET).

Results

Glucose metabolism peaked on the 3rd day and gradually decreased in several brain regions after DPI, which was in line with the behavioral and histological results. PET imaging showed that visual pathway was involved in the regulation of toothache. Meanwhile, the process of emotional regulation underlying toothache was mediated by N-methyl-D-aspartic receptor subunit 2B (NR2B) in the caudal anterior cingulate cortex (cACC).

Conclusion

Our results revealed the spatiotemporal neurofunctional patterns during toothache process and preliminarily elucidated the role of NR2B in cACC in the regulation of toothache-related affective behaviors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05764-2.

Translational PET applications for brain circuit mapping with transgenic neuromodulation tools

Transgenic neuromodulation tools have transformed the field of neuroscience over the past two decades by enabling targeted manipulation of neuronal populations and circuits with unprecedented specificity. Chemogenetic and optogenetic neuromodulation systems are among the most widely used and allow targeted control of neuronal activity through the administration of a selective compound or light, respectively. Innovative genetic targeting strategies are utilized to transduce specific cells to express transgenic receptors and opsins capable of manipulating neuronal activity. These allow mapping of neuroanatomical projection sites and link cellular manipulations with brain circuit functions and behavior. As these tools continue to expand knowledge of the nervous system in preclinical models, developing translational applications for human therapies is becoming increasingly possible. However, new strategies for implementing and monitoring transgenic tools are needed for safe and effective use in translational research and potential clinical applications. A major challenge for such applications is the need to track the location and function of chemogenetic receptors and opsins in vivo, and new developments in positron emission tomography (PET) imaging techniques offer promising solutions. The goal of this review is to summarize current research combining transgenic tools with PET for in vivo mapping and manipulation of brain circuits and to propose future directions for translational applications.