positron-emission-tomography-based-dose-painting-radiation-therapy

Positron Emission Tomography-based Dose Painting Radiation Therapy in a Glioblastoma Rat Model using the Small Animal Radiation Research Platform

A rat glioblastoma model to mimic chemo-radiation treatment of human glioblastoma in the clinic was previously established. Similar to the clinical ...

Ghent University

It has been shown that vagus nerve stimulation (VNS) has an antidepressant-like effect in the forced swim test. The mechanism of action underlying this effect is incompletely understood, but there is evidence suggesting that the locus coeruleus (LC) may play an important role. In this study, noradrenergic LC neurons were selectively lesioned to test their involvement in the antidepressant-like effect of VNS in the forced swim test. Forced swim test behavior was assessed in rats that were subjected to VNS or sham treatment. In half of the VNS-treated animals, the noradrenergic neurons from the LC were lesioned using the selective neurotoxin DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride], yielding three experimental arms: sham, VNS and DSP-4-VNS (n = 8 per group). Furthermore, the open field test was performed to evaluate locomotor activity. A dopamine-β-hydroxylase immunostaining was performed to confirm lesioning of noradrenergic LC neurons. VNS significantly reduced the percentage of immobility time in the forced swim test compared to sham treatment (median: 56%, interquartile range: 41% vs. median: 75%, interquartile range: 12%). This antidepressant-like effect of VNS could not be demonstrated in the DSP-4-VNS group (median: 79%, interquartile range: 33%). Locomotor activity in the open field test was not different between the three treatment arms. The absence of hippocampal dopamine-β-hydroxylase immunostaining in the DSP-4-treated rats confirmed the lesioning of noradrenergic neurons originating from the brainstem LC. The results of this study demonstrate that the noradrenergic neurons from the LC play an important role in the antidepressant-like effect of VNS.

The antidepressant-like effect of vagus nerve stimulation is mediated through the locus coeruleus.

 Vagus nerve stimulation (VNS) modulates hippocampal dentate gyrus (DG) electrophysiology and induces hypothermia in freely moving rats. This study evaluated whether hippocampal (CA1) electrophysiology is similarly modulated and to what extent this is associated with VNS-induced hypothermia.  Six freely moving rats received a first 4h session of rapid cycling VNS (7s on/18s off), while CA1 evoked potentials, EEG and core temperature were recorded. In a second 4h session, external heating was applied during the 3rd and 4thh of VNS counteracting VNS-induced hypothermia.  VNS decreased the slope of the field excitatory postsynaptic potential (fEPSP), increased the population spike (PS) amplitude and latency, decreased theta (4-12Hz) and gamma (30-100Hz) band power and theta peak frequency. Normalizing body temperature during VNS through external heating abolished the effects completely for fEPSP slope, PS latency and gamma band power, partially for theta band power and theta peak frequency and inverted the effect on PS amplitude. . Rapid cycle VNS modulates CA1 electrophysiology similarly to DG, suggesting a wide-spread VNS-induced effect on hippocampal electrophysiology. Normalizing core temperature elucidated that VNS-induced hypothermia directly influences several electrophysiological parameters but also masks a VNS-induced reduction in neuronal excitability.

Hypothermia Masks Most of the Effects of Rapid Cycling VNS on Rat Hippocampal Electrophysiology.

Vagus nerve stimulation (VNS) therapy is associated with laryngeal muscle activation and induces voice modifications, well-known side effects of the therapy resulting from co-activation of the recurrent laryngeal nerve. In this study, we describe the non-invasive transcutaneous recording of laryngeal motor evoked potentials (LMEPs), which could serve as a biomarker of effective nerve activation and individual titration in patients with drug-resistant epilepsy. We recruited drug-resistant epileptic patients treated for at least 6 months with a VNS. Trains of 600-1200 VNS pulses were delivered with increasing current outputs. We placed six skin electrodes on the ventral surface of the neck, in order to record LMEPs whenever the laryngeal muscular threshold was reached. We studied the internal consistency and the variability of LMEP recordings, and compared different methods for amplitude calculation. Recruitment curves were built based on the stimulus-response relationship. We also determined the electrical axis of the LMEPs dipole in order to define the optimal electrode placement for LMEPs recording in a clinical setting. LMEPs were successfully recorded in 11/11 patients. The LMEPs threshold ranged from 0.25 to 1 mA (median 0.50 mA), and onset latency was between 5.37 and 8.77 ms. The signal-to-noise ratio was outstanding in 10/11 patients. In these cases, excellent reliability (Intraclass correlation coefficient, ICC > 0.90 across three different amplitude measurements) was achieved with 10 sample averages. Moreover, our recordings showed very good internal consistency (Cronbach's alpha > 0.95 for 10 epochs). Area-under-the-curve and peak-to-peak measurement proved to be complementary methods for amplitude calculation. Finally, we determined that an optimal derivation requires only two recording electrodes, aligned on a horizontal axis around the laryngeal prominence. In conclusion, we describe here an optimal methodology for the recording of VNS-induced motor evoked responses from the larynx. Although further clinical validation is still necessary, LMEPs might be useful as a non-invasive marker of effective nerve activation, and as an aid for the clinician to perform a more rational titration of VNS parameters.

Vagus Nerve Stimulation-Induced Laryngeal Motor Evoked Potentials: A Possible Biomarker of Effective Nerve Activation.

Considering the need for rapid change of treatment in recurrent glioblastoma (GB), it is of utmost importance to characterize PET radiopharmaceuticals that allow early discrimination of tumor from therapy-related effects. In this study, we examined the value of 2-[F]FELP as a LAT1 tumor-specific PET tracer in comparison with [F]FDG and [F]FET in a combined orthotopic rat radiation necrosis and glioblastoma model. A second experiment compared 2-[F]FELP to [F]FDG in a mouse glioblastoma - inflammation model.

2-[F]FELP, a novel LAT1-specific PET tracer, for the discrimination between glioblastoma, radiation necrosis and inflammation.

Recent experiments in rats have demonstrated significant effects of VNS on hippocampal excitability but were partially attributed to hypothermia, induced by the applied VNS parameters.

Identification of vagus nerve stimulation parameters affecting rat hippocampal electrophysiology without temperature effects.

Intracerebral hemorrhage (ICH) is a known risk factor for the development of seizures, but little is known about the pathophysiology of seizures in the acute phase post-ICH and their influence on functional outcome. With the use of an animal model, the underlying pathophysiology could be further unraveled. The aim of our study was to optimize the rat collagenase stroke model for the detection of acute symptomatic seizures using video-EEG monitoring.

Acute symptomatic seizures following intracerebral hemorrhage in the rat collagenase model.

Seizures are common in patients with high-grade gliomas (30-60%) and approximately 15-30% of glioblastoma (GB) patients develop drug-resistant epilepsy. Reliable animal models are needed to develop adequate treatments for glioma-related epilepsy. Therefore, fifteen rats were inoculated with F98 GB cells (GB group) and four rats with vehicle only (control group) in the right entorhinal cortex. MRI was performed to visualize tumor presence. A subset of seven GB and two control rats were implanted with recording electrodes to determine the occurrence of epileptic seizures with video-EEG recording over multiple days. In a subset of rats, tumor size and expression of tumor markers were investigated with histology or mRNA in situ hybridization. Tumors were visible on MRI six days post-inoculation. Time-dependent changes in tumor morphology and size were visible on MRI. Epileptic seizures were detected in all GB rats monitored with video-EEG. Twenty-one days after inoculation, rats were euthanized based on signs of discomfort and pain. This study describes, for the first time, reproducible tumor growth and spontaneous seizures upon inoculation of F98 cells in the rat entorhinal cortex. The development of this new model of GB-related epilepsy may be valuable to design new therapies against tumor growth and associated epileptic seizures.

Development of a Rat Model for Glioma-Related Epilepsy.

Intracerebral hemorrhage (ICH) is a known risk factor for the development of acute symptomatic as well as late unprovoked seizures. The underlying pathophysiology of post-ICH seizures is incompletely understood and there are no reliable predictive biomarkers. An animal model to study post-ICH seizures is currently lacking. The aim of this study was to investigate (1) the occurrence of seizures and interictal epileptiform activity in the ICH rat collagenase model using long-term video-EEG monitoring (VEM) and (2) whether seizure occurrence was associated with interictal epileptiform activity and histological features.

Seizures and Interictal Epileptiform Activity in the Rat Collagenase Model for Intracerebral Hemorrhage.

Magnetic resonance imaging (MRI) is frequently used for preclinical treatment monitoring in glioblastoma (GB). Discriminating between tumors and tumor-associated changes is challenging on in vivo MRI. In this study, we compared in vivo MRI scans with ex vivo MRI and histology to estimate more precisely the abnormal mass on in vivo MRI. Epileptic seizures are a common symptom in GB. Therefore, we used a recently developed GB-associated epilepsy model from our group with the aim of further characterizing the model and making it useful for dedicated epilepsy research. Ten days after GB inoculation in rat entorhinal cortices, in vivo MRI (T2w and mean diffusivity (MD)), ex vivo MRI (T2w) and histology were performed, and tumor volumes were determined on the different modalities. The estimated abnormal mass on ex vivo T2w images was significantly smaller compared to in vivo T2w images, but was more comparable to histological tumor volumes, and might be used to estimate end-stage tumor volumes. In vivo MD images displayed tumors as an outer rim of hyperintense signal with a core of hypointense signal, probably reflecting peritumoral edema and tumor mass, respectively, and might be used in the future to distinguish the tumor mass from peritumoral edema-associated with reactive astrocytes and activated microglia, as indicated by an increased expression of immunohistochemical markers-in preclinical models. In conclusion, this study shows that combining imaging techniques using different structural scales can improve our understanding of the pathophysiology in GB.

Comparison of In Vivo and Ex Vivo Magnetic Resonance Imaging in a Rat Model for Glioblastoma-Associated Epilepsy.

Vagus nerve stimulation (VNS) is an adjunctive therapy for drug-resistant epilepsy. Noninvasive evoked potential recordings in laryngeal muscles (LMEPs) innervated by vagal branches may provide a marker to assess effective vagal nerve fiber activation. We investigated VNS-induced LMEPs in patients with epilepsy in acute and chronic settings.

Charlotte Bouckaert

Department of Head and Skin

Ghent University

Positron Emission Tomography-based Dose Painting Radiation Therapy in a Glioblastoma Rat Model using the Small Animal Radiation Research Platform