Closed-Loop Neurostimulation for Biomarker-Driven, Personalized Treatment of Major Depressive Disorder

Deep brain stimulation involves the administration of electrical stimulation to targeted brain regions for therapeutic benefit. In the context of major depressive disorder (MDD), most studies to date have administered continuous or open-loop stimulation with promising but mixed results. One factor contributing to these mixed results may stem from when the stimulation is applied. Stimulation administration specific to high-symptom states in a personalized and responsive manner may be more effective at reducing symptoms compared to continuous stimulation and may avoid diminished therapeutic effects related to habituation. Additionally, a lower total duration of stimulation per day is advantageous for reducing device energy consumption. This protocol describes an experimental workflow using a chronically implanted neurostimulation device to achieve closed-loop stimulation for individuals with treatment-refractory MDD. This paradigm hinges on determining a patient-specific neural biomarker that is related to states of high symptoms and programming the device detectors, such that stimulation is triggered by this read-out of symptom state. The described procedures include how to obtain neural recordings concurrent with patient symptom reports, how to use these data in a state-space model approach to differentiate low- and high-symptom states and corresponding neural features, and how to subsequently program and tune the device to deliver closed-loop stimulation therapy.

Induction of DNA double-strand breaks by ionizing radiation at the c-myc locus compared with the whole genome: a study using pulsed-field gel electrophoresis and gene probing

Ionizing radiation-induced double-strand breaks (dsb) in a human colon carcinoma-derived cell line COLO320HSR were determined from the fragment size distribution of non-specifically labelled DNA and Sfi I restriction enzyme-digested DNA uniformly labelled with a c-myc probe. The dose-effect relation for the induction of DNA dsb was linear with no significant difference between slopes for the curves in the whole genome (7.2 +/- 0.3 x 10(-9) dsb/bp/Gy) and in the 130 kbp restriction fragments containing c-myc (6.5 +/- 0.5 x 10(-9) dsb/bp/Gy). The size distribution of the c-myc fragments showed deviations from the random-breakage model, indicating heterogeneity of dsb induction at this locus.

A time-saving system for irradiations of experimental tumors

PURPOSE

Experimental in vivo radiotherapy frequently aims at the imitation of clinically applied fractionation schedules. However, the reliability of the anesthetic procedure and limited access to the treatment machines in clinical departments are major factors complicating the practical realisation of the experiment. Therefore, a reliable and time saving system for irradiations of xenografted tumors has been developed, which allows repeated irradiations, even in relatively short intervals available for experimental irradiations.

MATERIAL AND METHODS

The system presented here consists of an acrylic distributor for an anesthetic gas mixture employing enflurane (Ethrane) in the center of the set-up. Ten mice are positioned radially around the midpoint of the set-up so that they can be irradiated simultaneously. The xenotransplanted tumors growing on the right hind leg of mice are placed in a predefined position, which was found to be of advantage in order to position the tumors for fractionated treatments in identical setting. Tumor-bearing mice are irradiated with 15 MeV photons generated by a linear accelerator at a dose rate of 2.5 Gy/min. One of the significant feature of the setup is the ability to irradiate in acute hypoxia which is obtained by use of an integrated tourniquet. The dose modifying effects of different gases can be investigated by simply using them as carrier for the enflurane.

RESULTS

With the use of the set-up several different experiments were performed so far. At most ten fractions were given, one fraction per day. Even after these repeated treatment the loss of animals due to narcosis was less than 2%. The dose variation within the treatment field was found to be less than 4% as measured with TLD dosimetry. The remaining body of the mice is shielded effectively from the direct beam as the whole body dose of mice is 8% of the total tumor absorbed dose. The efficacy of the tourniquet technique for acute hypoxic irradiations was illustrated with the use of 99mTc-labelled albumin showing a complete stop of blood flow in the clamped leg. The steep dose-response curve obtained for single dose irradiation of a neurogenic sarcoma is based on the physical and experimental precision which can be reached with the technique suggested here.

CONCLUSION

Due to the high dose rate and the possibility to irradiate ten animals simultaneously the set-up introduced here is greatly time saving. The versatile applicability makes the new set-up a valuable tool for tumor radiobiology.