Nonlinear effects at the electrode-tissue interface of deep brain stimulation electrodes

Objective.The electrode-tissue interface provides the critical path for charge transfer in neurostimulation therapies and exhibits well-established nonlinear properties at high applied currents or voltages. These nonlinear properties may influence the efficacy and safety of applied stimulation but are typically neglected in computational models. In this study, nonlinear behavior of the electrode-tissue interface impedance was incorporated in a computational model of deep brain stimulation (DBS) to simulate the impact on neural activation and safety considerations.Approach.Nonlinear electrode-tissue interface properties were incorporated in a finite element model of DBS electrodesin vitroandin vivo,in the rat subthalamic nucleus, using an iterative approach. The transition point from linear to nonlinear behavior was determined for voltage and current-controlled stimulation. Predicted levels of neural activation during DBS were examined and the region of linear operation of the electrode was compared with the Shannon safety limit.Main results.A clear transition of the electrode-tissue interface impedance to nonlinear behavior was observed for both current and voltage-controlled stimulation. The transition occurred at lower values of activation overpotential for simulatedin vivothanin vitroconditions (91 mV and 165 mV respectively for current-controlled stimulation; 110 mV and 275 mV for voltage-controlled stimulation), corresponding to an applied current of 30μA and 45μA, or voltage of 330 mV at 1 kHz. The onset of nonlinearity occurred at lower values of the overpotential as frequency was increased. Incorporation of nonlinear properties resulted in activation of a higher proportion of neurons under voltage-controlled stimulation. Under current-controlled stimulation, the predicted transition to nonlinear behavior and Faradaic charge transfer at stimulation amplitudes of 30μA, corresponds to a charge density of 2.29μC cm-2and charge of 1.8 nC, well-below the Shannon safety limit.Significance.The results indicate that DBS electrodes may operate within the nonlinear region at clinically relevant stimulation amplitudes. This affects the extent of neural activation under voltage-controlled stimulation and the transition to Faradaic charge transfer for both voltage- and current-controlled stimulation with important implications for targeting of neural populations and the design of safe stimulation protocols.

Stimulation-induced changes at the electrode-tissue interface and their influence on deep brain stimulation

OBJECTIVE

During deep brain stimulation (DBS) the electrode-tissue interface forms a critical path between device and brain tissue. Although changes in the electrical double layer and glial scar can impact stimulation efficacy, the effects of chronic DBS on the electrode-tissue interface have not yet been established.

APPROACH

In this study, we characterised the electrode-tissue interface surrounding chronically implanted DBS electrodes in rats and compared the impedance and histological properties at the electrode interface in animals that received daily stimulation and in those where no stimulation was applied, up to eight weeks post-surgery. A computational model was developed based on the experimental data, which allowed the dispersive electrical properties of the surrounding encapsulation tissue to be estimated. The model was then used to study the effect of stimulation-induced changes in the electrode-tissue interface on the electric field and neural activation during voltage- and current-controlled stimulation.

MAIN RESULTS

Incorporating the observed changes in simulations in silico, we estimated the frequency-dependent dielectric properties of the electrical double layer and surrounding encapsulation tissue. Through simulations we show how stimulation-induced changes in the properties of the electrode-tissue interface influence the electric field and alter neural activation during voltage-controlled stimulation. A substantial increase in the number of stimulated collaterals, and their distance from the electrode, was observed during voltage-controlled stimulation with stimulated ETI properties. In vitro examination of stimulated electrodes confirmed that high frequency stimulation leads to desorption of proteins at the electrode interface, with a concomitant reduction in impedance.

SIGNIFICANCE

The demonstration of stimulation-induced changes in the electrode-tissue interface has important implications for future DBS systems including closed-loop systems where the applied stimulation may change over time. Understanding these changes is particularly important for systems incorporating simultaneous stimulation and sensing, which interact dynamically with brain networks.

Prof. B. Ramamurthi - A Glimpse into his Contributions to Neuroscience

Prof B Ramamurthi was a pioneer of Indian neurosurgery and a major force in the development of Indian neuroscience. Founding the Madras Institute of Neurology and later the A Lakshmipathi Neurosurgical Centre (ALNC), both at Madras (or Chennai as it is now called), he developed centres of excellence in his career that spanned over five decades. During this period of time he made Madras, a destination for neurosurgery and neuroscience. Along with his colleagues a large number of publications were produced which influenced the world. Notable among his contributions were those in Stereotaxy for movement disorders, epilepsy, pain and psychiatric illness. He also had notable contributions in brain tumours especially acoustic neurinomas and pituitary tumours. His papers on the low incidence of aneurysms is still quoted widely. Head injuries formed a major part of the neurosurgical work and major contributions were made in that field too. As a developing country with socio-economic issues, infections of the nervous system were seen commonly. His publications on tuberculomas of the brain are noteworthy. He was intrigued by the neurophysiological basis of consciousness. He writings on the subject reflect his attempt to bring together ancient eastern thoughts and concepts of consciousness and life and western science. In the later part of his career he spoke on ethics in and the changing milieu of neurosurgery. While contributions to spinal surgery were not seen in the first half of his career, he along with his colleagues from ALNC published original articles on spinal surgery especially tumours and OPLL. Prof B Ramamurthi, has not only influenced, taught and mentored, during his lifetime, a great many neuroscientists, but he also continues to do so through his publications which continue to be relevant in todays world. A glimpse into his contributions show us how without the technology of today a lot was achieved - and we need to see that, to inspire us to achieve more and to strive for greater heights.

Cerebello-pontine and Cerebello-medullary Fissure Choroid Plexus Papilloma in a Child - Case Report and Review of Literature

Choroid plexus papillomas (CPP) are commonly seen in the supratentorial compartment in children and only very rarely in the posterior fossa. CPP in the cerebello-pontine angle and cerebello-medullary fissure (CPA) in the pediatric age group are extremely rare with only seven previous cases reported in literature. The authors present the case of a 7-year-old girl who presented with neck tilt, imbalance, and headache. The MRI showed a lesion with a frond-like appearance in the CPA with heterogeneous enhancement. The tumor was excised radically using a cerebello-medullary fissure approach. The authors review and analyze the literature on this rare pediatric tumor, with specific attention to radiology and the surgical aspects.

Mandible reconstruction using a vascularized fibula flap from a post-polio paralytic limb

The case of 69-year-old man with a post-polio paralytic limb who was diagnosed with carcinoma of the lower alveolus is presented. A successful mandible reconstruction was performed using a vascularized fibula osteocutaneous flap harvested from the polio-affected limb. The skin perfusion and quality of the bone were good. The donor defect healed uneventfully. Harvesting the flap from the polio-affected limb also significantly reduced the donor site morbidity. This case is novel in presenting the successful use of a free fibula flap harvested from a leg affected by paralytic poliomyelitis.

Fabrication of tri-layered electrospun polycaprolactone mats with improved sustained drug release profile

Modulation of initial burst and long term release from electrospun fibrous mats can be achieved by sandwiching the drug loaded mats between hydrophobic layers of fibrous polycaprolactone (PCL). Ibuprofen (IBU) loaded PCL fibrous mats (12% PCL-IBU) were sandwiched between fibrous polycaprolactone layers during the process of electrospinning, by varying the polymer concentrations (10% (w/v), 12% (w/v)) and volume of coat (1 ml, 2 ml) in flanking layers. Consequently, 12% PCL-IBU (without sandwich layer) showed burst release of 66.43% on day 1 and cumulative release (%) of 86.08% at the end of 62 days. Whereas, sandwich groups, especially 12% PCLSW-1 & 2 (sandwich layers-1 ml and 2 ml of 12% PCL) showed controlled initial burst and cumulative (%) release compared to 12% PCL-IBU. Moreover, crystallinity (%) and hydrophobicity of the sandwich models imparted control on ibuprofen release from fibrous mats. Further, assay for cytotoxicity and scanning electron microscopic images of cell seeded mats after 5 days showed the mats were not cytotoxic. Nuclear Magnetic Resonance spectroscopic analysis revealed weak interaction between ibuprofen and PCL in nanofibers which favors the release of ibuprofen. These data imply that concentration and volume of coat in flanking layer imparts tighter control on initial burst and long term release of ibuprofen.

Forty years of clinical excellence at the Dr A Lakshmipathi Neurosurgical Centre and Post-Graduate Institute of Neurological Surgery, Voluntary Health Services (VHS) Hospital

The Achanta Lakshmipathi Neurosurgical Center (ALNC) and Post Graduate Institute of Neurological Surgery is a private teaching neurosurgical institution located in the VHS (Voluntary Health Services) Hospital Chennai. It has been a leader and trendsetter among the private academic neurosurgical training institutions, and because of its unique legacy, has influenced the progress of Neurosurgery in India. The center was the second neurosurgical Institute to be created by Prof. B Ramamurthi and has trained neurosurgeons in the unique ALNC school of Neurosurgery. The Institute has grown to become a centre of excellence in microsurgery, and spinal surgery and has become a training centre for neurosurgery since 1985. The unique humanitarian aspects of the Voluntary Health Services Hospital helped in bringing the best of Neurosurgery to all strata of society. Forty years after its inception, the ALNC continues its delivery of excellence in clinical neurosurgery and academics.

Correlation between EGFR Gene Mutations and Lung Cancer: a Hospital-Based Study

Epidermal growth factor receptor (EGFR) is one of the targeted molecular markers in many cancers including lung malignancies. Gefitinib and erlotinib are two available therapeutics that act as specific inhibitors of tyrosine kinase (TK) domains. We performed a case-control study with formalin-fixed paraffin-embedded tissue blocks (FFPE) from tissue biopsies of 167 non-small cell lung carcinoma (NSCLC) patients and 167 healthy controls. The tissue biopsies were studied for mutations in exons 18-21 of the EGFR gene. This study was performed using PCR followed by DNA sequencing. We identified 63 mutations in 33 men and 30 women. Mutations were detected in exon 19 (delE746-A750, delE746-T751, delL747-E749, delL747-P753, delL747-T751) in 32 patients, exon 20 (S786I, T790M) in 16, and exon 21 (L858R) in 15. No mutations were observed in exon 18. The 63 patients with EFGR mutations were considered for upfront therapy with oral tyrosine kinase inhibitor (TKI) drugs and have responded well to therapy over the last 15 months. The control patients had no mutations in any of the exons studied. The advent of EGFR TKI therapy has provided a powerful new treatment modality for patients diagnosed with NSCLC. The study emphasizes the frequency of EGFR mutations in NSCLC patients and its role as an important predictive marker for response to oral TKI in the south Indian population.

Evaluation of optimum roughage to concentrate ratio in maize stover based complete rations for efficient microbial biomass production using in vitro gas production technique

AIM

A study was undertaken to evaluate the optimum roughage to concentrate ratio in maize stover (MS) based complete diets for efficient microbial biomass production (EMBP) using in vitro gas production technique.

MATERIALS AND METHODS

MS based complete diets with roughage to concentrate ratio of 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, and 30:70 were formulated, and 200 mg of oven-dried sample was incubated in water bath at 39°C along with media (rumen liquor [RL] - buffer) in in vitro gas syringes to evaluate the gas production. The gas produced was recorded at 8 and 24 h of incubation. In vitro organic matter digestibility (IVOMD), metabolizable energy (ME), truly digestible organic matter (TDOM), partitioning factor (PF), and EMBP were calculated using appropriate formulae. Ammonia nitrogen and total volatile fatty acids (TVFAs) production were analyzed in RL fluid-media mixture after 24 h of incubation.

RESULTS

In vitro gas production (ml) at 24 h incubation, IVOMD, ME, TDOM, TVFA concentration, and ammonia nitrogen production were increased (p<0.01) in proportion to the increase in the level of concentrate in the diet. Significantly (p<0.01) higher PF and EMBP was noticed in total mixed ration with roughage to concentrate ratio of 60:40 and 50:50 followed by 70:30 and 40:60.

CONCLUSION

Based on the results, it was concluded that the MS can be included in complete rations for ruminants at the level of 50-60% for better microbial biomass synthesis which in turn influences the performance of growing sheep.

Effect of substituting increasing levels of organic Zn for inorganic Zn on performance, hematological and serum biochemical constituents, antioxidant status and immune response in rat

The effect of replacing dietary Zn supplemented from inorganic (ZnCO₃) source with organic Zn (Zn methionine; Zn-met) was investigated in 72 rats (98.42 ± 1.483 g) by randomly allotting to 4 diets (6 replicates/diet, 3 rats/replicate). Basal diet was prepared with purified ingredients without Zn. The control diet (AIN-76A) contained 12 ppm of Zn from ZnCO₃ (100-I). In the other diets ZnCO₃ was replaced with Zn-met at the rates of 50 (50I:50O), 75 (25I:75O) or 100% (100-O). Weekly body weight and daily feed intake were recorded for 14 weeks. Blood was collected by retro-orbital puncture on the 70th and 80th day to determine haematological and various serum biochemical constituents, and antioxidant enzyme activities in haemolysate, respectively. Rats were antigenically challenged with sheep RBC on day 73 to assess humoral immune response (HIR), and on day 95 for cell mediated immune response (CMIR) and rats were sacrificed at the end of rearing period to collect liver, muscle, pancreas and kidneys for Zn estimation and oxidative stress markers in liver. The data were analysed using completely randomized design. Weight gain and feed intake, hematological and serum biochemical constituents, Zn content in organs (except liver) were not influenced by replacing ZnCO₃ with Zn-met. Zinc concentrations in the serum and liver were higher (P<0.05) with 50% replacement of ZnCO₃ with Zn-met compared to 0 or 100% replacement. Lower (P<0.05) lipid peroxidation and higher (P<0.05) glutathione peroxidase and glutathione reductase activities were observed with 50 and 75% replacement of ZnCO₃ with Zn-met compared to 0 or 100% replacement. Protein carbonyls and reduced glutathione in liver were not affected, while TBARS decreased (P<0.05) with substituting Zn-met (50-100%) for ZnCO₃. The HIR and CMIR increased with increasing Zn-met supplementation and the highest response was observed with 75-100% replacement of ZnCO₃ with Zn-met. It is concluded that replacement of 50 or 75% of ZnCO₃ with Zn-met increased antioxidant and immune response in rats with no effect on growth.

Replacement of inorganic zinc with lower levels of organic zinc (zinc nicotinate) on performance, hematological and serum biochemical constituents, antioxidants status, and immune responses in rats

Aim:

A study was undertaken to investigate the effect of organic zinc (zinc nicotinate, Zn-nic) supplementation (6, 9, and 12 ppm) compared to inorganic zinc (12 ppm) on growth performance, hematology, serum biochemical constituents oxidative stress, and immunity in weaned female Sprague–Dawley rats.

Material and Methods:

A 48 weaned rats (285.20±1.95 g) were randomly distributed to 4 dietary treatments with 6 replicates in each and reared in polypropylene cages for 10 weeks. Basal diet (BD) was formulated with purified ingredients without zinc (Zn). Four dietary treatments were prepared by adding 12 ppm Zn from ZnCO₃ (control) and 6, 9, and 12 ppm Zn from Zn-nic to the BD. On 42^nd day, blood was collected by retro-orbital puncture for analyzing hematological constituents, glucose, cholesterol, alkaline phosphatase, total protein, albumin, and globulin and antioxidant enzyme activities. At 43^rd day, rats were antigenically challenged with sheep red blood cell (RBC) to assess humoral immune response and on 70^th day cell-mediated immune response.

Results:

Weekly body weight gains, daily feed intake, blood hematological constituents (white blood cell, RBC, hemoglobin concentration, packed cell volume, mean corpuscular volume, lymphocyte, monocyte, and granulocyte concentration) and serum glucose, total protein levels were comparable among the rats feed Zn from ZnCO₃ and Zn-nic (6, 9, and 12 ppm). Serum cholesterol reduced with organic Zn supplementation at either concentration (6-12 ppm). Serum globulin concentration reduced (p<0.05) with 6 ppm Zn-nic supplementation compared to other dietary treatments. Lipid peroxidation lowered (p<0.05) reduced with 12 ppm organic Zn; thiobarbituric acid reacting substances and protein carbonyls concentrations in liver reduced (p<0.05) with 9 and 12 ppm levels of organic Zn supplementation compared to 12 ppm Zn supplementation from inorganic source. RBC catalase and glutathione peroxidase enzymes activities were highest (p<0.05) in rats supplemented with 12 ppm Zn-nic, followed by 9 ppm. Comparable immune response (humoral and cell-mediated) was observed between 12 ppm inorganic Zn and 9 ppm organic Zn and higher (p<0.05) immune response was noticed at 12 ppm Zn-nic supplementation.

Conclusion:

Based on the results, it is concluded that dietary Zn concentration can be reduced by 50% (6 ppm) as Zn nicotinate without affecting growth performance, hemato-biochemical constituents, antioxidant status, and immunity. In addition, replacement of 12 ppm inorganic Zn with 12 ppm organic Zn significantly improved antioxidant status and immune response.

Effect of selenium supplementation on performance, cost economics, and biochemical profile of Nellore ram lambs

AIM

Present experiment was conducted to investigate the effect of selenium (Se) supplementation on performance, carcass characteristics, meat composition, shelflife of meat and biochemical profile in Nellore ram lambs.

MATERIALS AND METHODS

24 male Nellore ram lambs (15.75±0.47 kg) were randomly divided into four dietary groups with six lambs in each and reared under uniform management conditions for 120 days. Basal diet was not supplemented with Se and consisted of green fodder (Se 0.09 mg/kg dry matter [DM]), dry roughage (Se 0.11 mg/kg DM) and concentrate mixture (Se 0.019 mg/kg DM) and fed individually. Dietary treatments were prepared by adding graded levels Se (0, 0.45, 0.9, and 1.8 ppm) to concentrate mixture (1% body weight [BW]) from sodium selenite. Feed offered and refusal measured daily; and BWs were measured at fortnight interval to find out average daily gain (g), feed conversion ratio (FCR), cost economics and plane of nutrition. Serum biochemical profile (concentration of glucose, total protein, albumin, globulin, cholesterol, and hemoglobin) was assessed on 0, 60(th), and 120(th) day. At the end of experiment, the carcass characteristics (dressing percentage, cut-up parts, meat to bone ratio) and meat chemical composition were evaluated. Meat keeping (thiobarbituric acid reactive substances) quality from different groups was evaluated on day 0, 3, and 6 post-slaughter.

RESULTS

Dietary Se supplementation did not show any effect on weight gain, FCR, cost economics, plane of nutrition, and serum biochemical profile in Nellore ram lambs. However, Se supplemented lambs had numerically higher weight gain than the unsupplemented lambs. Similarly, carcass characteristics and keeping quality were comparable among the four treatments. However, numerical increase in post-slaughter keeping quality with increasing Se supplementation was observed.

CONCLUSION

It can be concluded that supplementation of Se in the form of sodium selenite (inorganic source) at different levels did not influence animal performance in growing Nellore ram lambs had no effect on lamb performance, cost economics, carcass characteristics, and serum biochemical profile.

Safety and efficacy of hepatitis B vaccination in cirrhosis of liver

Introduction. Patients with chronic liver disease (CLD) are more likely to have severe morbidity and fatality rate due to superimposed acute or chronic hepatitis B (HBV) infection. The literature has shown that hepatitis B vaccines are safe and effective in patients with CLD, but the data in cirrhosis liver is lacking. We assessed the safety and immunogenicity of HBV vaccine in patients with cirrhosis liver. Methods. CTP classes A and B CLD patients negative for hepatitis B surface antigen and antibody to hepatitis B core antigen were included. All patients received three doses of hepatitis B vaccine 20 mcg intramuscularly at 0, 30, and 60 days. Anti-HBs antibody was measured after 120 days. Results. 52 patients with mean age 47.48 ± 9.37 years were studied. Response rates in CTP classes A and B were 88% and 33.3%. We observed that the alcoholic chronic liver disease had less antibody response (44%) than other causes of chronic liver disease such as cryptogenic 69% and HCV 75%. Conclusions. Patients with cirrhosis liver will have low antibody hepatitis B titers compared to general population. As the age and liver disease progress, the response rate for hepatitis B vaccination will still remain to be weaker.