We have investigated the effects of high frequency (HF) signal on firing activity in a biologically realistic system--the noisy Hodgkin-Huxley (HH) neuron model via numerical simulations. The results show that when the HF amplitude to frequency ratio (AFR) increases, the firing rate is diminished and stochastic resonance disappears, even the HH neuron model is processing a stimulus of its most sensitive frequency. When the noise intensity is strong, the vibration resonance can be observed. Moreover, the fluctuation around the resting potential will be replaced by an oscillation of the same high frequency with the increasing AFR. The inhibition of the firing activity is consistent with the results of experiment in vivo that HF current can stop the transmission of action potential in peripheral nerve. This study is of functional significance to the biomedical research on the damages caused by electro-pollution in vivo and signal processing.
Action Potentials ; Artifacts ; Computer Simulation ; Humans ; Models, Neurological ; Neurons ; physiology ; Stochastic Processes

In nonlinear systems, noise can improve the responses of the systems with appropriate noise intensity. This phenomenon is called stochastic resonance. Biological neural systems are noisy and stochastic resonance has been found in them experimentally and theoretically. Now many researches focus on the signal transmission and processing in neural models. So this paper introduces the researches of stochastic resonance in noisy neural models. Then the recent research achievement and progress are reviewed in the following three aspects: noise; the development of stochastic resonance; and neural network. At last, the foreground of the study is discussed.
Humans ; Models, Neurological ; Neurons ; physiology ; Nonlinear Dynamics ; Signal Transduction ; Stochastic Processes

Up to 70% of patients with late-stage breast cancer have bone metastasis. Current treatment regimens for breast cancer bone metastasis are palliative with no therapeutic cure. Disseminated tumor cells (DTCs) colonize inside the osteogenic niches in the early stage of bone metastasis. Drug delivery into osteogenic niches to inhibit DTC colonization can prevent bone metastasis from entering its late stage and therefore cure bone metastasis. Here, we constructed a 50% DSS6 peptide conjugated nanoparticle to target the osteogenic niche. The osteogenic niche was always located at the endosteum with immature hydroxyapatite. Arsenic-manganese nanocrystals (around 14 nm) were loaded in osteogenic niche-targeted PEG-PLGA nanoparticles with an acidic environment-triggered arsenic release. Arsenic formulations greatly reduced 4T1 cell adhesion to mesenchymal stem cells (MSCs)/preosteoblasts (pre-OBs) and osteogenic differentiation of osteoblastic cells. Arsenic formulations also prevented tumor cell colonization and dormancy via altering the direct interaction between 4T1 cells and MSCs/pre-OBs. The chemotactic migration of 4T1 cells toward osteogenic cells was blocked by arsenic in mimic 3D osteogenic niche. Systemic administration of osteogenic niche-targeted arsenic nanoparticles significantly extended the survival of mice with 4T1 syngeneic bone metastasis. Our findings provide an effective approach for osteogenic niche-specific drug delivery and suggest that bone metastasis can be effectively inhibited by blockage of tumor cell colonization in the bone microenvironment.