Stimulus contrast modulates burst activity in the lateral geniculate nucleus.

Burst activity is a ubiquitous feature of thalamic neurons and is well documented for visual neurons in the lateral geniculate nucleus (LGN). Although bursts are often associated with states of drowsiness, they are also known to convey visual information to cortex and are particularly effective in evoking cortical responses. The occurrence of thalamic bursts depends on (1) the inactivation gate of T-type Ca2+ channels (T-channels), which become de-inactivated following periods of increased membrane hyperpolarization, and (2) the opening of the T-channel activation gate, which has voltage-threshold and rate-of-change (δv/δt) requirements. Given the time/voltage relationship for the generation of Ca2+ potentials that underlie burst events, it is reasonable to predict that geniculate bursts are influenced by the luminance contrast of drifting grating stimuli, with the null phase of higher contrast stimuli evoking greater hyperpolarization followed by a larger dv/dt than the null phase of lower contrast stimuli. To determine the relationship between stimulus contrast and burst activity, we recorded the spiking activity of cat LGN neurons while presenting drifting sine-wave gratings that varied in luminance contrast. Results show that burst rate, reliability, and timing precision are significantly greater with higher contrast stimuli compared with lower contrast stimuli. Additional analysis from simultaneous recordings of synaptically connected retinal ganglion cells and LGN neurons further reveals the time/voltage dynamics underlying burst activity. Together, these results support the hypothesis that stimulus contrast and the biophysical properties underlying the state of T-type Ca2+ channels interact to influence burst activity, presumably to facilitate thalamocortical communication and stimulus detection.

A study of the potential application of digital PCR in the detection of fecal contamination of strawberries using Bacteroides markers.

Food-borne illnesses can result from contamination of agricultural products. In this study, we examined nanoplate digital PCR (dPCR) to test for fecal contamination of agricultural products. In nanoplate technique, the PCR mastermix is divided into 8.526,000 partitions, providing direct detection of individual DNA molecules, with correction by Poisson distribution. In this project, strawberries were inoculated with fecal material from animals, and the result detected by nanoplate digital PCR. A detection limit of 250 fg/uL was determined. Overall, dPCR offers a quick and sensitive method to detect contaminated produce.