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1. Habituation is the declining responsiveness of a neural circuit (or behavior) to repetitive stimulation. Dishabituation (or arousal) can be brought about by the sudden presentation of an additional, novel stimulus. A clear example of arousal in the locust is provided by the visual system: the habituated response of the descending contralateral movement detector (DCMD) interneuron to repetitive visual stimuli can be dishabituated by a variety of other visual and tactile stimuli. 2. Application of octopamine to the locust brain and optic lobes dishabituates the DCMD in a manner similar to the effect of visual and tactile stimulation. 3. The locust CNS contains two pairs of octopamine-immunoreactive cells, the protocerebral medulla 4 (PM4) neurons, that could potentially mediate this dishabituation effect; PM4 neurons arborize in the optic lobe, they contain octopamine, and they respond to the same visual and tactile stimuli that dishabituate the DCMD. 4. To investigate whether PM4 activity dishabituates the DCMD, we recorded intracellularly from one of the PM4 neurons while recording extracellularly from the DCMD. When the PM4 neuron is injected with hyperpolarizing current to render it completely inactive, the DCMD exhibits its characteristic habituation to a moving visual stimulus. However, depolarizing the PM4 neuron, to produce action potentials at approximately 20 Hz, significantly increases the number of DCMD action potentials per stimulus. 5. The PM4 neurons may therefore play an important role in dishabituating the DCMD to novel stimuli. This effect is presumably mediated by PM4 neurons releasing endogenous octopamine within the optic lobe.

To explore the variability in biosensor studies, 150 participants from 20 countries were given the same protein samples and asked to determine kinetic rate constants for the interaction. We chose a protein system that was amenable to analysis using different biosensor platforms as well as by users of different expertise levels. The two proteins (a 50-kDa Fab and a 60-kDa glutathione S-transferase [GST] antigen) form a relatively high-affinity complex, so participants needed to optimize several experimental parameters, including ligand immobilization and regeneration conditions as well as analyte concentrations and injection/dissociation times. Although most participants collected binding responses that could be fit to yield kinetic parameters, the quality of a few data sets could have been improved by optimizing the assay design. Once these outliers were removed, the average reported affinity across the remaining panel of participants was 620 pM with a standard deviation of 980 pM. These results demonstrate that when this biosensor assay was designed and executed appropriately, the reported rate constants were consistent, and independent of which protein was immobilized and which biosensor was used.

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