Animal models of neurological disorders

Fluorescent Biosensors for Neurotransmission and Neuromodulation: Engineering and Applications

Understanding how neuronal activity patterns in the brain correlate with complex behavior is one of the primary goals of modern neuroscience. Chemical transmission is the major way of communication between neurons, however, traditional methods of detection of neurotransmitter and neuromodulator transients in mammalian brain lack spatiotemporal precision. Modern fluorescent biosensors for neurotransmitters and neuromodulators allow monitoring chemical transmission in vivo with millisecond precision and single cell resolution. Changes in the fluorescent biosensor brightness occur upon neurotransmitter binding and can be detected using fiber photometry, stationary microscopy and miniaturized head-mounted microscopes. Biosensors can be expressed in the animal brain using adeno-associated viral vectors, and their cell-specific expression can be achieved with Cre-recombinase expressing animals. Although initially fluorescent biosensors for chemical transmission were represented by glutamate biosensors, nowadays biosensors for GABA, acetylcholine, glycine, norepinephrine, and dopamine are available as well. In this review, we overview functioning principles of existing intensiometric and ratiometric biosensors and provide brief insight into the variety of neurotransmitter-binding proteins from bacteria, plants, and eukaryotes including G-protein coupled receptors, which may serve as neurotransmitter-binding scaffolds. We next describe a workflow for development of neurotransmitter and neuromodulator biosensors. We then discuss advanced setups for functional imaging of neurotransmitter transients in the brain of awake freely moving animals. We conclude by providing application examples of biosensors for the studies of complex behavior with the single-neuron precision.

Screening pesticides for neuropathogenicity

Pesticides are routinely screened in studies that follow specific guidelines for possible neuropathogenicity in laboratory animals. These tests will detect chemicals that are by themselves strong inducers of neuropathogenesis if the tested strain is susceptible relative to the time of administration and methodology of assessment. Organophosphate induced delayed neuropathy (OPIDN) is the only known human neurodegenerative disease associated with pesticides and the existing study guidelines with hens are a standard for predicting the potential for organophosphates to cause OPIDN. Although recent data have led to the suggestion that pesticides may be risk factors for Parkinsonism syndrome, there are no specific protocols to evaluate this syndrome in the existing study guidelines. Ideally additional animal models for human neurodegenerative diseases need to be developed and incorporated into the guidelines to further assure the public that limited exposure to pesticides is not a risk factor for neurodegenerative diseases.

The operant serial implicit learning task reveals early onset motor learning deficits in the HdhQ92knock-in mouse model of Huntington's disease

A range of genetic mouse models of Huntington's disease have been created. However, as knock-in models typically have milder phenotypes, they have frequently been overlooked as therapeutic tools in favour of the transgenic models that display severe behavioural symptoms. More sensitive tests are therefore required to reveal abnormalities and release the potential of knock-in lines. An implicit learning task for mice has been developed in the nine-hole operant box test apparatus, in which mice must respond to a sequence of lights in order to earn a reward. A light stimulus was presented randomly in one of five holes, to which a nose poke response resulted in the light being extinguished and a second light illuminated in a different hole. Response to the second light resulted in a liquid reward. To probe implicit learning, a predictable stimulus sequence was embedded among many unpredictable sequences. In the current study, the Hdh(Q92) mouse model of Huntington's disease was examined. At 4 months of age, Hdh(Q92/Q92) mice demonstrated clear and significant deficits in both accuracy and reaction time on all trials of the implicit learning task, with improved performance on predictable trials. We believe this to be the earliest reported behavioural deficit in the Hdh(Q92) knock-in mouse line. The results of this study validate the serial implicit learning task as a sensitive tool for the examination of implicit and motor learning deficits in mutant mice, and may provide a powerful test for probing potential treatments for Huntington's disease.