Neuroscience

Animal models are an important tool for studying neuropsychiatric disorders. However, a major challenge for researchers working with laboratory rodents is trying to reproduce ‘core’ symptoms of complex human disorders such as schizophrenia. Despite this challenge, however, it is still conceivable to use animal models designed to reproduce some of the disease’s ‘endo-phenotypes’. One example is the prepulse inhibition (PPI) of the startle reflex. PPI is a form of startle plasticity and is characterized by a normal reduction in startle magnitude that occurs when an intense startling stimulus (or pulse) is preceded by a weaker pre-stimulus (or prepulse). The PPI paradigm is commonly used to evaluate sensorimotor gating and it has been described in numerous species including humans and rodents. Deficits in PPI have been observed in subjects with schizophrenia and other neuropsychiatric diseases, as well as in established animal models of these disorders. The PPI paradigm is therefore largely used to explore genetic and neurobiological mechanisms underlying the sensorimotor gating phenotypes found in these disorders. Thus, it is necessary to set up reliable and reproducible protocols to study PPI in mice.

Thermo-nociception, the detection and behavioral response to noxious temperatures, is a highly conserved action to avoid injury and ensure survival. Basic molecular mechanisms of thermal responses have been elucidated in several model organisms and are of clinical relevance as thermal hypersensitivity (thermos-allodynia) is common in neuropathic pain syndromes. Drosophila larvae show stereotyped escape behavior upon noxious heat stimulation, which can be easily quantified and coupled with molecular genetic approaches. It has been successfully used to elucidate key molecular components and circuits involved in thermo-nociceptive responses. We provide a detailed and updated protocol of this previously described method (Tracey et al., 2003) to apply a defined local heat stimulus to larvae using a fast-regulating hot probe.

Drosophila melanogaster larvae have been extensively used as a model to study the molecular and cellular basis of nociception. The larval nociceptors, class IV dendritic arborization (C4da) neurons, line the body wall of the animal and respond to various stimuli including noxious heat and touch. Activation of C4da neurons results in a stereotyped escape behavior, characterized by a 360° rolling response along the body axis followed by locomotion speedup. The genetic accessibility of Drosophila has allowed the identification of mechanosensory channels and circuit elements required for nociceptive responses, making it a useful and straightforward readout to understand the cellular and molecular basis of nociceptive function and behavior. We have optimized the protocol to assay mechanonociceptive behavior in Drosophila larvae.

Animals use behavioral strategies to seek optimal environments. Population behavioral assays provide a robust means to determine the effect of genetic perturbations on the ability of animals to sense and respond to changes in the environment. Here, we describe a C. elegans population behavioral assay used to measure locomotory responses to changes in environmental oxygen (O₂) and carbon dioxide (CO₂) concentrations. These behavioral assays are high-throughput and enable examination of genetic, neuronal and circuit function.

The proof of concept for bioluminescence monitoring of neural activity in zebrafish with the genetically encoded calcium indicator GFP-aequorin has been previously described (Naumann et al., 2010) but challenges remain. First, bioluminescence signals originating from a single muscle fiber can constitute a major pitfall. Second, bioluminescence signals emanating from neurons only are very small. To improve signals while verifying specificity, we provide an optimized 4 steps protocol achieving: 1) selective expression of a zebrafish codon-optimized GFP-aequorin, 2) efficient soaking of larvae in GFP-aequorin substrate coelenterazine, 3) bioluminescence monitoring of neural activity from motor neurons in free-tailed moving animals performing acoustic escapes and 4) verification of the absence of muscle expression using immunohistochemistry.