Switch-like and persistent memory formation in individual larval Drosophila

Associative learning allows animals to use past experience to predict future events. The circuits underlying memory formation support immediate and sustained changes in function, often in response to a single example. Larval Drosophila is a genetic model for memory formation that can be accessed at the molecular, synaptic, cellular, and circuit levels, often simultaneously, but the standard behavioral assay for learning and memory does not address individual animals. It has also been difficult to form long lasting memories, especially those requiring synaptic reorganization. We demonstrate a new assay for learning and memory capable of tracking the changing preferences of individual larvae. We use this assay to explore how activation of a pair of reward neurons changes the response to the innately aversive gas Carbon Dioxide, CO2. We confirm that when coupled to odor presentation in appropriate temporal sequence, optogenetic reward reduces avoidance of CO2. We find that learning is quantized, all-or-nothing, and can be extinguished by repeated unrewarded exposure to CO2. We find that memories can be stabilized against extinction by repeated training or overnight consolidation. Finally, we demonstrate long-lasting protein synthesis dependent and independent memory formation.

MrgprC11+ sensory neurons mediate glabrous skin itch

Itch arising from glabrous skin (palms and soles) has attracted limited attention within the field due to the lack of methodology. This is despite glabrous itch arising from many medical conditions such as plantar and palmar psoriasis, dyshidrosis, and cholestasis. Therefore, we developed a mouse glabrous skin behavioral assay to investigate the contribution of three previously identified pruriceptive neurons in glabrous skin itch. Our results show that MrgprA3+ and MrgprD+ neurons, although key mediators for hairy skin itch, do not play important roles in glabrous skin itch, demonstrating a mechanistic difference in itch sensation between hairy and glabrous skin. We found that MrgprC11+ neurons are the major mediators for glabrous skin itch. Activation of MrgprC11+ neurons induced glabrous skin itch, while ablation of MrgprC11+ neurons reduced both acute and chronic glabrous skin itch. Our study provides insights into the mechanisms of itch and opens up new avenues for future glabrous skin itch research.

Forelimb Cortical Stroke Reduces Precision of Motor Control in Mice

Background and Objective. Rodent models of stroke impairment should capture translatable features of behavioral injury. This study characterized poststroke impairment of motor precision separately from strength in an automated behavioral assay. Methods. We measured skilled distal forelimb reach-and-grasp motions within a target force range requiring moderate-strength. We assessed whether deficits reflected an increase in errors on only one or both sides of the target force range after photothrombotic cortical stroke. Results. Pull accuracy was impaired for 6 weeks after stroke, with errors redistributing to both sides of the target range. No decrease in maximum force was measured. Conclusions. This automated reach task measures sustained loss of motor precision following cortical stroke in mice.