Neural Signaling Dynamics of Conditioning in C. elegans

Retrograde signaling from downstream effectors (i.e., motor neurons) can modulate plasticity. Much research has focused on the learned association of closely timed sensory stimuli. By comparison, there is less research probing the potential influence of how or if activation at downstream neuromuscular junctions (NMJ) could modulate associative conditioning. Using channelrhodopsin activation of body wall muscle and different motor neuron subsets (cholinergic motor neurons that drive contraction and GABAergic motor neurons that drive relaxation of muscle) in the Caenorhabditis elegans (C. elegans) model system, we examined if concurrent excitation in these downstream circuits influences associative conditioning. Conditioning consisted of pairing two distinct sensory stimuli, mechanosensory (vibration) and blue light (~480nm). Each stimulus drives a locomotor response on its own and we have shown that pairing delivery of these two stimuli alters the subsequent locomotor response to vibration. Animals that expressed channelrhodopsin in the body wall muscle (pmyo-3::ChR2), excitatory motor neurons (punc-17::ChR2) or the inhibitory motor neurons (punc-47::ChR2) received associative vibration-light conditioning. Thus, the blue light stimulus simultaneously functioned as both associating sensory stimulus and activator of channelrhodopsin, when the necessary cofactor was present, all-trans-retinol (ATR+). Results showed wild type C. elegans typically pause for a longer duration following associative vibration-light conditioning. Following vibration-light conditioning, pmyo-3::ChR2 exhibited a complete disruption of learning. While trained ATR+ punc-17::ChR2 and punc-47::ChR2 animals showed partially disrupted conditioned locomotor behavior, as compared to controls. Together, this data suggests that co-activation of the downstream body wall muscle and motorneurons interferes with upstream associative conditioning

Uncovering the Molecular Mechanism Behind Associative Learning in C. elegans

The current project uses the Caenorhabditis elegans (C. elegans) model organism to investigate the cellular and molecular mechanisms behind associate learning. Calcium/calmodulin-kinase II (CaMKII) is a molecule that has long been linked to learning. In C. elegans the gene unc-43 encodes the ortholog of CaMKII. Our lab has previously demonstrated that worms have deficits in learning when a particular isoform of CaMKII is knocked out. The worm CaMKII strain, unc-43(gk452), carries a deletion mutation for the CaMKIIT isoform and shows learning deficits as measured by assays including, associative chemotaxis, and chemoavoidance. The current study aims to determine if this strain shows similar deficits following introduction of a rapid acquisition protocol involving stimulus pairing. To this end, a low frequency tone (100 Hz; CS) produces a vibration that the worm comes to associate with a light (either UV or blue wavelength; US). Data indicate that the unc-43(gk452) strain responds differently following pairing compared to controls. Current work includes generating a rescue strain using microinjection to restore exon 1 of this CaMKII isoform and determining if this is sufficient to return learning to wild-type levels