Kano, Amane et al. (2021) International Worm Meeting "Two thermosensory neurons AFD and AWC regulate purity of frequency components in temperature-evoked sinusoidal crawling"

Mori, Ikue, Matsuyama, Hironori J., Kano, Amane

[International Worm Meeting, 2021]

Migration behavior by the innate force such as walking, flapping and crawling is composed of periodic bending and stretching of the body parts. These behaviors consist of various frequency components. Walking includes marching consisting of a single frequency component and tottering consisting of multiple frequency components. Despite quantifying the purity of frequency components of the behavioral states and elucidating neural mechanisms controlling them are important for ethology and neuroscience, it is unclear how the nervous systems regulate the purity of frequency components. To address this question, we quantified the crawling behavior of C. elegans responding to thermal stimuli by using spectral entropy that represents the purity of frequency components of crawling behavior. Animals were subjected to two types of temperature stimuli: linear increments across the cultivation temperature (Tc) of animals with slow (0.02°C/s) and rapid (0.1°C/s) rate. Around Tc with slow temperature increment, animals showed pure crawling behavior consisting of small number of frequency components. To identify neurons required for the purity control of the crawling under temperature increment, we examined spectral entropy for the strains, in which thermosensory neurons AFD and AWC were genetically ablated. AFD-ablated animals showed more disordered crawling near Tc than that of wild type under slow temperature increment, indicating that AFD is required for pure sinusoidal crawling near Tc under slow temperature increment. By contrast, AWC-ablated animals showed purer crawling near Tc than that of wild type under both slow and rapid temperature increments, indicating that AWC disorders sinusoidal crawling near Tc. To clarify the relationship between AFD and AWC in the purity regulation of the crawling behavior, we performed behavioral test using a strain defective in temperature sensing in both AFD and AWC. This strain showed additive phenotype of those of AFD- and AWC-ablated strains under both slow and rapid temperature increments, suggesting that AFD and AWC regulate sinusoidal crawling in parallel. We also found that AFD and AWC affected each other's calcium responses to the thermal stimuli. Our results suggest that two different sensory neurons that communicate each other possess opposing functions in regulation of a temperature-responding behavior: one organizes and the other disorders sinusoidal crawling.

Kano, Amane et al. (2019) International Worm Meeting "Toward understanding neural computations in an interneuron AIY through optogenetical manipulation of its presynaptic sensory neurons AFD and AWC."

Kano, Amane, Tsukada, Yuki, Mori, Ikue

[International Worm Meeting, 2019]

How an interneuron integrates environmental cues transformed by sensory neurons is an important problem in neuroscience. The simplest model to elucidate this problem is a neural circuit consisting of two sensory neurons and their postsynaptic interneuron. One such model in C. elegans is a circuit consisting of thermosensory neurons AFD and AWC, and their postsynaptic interneuron AIY, which has been identified as a part of the circuit for thermotaxis (Mori & Ohshima, Nature, 1995; Kuhara, Okumura et al., Science, 2008). Previously, one of our studies shows that AFD either excited or inhibited AIY activity depending on thermal stimuli (Kuhara et al., Nat. Commun., 2011). Similarly, other study reports that activation of AWC suppressed AIY in response to thermal stimulus (Kuhara, Okumura et al., Science, 2008). However, how AIY responses depend on states of both AFD and AWC activities remains unclear. In this study, we investigated how AIY activity is affected by optogenetically controlling states of AFD and AWC activities. We first introduced GCaMP6f and Chrimson in either AFD or AWC, and confirmed that AFD and AWC activity could be excited by Chrimson. We next quantified AIY activity under controlling AFD, AWC, or both AFD and AWC was evoked by Chrimson by scoring spike-like AIY activity peaks to define as the frequency of AIY activity. We found that when AFD was excited by Chrimson, the frequency of AIY activity also increased. By contrast, when AWC was excited by Chrimson, the frequency of AIY activity was unchanged. However, when both AFD and AWC were simultaneously evoked, we observed two states, increment or decrement, of the frequency of AIY activity. Our results suggest that AIY responses are indeed dependent on the state of both AFD and AWC. Based on this result on simultaneous evoking of AFD and AWC activity, we are currently seeking the critical time window between excitation of AFD and AWC, which may affect AIY responses. To reveal critical time window, we use projection mapping system that enables illumination of pinpointed areas. We so far established our projection mapping system to illuminate AFD soma and AWC soma, both of which are about 10 m close to each other. We are also improving the software aiming to detect the increment of calcium signal and feedback it to excitation timing and illumination areas. By using this feedback software, we hope to reveal how states of AFD and AWC dynamically affect AIY activity, thereby contributing to clarify how sensory signals integrate within an interneuron.

Lau H et al. (2010) Neuronal Development, Synaptic Function and Behavior, Madison, WI "Chemosensory Context Conditioning in C. elegans: A Non-Food Related Form of Associative Learning"

Rankin C H, Lau H

[Neuronal Development, Synaptic Function and Behavior, Madison, WI, 2010]

In context conditioning of mechanosensory habituation, worms that are trained and tested in the presence of a chemosensory contextual cue show greater retention of memory when compared to animals trained and tested in different contextual cues. This was shown in short-term (1 hr) context conditioning of habituation to mechanical tap stimuli in the presence of a chemosensory taste context cue, sodium acetate (Rankin, 2000). Here, we have shown context conditioning for an olfactory chemosensory cue (diacetyl) and dissociated the taste and smell pathways for this form of learning. odr-7 (an olfactory-specific nuclear receptor) worms, with non-functional AWA olfactory chemosensory neuron (that detects diacetyl), showed short-term context conditioning to the taste but not to the odor; the reverse was true for osm-3 (a homodimeric forming kinesin motor protein) worms with non-functional taste chemosensory neurons. This dissociation allows us to distinguish learning genes from genes involved in the detection of taste or smell. We are also examining long-term associative memory (24 hr) for context conditioning; context conditioning did not enhance normal long-term habituation, however, it produced memory in a training procedure that normally does not produce memory. Our results showed that glr-1 (an AMPA-type ionotropic glutamate receptor subunit) and nmr-1 (an NMDA-type ionotropic glutamate receptor subunit) worms did not show either short- or long-term context conditioning. Since nmr-1 was previously shown to be important in associative learning (Kano et al., 2008), we are investigating in which interneurons nmr-1 is essential for worms to show context conditioning. This will elucidate the cellular mechanisms of non-associative and associative learning both in the short- and long-term, providing insight into how interneurons integrate chemosensory context cues with mechanosensory taps.

Lau, H. L. et al. (2009) International Worm Meeting "Chemosensory Context Conditioning in Caenorhabditis elegans: A Non-Food Related Form of Associative Learning."

Rankin, C. H., Lau, H. L.

[International Worm Meeting, 2009]

We are studying context conditioning of mechanosensory habituation: in context conditioning of habituation, worms that are trained and tested in the presence of a chemosensory contextual cue show greater retention of a memory when compared to animals trained and tested in different contextual cues/environments. Previous results showed that retention of habituation to mechanical tap stimuli was greater if habituation training and testing occurred in the presence of the same chemosensory taste cue (soluble sodium acetate; Rankin, 2000); we have now also shown this for an olfactory chemosensory cue (volatile diacetyl). In the earlier study, we confirmed the associative nature of this learning by demonstrating that it showed both extinction and latent inhibition. In this study, we have dissociated the neural circuits for the taste and smell pathways underlying this form of learning. odr-7 (encodes an olfactory-specific member of the nuclear receptor) worms, with non-functional AWA olfactory chemosensory neurons (that detects diacetyl), showed context conditioning to the sodium acetate taste but not to the diacetyl odor. Conversely, osm-3 (encodes a homodimeric forming kinesin motor protein) worms, with non-functional taste chemosensory neurons (that detect sodium acetate), showed context conditioning to the diacetyl odor but not to the sodium acetate taste. This dissociation between taste and smell allows us to distinguish between non-associative (habituation) and associative (chemosensory context conditioning of habituation) learning genes. Additionally, these associative learning genes can be further discriminated from genes involved in the detection of taste or smell. A number of genes in C. elegans, such as nmr-1 (encodes an NMDA-type ionotropic glutamate receptor subunit; Kano et al., 2008), have been suggested to be involved in associative learning. We found that nmr-1 worms were not able to show context conditioning. nmr-1 is expressed in several interneurons in our associative learning neural circuit, so we are currently investigating in which interneurons nmr-1 is essential for worms to show chemosensory context conditioning to mechanosensory habituation. This will help to elucidate the cellular mechanisms of this form of associative learning; providing insight into how interneurons integrate chemosensory context cues with mechanosensory taps to alter subsequent behavior.