Aplysia. a California snail, has ascended into neurologic prominence. due in part to the work of Eric Kandel. He recognired early the value of studying a simple organism in which the neurons and neural circuits responsible for behavior can be correlated with electrophysiological techniques, and has devoted a major effort to this end. Progress made in the last decade is put in a larger context by giving a general review of behavior and neurophysiology. Directed toward a graduate student level, it assumes the reader to be an intelligent, basically naive scientist and methodically lays the groundwork for the later chapters where the neural basis for synaptic plasticity and habituation are analyzed. Kandel describes h i s work on Dale’s postulate that a cell mediates the xame transmitter and causes the same postsynaptic effect in all of its connections. As Kandel has shown, however, the transmitter effect in the Aplysia is determined by the postsynaptic receptor itself. That is, the same transmitter is capable of eliciting excitation, inhibition or a mixture of both, depending on the ion species enabled by the transmitter at the receptor membrane sites. Whether single transmitters are used commonly in other animals having a more elaborate biochemistry and a larger number of neurons is a moot point. Kandel also analyzes the cellular basis for gill withdrawal, for inking and egg laying, and for the neural control of circulation. Finally, he considers how gill withdrawal is habituated and shows that transmitter release, under control of a group of sensory neurons, accounts for changes in the reflex on a short and long term basis. Although it is not certain that habituation in humans or in other vertebrates is caused by a similar mechanism, it will undoubtedly be encountered often since nature seldom discards a successful mechanism. In the end, however, the mind and soulofthe Aplysia have so far eluded the microelectrode, and the beast is probably not all that simple. It is still not clear what gives the Aplysia the ability to recognize and flee from starfish, become imtable and attempt to escape when continuously stimulated, or lust for gang sex. The text is clear, concise. easy to comprehend, and well-illustrated. In a work of this magnitude some subjects necessarily get short shrift, and there is little mention of the controversies which undoubtedly abound in the field. Nevertheless, the book is interesting, well-written, and documents the value of a combined neurophysiologic and behavioral approach. It is clear that this approach holds considerable potential for fundamental studies of behavior, and one looks forward to further investigations of the life and times of the Aplysia.

Cellular Basis of Behavior

The structure of the nervous system.

In a routine review, Kandel's own sentence, "The accelerated progress in cell biology during the past ten years has led to concepts and methods that have made it possible to analyze behavior in a more fundamental way than previously," could have been used as a convenient opening phrase. Cellular Basis of Behavior , however, is more than its subtitle, An Introduction to Behavioral Neurobiology , suggests and also more than a text "usable by undergraduate and graduate students—even those having little background in behavior, neurobiology or invertebrate zoology,... an overview... for scientists in other fields" would need to be. It is a carefully formulated personal statement about an area whose landscape still reveals cracks and craters, traces of the violent action that has shaped it for decades. An investigator dedicated to the study of behavior is still embattled on many fronts, each of them demanding different strategies and tactics for action, defense

Cellular Basis of Behavior: An Introduction to Behavioral Neurology

C. elegans can learn to avoid pathogenic bacteria through several mechanisms, including bacterial small RNA-induced learned avoidance behavior, which can be inherited transgenerationally. Previously, we discovered that a small RNA from a clinical isolate of Pseudomonas aeruginosa, PA14, induces learned avoidance and transgenerational inheritance of that avoidance in C. elegans. Pseudomonas aeruginosa is an important human pathogen, and there are other Pseudomonads in C. elegans' natural habitat, but it is unclear whether C. elegans ever encounters PA14-like bacteria in the wild. Thus, it is not known if small RNAs from bacteria found in C. elegans' natural habitat can also regulate host behavior and produce heritable behavioral effects. Here we screened a set of wild habitat bacteria, and found that a pathogenic Pseudomonas vranovensis strain isolated from the C. elegans microbiota, GRb0427, regulates worm behavior: worms learn to avoid this pathogenic bacterium following exposure, and this learned avoidance is inherited for four generations. The learned response is entirely mediated by bacterially-produced small RNAs, which induce avoidance and transgenerational inheritance, providing further support that such mechanisms of learning and inheritance exist in the wild. We identified Pv1, a small RNA expressed in P. vranovensis, that has a 16-nucleotide match to an exon of the C. elegans gene maco-1. Pv1 is both necessary and sufficient to induce learned avoidance of Grb0427. However, Pv1 also results in avoidance of a beneficial microbiome strain, P. mendocina. Our findings suggest that bacterial small RNA-mediated regulation of host behavior and its transgenerational inheritance may be functional in C. elegans' natural environment, and that this potentially maladaptive response may favor reversal of the transgenerational memory after a few generations. Our data also suggest that different bacterial small RNA-mediated regulation systems evolved independently, but define shared molecular features of bacterial small RNAs that produce transgenerationally-inherited effects. 

pdf/a-natural-bacterial-pathogen-of-c-elegans-uses-a-small-rna-504ucmymaj.pdf

A natural bacterial pathogen of C. elegans uses a small RNA to induce transgenerational inheritance of learned avoidance

Animals are exposed to many microbes in their environment, some of which have been shown to colonize various tissues including the intestine. The composition of the intestinal microbiota affects many aspects of the host's physiology and health. Despite this, very little is known about whether host behavior contributes to the colonization. We approach this question in the nematode C. elegans, which feeds on bacteria and also harbors an intestinal microbiome. We examined the behavior of C. elegans towards CeMbio, a simplified microbiome consisting of twelve strains that represent the bacteria found in the animal's natural environment. We observed that C. elegans raised on E. coli shows a strong preference for three members of CeMbio (Lelliottia amnigena JUb66, Enterobacter hormaechei CEent1, and Pantoea nemavictus BIGb0393) compared to E. coli. Previously, these three bacterial strains have been shown to support faster C. elegans development time than E. coli OP50 and are low colonizers compared to eight other members of CeMbio. We then used gas chromatography coupled to mass spectrometry to identify that these three bacteria release isoamyl alcohol, a previously described C. elegans chemoattractant. We suggest that C. elegans seeks bacteria that release isoamyl alcohol and support faster growth. 

Chemical basis of microbiome preference in the nematode C. elegans

Memory is one of the most important abilities of the brain. It is defined as an alteration in behavior as a consequence of an experience. For example, the C. elegans nematode will downregulate its chemotactic response to the innately attractive odor, butanone, if the odor is not paired with food. Through repeated, spaced training with this odor in the absence of food, C. elegans will maintain this memory for a prolonged period of time. Although transient receptor potential (TRP) channels are classically thought of as primary sensory receptors, it was reported that the OSM-9/TRPV5/TRPV6 (TRP vanilloid 5/6) channel is required for single exposure learning. Here we describe a new role for osm-9 in consolidation of memory that is induced by repeated, spaced training. In this paradigm, osm-9 mutant animals learn as well as wild-types, but are unable to consolidate the memory. Though sleep is required for memory consolidation, loss of the TRPV channel OSM-9 does not affect sleep. This indicates that the TRP channel promotes memory in a process that acts outside the sleep pathway. We investigate the endogenous expression pattern of OSM-9 and show that it is not expressed in the butanone-responsive AWC olfactory sensory neuron. Instead, it is expressed in the paired AWA olfactory neuron, the ASH nociceptive neurons, the OLQ and two other unidentified sensory neurons which are most likely ADF and ADL as they express osm-9 mRNA. Because OSM-9 acts in sensory neurons that do not participate in butanone sensation, this indicates that the circuit participates in olfactory memory consolidation.

https://www.biorxiv.org/content/biorxiv/early/2020/12/12/2020.11.27.400747.full.pdf

Olfactory memory consolidation requires the TRPV channel OSM-9 in sensory neurons of the circuit.

C. elegans’ experiences and microbiome have been shown to shape its responses to certain stimuli; a recent study found that C. elegans grown on Providencia alcalifaciens JUb39 exhibited increased attraction to that same growth bacteria while also lowered repulsion to the odor 1-octanol (O’Donnell et al. 2020). This prompted us to ask whether other strains of bacteria could likewise alter C. elegans’ responses to bacterial food and volatile chemicals. So, to expand upon current knowledge, we cultured wild-type C. elegans (N2) on an unidentified Escherichia coli ( E. coli sp?), Pseudomonas mendocina (MSPm1), Pseudomonas lurida (MYb11), Stenotrophomonas maltophilia (JUb19), or Proteus mirabilis strain ( P. mirabilis sp?). After several generations, we examined how their choice of bacterial food was affected. In addition, we looked at their response to the olfactory stimuli 2-butanone; 2,3-butanedione; 2,3-pentanedione; and 2-nonanone, as well as their response to the gustatory stimulus sodium chloride. Interestingly, we found that growth on any of these bacterial strains led to their bacterial preferences and behavioral responses to 2-butanone; 2,3-pentanedione; diacetyl; and sodium chloride remaining unchanged. However, we also saw that C. elegans showed a preference for MSPm1 and P. mirabilis sp? to HB101, and HB101 to MYb11. Furthermore, worms that are grown on MSPm1 showed stronger attraction to a 1:10 dilution of 2-nonanone (AWB-sensed odorant) as compared to worms grown on the other bacterial strains.

C. elegans show Preference for Pseudomonas mendocina (MSPm1) and Proteus mirabilis ( P. mirabilis sp?) , and Repulsion to Pseudomonas lurida (MYb11); Growth on Pseudomonas mendocina (MSPm1) Increases Attraction to 2-nonanone

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Olfactory memory consolidation requires the TRPV channel OSM-9 in sensory neurons of the circuit.

C. elegans show Preference for Pseudomonas mendocina (MSPm1) and Proteus mirabilis ( P. mirabilis sp?) , and Repulsion to Pseudomonas lurida (MYb11); Growth on Pseudomonas mendocina (MSPm1) Increases Attraction to 2-nonanone