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Understanding how motoneuron activity is finely tuned remains an open question. Leeches are a highly suitable organism for studying motor control due to their well-characterized behaviors and relatively simple nervous system. On solid surfaces, leeches display crawling, a rhythmic motor pattern that can be elicited in the isolated nerve cord or even in single ganglia isolated from it. This study aimed to learn how this motor output is shaped by concurrent premotor signals. Specifically, we analyzed how electrophysiological manipulation of a premotor nonspiking (NS) neuron, which forms a recurrent inhibitory circuit (analogous to that formed by vertebrate Renshaw cells), shapes the leech crawling motor pattern. The study included a quantitative analysis of putative motor units active throughout the fictive crawling cycle that shows that the rhythmic motor output in isolated ganglia mirrors the phase relationships observed in vivo. Taken together, the study reveals that the premotor NS neurons, under the control of the segmental pattern generator, modulated the degree of excitation of motoneurons during crawling in a phase-specific manner.

Studies of pain/nociception often rely on simple reflexes to assess pain-related changes in behavior. However, there is considerable interest in utilizing more complex, self-initiated behaviors in place of stimulus-evoked reflexes. In this study we report an operant conditioning assay using Hirudo verbana (the medicinal leech) to assess the effects of injury on motivational and cognitive processes. Animals were placed in an arena consisting of an illuminated and a dark chamber with a connecting section in between. The connecting section was partially filled with gravel, which acted as an obstacle and delayed escape from the illuminated to the dark side. With repeated experience H. verbana learned to overcome the gravel obstacle, reflected as a decreased escape latency from the illuminated chamber. The capacity for this enhanced escape behavior was retained for up to two hours. In animals that received an injury to the posterior sucker, learning and memory of this operant escape task was disrupted. Injured animals also exhibited mechanosensory sensitization, changes in locomotion, changes in exploratory behavior, and increased negative phototaxis. Over 12 days, changes in locomotion, exploratory behavior, and phototaxis recovered to pre-injury levels, although mechanosensory sensitization remained. Disruptions in cognitive behavior also recovered during this period with the capacity for operant conditioning returning six days after injury and two hour retention of conditioning returning by day 12. This study shows that injury produces a complex and coordinated set of sensory, motor, and integrative changes in H. verbana that may be relevant to understanding the biological processes behind pain in vertebrates.

Glossiphoniidae is a family of freshwater leeches, notable for their unique behaviour of parental care. After hatching, juveniles remain on the ventral side of their parent, where they receive protection and grow until they are ready to depart from the parent leech. The detachment of juveniles is a crucial stage for their development and independence from their parents, potentially influenced by various factors. To investigate these factors, ten parental individuals of Orientobdelloides siamensis were studied in the laboratory. Three to five days after copulation, all parental leeches deposited approximately 361.6±37.79 eggs on the substrate, which were covered until the end of the brooding period. Incubation of their single-egg cocoons took 7–9 days. Subsequently, the newborns attached to the ventral annulus of the parent by their caudal sucker. Seven to eleven days after hatching, the caudal sucker of juveniles expanded over the parent’s annulus, indicating readiness to depart. The young leeches detached from the parental venter, moved to the substrate, and continued living under the ventral side of their parent. Finally, to determine the timing of juvenile detachment, the space availability beneath the parental venter and yolk depletion after hatching were analyzed. By observing morphological characteristics and behaviors, this study was able to investigate the interaction between these factors, and their correlation with juvenile detachment in O . siamensis .

Fluorescence imaging is an attractive method for monitoring neuronal activity. A key challenge for optically monitoring voltage is development of sensors that can give large and fast responses to changes in transmembrane potential. We now present fluorescent sensors that detect voltage changes in neurons by modulation of photo-induced electron transfer (PeT) from an electron donor through a synthetic molecular wire to a fluorophore. These dyes give bigger responses to voltage than electrochromic dyes, yet have much faster kinetics and much less added capacitance than existing sensors based on hydrophobic anions or voltage-sensitive ion channels. These features enable single-trial detection of synaptic and action potentials in cultured hippocampal neurons and intact leech ganglia. Voltage-dependent PeT should be amenable to much further optimization, but the existing probes are already valuable indicators of neuronal activity.

During captivity, round stingrays, Urobatis halleri, became infected with the marine leech Branchellion lobata. When adult leeches were deprived of blood meal, they experienced a rapid decrease in body mass and did not survive beyond 25 days. If kept in aquaria with host rays, B. lobata fed frequently and soon produced cocoons, which were discovered adhered to sand grains. A single leech emerged from each cocoon (at ~ 21 days), and was either preserved for histology or molecular analysis, or monitored for development by introduction to new hosts in aquaria. Over a 74-day observation period, leeches grew from ~ 2 to 8 mm without becoming mature. Newly hatched leeches differed from adults in lacking branchiae and apparent pulsatile vesicles. The microbiome of the hatchlings was dominated by a specific, but undescribed, member of the gammaproteobacteria, also recovered previously from the adult leech microbiome. Raising B. lobata in captivity provided an opportunity to examine their reproductive strategy and early developmental process, adding to our limited knowledge of this common group of parasites.

The input, hidden and output layers cultivate a hierarchical framework of the feedforward neural networks (FNNs) characterized by unidirectional information flow and feedback feedback-free loop connection, the network highlights attributes of fortified scalability and adaptability, elevated parallel computation and training efficiency, uncluttered structure and easy implementation. The blood-sucking leech optimization (BSLO) is predicated on the foraging patterns of blood-sucking leeches in rice paddies, which incorporates exploration, exploitation, switching mechanism of directional leeches, recherche mechanism of directionless leeches, and re-tracking mechanism to accomplish global coarse discovery and local elaborated extraction, and ascertain the fantastic solution. To expedite solution efficiency and reinforce mining precision, this paper proposes an enhanced BSLO with the simplex method (SBSLO) to train the FNNs, the objective is to quantify the discrepancy between anticipated output and realistic output, assess training efficacy and classification accuracy of prediction samples, and establish the fantastic connection weights and bias thresholds. Simplex method not only strengthens directional exploration precision and bolsters population diversity to mitigate premature convergence and facilitate escape from local optimum but also advances constraint processing capability and emphasizes noteworthy robustness and generalization to reinforce convergence procedure and elevate solution quality. The stability and dependability of the SBSLO are validated by seventeen sample datasets, and the SBSLO is compared with KOA, NRBO, HLOA, IAO, WO, PKO, EGO, HEOA, APO, FLO, PO and BSLO. The experimental results demonstrate that the SBSLO amalgamates the collective cooperative exploration of the BSLO with the refined directional exploitation of the simplex method to leverage complementary advantages, alleviate local search stagnation, boost training efficiency and prediction precision, strengthen stability and robustness, and foster convergence speed and solution quality.

Long-term monitoring of host-parasite interactions is important for understanding the consequences of infection on host fitness and population dynamics. In an eight-year survey of the loggerhead sea turtle ( Caretta caretta ) population nesting in Cabo Verde, we determined the spatiotemporal variation of Ozobranchus margoi , a sanguivorous leech best known as a vector for sea turtle fibropapilloma virus. We quantified O. margoi association with turtles’ δ 15 N and δ 13 C stable isotopes to identify where infection occurs. We then measured the influence of infection on reproduction and offspring fitness. We found that parasite prevalence has increased from 10% of the population in 2010, to 33% in 2017. Stable isotope analysis of host skin samples suggests transmission occurs within the host’s feeding grounds. Interestingly, we found a significant interaction between individual size and infection on the reproductive success of turtles. Specifically, small, infected females produced fewer offspring of poorer condition, while in contrast, large, infected turtles produced greater clutch sizes and larger offspring. We interpret this interaction as evidence, upon infection, for a size-dependent shift in reproductive strategy from bet hedging to terminal investment, altering population dynamics. This link between infection and reproduction underscores the importance of using long-term monitoring to quantify the impact of disease dynamics over time.

Dorsal Excitor motor neuron DE-3 in the medicinal leech plays three very different dynamical roles in three different behaviors. Without rewiring its anatomical connectivity, how can a motor neuron dynamically switch roles to play appropriate roles in various behaviors? We previously used voltage-sensitive dye imaging to record from DE-3 and most other neurons in the leech segmental ganglion during (fictive) swimming, crawling, and local-bend escape (Tomina and Wagenaar, 2017). Here, we repeated that experiment, then re-imaged the same ganglion using serial blockface electron microscopy and traced DE-3’s processes. Further, we traced back the processes of DE-3’s presynaptic partners to their respective somata. This allowed us to analyze the relationship between circuit anatomy and the activity patterns it sustains. We found that input synapses important for all the behaviors were widely distributed over DE-3’s branches, yet that functional clusters were different during (fictive) swimming vs. crawling.

Placobdelloides siamensis is a glossiphoniid leech with a short life cycle. In a laboratory setting, ten mature P . siamensis left their host (a turtle) after feeding for approximately three days and initiated copulation. The adults spent 3–4 days gestating before depositing eggs (272.8±62.9 eggs/clutch; range: 186–359 eggs/clutch). The eggs then changed from a creamy white to a creamy brownish color before hatching. Hatching occurred after incubation on the parent's ventral surface for 5–7 days. The transparent brood, with a single pair of red eyes, spent a couple of weeks under the venters of their parents. After this period, they left their parents and grew to maturity in 10–15 days; leeches were considered mature when their color was similar to that of their parents and they performed their first copulation. In addition, the mature leeches survived for 163 days on one feeding.

We investigated decision-making in the leech nervous system by stimulating identical sensory inputs that sometimes elicit crawling and other times swimming. Neuronal populations were monitored with voltage-sensitive dyes after each stimulus. By quantifying the discrimination time of each neuron, we found single neurons that discriminate before the two behaviors are evident. We used principal component analysis and linear discriminant analysis to find populations of neurons that discriminated earlier than any single neuron. The analysis highlighted the neuron cell 208. Hyperpolarizing cell 208 during a stimulus biases the leech to swim; depolarizing it biases the leech to crawl or to delay swimming.