Ion Homeostasis in the Leech: Contribution of Organic Anions

Interfacing electronics with neural tissue is crucial for understanding complex biological functions, but conventional bioelectronics consist of rigid electrodes fundamentally incompatible with living systems. The difference between static solid-state electronics and dynamic biological matter makes seamless integration of the two challenging. To address this incompatibility, we developed a method to dynamically create soft substrate-free conducting materials within the biological environment. We demonstrate in vivo electrode formation in zebrafish and leech models, using endogenous metabolites to trigger enzymatic polymerization of organic precursors within an injectable gel, thereby forming conducting polymer gels with long-range conductivity. This approach can be used to target specific biological substructures and is suitable for nerve stimulation, paving the way for fully integrated, in vivo–fabricated electronics within the nervous system.

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“…S13). As in zebrafish brains, lactate concentrations in leeches are higher than those of glucose ( 31 ).…”

Section: Ex Vivo Polymerization Around the Nervous System Of Medicina...mentioning

confidence: 99%

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

Strakosas

Biesmans

Abrahamsson

et al. 2023

Science

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A detached branch stops being recognized as self by other branches of a neuron

Wang

Macagno

1998

J. Neurobiol.

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The multiple peripheral projections of a single leech mechanosensory neuron form individual arbors that do not overlap at all with each other, a phenomenon that has been termed “self‐avoidance” (Yau, 1976; Kramer and Stent, 1985). This is in marked contrast to the peripheral arbors of adjacent segmental homologues, which partially overlap with each other at their boundaries in target areas of the body wall (Nicholls and Baylor, 1968; Gan and Macagno, 1995). How a neurite differentiates between sibling neurites of the same cell and those of a homologue is not known, but possible mechanisms include the recognition of surface markers of neuronal identity or the detection of cell‐specific patterns of activity. In order to test whether this self‐recognition requires a neurite to be in direct communication with its soma, we used a laser microbeam to sever a branch of a dye‐filled pressure‐sensitive (P) neuron in an intact leech embryo. Time‐lapse observations of the P cell arbor in the living, unanesthetized, animal for up to 24 h following the surgery showed that the detached branch continued to show dynamic growth behavior throughout the period of observation. However, the detached branch ceased being avoided by the rest of the cell within a few hours, other, attached branches of the neuron overgrowing its territory and directly overlapping with it. Our experiments provide direct evidence for the existence of strong growth‐inhibiting interactions between sibling processes, and indicate that self‐avoidance by the growing neurites of a cell requires physical continuity between these neurites. © 1998 John Wiley & Sons, Inc. J Neurobiol 35: 53–64, 1998

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External CO₂ levels influence energy yielding metabolic pathways under hypoxia in the leech, Hirudo medicinalis

Hildebrandt

1992

J. Exp. Zool.

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Medicinal leeches, Hirudo medicinalis L., were exposed to hypocapnic (nominal pC02 0.0 kPa) or hypercapnic (pC0, 1.3 kPa) hypoxia (p02 2.0 kPa) for up to 4 days. Changes in blood concentrations and tissue content of organic acids were measured.In the early phase of hypercapnic hypoxia leeches accumulated mainly succinate, and the normally high malate concentrations in blood and tissue were reduced concomitantly. Between 2 and 24 h of hypoxia the animals started to produce propionate which is the major end-product of this type of hypoxia. Only low concentrations of lactate were found in blood and tissue. During the initial phase of hypocapnic hypoxia an accumulation of succinate was also observed, but at a higher rate than during hypercapnic hypoxia. Subsequently, propionate was also produced. Between 24 and 48 h of hypocapnic hypoxia the concentrations of succinate in blood and tissue decreased rapidly and lactate appeared as an end-product of anaerobic metabolism.The results indicate that, in leeches under "environmental" hypoxia, the external concentration of carbon dioxide affects the pathway of carbohydrate metabolism resulting in either succinatelpmpionate production or in lactate accumulation. 0 1992 Wiley-Liss, Inc.Many aquatic animals have to cope with situations of limited oxygen availability in their habitat. To sustain longer periods of severe hypoxia it is essential to maintain energy supply from metabolic pathways which are not dependent on the presence of oxygen. Transition to anaerobic metabolism and, in many cases, a decrease in metabolic rate occur when the oxygen partial pressure of the environment drops below critical values (Zebe and Schottler, '86; Hochachka, '86).In many animals under hypoxic conditions the degradation of glycogen to lactate via the EmbdenMeyerhof-Parnas pathway (anaerobic glycolysis) is the main energy-yielding process. In contrast, especially in those animals which are obligate anaerobes or sustain longer periods of "environmental" hypoxia (e.g., parasitic helminths in the intestine of vertebrates, some molluscs, and annelids), glycogen is degraded to succinate and propionate (Hochachka and Mustafa, '72) which is, in terms of ATP production, a more efficient metabolic pathway than lactate generation (Schottler, '77; Schroff and Zebe, '80).Succinate production in anaerobic annelids requires the carboxylation of phosphoenolpyruvate (PEP) which is catalyzed by phosphoenolpyruvate carboxykinase (PEPCK) (Hoffmann et al., '79). Another enzyme, pyruvate kinase (PK), competes for PEP at this metabolic branchpoint converting PEP to pyruvate, which is a n intermediate metabolite for lactate production. The direction of carbohydrate metabolism a t the level of PEP is determined by the activity ratio of PEPCK to PK as confirmed by the observation that specific inhibition of the PEPCK in hypoxic Arenicola marina resulted in lactate accumulation (Schottler and Wienhausen, '81) although lactate is not a regular end-product of anaerobiosis in this species. Various mechanisms have...

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Ion Homeostasis in the Leech: Contribution of Organic Anions

Cited by 15 publications

References 15 publications

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

A detached branch stops being recognized as self by other branches of a neuron

External CO₂ levels influence energy yielding metabolic pathways under hypoxia in the leech, Hirudo medicinalis

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Ion Homeostasis in the Leech: Contribution of Organic Anions

Cited by 15 publications

References 15 publications

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

A detached branch stops being recognized as self by other branches of a neuron

External CO2 levels influence energy yielding metabolic pathways under hypoxia in the leech, Hirudo medicinalis

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Product

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External CO₂ levels influence energy yielding metabolic pathways under hypoxia in the leech, Hirudo medicinalis