Neuronal galvanotropism is the ability to direct the outgrowth of

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

al processes through the use of an

extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

. This technique has been researched since the late 1920s and has been shown to direct the formation of both axonic and

dendritic Dendrite derives from the Greek word "dendron" meaning ( "tree-like"), and may refer to: Biology *Dendrite, a branched projection of a neuron *Dendrite (non-neuronal), branching projections of certain skin cells and immune cells Physical * Dendr ...

processes in

cell culture Cell culture or tissue culture is the process by which cells are grown under controlled conditions, generally outside of their natural environment. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. This te ...

. It is only possible to direct outgrowth of

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...

preparations at this point. In vitro preparations involve the use of a culture dish, in which there is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

-specific neuronal

growth factor A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation. Usually it is a secreted protein or a steroid hormone. Growth factors are important for regu ...

. Neurons are removed from a chosen animal, plated onto the dish and allowed to grow (often kept in incubation). The application of an extracellular electric field shows that the cells will grow processes in a direction that demonstrates the direction of the applied electric field. This could be either in the direction of the

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

, depending on the type of substrate the cells are plated onto. The mechanism underlying this behavior is thought to involve the effect of the electric field on receptors and

membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...

s on the cell's surface. These charged proteins would experience an electrophoretic force pulling them toward the oppositely charged

pole Pole may refer to: Astronomy *Celestial pole, the projection of the planet Earth's axis of rotation onto the celestial sphere; also applies to the axis of rotation of other planets *Pole star, a visible star that is approximately aligned with the ...

of the electric field. Most of these membrane

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s are negatively charged, but the growth, when observed appears to be directed to the negative pole (cathode). This is a strange behavior that can only be accounted for by electroosmotic effects. Positively charged

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s outside the cell experience a force towards the cathode. There is a flux of these ions outside the cell and the shear force of solution movement is thought to pull the

neurite A neurite or neuronal process refers to any projection from the cell body of a neuron. This projection can be either an axon or a dendrite. The term is frequently used when speaking of immature or developing neurons, especially of cells in culture ...

in the cathodal direction. Also, the electric field may depolarize the cell near the cathodal side opening voltage-gated

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

channels and allowing calcium ions to enter the cell. Calcium is widely believed to be a factor in neurite outgrowth. This theory has been challenged in a recent paper by scientists at

Purdue University Purdue University is a public land-grant research university in West Lafayette, Indiana, and the flagship campus of the Purdue University system. The university was founded in 1869 after Lafayette businessman John Purdue donated land and money ...

. Recent studies also involve differentiating between the effect of current on growth direction and the effect of a simple electric field. Studies involving AC and DC fields are also being conducted. This is currently a highly researched topic, in which many

neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

labs around the world are attempting to be the first to have a feasible method of directing outgrowth. Potential applications involve the direction and regeneration of severed

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

s although these would only become available in the very distant future. This technique would also be useful in the study of neuronal networks. Neurites could be directed toward each other over large distances and allowed to form

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

s. Networks of hundreds or thousands of cells could be constructed and studied.

References

{{Reflist Electrophysiology