Ampullae of Lorenzini (singular ''Ampulla'') are

electroreceptor Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...

s, sense organs able to detect electric fields. They form a network of mucus-filled pores in the skin of cartilaginous fish (

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

s, rays, and

chimaera Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. At ...

s) and of basal actinopterygians (bony fishes) such as reedfish,

sturgeon Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous, and are descended from other, earlier acipenseriform fish, which date back to the Early ...

, and

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

. They are associated with and evolved from the mechanosensory lateral line organs of early vertebrates. Most bony fishes and terrestrial vertebrates have lost their ampullae of Lorenzini.

History

Ampullae were initially described by Marcello Malpighi and later given an exact description by the Italian physician and ichthyologist Stefano Lorenzini in 1679, though their function was unknown. Electrophysiological experiments in the 20th century suggested a sensibility to

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

, mechanical pressure, and possibly salinity. In 1960 the ampullae were identified as specialized receptor organs for sensing

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 ...

s. One of the first descriptions of calcium-activated potassium channels was based on studies of the ampulla of Lorenzini in the

skate Skate or Skates may refer to: Fish * Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongi ...

Evolution

Ampullae of Lorenzini are physically associated with and evolved from the mechanosensory

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

organs of early

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

s. Passive

electroreception Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to st ...

using ampullae is an

ancestral trait In phylogenetics, a primitive (or ancestral) character, trait, or feature of a lineage or taxon is one that is inherited from the common ancestor of a clade (or clade group) and has undergone little change since. Conversely, a trait that appea ...

in the vertebrates, meaning that it was present in their last common ancestor. Ampullae of Lorenzini are present in

cartilaginous fish Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...

es (

s, rays, and

s),

es,

bichir Bichirs and the reedfish comprise Polypteridae , a family of archaic ray-finned fishes and the only family in the order Polypteriformes .Helfman GS, Collette BB, Facey DE, Bowen BW. 2009. The Diversity of Fishes. West Sussex, UK: Blackwell Pu ...

coelacanth The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...

paddlefish Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their titular elong ...

es, aquatic

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

s, and

caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics o ...

s. Ampullae of Lorenzini appear to have been lost early in the

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

of bony fishes and

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s, though the evidence for absence in many groups is incomplete and unsatisfactory.

Anatomy

Each ampulla is a bundle of sensory cells containing multiple

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 ...

fibres in a sensory bulb (the endampulle) in a

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...

sheath, and a gel-filled canal (the ampullengang) which opens to the surface by a pore in the skin. The gel is a

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glyco ...

-based substance with the same resistivity as seawater, and electrical properties similar to a

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...

. Pores are concentrated in the skin around the snout and mouth of sharks and rays, as well as the anterior nasal flap, barbel, circumnarial fold and lower labial furrow. Canal size typically corresponds to the body size of the animal but the number of ampullae remains the same. The canals of the ampullae of Lorenzini can be pored or non-pored. Non-pored canals do not interact with external fluid movement but serve a function as a tactile receptor to prevent interferences with foreign particles. File:Lorenzini pores on snout of tiger shark.jpg, Pores of ampullae of Lorenzini in snout of tiger shark File:Electroreceptors in a sharks head.svg, The electroreceptive ampullae of Lorenzini (red dots) evolved from the mechanosensory

organs (gray lines) of early vertebrates. File:Ampullae of Lorenzini inner side.jpg, Inner view of ampullae of Lorenzini. The bulbs appear as many pale translucent spheres on either side of the midline.

Electroreception

The ampullae detect electric fields in the water, or more precisely the potential difference between the voltage at the skin pore and the voltage at the base of the electroreceptor cells. A positive pore stimulus decreases the rate of nerve activity coming from the electroreceptor cells, while a negative pore stimulus increases the rate. Each ampulla contains a single layer of receptor cells, separated by supporting cells. The cells are connected by apical tight junctions so that no current leaks between them. The apical faces of the receptor cells have a small surface area with a high concentration of

voltage-dependent calcium channel Voltage-gated calcium channels (VGCCs), also known as voltage-dependent calcium channels (VDCCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (''e.g.'', muscle, glial cells, neurons, etc.) with a permea ...

s (which trigger depolarisation) and calcium-activated potassium channels (for repolarisation afterwards). Because the canal wall has a very high resistance, all the voltage difference between the pore of the canal and the ampulla is dropped across the 50 micron-thick receptor epithelium. Because the basal membranes of the receptor cells have a lower resistance, most of the voltage is dropped across the excitable apical faces which are poised at the threshold. Inward calcium current across the receptor cells depolarises the basal faces, causing a large

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells ...

, a wave of depolarisation followed by repolarisation (as in a nerve fibre). This triggers presynaptic calcium release and release of excitatory

transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...

onto the afferent nerve fibres. These fibres signal the size of the detected electric field to the fish's brain. The ampulla contains large conductance calcium-activated potassium channels ( BK channels). Sharks are much more sensitive to electric fields than electroreceptive freshwater fish, and indeed than any other animal, with a threshold of sensitivity as low as 5 nV/cm. The collagen jelly, a

hydrogel A hydrogel is a crosslinked hydrophilic polymer that does not dissolve in water. They are highly absorbent yet maintain well defined structures. These properties underpin several applications, especially in the biomedical area. Many hydrogels ar ...

, that fills the ampullae canals has one of the highest proton conductivity capabilities of any biological material. It contains

keratan sulfate Keratan sulfate (KS), also called keratosulfate, is any of several sulfated glycosaminoglycans (structural carbohydrates) that have been found especially in the cornea, cartilage, and bone. It is also synthesized in the central nervous system whe ...

in 97% water, and has a conductivity of about 1.8 mS/cm. All animals produce an electrical field caused by muscle contractions; electroreceptive fish may pick up weak electrical stimuli from the muscle contractions of their prey. The sawfish has more ampullary pores than any other cartilaginous fish, and is considered an electroreception specialist. Sawfish have ampullae of Lorenzini on their head, ventral and dorsal side of their rostrum leading to their gills, and on the dorsal side of their body.

Magnetoreception

Ampullae of Lorenzini also contribute to the ability to receive geomagnetic information. As magnetic and electrical fields are related, magnetoreception via

electromagnetic induction Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field. Michael Faraday is generally credited with the discovery of induction in 1831, and James Cle ...

in the ampullae of Lorenzini is possible. Many cartilaginous fish respond to artificially generated magnetic fields in association with food rewards, demonstrating their capability. Magnetoreception may explain the ability of sharks and rays to form strict migratory patterns and to identify their geographic location.

Temperature sense

The mucus-like substance inside the tubes may perhaps transduce temperature changes into an electrical signal that the animal may use to detect temperature gradients.

References

{{DEFAULTSORT:Ampullae Of Lorenzini Cartilaginous fish Chimaeriformes Fish anatomy Rays Sensory organs in animals Sharks