Electrocyte physiology: 50 years later

Abstract

SummaryWeakly electric gymnotiform and mormyrid fish generate and detect weak electric fields to image their worlds and communicate. These multi-purpose electric signals are generated by electrocytes, the specialized electric organ (EO) cells that produce the electric organ discharge (EOD). Just over 50years ago the first experimental analyses of electrocyte physiology demonstrated that the EOD is produced and shaped by the timing and waveform of electrocyte action potentials (APs). Electrocytes of some species generate a single AP from a distinct region of excitable membrane, and this AP waveform determines EOD waveform. In other species, electrocytes possess two independent regions of excitable membrane that generate asynchronous APs with different waveforms, thereby increasing EOD complexity. Signal complexity is further enhanced in some gymnotiforms by the spatio-temporal activation of distinct EO regions with different electrocyte properties. For many mormyrids, additional EOD waveform components are produced by APs that propagate along stalks that connect postsynaptic regions to the main body of the electrocyte. I review here the history of research on electrocyte physiology in weakly electric fish, as well as recent discoveries of key phenomena not anticipated during early work in this field. Recent areas of investigation include the regulation of electrocyte activity by steroid and peptide hormones, the molecular evolution of electrocyte ion channels, and the evolutionary selection of ion channels expressed in excitable cells. These emerging research areas have generated renewed interest in electrocyte function and clear future directions for research addressing a broad range of new and important questions.

Electroreception, electrogenesis and electric signal evolution

“…3–15 Hz in siluriforms (Peters & Bretschneider, ; Peters & Buwalda, ; Zakon, ), 10–30 Hz in mormyroids and gymnotiforms (Zakon, ) and 10 Hz in Xenomystus nigri (Günther 1868) (the only species in the subfamily Xenomystinae; Bullock & Northcutt, ). For reviews of the morphological and physiological diversity and body surface distribution of teleost ampullary electroreceptors, see Zakon (, ), Jørgensen (), Bodznick and Montgomery () and Markham ().…”

A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species

“…There is a rich and rapidly growing literature on the behavior, neuroethology, physiology, energetics, and hormonal basis of EOD generation and EOD plasticity in Brachyhypopomus -focused primarily on the model species B. gauderio, which is reviewed in part by Assad et al ( , 1998, Stoddard (2006), Gavassa et al (2013), Markham (2013), Silva et al (2013), and Salazar et al (2013).…”

The energetics of electric organ discharge generation in gymnotiform weakly electric fish

“…The EOD of weakly electric fish is under the control of a pacemaker nucleus (PN) in the hindbrain whose action potential output shows a one-to-one relationship to the electrical pulses generated by the EO (Fig.2) (see Markham, 2013). The PN consists of pacemaker neurons, which are intrinsic to the nucleus, and relay neurons, whose axons transmit action potentials down the spinal cord, where they activate spinal motor neurons.…”