Electric Fish I) Electroreception

A) Receptors – modified hair cells – sense electric fields generated by other animals or objects in environment

B) Weakly electric fish – emit electric field (electric organ) and can sense distortions in this field produced by objects in external environment

C) Strongly electric fish – electric eels - predation (Africa) (South America) II. Physiology A) Electric Field Characteristics

Constant Voltage

Current Flow

Undistorted electric field

Insulator Conductor

Heiligenberg, J Comp Physiol 87:137-164, 1973

Distorted Electric Field B) Electric Organ

1) Modified Muscle Cells – stacked end to end 2) Generating an Electric Field (Electric Organ Discharge – EOD)

+70

-80 0 excitable -80

inexcitable -150 0

-150 -80 -80

0 0 2) Generating an Electric Field

+70

-80 0 excitable -300 -80 -230

inexcitable -150 0

-150 -80 -80

0 0 3) Electroreceptors

a) Modified hair cells – sensitive to amount of current across skin

b) Two types –

i) ampullary organ – in all fish that have electrosensation Lateral Line Nerve ii) tuberous organ – only in fish that generate an EOD

c) Cranial Nerve – Lateral Line Nerve III. Anatomy A) Lateral Line nerve – near 8th cranial nerve B) Electrosensory lateral line lobe – C) Torus semicircularis (homologous to inferior colliculus) 1) projection to tectum and tegmentum D) Nucleus electrosensorius E) Prepacemaker nucleus F) Pacemaker nucleus G) Electromotor neurons (ventral horn of spinal cord) IV Electrosensation – ampullary receptors in weakly electric fish

A) The problem – how to distinguish external electric field from the one generated by the fish?

1) Proposed solution – reafference – efference copy – corollary discharge

B) Experiment – CC Bell and colleagues

1) Record from ELL

2) Curarize animal – record blocks EOD

3) Record from motoneuron – command signal - C

4) Generate artificial electric field - STIM

Bell, J Neurophysiol 47: 1043-156, 1982 C) The Result

Command Only Invert Electric Field

Paired

Later

Command Only

Later again 1) Motor command and sensory consequence must be in temporal proximity