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Labelling of electroreceptive afferents in a gymnotoid fish by intracellular injection of HRP: The mystery of multiple maps


Physiologically identified primary electroreceptive afferents in the gymnotiform fish,Eigenmannia, were labelled by intracellular injection of horseradish peroxidase (HRP) in order to determine their termination sites in the posterior lateral line lobe (PLLL) (Fig. 1). For each terminal field we mapped the location of the associated receptor pore on the body surface and found:

  1. 1)

    Ampullary units project in a somatotopically ordered manner to the medial PLLL.

  2. 2)

    Tuberous units, both P- and T-types, project in a somatotopically ordered manner to three separate regions of the PLLL, called central-medial, central-lateral and lateral (Figs. 2–4). Each tuberous unit projects to all three maps and the projections of P- and T-units are in somatotopic register.

In addition to electroreceptive units, mechanoreceptive units were also encountered in the anterior lateral line nerve ganglion, but their central projections were found outside of the PLLL, in the anterior lateral line lobe (ALLL) and in the eminentia granularis. This finding is in accordance with the notion of modality-specific separation of central projections, forwarded by Maler et al. (1974).

Tuberous electroreceptive afferents have larger somata and faster nerve conduction the further their receptor pores are located towards the tail end of the body (Fig. 5, 6). The faster nerve conduction of afferents from more distant regions of the body surface minimizes temporal disparity in the arrival of spikes linked to synchronous electrical events in widely separated regions of the body surface.

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anterior lateral line lobe


electric organ discharge


horseradish peroxidase


posterior lateral line lobe


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Heiligenberg, W., Dye, J. Labelling of electroreceptive afferents in a gymnotoid fish by intracellular injection of HRP: The mystery of multiple maps. J. Comp. Physiol. 148, 287–296 (1982).

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  • Body Surface
  • Lateral Line
  • Central Projection
  • Electrical Event
  • Terminal Field