The Journal of Neuroscience, February 1, 1998, 18(3):1171-1185
Neural Substrates for Species Recognition in the Time-Coding
Electrosensory Pathway of Mormyrid Electric Fish
Matthew A.
Friedman and
Carl D.
Hopkins
Section of Neurobiology and Behavior, Cornell University, Ithaca,
New York 14853
Mormyrid electric fish have species- and sex-typical electric organ
discharges (EODs). One class of tuberous electroreceptors, the
knollenorgans, plays a critical role in electric communication; one
function is species recognition of EOD waveforms. In this paper, we
describe cell types in the knollenorgan central pathway, which appear
responsible for analysis of the temporal patterns of spikes encoded by
the knollenorgans in response to EOD stimuli. Secondary sensory neurons
in the nucleus of the electrosensory lateral line lobe (NELL) act as
relays of peripheral responses. They fire a single phase-locked spike
to an outside positive-going voltage step. Axons from the NELL project
to the toral nucleus exterolateralis pars anterior (ELa). Immediately
after they enter the ELa, they send collaterals to terminate on one to
three ELa large cells and then continue in a lengthy neuronal pathway
that traverses the ELa several times. After a path length of up to 5 mm, the NELL axon terminates on as many as 70 ELa small cells. Thus the
large cells appear to be excited first, followed by the small cells,
with the intervening length of the axon serving as a delay line. The
large cells also respond with phase-locked spikes to voltage steps.
Large cell axons extend for ~1 mm and terminate on several small
cells within the ELa. The terminals are known to be GABAergic inputs
and are presumed inhibitory. We propose that small cells receive direct
inhibition from large cells and delayed excitation from NELL axons. The
small cells may act as anti-co-incidence detectors to analyze the
temporal structure of the EOD waveform.
Key words:
mormyrid; electric fish; knollenorgan; electroreception; time-coding; delay line; co-incidence detector
Copyright © 1998 Society for Neuroscience 0270-6474/98/1831171-15$05.00/0
