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A central pacemaker that underlies the production of seasonal and sexually dimorphic social signals: anatomical and electrophysiological aspects

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Abstract

Our long-term goal is to approach the understanding of the anatomical and physiological bases for communication signal diversity in gymnotiform fishes as a model for vertebrate motor pattern generation. Brachyhypopomus gauderio emits, in addition to its electric organ discharge (EOD) at basal rate, a rich repertoire of rate modulations. We examined the structure of the pacemaker nucleus, responsible for the EOD rate, to explore whether its high output signal diversity was correlated to complexity in its neural components or regional organization. We confirm the existence of only two neuron types and show that the previously reported dorsal–caudal segregation of these neurons is accompanied by rostral–caudal regionalization. Pacemaker cells are grouped dorsally in the rostral half of the nucleus, and relay cells are mainly ventral and more abundant in the caudal half. Relay cells are loosely distributed from the center to the periphery of the nucleus in correlation to somata size. Our findings support the hypothesis that regional organization enables a higher diversity of rate modulations, possibly offering distinct target areas to modulatory inputs. Since no anatomical or electrophysiological seasonal or sexual differences were found, we explored these aspects from a functional point of view in a companion article.

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Abbreviations

EO:

Electric organ

EOD:

Electric organ discharge

Cd:

Caudal

CV:

Coefficient of variation

Dr:

Dorsal

EBST:

Electromotor bulb spinal tract

PM:

Pacemaker neurons

PN:

Pacemaker nucleus

PPNc:

Diencephalic prepacemaker chirp region

R:

Relay neurons

Rt:

Rostral

sPPN:

Sublemniscal prepacemaker

Vt:

Ventral

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Acknowledgments

We wish to thank Omar Trujillo, Kent Dunlap and Phil Stoddard for their generous revision and suggestions to our manuscript. We thank Catherine Carr for her valuable comments and Amalia Dutra, Hugo Peluffo and Angel Caputi who very kindly donated antibodies used in this study. We are grateful to Rossana Perrone and Ana Silva who performed the behavioral experiments and participated in all field trips. All procedures with animals were performed in accordance with the guidelines of the local ethical committee (Comisión Honoraria de Experimentación Animal, CHEA, Universidad de la República, Uruguay). This research was financed by PDT 043 and PEDECIBA.

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Correspondence to Laura Quintana.

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3D representation of the PN of Brachyhypopomus gauderio. In a frontal view the PN is tilted slightly counter clockwise. Rostral: indicated with a star. Red pacemaker cells, cyan relay cells.

3D representation of the PN of Brachyhypopomus gauderio. In a frontal view the PN is tilted slightly counter clockwise. Rostral: indicated with a star. Red pacemaker cells, cyan relay cells.

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Quintana, L., Pouso, P., Fabbiani, G. et al. A central pacemaker that underlies the production of seasonal and sexually dimorphic social signals: anatomical and electrophysiological aspects. J Comp Physiol A 197, 75–88 (2011). https://doi.org/10.1007/s00359-010-0588-3

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Keywords

  • Electric fish
  • Medullary nucleus
  • Communication
  • Brachyhypopomus gauderio
  • CPG