Hindbrain auditory circuits of turtles
-
1
University of Maryland, Biology, United States
-
2
Oberlin College, United States
The hindbrain auditory circuit has been studied extensively across many taxa, but with only a few studies in turtles (Miller and Kasahara, 1979; Belekhova et al, 1984; Browner and Marbey, 1988). In order to clarify the connections in the circuit and clearly describe the cell types, we injected small amounts of neurobiotin directly into either the brainstem or midbrain nuclei of Trachemys scripta elegans or Pseudemys floridana (both amphibious turtles). The brains were sectioned and labeled using ABC reaction followed by SG reaction (both Vector Labs). Labeled neurons were reconstructed using Neurolucida (MBF Bioscience, Williston, VT).
The auditory nerve terminates in both Nucleus Magnocellularis (NM) and Nucleus Angularis (NA). We measured the size of the auditory nerve terminals in NA and NM. NM cells were densely covered with bouton terminals on the soma and neuropil. The mean bouton area was 5.3um ± 2.7um. Boutons were round with a mean form factor of 0.78 ± 0.13. Terminals onto NA were varicose with both boutons and complex terminals. These terminals were less dense, although their mean area was comparable to NM (5.26um ± 2.48um). The NA terminals were less round with a mean form factor of 0.63 ± 0.11.
In the brainstem, we identified 3 nuclei: NM, NA, and Nucleus Laminaris (NL). NM is located at the medial edge of the dorsal part of the brainstem, and ranges from caudal to and overlapping the VIII nerve root. NM contains relatively large, round cells (soma area 169.1 ±60.5 um2) with an average form factor of 0.8±0.1. NM cells are highly varied in dendtrite morphology. NM neurons project across the dorsal midline to terminate in the contralateral NL and send projections to the ipsilateral NL.
NL is located ventral to NM, and contains vertically oriented bitufted cells arranged in a mediolaterally oriented lamina, as well as horizontally oriented bitufted cells dorsal to the lamina. The soma areas of NL neurons were 127.1± 28.4um2. The vertical NL cells were more round (form factor of 0.87±0.03) than the horizontal NL cells (form factor of 0.7±0.1).
The neurons of NA are heterogeneous, and fall into two broad categories: multipolar and stubby. These cells do not vary significantly in soma size or in form factor. The multipolar cells have a total dendrite length of 221.7±99.9 um. The stubby cells have a total dendrite length of 8.15±6.39 um. NA extends further rostral than NM. NA, NL and the superior olive project to torus semicircularis, with input from NA and NL being largely contralateral.
These connections are similar to those observed in the other reptiles, including archosaurs.
References
Belekhova, M. G., Zharskaja, V. D., Khachunts, A. S., Gaidanenko, G. V., & Tumanova, N. L. (1985). Connections of the mesencephalic, thalamic and telencephalic auditory centers in turtles: Some structural bases for audiosomatic interrelations. Journal fur Hirnforschung, 26(2), 127–152.
Browner, R. H., & Marbey, D. (1988). The nucleus magnocellularis in the red-eared turtle, Chrysemys scripta elegans: Eighth nerve endings and neuronal types. Hear Res, 33, 257–272.
Miller, M. R., & Kasahara, M. (1979). The cochlear nuclei of some turtles. J Comp Neur, 185, 221–236.
Keywords:
Anatomy,
auditory,
evolution,
turtle
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for participant symposium and student poster award)
Topic:
Sensory: Audition
Citation:
Willis
KL,
McCormick
CA and
Carr
CE
(2012). Hindbrain auditory circuits of turtles.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00034
Copyright:
The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers.
They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.
The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.
Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.
For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.
Received:
27 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Ms. Katie L Willis, University of Maryland, Biology, College Park, MD, 20742, United States, kwillis@umd.edu