Meeting Abstract

P2.196  Saturday, Jan. 5  Turtle hindbrain auditory circuits WILLIS, K L*; CARR, C E; Univ of Maryland; Univ of Maryland kwillis@umd.edu

Tract tracing techniques were used to describe the connections of the turtle hindbrain auditory nuclei. Dye was injected into the auditory nerve brainstem or midbrain auditory nuclei; brains were maintained in cold, oxygenated ACSF for dye transport (3-5 days). Brains were sectioned and labeled using an ABC followed by SG reaction (Vector Labs). Labeled neurons were reconstructed using Neurolucida (MBF Bioscience). The auditory nerve terminated in both Nucleus Magnocellularis (NM) and Nucleus Angularis (NA). Single auditory nerve fibers bifurcate to NM and NA. In NM, auditory nerve terminals formed dense bouton terminals on the soma and neuropil. Nerve terminals in NA were varicose, and formed both boutons and complex endings. They were also less dense, although their mean area was comparable to terminals in NM. In the brainstem, NM contained relatively large, round cells. It was located at the medial edge of the dorsal brainstem, and extended from caudal to and overlapping with the VIII nerve root. NM cells were morphologically variable, and projected to both the ipsilateral nucleus lamiaris (NL) and across the dorsal midline to the contralateral NL. NL was located ventral to NM, and contained vertically-oriented bitufted cells arranged in a mediolaterally oriented lamina, as well as horizontally-oriented bitufted cells dorsal to the lamina. The vertical NL cells were more round than the horizontal NL cells. NL projects to torus semicircularis (TS). NA neurons were heterogeneous, and fell into two broad categories on the basis of dendritic morphology: multipolar and stubby. NA neurons did not otherwise vary significantly in soma size or form factor. NA extended further rostral than NM. NA, NL and the superior olive projected to TS, with input from NL and NA being largely contralateral. NA also received descending projections back from TS.