[Abstract Title]. - Society for Neuroscience

outside the SC was the ipsilateral substantia nigra pars reticulata (SNr), although cells were also
present in the contralateral cMRF. The medial pons was relatively free of label, with a few cells
present ipsilaterally in RIP and the PPRF. However, labeled neurons were found in and around
the contralateral nucleus prepositus hypoglossi (PH). Ventrolaterally, labeled neurons were
found adjacent to the exiting facial nerve. Retrogradely labeled neurons were also present in the
interposed and fastigial portions of the deep cerebellar nuclei. Just a few neurons were present in
the MdRF, and in the cervical spinal cord, labeled neurons were scattered in the ventral horn.
These findings have implications for our understanding of cMRF function. It has been suggested
that the cMRF might provide a conduit to the SC for ascending information on saccade duration
and direction. While some feedback was observed for most of the cMRF‟s downstream targets,
extensive connections to support this proposed function were not found. Instead, the cMRF
seems to receive its greatest input from structures that also supply the SC, like the SNr, ZI, and
PH. If the cMRF reticulotectal projection is inhibitory, then the GABAergic cells in SNr and ZI
appear to be in position to release this inhibition.
Disclosures: S. Warren, None; L. Zhou, None; P.J. May, None.
Poster
263. Eye Movements: Eye and Head Control
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 263.4/DD4
Topic: D.06.c. Eye and head control
Support: EY014263
Title: The macaque central mesencephalic reticular formation sends inhibitory feedback to
ipsilateral tectal neurons
Authors: N. WANG 1 , S. WARREN 1 , *P. J. MAY 2 ;
1 Dept Anat., 2 Dept Anat, Ophthalmol & Neurol, Univ. Mississippi Med. Ctr., Jackson, MS
Abstract: The central mesencephalic reticular formation (cMRF) is believed to play a role in the
control of gaze, as its cells exhibit saccade-related activity and its primary input is from
collaterals of crossed descending tectal fibers. Previously, it has been demonstrated that cMRF
neurons receiving collicular input provide a bilateral projection back to the superior colliculus
(SC), which terminates predominantly in the intermediate gray layer (SGI). However, while it is
presumed that tectoreticular inputs excite cMRF neurons, it is not known whether cMRF
reticulotectal axons provide an excitatory or inhibitory feedback. Nor have the neuronal targets
of this feedback been specified. The present study provides a detailed ultrastructural description