405 Ann. N.Y. Acad. Sci. 956: 405–408 (2002). © 2002 New York Academy of Sciences. Midbrain Reticular Formation Circuitry Subserving Gaze in the Cat PAUL J. MAY, a SUSAN WARREN, a BINGZHONG CHEN, b FRANCES J.R. RICHMOND, c AND ETIENNE OLIVIER d a Departments of Anatomy, Neurology and Ophthalmology, University of Mississippi Medical Center, Jackson, Missisippi 39216, USA b Department of Anatomy and Neurobiology, University of Maryland at Baltimore, Baltimore, Maryland 21201, USA c Department of Pharmacy and the Alfred E. Mann Institute of Biomedical Engineering, University of Southern California, Los Angeles, California 90033, USA d Laboratory of Neurophysiology, University of Louvain School of Medicine, Brussels, B-1200 Belgium KEYWORDS: oculomotor; gaze; reticulospinal; reticulotectal Physiological experiments in primates have identified a region of the midbrain teg- mentum, the central mesencephalic reticular formation (cMRF), which plays a role in gaze control. 1 Specifically, stimulation of this region produces horizontal sac- cades; recordings from this region reveal neurons with saccade-related activity; and chemical inactivation of this region produces contralateral head tilt and spontaneous saccades. 1,2 More rostral regions of the midbrain reticular formation (MRF), just lateral to the interstitial nucleus of Cajal (InC), have neurons with vertical move- ment fields, and chemical inactivation of this region produces hypometric vertical saccades. 2 In the macaque, there is an extensive overlap of tectoreticular terminals and reticulotectal cells in the region corresponding to the cMRF. 3 The present study explored whether an area similar to the cMRF is present in the cat by analyzing the distribution of MRF neurons targeting the superior colliculus (SCol) and cervical spinal cord. These studies were carried out in eight adult cats under approved protocols ad- hering to the NIH guidelines. In the single-injection animals, 0.1–0.5 μl of a 10% BDA was injected into either the SCol or cervical cord. The SCol was approached dorsally, by aspirating the overlying cortex, while the cervical cord (C1) was ap- proached through the foramen magnum. In the dual-tracer animals, both approaches were used to inject 5% Fast Blue into the SCol and 5% Fluoro-Gold into C1 (0.5 μl each). Standard perfusion and processing techniques were used. 3 Address for correspondence: Dr. Paul May, Department of Anatomy, University of Missis- sippi Medical Center, 2500 N. State Street, Jackson, MS 39216. Voice: 601-984-1662; fax: 601-984-1655. pjm@anat.umsmed.edu