Descending projections from the cortical accommodation area in the cat

Results in previous studies indicated that the lateral suprasylvian (LS) area, the cortical area surrounding the middle suprasylvian sulcus (Mss) of the cat, has important roles in the control of accommodation. The current study was conducted to investigate descending projections from the accommodation-related area in the LS area to the brainstem.

Wheat germ agglutinin-horseradish peroxydase (WGA-HRP) was injected into the accommodation-related area in the pretectum or in the rostral superior colliculus (SC) of the cat. These regions are thought to be involved in the control of accommodation based on results of previous studies. The authors investigated locations of retrogradely labeled cells in the LS area. In addition, the authors compared amplitudes of accommodative responses evoked by stimulation of the LS area before and after neuronal activities in the rostral SC were inhibited by the injection of muscimol (gamma-aminobutyric acid agonist) into the accommodation-related area in the rostral SC.

After injections of WGA-HRP into the accommodation-related area in the rostral SC, retrogradely labeled cells were observed in the lower part of the medial bank of the Mss, which corresponded to the accommodation-related area in the LS area. Conversely, after injections of WGA-HRP into the accommodation-related area in the pretectum, retrogradely labeled cells were seen in the upper part of the medial bank of the Mss, which did not correspond to the accommodation-related area in the LS area. Accommodation responses evoked by stimulation of the LS area were abolished by the injection of muscimol into the accommodation-related area in the rostral SC.

These findings suggest that accommodation-related signals from the LS area mainly project to the rostral SC, but not to the pretectum.