Collateralization of the tectonigral projection with other major output pathways of superior colliculus in the rat
Article first published online: 20 DEC 2006
Copyright © 2006 Wiley-Liss, Inc.
Journal of Comparative Neurology
Volume 500, Issue 6, pages 1034–1049, 20 February 2007
How to Cite
Coizet, V., Overton, P. G. and Redgrave, P. (2007), Collateralization of the tectonigral projection with other major output pathways of superior colliculus in the rat. J. Comp. Neurol., 500: 1034–1049. doi: 10.1002/cne.21202
- Issue published online: 20 DEC 2006
- Article first published online: 20 DEC 2006
- Manuscript Accepted: 28 AUG 2006
- Manuscript Revised: 23 AUG 2006
- Manuscript Received: 30 JUN 2006
- Wellcome Trust. Grant Numbers: 068021, 062742
- basal ganglia;
- substantia nigra;
Dopaminergic (DA) neurons exhibit a short-latency, phasic response to unexpected, biologically salient stimuli. The superior colliculus (SC) is also sensitive to such stimuli and sends a projection directly to DA-containing regions of the ventral midbrain. Recent evidence suggests that the SC is a critical relay for transmitting short-latency visual information to DA neurons. An important question is whether the ventral midbrain is an exclusive target of tectonigral neurons, or whether the tectonigral projection is a collateral branch of other tectofugal pathways. Double-label retrograde anatomical tracing techniques were used to address this issue. Injections of either Diamidino Yellow or Fluorogold into substantia nigra pars compacta (SNc) were combined with larger injections of True Blue into one of the following efferent projections of the SC: 1) target regions of the ipsilateral ascending projection to the thalamus; 2) the crossed descending tecto-reticulo-spinal pathway; 3) target structures of the ipsilateral descending projection; and 4) the contralateral superior colliculus. Moderate numbers of double-labeled neurons were observed following combined injections into substantia nigra and individual nuclei in the thalamus (ventromedial nucleus, 21.3%; central lateral, 18.4%; parafasicular nucleus 6.0%). Much less double-labeling was associated with injections into either of the descending projections (crossed, 1.0–3.2%; uncrossed, 0.2–2.7%) or the contralateral SC (0.7–1.9%). These results suggest: i) the SC may provide a coordinated input concerning the occurrence of unpredicted sensory events to both the substantia nigra and striatum (via the thalamus); and ii) few gaze-related motor signals are simultaneously relayed to DA-containing regions of the ventral midbrain. J. Comp. Neurol. 500:1034–1049, 2007. © 2006 Wiley-Liss, Inc.