Morphology and topographical organization of the retrospleniocollicular connection: a pathway to relay contextual information from the environment to the superior colliculus.
The retrospleniocollicular connection is of interest because it constitutes one link between the limbic system, which is considered the anatomical substrate of emotional experience, and the superior colliculus (SC), which mediates approach and avoidance behavior. The morphology, topography, and origin of the retrospleniocollicular connections were studied by using anterograde [biotinylated dextranamine 10,000 (BDA)] and retrograde [Fluoro-Gold (FG)] tracers. After BDA injections involving retrosplenial granular and agranular cortices, terminal fibers innervating all collicular layers except stratum griseum superficiale were found throughout nearly the entire colliculi. Axons branched within restricted portions of the dorsoventral collicular axis with variable morphologies, suggesting functional heterogeneity. Terminal fields originating in anterior and posterior regions of the retrosplenial cortex were preferentially distributed in laterodorsal and medioventral collicular regions, respectively, but there were also large, densely innervated regions in which the terminal fields overlapped. FG injections in the SC confirmed the retrospleniocollicular topography and demonstrated that this connection originated from layer V pyramidal cells of all retrosplenial areas. The distribution of retrospleniocollicular boutons was related to that of the AChE modules, which are associated with connections in the intermediate layers of the SC. In lateral portions of the SC intermediate layers, most retrospleniocollicular boutons were found in medium AChE stained regions, whereas in medial portions, they terminated in AChE-poor domains. The present results demonstrate that the retrosplenial cortex is the origin of a broad and dense network of axonal branches that may modulate SC-mediated motor and physiological responses involved in emotional behavior.
García Del Caño
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Department of Neuroscience, Faculty of Medicine, University of the Basque Country, Bizkaia, Spain.
Gerrikagoitia
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Martínez-Millán
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D000110:Acetylcholinesterase / Q000378:metabolism; D000344:Afferent Pathways / Q000201:enzymology / Q000502:physiology / Q000648:ultrastructure; D000818:Animals; D001931:Brain Mapping; D004777:Environment; D006651:Histocytochemistry / Q000379:methods; D008297:Male; D009411:Nerve Endings / Q000201:enzymology / Q000648:ultrastructure; D009424:Nervous System Physiological Phenomena; D051381:Rats / Q000502:physiology*; D017207:Rats, Sprague-Dawley; D013154:Spleen / Q000294:innervation*; D013194:Staining and Labeling; D013477:Superior Colliculi / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology; D009626:Terminology as Topic
D000110:Acetylcholinesterase