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Topographic projections to the visual cortex from the basal forebrain in the rat
1Division of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013.
Brain Research
|October 27, 1987
Summary
Cholinergic neurons in the basal forebrain project to the visual cortex. This study maps this projection, revealing a medial-to-lateral organization within the visual cortex based on basal forebrain neuron location.
Area of Science:
- Neuroscience
- Anatomy
Background:
- Cholinergic neurons in the basal forebrain project widely throughout the neocortex.
- The topographic organization of these projections to specific cortical areas is not fully understood.
Purpose of the Study:
- To determine the topographic organization of the basal forebrain cholinergic projection to the rat visual cortex.
- To investigate the relationship between specific basal forebrain nuclei and visual cortical areas.
Main Methods:
- Wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injections into specific layers of visual cortical areas (17, 18a, 18b) in Long-Evans hooded rats.
- Retrograde neuronal tracing to identify the origin of projections within the basal forebrain.
Main Results:
- Injections into area 18a labeled neurons primarily in caudal basal forebrain (e.g., basal nucleus of Meynert).
- Injections into area 18b labeled neurons mainly in rostral basal forebrain (e.g., horizontal limb of the diagonal band).
- Area 17 injections showed patterns mirroring adjacent extrastriate areas, with lateral area 17 projecting to caudal basal forebrain and medial area 17 to rostral basal forebrain.
Conclusions:
- The cholinergic corticopetal projection to the visual cortex exhibits a medial-to-lateral organization.
- Specific regions of the basal forebrain project differentially to distinct sectors of the visual cortex.