Internal connectivity of the homing pigeon (Columba livia) hippocampal formation: an anterograde and retrograde tracer study.
The avian hippocampal formation (HF) is a structure necessary for learning and remembering aspects of environmental space. Therefore, understanding the connections between different HF regions is important for determining how spatial learning processes are organized within the avian brain. The prevailing feed-forward, trisynaptic internal connectivity of the mammalian hippocampus and its importance for cognition have been well described, but the internal connectivity of the avian HF has only recently been investigated. To examine further the connectivity within the avian HF, small amounts of cholera toxin subunit B, primarily a retrograde tracer (n = 15), or biotinylated dextran amine, primarily an anterograde tracer (n = 10), were injected into localized regions of the HF. Examination of the immunohistochemically labeled tissue showed projections from extrinsic sensory processing areas into dorsolateral HF and the dorsal portion of the dorsomedial HF (DMd). DMd in turn projected into the medial (VM) and lateral (VL) ventral cell layers. A projection from VM into VL was found, and together these areas and DM provided input into the contralateral ventral cell layers. Ipsilaterally, a ventral portion of dorsomedial HF (DMv) received input from VL and VM. From DMv, projections exited HF laterally. The highlighted projections formed a discernible feed-forward processing network through the avian HF that resembled the trisynaptic circuit of the mammalian HF.
Kahn
Meghan C
MC
Department of Psychology and J P Scott Center for Neuroscience, Mind and Behavior, Bowling Green State University, Bowling Green, Ohio 43403, USA. kahnmc@bgnet.bgsu.edu
Hough
Gerald E
GE
Ten Eyck
Gary R
GR
Bingman
Verner P
VP
D000818:Animals; D010856:Columbidae / Q000033:anatomy & histology / Q000502:physiology*; D006624:Hippocampus / Q000033:anatomy & histology / Q000737:chemistry* / Q000502:physiology*; D007150:Immunohistochemistry; D009434:Neural Pathways / Q000033:anatomy & histology / Q000737:chemistry / Q000502:physiology