Differential projections of the densocellular and intermediate parts of the hyperpallium in the pigeon (Columba livia)

• Published in: Journal of comparative neurology (1911) Vol. 526; no. 1; pp. 146 - 165
• Main Authors: Atoji, Yasuro, Sarkar, Sonjoy, Wild, J. Martin
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.01.2018
• Subjects: Afferent Pathways - physiology; Animals; Biotin - analogs & derivatives; Biotin - metabolism; bird; Cholera toxin; Cholera Toxin - metabolism; Columbidae - anatomy & histology; Dextran; Dextrans - metabolism; Efferent Pathways - physiology; Female; fiber connection; glutamate receptor; Glutamatergic transmission; Glutamic acid receptors (ionotropic); Glutamic acid transporter; hippocampal formation; Hippocampus; Hippocampus - anatomy & histology; Hyperstriatum; Male; mRNA; Neurons; Olfactory Bulb - anatomy & histology; Olfactory system; RNA, Messenger - metabolism; RRID: AB_10013220; RRID: AB_2313640; Tracers; Vesicular Glutamate Transport Protein 2 - genetics; Vesicular Glutamate Transport Protein 2 - metabolism; vesicular glutamate transporter 2; Wulst; α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid; hippocampal formation; RRID: AB_10013220; RRID: AB_2313640; vesicular glutamate transporter 2; glutamate receptor; bird; fiber connection; Wulst
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.24328

The visual Wulst in birds shows a four‐layered structure: apical part of the hyperpallium (HA), interstitial part of HA (IHA), intercalated part of hyperpallium (HI), and densocellular part of hyperpallium (HD). HD also connects with the hippocampus and olfactory system. Because HD is subjacent to HI, the two have been treated as one structure in many studies, and the fiber connections of HD have been examined by afferents and efferents originating outside HD. However, to clarify the difference between these two layers, they need to be treated separately. In the present study, the fiber connections of HD and HI were analyzed with tract‐tracing techniques using a combination of injections of cholera toxin subunit B (CTB) for retrograde tracing and biotinylated dextran amine (BDA) for anterograde tracing. When the two tracers were bilaterally injected in HD, a major reciprocal connection was seen with the dorsolateral subdivision (DL) of the hippocampal formation. When CTB and BDA were bilaterally injected in HI, strong reciprocal connections were found between HI and HA. Next, projection neurons in HD and HI were examined by double staining for CTB combined with vesicular glutamate transporter 2 (vGluT2) mRNA in situ hybridization. After CTB was injected in DL or HA, many neurons revealed CTB+/vGluT2+ in HD or HI, respectively. Furthermore, in situ hybridization showed that DL and HA contained neurons expressing various subunits of ionotropic glutamate receptors: AMPA, kainate, and NMDA types. These results suggest that glutamatergic neurons in HD and HI project primarily to DL and HA, respectively. The glutamatergic projections of two adjacent parts of the pigeon visual Wulst, densocellular (HD) and Intercalated (HI) hyperpallium, were traced separately and predominantly to the dorsolateral division of the hippocampal formation (DL) and apical hyperpallium (HA), respectively. Routes of visual and other sensory inputs to the hippocampus are discussed.