Definition and novel connections of the entopallium in the pigeon (Columba livia)

Abstract

The avian entopallium (E) is the major thalamorecipient zone, within the telencephalon, of the tectofugal visual system. Because of discrepancies concerning the structure of this nuclear mass in pigeons, and in light of recent evidence concerning entopallial projections in other avian species, we here redefine and chart some novel entopallial projections in the pigeon by using a combination of cytochrome oxidase (CO) activity, calcium binding protein immunohistochemistry (CBPi), normal histology, and tract tracing. We show that 1) E is defined by the accurate overlap of CO activity and the dense terminations of thalamic (rotundal) efferents; 2) the perientopallium (Ep), E's overlying belt region, receives a relatively sparse rotundal input and is a major source of projections to wider regions of the hemisphere; and 3) E can be subdivided into internal (Ei) and external (Ex) portions on the basis of normal histology, CBPi, and differential projections. Thus, Ei, but not Ex, makes a reciprocal connection with a distinct nucleus in the ventrolateral mesopallium and is a major source of projections to the lateral striatum. These findings suggest the necessity for a revision of the original proposal of a strictly serial flow of visual information through the entopallial complex and further regions of the hemisphere and also require a modification of the long-standing view that E is comparable to only one specific lamina (IV) of extrastriate visual cortex of mammals. Rather, E appears to be composed of a variety of neuronal types possibly equivalent to those in several neocortical laminae.

Serotonin 5-HT1A receptor binding sites in the brain of the pigeon (Columba livia)

“…In our study, this area showed a dense labeling for 5-HT 1A receptors that differed clearly from the rest of the mesopallium confirming a nuclear structure. Therefore, our findings support the idea of Krützfeldt and Wild (2005) that this area is comparable with the nucleus MVL in the zebra finch.…”

“…Herein, our results support this suggestion, because layers II and III of the human extrastriate cortex also contain the highest numbers of 5-HT 1A receptors when compared with the other neocortical layers (Zilles et al, 2004;Eickhoff et al, 2007). The input region of the entopallium is the entopallial core, which can be further subdivided into an entopallium externum (Ee) and internum (Ei) (Hellmann et al, 1995;Krützfeldt and Wild, 2005). Our results in principle support such a subdivision.…”

“…This could imply that these subdivisions have functional implications, which have to be analyzed in further studies determining the role of the entopallium within the tectofugal pathway. To date, it is not clear whether neurons of the core components are comparable with layer IV neurons in the neocortex of mammals, or whether they are a mixture composed of layer IV and V neurons (Krützfeldt and Wild, 2005). Our results show a low concentration for 5-HT 1A receptors in Eie and Eii.…”

“…In pigeons, the medial entopallium has strong reciprocal connections to an area of the ventrolateral mesopallium dorsal to the entopallium (Krützfeldt and Wild, 2005). This area is distinct in Nissl-stained sections and was described in the former hyperstriatum ventrale as hyperstriatum ventrale ventrolaterale (HVvl) (Husband and Shimizu, 1999).…”

Attentional Capture? Synchronized Feedback Signals from the Isthmi Boost Retinal Signals to Higher Visual Areas

“…The Rt sends an organized projection to the entopallium, such that separate regions of the entopallium receive topographic input from different rotundal subdivisions (Laverghetta and Shimizu, 2003;Krützfeldt and Wild, 2005;Fredes et al, 2010). To determine whether the effect of the Ipc on the ascending tectal pathway extends to the entopallium, we made 74 simultaneous recordings in both structures, 36 of which were tested in a systematic way to be used for quantitative analysis.…”