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

Abstract

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 CTB1/vGluT21 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. K E Y W O R D Sbird, fiber connection, glutamate receptor, hippocampal formation, vesicular glutamate transporter 2, Wulst, RRID: AB_10013220, RRID: AB_2313640 | I N TR ODU C TI ONThe avian Wulst (hyperpallium or dorsal pallium) is composed, ventrally from the pial surface, of four layers or 'pseudolayers ' (Medina, 2007): the apical part of the hyperpallium (HA), the interstitial part of the apical hyperpallium (IHA), the intercalated part of the hyperpallium (HI), and the densocellular part of the hyperpallium (HD) (Reiner et al., 2004). The Wulst extends caudally from the level of the olfactory bulbs to roughly half to three quarters of the way through the hemisphere, where it is bounded by medial pallial structures (Karten & Hodos, 1967;Puelles, Martinez-de-la-Torre, Paxinos, Watson, & Martinez, 2007). It is composed of two, relatively distinct, functional regions. A small 'rostral Wulst' is somatosensory in nature, whereas a much larger part, with which the present paper is particularly concerned, extends Abbreviations: AI, intermediate arcopallium; BDA, biotinylated dextran amine; CDL, dorsolateral corticoid area; CTB, cholera toxin B; DIP, dorsointermediate posterior thalamic nucleus; DL, dorsolateral subdivision of hippocampal formation; DLL, lateral part of dorsolateral anterior thalamic nucleus; DLM, medial part of dorsolateral anterior thalamic nucleus; DLP, dorsolateral posterior thalamic nucleus; ...

A canonical interlaminar circuit in the sensory dorsal ventricular ridge of birds: The anatomical organization of the trigeminal pallium

“…Interestingly, several physiological studies reported a columnar organization of sensory responses in the visual wulst area (Baron et al, 2007; Liu & Pettigrew, 2003; Pettigrew, 1979; Pinto & Baron, 2009). Columnarity in the wulst is also suggested by the disposition of the axonal processes running between intermediate and apical layers (Atoji et al, 2018; Atoji & Wild, 2019). The recent report from Stacho et al (2020) includes evidence sustaining these previous observations.…”

Light-incubation effects on lateralisation of single unit responses in the visual Wulst of domestic chicks

“…From there, projections reach back to the thalamus and to the lowest layers of the visual Wulst (HI-hyperpallium intercalatum and HD-hyperpallium densocellulare). Visual Wulst sends projections to various structures including the hippocampal formation and the nido-and mesopallium (Shanahan et al 2013;Atoji et al 2018). The visual Wulst contains many visually responsive neurons (Revzin 1969;Gusel'nikov et al 1977;Ng et al 2010), which are organised according to multiple retinotopic maps (Michael et al 2015;Bischof et al 2016) and are sensitive to motion and orientation akin to those found in the mammalian visual cortex.…”

Neurophysiology of Avian Sleep: Comparing Natural Sleep and Isoflurane Anesthesia

“…Consequently, we will refer to the hyperpallium as being cortical hereafter. Starting dorsomedially, the hyperpallium is made up of the hyperpallium apicale (HA), interstitial nucleus of the HA (IHA), hyperpallium intercalatum (HI), and hyperpallium densocellulare (HD) (Atoji et al, 2018). Similar to layer 4 of the neocortex, IHA is the primary recipient of visual input from the dorsal part of the lateral geniculate nucleus [LGN, avian nucleus geniculatus lateralis pars dorsalis (GLd)] (Karten et al, 1973; Watanabe et al, 1983; Wild, 1987; Ng et al, 2010); though HI and, to a lesser extent, HD also receive some input from the GLd.…”