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– Major structures comprising the avian central extended amygdala (EAce) complex, as seen in frontal (A,B) or oblique-horizontal (C – F) sections showing mRNA expression of Lmo3 (A,B), SP (C,D) or Pax6 (E,F). Scale bars in A and C = 1 mm (applies to A – F). Expression of the gene Lmo3 helps to delineate the dorsal part of lateral bed nucleus of the stria terminalis (BSTLd) and part of a lateral corridor that includes the intrapeduncular nucleus (INP) and the EAce cell corridor, located below the globus pallidus (GP). The striatal division is rich in cells expressing substance P (SP) or Pax6, and both markers are enriched in the striatal (lateral) part of the EAce complex. In addition, many cells expressing Pax6 or SP also invade (apparently by tangential migration) the pallidal (more medial) parts of the EAce complex, including the EAcem and part of the dorsal BSTL. Refer to list of abbreviations for names of other structures identified. From Abellán and Medina (2009).
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The subpallial region of the avian telencephalon contains neural systems whose functions are critical to the survival of individual vertebrates and their species. The subpallial neural structures can be grouped into five major functional systems, namely the dorsal somatomotor basal ganglia; ventral viscerolimbic basal ganglia; subpallial extended a...
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... that the central extended amygdala in chick includes a territory below the globus pallidus identified by the Nomenclature Forum as the SpA and a more lateral territory below the caudolateral striatum that the Forum did not recognize. Abellán and Medina termed these two regions the medial and lateral parts of the avian extended central amygdala (Fig. 10). They noted that the medial portion of the central extended amygdala, below the globus pallidus, may correspond to the sublenticular corridor of the central extended amygdala of mammals (Reiner et al., 2004a), and include striatal and pallidal cells (Abellán and Medina, 2009). They proposed that the lateral portion of the central ...
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... its role in autonomic functions, the central extended amygdala receives input from the posterior intralaminar thalamus, the parabrachial nucleus, the nucleus of the solitary tract, the insular cortex, and the pallial amygdala. It is distinc- tively rich in calcitonin gene related peptide (CGRP) terminals, representing the parabrachial and posterior intralaminar thalamic input (D'Hanis et al., 2007). The mammalian central amygdala itself is primarily a striatal derivative (Bupesh et al., 2011b; García-López et al., 2008; Puelles et al., 2000; Tole et al., 2005; Waclaw et al., 2010), and recent fate mapping data indicate that it contains Pax6 -expressing cells derived from dorsal LGE and Islet1 -expressing cells derived from ventral LGE (Bupesh et al., 2011b; Waclaw et al., 2010). Howev- er, recent evidence also indicates that the medial part of the central amygdala, and possibly the sublenticular corridor of the central extended amygdala contain a mixture of neurons of striatal and pallidal origin (Bupesh et al., 2011b). Pallidal neurons invading the central amygdala and the corridor contain somatostatin (Bupesh et al., 2011b; García-López et al., 2008). The BSTL is primarily a pallidal derivative, but some striatal cells expressing Pax6 , Islet1 or Lmo4 invade the BSTL (Bupesh et al., 2011b; García-López et al., 2008; reviewed in Medina and Abellán, 2009). The central extended amygdaloid complex in birds includes at least two components: the so- called subpallial amygdaloid area (SpA; Reiner et al., 2004a; Roberts et al., 2002; Wild et al., 1990; Yamamoto et al., 2005), and the BSTL (Abellán and Medina, 2008, 2009; Aste et al., 1998b; Jurkevich et al., 1999; Reiner et al., 2004b; Roberts et al., 2002). Both of these were recognized by the Nomenclature Forum, though not specifically in relationship to an entity termed the extended central amygdala. The Nomenclature Forum also did not recognize a central amygdaloid nucleus in birds. The current understanding of the subdivisions of avian central extended amygdala and the BSTL are discussed in the following sections. amygdala. Abellán and Medina (2009) recognized that the central extended amygdala in chick includes a territory below the globus pallidus identified by the Nomenclature Forum as the SpA and a more lateral territory below the caudolateral striatum that the Forum did not recognize. Abellán and Medina termed these two regions the medial and lateral parts of the avian extended central amygdala (Fig. 10). They noted that the medial portion of the central extended amygdala, below the globus pallidus, may correspond to the sublenticular corridor of the central extended amygdala of mammals (Reiner et al., 2004a), and include striatal and pallidal cells (Abellán and Medina, 2009). They proposed that the lateral portion of the central extended amygdala may correspond to at least part of the mammalian central amygdala, by the criteria that it lies directly below the caudolateral striatum and is rich in striatal, Pax6 -expressing (Figs. 10E, F) neurons (Abellán and Medina, 2009). They additionally recognized a caudolateral ventral part of LSt (which they termed CLSt) as part of the central extended amygdala as well, and suggested that this also was part of the avian homologue of mammalian central amygdala (Figs. 10E, F). Considerable neurochemical and hodological evidence shows a strong similarity between the mammalian sublenticular extended amygdala and the medial part of the avian central extended amygdala of Abellán and Medina (2009), or subpallial amygdala (SpA) as the Nomenclature Forum termed it. As true of mammalian sublenticular central amygdala, neurons of the avian central extended amygdala are GABAergic (Abellán and Medina, 2009; Yamamoto et al., 2005). Moreover, many of these neurons are striatal in neurochemistry, containing the characteristic striatal amygdaloid neuropeptides enkephalin, neurotensin and/or corticotropin releasing hormone (Atoji et al., 1996; Molnar et al., 1994; Reiner et al., 2004a; Richard et al., 2004; Roberts et al., 2002; Yamamoto et al., 2005). The inputs to the medial and lateral portions of the extended central amygdala of birds also resemble those of the mammalian central extended amygdala. In both, this region receives viscerolimbic input from the parabrachial nucleus (Wild et al., 1990), the nucleus of the solitary tract, and the pallial amygdala (Atoji et al., 2006; Veenman et al., 1995). Moreover, the avian central extended amygdala, as well as the CLSt, is enriched in CGRP terminals, (Lanuza et al., 2000; Reiner et al., 2004b; Roberts et al., 2002; Yamamoto et al., 2005). Note, however, that neither the lateral central extended amygdala nor the CLSt in birds is nearly as rich in CGRP+ fibers as their suggested mammalian homologue, the central amygdala. As in mammals, the GABAer- gic/neuropeptidergic neurons of the central extended amygdala in birds give rise to its outputs, notably to the BSTL and its subnuclei (Fig. 10) and the nucleus of the solitary tract/dorsal vagal nucleus (Abellán and Medina, 2009; Atoji et al., 2006; Berk, 1987; Richard et al., 2004; Yamamoto et al., 2005), and may account for some fibers in those regions containing enkephalin, neurotensin and/or corticotropin releasing hormone. In summary, considerable data support the homology of the medial part of the avian central extended amygdala (i.e. the subpallial amygdala) to the mammalian sublenticular central extended amygdala, including the presence of a neurochemically and hodologically similar region in reptiles (Martínez-García et al., 2008). A homology of the lateral part of the avian central extended amygdala (CLSt) to the mammalian central amygdala also is supported by considerable data, although differences between these two structures suggest further study of this issue is needed. 3.3.1.2. Striatal capsule. The intercalated cell masses of the mammalian amygdala are subpallial neurons interposed between the central amygdala and the basal complex of the pallial amygdala and the ventral endopiriform nucleus. The amygdaloid intercalated cell masses appear to represent an integral part of the central extended amygdala in mammals, and develop from the dorsal part of the striatal subdivision of the developing subpallium, that is the LGE (García-López et al., 2008; Kaoru et al., 2010; Medina and Abellán, 2009; Waclaw et al., 2010). The amygdaloid intercalated cell masses have a GABAergic projection to the central amygdala and the cholinergic corticopetal cell groups of the basal telencephalon (including the basal magnocellular complex), and they are involved in extinction of fear memories (Paré et al., 2004). A distinctive set of subpallial neurons interposed between the nidopallium and the lateral striatum has recently been termed the avian striatal capsule (Puelles et al., 2007), and been proposed to be comparable to the intercalated cell masses of the mammalian amygdala (Abellán and Medina, 2009). Data supporting the proposal include similar developmental origin from the dorsal part of the avian LGE homologue, some molecular traits, and their position at the border between the subpallium and what Abellán and Medina (2009) identify as ventral pallium and thus regard as comparable to mammalian ventral pallium, including part of the basal amygdalar complex and the ventral endopiriform nucleus (Figs. 3C – F). The connections of the avian striatal capsule are unknown and therefore no hodological support exists at this time. Moreover, the avian striatal capsule is not juxtaposed to the proposed avian central amygdala (subpallial amygdalar area), unlike the intercalated cell masses of the mammalian amygdala. 3.3.1.3. Lateral bed nucleus of the stria terminalis (BSTL). As noted by the Nomenclature Forum, the BSTL in birds and mammals is located at the base of the lateral ventricle near the level of the septopallio-mesencephalic tract and anterior commissure (Figs. 8C, D). It is characterized by a relative abundance of neurotensinergic (Atoji et al., 1996; Reiner and Carraway, 1987; Reiner et al., 2004b), enkephalinergic (Molnar et al., 1994), and corticotropin-releasing hormone (CRH) neurons (Panzica et al., 1986; Richard et al., 2004), and many calcitonin gene related peptide (CGRP; Lanuza et al., 2000) and noradrenergic fibers (Reiner et al., 1994). In contrast a paucity of cholinergic cells/fibers (Medina and Reiner, 1994), sparse dopaminergic terminals (Bailhache and Balthazart, 1993; Reiner et al., 1994, 2004b), and few substance P-containing neurons and fibers (Reiner et al., 1983, 2004b) have been reported. Like the mammalian BSTL (Gray and Magnuson, 1987; Moga et al., 1989; van der Kooy et al., 1984), the avian BSTL is reciprocally connected with the hypothalamus, parabrachial nucleus, the nucleus of the solitary tract, and the dorsal motor nucleus of the vagus (Arends et al., 1988; Atoji et al., 2006; Bálint et al., 2011; Berk, 1987; Wild et al., 1990). The BSTL in mammals and birds, however, appears to be a complex territory with striatal and pallidal cell subpopulations. In brief, the dorsal and medial parts of the BSTL in birds and mammals are rich in cells that develop from a comparable pallidal embryonic subdomain (Abellán and Medina, 2009; García-López et al., 2008; Xu et al., 2008), and in birds has been termed the dorsal BSTL by Abellán and Medina (2009). Lateral to this, in a region termed by them the dorsolateral BSTL, reside abundant neurons expressing Pax6 / Lmo4 that appear to derive from the striatal progenitor zone (Figs. 10E, F; Abellán and Medina, 2008, 2009; García- López et al., 2008; Xu et al., 2008). The BSTL in mammals also contains a minor subpopulation of Pax6-expressing neurons derived from dorsal LGE, and an abundant subpopulation of Islet1-expressing neurons derived from ventral LGE (Bupesh et al., 2011b). The dorsolateral BSTL of birds is the subdivision rich in neurons possessing such striatal markers as ...
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... The pallium, especially the dorsal pallium, largely differs in each lineage of vertebrates: it is absent as a morphological entity in amphioxus 2 and is present as only a layered area in fishes and amphibians, while it is a simply layered region in reptiles and aves, but a large intricate multilayered cortex in mammals 3 . In contrast, the subpallial regions or the subpallium, the deep-seated basal ganglia (striatum and pallidum), are highly conserved in vertebrates with respect to the expression patterns of transcription factors, neuronal types and some neural connections, despite varieties in shapes and sizes [4][5][6] . Thus, from an evolutionarily point of view, the pallium has undergone divergent trajectories in different vertebrates, and the dorsal pallium has experienced the greatest development in mammals 7,8 . ...
The mechanisms underlying the organization and evolution of the telencephalic pallium are not yet clear.. To address this issue, we first performed comparative analysis of genes critical for the development of the pallium (Emx1/2 and Pax6) and subpallium (Dlx2 and Nkx1/2) among 500 vertebrate species. We found that these genes have no obvious variations in chromosomal duplication/loss, gene locus synteny or Darwinian selection. However, there is an additional fragment of approximately 20 amino acids in mammalian Emx1 and a poly-(Ala)6–7 in Emx2. Lentiviruses expressing mouse or chick Emx2 (m-Emx2 or c-Emx2 Lv) were injected into the ventricle of the chick telencephalon at embryonic Day 3 (E3), and the embryos were allowed to develop to E12–14 or to posthatchling. After transfection with m-Emx2 Lv, the cells expressing Reelin, Vimentin or GABA increased, and neurogenesis of calbindin cells changed towards the mammalian inside-out pattern in the dorsal pallium and mesopallium. In addition, a behavior test for posthatched chicks indicated that the passive avoidance ratio increased significantly. The study suggests that the acquisition of an additional fragment in mammalian Emx2 is associated with the organization and evolution of the mammalian pallium.
... Regulation of the fear/stress response by the extended amygdala in nonmammals is still poorly understood. In birds, this is in part due to the high divergence of the telencephalon in evolution, which has made it challenging to identify the amygdala in sauropsids (reviewed by Kuenzel et al., 2011;Martínez-García et al., 2002Medina et al., 2011Medina et al., , 2017Medina et al., , 2023Reiner et al., 2004). The avian BSTL was identified in the pallidal territory of the subpallium, adjacent to the lateral ventricle (Aste et al., 1998;Kuenzel et al., 2011;Puelles et al., 2000;Reiner et al., 2004). ...
... In birds, this is in part due to the high divergence of the telencephalon in evolution, which has made it challenging to identify the amygdala in sauropsids (reviewed by Kuenzel et al., 2011;Martínez-García et al., 2002Medina et al., 2011Medina et al., , 2017Medina et al., , 2023Reiner et al., 2004). The avian BSTL was identified in the pallidal territory of the subpallium, adjacent to the lateral ventricle (Aste et al., 1998;Kuenzel et al., 2011;Puelles et al., 2000;Reiner et al., 2004). This nucleus has descending projections to hypothalamic and brainstem centers similar to those of mammalian BSTL involved in the regulation of the endocrine, autonomic, and behavioral aspects of the stress response (Atoji et al., 2006;Hanics et al., 2017). ...
... In mammals, CRF and ENK cells of the central amygdala play different roles: while CRF cells are involved in long-term components of fear learning and recall (related to anxiety; Asok et al., 2018;Davis et al., 2010;Gafford & Ressler, 2015;Pitts et al., 2009;Pomrenze et al., 2019), ENK/PKCδ cells promote anxiolysis and analgesia (Douceau et al., 2022;Paretkar & Dimitrov, 2019). Like in mammals, ENK cells and CRF cells of the avian central amygdala have subpallial origin Vicario et al., 2014Vicario et al., , 2015Vicario et al., , 2017present study) and are likely GABAergic, as typical for cells in the subpallium Kuenzel et al., 2011;Medina et al., 2011Medina et al., , 2017Medina et al., , 2023. Thus, projections from these cells to BSTL would lead to the inhibition of BSTL cells (Figure 10). ...
In mammals, the central extended amygdala is critical for the regulation of the stress response. This regulation is extremely complex, involving multiple subpopulations of GABAergic neurons and complex networks of internal and external connections. Two neuron subpopulations expressing corticotropin‐releasing factor (CRF), located in the central amygdala and the lateral bed nucleus of the stria terminalis (BSTL), play a key role in the long‐term component of fear learning and in sustained fear responses akin to anxiety. Very little is known about the regulation of stress by the amygdala in nonmammals, hindering efforts for trying to improve animal welfare. In birds, one of the major problems relates to the high evolutionary divergence of the telencephalon, where the amygdala is located. In the present study, we aimed to investigate the presence of CRF neurons of the central extended amygdala in chicken and the local connections within this region. We found two major subpopulations of CRF cells in BSTL and the medial capsular central amygdala of chicken. Based on multiple labeling of CRF mRNA with different developmental transcription factors, all CRF neurons seem to originate within the telencephalon since they express Foxg1, and there are two subtypes with different embryonic origins that express Islet1 or Pax6. In addition, we demonstrated direct projections from Pax6 cells of the capsular central amygdala to BSTL and the oval central amygdala. We also found projections from Islet1 cells of the oval central amygdala to BSTL, which may constitute an indirect pathway for the regulation of BSTL output cells. Part of these projections may be mediated by CRF cells, in agreement with the expression of CRF receptors in both Ceov and BSTL. Our results show a complex organization of the central extended amygdala in chicken and open new venues for studying how different cells and circuits regulate stress in these animals.
... The latter pathway is also present in birds. Connectivity and chemoarchitecture of these regions, homologous with mammalian progenitor zones, basal ganglia, and extended amygdala (Bupesh et al., 2011;Kuenzel et al., 2011;Vicario et al., 2014Vicario et al., , 2015Vicario et al., , 2017Martínez-Cerdeño et al., 2018), have been extensively investigated also by our research group (Bálint et al., 2004;Montagnese et al., 2004Montagnese et al., , 2008Hanics et al., 2012Hanics et al., , 2017 found to impair socially motivated vocalization of domestic chicks (Zachar et al., 2017). A great deal of studies has tackled the pre-and postnatal development of dopaminergic neurons and pathways (see below), the developmental dynamics of the ventrotegmentalaccumbens (mesolimbic) pathway, including the chemorepellent or chemoattractant factors specifically involved in the segregation of distinct dopaminergic pathways/connections (see Bissonette and Roesch, 2016). ...
Gestational exposure of mice to valproic acid (VPA) is one currently used experimental model for the investigation of typical failure symptoms associated with autism spectrum disorder (ASD). In the present study we hypothesized that the reduction of dopaminergic source neurons of the VTA, followed by perturbed growth of the mesotelencephalic dopamine pathway (MT), should also modify pattern formation in the dopaminoceptive target regions (particularly its mesoaccumbens/mesolimbic portion). Here, we investigated VPA-evoked cellular morphological (apoptosis-frequency detected by Caspase-3, abundance of Ca-binding proteins, CaBP), as well as synaptic proteomic (western blotting) changes, in selected dopaminoceptive subpallial, as compared to pallial, regions of mice, born to mothers treated with 500 mg/kg VPA on day 13.5 of pregnancy. We observed a surge of apoptosis on VPA treatment in nearly all investigated subpallial and pallial regions; with a non-significant trend of similar increase the nucleus accumbens (NAc) at P7, the age at which the MT pathway reduction has been reported (also supplemented by current findings). Of the CaBPs, calretinin (CR) expression was decreased in pallial regions, most prominently in retrosplenial cortex, but not in the subpallium of P7 mice. Calbindin-D 28K (CB) was selectively reduced in the caudate-putamen (CPu) of VPA exposed animals at P7 but no longer at P60, pointing to a potency of repairment. The VPA-associated overall increase in apoptosis at P7 did not correlate with the abundance and distribution of CaBPs, except in CPu, in which the marked drop of CB was negatively correlated with increased apoptosis. Abundance of parvalbumin (PV) at P60 showed no significant response to VPA treatment in any of the observed regions we did not find colocalization of apoptotic (Casp3+) cells with CaBP-immunoreactive neurons. The proteomic findings suggest reduction of tyrosine hydroxylase in the crude synaptosome fraction of NAc, but not in the CPu, without simultaneous decrease of the synaptic protein, synaptophysin, indicating selective impairment of dopaminergic synapses. The morpho-functional changes found in forebrain regions of VPA-exposed mice may signify dendritic and synaptic reorganization in dopaminergic target regions, with potential translational value to similar impairments in the pathogenesis of human ASD.
... These cells were previously observed in chicken and quail using immunohistochemistry, but were proposed to belong to the extended amygdala (Richard et al., 2004). Like in mammals (Alheid & Heimer, 1988), corticopetal subpallial cells in chicken partially overlap the extended amygdala, the pallidal parts of the basal ganglia, and the lateral and medial forebrain bundles, but they belong to a different functional system characterized by projections to the pallium (Leutgeb et al., 1996;discussed by Abellán & Medina, 2009;Kuenzel et al., 2011). Corticopetal cells include cholinergic, GABAergic and glutamatergic neuronal subpopulations Medina & Reiner, 1994), and it would be interesting to investigate coexpression of these neurotransmitters with CRF. ...
Understanding the neural mechanisms that regulate the stress response is critical to know how animals adapt to a changing world and is one of the key factors to be considered for improving animal welfare. Corticotropin-releasing factor (CRF) is crucial for regulating physiological and endocrine responses, triggering the activation of the sympathetic nervous system and the hypothalamo-pituitary-adrenal axis (HPA) during stress. In mammals, several telencephalic areas, such as the amygdala and the hippocampus, regulate the autonomic system and the HPA responses. These centers include subpopulations of CRF containing neurons that, by way of CRF receptors, play modulatory roles in the emotional and cognitive aspects of stress. CRF binding protein also plays a role, buffering extracellular CRF and regulating its availability. CRF role in activation of the HPA is evolutionary conserved in vertebrates, highlighting the relevance of this system to help animals cope with adversity. However, knowledge on CRF systems in the avian telencephalon is very limited, and no information exists on detailed expression of CRF receptors and binding protein. Knowing that the stress response changes with age, with important variations during the first week posthatching, the aim of this study was to analyze mRNA expression of CRF, CRF receptors 1 and 2, and CRF binding protein in chicken telencephalon throughout embryonic and early posthatching development, using in situ hybridization. Our results demonstrate an early expression of CRF and its receptors in pallial areas regulating sensory processing, sensorimotor integration and cognition, and a late expression in subpallial areas regulating the stress response. However, CRF buffering system develops earlier in the subpallium than in the pallium. These results help to understand the mechanisms underlying the negative effects of noise and light during prehatching stages in chicken, and suggest that stress regulation becomes more sophisticated with age.
... Rostral is approximately right, dorsal up, and bars = 1 mm. Abbreviations: HVC (proper name), lMAN (lateral magnocellular nucleus of the anterior nidopallium), RA (robust nucleus of the arcopallium), Area X (Area X of striatum, note that songbird striatum also contains pallidal projection neurons and interneurons that anatomically distinguish it from mammalian striatum that separates these features 20 ). Brain regions from both vocal-motor (HVC and RA) and -learning circuits (Area X) were micropunch dissected, total RNA extracted, cDNA synthesized, and PCR amplified. ...
The non-euphorigenic phytocannabinoid cannabidiol (CBD) has been used successfully to treat childhood-onset epilepsies. These conditions are associated with developmental delays that often include vocal learning. Zebra finch song, like language, is a complex behavior learned during a sensitive period of development. Song quality is maintained through continuous sensorimotor refinement involving circuits that control learning and production. Within the vocal motor circuit, HVC is a cortical-like region that when partially lesioned temporarily disrupts song structure. We previously found CBD (10 mg/kg/day) improves post-lesion vocal recovery. The present studies were done to begin to understand mechanisms possibly responsible for CBD vocal protection. We found CBD markedly reduced expression of inflammatory mediators and oxidative stress markers. These effects were associated with regionally-reduced expression of the microglial marker TMEM119. As microglia are key regulators of synaptic reorganization, we measured synapse densities, finding significant lesion-induced circuit-wide decreases that were largely reversed by CBD. Synaptic protection was accompanied by NRF2 activation and BDNF/ARC/ARG3.1/MSK1 expression implicating mechanisms important to song circuit node mitigation of oxidative stress and promotion of synaptic homeostasis. Our findings demonstrate that CBD promotes an array of neuroprotective processes consistent with modulation of multiple cell signaling systems, and suggest these mechanisms are important to post-lesion recovery of a complex learned behavior.
... These cells were previously observed in chicken and quail using immunohistochemistry, but were proposed to belong to the extended amygdala (Richard et al., 2004). Like in mammals (Alheid and Heimer, 1988), corticopetal subpallial cells in chicken partially overlap the extended amygdala, the pallidal parts of the basal ganglia, and the lateral and medial forebrain bundles, but they belong to a different functional system characterized by projections to the pallium (Leutgeb et al., 1996;discussed by Abellán and Medina, 2009;Kuenzel et al., 2011). Corticopetal cells include cholinergic, GABAergic and glutamatergic neuronal subpopulations (Medina and Reiner, 1994;, and it would be interesting to investigate coexpression of these neurotransmitters with CRF. ...
Understanding the neural mechanisms that regulate the stress response is critical to know how animals adapt to a changing world and is one of the key factors to be considered for improving animal welfare. Corticotropin releasing factor (CRF) is crucial for regulating physiological and endocrine responses, triggering the activation of the sympathetic nervous system and the hypothalamo - pituitary - adrenal axis (HPA) during stress. In mammals, several telencephalic areas, such as the amygdala and the hippocampus, regulate the autonomic system and the HPA responses. These centers include subpopulations of CRF containing neurons that, by way of CRF receptors, play modulatory roles in the emotional and cognitive aspects of stress. CRF binding protein also plays a role, buffering extracellular CRF and regulating its availability. CRF role in activation of the HPA is evolutionary conserved in vertebrates, highlighting the relevance of this system to help animals cope with adversity. However, knowledge on CRF systems in the avian telencephalon is very limited, and no information exists on detailed expression of CRF receptors and binding protein. Knowing that the stress response changes with age, with important variations during the first week posthatching, the aim of this study was to analyze mRNA expression of CRF, CRF receptors 1 and 2, and CRF binding protein in chicken telencephalon throughout embryonic and early posthatching development, using in situ hybridization. Our results demonstrate an early expression of CRF and its receptors in pallial areas regulating sensory processing, sensorimotor integration and cognition, and a late expression in subpallial areas regulating the stress response. However, CRF buffering system develops earlier in the subpallium than in the pallium. These results help to understand the mechanisms underlying the negative effects of noise and light during prehatching stages in chicken, and suggest that stress regulation becomes more sophisticated with age.
... In contrast to this, the amygdala -most particularly its pallidal division -is highly divergent, and its identification in sauropsids is highly controversial [reviewed by Medina et al., 2017;Pessoa et al., 2019]. Even in the subpallium, which is highly conserved between mammals and birds [Reiner et al., 2004;Belgard et al., 2013], researchers have found important difficulties to identify typical amygdala subdivisions such as the central amygdala nucleus [reviewed by Reiner et al., 2004;Kuenzel et al., 2011]. Studying how this structure evolved can help to better understand basic principles on its organization, but also to identify variations in neural mechanisms that are behind different adaptations in the regulation of essential behaviors. ...
The amygdala is a central node in functional networks regulating emotions, social behavior and social cognition. It develops in the telencephalon and includes pallial and subpallial parts, but these are extremely complex with multiple subdivisions, cell types and connections. The homology of the amygdala in non-mammals is highly controversial, especially for the pallial part, and we are still far from understanding general principles on its organization that are common to different groups. Here we review data on the adult functional architecture and developmental genoarchitecture of the amygdala in different amniotes (mammals and sauropsids), which are helping to disentangle and to better understand this complex structure. The use of an evolutionary developmental biology (evodevo) approach has helped to distinguish three major divisions in the amygdala, derived from the pallium, the subpallium and from a newly identified division called telencephalon-opto-hypothalamic domain (TOH). This approach has also helped to identify homologous cell populations with identical embryonic origins and molecular profiles in the amygdala of different amniotes. While subpallial cells produce different subtypes of GABAergic neurons, the pallium and TOH are major sources of glutamatergic cells. Available data point to a development-based molecular code that contributes to shape distinct functional subsystems in the amygdala, and comparative genoarchitecture is helping to delineate the cells involved in same subsystems in non-mammals. Thus, the evodevo approach can provide crucial information to understand common organizing principles of the amygdalar cells and networks that control behavior, emotions and cognition in amniotes.
... Moreover, it projects to the paraventricular hypothalamic nucleus (Atoji et al., 2006), being thus able to regulate the hypothalamic-pituitary-adrenal axis (Smulders, 2021), and receives input from a posterior part of the arcopallium (part of the avian pallial amygdala) (Atoji et al., 2006) that is also involved in control of fear behavior (Saint-Dizier et al., 2009). The subpallial amygdalar area interposed between the arcopallium and the BSTL also projects to the BSTL and seems to belong to the same functional network (Kuenzel et al., 2011). Using an evolutionary developmental neurobiology approach, we recently identified several subdivisions and cell subpopulations within this subpallial amygdala region that, together with the BSTL, appear to form the avian central extended amygdala (Vicario et al., 2014(Vicario et al., , 2015. ...
The central extended amygdala, including the lateral bed nucleus of the stria terminalis and the central amygdala, plays a key role in stress response. To understand how the central extended amygdala regulates stress it is essential to dissect this structure at molecular, cellular and circuit levels. In mammals, the central amygdala contains two distinct cell populations that become active (on cells) or inactive (off cells) during the conditioned fear response. These two cell types inhibit each other and project mainly unidirectionally to output cells, thus providing a sophisticated regulation of stress. These two cell types express either protein kinase C-delta/enkephalin or somatostatin, and were suggested to originate in different embryonic domains of the subpallium that respectively express the transcription factors Pax6 or Nkx2.1 during development. The regulation of the stress response by the central extended amygdala is poorly studied in non-mammals. Using an evolutionary developmental neurobiology approach, we previously identified several subdivisions in the central extended amygdala of chicken. These contain Pax6, Islet1 and Nkx2.1 cells that originate in dorsal striatal, ventral striatal or pallidopreoptic embryonic divisions, and also contain neurons expressing enkephalin and somatostatin. To know the origin of these cells, in this study we carried out multiple fluorescent labeling to analyze coexpression of different transcription factors with enkephalin or somatostatin. We found that many enkephalin cells coexpress Pax6 and likely derive from the dorsal striatal division, resembling the off cells of the mouse central amygdala. In contrast, most somatostatin cells coexpress Nkx2.1 and derive from the pallidal division, resembling the on cells. We also found coexpression of enkephalin and somatostatin with other transcription factors. Our results show the existence of multiple cell types in the central extended amygdala of chicken, perhaps including on/off cell systems, and set the basis for studying the role of these cells in stress regulation.
... The POA has projections to numerous nuclei that are activated during HAT exposure in pigeons [67]. Specifically, projections from the POA extend to the nucleus of the anterior pallial commissure (now named the nucleus of the hippocampal commissure (NHpC) [68]), the PVN, the LH, and the DMN [67]. Of these projections, the ones most commonly studied are the preoptic projections to thyrotropin-releasing hormone (TRH) neurons in the PVN. ...
Heat stress is one of the major environmental conditions causing significant losses in the poultry industry and having negative impacts on the world’s food economy. Heat exposure causes several physiological impairments in birds, including oxidative stress, weight loss, immunosuppression, and dysregulated metabolism. Collectively, these lead not only to decreased production in the meat industry, but also decreases in the number of eggs laid by 20%, and overall loss due to mortality during housing and transit. Mitigation techniques have been discussed in depth, and include changes in air flow and dietary composition, improved building insulation, use of air cooling in livestock buildings (fogging systems, evaporation panels), and genetic alterations. Most commonly observed during heat exposure are reduced food intake and an increase in the stress response. However, very little has been explored regarding heat exposure, food intake and stress, and how the neural circuitry responsible for sensing temperatures mediate these responses. That thermoregulation, food intake, and the stress response are primarily mediated by the hypothalamus make it reasonable to assume that it is the central hub at which these systems interact and coordinately regulate downstream changes in metabolism. Thus, this review discusses the neural circuitry in birds associated with thermoregulation, food intake, and stress response at the level of the hypothalamus, with a focus on how these systems might interact in the presence of heat exposure.
... Despite this long separation period, both classes of vertebrates have a cerebrum that can be divided into pallial and subpallial regions. The subpallium, with the striatum as its largest component, has a very similar organization in mammals and birds (Kuenzel et al., 2011). However, the anatomic structure of the pallium is quite different. ...
Adaptively and flexibly modifying one's behavior depending on the current demands of the situation is a hallmark of executive function. Here, we examined whether pigeons could flexibly shift their attention from one set of features that were relevant in one categorization task to another set of features that were relevant in a second categorization task. Critically, members of both sets of features were available on every training trial, thereby requiring that attention be adaptively deployed on a trial-by-trial basis based on contextual information. The pigeons not only learned to correctly categorize the stimuli but, as training progressed, they concentrated their pecks to the training stimuli (a proxy measure for attention) on those features that were relevant in a specific context. The pigeons selectively tracked the features that were relevant in Context 1-but were irrelevant in Context 2-and they selectively tracked the features that were relevant in Context 2-but were irrelevant in Context 1. This adept feature tracking requires disengaging attention from a previously relevant feature and shifting attention to a previously ignored feature on a trial-by-trial basis. Pigeons' adaptive and flexible performance provides strong empirical support for the involvement of focusing and shifting attention under exceptionally challenging training conditions. (PsycInfo Database Record (c) 2021 APA, all rights reserved).
