Cellular Localization of AMPA Type Glutamate Receptor Subunits in the Basal Ganglia of Pigeons (Columba livia)

Neurochemistry and circuit organization of the lateral spiriform nucleus of birds: A uniquely nonmammalian direct pathway component of the basal ganglia

We used diverse methods to characterize the role of avian lateral spiriform nucleus (SpL) in basal ganglia motor function. Connectivity analysis showed that SpL receives input from globus pallidus (GP), and the intrapeduncular nucleus (INP) located ventromedial to GP, whose neurons express numerous striatal markers. SpL-projecting GP neurons were large and aspiny, while SpL-projecting INP neurons were medium sized and spiny. Connectivity analysis further showed that SpL receives inputs from subthalamic nucleus (STN) and substantia nigra pars reticulata (SNr), and that the SNr also receives inputs from GP, INP, and STN. Neurochemical analysis showed that SpL neurons express ENK, GAD, and a variety of pallidal neuron markers, and receive GABAergic terminals, some of which also contain DARPP32, consistent with GP pallidal and INP striatal inputs. Connectivity and neurochemical analysis showed that the SpL input to tectum prominently ends on GABAA receptor-enriched tectobulbar neurons. Behavioral studies showed that lesions of SpL impair visuomotor behaviors involving tracking and pecking moving targets. Our results suggest that SpL modulates brainstem-projecting tectobulbar neurons in a manner comparable to the demonstrated influence of GP internus on motor thalamus and of SNr on tectobulbar neurons in mammals. Given published data in amphibians and reptiles, it seems likely the SpL circuit represents a major direct pathway-type circuit by which the basal ganglia exerts its motor influence in nonmammalian tetrapods. The present studies also show that avian striatum is divided into three spatially segregated territories with differing connectivity, a medial striato-nigral territory, a dorsolateral striato-GP territory, and the ventrolateral INP motor territory.

Dorsal pallidal neurons directly link the nidopallium and midbrain in the zebra finch (Taeniopygia guttata)

The dorsal pallidum in birds is considered similar, if not homologous, to the globus pallidus (GP) of mammals. The dorsal pallidum projects to both thalamic and midbrain targets similar to the direct and indirect pathways arising from the internal and external segments of the GP. In the present study, retrograde and anterograde tracing studies revealed a previously undescribed projection of the avian dorsal pallidum. This arises from a specific dorsomedial component, which terminates in the intercollicular nucleus and partly surrounds the avian equivalent of the central nucleus of the inferior colliculus. The respiratory-vocal dorsomedial nucleus of the intercollicular complex, however, does not receive these projections. The somata of the pallidal neurons retrogradely labeled from injections in the intercollicular nucleus were large and generally multipolar and had extensive, sparsely branching central processes (presumptive dendrites) that together extended up to 2 mm dorsally into the intermediate and caudomedial nidopallium. The size and morphology of these neurons were similar to those of large pallidal neurons labeled by calretinin immunoreactivity, which could be co-localized to the same cells. Thus, rather than being directly involved in the control of movement, the large dorsomedial neurons of the caudal dorsal pallidum may be involved in sensory processing, in that they provide an unusual direct link between sensory (auditory/somatosensory) regions of the nidopallium and sensory regions of the intercollicular nucleus of the midbrain. J. Comp. Neurol. 525:1731-1742, 2017. © 2016 Wiley Periodicals, Inc.

Neurochemical compartmentalization within the pigeon basal ganglia

The goals of this study were to use multiple informative markers to define and characterize the neurochemically distinct compartments of the pigeon basal ganglia, especially striatum and accumbens. To this end, we used antibodies against 12 different neuropeptides, calcium-binding proteins or neurotransmitter-related enzymes that are enriched in the basal ganglia. Our results clarify boundaries between previously described basal ganglia subdivisions in birds, and reveal considerable novel heterogeneity within these previously described subdivisions. Sixteen regions were identified that each displayed a unique neurochemical organization. Four compartments were identified within the dorsal striatal region. The neurochemical characteristics support previous comparisons to part of the central extended amygdala, somatomotor striatum, and associational striatum of mammals, respectively. The medialmost part of the medial striatum, however, has several unique features, including prominent pallidal-like woolly fibers and thus may be a region unique to birds. Four neurochemically distinct regions were identified within the pigeon ventral striatum: the accumbens, paratubercular striatum, ventrocaudal striatum, and the ventral area of the lateral part of the medial striatum that is located adjacent to these regions. The pigeon accumbens is neurochemically similar to the mammalian rostral accumbens. The pigeon paratubercular and ventrocaudal striatal regions are similar to the mammalian accumbens shell. The ventral portions of the medial and lateral parts of the medial striatum, which are located adjacent to accumbens shell-like areas, have neurochemical characteristics as well as previously reported limbic connections that are comparable to the accumbens core. Comparisons to neurochemically identified compartments in reptiles, mammals, and amphibians indicate that, although most of the basic compartments of the basal ganglia were highly conserved during tetrapod evolution, uniquely avian compartments may exist as well.

Axonal branching patterns of ventral pallidal neurons in the rat

The ventral pallidum (VP) is a key component of the cortico-basal ganglia circuits that process motivational and emotional information, and also a crucial site for reward. Although the main targets of the two VP compartments, medial (VPm) and lateral (VPl) have already been established, the collateralization patterns of individual axons have not previously been investigated. Here we have fully traced eighty-four axons from VPm, VPl and the rostral extension of VP into the olfactory tubercle (VPr), using the anterograde tracer biotinylated dextran amine in the rat. Thirty to fifty percent of axons originating from VPm and VPr collateralized in the mediodorsal thalamic nucleus and lateral habenula, indicating a close association between the ventral basal ganglia-thalamo-cortical loop and the reward network at the single axon level. Additional collateralization of these axons in diverse components of the extended amygdala and corticopetal system supports a multisystem integration that may take place at the basal forebrain. Remarkably, we did not find evidence for a sharp segregation in the targets of axons arising from the two VP compartments, as VPl axons frequently collateralized in the caudal lateral hypothalamus and ventral tegmental area, the well-known targets of VPm, while VPm axons, in turn, also collateralized in typical VPl targets such as the subthalamic nucleus, substantia nigra pars compacta and reticulata, and retrorubral field. Nevertheless, VPl and VPm displayed collateralization patterns that paralleled those of dorsal pallidal components, confirming at the single axon level the parallel organization of functionally different basal ganglia loops.

The avian subpallium: new insights into structural and functional subdivisions occupying the lateral subpallial wall and their embryological origins

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 amygdala including the central and medial extended amygdala and bed nuclei of the stria terminalis; basal telencephalic cholinergic and non-cholinergic corticopetal systems; and septum. The paper provides an overview of the major developmental, neuroanatomical and functional characteristics of the first four of these neural systems, all of which belong to the lateral telencephalic wall. The review particularly focuses on new findings that have emerged since the identity, extent and terminology for the regions were considered by the Avian Brain Nomenclature Forum. New terminology is introduced as appropriate based on the new findings. The paper also addresses regional similarities and differences between birds and mammals, and notes areas where gaps in knowledge occur for birds.

Axonal branching patterns of nucleus accumbens neurons in the rat

The patterns of axonal collateralization of nucleus accumbens (Acb) projection neurons were investigated in the rat by means of single-axon tracing techniques using the anterograde tracer biotinylated dextran amine. Seventy-three axons were fully traced, originating from either the core (AcbC) or shell (AcbSh) compartment, as assessed by differential calbindin D28k-immunoreactivity. Axons from AcbC and AcbSh showed a substantial segregation in their targets; target areas were either exclusively or preferentially innervated from AcbC or AcbSh. Axon collaterals in the subthalamic nucleus were found at higher than expected frequencies; moreover, these originated exclusively in the dorsal AcbC. Intercompartmental collaterals were observed from ventral AcbC axons into AcbSh, and likewise, interconnections at pallidal and mesencephalic levels were also observed, although mostly from AcbC axons toward AcbSh targets, possibly supporting crosstalk between the two subcircuits at several levels. Cell somata giving rise to short-range accumbal axons, projecting to the ventral pallidum (VP), were spatially intermingled with others, giving rise to long-range axons that innervated VP and more caudal targets. This anatomical organization parallels that of the dorsal striatum and provides the basis for possible dual direct and indirect actions from a single axon on either individual or small sets of neurons.

Animal consciousness: a synthetic approach

Despite anecdotal evidence suggesting conscious states in a variety of non-human animals, no systematic neuroscientific investigation of animal consciousness has yet been undertaken. We set forth a framework for such an investigation that incorporates integration of data from neuroanatomy, neurophysiology, and behavioral studies, uses evidence from humans as a benchmark, and recognizes the critical role of explicit verbal report of conscious experiences in human studies. We illustrate our framework with reference to two subphyla: one relatively near to mammals - birds - and one quite far -cephalopod molluscs. Consistent with the possibility of conscious states, both subphyla exhibit complex behavior and possess sophisticated nervous systems. Their further investigation may reveal common phyletic conditions and neural substrates underlying the emergence of animal consciousness.

Morphometric analysis of the AMPA-type neurons in the Deiter's vestibular complex of the chick brain

Chicken (Gallus gallus) brains were used to investigate the typology and the immunolabel pattern for the subunits composing the AMPA-type glutamate receptors (GluR) of hindbrain neurons of the dorsal (dND) and ventral nuclei (vND) of the Deiter's vestibular complex (CD), which is the avian correspondent of the lateral vestibular nucleus (LVN) of mammals. Our results revealed that neurons of both divisions were poor in GluR1. The vND, the GluR2/3+ and GluR4+ label presented no area or neuronal size preference, although most neurons were around 75%. The dND neurons expressing GluR2/3 are primarily around 85%, medium to large-sized 85%, and predominantly 60% located in the medial portion of the rostral pole and in the lateral portion of the caudal pole. The majority of dND neurons containing GluR4 are also around 75%, larger (70% are large and giant), exhibiting a distribution that seems to be complementary to that of GluR2/3+ neurons. This distinct arrangement indicates functional differences into and between the DC nuclei, also signaling that such variation could be attributed to the diverse nature of the subunit composition of the GluRs. Discussion addresses the morphological and functional correlation of the avian DC with the LVN of mammals in addition to the high morphological correspondence, To include these data into the modern comparative approach we propose to adopt a similar nomenclature for the avian divisions dND and vND that could be referred as dLVN and vLVN.

Differential distribution of L-aspartate- and L-glutamate-immunoreactive structures in the arcopallium and medial striatum of the domestic chick (Gallus domesticus)

The role of amino acid neurotransmitters in learning and memory is well established. We investigated the putative role of L-aspartate as a neurotransmitter in the arcopallial-medial striatal pathway, which is known to be involved in passive avoidance learning in domestic chicks. Double immunocytochemistry against L-aspartate and L-glutamate was performed at both light and electron microscopic levels. L-aspartate- and L-glutamate-immunoreactive neurons in the arcopallium and posterior amygdaloid pallium were identified and counted by using fluorescence microscopy and confocal laser scanning microscopy. Most labeled neurons of arcopallium were enriched in glutamate as well as aspartate. However, the arcopallium and posterior amygdaloid pallium differed from a neighboring telencephalic region (nidopallium; formerly neostriatum) by containing a substantial proportion of cells singly labeled for L-aspartate (15%, vs. 5.3% in the nidopallium). Aspartate-labeled neurons constitute approximately 20%, 25%, 42%, and 28% of total in the posterior amygdaloid pallium and the medial, dorsal, and anterior arcopallia, respectively. Immunoelectron microscopy showed that L-aspartate was enriched in terminals of the medial striatum. The labeled terminals had clear and round vesicles and asymmetric junctions; similar to those immunoreactive to L-glutamate. Axon terminals singly labeled for L-aspartate made up 17% of the total. In addition, 7% of neuronal perikarya and 26% of all dendritic profiles appeared to be labeled specifically with L-aspartate but not L-glutamate. The results indicate that L-aspartate may play a specific role (as distinct from that of L-glutamate) in the intrinsic and extrinsic circuits instrumental in avian learning and memory.