The distribution and cellular localization of glutamic acid decarboxylase-65 (GAD65) mRNA in the forebrain and midbrain of domestic chick

Glutamic acid decarboxylase immunoreactivity in the olfactory bulb of a reptile

The objective is to determine the distribution of glutamic acid decarboxylase (GAD) in the olfactory bulb of a crocodilian, Caiman crocodilus . Avidin-biotin immunohistochemical methodology using a polyclonal antibody to GAD raised in sheep was employed. The following controls were used: substitution of the primary antibody with preimmune sheep serum at concentrations equal to that of the primary antibody; omission of the primary antibody; and omission of the primary antibody and biotinylated rabbit antisheep immunoglobulin. No GAD (+) cells were observed in the control sections. Based on cell and fiber staining, the layering and neuronal organization of the olfactory bulb in Caiman were similar to other vertebrates, including other reptiles. The following elements were GAD (+): granule cells, certain neurons in the outer plexiform layer, periglomerular neurons, and the glomeruli themselves. GAD (+) puncta were present throughout the olfactory bulb. In conclusion, these results in Caiman were similar, in part, to comparable studies in mammals and birds. Taken together, these data indicate that crocodiles not only have a similar pattern of layers that other amniotes possess but also that the immunocytochemical signatures of certain elements of the olfactory bulb are likewise shared.

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.

Distribution of gamma-aminobutyric acid immunoreactivity in the brain of the Siberian sturgeon (Acipenser baeri): Comparison with other fishes

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system (CNS) of vertebrates. Immunohistochemical techniques with specific antibodies against GABA or against its synthesizing enzyme, glutamic acid decarboxylase (GAD) allowed characterizing GABAergic neurons and fibers in the CNS. However, studies on the CNS distribution of GABAergic neurons and fibers of bony fishes are scant and were done in teleost species. With the aim of understanding the early evolution of this system in bony vertebrates, we analyzed the distribution of GABA-immunoreactive (-ir) and GAD-ir neurons and fibers in the CNS of a basal ray-finned fish, the Siberian sturgeon (Chondrostei, Acipenseriformes), using immunohistochemical techniques. Our results revealed the presence and distribution of GABA/GAD-ir cells in different regions of the CNS such as olfactory bulbs, pallium and subpallium, hypothalamus, thalamus, pretectum, optic tectum, tegmentum, cerebellum, central grey, octavolateralis area, vagal lobe, rhombencephalic reticular areas, and the spinal cord. Abundant GABAergic innervation was observed in most brain regions, and GABAergic fibers were very abundant in the hypothalamic floor along the hypothalamo-hypophyseal tract and neurohypophysis. In addition, GABA-ir cerebrospinal fluid-contacting cells were observed in the alar and basal hypothalamus, saccus vasculosus, and spinal cord central canal. The distribution of GABAergic systems in the sturgeon brain shows numerous similarities to that observed in lampreys, but also to those of teleosts and tetrapods.

Expression patterns of prosaposin and neurotransmitter-related molecules in the chick paratympanic organ

The paratympanic organ (PTO) is a small sense organ in the middle ear of birds that contains hair cells similar to those found in vestibuloauditory organs and receives afferent fibers from the geniculate ganglion. To consider the histochemical similarities between the PTO and vestibular hair cells, we examined the expression patterns of representative molecules in vestibular hair cells, including prosaposin, G protein-coupled receptor (GPR) 37 and GPR37L1 as prosaposin receptors, vesicular glutamate transporter (vGluT) 2 and vGluT3, nicotinic acetylcholine receptor subunit α9 (nAChRα9), and glutamic acid decarboxylase (GAD) 65 and GAD67, in the postnatal day 0 chick PTO and geniculate ganglion by in situ hybridization. Prosaposin mRNA was observed in PTO hair cells, supporting cells, and geniculate ganglion cells. vGluT3 mRNA was observed in PTO hair cells, whereas vGluT2 was observed in a small number of ganglion cells. nAChRα9 mRNA was observed in a small number of PTO hair cells. The results suggest that the histochemical character of PTO hair cells is more similar to that of vestibular hair cells than that of auditory hair cells in chicks.

Evolution of Local Circuit Neurons in Two Sensory Thalamic Nuclei in Amniotes

Local circuit neurons are present in the thalamus of all vertebrates where they are considered inhibitory. They play an important role in computation and influence the transmission of information from the thalamus to the telencephalon. In mammals, the percentage of local circuit neurons in the dorsal lateral geniculate nucleus remains relatively constant across a variety of species. In contrast, the numbers of local circuit neurons in the ventral division of the medial geniculate body in mammals vary significantly depending on the species examined. To explain these observations, the numbers of local circuit neurons were investigated by reviewing the literature on this subject in these two nuclei in mammals and their respective homologs in sauropsids and by providing additional data on a crocodilian. Local circuit neurons are present in the dorsal geniculate nucleus of sauropsids just as is the case for this nucleus in mammals. However, sauropsids lack local circuits neurons in the auditory thalamic nuclei homologous to the ventral division of the medial geniculate body. A cladistic analysis of these results suggests that differences in the numbers of local circuit neurons in the dorsal lateral geniculate nucleus of amniotes reflect an elaboration of these local circuit neurons as a result of evolution from a common ancestor. In contrast, the numbers of local circuit neurons in the ventral division of the medial geniculate body changed independently in several mammalian lineages.

Do crocodiles have a zona incerta?

In mammals, the zona incerta is thought to be involved in a number of behaviors: visceral activity, arousal, attention, and posture and locomotion. These diverse and complex features suggested that the zona incerta functions as a global or integrative node. Nevertheless, despite multiple investigations into its anatomy, physiology, and behavior in a variety of mammals, no specific character identifies the zona incerta besides its appearance in fiber-stained material and its relationship to surrounding structures. One such structure is the thalamic reticular nucleus whose caudal pole often contains some intermingled cells of the zona incerta. In crocodilians, the entopeduncular nucleus (ep) abuts the caudal pole of the thalamic reticular nucleus and displays different immunohistochemical properties and soma size when compared with neurons in the thalamic reticular nucleus itself. To determine if neurons in the ep differed from those in the thalamic reticular nucleus in Alligator mississippiensis, the ep was investigated using Golgi methodology. The morphology and soma size of neurons in the ep differed from those in the thalamic reticular nucleus and indicated that these two areas are indeed separate neuronal aggregates. Based on these data and the known relationships of the zona incerta to surrounding structures in mammals, the ep of crocodilians is suggested to be the counterpart of the zona incerta of mammals.

A thermoregulatory role of the medullary raphe in birds

The brainstem region medullary raphe modulates non-shivering and shivering thermogenesis and cutaneous vasomotion in rodents. Whether the same scenario occurs in the other endothermic group, i.e. birds, is still unknown. Therefore, we hypothesised that the medullary raphe modulates heat gain and loss thermoeffectors in birds. We investigated the effect of glutamatergic and GABAergic inhibitions in this specific region on body temperature (Tb), oxygen consumption (thermogenesis), ventilation (O2 supply in cold, thermal tachypnea in heat) and heat loss index (cutaneous vasomotion) in one-week-old chicken exposed to neutral (31°C), cold (26°C) and heat (36°C) conditions. Intra-medullary raphe antagonism of NMDA glutamate (AP5; 0.5, 5 mM) and GABAA (bicuculline; 0.05, 0.5 mM) receptors reduced Tb of chicks at 31°C and 26oC, due mainly to an O2 consumption decrease. AP5 transiently increased breathing frequency during cold exposure. At 31°C, heat loss index was higher in the bicuculline and AP5 groups (higher doses) than vehicle at the beginning of the Tb reduction. No treatment affected any variable tested at 36oC. The results suggest that glutamatergic and GABAergic excitatory influences on the medullary raphe of chicks modulate thermogenesis and glutamatergic stimulation prevents tachypnea, without having any role in warmth-defence responses. A double excitation influence on the medullary raphe may provide a protective neural mechanism for supporting thermogenesis during early life, when energy expenditure to support growth and homeothermy is high. This novel demonstration of a thermoregulatory role for the raphe in birds suggests a convergent brainstem neurochemical regulation of body temperature in endotherms.

Blood Testosterone Concentration and Testosterone-induced Aggressive Behavior in Male Layer Chicks: Comparison between Isolated- and Grouped-Raising

Testosterone (T) is known to induce aggressive behavior, mainly in male animals. Subcutaneous implantation of T-filled silastic tubes, rather than intramuscular injection of T, is generally recommended for long-term treatment using exogenous T. However, the effect of T implantation on chicken aggressive behavior has not been investigated. In addition, the concentration of T required to induce aggressive behavior or whether rearing conditions such as isolated- or grouped-raising affect T-induced aggressive behavior in chickens is not known. The present study aimed to examine the relationship between the lengths of T-filled tubes, blood T concentration, and aggressive behavior in group- and isolation-raised male layer chicks. The testes were bilaterally removed and silactic tubes of various lengths filled with crystalline T were subcutaneously implanted at 14 days of age. A social interaction test was performed to quantitatively assess chick aggressive behavior at 32 days of age. Comb weight and size were used to assess the activation of endogenous androgen receptors. Total aggression frequencies (TAF) and aggression establishment rate (AER) were used to evaluate aggressiveness. Significant positive correlations (P<0.001) were observed between the comb parameters and plasma T concentration. In the isolation-raised chicks, the TAF and AER were high irrespective of the lengths of the implanted T tubes or the corresponding plasma T concentrations. However, in the group-raised chicks, the AER tended to differ between the T-implanted aggressors (P=0.0902), and the AER significantly increased with implantation of 1.0-cm-long T-filled tubes (P<0.05), which corresponded to approximately 47 pg/mL plasma T concentration. These results suggest that both grouped raising and approximately 47 pg/mL plasma T concentration are required for the induction of T-dependent aggressive behavior, and that isolation-induced aggressive behavior is T-independent in male layer chicks.

Molecular architecture of the zebra finch arcopallium

The arcopallium, a key avian forebrain region, receives inputs from numerous brain areas and is a major source of descending sensory and motor projections. While there is evidence of arcopallial subdivisions, the internal organization or the arcopallium is not well understood. The arcopallium is also considered the avian homologue of mammalian deep cortical layers and/or amygdalar subdivisions, but one-to-one correspondences are controversial. Here we present a molecular characterization of the arcopallium in the zebra finch, a passerine songbird species and a major model organism for vocal learning studies. Based on in situ hybridization for arcopallial-expressed transcripts (AQP1, C1QL3, CBLN2, CNTN4, CYP19A1, ESR1/2, FEZF2, MGP, NECAB2, PCP4, PVALB, SCN3B, SCUBE1, ZBTB20, and others) in comparison with cytoarchitectonic features, we have defined 20 distinct regions that can be grouped into six major domains (anterior, posterior, dorsal, ventral, medial, and intermediate arcopallium, respectively; AA, AP, AD, AV, AM, and AI). The data also help to establish the arcopallium as primarily pallial, support a unique topography of the arcopallium in passerines, highlight similarities between the vocal robust nucleus of the arcopallium (RA) and AI, and provide insights into the similarities and differences of cortical and amygdalar regions between birds and mammals. We also propose the use of AMV (instead of nucleus taenia/TnA), AMD, AD, and AI as initial steps toward a universal arcopallial nomenclature. Besides clarifying the internal organization of the arcopallium, the data provide a coherent basis for further functional and comparative studies of this complex avian brain region.

The Medial Ventrothalamic Circuitry: Cells Implicated in a Bimodal Network

Previous avian thalamic studies have shown that the medial ventral thalamus is composed of several nuclei located close to the lateral wall of the third ventricle. Although the general connectivity is known, detailed morphology and connectivity pattern in some regions are still elusive. Here, using the intracellular filling technique in the chicken, we focused on two neural structures, namely, the retinorecipient neuropil of the n. geniculatus lateralis pars ventralis (GLv), and the adjacent n. intercalatus thalami (ICT). We found that the GLv-ne cells showed two different neuronal types: projection cells and horizontal interneurons. The projection cells showed variable morphologies and dendritic arborizations with axons that targeted the n. lentiformis mesencephali (LM), griseum tectale (GT), ICT, n. principalis precommissuralis (PPC), and optic tectum (TeO). The horizontal cells showed a widespread mediolateral neural process throughout the retinorecipient GLv-ne. The ICT cells, on the other hand, had multipolar somata with wide dendritic fields that extended toward the lamina interna of the GLv, and a projection pattern that targeted the n. laminaris precommissuralis (LPC). Together, these results elucidate the rich complexity of the connectivity pattern so far described between the GLv, ICT, pretectum, and tectum. Interestingly, the implication of some of these neural structures in visuomotor and somatosensory roles strongly suggests that the GLv and ICT are part of a bimodal circuit that may be involved in the generation/modulation of saccades, gaze control, and space perception.

NMDA receptors in the avian amygdala and the premotor arcopallium mediate distinct aspects of appetitive extinction learning

Extinction learning is an essential mechanism that enables constant adaptation to ever-changing environmental conditions. The underlying neural circuit is mostly studied with rodent models using auditory cued fear conditioning. In order to uncover the variant and the invariant neural properties of extinction learning, we adopted pigeons as an animal model in an appetitive sign-tracking paradigm. The animals firstly learned to respond to two conditioned stimuli in two different contexts (CS-1 in context A and CS-2 in context B), before conditioned responses to the stimuli were extinguished in the opposite contexts (CS-1 in context B and CS-2 in context A). Subsequently, responding to both stimuli was tested in both contexts. Prior to extinction training, we locally injected the N-methyl-d-aspartate receptor (NMDAR) antagonist 2-Amino-5-phosphonovaleric acid (APV) in either the amygdala or the (pre)motor arcopallium to investigate their involvement in extinction learning. Our findings suggest that the encoding of extinction memory required the activation of amygdala, as visible by an impairment of extinction acquisition by concurrent inactivation of local NMDARs. In contrast, consolidation and subsequent retrieval of extinction memory recruited the (pre)motor arcopallium. Also, the inactivation of arcopallial NMDARs induced a general motoric slowing during extinction training. Thus, our results reveal a double dissociation between arcopallium and amygdala with respect to acquisition and consolidation of extinction, respectively. Our study therefore provides new insights on the two key components of the avian extinction network and their resemblance to the data obtained from mammals, possibly indicating a shared neural mechanism underlying extinction learning shaped by evolution.

Screening of the Behavioral Tests for Monitoring Agonistic Behavior of Layer Chicks

Chicken agonistic behavior, a type of social behavior related to threatening and fighting, is among the most serious problems in the poultry industry. However, due to luck of effective models for investigating the brain mechanisms of the behavior, no effective measures have been taken. This study, therefore, aimed to select the behavioral tests available for monitoring chicken agonistic behavior. Two behavioral tests, resident-intruder (R-I) test and social interaction (SI) test, were performed for 10 minutes in 10 pairs of male layer chicks at 8, 12, 16, 20, and 24 days of age, and total agonistic frequencies (TAF: Sum of the frequencies of agonistic displays like pecking, biting, kicking, threatening, and leaping) and latency (the period of time from the beginning of the behavioral test to the occurrence of the first agonistic behavior) were measured as indices of agonistic behavior. Two-way repeated measures ANOVA revealed significant differences in TAF and latency between aggressors and opponents in both the behavioral tests. In the R-I test, the TAF of aggressors significantly increased from 8 to 20 days of age, and the latency significantly decreased from 8 to 24 days of age. In the SI test, however, the TAF of aggressors significantly increased and the latency significantly decreased only from 16 to 20 days of age. When the criterion of high agonistic behavior was defined as the TAF, where aggressors showed more than 30 times of TAF and the opponents did less than one-third TAF of aggressors, the aggression establishment rate (AER), which is equal to the number of aggressors showing high agonistic behavior per total behavioral trials, was significantly higher in the R-I test than in the SI test. These results suggest that the R-I test, rather than the SI test, is an effective tool for monitoring agonistic behavior of layer chicks.

GABAergic Neurons and Their Modulatory Effects on GnRH3 in Zebrafish

γ-Aminobutyric acid (GABA) is a major amino acid neurotransmitter in the vertebrate brain. To provide detailed information on the distribution of the GABA in zebrafish (Danio rerio), neurons were labeled with mCherry driven by the glutamic acid decarboxylase 67 (gad67) promoter. In the transgenic line Tg(gad67:mCherry), mCherry-positive gad67 cell bodies were predominantly localized to the olfactory bulb, pallial zones, subpallium zones, parvocellular preoptic nucleus, periventricular gray zone of optic tectum, torus semicircularis, posterior tuberculum, medial longitudinal fascicle, caudal zone of periventricular hypothalamus, and oculomotor nucleus. mCherry-positive fibers were widely distributed in the olfactory bulbs, subpallium, thalamus, ventral hypothalamic zone, tectum opticum, mesencephalon, and rhombencephalon. mCherry-positive neurons were also observed in the retina and the spinal cord. The anatomical relationships between GABAergic and gonadotrophin-releasing hormone 3 (GnRH3) neurons were investigated by crossing Tg(gad67:mCherry) fish with the previously established Tg(gnrh3:EGFP) transgenic line. GnRH3 cell bodies and fibers were contacted by GABAergic fibers directly in the ventral telencephalon and anterior tuberal nucleus. A subpopulation of GnRH3 neurons in the ventral telencephalic area was also labeled with mCherry, so some GnRH3 neurons are also GABAergic. GABAB receptor agonist (baclofen) and antagonist (CGP55845) treatments indicated that GABAB receptor signaling inhibited gnrh3 expression in larval fish but was stimulatory in adult fish. The expression of pituitary lhβ and fshβ was stimulated by intraperitoneal injection of baclofen in adult fish. We conclude that GABA via GABAB receptors regulates GnRH3 neurons in a developmentally dependent manner in zebrafish.

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.

Distribution of calcium-binding proteins in the pigeon visual thalamic centers and related pretectal and mesencephalic nuclei. Phylogenetic and functional determinants

Multichannel processing of environmental information constitutes a fundamental basis of functioning of sensory systems in the vertebrate brain. Two distinct parallel visual systems - the tectofugal and thalamofugal exist in all amniotes. The vertebrate central nervous system contains high concentrations of intracellular calcium-binding proteins (CaBPrs) and each of them has a restricted expression pattern in different brain regions and specific neuronal subpopulations. This study aimed at describing the patterns of distribution of parvalbumin (PV) and calbindin (CB) in the visual thalamic and mesencephalic centers of the pigeon (Columba livia). We used a combination of immunohistochemistry and double labeling immunofluorescent technique. Structures studied included the thalamic relay centers involved in the tectofugal (nucleus rotundus, Rot) and thalamofugal (nucleus geniculatus lateralis, pars dorsalis, GLd) visual pathways as well as pretectal, mesencephalic, isthmic and thalamic structures inducing the driver and/or modulatory action to the visual processing. We showed that neither of these proteins was unique to the Rot or GLd. The Rot contained i) numerous PV-immunoreactive (ir) neurons and a dense neuropil, and ii) a few CB-ir neurons mostly located in the anterior dorsal part and associated with a light neuropil. These latter neurons partially overlapped with the former and some of them colocalized both proteins. The distinct subnuclei of the GLd were also characterized by different patterns of distribution of CaBPrs. Some (nucleus dorsolateralis anterior, pars magnocellularis, DLAmc; pars lateralis, DLL; pars rostrolateralis, DLAlr; nucleus lateralis anterior thalami, LA) contained both CB- and PV-ir neurons in different proportions with a predominance of the former in the DLAmc and DLL. The nucleus lateralis dorsalis of nuclei optici principalis thalami only contained PV-ir neurons and a neuropil similar to the interstitial pretectal/thalamic nuclei of the tectothalamic tract, nucleus pretectalis and thalamic reticular nucleus. The overlapping distribution of PV and CB immunoreactivity was typical for the pretectal nucleus lentiformis mesencephali and the nucleus ectomamillaris as well as for the visual isthmic nuclei. The findings are discussed in the light of the contributive role of the phylogenetic and functional factors determining the circuits׳ specificity of the different CaBPr types.

Microconnectomics of the pretectum and ventral thalamus in the chicken (Gallus gallus)

The avian pretectal and ventrothalamic nuclei, encompassing the griseum tectale (GT), n. lentiformis mesencephali (LM), and n. geniculatus lateralis pars ventralis (GLv), are prominent retinorecipient structures related to optic flow operations and visuomotor control. Hence, a close coordination of these neural circuits is to be expected. Yet the connectivity among these nuclei is poorly known. Here, using intracellular labeling and in situ hybridization, we investigated the detailed morphology, connectivity, and neurochemical identity of neurons in these nuclei. Two different cell types exist in the GT: one that generates an axonal projection to the optic tectum (TeO), LM, GLv, and n. intercalatus thalami (ICT), and a second population that only projects to the LM and GLv. In situ hybridization revealed that most neurons in the GT express the vesicular glutamate transporter (VGluT2) mRNA, indicating a glutamatergic identity. In the LM, three morphological cell types were defined, two of which project axons towards dorsal targets. The LM neurons showed strong VGluT2 expression. Finally, the cells located in the GLv project to the TeO, LM, GT, n. principalis precommisuralis (PPC), and ICT. All neurons in the GLv showed strong expression of the vesicular inhibitory amino acid transporter (VIAAT) mRNA, suggesting a GABAergic identity. Our results show that the pretectal and ventrothalamic nuclei are highly interconnected, especially by glutamatergic and GABAergic neurons from the GT and GLv, respectively. This complex morphology and connectivity might be required to organize orienting visuomotor behaviors and coordinate the specific optic flow patterns that they induce. J. Comp. Neurol. 524:2208-2229, 2016. © 2015 Wiley Periodicals, Inc.

Morphology, projection pattern, and neurochemical identity of Cajal's "centrifugal neurons": the cells of origin of the tectoventrogeniculate pathway in pigeon (Columba livia) and chicken (Gallus gallus)

The nucleus geniculatus lateralis pars ventralis (GLv) is a prominent retinal target in all amniotes. In birds, it is in receipt of a dense and topographically organized retinal projection. The GLv is also the target of substantial and topographically organized projections from the optic tectum and the visual wulst (hyperpallium). Tectal and retinal afferents terminate homotopically within the external GLv-neuropil. Efferents from the GLv follow a descending course through the tegmentum and can be traced into the medial pontine nucleus. At present, the cells of origin of the Tecto-GLv projection are only partially described. Here we characterized the laminar location, morphology, projection pattern, and neurochemical identity of these cells by means of neural tracer injections and intracellular fillings in slice preparations and extracellular tracer injections in vivo. The Tecto-GLv projection arises from a distinct subset of layer 10 bipolar neurons, whose apical dendrites show a complex transverse arborization at the level of layer 7. Axons of these bipolar cells arise from the apical dendrites and follow a course through the optic tract to finally form very fine and restricted terminal endings inside the GLv-neuropil. Double-label experiments showed that these bipolar cells were choline acetyltransferase (ChAT)-immunoreactive. Our results strongly suggest that Tecto-GLv neurons form a pathway by which integrated tectal activity rapidly feeds back to the GLv and exerts a focal cholinergic modulation of incoming retinal inputs.

Dysfunction of hippocampal interneurons in epilepsy

Gamma-amino-butyric acid (GABA)-containing interneurons are crucial to both development and function of the brain. Down-regulation of GABAergic inhibition may result in the generation of epileptiform activity. Loss, axonal sprouting, and dysfunction of interneurons are regarded as mechanisms involved in epileptogenesis. Recent evidence suggests that network connectivity and the properties of interneurons are responsible for excitatory-inhibitory neuronal circuits. The balance between excitation and inhibition in CA1 neuronal circuitry is considerably altered during epileptic changes. This review discusses interneuron diversity, the causes of interneuron dysfunction in epilepsy, and the possibility of using GABAergic neuronal progenitors for the treatment of epilepsy.

Laminar segregation of GABAergic neurons in the avian nucleus isthmi pars magnocellularis: a retrograde tracer and comparative study

The isthmic complex is part of a visual midbrain circuit thought to be involved in stimulus selection and spatial attention. In birds, this circuit is composed of the nuclei isthmi pars magnocellularis (Imc), pars parvocellularis (Ipc), and pars semilunaris (SLu), all of them reciprocally connected to the ipsilateral optic tectum (TeO). The Imc conveys heterotopic inhibition to the TeO, Ipc, and SLu via widespread γ-aminobutyric acid (GABA)ergic axons that allow global competitive interactions among simultaneous sensory inputs. Anatomical studies in the chick have described a cytoarchitectonically uniform Imc nucleus containing two intermingled cell types: one projecting to the Ipc and SLu and the other to the TeO. Here we report that in passerine species, the Imc is segregated into an internal division displaying larger, sparsely distributed cells, and an external division displaying smaller, more densely packed cells. In vivo and in vitro injections of neural tracers in the TeO and the Ipc of the zebra finch demonstrated that neurons from the external and internal subdivisions project to the Ipc and the TeO, respectively, indicating that each Imc subdivision contains one of the two cell types hodologically defined in the chick. In an extensive survey across avian orders, we found that, in addition to passerines, only species of Piciformes and Rallidae exhibited a segregated Imc, whereas all other groups exhibited a uniform Imc. These results offer a comparative basis to investigate the functional role played by each Imc neural type in the competitive interactions mediated by this nucleus.

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.

Localization of cerebellin-2 in late embryonic chicken brain: implications for a role in synapse formation and for brain evolution

Cerebellin-1 (Cbln1), the most studied member of the cerebellin family of secreted proteins, is necessary for the formation and maintenance of parallel fiber-Purkinje cell synapses. However, the roles of the other Cblns have received little attention. We previously identified the chicken homolog of Cbln2 and examined its expression in dorsal root ganglia and spinal cord (Yang et al. [2010] J Comp Neurol 518:2818-2840). Interestingly, Cbln2 is expressed by mechanoreceptive and proprioceptive neurons and in regions of the spinal cord where those afferents terminate, as well as by preganglionic sympathetic neurons and their sympathetic ganglia targets. These findings suggest that Cbln2 may demonstrate a tendency to be expressed by synaptically connected neuronal populations. To further assess this possibility, we examined Cbln2 expression in chick brain. We indeed found that Cbln2 is frequently expressed by synaptically connected neurons, although there are exceptions, and we discuss the implications of these findings for Cbln2 function. Cbln2 expression tends to be more common in primary sensory neurons and in second-order sensory regions than it is in motor areas of the brain. Moreover, we found that the level of Cbln2 expression for many regions of the chicken brain is very similar to that of the mammalian homologs, consistent with the view that the expression patterns of molecules playing fundamental roles in processes such as neuronal communication are evolutionarily conserved. There are, however, large differences in the pattern of Cbln2 expression in avian as compared to mammalian telencephalon and in other regions that show the most divergence between the two lineages.

The HUDSEN Atlas: a three-dimensional (3D) spatial framework for studying gene expression in the developing human brain

We are developing a three-dimensional (3D) atlas of the human embryonic brain using anatomical landmarks and gene expression data to define major subdivisions through 12 stages of development [Carnegie Stages (CS) 12-23; approximately 26-56 days post conception (dpc)]. Virtual 3D anatomical models are generated from intact specimens using optical projection tomography (OPT). Using MAPAINT software, selected gene expression data, gathered using standard methods of in situ hybridization and immunohistochemistry, are mapped to a representative 3D model for each chosen Carnegie stage. In these models, anatomical domains, defined on the basis of morphological landmarks and comparative knowledge of expression patterns in vertebrates, are linked to a developmental neuroanatomic ontology. Human gene expression patterns for genes with characteristic expression in different vertebrates (e.g. PAX6, GAD65 and OLIG2) are being used to confirm and/or refine the human anatomical domain boundaries. We have also developed interpolation software that digitally generates a full domain from partial data. Currently, the 3D models and a preliminary set of anatomical domains and ontology are available on the atlas pages along with gene expression data from approximately 100 genes in the HUDSEN Human Spatial Gene Expression Database (http://www.hudsen.org). The aim is that full 3D data will be generated from expression data used to define a more detailed set of anatomical domains linked to a more advanced anatomy ontology and all of these will be available online, contributing to the long-term goal of the atlas, which is to help maximize the effective use and dissemination of data wherever it is generated.

The distribution of GAD67-mRNA in the adult zebrafish (teleost) forebrain reveals a prosomeric pattern and suggests previously unidentified homologies to tetrapods

We used in situ hybridization on sections to examine the distribution of GAD67-expressing cell populations in the entire forebrain of the adult zebrafish. GAD67 is predominantly expressed in the olfactory bulb (OB), all regions of the subpallium (including the dorsal, ventral, central, and lateral nucleus of the area ventralis [Vd, Vv, Vc, and Vl, respectively]), as well as preoptic (PPa, PPp, and PM), pretectal (PPd, PPv, PCN, PSp, and PSm), ventral (= pre-) thalamic (I, VM, and VL), hypothalamic (Hr, Hi, and Hc), preglomerular (P, PGa, PGl, PGm, and RT), and posterior tubercular (TPp and TPm) nuclei. Only scattered GAD67-expressing cells are seen in all pallial zones (Dm, Dd, Dc, Dl, and Dp) and in the previously unidentified bed nucleus of the stria medullaris (BNSM). The BNSM appears to be the adult teleostean derivative of the larval eminentia thalami (EmT). We identify the GAD67-positive entopeduncular nucleus proper (EN) as being homologous to the entopeduncular nucleus of nonprimate mammals. GAD67 is strongly expressed in the anterior thalamic nucleus (A). The anterior thalamic nucleus is laterally bordered by a distinct GAD67-expressing cell population, which we interpret as the previously unidentified reticular thalamic nucleus (RTN) of teleosts. Furthermore, we identified a GAD67-positive thalamic nucleus, the intercalated nucleus (IC), which is sandwiched between the GAD67-negative dorsal (DP) and central posterior (CP) thalamic nuclei. Overall, the distribution of GAD67-expressing cells highly resembles the distribution of gamma-aminobutyric acid (GABA)/GAD67-expressing cells found in the early zebrafish (teleost) forebrain and thus allows us to propose a prosomeric fate map of GABAergic cell populations.

Distinct roles of metabotropic glutamate receptor activation on inhibitory signaling in the ventral lateral geniculate nucleus

The ventral lateral geniculate nucleus (vLGN) has been implicated in numerous functions including circadian rhythms, brightness discrimination, pupillary light reflex, and other visuomotor functions. The contribution of inhibitory mechanisms in the regulation of vLGN neuron excitability remains unexplored. We examined the actions of metabotropic glutamate receptor (mGluR) activation on the intrinsic excitability and inhibitory synaptic transmission in different lamina of vLGN. Activation of mGluRs exerts distinct pre- and postsynaptic actions in vLGN neurons. In the lateral magnocellular subdivision of vLGN (vLGNl), the general mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) enhanced the frequency of GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSC) that persisted in the presence of sodium channel blocker tetrodotoxin (TTX) in a subpopulation of neurons (TTX insensitive). This increase is attributed to the increased output of dendritic GABA release from vLGN interneurons. In contrast, in the medial subdivision of vLGN (vLGNm), the mGluR agonist-mediated increase in sIPSC frequency was completely blocked by TTX. The selective Group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) increased sIPSC frequency, whereas the selective Group II mGluR agonist (2R, 4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC) significantly decreased sIPSC frequency in vLGNl neurons. Optic tract stimulation also produced an mGluR-dependent increase in sIPSC frequency in vLGNl neurons. In contrast, we were unable to synaptically evoke alterations in sIPSC activity in vLGNm neurons. In addition to these presynaptic actions, DHPG depolarized both vLGNl and vLGNm neurons. In vLGN interneurons, mGluR activation produced opposing actions: APDC hyperpolarized the membrane potential, whereas DHPG produced a membrane depolarization. The present findings demonstrate diverse actions of mGluRs on vLGN neurons localized within different vLGN lamina. Considering these different lamina are coupled with distinct functional roles, thus these diverse actions may be involved in distinctive forms of visual and visuomotor information processing.

Effect of GABAergic substances on firing rate and thermal coefficient of hypothalamic neurons in the juvenile chicken

The goal of the study is to investigate the GABAergic action on firing rate (FR) and temperature coefficient (TC) on hypothalamic neurons in the juvenile chicken. Extracellular recordings were obtained from 37 warm-sensitive, 32 cold-sensitive and 56 temperature-insensitive neurons in brain slices to determine the effect of GABA(A)-receptor agonist muscimol, GABA(A)-receptor antagonist bicuculline, GABA(B)-receptor agonist baclofen and GABA(B)-receptor antagonist CGP 35348. Muscimol and baclofen in equimolar concentrations (1 microM) significantly inhibited FR of the neurons, regardless of their type of thermosensitivity. In contrast, bicuculline, as well as CGP 35348 (10 microM) increased FR of the majority of the neurons. The TC of most chick hypothalamic neurons could not be estimated during muscimol application because FR was completely inhibited. GABA(B)-receptor agonist specifically increased TC. This effect was restricted to cold-sensitive neurons, which were determined in a high number. The TC was significantly increased (p<0.05) by baclofen and significantly decreased (p<0.05) by CGP 35348. The effects of muscimol and baclofen on FR and TC were prevented by co-perfusion of the appropriate antagonists bicuculline and CGP 35348. The results suggest that the fundamental mechanisms of GABAergic influence on temperature sensitive and insensitive neurons in the chicken PO/AH are conserved during evolution of amniotes.

GABA distribution in lamprey is phylogenetically conserved

The localization of gamma-aminobutyric acid (GABA) has been well described in most classes of vertebrates but not in adult lampreys. The question if the GABA distribution is similar throughout the vertebrate subphylum is therefore still to be addressed. We here investigate two lamprey species, the sea lamprey, Petromyzon marinus, and the river lamprey, Lampetra fluviatilis, and compare the GABA pattern with that of other vertebrates. The present immunohistochemical study provides an anatomical basis for the general distribution and precise localization of GABAergic neurons in the adult lamprey forebrain and brainstem. GABA-immunoreactive cells were organized in a virtually identical manner in the two species. They were found throughout the brain, with the following regions being of particular interest: the granular cell layer of the olfactory bulb, the nucleus of the anterior commissure, the septum, the lateral and medial pallia, the striatum, the nucleus of the postoptic commissure, the thalamus, the hypothalamus, and pretectal areas, the optic tectum, the torus semicircularis, the mesencephalic tegmentum, restricted regions of the rhombencephalic tegmentum, the octavolateral area, and the dorsal column nucleus. The GABA distribution found in cyclostomes is very similar to that of other classes of vertebrates, including mammals. Since the lamprey diverged from the main vertebrate line around 450 million years ago, this implies that already at that time the basic vertebrate plan for the GABA innervation in different parts of the brain had been developed.

Activation of cholecystokinin neurons in the dorsal pallium of the telencephalon is indispensable for the acquisition of chick imprinting behavior

Chick imprinting behavior is a good model for the study of learning and memory. Imprinting object is recognized and processed in the visual wulst, and the memory is stored in the intermediate medial mesopallium in the dorsal pallium of the telencephalon. We identified chicken cholecystokinin (CCK)-expressing cells localized in these area. The number of CCK mRNA-positive cells increased in chicks underwent imprinting training, and these cells expressed nuclear Fos immunoreactivity at high frequency in these regions. Most of these CCK-positive cells were glutamatergic and negative for parvalbumin immunoreactivity. Semi-quantitative PCR analysis revealed that the CCK mRNA levels were significantly increased in the trained chicks compared with untrained chicks. In contrast, the increase in CCK- and c-Fos-double-positive cells associated with the training was not observed after closure of the critical period. These results indicate that CCK cells in the dorsal pallium are activated acutely by visual training that can elicit imprinting. In addition, the CCK receptor antagonist significantly suppressed the acquisition of memory. These results suggest that the activation of CCK cells in the visual wulst as well as in the intermediate medial mesopallium by visual stimuli is indispensable for the acquisition of visual imprinting.

Expression of gamma-aminobutyric acid and glutamic acid decarboxylases in rat descending colon and their relation to epithelial differentiation

OBJECTIVE

To detect the expression of gamma-aminobutyric acid (GABA) and glutamic acid decarboxylases (GADs; including two isoforms GAD65 and GAD67) in the epithelial growth zones of the descending colon in rats, and to investigate their relation to epithelial differentiation and proliferation.

METHODS

The expression of GABA and GADs in rat descending colon was investigated by immunofluorescent staining and confocal laser scanning techniques, and goblet cells were further investigated by wheat-germ agglutinin histochemistry. In addition, GAD65 and GAD67 mRNAs were also detected by reverse transcription-polymerase chain reaction. Furthermore, evaluation of cell kinetics in colonic epithelia was conducted by ABC immunostaining using a monoclonal antibody against proliferating cell nuclear antigen (PCNA).

RESULTS

Immunoreactive GABA and GADs were distributed in the upper third of the crypts and at the luminal surface in the rat descending colon. Strong staining for GABA and GADs was localized mainly in the cytoplasm of epithelial cells near the neck of the crypts and along the luminal surface. In addition, GABA and GAD65 were also detected at the lamina propria in colonic mucosa. No staining for GABA or GADs was found in goblet cells. GAD65 and GAD67 mRNAs were identified in homogenates of rat descending colon. PCNA labeled nuclei were found in the lower two-thirds of the crypts.

CONCLUSIONS

The expression of GABA and GADs in the maturation and function zones of rat descending colon suggests that GABA may be involved in the differentiation of colonic epithelial cells.

Mammalian and avian neuroanatomy and the question of consciousness in birds

Some birds display behavior reminiscent of the sophisticated cognition and higher levels of consciousness usually associated with mammals, including the ability to fashion tools and to learn vocal sequences. It is thus important to ask what neuroanatomical attributes these taxonomic classes have in common and whether there are nevertheless significant differences. While the underlying brain structures of birds and mammals are remarkably similar in many respects, including high brain-body ratios and many aspects of brain circuitry, the architectural arrangements of neurons, particularly in the pallium, show marked dissimilarity. The neural substrate for complex cognitive functions that are associated with higher-level consciousness in mammals and birds alike may thus be based on patterns of circuitry rather than on local architectural constraints. In contrast, the corresponding circuits in reptiles are substantially less elaborated, with some components actually lacking, and in amphibian brains, the major thalamopallial circuits involving sensory relay nuclei are conspicuously absent. On the basis of these criteria, the potential for higher-level consciousness in these taxa appears to be lower than in birds and mammals.

Organization and evolution of the avian forebrain

Early 20th-century comparative anatomists regarded the avian telencephalon as largely consisting of a hypertrophied basal ganglia, with thalamotelencephalic circuitry thus being taken to be akin to thalamostriatal circuitry in mammals. Although this view has been disproved for more than 40 years, only with the recent replacement of the old telencephalic terminology that perpetuated this view by a new terminology reflecting more accurate understanding of avian brain organization has the modern view of avian forebrain organization begun to become more widely appreciated. The modern view, reviewed in the present article, recognizes that the avian basal ganglia occupies no more of the telencephalon than is typically the case in mammals, and that it plays a role in motor control and motor learning as in mammals. Moreover, the vast majority of the telencephalon in birds is pallial in nature and, as true of cerebral cortex in mammals, provides the substrate for the substantial perceptual and cognitive abilities evident among birds. While the evolutionary relationship of the pallium of the avian telencephalon and its thalamic input to mammalian cerebral cortex and its thalamic input remains a topic of intense interest, the evidence currently favors the view that they had a common origin from forerunners in the stem amniotes ancestral to birds and mammals.

Fiber connections of the compact division of the posterior pallial amygdala and lateral part of the bed nucleus of the stria terminalis in the pigeon (Columba livia)

The compact division of the posterior pallial amygdala (PoAc) and lateral part of the bed nucleus of the stria terminalis (BSTL) are components of the limbic system in the pigeon brain. In this study, we examined the position and fiber connections of these two nuclei by using Nissl staining and tract-tracing methods. PoAc occupies a central division in the posterior pallial amygdala. BSTL faces the ventral horn of the lateral ventricle and extends between A 7.25 and A 10.50. PoAc and BSTL connect bidirectionally by the stria terminalis. PoAc connects reciprocally with two nuclear groups in the cerebrum: 1) a continuum consisting of the caudoventral nidopallium, lateral part of the caudoventral nidopallium (NCVl), subnidopallium beneath NCVl, and piriform cortex and 2) rostral areas of the hemisphere, including the frontolateral and frontomedial nidopallium and the densocellular part of the hyperpallium. Extratelencephalic projections of PoAc terminate in the dorsomedial thalamic nuclei and reach the lateral hypothalamic area via the hypothalamic part of the occipito-mesencephalic tract. BSTL also connects reciprocally with two main regions: 1) the same continuum as for PoAc projections, except the piriform cortex and 2) rostral areas of the hemisphere, including the olfactory tubercle and nucleus accumbens. Extratelencephalic reciprocal connections are with the substantia nigra, nucleus subceruleus dorsalis, parabrachial nucleus, locus coeruleus, and nucleus of the solitary tract. The dorsomedial subdivision of the hippocampal formation projects massively to PoAc and BSTL. These findings indicate that PoAc and BSTL are important components of an interconnected neural circuit involving widespread regions of the neuraxis and mediating limbic-visceral functions.

Characteristic expression of γ-aminobutyric acid and glutamic acid decarboxylase in epithelial cells of rat descending colon

AIM: To detect the expression of γ-aminobutyric acid (GABA) and glutamate decarboxylases (GADs) in the epithelial growth zones of rat descending colon, and to investigate their relations with cell differentiation and proliferation.

METHODS: Immunocytochemical expression of GABA and GADs in the epithelial cells of rat descending colon was investigated by immunofluorescent staining and confocal laser scanning techniques, and the goblet cells were further revealed by wheat-germ agglutinin (WGA) histochemistry. GAD65 and GAD67 mRNAS were also detected by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. Furthermore, evaluation of cell kinetics in colonic epithelia was conducted by [³H]-thymidine autoradiography.

RESULTS: Immunoreactive GABA and GAD65 were distributed in the upper third of the crypts and at the luminal surface in the rat descending colon. Strong staining for GABA and GAD65 was localized mainly in the cytoplasm of epithelial cells near the neck of the crypts and along the luminal surface. Immunoreactivity of GAD67, however, was localized only on the luminal surface. In addition, GABA and GAD65 were detected at lamina propria in clonic mucosa. No staining for GABA or GADs was found in goblet cells. GAD65 and GAD67 mRNAs were both identified in the homogenates of rat descending colon, and the epithelium showed stronger hybridization signal for GAD65 mRNA than that for GAD67. Meanwhile, [³H]-thymidine labeled cells were found in the lower two-thirds of the crypts.

CONCLUSION: The expression of GABA and GADs in the maturation and function zones suggests that GABA might be involved in the differentiation and proliferation of the colonic epithelial cells.

Subpallial amygdala and nucleus taeniae in birds resemble extended amygdala and medial amygdala in mammals in their expression of markers of regional identity

Two regions were recently recognized as subpallial amygdaloid nuclei in birds, the nucleus taeniae of the amygdala (TnA) and the newly identified subpallial amygdala (SpA). Here we further confirm these nuclei to be subpallial and amygdaloid and show similarity to specific mammalian subpallial amygdaloid nuclei. By its topological, connectional and neurochemical traits, avian TnA has been suggested to be comparable to mammalian medial amygdala (MeA) and SpA to be comparable to the sublenticular part of mammalian extended amygdala (ExA). We examined molecular traits of these areas using immunohistochemistry for limbic system-associated membrane protein (LAMP) and in situ hybridization for glutamic acid decarboxylase-65 (GAD65) and chicken ovalbumin upstream promoter-transcription factor II (COUP-TF II). Mammalian GAD65 is a subpallial marker and was enriched in ExA and MeA. Chick GAD65 was enriched in SpA and TnA, indicating that they are subpallial. LAMP, which is enriched in limbic regions such as mammalian ExA and MeA, was enriched in avian SpA and TnA. COUP-TF II was enriched in mammalian amygdala including MeA and ExA to a lesser extent. In birds, COUP-TF II was enriched in TnA and moderate in SpA. Overlap of these markers confirms avian TnA resembles mammalian MeA and SpA resembles ExA.

Songbirds and the revised avian brain nomenclature

It has become increasingly clear that the standard nomenclature for many telencephalic and related brainstem structures of the avian brain is based on flawed once-held assumptions of homology to mammalian brain structures, greatly hindering functional comparisons between avian and mammalian brains. This has become especially problematic for those researchers studying the neurobiology of birdsong, the largest single group within the avian neuroscience community. To deal with the many communication problems this has caused among researchers specializing in different vertebrate classes, the Avian Brain Nomenclature Forum, held at Duke University from July 18-20, 2002, set out to develop a new terminology for the avian telencephalon and some allied brainstem cell groups. In one major step, the erroneous conception that the avian telencephalon consists mainly of a hypertrophied basal ganglia has been purged from the telencephalic terminology, and the actual parts of the basal ganglia and its brainstem afferent cell groups have been given new names to reflect their now-evident homologies. The telencephalic regions that were incorrectly named to reflect presumed homology to mammalian basal ganglia have been renamed as parts of the pallium. The prefixes used for the new names for the pallial subdivisions have retained most established abbreviations, in an effort to maintain continuity with the pre-existing nomenclature. Here we present a brief synopsis of the inaccuracies in the old nomenclature, a summary of the nomenclature changes, and details of changes for specific songbird vocal and auditory nuclei. We believe this new terminology will promote more accurate understanding of the broader neurobiological implications of song control mechanisms and facilitate the productive exchange of information between researchers studying avian and mammalian systems.