The organization of the nucleus basalis-neostriatum complex of the mallard (Anas platyrhynchos L.) and its connections with the archistriatum and the paleostriatum complex

Arterial Supply of the Basal Ganglia: A Fiber Dissection Study

BACKGROUND

The basal ganglia, a group of subcortical nuclei located deep in the insular cortex, are responsible for many functions such as motor learning, emotion, and behavior control. Nowadays, because it has been shown that deep brain stimulation and insular tumor surgery can be performed by endovascular treatment, the importance of the vascular anatomy of the basal ganglia is being increasingly recognized.

OBJECTIVE

To explain the arterial blood supply of the basal ganglia using white matter dissection.

METHODS

The Klingler protocol was used to prepare 12 silicone-injected human hemispheres. The dissections were performed from lateral to medial with the fiber dissection technique to preserve arteries.

RESULTS

The globus pallidus blood supply came from the medial lenticulostriate, lateral lenticulostriate, and anterior choroidal arteries; the substantia nigra and subthalamic nucleus were supplied by the branches of posterior cerebral artery; the putamen was supplied by the lateral and medial lenticulostriate arteries; and the caudate nucleus was supplied by the lateral lenticulostriate and medial lenticulostriate arteries and the recurrent artery of Heubner.

CONCLUSION

Knowledge of the detailed anatomy of the basal ganglia and its vascular supply is essential for avoiding postoperative ischemic complications in surgeries related to the insula. In addition, knowledge of this anatomy and vascular relationship opens the doors to endovascular deep brain stimulation treatment. This study provides a 3-dimensional understanding of the blood supply to the basal ganglia by examining it using the fiber dissection technique. Further studies could use advanced imaging modalities to explore the vascular relationships with critical structures in the brain.

A brain atlas of the carrion crow (Corvus corone)

Corvidae, passerine songbirds such as jays, crows, and ravens known as corvids, have become model systems for the study of avian cognition. The superior cognitive capabilities of corvids mainly emerge from a disproportionally large telencephalon found in these species. However, a systematic mapping of the neuroanatomy of the corvid brain, and the telencephalon in particular, is lacking so far. Here, we present a brain atlas of the carrion crow, Corvus corone, with special emphasis on the telencephalic pallium. We applied four staining techniques to brain slices (Nissl, myelin, combination of Nissl and myelin, and tyrosine hydroxylase targeting catecholaminergic neurons). This allowed us to identify brain nuclei throughout the brain and delineate the known pallial subdivisions termed hyperpallium, entopallium, mesopallium, nidopallium, arcopallium, and hippocampal complex. The extent of these subdivisions and brain nuclei are described according to stereotaxic coordinates. In addition, 3D depictions of pallial regions were reconstructed from these slices. While the overall organization of the carrion crow's brain matches other songbird brains, the relative proportions and expansions of associative pallial areas differ considerably in agreement with enhanced cognitive skills found in corvids. The presented global organization of the crow brain in stereotaxic coordinates will help to guide future neurobiological studies in corvids.

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

The dorsal ventricular ridge (DVR), which is the largest component of the avian pallium, contains discrete partitions receiving tectovisual, auditory, and trigeminal ascending projections. Recent studies have shown that the auditory and the tectovisual regions can be regarded as complexes composed of three highly interconnected layers: an internal senso-recipient one, an intermediate afferent/efferent one, and a more external re-entrant one. Cells located in homotopic positions in each of these layers are reciprocally linked by an interlaminar loop of axonal processes, forming columnar-like local circuits. Whether this type of organization also extends to the trigemino-recipient DVR is, at present, not known. This question is of interest, since afferents forming this sensory pathway, exceptional among amniotes, are not thalamic but rhombencephalic in origin. We investigated this question by placing minute injections of neural tracers into selected locations of vital slices of the chicken telencephalon. We found that neurons of the trigemino-recipient nucleus basorostralis pallii (Bas) establish reciprocal, columnar and homotopical projections with cells located in the overlying ventral mesopallium (MV). "Column-forming" axons originated in B and MV terminate also in the intermediate strip, the fronto-trigeminal nidopallium (NFT), in a restricted manner. We also found that the NFT and an internal partition of B originate substantial, coarse-topographic projections to the underlying portion of the lateral striatum. We conclude that all sensory areas of the DVR are organized according to a common neuroarchitectonic motif, which bears a striking resemblance to that of the radial/laminar intrinsic circuits of the sensory cortices of mammals.

Endocranial Anatomy of the Giant Extinct Australian Mihirung Birds (Aves, Dromornithidae)

Dromornithids are an extinct group of large flightless birds from the Cenozoic of Australia. Their record extends from the Eocene to the late Pleistocene. Four genera and eight species are currently recognised, with diversity highest in the Miocene. Dromornithids were once considered ratites, but since the discovery of cranial elements, phylogenetic analyses have placed them near the base of the anseriforms or, most recently, resolved them as stem galliforms. In this study, we use morphometric methods to comprehensively describe dromornithid endocranial morphology for the first time, comparing Ilbandornis woodburnei and three species of Dromornis to one another and to four species of extant basal galloanseres. We reveal that major endocranial reconfiguration was associated with cranial foreshortening in a temporal series along the Dromornis lineage. Five key differences are evident between the brain morphology of Ilbandornis and Dromornis, relating to the medial wulst, the ventral eminence of the caudoventral telencephalon, and morphology of the metencephalon (cerebellum + pons). Additionally, dromornithid brains display distinctive dorsal (rostral position of the wulst), and ventral morphology (form of the maxillomandibular [V2+V3], glossopharyngeal [IX], and vagus [X] cranial nerves), supporting hypotheses that dromornithids are more closely related to basal galliforms than anseriforms. Functional interpretations suggest that dromornithids were specialised herbivores that likely possessed well-developed stereoscopic depth perception, were diurnal and targeted a soft browse trophic niche.

Trigeminal and telencephalic projections to jaw and other upper vocal tract premotor neurons in songbirds: sensorimotor circuitry for beak movements during singing

During singing in songbirds, the extent of beak opening, like the extent of mouth opening in human singers, is partially correlated with the fundamental frequency of the sounds emitted. Since song in songbirds is under the control of "the song system" (a collection of interconnected forebrain nuclei dedicated to the learning and production of song), it might be expected that beak movements during singing would also be controlled by this system. However, direct neural connections between the telencephalic output of the song system and beak muscle motor neurons in the brainstem are conspicuous by their absence, leaving unresolved the question of how beak movements are affected during singing. By using standard tract tracing methods, we sought to answer this question by defining beak premotor neurons and examining their afferent projections. In the caudal medulla, jaw premotor cell bodies were located adjacent to the terminal field of the output of the song system, into which many premotor neurons extended their dendrites. The premotor neurons also received a novel input from the trigeminal ganglion and an overlapping input from a lateral arcopallial component of a trigeminal sensorimotor circuit that traverses the forebrain. The ganglionic input in songbirds, which is not present in doves and pigeons that vocalize with a closed beak, may modulate the activity of beak premotor neurons in concert with the output of the song system. These inputs to jaw premotor neurons could, together, affect beak movements as a means of modulating filter properties of the upper vocal tract during singing.

Developmental Modes and Developmental Mechanisms can Channel Brain Evolution

Anseriform birds (ducks and geese) as well as parrots and songbirds have evolved a disproportionately enlarged telencephalon compared with many other birds. However, parrots and songbirds differ from anseriform birds in their mode of development. Whereas ducks and geese are precocial (e.g., hatchlings feed on their own), parrots and songbirds are altricial (e.g., hatchlings are fed by their parents). We here consider how developmental modes may limit and facilitate specific changes in the mechanisms of brain development. We suggest that altriciality facilitates the evolution of telencephalic expansion by delaying telencephalic neurogenesis. We further hypothesize that delays in telencephalic neurogenesis generate delays in telencephalic maturation, which in turn foster neural adaptations that facilitate learning. Specifically, we propose that delaying telencephalic neurogenesis was a prerequisite for the evolution of neural circuits that allow parrots and songbirds to produce learned vocalizations. Overall, we argue that developmental modes have influenced how some lineages of birds increased the size of their telencephalon and that this, in turn, has influenced subsequent changes in brain circuits and behavior.

Noradrenergic projections to the song control nucleus area X of the medial striatum in male zebra finches (Taeniopygia guttata)

There is considerable functional evidence implicating norepinephrine in modulating activity in the vocal control circuit of songbirds. However, our knowledge of noradrenergic inputs to the song system is incomplete. In this study, cholera toxin subunit B (CTB) injections into area X revealed projections from the noradrenergic nuclei locus coeruleus and subcoeruleus, and injections of biotinylated dextran amines into these noradrenergic nuclei labeled fibers in area X. The nonreciprocity of this connection was demonstrated by the absence of retrogradely labeled cells in area X following injections of CTB into the locus coeruleus. Additionally, we found novel inputs to area X from the nidopallium and arcopallium, the mesencephalic central gray, and the dorsolateralis anterior (DLL) and posterior (DLP) lateralis in the thalamus. Area X can be clearly distinguished from the surrounding medial striatum based on cytoarchitectural and chemical neuroanatomical criteria. We show here that neuromodulatory inputs to area X however, exhibit a considerable degree of overlap with the surrounding area. This finding suggests that regional specificity in neuromodulator action is most likely afforded by a specialization in receptor density and enzyme distribution rather than projections from the synthesizing nuclei. Our results extend current knowledge about noradrenergic projections to specialized nuclei of the song control circuit and provide neuroanatomical evidence for the functional action of norepinephrine-modulating context-dependent ZENK expression in area X. Furthermore, the novel projections to area X from telencephalic and thalamic areas could be new and interesting nodes in the striatopallidothalamic loop spanning the songbird brain.

Afferentation of the lateral nidopallium: A tracing study of a brain area involved in sexual imprinting in the zebra finch (Taeniopygia guttata)

The lateral forebrain of zebra finches that comprises parts of the lateral nidopallium and parts of the lateral mesopallium is supposed to be involved in the storage and processing of visual information acquired by an early learning process called sexual imprinting. This information is later used to select an appropriate sexual partner for courtship behavior. Being involved in such a complicated behavioral task, the lateral nidopallium should be an integrative area receiving input from many other regions of the brain. Our experiments indeed show that the lateral nidopallium receives input from a variety of telencephalic regions including the primary and secondary areas of both visual pathways, the globus pallidus, the caudolateral nidopallium functionally comparable to the prefrontal cortex, the caudomedial nidopallium involved in song perception and storage of song-related memories, and some parts of the arcopallium. There are also a number of thalamic, mesencephalic, and brainstem efferents including the catecholaminergic locus coeruleus and the unspecific activating reticular formation. The spatial distribution of afferents suggests a compartmentalization of the lateral nidopallium into several subdivisions. Based on its connections, the lateral nidopallium should be considered as an area of higher order processing of visual information coming from the tectofugal and the thalamofugal visual pathways. Other sensory modalities and also motivational factors from a variety of brain areas are also integrated here. These findings support the idea of an involvement of the lateral nidopallium in imprinting and the control of courtship behavior.

Thalamotelencephalic organization in birds

Investigation of thalamo-telencephalic connections reveals correspondences between the avian and mammalian thalamic subdivisions (which may or may not mean true homologies). Based mainly on hodological comparisons, the avian thalamus possesses the principal anatomical and functional subdivisions characteristic for mammals. The current review is focused on a comparative analysis of intralaminar, midline and mediodorsal nuclei. There is evidence for matching subdivisions in the case of midline thalamic and mediodorsal nuclei within the avian dorsal thalamic zone, whereas such correspondence is evident, if less complete, in the case of the intralaminar nuclei. Thalamic connections are also relevant to the debated issue of the avian 'prefrontal' cortex. From the current study it is suggested that the prefrontal analogue regions of the bird may spread across the rostrocaudal extent of telencephalon, the rostral nidopallial/mesopallial region (formerly known as medial neostriatum/hyperstriatum) being one subdivision, receiving direct input from the paraventricular thalamic nucleus homologue of midline thalamic region (the medial juxtaventricular region of the nucleus dorsomedialis posterior). Hodological evidence from the current study and other reports argues for the possibility that the area corticoidea dorsolateralis might be hodologically comparable to the cingulate cortex, receiving input from a mediodorsal thalamic-relevant subdivision (lateral subdivision of nucleus dorsomedialis anterior, and medial aspect of nucleus dorsolateralis pars medialis), which also projects on the caudal nidopallium close to (but not coextensive with) the nidopallium caudolaterale, another potential analogue of avian prefrontal cortex. The rostral dorsolateral aspect of nucleus dorsomedialis anterior thalami and the dorsal aspect of nucleus dorsolateralis pars medialis are partially comparable to the mammalian intralaminar nuclei, sharing connections to non-limbic 'corticoid' areas (the Wulst), and the reticular thalamic nuclei.

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.

The avian song system in comparative perspective

The song system of oscine birds has become a versatile model system that is used to study diverse problems in neurobiology. Because the song system is often studied with the intention of applying the results to mammalian systems, it is important to place song system brain nuclei in a broader context and to understand the relationships between these avian structures and regions of the mammalian brain. This task has been impeded by the distinctiveness of the song system and the vast apparent differences between the forebrains of birds and mammals. Fortunately, accumulating data on the development, histochemistry, and anatomical organization of avian and mammalian brains has begun to shed light on this issue. We now know that the forebrains of birds and mammals are more alike than they first appeared, even though many questions remain unanswered. Furthermore, the song system is not as singular as it seemed-it has much in common with other neural systems in birds and mammals. These data provide a firmer foundation for extrapolating knowledge of the song system to mammalian systems and suggest how the song system might have evolved.

Revised nomenclature for avian telencephalon and some related brainstem nuclei

The standard nomenclature that has been used for many telencephalic and related brainstem structures in birds is based on flawed assumptions of homology to mammals. In particular, the outdated terminology implies that most of the avian telencephalon is a hypertrophied basal ganglia, when it is now clear that most of the avian telencephalon is neurochemically, hodologically, and functionally comparable to the mammalian neocortex, claustrum, and pallial amygdala (all of which derive from the pallial sector of the developing telencephalon). Recognizing that this promotes misunderstanding of the functional organization of avian brains and their evolutionary relationship to mammalian brains, avian brain specialists began discussions to rectify this problem, culminating in the Avian Brain Nomenclature Forum held at Duke University in July 2002, which approved a new terminology for avian telencephalon and some allied brainstem cell groups. Details of this new terminology are presented here, as is a rationale for each name change and evidence for any homologies implied by the new names. Revisions for the brainstem focused on vocal control, catecholaminergic, cholinergic, and basal ganglia-related nuclei. For example, the Forum recognized that the hypoglossal nucleus had been incorrectly identified as the nucleus intermedius in the Karten and Hodos (1967) pigeon brain atlas, and what was identified as the hypoglossal nucleus in that atlas should instead be called the supraspinal nucleus. The locus ceruleus of this and other avian atlases was noted to consist of a caudal noradrenergic part homologous to the mammalian locus coeruleus and a rostral region corresponding to the mammalian A8 dopaminergic cell group. The midbrain dopaminergic cell group in birds known as the nucleus tegmenti pedunculopontinus pars compacta was recognized as homologous to the mammalian substantia nigra pars compacta and was renamed accordingly; a group of gamma-aminobutyric acid (GABA)ergic neurons at the lateral edge of this region was identified as homologous to the mammalian substantia nigra pars reticulata and was also renamed accordingly. A field of cholinergic neurons in the rostral avian hindbrain was named the nucleus pedunculopontinus tegmenti, whereas the anterior nucleus of the ansa lenticularis in the avian diencephalon was renamed the subthalamic nucleus, both for their evident mammalian homologues. For the basal (i.e., subpallial) telencephalon, the actual parts of the basal ganglia were given names reflecting their now evident homologues. For example, the lobus parolfactorius and paleostriatum augmentatum were acknowledged to make up the dorsal subdivision of the striatal part of the basal ganglia and were renamed as the medial and lateral striatum. The paleostriatum primitivum was recognized as homologous to the mammalian globus pallidus and renamed as such. Additionally, the rostroventral part of what was called the lobus parolfactorius was acknowledged as comparable to the mammalian nucleus accumbens, which, together with the olfactory tubercle, was noted to be part of the ventral striatum in birds. A ventral pallidum, a basal cholinergic cell group, and medial and lateral bed nuclei of the stria terminalis were also recognized. The dorsal (i.e., pallial) telencephalic regions that had been erroneously named to reflect presumed homology to striatal parts of mammalian basal ganglia were renamed as part of the pallium, using prefixes that retain most established abbreviations, to maintain continuity with the outdated nomenclature. We concluded, however, that one-to-one (i.e., discrete) homologies with mammals are still uncertain for most of the telencephalic pallium in birds and thus the new pallial terminology is largely devoid of assumptions of one-to-one homologies with mammals. The sectors of the hyperstriatum composing the Wulst (i.e., the hyperstriatum accessorium intermedium, and dorsale), the hyperstriatum ventrale, the neostriatum, and the archistriatum have been renamed (respectively) the hyperpallium (hypertrophied pallium), the mesopallium (middle pallium), the nidopallium (nest pallium), and the arcopallium (arched pallium). The posterior part of the archistriatum has been renamed the posterior pallial amygdala, the nucleus taeniae recognized as part of the avian amygdala, and a region inferior to the posterior paleostriatum primitivum included as a subpallial part of the avian amygdala. The names of some of the laminae and fiber tracts were also changed to reflect current understanding of the location of pallial and subpallial sectors of the avian telencephalon. Notably, the lamina medularis dorsalis has been renamed the pallial-subpallial lamina. We urge all to use this new terminology, because we believe it will promote better communication among neuroscientists. Further information is available at http://avianbrain.org

Definition and connections of the entopallium in the zebra finch (Taeniopygia guttata)

In birds the entopallium (formerly known as the core region of ectostriatum) is the major thalamorecipient zone, within the telencephalon, of the tectofugal visual system. Here we sought to redefine the entopallium in the zebra finch, particularly with respect to a laterally adjacent zone, known as the perientopallium (formerly known as the periectostriatal belt), and to determine its projections. We show that the entopallium can be defined by the almost complete overlap of dense terminations of thalamic rotundal afferents and intense cytochrome oxidase activity and parvalbumin immunoreactivity. The perientopallium, on the other hand, can be defined by relatively sparse projections from nucleus rotundus, a calretinin-positive plexus of nerve fibers, and weak cytochrome oxidase activity and parvalbumin immunoreactivity. Within the entopallium, medial and lateral parts can be distinguished on the basis of cell packing density, differential patterns of parvalbumin immunoreactivity and cytochrome oxidase activity, and different projections. We show that the entopallium projects laterally and diffusely to the perientopallium and nidopallium (formerly the neostriatum) and specifically and densely to a teardrop-shaped nucleus in the ventrolateral mesopallium (formerly known as the hyperstriatum ventrale), here called MVL (abbreviation used as a proper name). This latter projection arises predominantly from medial parts of the entopallium, which also receives a reciprocal projection from MVL, and projects to the lateral striatum. These findings suggest that the entopallium can be divided into medial and lateral parts having different functions, one of which is to provide for an extratelencephalic outflow from the medial part, via the lateral striatum. The findings also challenge the idea that informational flow through the various stations of the telencephalic tectofugal visual system is largely sequential and, together with findings in the chicken (Alpar and Tömböl), suggest instead that further substantial projections to telencephalic visual areas in birds can arise independently from both E (entopallium) and Ep (perientopallial belt).

Topographical organization of an indirect telencephalo-cerebellar pathway through the nucleus paracommissuralis in a teleost, Oreochromis niloticus

The nucleus paracommissuralis (NPC) of teleosts is a relay nucleus of an indirect telencephalo-cerebellar pathway. However, cells of origin in telencephalic subdivisions and terminal patterns of the NPC fibers in the cerebellum remain unclear. We studied these issues by means of tract-tracing methods in a cichlid, tilapia (Oreochromis niloticus). After tracer injections into the NPC, retrogradely labeled cells were found bilaterally in dorsal and ventral regions of the area dorsalis telencephali pars centralis (dDc and vDc) and area dorsalis telencephali pars dorsalis (Dd). Anterogradely labeled terminals were found in a caudal part of the bilateral corpus cerebelli (CC). The labeled terminals were restricted in the granular layer, which can be divided into dorsal and ventral regions based on cytoarchitecture. We injected tracers separately into the three telencephalic portions (dDc, vDc, and Dd) and into the dorsal or ventral regions of granular layer in the caudal CC. The results revealed a topographical organization of the indirect telencephalo-cerebellar pathway. A medial portion of the NPC received fibers from the vDc and projected to the ventral region of the caudal CC. An intermediate portion of the NPC received fibers from the dDc and Dd, and in turn projected to the dorsal region of the caudal CC. A lateral portion of the NPC received fibers from the Dd and in turn projected to the dorsal region of the caudal CC. The Dc is known to receive visual input via the area dorsalis telencephali pars lateralis, and the Dd is presumably a multimodal telencephalic portion. The present study suggests that the indirect telencephalo-cerebellar pathway through the NPC might convey descending visual and multimodal information to the CC in a topographical manner. We also demonstrated other indirect telencephalo-cerebellar pathways through the nucleus lateralis valvulae and the area pretectalis.

The distribution of dopamine, substance P, vasoactive intestinal polypeptide and neuropeptide Y immunoreactivity in the brain of the collared dove, Streptopelia decaocto

This study is part of a program intended to provide the neuroanatomical framework for investigations of the role of brain areas in specific aspects of behavior in the collared dove. In the present study, the distribution of dopamine-, substance P-, vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-immunoreactivity are mapped throughout the brain of this bird. For each substance, our observations are compared with data from studies in other species of birds. Over all, our data confirm the results of previous reports, but a few differences with data from some of these studies are found. The immunohistochemical data are used in an attempt to define more precisely cell areas and their subdivisions in the avian forebrain and brainstem, and to compare these areas to nuclei in the brain of mammals.

Organization of intratelencephalic projections to the visual Wulst of the chick

The avian visual Wulst, said to be the equivalent of the striate cortex in mammals, is the telencephalic visual area of the thalamofugal visual pathway. In this study, by means of retrograde labelling with fluorescent tracers injected into the Wulst regions in the left and right hemispheres, we have investigated the organization of the intratelencephalic projections to the visual Wulst in chicks. After injecting Fluorogold (FG), True blue (TB) or rhodamine into the visual Wulst, fluorescent-labelled neurones were found in the ipsilateral neostriatum frontale, pars lateralis (NFl), the ipsilateral neostriatum intermedium (NI) and the ipsilateral dorso-lateral neostriatum. Labelled neurones were also found in both the ipsilateral and contralateral archistriata. In addition, some neurones in the archistriatum were double-labelled, which indicates that these archistriatal neurones have axon collaterals projecting to the visual Wulst on both sides of the forebrain. Through these intratelencephalic afferents to the visual Wulst, visual information transmitted in the thalamofugal pathway may be modulated by other telencephalic areas. The possible roles of these connections in regulating behaviour are discussed.

Rostral wulst of passerine birds: II. Intratelencephalic projections to nuclei associated with the auditory and song systems

We have previously shown that the hyperstriatum accessorium (HA) of the rostral wulst in zebra finches and green finches is the origin of a pyramidal-like tract with substantial projections to the brainstem and cervical spinal cord. Here, we show that the HA also is the origin of a set of intratelencephalic projections with terminal fields in the lateral part of the frontal neostriatum, the shell surrounding the lateral magnocellular nucleus of the anterior neostriatum, the lobus parolfactorius surrounding area X, the nucleus interface, auditory fields L1 and L3, the shelf underlying the high vocal center, the dorsolateral caudal neostriatum, the dorsocaudal part of the nucleus robustus archistriatalis, and the ventral archistriatum. The cells of origin of these projections are located predominantly laterally in the HA, close to and sometimes within the intercalated HA, which receives somatosensory projections from the dorsal thalamus. The specific implications of these findings for auditory and vocal function are unclear, but the apparent overlap of auditory and somatosensory inputs in several of these regions suggests the possibility of mechanisms for stimulus enhancement or depression, depending on the congruence of stimuli within a cell's "in-register" multiple receptive fields.

Methionine enkephalin immunoreactivity in the brain of the budgerigar (Melopsittacus undulatus): similarities and differences with respect to oscine songbirds

The brain of the budgerigar (Melopsittacus undulatus), a small parrot that acquires new vocalizations throughout life, was examined for immunoreactivity to the opioid peptide methionine enkephalin (mENK). mENK is a highly prominent feature of the chemical architecture of the forebrain vocal system of oscine songbirds. Forebrain vocal control nuclei are believed to have evolved independently in parrots and songbirds (Streidter [1994] J. Comp. Neurol. 343:35-56); however, recent studies have found similarities in the neural organization of vocal control pathways in budgerigars and songbirds (Durand et al. [1997] J. Comp. Neurol. 377:179-206). Among the similarities are the existence of recursive pathways interconnecting vocal control neurons in the archistriatum, basal ganglia (i.e., lobus parolfactorius), and dorsal thalamus. In the present study, we found that all vocal control nuclei within the budgerigar forebrain exhibit prominent mENK-like immunoreactivity (ELI) in fibers and somata. We also found striking similarities between the morphology of ELI elements in budgerigar vocal control nuclei and that described previously in songbird vocal nuclei. Despite these similarities, the budgerigar dorsal striatopallidum (lobus parolfactorius, paleostriatum augmentatum, and paleostriatum primitivum) and somatomotor (anterior) archistriatum exhibit unique patterns of ELI. The dorsal striatopallidum contained far less ELI, whereas the archistriatum contained far more than would be expected on the basis of previous studies of opioid peptides in other avian species, including pigeons, chickens, and songbirds. These differences may reflect neural specializations unique to the budgerigar that contribute to the extraordinary flexibility of the vocal motor system of this species to acquire socially significant stimuli throughout life.

The dopaminergic innervation of the pigeon telencephalon: distribution of DARPP-32 and co-occurrence with glutamate decarboxylase and tyrosine hydroxylase

Dopaminergic axons arising from midbrain nuclei innervate the mammalian and avian telencephalon with heterogeneous regional and laminar distributions. In primate, rodent, and avian species, the neuromodulator dopamine is low or almost absent in most primary sensory areas and is most abundant in the striatal parts of the basal ganglia. Furthermore, dopaminergic fibres are present in most limbic and associative structures. Herein, the distribution of DARPP-32, a phosphoprotein related to the dopamine D1-receptor, was investigated in the pigeon telencephalon by immunocytochemical techniques. Furthermore, co-occurrence of DARPP-32-positive perikarya with tyrosine hydroxylase-positive pericellular axonal "baskets" or glutamate decarboxylase-positive neurons, as well as co-occurrence of tyrosine hydroxylase and glutamate decarboxylase were examined. Specificity of the anti-DARPP-32 monoclonal antibody in pigeon brain was determined by immunoblotting. The distribution of DARPP-32 shared important features with the distribution of D1-receptors and dopaminergic fibres in the pigeon telencephalon as described previously. In particular, DARPP-32 was highly abundant in the avian basal ganglia, where a high percentage of neurons were labelled in the "striatal" parts (paleostriatum augmentatum, lobus parolfactorius), while only neuropil staining was observed in the "pallidal" portions (paleostriatum primitivum). In contrast, DARPP-32 was almost absent or present in comparatively lower concentrations in most primary sensory areas. Secondary sensory and tertiary areas of the neostriatum contained numbers of labelled neurons comparable to that of the basal ganglia and intermediate levels of neuropil staining. Approximately up to one-third of DARPP-32-positive neurons received a basket-type innervation from tyrosine hydroxylase-positive fibres in the lateral and caudal neostriatum, but only about half as many did in the medial and frontal neostriatum, and even less so in the hyperstriatum. No case of colocalization of glutamate decarboxylase and DARPP-32 and no co-occurrence of glutamate decarboxylase-positive neurons and tyrosine hydroxylase-basket-like structures could be detected out of more than 2000 glutamate decarboxylase-positive neurons examined, although the high DARPP-32 and high tyrosine hydroxylase staining density hampered this analysis in the basal ganglia. In conclusion, the pigeon dopaminergic system seems to be organized similar to that of mammals. Apparently, in the telencephalon, dopamine has its primary function in higher level sensory, associative and motor processes, since primary areas showed only weak or no anatomical cues of dopaminergic modulation. Dopamine might exert its effects primarily by modulating the physiological properties of non-GABAergic and therefore presumably excitatory units.

Organization and efferent connections of the archistriatum of the mallard, Anas platyrhynchos L.: an anterograde and retrograde tracing study

The intratelencephalic and descending connections of the archistriatum of the mallard were studied using anterograde and retrograde tracers. Autoradiography after injections of [3H]-leucine served to visualize the intratelencephalic and extratelencephalic efferent connections of the archistriatum. Horseradish peroxidase (HRP), HRP-wheatgerm agglutinin, and fluorescent tracers were used to identify the precise origin of the projections to the various terminal fields found in the anterograde experiments. Four main regions can be recognized in the archistriatum of the mallard: (1) the rostral or anterior part that is a source of contralateral intratelencephalic projections, in particular to the contralateral archistriatum; (2) the dorsal intermediate archistriatum that is the origin of a large descending fiber system, the occipitomesencephalic tract, with projections to dorsal thalamic nuclei, the medial spiriform nucleus, the intercollicular nucleus, the deep tectum, parts of the mesencephalic and bulbar reticular formation, and the subnuclei of the descending trigeminal tract. There are no direct projections to motor nuclei. This part corresponds to the somatic sensorimotor part as defined by Zeier and Karten (1971, Brain Res. 31:313-326); it also contributes to the ipsilateral intratelencephalic connections and, to a lesser degree, to contralateral intratelencephalic connections. (3) The ventral intermediate archistriatum is another region that is also a source of intratelencephalic projections, in particular of those to the lobus parolfactorius. The most lateral zone sends fibers to the septal area. (4) The caudoventral intermediate and posterior archistriatum is another region that is a source of the projections to the hypothalamus and thus corresponds to the amygdaloid part of the archistriatum as defined by Zeier and Karten; it also contributes a modest component to the occipitomesencephalic tract. The different cell populations are not spatially separated, which makes it impossible to recognize distinct subnuclei within the four main regions of the archistriatum of the mallard.

Neural pathways for the control of birdsong production

As in humans, song production in birds involves the intricate coordination of at least three major groups of muscles: namely, those of the syrinx, the respiratory apparatus, and the upper vocal tract, including the jaw. The pathway in songbirds that controls the syrinx originates in the telencephalon and projects via the occipitomesencephalic tract directly upon vocal motoneurons in the medulla. Activity in this pathway configures the syrinx into phonatory positions for the production of species typical vocalizations. Another component of this pathway mediates control of respiration during vocalization, since it projects upon both expiratory and inspiratory groups of premotor neurons in the ventrolateral medulla, as well as upon several other nuclei en route. This pathway appears to be primarily involved with the control of the temporal pattern of song, but is also importantly involved in the control of vocal intensity, mediated via air sac pressure. There are extensive interconnections between the vocal and respiratory pathways, especially at brain-stem levels, and it may be these that ensure the necessary temporal coordination of syringeal and respiratory activity. The pathway mediating control of the jaw appears to be different from those mediating control of the syrinx and respiratory muscles. It originates in a different part of the archistriatum and projects upon premotor neurons in the medulla that appear to be separate from those projecting upon the syringeal motor nucleus. The separateness of this pathway may reflect the imperfect correlation of jaw movements with the dynamic and acoustic features of song. The brainstem pathways mediating control of vocalization and respiration in songbirds have distinct similarities to those in mammals such as cats and monkeys. However, songbirds, like humans, but unlike most other non-songbirds, have developed a telencephalic vocal control system for the production of learned vocalizations.

Synaptic terminals immunolabelled against glutamate in the lobus parolfactorius of domestic chicks (Gallus domesticus) in relation to afferents from the archistriatum

The lobus parolfactorius (LPO) has been implicated in memory formation associated with passive avoidance training of young posthatch domestic chicks. The anatomical circuitry underlying memory formation in the chick is likely to involve the intermediate medial hyperstriatum ventrale-archistriatum-LPO arc. In the present work, we attempted to combine an ultrastructural characterisation of archistriatal afferent terminals in LPO with a description of the synaptic structure of LPO, in particular those elements that are immunoreactive to glutamate and GABA. Ventral archistriatal regions of 7-day-old domestic chicks were iontophoretically injected with Phaseolus vulgaris leucoagglutinin and the anterograde transport of the tracer was detected in the LPO. Selected samples from these birds, and also from other day-old chicks, were resin-embedded and reacted for L-glutamate or GABA, using the postembedding immunocytochemical method. Glutamate was abundant in the neuropil of LPO and typically seen in axodendritic or axospinous terminals with asymmetrical junctions, often multiple or perforated postsynaptic appositions. Conversely, GABA was often present in aspinous dendrites, probably representing GABAergic local circuit neurons or (putative striatonigral) projection neurons. Archistriatal efferents terminating in LPO formed small en passant or terminal varicosities, with infrequent asymmetrical axospinous synapses. Glutamate was not detected in these boutons. The findings imply that the functional state of LPO, based on powerful glutamatergic excitation, may be modified by a non-glutamatergic archistriatal input.

Vocal control pathways through the anterior forebrain of a parrot (Melopsittacus undulatus)

A feature of the telencephalic vocal control system in the budgerigar (Melopsittacus undulatus) that has been hypothesized to represent a profound difference in organization from the oscine vocal system is its reported lack of an inherent circuit through the anterior forebrain. The present study reports anatomical connections that indicate the existence of an anterior forebrain circuit comparable in important ways to the "recursive" pathway of oscine songbirds. Results from anterograde and retrograde tracing experiments with biocytin and fluorescently labeled dextran amines indicate that the central nucleus of the anterior archistriatum (AAc) is the source of ascending projections upon the oval nuclei of the anterior neostriatum and ventral hyperstriatum (NAo and HVo, respectively). Efferent projections from the latter nuclei terminate in the lateral neostriatum afferent to AAc, thereby forming a short recurrent pathway through the pallium. Previously reported projections from HVo and NAo upon the magnocellular nucleus of the lobus parolfactorius (LPOm), and after LPOm onto the magnocellular nucleus of the dorsal thalamus (DMm; G.F. Striedter [1994] J. Comp. Neurol. 343:35-56), are confirmed. A specific projection from DMm onto NAom is also demonstrated; therefore, a recurrent pathway through the basal forebrain also exists in the budgerigar vocal system that is similar to the anterior forebrain circuit of oscine songbirds. Parallels between these circuits and mammalian basal ganglia-thalamo-cortical circuits are discussed. It is hypothesized that vocal control nuclei of the avian anterior neostriatum may perform a function similar to the primate supplemental motor area.

Organization of afferent and efferent projections of the nucleus basalis prosencephali in a passerine, Taeniopygia guttata

The connections of nucleus basalis (NB) of the rostral forebrain of the zebra finch were investigated electrophysiologically and with anterograde and retrograde tracing methods to determine their functional organization, the sources of their pontine afferents, and the targets of their telencephalic efferents. The nucleus was found to be partitioned into three major components, a rostral lingual part that received a hypoglossal projection via a lateral subnucleus of the principal sensory trigeminal nucleus (PrV), a middle beak part that received a trigeminal projection via a medial subnucleus of PrV, and a caudal auditory part that received a short latency auditory projection via the intermediate nucleus of the lateral lemniscus. Beak NB also received a projection from a paralateral lemniscal nucleus, and the dorsocaudal part of auditory NB and the medially adjacent neostriatum also received a projection from a lateral subnucleus of the superior vestibular nucleus (VS). The efferent projections of each of the three major parts of NB were mainly to the adjacent neostriatum frontale (NF), which then provided projections to the lobus parolfactorius (exclusive of area X), the lateral archistriatum intermedium (Ail), and the lateral neostriatum caudale (NCl). Ail received a projection from NCl and provided terminal fields to the contralateral NCl and the NF. The major projections of Ail, however, descended bilaterally through the brainstem via the occipitomesencephalic tracts, with dense terminations in the medial spiriform nucleus and with extensive bilateral terminations throughout the lateral reticular formation of the pons and medulla. For the most part, jaw, tongue, and tracheosyringeal motor nuclei did not receive terminations. The results suggest that NB in zebra finch, like NB in pigeon and duck, is likely to be a major component of trigeminal sensorimotor circuitry involved in feeding and in other oral-manipulative behaviors. Results also show that the auditory component of NB is not directly linked to the vocal control system at telencephalic levels, but the possibility remains that the lingual, beak, and auditory parts of NB play a role in vocalization by multisynaptic influences on cranial nerve motor nuclei innervating various parts of the vocal tract.

Ultrastructural morphology of synapses formed by corticostriatal terminals in the avian striatum

We studied the ultrastructural morphology of corticostriatal projections from two different avian 'neocortical' regions, namely, the hyperstriatum accessorium (HA) and the pallium externum (PE). Biotinylated dextran amine (BDA) was used to label the corticostriatal projection from either HA or PE to the striatum. The corticostriatal axons from both the PE and HA possessed numerous beaded varicosities with the striatum. These varicosities were filled with numerous round vesicles characterizing them as terminals. These terminals formed asymmetric synapses with spine heads and with dendrites of striatal neurons. The axospinous synapses outnumbered the axodendritic synapses by more than two to one. The diameters of labeled axons were typically 250-500 nm. The labeled terminals were typically 400-750 nm in diameter. No obvious differences between the ultrastructural morphology of the HA and the PE corticostriatal projections were observed. These data show that corticostriatal terminals and their synaptic contacts in birds are similar to those described in mammals.

Organization of the avian "corticostriatal" projection system: a retrograde and anterograde pathway tracing study in pigeons

Birds have well-developed basal ganglia within the telencephalon, including a striatum consisting of the medially located lobus parolfactorius (LPO) and the laterally located paleostriatum augmentatum (PA). Relatively little is known, however, about the extent and organization of the telencephalic "cortical" input to the avian basal ganglia (i.e., the avian "corticostriatal" projection system). Using retrograde and anterograde neuroanatomical pathway tracers to address this issue, we found that a large continuous expanse of the outer pallium projects to the striatum of the basal ganglia in pigeons. This expanse includes the Wulst and archistriatum as well as the entire outer rind of the pallium intervening between Wulst and archistriatum, termed by us the pallium externum (PE). In addition, the caudolateral neostriatum (NCL), pyriform cortex, and hippocampal complex also give rise to striatal projections in pigeon. A restricted number of these pallial regions (such as the "limbic" NCL, pyriform cortex, and ventral/caudal parts of the archistriatum) project to such ventral striatal structures as the olfactory tubercle (TO), nucleus accumbens (Ac), and bed nucleus of the stria terminalis (BNST). Such "limbic" pallial areas also project to medialmost LPO and lateralmost PA, while the hyperstriatum accessorium portion of the Wulst, the PE, and the dorsal parts of the archistriatum were found to project primarily to the remainder of LPO (the lateral two-thirds) and PA (the medial four-fifths). The available evidence indicates that the diverse pallial regions projecting to the striatum in birds, as in mammals, are parts of higher order sensory or motor systems. The extensive corticostriatal system in both birds and mammals appears to include two types of pallial neurons: 1) those that project to both striatum and brainstem (i.e., those in the Wulst and the archistriatum) and 2) those that project to striatum but not to brainstem (i.e., those in the PE). The lack of extensive corticostriatal projections from either type of neuron in anamniotes suggests that the anamniote-amniote evolutionary transition was marked by the emergence of the corticostriatal projection system as a prominent source of sensory and motor information for the striatum, possibly facilitating the role of the basal ganglia in movement control.

Differential induction of the ZENK gene in the avian forebrain and song control circuit after metrazole-induced depolarization

ZENK is an immediate early gene (IEG) that encodes a transcription factor protein, and its induction has been proposed as a necessary step in the cellular process underlying long-term memory formation. We have previously shown that ZENK is induced in adult songbird brain by the sound of birdsong, but, interestingly, induction did not occur in several areas known to respond to song stimuli. Conceivably, the ZENK gene may be repressed in these areas in adult birds. As a further test of this hypothesis, we administered metrazole, a strong GABAergic antagonist that leads to widespread excitation in the brain. Following metrazole, ZENK mRNA increases more than 10-fold throughout most of the telencephalon in both canaries and zebra finches, and primarily in neurons. In contrast, ZENK induction is much lower or absent in the archistriatum, the primary telencephalic sensory-recipient areas (including auditory field L), and the three telencephalic androgen receptor-containing song nuclei (high vocal center, lateral magnocellular nucleus of the anterior neostriatum, and the robust nucleus of the archistriatum). We did not observe any differences in ZENK induction patterns in juvenile versus adult zebra finches, or fall versus spring male canaries. Together with our previous studies of induction by song, these results suggest that in specific parts of the forebrain, including most of the song control system, IEG expression is subject to different constraints than in the rest of the forebrain. Understanding the molecular basis for this differential gene regulation may prove invaluable in understanding the organization of the song control circuit and the avian telencephalon.

Connectivity of the lobus parolfactorius of the domestic chicken (Gallus domesticus): an anterograde and retrograde pathway tracing study

In 1-week-old domestic chicks, the connectivity of the lobus parolfactorius (LPO), part of the avian basal ganglia, was investigated using Phaseolus vulgaris leucoagglutinin and horseradish peroxidase for anterograde and retrograde pathway tracing, respectively. Tyrosine hydroxylase immunocytochemistry was applied in combination with Phaseolus lectin to assess the overlap between LPO efferents and diencephalic and mesencephalic catecholamine centres. Anterograde projections from LPO were detected in the hyperstriatum, neostriatum, and paleostriatum. Intranuclear connections were also apparent within the LPO. Descending LPO efferents innervated the lateral mammillary and intramedial nuclei and the dorsomedial thalamic complex. Fibres from LPO were observed in the tectal gray, substantia nigra, area ventralis tegmentalis of Tsai, and the adjacent nucleus mesencephalicus profundus. Further caudally, projections from LPO reached the nucleus papillioformis, locus coeruleus, and subcoeruleus ventralis. LPO efferents were coextensive with tyrosine hydroxylase-positive cells in the nuclei mamillaris lateralis and intramedialis of the hypothalamus, area ventralis tegmentalis, substantia nigra, locus coeruleus, and subcoeruleus ventralis of mesencephalic and pontine tegmentum. Close contacts between LPO fibres and catecholamine cells were visible in the nigra and the area ventralis tegmentalis. Retrograde labelling from LPO was found in the archistriatum, dorsomedial thalamic complex, nuclei lateralis anterior and superficialis parvicellularis thalami, substantia nigra, central gray, area ventralis tegmentalis of Tsai, and locus coeruleus and in cells dorsal to the decussation of brachium conjunctivum. Reciprocal connections were verified between the LPO and the following areas: dorsomedial thalamic complex, central gray, substantia nigra, area ventralis of Tsai, and locus coeruleus.

Distributions of GABAA, GABAB, and benzodiazepine receptors in the forebrain and midbrain of pigeons

Autoradiographic and immunohistochemical methods were used to study the distributions of GABAA, GABAB and benzodiazepine (BDZ) receptors in the pigeon fore- and midbrain. GABAA, GABAB and BDZ binding sites were found to be abundant although heterogeneously distributed in the telencephalon. The primary sensory areas of the pallium of the avian telencephalon (Wulst and dorsal ventricular ridge) tended to be low in all three binding sites, while the surrounding second order belt regions of the pallium were typically high in all three. Finally, the outermost rind of the pallium (termed the pallium externum by us), which surrounds the belt regions and projects to the striatum of the basal ganglia, was intermediate in all three GABAergic receptors types. Although both GABAA and benzodiazepine receptors were abundant within the basal ganglia, GABAA binding sites were densest in the striatum and BDZ binding sites were densest in the pallidum. Among the brainstem regions receiving GABAergic basal ganglia input, the anterior and posterior nuclei of the ansa lenticularis showed very low levels of all three receptors, while the lateral spiriform nucleus and the ventral tegmental area/substantia nigra complex contained moderate abundance of the three binding sites. The dorsalmost part of the dorsal thalamus (containing nonspecific nuclei) was rich in all three binding sites, while the more ventral part of the dorsal thalamus (containing specific sensory nuclei), the ventral thalamus and the hypothalamus were poor in all three binding sites. The pretectum was also generally poor in all three, although some nuclei displayed higher levels of one or more binding sites. The optic tectum, inferior colliculus, and central gray were rich in all three sites, while among the isthmic nuclei, the parvicellular isthmic nucleus was conspicuously rich in BDZ sites. The results show a strong correlation of the regional abundance of GABA binding sites with previously described distributions of GABAergic fibers and terminals in the avian forebrain and midbrain. The regional distribution of these binding sites is also remarkably similar to that in mammals, indicating a conservative evolution of forebrain and midbrain GABA systems among amniotes.

Connections of the basal telencephalic areas c and d in the turtle brain

Tracer substances were injected into the basal telencephalic areas c and d of the turtle brain. These areas (Acd) have recently been shown to be connected reciprocally with the dorsal spino-medullary region, though the particular subregions involved in these projections remained unclear. We demonstrated that the efferent projections of area d terminate predominantly within or immediately adjacent to the trigeminal nuclear complex and in the high cervical spinal gray. The dendritic domain of the vagus-solitarius complex and the dorsal column nuclear complex might also receive some basal telencephalic efferents. The afferent projections to Acd, on the other hand, arise predominantly in the dorsal column nuclei as defined according to cytoarchitectural and hodological criteria. A few retrogradely labeled cells were found in the vagus-solitarius complex, the principal trigeminal nucleus and the high cervical spinal cord. Numerous labeled cells were found in the dorsolateral isthmo-rhombencephalic tegmentum, especially the n. visceralis secundarius, the n. vestibularis superior and parts of the lateral lemniscal complex. Aminergic cell populations projecting to Acd were the n. raphes inferior and superior, the locus coeruleus, the substantia nigra, pars compacta and the ventral tegmental area. Other meso-diencephalic cell groups were the griseum centrale (including the n. laminaris of the torus semicircularis), the n. interpeduncularis dorsalis, the nucleus of the fasciculus longitudinalis medialis, the nucleus and the nucleus interstitialis of flm, the n. interstitialis commissuralis posterior and then n. caudalis. Several hypothalamic regions, the reuniens complex and the perirotundal region of the thalamus also appeared to project heavily to Acd. Telencephalic areas retrogradely labeled after injection of tracer into Acd and its immediate surroundings were the rostral part of the lateral (olfactory) cortex, adjacent regions of the basal dorsal ventricular ridge and the n. centralis amygdalae, the n. tractus olfactorius lateralis as well as the areas g and h. The data suggest that areas c and d may correlate best with the 'extended' amygdala in mammals; further correlation with structures similar to the ventral striopallidum, however, cannot be excluded. Homostrategies are discussed with regard to the processing of higher-order somatovisceral information in turtles, birds and mammals.

Increases in neuronal bursting recorded from the chick lobus parolfactorius after training are both time-dependent and memory-specific

Day-old-chicks can be trained in one trial to avoid a methylanthranilate-coated bead (methyl-chicks). The lobus parolfactorius of the chick forebrain is an important structure for memory of this avoidance response. To examine training-induced electrophysiological changes in this structure, spontaneous neuronal bursting activity was measured from the lobus parolfactorius of anaesthetized, day-old methyl- and water-chicks (the latter chicks trained to peck at a water-coated bead) over the period 1-10 h post-test. Bursting was significantly higher in methyl-chicks over this period. This post-test increase was time-dependent: bursting in methyl-chicks was significantly higher only during the period 4-7 h post-test. In a second experiment, methyl-chicks were subjected to brief, subconvulsive electroshock 5 min post-training. When tested 1 h later about half of these chicks showed recall (avoided the bead) and half were amnesic (pecked the bead). These chicks were anaesthetized and bursting was recorded from the lobus parolfactorius. Chicks that showed recall exhibited a significantly higher level of bursting over the period 1-10 h post-test when compared to chicks that were amnesic. The time course of bursting was similar to that seen in non-electroshocked methyl-chicks. These results suggest that passive avoidance training induces a memory-specific, time-dependent increase in neuronal activity within the lobus parolfactorius of day-old chicks. This increase may be directly associated with long-term consolidation of memory for the task.

Peripheral and central terminations of hypoglossal afferents innervating lingual tactile mechanoreceptor complexes in Fringillidae

Injections of cholera toxin B subunit conjugated to horseradish peroxidase (CTB-HRP) were made into the lingual branch of the hypoglossal nerve in four species of finch in order to identify the innervation of the mechanoreceptors of the dermal papillae of the tongue, and simultaneously to determine the pattern of central projections of lingual hypoglossal afferents. The results showed that hypoglossal fibers innervate all the Herbst corpuscles and terminal cell receptors of the elaborately organized papillae of the dorsum of the tongue, of the shorter papillae in the ventral tongue, and the loose collection of Herbst corpuscles in the subpapillary region. Labelled fibers were also observed in the intralingual glands, in the intrinsic tongue muscles, and in the posterodorsal epithelium where they formed budlike structures. Retrogradely labelled cell bodies were located in the jugular ganglion and their central processes ascended and descended throughout the brainstem within the descending trigeminal tract (TTD). Terminal fields were observed within the dorsolateral part of the nucleus caudalis of TTD, predominantly ipsilaterally, and within the medial part of the dorsal horn of the first 4-6 cervical segments bilaterally. There were dense patches of termination over a dorsolateral subnucleus of the interpolated nucleus of TTD, and within two regions of the principal sensory trigeminal nucleus: a large one laterally and a small one medially. Terminal fields were also observed within the nucleus ventralis lateralis anterior of the rostral solitary complex, and within adjacent nuclei, which are probably equivalent to the dorsal sensory nuclei of the facial and glossopharyngeal nerves of other avian species. The results are interpreted in the light of the role of the tongue in species-specific patterns of feeding in finches, and the possible requirement for the central integration of touch and taste.