The avian somatosensory system. I. Primary spinal afferent input to the spinal cord and brainstem in the pigeon (Columba livia)

A comparative assessment of age-related nicotinamide adenine dinucleotide phosphate-diaphorase positivity in the spinal cord and medulla oblongata of pigeons, rats, and mice

Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (N-d) positive neurons have been extensively studied across various animals, and N-d neurodegenerative neurites have been detected in some aged animal models. However, detailed knowledge on N-d positivity and aging-related alterations in the spinal cord and medulla oblongata of pigeons is limited. In this study, we investigated N-d positivity and age-related changes in the pigeon's spinal cord and medulla oblongata and compared them to those in rats and mice. Pigeons, had more N-d neurons in the dorsal horn, around the central canal, and in the column of Terni in the thoracic and lumbar segments, with scattered neurons found in the ventral horn of the spinal segments. N-d neurons were also present in the white matter of the spinal cord. Morphometric analysis revealed that the size of N-d soma in the lumbosacral, cervical, and thoracic regions was substantially altered in aged pigeons compared to young birds. Furthermore, the lumbar to sacral segments underwent significant morphological alterations. The main findings of this study were the presence of age-related N-d positive bodies (ANB) in aged pigeons, predominantly in the external cuneate nucleus (CuE) and occasionally in the gracilis and CuEs. ANBs were also identified in the gracile nuclei and spinal cord in the aged rats and mice, whereas in aged rats, ANBs were detected in the CuE spinal nucleus. Immunohistochemistry showed that the age-related alterations occurred in the cell types and neuropeptides in old animals. The results suggest weak inflammatory response and neuronal dysfunction in the spinal cord in aged pigeons. Our results suggested that the ANB could be a potential aging marker for the central nervous system.

A novel relay nucleus between the inferior colliculus and the optic tectum in the chicken (Gallus gallus)

Processing multimodal sensory information is vital for behaving animals in many contexts. The barn owl, an auditory specialist, is a classic model for studying multisensory integration. In the barn owl, spatial auditory information is conveyed to the optic tectum (TeO) by a direct projection from the external nucleus of the inferior colliculus (ICX). In contrast, evidence of an integration of visual and auditory information in auditory generalist avian species is completely lacking. In particular, it is not known whether in auditory generalist species the ICX projects to the TeO at all. Here we use various retrograde and anterograde tracing techniques both in vivo and in vitro, intracellular fillings of neurons in vitro, and whole-cell patch recordings to characterize the connectivity between ICX and TeO in the chicken. We found that there is a direct projection from ICX to the TeO in the chicken, although this is small and only to the deeper layers (layers 13-15) of the TeO. However, we found a relay area interposed among the IC, the TeO, and the isthmic complex that receives strong synaptic input from the ICX and projects broadly upon the intermediate and deep layers of the TeO. This area is an external portion of the formatio reticularis lateralis (FRLx). In addition to the projection to the TeO, cells in FRLx send, via collaterals, descending projections through tectopontine-tectoreticular pathways. This newly described connection from the inferior colliculus to the TeO provides a solid basis for visual-auditory integration in an auditory generalist bird. J. Comp. Neurol. 525:513-534, 2017. © 2016 Wiley Periodicals, Inc.

Longitudinal projections of primary afferents from the single dorsal root ganglion of the cervical or lumbosacral enlargements in chickens

Central projections originated from a single dorsal root ganglion (DRG) were studied in the chicken focusing on the rostrocaudal extension of primary afferents in each lamina by using anterograde labeling by lectin-HRP injection into either the 15th or the 24th DRG. In the injection into the 15th DRG, labeled fibers (LFs) were found in a wide rostrocaudal range of laminas IV (the spinal segment (SS) 1-20) and V (SS 4-18) and in a narrow range of other laminas. In the injection into the 24th DRG, LFs were distributed in a similar rostrocaudal range in all laminas except for laminas VIII and IX. LFs in laminas VIII and IX were restricted in the tracer injected segment. LFs in the lateral funiculus derived from both the enlargements projected into the rostral lamina III in addition to the lower medulla oblongata. There was little overlap in the extent of the primary terminal areas from both the enlargements.

Morphometric analysis of telencephalic structure in a variety of neognath and paleognath bird species reveals regional differences associated with specific behavioral traits

Birds exhibit a huge array of behavior, ecology and physiology, and occupy nearly every environment on earth, ranging from the desert outback of Australia to the tropical rain forests of Panama. Some birds have adopted a fully nocturnal lifestyle, such as the barn owl and kiwi, while others, such as the albatross, spend nearly their entire life flying over the ocean. Each species has evolved unique adaptations over millions of years to function in their respective niche. In order to increase processing power or network efficiency, many of these adaptations require enlargements and/or specializations of the brain as a whole or of specific brain regions. In this study, we examine the relative size and morphology of 9 telencephalic regions in a number of Paleognath and Neognath birds and relate the findings to differences in behavior and sensory ecology. We pay particular attention to those species that have undergone a relative enlargement of the telencephalon to determine whether this relative increase in telencephalic size is homogeneous across different brain regions or whether particular regions have become differentially enlarged. The analysis indicates that changes in the relative size of telencephalic regions are not homogeneous, with every species showing hypertrophy or hypotrophy of at least one of them. The three-dimensional structure of these regions in different species was also variable, in particular that of the mesopallium in kiwi. The findings from this study provide further evidence that the changes in relative brain size in birds reflect a process of mosaic evolution.

The location of the major ascending and descending spinal cord tracts in all spinal cord segments in the mouse: actual and extrapolated

Information on the location of the major spinal cord tracts in the mouse is sparse. We have collected published data on the position of these tracts in the mouse and have used data from other mammals to identify the most likely position of tracts for which there is no mouse data. We have plotted the position of six descending tracts (corticospinal, rubrospinal, medial and lateral vestibulospinal, rostral and caudal reticulospinal) and eight ascending tracts (gracile; cuneate; postsynaptic dorsal columns; dorsolateral, lateral, and anterior spinothalamic; dorsal and ventral spinocerebellar) on diagrams of transverse sections of all mouse spinal cord segments from the first cervical to the third coccygeal segment.

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.

A pathway for predation in the brain of the barn owl (Tyto alba): projections of the gracile nucleus to the "claw area" of the rostral wulst via the dorsal thalamus

The Wulst of birds, which is generally considered homologous with the isocortex of mammals, is an elevation on the dorsum of the telencephalon that is particularly prominent in predatory species, especially those with large, frontally placed eyes, such as owls. The Wulst, therefore, is largely visual, but a relatively small rostral portion is somatosensory in nature. In barn owls, this rostral somatosensory part of the Wulst forms a unique physical protuberance dedicated to the representation of the contralateral claw. Here we investigate whether the input to this "claw area" arises from dorsal thalamic neurons that, in turn, receive their somatosensory input from the gracile nucleus. After injections of biotinylated dextran amine into the gracile nucleus and cholera toxin B chain into the claw area, terminations from the former and retrogradely labeled neurons from the latter overlapped substantially in the thalamic nucleus dorsalis intermedius ventralis anterior. These results indicate the existence in this species of a "classical" trisynaptic somatosensory pathway from the body periphery to the telencephalic Wulst, via the dorsal thalamus, one that is likely involved in the barn owl's predatory behavior. The results are discussed in the context of somatosensory projections, primarily in this and other avian species.

Neurobiological basis of sensory perception: welfare implications of beak trimming

The practice of beak trimming in the poultry industry occurs to prevent excessive body pecking, cannibalism, and to avoid feed wastage. To assess the welfare implications of the procedure, an emphasis of this paper has been placed on the anatomical structures that comprise the beak and mouth parts and a representation of the structures removed following beak trimming. Five animal welfare concerns regarding the procedure have been addressed, including the following: loss of normal beak function, short-term pain and temporary debilitation, tongue and nostril damage, neuromas and scar tissue, and long-term and phantom limb pain. Because all of the concerns involve the nervous system, the current knowledge of the avian somatosensory system was summarized. The critical components include touch, pain, and thermal receptors in the buccal cavity and bill, the trigeminal system, and neural projections mapped to the pallium (cortical-like tissue in the avian forebrain). At the present time, a need remains to continue the practice of beak trimming in the poultry industry to prevent head, feather, and vent pecking in some lines of birds. The procedure, however, should involve conservative trimming and be limited to young birds. Importantly, data show that removing 50% or less of the beak of chicks can prevent the formation of neuromas and allow regeneration of keratinized tissue to prevent deformed beaks and therefore positively affect the quality of life of birds during their lifetime.

Are paragriseal cells in the avian lumbosacral spinal cord displaced ventral spinocerebellar tract neurons?

In lumbosacral segments the spinal cord of birds contains numerous paragriseal neurons lying in the white matter of lateral and ventral funiculus. These paragriseal cells project to the cerebellum. Neurons of the dorsal horn (mainly Clarke's column) make up a dorsal spinocerebellar tract and neurons of the ventral horn (mainly spinal border cells) are at the origin of a ventral spinocerebellar tract. It was the aim of this investigation to look for the distribution of spinocerebellar ventral horn neurons and paragriseal cells in the thoracolumbosacral spinal cord of pigeons and to compare this distribution with that of the cervical enlargement. Neuroanatomical tracers were injected into the anterior cerebellum of pigeons and labeled spinal neurons were counted throughout the length of the spinal cord. In the cervical enlargement the number of spinocerebellar ventral horn neurons increases more rostral than that of dorsal horn neurons but the number of both groups of neurons decreases simultaneously at the caudal end of the enlargement. In the ventral horn of thoracolumbosacral segments the number of spinocerebellar ventral horn neurons and paragriseal cells increases again more rostrally than that of dorsal horn cells. However, the number of ventral horn cells decreases whereas that of paragriseal cells and of dorsal horn cells is maintained. This shows that the number of ventral horn cells decreases in favor of paragriseal cells, which supports the suggestion that paragriseal cells are displaced ventral horn spinocerebellar neurons. It is discussed whether the paragriseal neurons migrate toward their input.

Distribution of NADPH diaphorase-containing neurons in the pigeon central nervous system

The aim of the present study was to determine the distribution of nitric oxide-synthesizing neurons in the pigeon brain and spinal cord. Tissue sections were stained for reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d). In the telencephalon, intensely stained neurons with dendrites extending distally were seen in most regions. The ectostriatum was characterized by intensely and diffusely stained neuropil. In the diencephalon, intensely positive neurons were seen in the lateral hypothalamic region and lateral mammillary nucleus. In the mesencephalon, intensely stained, multipolar neurons were abundantly scattered in the central gray, nucleus intercollicularis, reticular formation, nucleus tegmenti pedunculo-pontinus, pars compacta, area ventralis of Tsai, and ansa lenticularis. In the rhombencephalon, positively-stained neurons were found in the pontine nuclei and reticular formation. The cerebellar cortex, except for Purkinje cells, was a preferential region for NADPH-d activity. Positive end-bulbs made contact on somata in the nucleus magnocellularis cochlearis. In the spinal cord, NADPH-d positive neurons were seen in layer II and the marginal nucleus. Our results demonstrated that the distribution of NADPH-d-containing neurons in the pigeon brain and spinal cord is more complex than in other avian species. Our findings indicate that NADPH-d-containing neurons are present in several sensory pathways, including olfactory, visual, auditory, and somatosensory tracts, although some nuclei in each system did not show NADPH-d activity. The wide distribution of NADPH-d activity in the pigeon CNS suggests that nitric oxide modulates sensory transmission in avian central nervous system.

The avian somatosensory system: the pathway from wing to Wulst in a passerine (Chloris chloris)

The organization of the wing component of the dorsal column-medial lemniscal pathway, and somatosensory projections from the thalamus to the Wulst, are described for an oscine member of the major group of birds, the Passeriformes. Wing primary afferents terminate throughout the cervical spinal cord, but between the brachial enlargement and the spino-medullary junction, they are confined to medial lamina V. Within the medulla, terminations extend rostrally and laterally to occupy the cuneate (Cu) and external cuneate nuclei (CuE). Ascending projections from Cu and CuE form the contralateral medial lemniscus, which has extensive projections to the midbrain and to the thalamus. In the midbrain the projections surround the central auditory nucleus densely, and terminate more sparsely within it. In the thalamus, specific terminations were observed in nucleus uvaeformis and in the nucleus dorsalis intermedius ventralis anterior (DIVA). DIVA projects to the ipsilateral rostral Wulst where it terminates in the intercalated hyperstriatum accessorium, in a distinct, regular patchy fashion. The somatosensory projections to the telencephalon in green finch are similar to those in pigeon, but dissimilar to those in budgerigar.

A non-thalamic pathway contributes to a whole body map in the brain of the budgerigar

Nucleus basalis (Bas) of the budgerigar contains an ordered, but distorted, somatotopic representation of the whole body, as does the primary somatosensory cortex (SI) of mammals. Unlike SI, however, the beak and body regions of Bas receive their sensory input via disynaptic pathways relaying in the pons. That to the body parts originates in a previously undescribed nucleus that receives its inputs from primary afferents via a novel, ipsilateral somatosensory pathway.

Central projections and somatotopic organisation of trigeminal primary afferents in pigeon (Columba livia)

Injections of cholera toxin B-chain conjugated to horseradish peroxidase into individual peripheral branches of the trigeminal nerve or into the trigeminal ganglion showed that an ascending trigeminal tract (TTA) terminated in distinct ventral and dorsal divisions of the principal sensory nucleus (PrVv and PrVd, respectively), and a descending tract (TTD) terminated within pars oralis, pars interpolaris, and pars caudalis divisions of the nucleus of TTD (nTTD) and within the dorsal horn of the first six cervical spinal segments. In PrVd, mandibular, ophthalmic, and maxillary projections were predominantly located dorsally, ventrally, and medially, respectively. In nTTD, mandibular projections lay dorsomedially, ophthalmic projections lay ventrolaterally, and maxillary projections lay in between. At caudal medullary and spinal levels, mandibular projections were situated medially, ophthalmic projections were situated laterally, and maxillary projections were situated centrally. The terminations within the dorsal horn were most dense in laminae III and IV and were least dense in lamina II, with laminae III-IV also receiving topographically organised contralateral projections. Extratrigeminal projections were mainly to the external cuneate nucleus by way of a lateral descending trigeminal tract (lTTD; Dubbeldam and Karten [1978] J. Comp. Neurol. 180:661-678) and to the region of the tract of Lissauer and lamina I of the dorsal horn. Other projections were to a region medial to the apex of pars interpolaris, to the nuclei ventrolateralis anterior (Vla) and presulcalis anterior (Pas) of the solitary complex, and sparsely to the lateral reticular formation (plexus of Horsley) ventral to TTD. No projections were seen to the trigeminal motor nuclei or to the cerebellum.

Projections of ankle joint afferents to the spinal cord and brainstem of the chicken (Gallus g. domesticus)

The projections of the ankle joint capsule afferents were studied by transganglionic transport of horseradish peroxidase injected directly into the ankle joint. The number and size of the labelled dorsal root ganglion cells were measured from synsacral nerves 2-9. In the dorsal root ganglia, all sizes of sensory neurones were labelled, and the largest number of labelled cells was in ganglia 5-7. The extensive sympathetic innervation of the ankle joint was identified by the large number of cell bodies labelled in the sympathetic ganglia of the paravertebral chain. Labelled afferent fibres projected to the spinal cord from the 2nd to the 8th synsacral nerves, with the rostral projection mainly via Lissauer's tract and the dorsal funiculus. Terminal labelling in the dorsal horn was identified in laminae I-III and VI, with a slight projection to V. Two areas of dense labelling, which did not correspond with the largest number of labelled dorsal root ganglion cells, were identified. A rostral area with the highest density of label was observed at the level of synsacral nerves 3-4 and a second slightly less dense area between synsacral nerves 7-8. In the caudal medulla, diffuse terminal labelling was observed in the nucleus gracilis et cuneatus, nucleus of the tractus solitarius, and the nucleus cuneatus externus. These results are discussed in a comparative context to identify similarities and differences between different primary afferent projections in birds and mammals and to highlight the possible functional significance of the avian articular afferent projection.

Convergence of somatosensory and auditory projections in the avian torus semicircularis, including the central auditory nucleus

Projections of dorsal column, spinal, and cochlear nuclei upon the central nucleus of the torus semicircularis (otherwise known as nucleus mesencephalicus lateralis, pars dorsalis, or MLd) and upon other toral nuclei were investigated in pigeon by anterograde and retrograde tracing and electrophysiological methods. The anatomical results showed that caudal regions of the dorsal column nuclei and medial lamina V of the upper four cervical spinal segments have extensive projections upon the contralateral central auditory nucleus and upon other nuclei of the torus, in particular the core portion of the preisthmic superficial area of Puelles et al. (L. Puelles, C. Rrobles, M. Martiez-de-la-Torre, and S. Martinez, 1994, J. Comp. Neurol. 340:98-125). The projections of nucleus angularis were found to terminate throughout most of the contralateral central nucleus except the dorsomedial portion at rostral levels, where the majority of the projections of nucleus laminaris were concentrated. Nucleus angularis (and to a lesser extent nucleus laminaris) was also found to have substantial projections to certain noncentral toral nuclei, in particular to the caudomedial shell nucleus of Puelles et al. (1994). As shown positively with both Nissl and cytochrome oxidase staining and negatively with substance P labeling, this nucleus is a medial extension of more caudal regions of the central nucleus, and it is suggested that it should be included as part of the auditory midbrain. The electrophysiological results confirmed the anatomical findings by showing that evoked potentials and multiunit activity can be recorded throughout the central and noncentral toral nuclei by using electrical stimulation of the radial nerve and auditory click stimuli. The core portion of the preisthmic superficial area, however, can be regarded as a distinct somatosensory nucleus of the midbrain. It is concluded that there is substantial convergence of somatosensory and auditory inputs within both central auditory and noncentral nuclei of the torus semicircularis in pigeon.

Central projections of primary afferents from the interosseous nerve in the pigeon

The interosseous nerve in the pigeon's leg innervates a string of Herbst corpuscles. Because Herbst corpuscles are vibration-sensitive, this study, using neuronal tracing methods, was expected to show the central representation of vibration sense. After application of a mixture of free and lectin-conjugated horseradish peroxidase to the interosseous nerve, labeled cell bodies of sensory and postganglionic neurons were mainly located in the dorsal root ganglia and paravertebral sympathetic ganglia L3/L4. In spinal segments L3/L4 fibers and terminals were mainly distributed at the lateral border of the head of the dorsal horn. In more cranial or caudal segments terminal fields were at intermediate parts of laminae I/II and laminae IV/V. Some labeled fibers entered the dorsal horn from medial to terminate in lamina IV. Primary afferents of the interosseous nerve projected directly to the gracile nucleus in the brainstem and distributed all along its rostrocaudal extent. Because the main terminal fields in the spinal cord are typical for the projection of small afferent fibers, vibration information seems to reach the brainstem via the dorsal column primary afferents.

Visual and somatosensory inputs to the avian song system via nucleus uvaeformis (Uva) and a comparison with the projections of a similar thalamic nucleus in a nonsongbird, Columba livia

Nucleus uvaeformis (Uva), previously identified as a component of song control circuitry in songbirds, and nucleus dorsolateralis posterior thalami, pars caudalis (DLPc) in pigeon, were compared with respect to their relative positions in the dorsolateral part of the posterior thalamus, their cell types, and their afferent and efferent projections. Both nuclei are closely related to the habenulointerpeduncular tract, have similar cell types, and receive a dense projection from deep layers of the optic tectum, predominantly ipsilaterally, and a distinct projection from the dorsal column and external cuneate nuclei, predominantly contralaterally. Recordings of multiple unit activity evoked by visual and somatosensory stimuli were used to guide injections of tracer into either DLPc or Uva, and the projections to the telencephalon were charted. Both nuclei were found to have a major terminal field in the medial part of the ipsilateral neostriatum intermedium (NI), known as nucleus interfacialis (NIf) in songbirds, and a minor terminal field in the roof of the neostriatum caudale (NC). In pigeon, the DLPc terminations in NC were within a region known as neostriatum dorsale (Nd), and, in male songbirds, the Uva terminations were in the high vocal center (HVC). Recordings of visual and somatosensory evoked activity were then used to guide injections of tracer into NI, and the afferent and efferent projections were again compared in pigeon and songbirds. The projections from either DLPc or Uva were confirmed, and terminal fields were observed either in Nd in pigeon, the dorsolateral part of NC in female songbirds, or HVC in male songbirds. Injections of tracer into either Nd or HVC confirmed their sources of afferents in DLPc or Uva, respectively, and in NI, but there was incomplete overlap of the distribution of retrogradely labelled cells in NI and the terminal fields of DLPc or Uva. It is concluded that DLPc and Uva are comparable nuclei having similar afferent and efferent projections relaying visual and somatosensory information to the telencephalon. The possible role of this information in vocal control is discussed.

Direct and indirect "cortico"-rubral and rubro-cerebellar cortical projections in the pigeon

In birds the red nucleus is the most rostral cell group in the brain having projections to all levels of the spinal cord (Cabot et al., Prog. Brain Res., 57:79-108, 1982), but its sources of afferents are incompletely known. In order to determine these, a series retrograde and anterograde tracing experiments was carried out, largely with cholera toxin B-chain conjugated to horseradish peroxidase. The results show that a sparse and diffuse projection to the red nucleus arises from deep regions of the hyperstriatum accessorium (HA) of the anterior Wulst, and that a much more dense projection arises from the caudal part of the nucleus principalis precommissuralis and the medial part of the medial spiriform nucleus (SpMm). These last two sources were themselves shown to receive a substantial projection from HA of the anterior Wulst. The red nucleus was also shown to project upon the cerebellar cortex of lobule VI, and SpM upon the cerebellar cortex of lobules VI through IX (Karten and Finger, Brain Res., 102:335-338, 1976; Clarke, J. Comp. Neurol., 174:535-552, 1977). Double retrograde labelling experiments with fluorescein and rhodamine labelled latex microspheres injected into the cerebellar cortex and spinal cord showed that the rubrocerebellar cortical neurons are a different population from, although intermixed with, the rubrospinal neurons.

Spinal neurons projecting to anterior or posterior cerebellum in the pigeon

Spinal afferent fibers have been shown to project both to lobules III-VI and lobule IX of the cerebellum in the pigeon. In the present investigation the cells of origin of these projections and the course of the axons at spinal levels have been studied by the retrograde transport of fluorescent dyes injected into both parts of the cerebellum. In the upper cervical segments labeled neurons are located predominantly in the ventral horn; the axons cross to the contralateral side. In the cervical enlargement labeled neurons concentrate in the avian cervical Clarke's column (ClC) and in cervical "spinal border cells" (SBC). The axons of ClC neurons project ipsilaterally into the dorsolateral funiculus and SBC project ipsilaterally into the ventrolateral funiculus. In caudal cervical and in thoracic segments dorsal horn neurons (laminae IV/V) are at the origin of an ipsilateral spinocerebellar pathway in the dorsalmost part of the lateral funiculus. In the lumbosacral enlargement there are mainly three spinocerebellar cell groups all of which project contralaterally into the ventral funiculus: ClC, SBC and paragriseal cells. During its ascent this pathway shifts to the lateral funiculus. In addition there is a crossed pathway from ventral horn cells throughout the spinal cord. Whereas approximately equal numbers of dorsal horn cells project to lobules III-VI and to lobule IX, the number of ClC neurons is strongly reduced after lobule IX injections and SBC neurons are nearly absent. Altogether lobule IX has a substantial input from dorsal horn neurons (cutaneous mechanoreception) whereas that to lobules III-VI is dominated by ClC and SBC (proprioreception).

Somatotopic organization of hindlimb skin sensory inputs to the dorsal horn of hatchling chicks (Gallus g. domesticus)

The somatotopic organization of skin sensory nerve projections to the lumbosacral dorsal horn of hatchling chickens was determined with the aid of transganglionic transport of horseradish peroxidase (HRP) processed with tetramethylbenzidine histochemistry. A total of eight hindlimb nerves were studied, five of which were purely cutaneous. When combined, the innervation fields of these nerves covered most of the hindlimb surface, allowing a nearly complete somatotopic map of the hindlimb to be generated. This report describes a novel pattern of cutaneous nerve projections to the dorsal horn. Unlike other vertebrates, cutaneous nerves of chickens formed two separate, somatotopically organized projections across the mediolateral axis of the dorsal horn; when serially reconstructed and superimposed, these projections produced two nonoverlapping somatotopic maps of the skin surface lying side by side. Each of these separate maps was nearly identical to the other in overall topology. These two separate maps appear to represent distinct modalities of sensory information, as projections composing the medial map were preferentially labeled by choleragenoid-HRP, whereas those composing the lateral map were preferentially labeled by wheat germ agglutinin-HRP. In mammals, these HRP ligands selectively label the central projections of myelinated and unmyelinated cutaneous afferents, respectively. The present study, therefore, strongly supports the cytoarchitectonic findings of Brinkman and Martin (Brain Res. 56:43-62, '73) that lamina III lies medial, rather than ventral, to lamina II in the chicken dorsal horn. Further, the present studies also suggest that laminae II and III of chickens are homologous to the homonymous laminae in the dorsal horn of mammals.

A novel spinal pathway and other connections to the spinocerebellum in the pigeon

Avian dorsal column nuclei do not project to the cerebellum. Injections of fluorescent tracers into the spinocerebellum of homing pigeons (Columba livia) disclosed a group of neurons located rostral to the dorsal column nuclei which receives spinal primary afferents, as confirmed by double-labeling experiments. Since this group has some similarities to the mammalian group x (location medial to the restiform body, spinal afferents, efferents to the cerebellum), this name was adopted for the pigeon. Further brainstem nuclei projecting to anterior or posterior spinocerebellum and with some relevance to transmission of spinal signals are described.

Cells of origin of avian postsynaptic dorsal column pathways

Whereas in the cervical spinal cord of pigeons lamina IV and medial lamina V neurons are at the origin of postsynaptic pathways to the dorsal column nuclei, lumbar lamina IV neurons do not project substantially beyond the cervical enlargement. There is, however a distinct group of medially located lumbar lamina V neurons which projects ipsilaterally to the dorsal column nuclei.

Sensory properties and afferents of the N. dorsolateralis posterior thalami of the pigeon

According to previous studies, the avian n. dorsolateralis posterior thalami (DLP) receives visual and somatosensory afferents. While some authors (e.g., Gamlin and Cohen: J. Comp. Neurol. 250:296-310, '86) proposed a distinction between a visual caudal (DLPc) and a somatosensory rostral (DLPr) part, other authors (e.g., Wild: Brain Res. 412:205-223, '87) could not confirm such a differentiation. The aim of the present experiment was to study with physiological and anatomical methods the proposed parcellation of the DLP into various components dealing with different modalities. The physiological properties of the DLP of the pigeon were analysed with extracellular single unit recordings. With the same approach, neurons of the n. dorsalis intermedius ventralis anterior (DIVA), a somatosensory relay nucleus in the dorsal thalamus, were also analysed. The afferents of the DLP were studied by using anatomical tract tracing techniques with retrograde and anterograde tracers. The sensory properties of DLP cells revealed that somatosensory, visual, and auditory modalities affect the neuronal firing frequency in this nucleus. All three modalities were present throughout the full caudorostral extent of the DLP. Cells recorded in DIVA responded nearly exclusively to somatosensory stimulation. Unlike the DLP, single units in DIVA generally had smaller receptive fields encompassing only one extremity. The analysis of afferent connections of the DLP by using injections of retrograde and anterograde tracers (HRP, WGA-HRP, Fast Blue, and Rhodamine-beta-isothiocyanate) demonstrated extensive projections from the nuclei gracilis et cuneatus (GC) and more sparse projections from the nucleus tractus descendens trigemini (TTD), and the nucleus cuneatus externus (CE). Brainstem afferents of the DLP came from different vestibular nuclei, various areas of the brainstem reticular formation, and the optic tectum. Prosencephalic afferents originated in the n. posteroventralis thalami (PV), the n. ventromedialis posterior thalami (VMP), the n. dorsalis intermedius ventralis anterior (DIVA), and the nucleus reticularis superior pars dorsalis and ventralis (RSd and RSv). Telencephalic afferents of the DLP came from the hyperstriatum accessorium (HA) and a group of cells at the borderline between the hyperstriatum intercalatus superior (HIS) and the hyperstriatum dorsale (HD). The somatosensory afferents of the DLP probably originate from the GC, TTD, and CE, whereas it is likely that the visual input is mediated by the optic tectum. The anatomical source for the acoustic input is unclear. The very long latencies of auditory DLP neurons make it likely that the acoustic input originates at least partly in the reticular formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Avian somatosensory system: II. Ascending projections of the dorsal column and external cuneate nuclei in the pigeon

The ascending projections of the dorsal column and external cuneate nuclei (DCN/CuE) in the pigeon were investigated in anterograde tracing experiments by using autoradiography or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). The results show that the majority of ascending projections decussate via internal arcuate fibers to form a contralateral medial lemniscus which ascends in a ventral position. In the brainstem, terminal fields were observed in the ventral lamella of the inferior olive (OI), the parabrachial nuclei (PB) of the dorsolateral pons, the intercollicular nucleus (ICo) of the midbrain, and the nucleus pretectalis diffusus (PD). In the diencephalon there were terminal fields in the strata cellulare externum and internum (SCE and SCI) of the caudal hypothalamus; in the intercalated (ICT), ventrolateral (VLT), and reticular nuclei of the ventral thalamus; in the nuclei principalis precommissuralis (PPC), spiriform medialis (SpM), and dorsolateralis posterior, pars caudalis (cDLP) of the caudal thalamus; and in the nuclei dorsalis intermedius ventralis anterior (DIVA), dorsolateralis posterior, pars rostralis (rDLP), dorsolateralis anterior (DLA), and dorsolateralis anterior, pars medialis (DLM) of the rostrodorsal thalamus. The origins of these projections within the DCN/CuE complex were verified in retrograde tracing experiments with WGA-HRP and were found to be partly differentiable with respect to their targets. The projections to DIVA, rDLP, DLA, DLM, cDLP, and SpM arise from all rostrocaudal levels of the DCN/CuE complex; those to ICo arise from caudomedial nuclear regions, while those to the hypothalamus and ventral thalamus arise from rostrolateral nuclear regions. Projections to PB arise from lamina I neurons of the dorsal horn of upper cervical spinal cord segments and from CuE. No evidence was found of a projection to the cerebellum. The distribution of the cells of origin of the medial lemniscus (ML) within the DCN/CuE complex was found to be largely coextensive with the areas of termination of primary spinal (Wild: J. Comp. Neurol. 240:377-395, '85) and some trigeminal (Dubbledam and Karten: J. Comp. Neurol. 180:661-678, '78) afferents. Furthermore, the areas of termination of the ML within the rostrodorsal and caudal thalamus are also either coextensive or closely associated with nuclei which provide a somatosensory projection to separate regions of the telencephalon (Wild: Brain Res. 412:205-223, '87). There are thus clear similarities in the overall pattern of somatosensory projections in the pigeon and in many mammalian species.

Degeneration patterns in the chicken central nervous system induced by ingestion of the organophosphorus delayed neurotoxin tri-ortho-tolyl phosphate. A silver impregnation study

Exposure to certain organophosphorus compounds results in a neurological condition known as organophosphorus-induced delayed neurotoxicity (OPIDN). OPIDN is characterized clinically by an initial post-exposure delay period of 8-14 days after which signs of progressively developing ataxia and paralysis of the hindlimbs are observed. Although several studies have reported the presence of degeneration induced by organophosphorus delayed neurotoxins in specific central nervous system (CNS) structures, none have systematically examined CNS changes seen in the most frequently studied animal model for OPIDN--the domestic fowl. In the present study, we assessed the location and extent of anterograde degeneration in the chicken CNS following exposure to tri-o-tolyl phosphate (TOTP). All birds were dosed with 500 mg TOTP/kg body weight and killed after post-exposure periods of 1, 2, 3, or 4 weeks. The brains and spinal cords were processed with Fink-Heimer and Nissl stains. In the spinal cord, axon degeneration was noted in the fasciculus gracilis at cervical levels two weeks after exposure to TOTP. At 3 weeks, degeneration was also present in the cervical part of the dorsal spinocerebellar tract, in the lumbar part of the medial pontine-spinal tract, and in lamina VII in the lumbar ventral horn. In the medulla, moderate amounts of terminal and preterminal degeneration appeared at two weeks in the lateral vestibular, gracile, external cuneate, and lateral cervical nuclei. Lesser amounts of degeneration were noted in the solitary, inferior olivary, and raphae nuclei, in the medial, descending and lateral vestibular nuclei, and in the lateral paragigantocellular, gigantocellular, and lateral reticular nuclei. Fiber degeneration was also present in the medullary portions of the dorsal and ventral spinocerebellar tracts and spinal lemniscus. In the cerebellum, moderate amounts of terminal degeneration appeared in the deep cerebellar nuclei at one week while moderate mossy fiber degeneration was first noted in the granular layers of cerebellar folia I-V at 3 weeks. These results indicate (1) that, in the CNS, axonal and terminal degeneration resulting from TOTP intoxication appears to be confined to the spinal cord, medulla and cerebellum, (2) that the time of onset of degeneration in different fiber tracts and nuclei ranges from one to three weeks post-exposure, and (3) that the delay in the appearance of clinical signs of OPIDN is consistent with the delayed onset of degeneration in many of the affected CNS fiber systems.

Somatosensory areas in the telencephalon of the pigeon. II. Spinal pathways and afferent connections

There are two somatosensory areas in the telencephalon of the pigeon which receive an input from the spinal somatosensory system: one in the rostral Wulst which consists of the three hyperstriatal layers (h. accessorium (HA), h. intercalatus superior (HIS) and h. dorsale (HD] and one in the caudal telencephalon (neostriatum caudale (NC), neostriatum intermedium (NI) and hyperstriatum ventrale (HV]. Recordings of evoked single unit or multi unit activity and of field potentials before and after lesions of spinal pathways at a high cervical level (C4) were made to determine the contribution of these pathways to the transmission of somatosensory signals to these telencephalic areas. The rostral Wulst area receives somatic signals only through dorsal tracts contralateral to the recording site. Inputs from the wing arise mainly through the dorsal columns (DC) and those from the leg largely through the dorsolateral funiculus (DLF). The spinal projection pathway to the caudal neostriatal area includes the dorsal tracts and parts of the lateral funiculi on both sides. There was no difference in response form between the wing and leg responses. Signals transmitted through the lateral pathways were found to elicit the earliest responses (6-13 ms, electrical stimulation) in the caudal forebrain, while signals travelling through the DC arrive later in the caudal area (about 14 ms for wing stimulation) than in the rostral Wulst area (about 9 ms). The afferent thalamic and intratelencephalic connections of the two somatosensory areas in the telencephalon of the pigeon were investigated with retrograde transport of the neuronal tracers horseradish-peroxidase (HRP) or wheatgerm agglutinated HRP (WGA-HRP), Fast Blue (FB) and Rhodamine-isothiocyanat (RITC). Small tracer-injections were made under electrophysiological control at somatosensory responsive locations. These investigations confirm the projection of the caudal part of the nucleus dorsolateralis posterior (DLPc) to the caudal area and of the nucleus dorsalis intermedius ventralis anterior (DIVA) to the rostral area. In addition, it could be shown that the NI/NC projects to the HV thus confirming the electrophysiological results reported in a companion paper (Funke 1989) that the HV is a secondary area. The integrative function of HV is supported by connections to other sensory and motor telencephalic areas. Combined injections of FB and RITC revealed a topographic projection from the DIVA to the anterior Wulst.(ABSTRACT TRUNCATED AT 400 WORDS)

Projections of the nucleus of the tractus solitarius in the pigeon (Columba livia)

With the aid of autoradiographic and histochemical (WGA-HRP) tracing techniques, the projections of the nucleus of the tractus solitarius (nTS) in the pigeon have been delineated and related to the viscerotopic organization of the nucleus. As in mammals, nTS projects to both brainstem and forebrain structures. At medullary levels, projections were seen to nTS itself, to the dorsal motor nucleus of the vagus and to the subjacent and more ventral reticular formation. There is a substantial projection to the parabrachial nuclear complex with terminations in all its subnuclei and minor projections to locus coeruleus and several mesencephalic areas, including the ventral area of Tsai, the nucleus of the ascending brachium conjunctivum, and the compact portion of the tegmental pedunculopontine nucleus. At diencephalic levels, projections to the hypothalamus (magnocellular periventricular nucleus, stratum cellulare internum and externum) and dorsal thalamus were seen. Terminal fields within the basal telencephalon included the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, and the nucleus accumbens. The organization of nTS projections in pigeons is correlated with the pattern of inputs to specific nTS subnuclei. Lateral tier subnuclei receiving cardiovascular and pulmonary inputs project upon the ventrolateral reticular formation and the ventrolateral parabrachial complex. Medial tier subnuclei receiving gustatory and gastrointestinal inputs project upon dorsal and medial parabrachial nuclei. Transparabrachial projections arise from nTS subnuclei receiving little or no primary input from the viscera.

Spinal projections to the dorsal column nuclei in pigeons

The dorsal column (DC) system was investigated in the pigeon by electrophysiological and anatomical methods. Field potentials recorded from the dorsal column nuclei (DCN) and evoked by electrical stimulation of cutaneous nerves showed two peaks in the case of wing nerve stimulation and one peak with leg nerve stimulation. Lesions of the DC or the ipsilateral dorsolateral funiculus (DLF) at a high cervical level (C4) indicate that a main input exists from the wing through the DC and from the leg through the DLF. With small injections of the fluorescent dye Fast blue into parts of the DCN it could be shown that aside from a primary afferent projection a well-developed postsynaptic dorsal column system exists only for the wing and that it takes its origin in the neurons of the lamina IV of the spinal dorsal horn.

Multisensory convergence in the thalamus of the pigeon (Columba livia)

Neuronal activity was extracellularly recorded from the nucleus dorsolateralis posterior thalami (DLP) of anesthetized pigeons. The sensitivity of individual cells to stimuli of different sensory modalities: somatosensory, visual and auditory was investigated. A substantial population of the DLP neurons responded to mechanical stimulation of large, often bilateral areas of the animal's body surface. No somatotopic organization could be detected. The functional properties of these neurons resembled those described for mammalian nucleus posterior thalami neurons. The visually responsive cells could be driven from large areas of the visual field. Auditory sensitive neurons were optimally activated by wideband noise. Twenty-nine percent of the DLP recorded neurons showed polysensory properties responding either to somatosensory and visual or to somatosensory and auditory stimuli.

The avian somatosensory system: connections of regions of body representation in the forebrain of the pigeon

In order to establish the basic connectivity of physiologically identified somatosensory regions of the thalamus and telencephalon in the pigeon, injections of wheatgerm agglutinin-horseradish peroxidase were made under electrophysiological control and the projections were charted following conventional neurohistochemistry. The physiological recordings generally confirmed the findings of Delius and Bennetto (Brain Research, 37 (1972) 205-221) of somatosensory sites within the dorsal thalamus, anterior hyperstriatum and caudomedial neostriatum, and the anatomical results show that the thalamic cells of origin of the projections to the two telencephalic regions are largely separate: a rostral cell group comprising nucleus dorsalis intermedius ventralis anterior projects to the anterior hyperstriatum accessorium (HA), whilst a caudal cell group comprising caudal regions of nucleus dorsolateralis posterior (DLP) projects to the medial neostriatum intermedium and caudale (NI/NC). Caudal DLP is also the origin of a visual projection to NI/NC, and its terminal field also approximates that of the thalamic auditory nucleus ovoidalis. Since the anterior HA and NI/NC were here shown to be reciprocally connected, there is a possibility of multimodal input to both telencephalic regions. HA was also further defined as the origin of the basal branch of the septomesencephalic tract, and hence potentially provides an outlet for both telencephalic somatosensory regions. The results are discussed within a comparative context.

Cells of origin of ascending pathways in the spinal cord of the pigeon

Horseradish peroxidase was applied to ascending spinal pathways at high cervical levels to determine the cells of origin of these pathways in the pigeon. In addition to primary afferent fibers many ipsilaterally located lamina IV neurons of cervical segments project to the dorsal columns, indicating a substantial postsynaptic dorsal column pathway in birds. Cells projecting in the dorsolateral part of the white matter were predominantly located in lamina I and V throughout the spinal cord (bilaterally) and in the avian Clarke's column (ipsilateral at cervical and contralateral at lumbar levels). Neurons in the ventral horn (laminae VI-VIII) project to lateral and ventral parts of the lateral funiculus.