Immunohistochemical demonstration of calbindin-D 28K (CABP28K) in the spinal cord motoneurons of teleost fish

Complementary expression of calcium binding proteins delineates the functional organization of the locomotor network

Neuronal networks in the spinal cord generate and execute all locomotor-related movements by transforming descending signals from supraspinal areas into appropriate rhythmic activity patterns. In these spinal networks, neurons that arise from the same progenitor domain share similar distribution patterns, neurotransmitter phenotypes, morphological and electrophysiological features. However, subgroups of them participate in different functionally distinct microcircuits to produce locomotion at different speeds and of different modalities. To better understand the nature of this network complexity, here we characterized the distribution of parvalbumin (PV), calbindin D-28 k (CB) and calretinin (CR) which are regulators of intracellular calcium levels and can serve as anatomical markers for morphologically and potential functionally distinct neuronal subpopulations. We observed wide expression of CBPs in the adult zebrafish, in several spinal and reticulospinal neuronal populations with a diverse neurotransmitter phenotype. We also found that several spinal motoneurons express CR and PV. However, only the motoneuron pools that are responsible for generation of fast locomotion were CR-positive. CR can thus be used as a marker for fast motoneurons and might potentially label the fast locomotor module. Moreover, CB was mainly observed in the neuronal progenitor cells that are distributed around the central canal. Thus, our results suggest that during development the spinal neurons utilize CB and as the neurons mature and establish a neurotransmitter phenotype they use CR or/and PV. The detailed characterization of CBPs expression, in the spinal cord and brainstem neurons, is a crucial step toward a better understanding of the development and functionality of neuronal locomotor networks.

Zebrafish models of human motor neuron diseases: advantages and limitations

Motor neuron diseases (MNDs) are an etiologically heterogeneous group of disorders of neurodegenerative origin, which result in degeneration of lower (LMNs) and/or upper motor neurons (UMNs). Neurodegenerative MNDs include pure hereditary spastic paraplegia (HSP), which involves specific degeneration of UMNs, leading to progressive spasticity of the lower limbs. In contrast, spinal muscular atrophy (SMA) involves the specific degeneration of LMNs, with symmetrical muscle weakness and atrophy. Amyotrophic lateral sclerosis (ALS), the most common adult-onset MND, is characterized by the degeneration of both UMNs and LMNs, leading to progressive muscle weakness, atrophy, and spasticity. A review of the comparative neuroanatomy of the human and zebrafish motor systems showed that, while the zebrafish was a homologous model for LMN disorders, such as SMA, it was only partially relevant in the case of UMN disorders, due to the absence of corticospinal and rubrospinal tracts in its central nervous system. Even considering the limitation of this model to fully reproduce the human UMN disorders, zebrafish offer an excellent alternative vertebrate model for the molecular and genetic dissection of MND mechanisms. Its advantages include the conservation of genome and physiological processes and applicable in vivo tools, including easy imaging, loss or gain of function methods, behavioral tests to examine changes in motor activity, and the ease of simultaneous chemical/drug testing on large numbers of animals. This facilitates the assessment of the environmental origin of MNDs, alone or in combination with genetic traits and putative modifier genes. Positive hits obtained by phenotype-based small-molecule screening using zebrafish may potentially be effective drugs for treatment of human MNDs.

Immunohistochemical localization of calbindin-D28k and calretinin in the spinal cord of lungfishes

A common pattern of distribution of neurons and fibers containing the calcium-binding proteins calbindin-D28k (CB) and calretinin (CR) in the spinal cord of terrestrial vertebrates has been recently demonstrated. Lungfishes are considered the closest living relatives of tetrapods, but practically no experimental data exist on the organization of their spinal cord. By means of immunohistochemical techniques, the localization of CB and CR was investigated in the spinal cord of the African (Protopterus dolloi) and Australian (Neoceratodus forsteri) lungfishes. Abundant cell bodies and fibers immunoreactive for either CB or CR were widely distributed throughout the spinal cord. A large population of immunoreactive cells was found in the dorsal column of the gray matter in both species, and abundant cells were distributed in the lateral and ventral columns. Ventrolateral motoneurons and multipolar cells were only intensely CB and CR immunoreactive in Neoceratodus. For the most part, separate cell populations contained either CB or CR, but a small subset of dorsally located neurons contained both in the two lungfishes. Colocalization was found in motoneurons and in ventrolaterally located cells only in Neoceratodus. Fiber labeling showed a predominance of CR-containing axons in the lateral and ventral funiculi of presumed supraspinal origin. These results show that lung-fishes and tetrapods have many features in common, suggesting that primitive anatomical, and likely functional, organization of the spinal cord of tetrapods is present in lungfishes.

Immunohistochemical and hodological characterization of calbindin-D28k-containing neurons in the spinal cord of the turtle,Pseudemys scripta elegans

Neurons and fibers containing the calcium-binding protein calbindin-D28k (CB) were studied by immunohistochemical techniques in the spinal cord of adult and juvenile turtles, Pseudemys scripta elegans. Abundant cell bodies and fibers immunoreactive for CB were widely and distinctly distributed throughout the spinal cord. Most neurons and fibers were labeled in the superficial dorsal horn, but numerous cells were also located in the intermediate gray and ventral horn. In the dorsal horn, most CB-containing cells were located in close relation to the synaptic fields formed by primary afferents, which were not labeled for CB. Double immunohistofluorescence demonstrated distinct cell populations in the dorsal horn labeled only for CB or nitric oxide synthase, whereas in the dorsal part of the ventral horn colocalization of nitric oxide synthase was found in about 6% of the CB-immunoreactive cells in this region. Choline acetyltransferase immunohistochemistry revealed that only about 2% of the neurons in the dorsal part of the ventral horn colocalized CB, whereas motoneurons were not CB-immunoreactive. The involvement of CB-containing neurons in ascending spinal projections to the thalamus, tegmentum, and reticular formation was demonstrated combining the retrograde transport of dextran amines and immunohistochemistry. Similar experiments demonstrated supraspinal projections from CB-containing cells mainly located in the reticular formation but also in the thalamus and the vestibular nucleus. The revealed organization of the neurons and fibers containing CB in the spinal cord of the turtle shares distribution and developmental features, colocalization with other neuronal markers, and connectivity with other tetrapods and, in particular with mammals.

Immunohistochemical localization of calbindin-D28k and calretinin in the spinal cord of Xenopus laevis

Immunohistochemical techniques were used to investigate the distribution and morphology of neurons containing the calcium-binding proteins calbindin-D28k (CB) and calretinin (CR) in the spinal cord of Xenopus laevis and determine the extent to which this organization is comparable to that of mammals. Most CB- and CR-containing neurons were located in the superficial dorsal gray field, but with distinct topography. The lateral, ventrolateral, and ventromedial fields also possessed abundant neurons labeled for either CB or CR. Double immunohistofluorescence demonstrated that a subpopulation of dorsal root ganglion cells and neurons in the dorsal and ventrolateral fields contained CB and CR. By means of a similar technique, a cell population in the dorsal field was doubly labeled only for CB and nitric oxide synthase (NOS), whereas in the ventrolateral field colocalization of NOS with CB and CR was found. Choline acetyltransferase immunohistochemistry revealed that a subpopulation of ventral horn neurons, including motoneurons, colocalized CB and CR. The involvement of CB- and CR-containing neurons in ascending spinal projections was demonstrated combining the retrograde transport of dextran amines and immunohistochemistry. Cells colocalizing the tracer and CB or CR were quite numerous, primarily in the dorsal and ventrolateral fields. Similar experiments demonstrated supraspinal projections from CB- and CR-containing cells in the brainstem and diencephalon. The distribution, projections, and colocalization with neurotransmitters of the neuronal systems containing CB and CR in Xenopus suggest that CB and CR are important neuromodulator substances with functions conserved in the spinal cord from amphibians through mammals.

Calbindin-D28k and calretinin immunoreactivity in the spinal cord of the lizard Gekko gecko: Colocalization with choline acetyltransferase and nitric oxide synthase

The distribution of the calcium-binding proteins calbindin-D28k (CB) and calretinin (CR) was investigated in the spinal cord of the lizard Gekko gecko, by means of immunohistochemical techniques. Abundant cell bodies and fibers immunoreactive for either CB or CR were widely distributed throughout the spinal cord. Most neurons and fibers were labeled in the superficial dorsal horn, but numerous cells were also located in the intermediate gray and ventral horn. Distinct CB- and CR-containing cell populations were observed, although double immunohistochemistry revealed that 17-20% of the single-labeled cells for CB or CR in the dorsal horn contained both proteins. In addition, nitric oxide synthase was immunodetected in about 6% of the CB-positive neurons in the dorsal horn and in 10% in the ventral horn, whereas nitric oxide synthase was present in 9-13% of CR-positive cells in the dorsal horn and in 14% in the ventral horn. These doubly immunoreactive cells were restricted to areas IV, VII and VIII. Similar colocalization experiments revealed that 18-24% of the cholinergic cells in the ventral horn contained CB and 21-30% CR, with some variations throughout the length of the spinal cord. The pattern of distribution for CB and CR immunoreactivity in the spinal cord of the lizard, reported in the present study, is largely comparable to those reported for mammals, birds and anuran amphibians suggesting a high degree of conservation of the spinal systems modulated by these calcium-binding proteins.

Calbindin-D28k immunoreactivity in the spinal cord of Xenopus laevis and its participation in ascending and descending projections

Immunohistochemistry for calbindin-D28k (CB) revealed that the spinal cord of Xenopus laevis possess a large number of CB-containing neurons widely distributed in both the dorsal and ventral horns, including areas which possess long ascending projections to supraspinal structures. In addition, the presence of CB-immunoreactive axons in the spinal funiculi suggested that descending projections containing this calcium binding protein may originate in different brainstem nuclei. Apart from mapping CB-containing elements in the spinal cord, a double labeling approach was used that combined the retrograde transport of dextran amines with CB immunohistochemistry. Thus, dextran amine injections into the lateral reticular region of the rhombencephalon, the parabrachial region, the mesencephalon and the dorsal thalamus revealed many retrogradely labeled cells in the spinal cord, a few number of which were double labeled for CB and found in the superficial dorsal horn and in the ventral medial region of the ventral horn. Their axons passed mainly via the lateral funiculus. Tracer application into the cervical spinal cord, combined with CB immunohistochemistry, resulted in retrogradely labeled cells throughout the brain, five groups of which showed CB immunoreactivity: (1) the mesencephalic trigeminal nucleus, (2) the laterodorsal tegmental nucleus, (3) the raphe nucleus, (4) the middle reticular nucleus and (5) the inferior reticular nucleus. The presence of CB in spinal pathways suggests that CB may play a role in controlling spinal cells, mainly subserving visceroceptive and nociceptive information to supraspinal levels, and might also modulate reticulospinal pathways.

Calbindin and calretinin immunoreactivities identify different types of neurons in the adult lamprey spinal cord

The central pattern generator for locomotion in vertebrates is composed of different spinal neuronal populations that generate locomotor movement. In the lamprey spinal cord, several classes of interneurons have been identified based on morphologic and physiological criteria and integrated in the spinal cord circuits implicated in the generation of locomotion. However, the lack of histochemical markers for most of the interneurons makes it difficult to study whole populations along the spinal cord. We have investigated the immunoreactivity with antibodies raised against calbindin and calretinin. Several types of neurons could be classified: (1). strongly immunoreactive neurons located dorsomedially, (2). moderately immunoreactive neurons located laterally, (3). small weakly immunoreactive neurons, d). ventromedial neurons, (4). liquor contacting cells, and (5). motoneurons. The ventromedial group of calbindin-immunoreactive neurons also is immunoreactive for serotonin and, therefore, represents the ventromedial group of dopamine/serotonin spinal neurons. Some of the lateral calbindin-immunoreactive neurons may be CC-type cells (cells with caudal-crossed axons), because they are retrogradely labeled by tracer injections into the contralateral spinal cord. Other well-characterized cell types, such as sensory dorsal cells, lateral interneurons, descending propriospinal edge cells, and spinobulbar giant interneurons are negative for both calbindin and calretinin. Therefore, calbindin and calretinin are useful markers for the study of cell populations that may be integrated in locomotor circuits.

Calretinin expression in specific neuronal systems in the brain of an advanced teleost, the grey mullet (Chelon labrosus)

The distribution of calretinin (CR) in the brain of an "advanced" teleost, the grey mullet, was studied by using immunoblotting and immunocytochemical techniques. In immunoblots of protein extracts of rat and mullet brains, the CR antibody stained a single band of about 29 kDa. CR immunoreactivity was observed in specific neuronal populations of all brain regions. The primary olfactory system, the optic nerve fibers, and some sensory fibers of other cranial nerves exhibited strong CR immunoreactivity. In the forebrain, the CR-immunoreactive (CR-ir) populations were scarce in the telencephalon and hypophysiotrofic hypothalamus, but numerous in many specialized nuclei of the diencephalon (preglomerulosus complex, nucleus glomerulosus, anterior glomerular nucleus, nucleus diffusus) and pretectum (parvocellular and magnocellular superficial pretectal nuclei, central pretectal nucleus), which are related to sensory systems. The two main forebrain bundles, medial and lateral, contained numerous CR-ir fibers. The midbrain sensory centers (optic tectum and torus semicircularis) exhibited numerous CR-ir cells and fibers. Likewise, the secondary gustatory nucleus of the isthmus is one of the nuclei exhibiting more intense CR immunoreactivity. Characteristically, the efferent cerebellar system (eurydendroid cells and brachium conjunctivum) and some afferent cerebellar fibers were CR-ir. In the medulla oblongata, a number of reticular cells, the inferior olive, and the magnocellular octaval nucleus exhibited CR immunoreactivity. CR-ir motoneurons were also observed in the spinal cord and in the oculomotor nucleus. Together with results obtained in other vertebrates, present results suggest that neural systems using calretinin to maintain intracellular calcium concentration have been rather well conserved during vertebrate evolution.

Parvalbumin and calbindin D-28k in the human motor system and in motor neuron disease

Calbindin D-28k and parvalbumin are neuronal calcium binding proteins of interest in relation to neurodegenerative diseases. Expression of calbindin and parvalbumin may be one of the determinants of selective vulnerability in these disorders. The distribution of these proteins was surveyed in the normal human motor system and in motor neuron disease (MND) using immunocytochemistry in formalin fixed post-mortem tissues. CNS tissues from 14 MND patients (mean age 61.2 years, mean post-mortem delay 24.6 h) and seven controls (mean age 62.6 years, mean post-mortem delay 25.3 h) were studied. Preliminary studies on the effects of fixation were performed. In normal cases upper and lower motor neurons showed absent expression of both proteins. Several neuronal groups characteristically spared in MND showed varying patterns of immunoreactivity: oculomotor neurons showed parvalbumin staining of the perikaryon; the thoracic preganglionic sympathetic neurons showed calbindin staining in perikarya. Onuf's nucleus showed calbindin staining in the neuropil only. In motor neuron disease a loss of ventral horn interneurons and calbindin immunoreactive processes was observed with no other disease related changes in the spinal cord, brain-stem, or motor cortex. These findings are consistent with the hypothesis that the distribution of these proteins is one determinant of selective vulnerability to the neurodegenerative processes in MND acting via disturbance of neuronal calcium homeostasis.

Calbindin-D28K (CaBP28k)-like Immunoreactivity in Ascending Projections

This study concerns the involvement of calbindin-D28K (CaBP28k)-containing neurons in ascending spinal projections to the brainstem (nucleus of the solitary tract, lateral reticular nucleus area), pontine (parabrachial area) and mesencephalic (periaqueductal grey) structures. All these central structures are important in the processing of visceroception and visceronociception and all are targets for spinal efferents from similar areas. CaBP28k controls the excitability of cells by acting on intrinsic calcium metabolism. Results refer to the caudal spinal areas where the visceroceptive regions are concentrated. Experiments were performed through a double labelling approach that combined the retrograde transport of a protein - gold complex to identify the projection cells and immunohistochemistry to identify the CaBP28k-positive cells. The caudal spinal cord is rich in both CaBP28k-containing and projection cells. Cells colocalizing the protein and the retrograde tracer were quite numerous, with a particularly high concentration in the superficial layers of the dorsal horn (laminae I and outer II) and the lateral spinal nucleus. The other spinal areas containing immunoreactive projection cells were the reticular part of the neck of the dorsal horn, the medial laminae VII and VIII, lamina X and the sacral parasympathetic nucleus. The superficial layers and the neck of the dorsal horn are targets for nociceptive, visceroceptive and thermal inputs; the sacral parasympathetic column and lamina X are involved in visceroceptive integration. A functional role for the lateral spinal nucleus has not yet been established. Quite similar results were obtained for each of the ascending pathways under study. The high incidence of CaBP28k in spinal pathways suggests that calbindin has a major role in controlling the excitability of spinal cells subserving the processing of visceroception and/or visceronociception information to supraspinal levels. The participation of CaBP28k-immunoreactive cells in spinal ascending tract cells largely outnumbers those previously reported for various neuropeptides (Leah et al., Neuroscience, 24, 195 - 207, 1988)

Calbindin D-28k-immunoreactivity in rat muscle spindle; a light and electron microscopic study

The localization of the vitamin D-dependent calcium-binding protein, calbindin D-28k (CaBP), was studied immunocytochemically in rat striated muscle. CaBP-like immunoreactivity was found in some of the intrafusal fibres in muscle spindles. The spindle capsule and the perineurial sheath of the nerve bundles were occasionally immunoreactive to CaBP. In electron microscope the labelling for CaBP was found diffusely in sarcoplasm, in Z-bands and inside the terminal cisternae of intrafusal muscle fibres. The present findings suggest that CaBP may have a role in maintaining the appropriate microenvironment in the intracapsular space of muscle spindle and that CaBP may be involved in the function of intrafusal muscle fibres.

Calbindin D-28k and parvalbumin in the rat nervous system

This paper describes the distribution of structures stained with mono- and polyclonal antibodies to the calcium-binding proteins calbindin D-28k and parvalbumin in the nervous system of adult rats. As a general characterization it can be stated that calbindin antibodies mainly label cells with thin, unmyelinated axons projecting in a diffuse manner. On the other hand, parvalbumin mostly occurs in cells with thick, myelinated axons and restricted, focused projection fields. The distinctive staining with antibodies against these two proteins can be observed throughout the nervous system. Calbindin D-28k is primarily associated with long-axon neurons (Golgi type I cells) exemplified by thalamic projection neurons, strionigral neurons, nucleus basalis Meynert neurons, cerebellar Purkinje cells, large spinal-, retinal-, cochlear- and vestibular ganglion cells. Calbindin D-28k occurs in all major pathways of the limbic system with the exception of the fornix. Calbindin D-28k is, however, also found in some short-axon cells (Golgi type II), represented by spinal cord interneurons in layer II and interneurons of the cerebral cortex. It is also detectable in some ependymal cells and abundantly occurs in vegetative centres of the hypothalamus. The "paracrine core" of the nervous system and its adjunct (1985, Nieuwenhuys, Chemoarchitecture of the Brain. Springer, Berlin) is very rich in calbindin D-28k. The distribution of calbindin D-28k-positive neurons is very similar to that of the dihydroperydine subtype of calcium channels. Most of the cells containing calbindin D-28k are vulnerable to neurodegenerative processes. Parvalbumin-immunoreactive neurons have a different, and mostly complementary distribution compared with those which react with calbindin D-28k antisera, but in a few cases (Purkinje cells of the cerebellum, spinal ganglion neurons), both calcium-binding proteins co-exist in the same neuron. Many parvalbumin-immunoreactive cells in the central nervous system are interneurons (Golgi type II) and, to a lesser extent, long-axon cells (Golgi type I), whereas conditions are vice versa in the peripheral nervous system. Intrinsic parvalbuminic neurons are prominent in the cerebral cortex, hippocampus, cerebellar cortex and spinal cord. Long-axon parvalbumin-immunoreactive neurons are, for example, the Purkinje cells, neurons of the thalamic reticular nucleus, globus pallidus, substantia nigra (pars reticulata) and a subpopulation among large spinal-, retinal-, cochlear- and vestibular ganglion cells. Parvalbumin is rich in cranial nerve nuclei related to eye movements. In addition to nervous elements, parvalbumin immunoreactivity occurs in a few ependymal cells and in some pillar cells of the organ of Corti.(ABSTRACT TRUNCATED AT 400 WORDS)