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Structure of chick chromosomal genes for calbindin and calretinin.

The chick chromosomal gene for calbindin (the 28,000 Mr intestinal calcium-binding protein) was cloned, and all the exons and flanking regions were sequenced. The promoter region contains typical ATAAA and GGGCGG boxes, the latter being unusual in "non-housekeeping" genes. Three polyadenylation signals are found in the calbindin gene that correspond to the three known mRNAs. Transcription termination is not efficient because homology with consensus sequences found downstream from the polyadenylation signal is weak. There are ten introns, most of which do not fall at homologous positions, neither with respect to the sixfold repeating structure of the calbindin protein, nor with respect to previously sequenced genes for calmodulin and other calcium-binding proteins. The gene for the related protein calretinin was cloned and partially sequenced. The introns are in the same positions in the calretinin and calbindin genes. The introns have apparently been inserted during the divergence of the calcium-binding protein superfamily.

Animals↗

A comparative study of the calcium-binding proteins calbindin-D28K, calretinin, calmodulin and parvalbumin in the rat spinal cord.

Comparison of the immunocytochemical localizations revealed distinct patterns of differential distribution and overlapping of calbindin-D28K (CB-D28K), calretinin (CR), calmodulin (CM) and parvalbumin (PV) in the rat spinal cord. In some areas, one of the four calcium-binding proteins (CBPs) appears to be predominant, for example, CB-D28K in lamina I and ependymal cells, PV at the inner part of laminae II, CR in laminae V and VI and CM in motoneurons of lamina IX. In other regions of the spinal cord, more than one CBPs was abundant. CB-D28K and CR were similarly distributed in lamina II and the lateral spinal and cervical nucleus; CM and PV were similarly abundant in the ventromedial dorsal horn, internal basilar and central cervical nucleus; CR and PV were similarly abundant in the ventromedial dorsal horn, internal basilar and central cervical nucleus; CR and PV were similarly heterogeneous in the gracile fasciculus from caudal to rostral spinal cord. In the sacral dorsal gray commissure, the distribution patterns of CR and PV were clearly complementary. The unilateral ganglionectomies resulted in a substantial reduction of CBP-like immunoreactivity (CBP-LI) in the dorsal columns and a reduction of CM- and PV-LI in the ventromedial dorsal horn. In the motor system, only CM labeled large motoneurons in lamina IX and CB-D28K lightly stained pyramidal tract. The apparent absence of CM-LI in the superficial dorsal horn is contradictory to the presence of a CM-dependent nitric oxide synthase in the region. These data indicate that most CBP-LI in the dorsal column pathway had primary afferent origin, while the superficial dorsal horn exhibited intrinsic CBP immunoreactivity. The differential and selective localizations of CBPs in the spinal cord suggest a role for these proteins in spinal nociceptive processing, visceral regulation and dorsal column sensory pathways.

Animals↗

Triple immunofluorescence labelling of parvalbumin, calbindin-D28k and calretinin in rat and monkey brain.

This study presents novel techniques for the concomitant cytochemical detection of the calcium-binding proteins parvalbumin, calbindin-D28k and calretinin which are frequently used neuronal markers. For the triple immunofluorescence labelling of such antigens in rat and monkey brain--with emphasis on the cortex--we developed four different protocols which revealed obviously identical distribution patterns in consecutive sections. These methods included the simultaneous use of purified monoclonal antibodies directed against parvalbumin and calbindin--D28k--haptenized with biotin or digoxigenin--and subsequent visualization with fluorochromated hapten-recognizing immunoreagents. For the combined visualization of the calcium-binding proteins we applied the bright red fluorescent carbocyanine Cy3, blue fluorescent 7-amino-4-methylcoumarin-3-acetic acid (AMCA) and as green fluorophore either fluorescein or the newly introduced carbocyanine Cy2. The latter showed a higher fluorescence intensity and more resistance against photobleaching than fluorescein. In addition to clearly distinguished distribution patterns of the calcium-binding proteins, neurons co-expressing parvalbumin and calbindin-D28k in the parietal and piriform cortex of rat were demonstrated. The elaborated methods might stimulate the further detailed investigation of spatial and functional relationships between structures immunopositive for selected neuroanatomical markers.

Animals↗

Local circuit neurons of the prefrontal cortex in schizophrenia: selective increase in the density of calbindin-immunoreactive neurons.

Schizophrenia has been reported to be associated with alterations in GABAergic local circuit neurons of the prefrontal cortex. In this study, immunocytochemical techniques and antibodies against the calcium-binding proteins calbindin (CB) and calretinin (CR) were used to determine the laminar distribution and relative density of separate subpopulations of local circuit neurons in prefrontal cortical areas 9 and 46 from five pairs of schizophrenic and control subjects, matched for age, sex, and post-mortem interval. The laminar distribution pattern of CB-immunoreactive local circuit neurons was similar in both schizophrenic and control subjects. In both prefrontal regions, however, the density of CB-labeled neurons was 50-70% greater in schizophrenic subjects compared with control subjects, with cortical layers III and V/VI being preferentially affected. In contrast, the density of CR-IR neurons did not differ significantly between schizophrenic and control subjects. These findings reveal a selective increase in the density of a subpopulation of GABAergic local circuit neurons in the prefrontal cortex. Although other explanations for these observations must be considered, they may be consistent with the hypothesis that gene expression in GABAergic neurons is altered in schizophrenia.

Adult↗

Expression of calcium-binding proteins in the neurotrophin-3-dependent subpopulation of rat embryonic dorsal root ganglion cells in culture.

In this study we have examined the calcium-binding protein expression in rat embryonic (E16) dorsal root ganglia (DRG) neurons in vitro in the presence of neurotrophin-3 (NT-3). A comparison was made with the expression of calcium-binding proteins in DRG subpopulations that depended in vitro on nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF). Our results show that NT-3 promotes the survival of a DRG subpopulation of which over 75% expresses parvalbumin (PV). The majority of these PV-positive NT-3-dependent DRG neurons were large 'type A' neurons. Expression of calbindin-D28k (CaBP) and calretinin (Calr) in the NT-3-dependent DRG population was seen in smaller fractions (between 12 and 17%) of the surviving DRG neurons and in both type A and B neurons. The preferential expression of PV in NT-3-dependent type A neurons is unique in comparison to the expression of PV and the other calcium-binding proteins in DRG neurons surviving in vitro in the presence of NGF or BDNF.

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Calmodulin, calbindin-D28K and calretinin in rat and chicken pineal glands: immunocytochemical and immunoblotting analysis.

In pineal gland, melatonin is synthesized in pinealocytes. Pharmacological studies using calmodulin antagonists suggested that melatonin synthesis was regulated through calmodulin. However, immunohistochemical studies showed that calmodulin could only be detected in pineal glial cells, and not in pinealocytes. To further investigate this discrepancy, we have tried to detect calmodulin not seen by immunohistochemical methods. We have used rat and chicken pineal homogenate supernatants and Triton X-100-treated pellets denatured by sodium dodecyl sulfate, subjected to electrophoresis and immunoblotting using anti-calmodulin antibodies. Two different IgG (#465 and #860) purified from anti-calmodulin sera were used. In rat pineal homogenate supernatants, calmodulin could be detected by immunoblotting using both antibodies. Some calmodulin could also be detected in the Triton-treated pellet fractions, but no additional cross-reacting bands were detected. However, in both chicken pineal homogenate supernatants and Triton-extracted pellets, in addition to a calmodulin immunoreactive band, two other proteins with approximate molecular masses (M(r)) of 56 kDa and 60 kDa were detected using anti-calmodulin #465. For comparison, similar immunoblot experiments were performed for detection of calbindin-D28K and calretinin, two other calcium binding proteins expressed in different pineal cell populations. Interestingly, Triton extraction of chicken pineal pellets revealed additional bands cross-reacting with each antibody. Anti-calbindin-D28K cross-reacted strongly with a M(r) = 68 kDa protein and weakly with a M(r) = 56 kDa protein. Anti-calretinin cross-reacted strongly with a M(r) = 93 kDa protein and weakly with a M(r) = 56 kDa protein.

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Transient expression of calretinin during development of chick cerebellum. Comparison with calbindin-D28k.

Calcium ions play a critical role in neural development. Insights into the ontogeny of Ca2+ homeostasis were gained by investigating the developmental expression of two E-F hand calcium-binding proteins. Calretinin and calbindin were monitored through their immunoreactivity in the developing chick cerebellum (from E6 to E20). Calbindin was detected from E13 and in Purkinje cells only. Intensity of labelling increased with Purkinje cell development. Calretinin presented a transitory immunoreactivity between E11 and E20 in the internal granular cell layer. This cell layer contains cells which will differentiate into Golgi and granular cells which are calretinin-negative in adult chick cerebellum. Calretinin immunoreactivity presented a peak (both in number of cells and in intensity) at E15 and fell dramatically after E20 while calbindin immunoreactivity was restricted to the Purkinje cells and increased with the development of these cells.

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Calcium-binding proteins in primate basal ganglia.

This paper describes the distribution of the calcium-binding proteins calbindin-D28k. Parvalbumin and calretinin in primate basal ganglia. The data derive from immunocytochemical studies undertaken in squirrel monkeys (Saimiri sciureus) and in normal human individuals. In the striatum, calbindin labels medium-sized spiny projection neurons whereas parvalbumin and calretinin mark two separate classes of aspiny interneurons. The striatal matrix compartment is markedly enriched with calbindin while striatal patches (striosomes) display a calretinin-rich neuropil. In the pallidum, virtually all neurons contain parvalbumin but none express calbindin. Calretinin occurs only in a small subpopulation of both large and small pallidal neurons. In the subthalamic nucleus, there exists a multitude of parvalbumun-positive cells and fibers but the number of calretinin and calbindin-positive neuronal elements is small. In the substantia nigra/ventral tegmental area complex, calbindin and calretinin occur principally in dopaminergic neurons of the dorsal tier of the pars compacta and in those of the ventral tegmental area. Parvalbumin is strictly confined to the GABAergic neurons of the pars reticulata and lateralis. Calbindin-rich fibers abound in the pars reticulata and lateralis, while calretinin-positive axons are confined to the pars compacta. These results indicate that calbindin and parvalbumin are distributed according to a strikingly complementary pattern in primate basal ganglia. Calretinin is less ubiquitous but occurs in all basal ganglia components where it labels distinct subsets of neurons. Such highly specific patterns of distribution indicate that calbindin, parvalbumin and calretinin may work in synergy within primate basal ganglia.

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Distribution of calcium binding protein mRNAs in rat cerebellar cortex.

The distribution of three calcium binding protein mRNAs in the rat cerebellar cortex was investigated using alkaline phosphatase labelled specific antisense oligodeoxynucleotide probes. Calbindin D28k mRNA was detected in the Purkinje cells, parvalbumin mRNA was located in the Purkinje cells and also in basket/stellate cells of the molecular layer. Calretinin in contrast was found only in the granule cell layer. Use of multiple alkaline phosphatase (AP)-labelled oligodeoxynucleotides resulted in an increase in signal strength and reduced detection time with no increase in background staining indicating the utility of these enzyme labelled probes for non-isotopic in situ.

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Distribution of calmodulin, calbindin-D28k and calretinin among rat olfactory nerve bundles.

Calmodulin, calbindin-D28k and calretinin are calcium-binding proteins largely distributed in the bipolar olfactory receptor cells. In the olfactory epithelium their distribution seemed to be random. Using immunohistochemistry we have examined their localization in rat olfactory axons extending to the olfactory bulb. Sections were analyzed both horizontally and vertically. Almost all fibers were immunoreactive for one of the three intracellular calcium-binding proteins whose distribution was not random among the bundles. Three different subclasses of fibers could be detected: calbindin-D28k and calretinin immunoreactivities were restricted to external fibers whereas calmodulin immunoreactivity was intense, abundant and largely distributed throughout the internal portion of the olfactory nerve. This additional degree of organization detected in the olfactory axons might play a role in odor discrimination.

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Infrequent co-existence of nitric oxide synthase and parvalbumin, calbindin and calretinin immunoreactivity in rat pontine neurons.

Neurons in the laterodorsal tegmental nucleus (LDTg), ventrolateral dorsal tegmental nucleus (LDTgV), pedunculopontine tegmental nucleus (PPTg), lateral and medial parabrachial nuclei (LPB and MPB) were immunoreactive to brain nitric oxide synthase (NOS) or isoform I. Double-labeling experiments showed that very few NOS-containing neurons in the pons were immunoreactive to any of the three calcium-binding proteins: calbindin-D 28K (CB-IR), parvalbumin (PV-IR) and calretinin (CR-IR). These findings extend our previous observation in the neocortex and suggest that a population of central NOS-containing neurons can be neurochemically characterized as CB/CR/PV deficient.

Amino Acid Oxidoreductases↗

Compartmental organization of calretinin in the rat striatum.

The present study examined the compartmental distribution of a calcium-binding protein, calretinin, in the rat striatum. Calretinin-immunoreactive cells were homogeneously scattered throughout the striatum, but calretinin-immunoreactive fibers were clustered as patches in the medial, central and ventral caudoputamen and in the lateral nucleus accumbens. These patches corresponded to striosomes, identified by immunostaining for calbindin-D28 K in adjacent sections. In the medial nucleus accumbens, calretinin-immunoreactive fibers showed diffuse distribution with occasional islands of calretinin-poor zones. These islands contained tightly packed, Nissl-stained cells, which have been previously shown to correspond to mu-opiate receptor-rich patches. Calretinin-positive fibers fill striosomes/patches in the caudoputamen and in the lateral nucleus accumbens and avoid them in the medial nucleus accumbens.

Animals↗

Two calcium-binding proteins mark many chick sensory neurons.

The first immunohistochemical results with a new neuronal calcium-binding protein, calretinin, are presented. Calretinin is related to the 28,000 mol. wt calcium-binding protein, calbindin, and a survey of the chick brain by in situ hybridization has identified the brain nuclei that expressed the genes for the two proteins [Rogers J.H., J. Cell Biol. 105, 1343 (1987)]. Now, antisera have been raised against calretinin fusion proteins in order to visualize individual neurons. The antisera have been used in an immunohistochemical survey of calretinin and calbindin in the chick sensory nuclei and ganglia, where these two proteins are found to be particularly prevalent. In the central nervous system, they are seen in many secondary sensory neurons and local circuit neurons, the two proteins being almost always in separate cells. However, in ganglion cells of the spinal nerves, inner ear, and retina, they are often expressed together. Their distribution in the brain is generally different from that of a third calcium-binding protein, parvalbumin. These proteins may modulate many important calcium-dependent processes in neurons, and probably have multiple functions.

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Immunohistochemical identification of cholinergic neurons in the myenteric plexus of guinea-pig small intestine.

It is well established that acetylcholine is a neurotransmitter at several distinct sites in the mammalian enteric nervous system. However, identification of the cholinergic neurons has not been possible due to an inability to selectively label enteric cholinergic neurons. In the present study an immunohistochemical method has been developed to localize choline acetyltransferase, the synthetic enzyme for acetylcholine, in order that cholinergic neurons can be visualized. The morphology, neurochemical coding and projections of cholinergic neurons in the guinea-pig small intestine were determined using double-labelling immunohistochemistry. These experiments have revealed that many myenteric neurons are cholinergic and that they can be distinguished by their specific combinations of immunoreactivity for neurochemicals such as calretinin, neurofilament protein triplet, substance P, enkephalin, somatostatin, 5-hydroxytryptamine, vasoactive intestinal peptide and calbindin. On the basis of their previously described projections, functional roles could be attributed to each of these populations. The identified cholinergic neurons are: motorneurons to the longitudinal muscle (choline acetyltransferase/calretinin); motorneurons to the circular muscle (choline acetyltransferase/neurofilament triplet protein/substance P, choline acetyltransferase/substance P and choline acetyltransferase alone); orally directed interneurons in the myenteric plexus (choline acetyltransferase/calretinin/enkephalin); anally directed interneurons in the myenteric plexus (choline acetyltransferase/somatostatin, choline acetyltransferase/5-hydroxytryptamine, choline acetyltransferase/vasoactive intestinal peptide); secretomotor neurons to the mucosa (choline acetyltransferase/somatostatin); and sensory neurons mediating myenteric reflexes (choline acetyltransferase/calbindin). This information provides a unique opportunity to identify functionally distinct populations of cholinergic neurons and will be of value in the interpretation of physiological and pharmacological studies of enteric neuronal circuitry.

Animals↗

Calretinin in rat brain: an immunohistochemical study.

Calretinin is a calcium-binding protein related to calbindin-D28k; both are present in different though overlapping sets of neurons in brains of birds and mammals. We describe in detail the pattern of calretinin immunoreactivity in the rat brain. As in chick brain, calretinin immunoreactivity is abundant in various sensory pathways (particularly certain cells and fibres of the cochlear nuclei and olfactory bulb), in the heterogeneous parts of the brainstem and in parts of the hypothalamus. Many primary sensory fibres are strongly positive. Major groups of calretinin-positive neurons also include the thalamic reticular nucleus, triangular septal nucleus, lateral mammillary nucleus and substantia nigra pars compacta. Many other calretinin-positive cells are recognizable as local inhibitory neurons. Calretinin is absent from all but a few cells in the cerebral cortex, and is never found in motor neurons. There are also some distinctive positive structures whose identity is uncertain, notably irregular "shells" of cells and fibres around the thalamus and in the amygdala and an unnamed cell type in the vestibulocerebellum.

Animals↗

Calretinin is present in non-pyramidal cells of the rat hippocampus--II. Co-existence with other calcium binding proteins and GABA.

The possible co-existence of calretinin with other calcium binding proteins, parvalbumin and calbindin D28k, and with GABA, was studied in non-pyramidal cells of the rat dorsal hippocampal formation, using the mirror technique. The majority of the calretinin-containing neurons (83%) were found to be immunoreactive for GABA (79% in the dentate gyrus, 84% in the CA2-3, and 88% in the CA1 subfield). Most of the GABA-negative calretinin-immunoreactive neurons were located in the hilus of the dentate gyrus and in stratum lucidum of the CA3 subfield. Detailed analysis of the calretinin-immunoreactive cells of these subfields revealed that the two morphologically distinct types of calretinin neurons, i.e. the spiny and the spine-free cells, differ in their immunoreactivity for GABA. The overwhelming majority (92%) of the spine-free neurons were GABA-positive, whereas the immunoreactivity of spiny cells was ambiguous. At the sensitivity threshold of the immunocytochemical techniques used in the present study, most of the spiny cells (89%) had to be considered as GABA-negative, although the staining intensity in their cell bodies was somewhat above background level. Colchicine treatment resulted in a degeneration of calretinin-immunoreactive neurons; therefore, its effect on the GABA content of spiny neurons could not be evaluated. Nevertheless, the observations suggest that calretinin-containing neurons are heterogeneous both morphologically and neurochemically. Examination of the co-existence of calcium binding proteins revealed that none of the hippocampal cells contained both calretinin and parvalbumin in any regions of the hippocampal formation. Some overlap was detected between the calretinin- and the calbindin D28k-containing cell populations, 5.1% of the former and 6.2% of the latter were immunoreactive for both calcium binding proteins. This may be due to a small degree of cross-reactivity of the calbindin D28k antiserum with calretinin. Thus, our results demonstrate that the majority of calretinin-immunoreactive neurons are GABAergic and represent a subpopulation of non-pyramidal cells with no or only a negligible overlap with the subpopulations containing the other calcium binding proteins, parvalbumin and calbindin.

Animals↗

Calretinin and calbindin-D28k in rat brain: patterns of partial co-localization.

Calretinin and calbindin-D28k are homologous calcium-binding proteins, each present in a variety of neurons in the brain. Their distributions in the rat brain have been compared at the cellular level to determine whether they tend to occur in the same or in different cells, and to determine whether calbindin-positive cells show any common features once crossreaction with calretinin has been eliminated. The results show great heterogeneity. Most cells which contain one of the proteins do not contain the other, but many cells do contain both; even in the ventral cochlear nucleus, where there is abundant calretinin and most calbindin-like immunoreactivity is due to crossreaction, a few cells contain both proteins. In the substantia nigra and ventral tegmental area, many cells are double-positive but some only contain one or the other protein. Only the triangular septal nucleus is uniformly positive for both proteins. Cells which look like local-circuit neurons in many forebrain areas (cortex, hippocampus, olfactory bulb, anterior olfactory nucleus) are exclusively positive for either calretinin or calbindin, in spite of their similar morphology. In the more heterogeneous parts of the brain (including hypothalamus central gray and substantia gelatinosa), there are mixtures of calretinin-positive, calbindin-positive, and double-positive cells. In comparison with previous data on the chick, some aspects of the distributions are conserved, but double-positive cells are more frequent in the rat. The degree of heterogeneity observed, even within comparatively well-defined neuronal populations, makes it difficult to infer in what neuronal properties these proteins could be involved.

Animals↗

Mouse fetal trisomy 13 and hypotrophy of the spinal cord: effect on calbindin-D28k and calretinin expressed by neurons of the spinal cord and dorsal root ganglia.

Trisomy 13 was detected in 10% of mouse embryos obtained from pregnant females which were doubly heterozygous for Robertsonian chromosomes involving chromosome 13. The developing dorsal root ganglia and spinal cords were examined in trisomy 13 and littermate control mice between days 12 and 18 of gestation (E12-18). The overall size of the dorsal root ganglia and number of ganglion cells within a given ganglion were not altered, but the number of neurons immunoreactive for calbindin and calretinin was reduced. The trisomic spinal cord was reduced in size with neurons lying in a tightly compact distribution in the gray matter. In trisomic fetuses, the extent of the neuropil of the spinal cord was reduced, and may represent a diminished field of interneuronal connectivity, due to reduced arborization of dendritic processes of the neurons present, particularly of calbindin-immunostained neurons. Furthermore, the subpopulation of calretinin-immunoreactive neurons and axons was also reduced in developing trisomic gray and white matter, respectively. Thus, overexpression of genes on mouse chromosome 13 exerts a deleterious effect on the development of neuropil, affecting both dendritic and axonal arborization in the trisomy 13 mouse. The defect of calbindin or calretinin expression by subsets of dorsal root ganglion or spinal cord neurons may result from deficient cell-to-cell interactions with targets which are hypoplastic.

Animals↗