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Results for “Calbindin 2”

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At least 19 recordsLinked to original sources

PubMed1992

Nuclear magnetic resonance studies of the internal dynamics in Apo, (Cd2+)1 and (Ca2+)2 calbindin D9k. The rates of amide proton exchange with solvent.

The backbone dynamics of the EF-hand Ca(2+)-binding protein, calbindin D9k, has been investigated in the apo, (Cd2+)1 and (Ca2+)2 states by measuring the rate constants for amide proton exchange with solvent. 15N-1H correlation spectroscopy was utilized to follow direct 1H-->2H exchange of the slowly exchanging amide protons and to follow indirect proton exchange via saturation transfer from water to the rapidly exchanging amide protons. Plots of experimental rate constants versus intrinsic rate constants have been analyzed to give qualitative insight into the opening modes of the protein that lead to exchange. These results have been interpreted within the context of a progressive unfolding model, wherein hydrophobic interactions and metal chelation serve to anchor portions of the protein, thereby damping fluctuations and retarding amide proton exchange. The addition of Ca2+ or Cd2+ was found to retard the exchange of many amide protons observed to be in hydrogen-bonding environments in the crystal structure of the (Ca2+)2 state, but not of those amide protons that were not involved in hydrogen bonds. The largest changes in rate constant occur for residues in the ion-binding loops, with substantial effects also found for the adjacent residues in helices I, II and III, but not helix IV. The results are consistent with a reorganization of the hydrogen-bonding networks in the metal ion-binding loops, accompanied by a change in the conformation of helix IV, as metal ions are chelated. Further analysis of the results obtained for the three states of metal occupancy provides insight into the nature of the changes in conformational fluctuations induced by ion binding.

Amides↗

PubMed1999

On-line sample clean-up and chromatography coupled with electrospray ionization mass spectrometry to characterize the primary sequence and disulfide bond content of recombinant calcium binding proteins.

We have used on-line sample clean-up, concentration, and chromatography with electrospray ionization mass spectrometry (ESI-MS), to characterize and determine the presence of disulfide bonds in recombinant full-length rat brain calbindin D28K and two deletion mutants of the protein, one lacking EF-hand 2 (calbindin delta 2) and the other lacking EF-hands 2 and 6 (calbindin delta 2,6). The molecular weights of the expressed proteins dissolved in biological buffers were determined with high accuracy using a low-flow, pressurized chamber infusion system, that allows on-line protein clean-up by removing buffers/salts incompatible with ESI-MS. The molecular weight determinations showed that the amino-terminal methionine residues had been cleaved during the expression and isolation of the recombinant proteins. Approximately 85-90% of the protein sequences were confirmed by on-line HPLC-ESI-MS analysis of peptides generated by a lysyl endoproteinase C digestion. Comparisons of ESI-MS spectra of native and reduced calbindin D28K and delta 2 show that the full length- and delta 2 mutant-protein contain one disulfide bond. Molecular mass determinations of calbindin delta 2,6 showed that this protein contains a highly active cysteine residue that covalently binds a mercaptoethanol group, or forms a homodimer via a disulfide bond. The results show surprising differences amongst the deletion mutants of calbindin D28K with respect to the formation of disulfide bonds. These differences are not readily detected by other techniques and show that ESI-MS is a powerful, rapid method by which to detect disulfide linkages for intact proteins.

Amino Acid Sequence↗

PubMed1997

Structural basis for the negative allostery between Ca(2+)- and Mg(2+)-binding in the intracellular Ca(2+)-receptor calbindin D9k.

The three-dimensional structures of the magnesium- and manganese-bound forms of calbindin D9k were determined to 1.6 A and 1.9 A resolution, respectively, using X-ray crystallography. These two structures are nearly identical but deviate significantly from both the calcium bound form and the metal ion-free (apo) form. The largest structural differences are seen in the C-terminal EF-hand, and involve changes in both metal ion coordination and helix packing. The N-terminal calcium binding site is not occupied by any metal ion in the magnesium and manganese structures, and shows little structural deviation from the apo and calcium bound forms. 1H-NMR and UV spectroscopic studies at physiological ion concentrations show that the C-terminal site of the protein is significantly populated by magnesium at resting cell calcium levels, and that there is a negative allosteric interaction between magnesium and calcium binding. Calcium binding was found to occur with positive cooperativity at physiological magnesium concentration.

Allosteric Regulation↗

PubMed1991

Calcium binding proteins as molecular markers for cat geniculate neurons.

Immunocytochemistry revealed that in the cat dorsal lateral geniculate nucleus (dLGN) almost all parvalbumin-positive cells are GABAergic and about 56% of the calbindin D-28K (calbindin-immunoreactive neurons are also GABA-positive. On the other hand, in the same nucleus, almost all GABAergic neurons contain parvalbumin, and about 89% of the GABA-immunoreactive neurons contain calbindin. Double-labeling with calbindin and parvalbumin revealed that approximately 50% of the immunoreactive neurons are double-stained. In the PGN, virtually all neurons are GABA and parvalbumin-positive. Only a few scattered cells were also calbindin-immunoreactive. These results show that GABAergic geniculate cells can be differentiated on the basis of their calcium-binding protein immunoreactivity. Four types of immunoreactive cells are described here: (1) cells positive for GABA, parvalbumin and calbindin, (2) cells positive for GABA and parvalbumin, but negative for calbindin, (3) cells negative for GABA and parvalbumin, but positive for calbindin, (4) cells negative for GABA, parvalbumin and calbindin.

Animals↗

PubMed1990

Calbindin and calretinin localization in retina from different species.

Calbindin-D28K and calretinin are homologous calcium-binding proteins localized in many neurons of the central nervous systems. We have compared polyclonal antibodies against calbindin and calretinin and have shown by western blots using purified calbindin and calretinin from rat that (1) anti-calretinin does not recognize calbindin and (2) anti-calbindin presents some cross-reactivity with calretinin. In this report, we have compared by immunohistochemistry the localization of both calcium-binding proteins in the retina of monkey, pig, sheep, rat, cat, pigeon, and salamander. These results are compared with previous data for chick. There are many differences between species and not within species, but some aspects of the distribution are conserved. All species, except rat and monkey, have some cones which contain calbindin only. Most species also have some bipolar cells containing calbindin only. Calretinin is rarely seen in photoreceptors or bipolar cells. All species have horizontal cells which contain calretinin or calbindin or both. All species have amacrine cells and ganglion cells containing one or other protein. In the cat ganglion cell layer, the calretinin antisera define a new, asymmetric, type of cell.

Animals↗

PubMed1997

Protein solution structure calculations in solution: solvated molecular dynamics refinement of calbindin D9k.

The three-dimensional solution structures of proteins determined with NMR-derived constraints are almost always calculated in vacuo. The solution structure of (Ca2+)2-calbindin D9k has been redetermined by new restrained molecular dynamics (MD) calculations that include Ca2+ ions and explicit solvent molecules. Four parallel sets of MD refinements were run to provide accurate comparisons of structures produced in vacuo, in vacuo with Ca2+ ions, and with two different protocols in a solvent bath with Ca2+ ions. The structural ensembles were analyzed in terms of structural definition, molecular energies, packing density, solvent-accessible surface, hydrogen bonds, and the coordination of calcium ions in the two binding loops. Refinement including Ca2+ ions and explicit solvent results in significant improvements in the precision and accuracy of the structure, particularly in the binding loops. These results are consistent with results previously obtained in free MD simulations of proteins in solution and show that the rMD refined NMR-derived solution structures of proteins, especially metalloproteins, can be significantly improved by these strategies.

Calbindins↗

PubMed1996

Neurotrophin-4/5 selectively protects nigral calbindin-containing neurons in rats with medial forebrain bundle transections.

Three neurotrophic factors associated with the nigrostriatal dopaminergic system were tested for their trophic potential to rescue degenerating substantia nigra dopaminergic neurons in adult rats with transections of the medial forebrain bundle. Axotomy of nigral dopaminergic neurons results in a retrograde degeneration of their cell bodies. Unilateral transections resulted in a partial reduction of the number of dopaminergic neurons as identified by immunocytochemistry for tyrosine hydroxylase to approximately half of the number of neurons present on the intact contralateral substantia nigra. A similar percentage loss was found for the subpopulation of nigral neurons which contain the calcium binding protein calretinin. In contrast, the small subpopulation of neurons which contain calbindin was less sensitive to the lesion and showed only mild loss in the number of cells, which was reduced to 87% of control. Neurotrophin-4/5, transforming growth factor alpha or basic fibroblast growth factor were infused supranigrally for two weeks after transection. None of the trophic factors tested reversed the loss of tyrosine hydroxylase-positive or calretinin-positive cells. In contrast, neurotrophin-4/5, but not transforming growth factor alpha or basic fibroblast growth factor, was found to reverse the axotomy-induced loss of calbindin-positive neurons and indeed increased the number of cells to 45% above control levels. In addition, neurotrophin-4/5 elevated the number of calbindin-containing neurons in intact unlesioned animals to 15% above control. These findings suggest that neurotrophin-4/5 selectively acts on nigral calbindin neurons following medial forebrain bundle transection and prevents these cells from degenerating.

Animals↗

PubMed1996

Cytoarchitectural distribution of calcium binding proteins in midbrain dopaminergic regions of rats and humans.

The present study compares the distribution of three calcium binding proteins, calbindin-D28k, calretinin, and parvalbumin, in the midbrain tegmentum of rats and humans. In order to compare the distributions of these proteins directly, the cytoarchitecture of this region was evaluated by using immunohistochemistry for tyrosine hydroxylase and substance P in serial sections in both transverse and horizontal planes. There was a high degree of homology in the cytoarchitecture of the three main dopaminergic regions identified. The A8 group was localised in the retrorubral fields, which extended rostrally into the midbrain reticular fields in the human. The A9 group corresponded to the substantia nigra, which was delimited by its dense substance P innervation. The heterogeneous A10 group, situated along the dorsal border as well as medial to the A9 group, comprised multiple nuclei. The distribution of calcium binding proteins was similar in both species, although a larger proportion of neurons contained these proteins in the rat. Calbindin-D28k was localised in neurons within A8 and A10 nuclei and within the caudomedial A9 region (and rostrolateral A9 in the rat only). Calretinin was localised in similar regions. In contrast, neurons containing parvalbumin were concentrated in the substantia nigra pars reticulata. The results suggest that few dopaminergic neurons receiving striatal input in the substantia nigra contain calcium binding proteins; rather, the nondopaminergic nigral neurons contain parvalbumin. Interestingly, dopaminergic neurons are more numerous in humans, whereas nondopaminergic neurons predominate in rats, which suggests that functional differences may exist between rats and humans.

Adult↗

PubMed1996

GABAergic neurons in the rat dentate gyrus are innervated by subcortical calretinin-containing afferents.

Fibers of supramammillary origin establish putatively excitatory asymmetric synaptic connections with dentate granule cells. The present study was designed to determine whether hippocampal gamma-aminobutyric acid (GABA)-ergic nonprincipal cells are also targets of these calretinin (CR)-containing subcortical afferents. Light and electron microscopic double immunostaining for CR and parvalbumin (PA) or calbindin (CB) were performed in the rat dentate gyrus ipsilateral and contralateral to a unilateral fimbria-fornix transection. GABA-postembedding immunostaining was performed on ultrathin sections of this double-labeled material. Contralateral to the transection, CR-immunoreactive fibers formed multiple large boutons in the inner molecular layer. These fibers also impinged on PA-containing basket cells located adjacent to the granular layer and on CB-immunoreactive hilar neurons. Ipsilateral to the transection, CR-containing fibers in the inner molecular layer and boutons impinging on PA-containing or CB-immunoreactive neurons were absent. Parent cell bodies of extrinsic CR-containing afferents were traced using wheat germ agglutinin-conjugated horseradish peroxidase. Additional CR immunostaining of the subcortical region unveiled retrogradely labeled neurons that were also immunostained for CR only in the supramammillary area and the nucleus reuniens. The latter projection, however, terminates in CA1 and not in the dentate gyrus. Subcortical afferents impinging on dentate nonprincipal cells formed exclusively asymmetric synapses. Postembedding immunostaining demonstrated that CB-containing cells contain GABA, whereas CR-positive axon terminals forming asymmetric synapses are devoid of this labeling. These data indicate that dentate inhibitory neurons receive a putative excitatory input originating from the supramammillary nucleus. Thus, the supramamillo-hippocampal pathway may exert a powerful feed-forward inhibitory control of the signal flow in the rat dentate gyrus.

Animals↗

PubMed1996

Pattern of selected calcium-binding proteins in the vestibular nuclear complex of two rodent species.

The distribution of immunoreactivity to calbindin, calretinin, and parvalbumin in the vestibular nuclear complex and the adjacent nucleus prepositus hypoglossi was studied in rats and gerbils. The distribution of stained fibers was the same for both rodent species. All three calcium-binding proteins were present in vestibular afferents. However, none of the three proteins were present in all afferent fibers. Many fibers were labeled in the vestibular nerve and in fascicles of the descending vestibular nucleus, as well as ascending fibers in the superior vestibular nucleus and fibers directed to the medial vestibular nucleus. Labeled terminals were present in the medial vestibular nucleus, especially along the ventricular border, in the neuropil of the superior vestibular nucleus, and scattered in the descending and ventral portions of the lateral vestibular nucleus. Calbindin- and parvalbumin-positive terminals, but not calretinin-positive terminals, were present in the neuropil of the dorsal lateral vestibular nucleus, especially surrounding the large neuronal somas. Some of these terminals are presumably from cerebellar Purkinje cells, which were also labeled by both antibodies. The pattern of parvalbumin immunoreactivity was slightly different from that of calbindin, indicating that parvalbumin might be contained in additional fibers. Some neurons in the vestibular nuclear complex were labeled with antibodies to calretinin, but few cells were stained with either calbindin or parvalbumin antibodies. The largest group of calretinin-positive cells was a cluster of small- to medium-sized neurons located in a densely stained mesh of dendrites and terminals in the medial vestibular nucleus, adjacent to the ventricular border.

Animals↗

PubMed1996

Neurochemical development of the hippocampal region in the fetal rhesus monkey, III: calbindin-D28K, calretinin and parvalbumin with special mention of cajal-retzius cells and the retrosplenial cortex.

In spite of continuing controversy on the precise function of the calcium-binding proteins expressed in the hippocampal formation, nothing is known about their prenatal development in primates. In this study, calbindin-D28K, calretinin, and parvalbumin were localized in the hippocampal formation of seven rhesus monkey fetuses aged E47 to E90 (term 165 days). All of the three markers were expressed during the first half of gestation in distinct subsets of nonpyramidal neurons: calretinin-containing cells were the most numerous and relatively differentiated contrasting with a more restricted, less mature, parvalbumin-labeled population and a poor calbindin-positive nonpyramidal contingent. The granule cells and pyramidal neurons were calbindin-positive, including the pyramids of CA3 and the subicular complex, in contrast to the situation found in the adult monkey. The presubiculum and retrosplenial cortex, whose merging formed the caudal pole of the hippocampal formation, also expressed precociously the three calcium-binding proteins. A heterogeneous population of Cajal-Retzius-like cells was demonstrated in the marginal zone of the ventral hippocampal formation. The majority co-expressed calbindin-D28K and calretinin and displayed acetylcholinesterase activity but no GABA-like immunoreactivity. Major intrinsic and extrinsic pathways of the hippocampal system (mossy fiber system, alveus, fimbria, angular, and cingular bundles) were immunoreactive for calretinin and/or calbindin. The distinct developmental time course and regional pattern of distribution of calbindin-D28K, calretinin, and parvalbumin in the nonprincipal neurons suggests a precocious but asynchronous prenatal development of different inhibitory circuits in the hippocampal formation of primates. The labeling of several fiber systems in keeping with comparable early events in the entorhinal cortex (Berger et al.: Hippocampus 3:279-305, 1993), suggests the possibility of earlier functional circuits than hitherto inferred from the observations available in rodents, a hypothesis that deserves further investigation.

Animals↗

PubMed1996

Colocalization of calbindin D-28k, calretinin, and GABA immunoreactivities in neurons of the human temporal cortex.

The calcium-binding proteins calbindin D-28k (CalB) and calretinin (CalR) have been shown to be useful markers of neuronal subpopulations located mainly in layers II-III of the neocortex of a variety of species, including human. Double labeling immunocytochemical studies of CalB, CalR, and GABA in experimental animals have shown that CalB and CalR are present in separate subpopulations of neurons. However, there are no studies of colocalization of these calcium-binding proteins and GABA in the human neocortex. The principal goal of the present work was to investigate the degree of colocalization of these substances in layers II-III of the human temporal neocortex, using a postembedding immunocytochemical method. The patterns of staining for CalB, CalR, and GABA in the human cortex were similar to those found in monkey neocortex. However, the degree of colocalization for certain combinations was different from that reported in the monkey and other experimental animals. A relatively large proportion of CalB- and CalR-immunoreactive cells (approximately 71% and 74%, respectively) were found to be immunoreactive for GABA. However, the degree of colocalization of CalB with CalR was low (between 4% and 6%). Thus, our quantitative and qualitative data suggest that these calcium-binding proteins are present in similar cortical circuits in all primates, but that in the human neocortex, there might be additional GABAergic and perhaps also non-GABAergic interneurons with unique chemical characteristics.

Adolescent↗

PubMed1996

Quantitative immunocytochemical analysis of the spinal cord in G86R superoxide dismutase transgenic mice: neurochemical correlates of selective vulnerability.

Transgenic mice with a G86R mutation in the mouse superoxide dismutase (SOD-1) gene, which corresponds to a mutation that has been observed in familial amyotrophic lateral sclerosis (ALS), display progressive loss of motor function and provide a valuable model of ALS. The pathology in the spinal cords of these mice was evaluated to determine whether there are chemically identified populations of neurons that are either highly vulnerable or resistant to degeneration. Qualitatively, there were phosphorylated neurofilament protein (NFP)-immunoreactive inclusions and a pronounced loss of motoneurons in the ventral horn of the spinal cord without the presence of vacuoles that has been reported in other SOD-1 transgenic mice. Neuron counts from SOD-1 and control spinal cords revealed that the percentage loss of NFP-, choline acetyltransferase (ChAT)-, and calretinin (CR)-immunoreactive neurons was greater than the percentage loss of total neurons, suggesting that these neuronal groups are particularly vulnerable in SOD-1 transgenic mice. In contrast, calbindin-containing neurons did not degenerate significantly and represent a protected population of neurons. Quantitative double-labeling experiments suggested that the vulnerability of ChAT- and CR-immunoreactive neurons was due primarily to the presence of NFP within a subset of these neurons, which degenerated preferentially to ChAT- and CR-immunoreactive neurons that did not colocalize with NFP. Our findings suggest that NFP, which has been demonstrated previously to be involved mechanistically in motoneuron degeneration, may also be important in the mechanism of degeneration that is initiated by the SOD-1 mutation.

Animals↗

PubMed1997

Temporary sensory deprivation changes calcium-binding proteins levels in the auditory brainstem.

Auditory brainstem neurons probably depend on afferent input to maintain calcium homeostasis within a narrow range. These neurons are endowed with high concentrations of the calcium-binding proteins parvalbumin, calretinin, and calbindin D28k that are presumed to buffer cytosolic calcium transients. To determine the effects of functional deafferentation on these proteins in the auditory brainstem of adult guinea pigs, we have manipulated the sensory input with an intracochlear perfusion of the glutamate agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), which is known to transiently disconnect inner hair cells and primary auditory dendrites. Semiquantitative measures of immunostaining intensities showed rapid and reversible changes in calcium-binding protein levels. By 24 hours after AMPA treatment, calretinin immunostaining was reduced in deafferented neurons of the cochlear nuclei and their axons in the superior olivary nuclei. In contrast, calbindin D28k immunoreactivity levels by this time were higher in deafferented neurons of the medial nucleus of the trapezoid body and their axons in the lateral superior olivary nucleus (LSO). Parvalbumin immunostaining was also generally increased in deafferented neurons, but changes were less evident and more complex. The changes in all three immunoreactivities disappeared with the progressive restoration of afferent input. Normal levels were reestablished by 5 days after AMPA treatment, when afferent activity had almost completely recovered. These results show that calcium-binding protein immunostaining in auditory neurons is functionally responsive to afferent activity. The increased buffering capacity in deafferented neurons as shown by the rises in parvalbumin and calbindin D28k immunostaining may be part of mechanisms promoting neuronal survival after loss of sensory input. This input, on the other hand, may be necessary for maintaining the high calretinin levels normally present in cochlear nucleus neurons.

Animals↗

PubMed1997

Neurofilament and calcium-binding proteins in the human cingulate cortex.

Functional imaging studies of the human brain have suggested the involvement of the cingulate gyrus in a wide variety of affective, cognitive, motor, and sensory functions. These studies highlighted the need for detailed anatomic analyses to delineate its many cortical fields more clearly. In the present study, neurofilament protein, and the calcium-binding proteins parvalbumin, calbindin, and calretinin were used as neurochemical markers to study the differences among areas and subareas in the distributions of particular cell types or neuropil staining patterns. The most rostral parts of the anterior cingulate cortex were marked by a lower density of neurofilament protein-containing neurons, which were virtually restricted to layers V and VI. Immunoreactive layer III neurons, in contrast, were sparse in the anterior cingulate cortex, and reached maximal densities in the posterior cingulate cortex. These neurons were more prevalent in dorsal than in ventral portions of the gyrus. Parvalbumin-immunoreactive neurons generally had the same distribution. Calbindin- and calretinin-immunoreactive nonpyramidal neurons had a more uniform distribution along the gyrus. Calbindin-immunoreactive pyramidal neurons were more abundant anteriorly than posteriorly, and a population of calretinin-immunoreactive pyramidal-like neurons in layer V was found largely in the most anterior and ventral portions of the gyrus. Neuropil labeling with parvalbumin and calbindin was most dense in layer III of the anterior cingulate cortex. In addition, parvalbumin-immunoreactive axonal cartridges were most dense in layer V of area 24a. Calretinin immunoreactivity showed less regional specificity, with the exception of areas 29 and 30. These chemoarchitectonic features may represent cellular reflections of functional specializations in distinct domains of the cingulate cortex.

Aged↗

PubMed1997

Age-related changes in calbindin D-28k and calretinin immunoreactivity in the inferior colliculus of CBA/CaJ and C57Bl/6 mice.

This study examines calbindin D-28k and calretinin immunoreactivity in the inferior colliculus (IC) of young and old mice of two strains. The CBA/CaJ mouse maintains good hearing until very late in life, whereas the C57Bl/6 strain exhibits severe sensorineural hearing loss at an early age. Young and old mice of both strains were selected with matching auditory brainstem response audiograms and gap detection thresholds. Brain sections were reacted with anti-calbindin D-28k (CB) and anti-calretinin (CR). Staining patterns were characterized and cell counts performed. CB immunoreactivity was high only in the nucleus of the commissure (NCO); counts revealed a 22.3% decrease in the number of CB+ cells in old CBA mice and a 25.1% decrease in old C57 mice. Calretinin immunoreactivity was high in the pericentral regions of the IC, but the central nucleus was devoid of CR+ cells. The dorsal cortex, lateral nucleus, and NCO showed increases of 42.3, 49.0, and 61%, respectively, in the number of CR+ cells, but only in the old CBA mice. No significant change was observed in the old C57 mice. Whereas decreases in CB immunoreactivity are common with age, this study is the first to report an age-related increase in CR immunoreactivity in the auditory system. The increase in CR+ cells is a possible compensatory adaptation to the decrease in CB+ cells. That the number of CR+ cells remains constant with age in C57 mice suggests this compensation may depend upon stimulus-driven activity, but this requires further study.

Acoustic Stimulation↗

PubMed1998

Localization of parvalbumin, calretinin, and calbindin D-28k in identified extraocular motoneurons and internuclear neurons of the cat.

Calcium-binding proteins have been shown to be excellent markers of specific neuronal populations. We aimed to characterize the expression of calcium-binding proteins in identified populations of the cat extraocular motor nuclei by means of immunohistochemistry against parvalbumin, calretinin, and calbindin D-28k. Abducens, medial rectus, and trochlear motoneurons were retrogradely labeled with horseradish peroxidase from their corresponding muscles. Oculomotor and abducens internuclear neurons were retrogradely labeled after horseradish peroxidase injection into either the abducens or the oculomotor nucleus, respectively. Parvalbumin staining produced the highest density of immunoreactive terminals in all extraocular motor nuclei and was distributed uniformly. Around 15-20% of the motoneurons were moderately stained with antibody against parvalbumin, but their axons were heavily stained, indicating an intracellular segregation of parvalbumin. Colchicine administration increased the number of parvalbumin-immunoreactive motoneurons to approximately 85%. Except for a few calbindin-immunoreactive trochlear motoneurons (1%), parvalbumin was the only marker of extraocular motoneurons. Oculomotor internuclear neurons identified from the abducens nucleus constituted a nonuniform population, because low percentages of the three types of immunostaining were observed, calbindin being the most abundant (28.5%). Other interneurons located within the boundaries of the oculomotor nucleus were mainly calbindin-immunoreactive. The medial longitudinal fascicle contained numerous parvalbumin- and calretinin-immunoreactive but few calbindin-immunoreactive axons. The majority of abducens internuclear neurons projecting to the oculomotor nucleus (80.7%) contained calretinin. Moreover, the distribution of calretinin-immunoreactive terminals in the oculomotor nucleus overlapped that of the medial rectus motoneurons and matched the anterogradely labeled terminal field of the abducens internuclear neurons. Parvalbumin immunostained 42% of the abducens internuclear neurons. Colocalization of parvalbumin and calretinin was demonstrated in adjacent semithin sections, although single-labeled neurons were also observed. Therefore, calretinin is proven to be a good marker of abducens internuclear neurons. From all of these data, it is concluded that parvalbumin, calretinin, and calbindin D-28k selectively delineate certain neuronal populations in the oculomotor system and constitute valuable tools for further analysis of oculomotor function under normal and experimental conditions.

Abducens Nerve↗

PubMed1999

Calcium-binding proteins in the dorsal ventricular ridge of the lizard Psammodromus algirus.

The aim of the present work was to study further the intrinsic organization of the dorsal ventricular ridge of lizards. For that purpose, the morphology and distribution of cells and fibers containing the calcium-binding proteins calbindin-D28k, parvalbumin, and calretinin were investigated by using immunohistochemical methods. Colocalization of calcium-binding proteins with the neurotransmitter gamma-aminobutyric acid (GABA) was also studied because they are shown to coexist in many areas of the telencephalon where they define distinct subpopulations of GABAergic local circuit neurons. Neurons containing calcium-binding proteins are limited to the anterior part of the dorsal ventricular ridge (ADVR), whereas the posterior or caudal portion of the ridge is devoid of immunoreactive cells. This result gives further evidence for defining both regions of the dorsal ventricular ridge. Calcium-binding proteins mark three distinct populations of neurons within the ADVR. Two of them, parvalbumin- and calretinin-expressing cells, are GABAergic. On the other hand, calbindin-containing neurons do not express GABA, and the possibility is discussed that these cells are projection neurons. The distribution and overall density of fibers immunoreactive to calcium-binding proteins suggests that most fibers are of extrinsic origin, the thalamic nuclei projecting to the ADVR and the lateral amygdala being good candidates for their origin. The comparison of data on the populations of calcium-binding protein-containing neurons in the reptilian ADVR with those of mammals illustrate the difficulty in finding a mammalian homologue for this controversial region of the reptilian telencephalon.

Animals↗