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Calretinin (CR) is a neuronal EF-hand protein previously characterized as a calcium (micromolar affinity) binding protein. CR-containing neurons are spared in some neurodegenerative diseases, although it is as yet unconfirmed how CR plays an active role in this protection. Higher levels of some metal cations (e.g. copper and zinc) are associated with these diseases. At the same time, metals such as terbium (NMR and fluorescence) cadmium (NMR) and manganese (EPR) serve as useful calcium analogues in the study of EF-hand proteins. We survey the binding of the above-mentioned metal cations that might affect the structure and function of CR. Competitive 45Ca2+ -overlay, competitive terbium fluorescence and intrinsic tryptophan fluorescence are used to detect the binding of metal cations to CR. Terbium and copper (half-maximal effect of 15 uM) bind to CR. Terbium has a similar or greater affinity for the calcium-binding sites of CR than calcium. Copper quenches the fluorescence of terbium-bound CR, and CR tryptophan residues and com­petes weakly for 45Ca2+ -binding sites. Cadmium, magnesium, manganese and zinc bind less strongly (half-maximal effects above 0.1 mM). Therefore, only terbium appears to be a suitable analytical calcium analogue in further studies of CR. The principal conclusion of this work is that copper, in addition to calcium, might be a factor in the function of CR and a link between CR and neurodegenerative diseases.
An immunocytochemical double-staining method was applied in order to study the co-localisation of nitric oxide synthase (NOS) with three calcium-binding proteins, calbindin D28k (CB), calretinin (CR) and parvalbumin (PV) in the claustrum of the rat during the first 4 months of life (postnatal days: P0–P120). The co-localisation of NOS/PV and NOS/CB is reported. These neurons fall into the category of non-pyramidal cells. Double-labelled NOS/CB neurons are observed in the claustrum starting from P4, whereas double-labelled NOS/PV neurons are observed from P14 onwards. The percentages of double-labelled neurons increase in relation to the age. Double-labelled NOS/CB and NOS/PV neurons, although they do not constitute a numerous population, play an important role in the process of maturation of the claustrum. This is confirmed by the occurrence of these types of neurons at definite stages of maturation and by the increase in their number.
In our study we used c-Fos protein to identify whether cells containing calretinin (CR) in the rat piriform cortex are engaged in the response to stress stimulation and to find out how this expression changes during maturation (PC). The material consisted of Wistar strain rats of between 0 and 120 days of age divided into 9 groups. Each group consisted of 5 experimental and 3 control rats. Animals from the experimental groups were exposed to the open field test throughout 10 minutes. The control animals were kept in a home cage. In all age-related control rats weak c-Fos immunoreactivity was observed. Our results showed that cells containing c-Fos following an acute open field test were observed predominantly in layers II and III of the PC just after birth. Their number then increased and stabilised on P30. We had already observed immature CR-ir cells at birth. In the 4th week of life these neurons achieved maturity. Their number increased to P90 and decreased in older animals. CR-ir neurons were localised mainly in layer II and to a lesser degree in layers III and I of the PC. Double immunostaining c-Fos/CR revealed that the level of co-localisation was low. Only small differences were observed between the anterior and posterior parts of the PC. In the anterior part a higher number of CR-ir neurons was found. The difference in the level of co-localisation between the anterior and posterior parts was age-related and differentiated. Our results may suggest that during maturation CR-ir neurons of the piriform cortex are not the main population engaged in response to the open field test.
Immunohistochemical study of the cholinergic innervation of the hippocampal calretinin-containing cells was conducted on 28 rat brains of postnatal ages: P0, P4, P7, P14, P21, P30 and P60. Sections with double immunostaining for vesicular acetylcholine transporter (VAChT; the marker of cholinergic cells, fibres and terminals) and calretinin were analysed using confocal laser-scanning microscope. Obtained data demonstrate that during development as well as in adult species calretinin-containing neurones in the rat hippocampus form sparse synaptic contact with VAChT-ir terminals. It seems probable that cholinergic innervation is not crucial for the functioning of CR-ir cells — probably they remain under the greater influence of a system other than the cholinergic system.
The localisation of carletinin in the midbrains of 10 sexually mature chinchilla males was examined by carrying out the peroxidase-antiperoxidase immunocytochemical reaction using specific monoclonal antibody against calretinin. Intensive immunostaining for the protein was observed in the majority of fusiform, pyramidal, and stellate neurons of dorsal raphe nucleus. A similar calretinin distribution in neurons of this region to those observed in primates and rodents was demonstrated.
Immunohistochemical study of the cholinergic innervation of the hippocampal cells containing glutamic acid decarboxylase (GAD) and calcium binding proteins: parvalbumin (PV), calbindin D28k (CB) and calretinin (CR) was conducted on 5 adult rat brains. Analysis of sections with double immunostaining for vesicular acetylcholine transporter (VAChT; the marker of cholinergic cells, fibres and terminals) and respectively either GAD or PV, CB, CR, using confocal laser-scanning microscope shows that the intensive cholinergic innervations receive GAD, PV and CB-positive hippocampal cells. Cholinergic afferentations of the CR-positive neurones are considerably fewer.
Recent decades has brought significant advances in our knowledge of the chemical coding and function of enteric neurons. Calcium ions are important second messenger involved in many aspects of neuron physiology. In the present study, we analyzed immunohistochemically the presence of calcium binding proteins (calretinin and calbindin) in various subpopulations of enteric neurons from the ovine duodenum. Ten percent of submucous neurons were immunoreactive (IR) to calretinin. The presence of calretinin was not detected in myenteric neurons. Calretinin-expressing nerve fibres were found in both myenteric and submucous ganglia, between the circular and longitudinal smooth muscle layers and in the lamina muscularis mucosae. Calretinin-IR submucous neurons did not exhibit the presence of SP, NPY and VIP. Co-localization of calretinin and serotonin was found only in a small number of submucous neurons. Calbindin was expressed in 35% of myenteric neurons and in 60% of submucous neurons. Nerve fibres containing calbindin were localized in myenteric and submucous ganglia where they frequently formed basket-like formations. Calbindin-positive nerve fibres emerging from myenteric ganglia ran between the circular and longitudinal smooth muscle layers. Immunoreactivity to calbindin was also visualized in the lamina muscularis mucosae, around mucosal glands and blood vessels. None of calbindin-IR myenteric neurons revealed immunoreactivity to SP, NPY, VIP and serotonin. Virtually all calbindin-expressing submucous neurons were SP-positive. In moderate numbers of submucous perikarya, co-incidence of calbindin and NPY, calbindin and VIP or calbindin and serotonin was observed. We conclude that in the ovine duodenum, the expression of calretinin and calbindin is species specific. Co-localization studies and distribution patterns indicate that in the duodenum of the sheep, calretinin and calbindin may be present in several functional subclasses of enteric neurons.
We investigated distribution and morphology of neurons of the midbrain nuclei: the ventral tegmental area (VTA), substantia nigra (SN) and periaqueductal gray (PAG) of the adult grey short-tailed opossums that were double immunolabeled for the presence of calretinin (CR) and/or tyrosine hydroxylase (TH). The majority of TH-immunopositive neurons and fibers were located in the VTA, SN, and only scarce population of small neurons expressing TH was present in the PAG. In the SN 80% of TH-expressing neurons had large cell bodies, and only a small fraction had small perikarya. In the PAG populations of large and medium sized neurons were equal and 20% of neurons had small perikarya. Much scarcer population of TH-immunoreactive neurons in the PAG consisted of large or small neurons in its dorsal part (PAGd) and almost exclusively small neurons in the ventral part (PAGv). Distribution of neurons expressing TH and their types in the opossum are similar to those in rodents. The majority of CR-immunolabeled neurons were found in the VTA. In its subdivision, the parabrachal pigmented nucleus (PBP) cells expressing CR were approximately 28% more numerous than cells expressing TH. In spite of that, only 42% of TH-expressing neurons coexpressed CR. The high degree of colocalization TH and CR was observed in the SN. We propose that a higher percentage of TH/CR colocalization, which is observed in the opossums SN, may give them the ability to adapt to changes in their motor functions.
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