Co-localization of calretinin and parvalbumin with nicotinamide adenine dinucleotide phosphate-diaphorase in tench Mauthner cells

Regional chemoarchitecture of the brain of lungfishes based on calbindin D-28K and calretinin immunohistochemistry

Lungfishes are the closest living relatives of land vertebrates, and their neuroanatomical organization is particularly relevant for deducing the neural traits that have been conserved, modified, or lost with the transition from fishes to land vertebrates. The immunohistochemical localization of calbindin (CB) and calretinin (CR) provides a powerful method for discerning segregated neuronal populations, fiber tracts, and neuropils and is here applied to the brains of Neoceratodus and Protopterus, representing the two extant orders of lungfishes. The results showed abundant cells containing these proteins in pallial and subpallial telencephalic regions, with particular distinct distribution in the basal ganglia, amygdaloid complex, and septum. Similarly, the distribution of CB and CR containing cells supports the division of the hypothalamus of lungfishes into neuromeric regions, as in tetrapods. The dense concentrations of CB and CR positive cells and fibers highlight the extent of the thalamus. As in other vertebrates, the optic tectum is characterized by numerous CB positive cells and fibers and smaller numbers of CR cells. The so-called cerebellar nucleus contains abundant CB and CR cells with long ascending axons, which raises the possibility that it could be homologized to the secondary gustatory nucleus of other vertebrates. The corpus of the cerebellum is devoid of CB and CR and cells positive for both proteins are found in the cerebellar auricles and the octavolateralis nuclei. Comparison with other vertebrates reveals that lungfishes share most of their features of calcium binding protein distribution with amphibians, particularly with salamanders.

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.

Calcium binding protein calretinin (29kD) localization in the forebrain of the cichlid fish: An immunohistochemical study

Ionic regulation is essential for the metabolism and cellular function. For many physiological processes, ionic calcium (Ca(+2)) is important for example muscle contractions, nerve signaling, membrane permeability, cell division and hormone release. In nerve cells, the excess intracellular concentration of Ca(+2) causes cell death. It has been shown that certain calcium binding proteins (CaBPs) are essential for Ca(+2) homeostasis and protect neurons from excess Ca(+2) influx. We are for the first time showing an unusual calretinin (CR) expression and significant differences in its occurrence in the forebrain of the cichlid fish (Cynotilapia sp.) compared to other teleosts. CR labeled neurons were seen in the dorsal and lateral part of the dorsal telencephalic area, entopeduncular nucleus (EN), nucleus preopticus (NPO), diffuse nucleus of lateral torus (NDTL), ventral hypothalamic nucleus (VH), preglomerular nucleus (NPG) and optic tectum. Surprisingly, large numbers of CR immunoreactive perikarya were noted in the optic chiasma (Oc). These neurons were oval with elongated processes and forming a huge fiber network in the Oc. Enormously CR stained fibers were seen in the lateral and medial olfactory tract. Widespread distributions of strongly CR labeled fibers were observed around the EN projecting dorsally into the telencephalon, Oc and optic nerve. Presence of CR in the NPO suggests that it may be involved in the hormonal regulation by the pituitary. As in vertebrates EN plays an important role in sensory functions, massive localization CR in the EN may suggests role of CR in sensory functions of the cichlid fish.

Sexually dimorphic distribution of calcium-binding protein, calretinin in the preoptic area of the freshwater catfish, Clarias batrachus (Linn.)

Preoptic area (POA) plays an important role in the hormonal regulation of the pituitary gland in vertebrates. In this study we report the sexually dimorphic distribution of calcium-binding proteins calretinin (CR) in the POA in the freshwater catfish, Clarias batrachus. Nissl staining highlighted the presence of the nucleus praeopticus periventricularis (NPP) and other subdivisions of the nucleus praeopticus (NPO), including supraoptic (NPOs), paraventricular (NPOp) and magnocellular (NPOm) divisions. In NPO, CR immunoreactivity was noted only in females but not in males. In both sexes, CR stained perikarya were found in the NPP. Sexually dimorphic localization of CR in the POA supports the notion that CR may play a gender-specific role and may be involved in hormonal regulation in fishes.

Immunohistochemical distribution of calretinin and calbindin (D-28k) in the brain of the cladistian Polypterus senegalus

Polypteriform fishes are believed to be basal to other living ray-finned bony fishes, and they may be useful for providing information of the neural organization that existed in the brain of the earliest ray-finned fishes. The calcium-binding proteins calretinin (CR) and calbindin-D28k (CB) have been widely used to characterize neuronal populations in vertebrate brains. Here, the distribution of the immunoreactivity against CR and CB was investigated in the olfactory organ and brain of Polypterus senegalus and compared to the distribution of these molecules in other ray-finned fishes. In general, CB-immunoreactive (ir) neurons were less abundant than CR-ir cells. CR immunohistochemistry revealed segregation of CR-ir olfactory receptor neurons in the olfactory mucosa and their bulbar projections. Our results confirmed important differences between pallial regions in terms of CR immunoreactivity of cell populations and afferent fibers. In the habenula, these calcium-binding proteins revealed right-left asymmetry of habenular subpopulations and segregation of their interpeduncular projections. CR immunohistochemistry distinguished among some thalamic, pretectal, and posterior tubercle-derived populations. Abundant CR-ir populations were observed in the midbrain, including the tectum. CR immunoreactivity was also useful for characterizing a putative secondary gustatory/visceral nucleus in the isthmus, and for distinguishing territories in the primary viscerosensory column and octavolateral region. Comparison of the data obtained within a segmental neuromeric context indicates that some CB-ir and CR-ir populations in polypteriform fishes are shared with other ray-finned fishes, but other positive structures appear to have evolved following the separation between polypterids and other ray-finned fishes.

The ontogeny of Mauthner cells in the brain of Labeo rohita as revealed by NADPH-d and nNOS immunohistochemistry

Nitric oxide (NO) is well demonstrated to act as a neuronal messenger in neurotransmission in vertebrate animals. We are for the first time reporting nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and neuronal nitric oxide synthase (nNOS) in the Mauthner cells (MC) of the carp, Labeo rohita brain during post-embryonic development. The NADPH-d and nNOS-positive MC were seen intensely labeled in all young stages on either side of the ventricle in the hindbrain. In adult, these cells were moderately stained with NADPH-d but not with nNOS. Further, the morphometeric analysis of the staining intensities showed the decrease in the optical densities of the MC as the development progresses. The gradual increase in cell diameter was evident from hatchling to adult (18-22 μm to 98-106 μm), while the nuclear diameter remained nearly unchanged (10-12 μm to 18-20 μm). In fishes, MC are known to be involved in the control of startle response. The NADPH-d enzymatic activity seen in the MC of early development may play an important role to activate the startle response to fast escape from the predators and unfavorable environmental conditions to survive during early phase of life. As nNOS is absent in the adult MC, we assume that the adult MC express a different splice variant of nNOS which is detected by NADPH-d, but not by the currently used antibody. Hence, the presence of nNOS (enzyme required for the synthesis of NO) in the MC suggests the involvement of NO in neurotransmission to generate the startle response rapidly. Furthermore, we also suggest that NO may be involved in other aspects such as pathway finding, neuronal cell migration, signaling and refinement during the development of the brain of L. rohita.

Localization of calcium-binding protein (calretinin, 29kD) in the brain and pituitary gland of teleost fish: An immunohistochemical study

Immunocytochemical techniques were used to investigate the distribution of calretinin in the brain and pituitary gland of the hardhead catfish Arius felis. Calretinin immunoreactive neurons were found in the telencephalon (lateral nucleus of ventral telencephalic area), diencephalon (around the medial forebrain bundle, lateral tuberal nucleus, central pretectal nucleus, posterior periventricular hypothalamic nucleus, medial preglomerular nucleus, diffuse nucleus of the inferior lobe), mesencephalon (nucleus of the medial longitudinal fascicle, ventral nucleus of the semicircular torus), cerebellum (valvula cerebelli, eurydendroid cells) and rhombencephalon (secondary gustatory nucleus, isthmic nucleus, trigeminal motor nucleus, medial auditory nucleus of the medulla, medial and inferior reticular formation, anterior, descending, posterior and tangential octaval nuclei). Calretinin-labeled fibers were observed in the optic nerve and at the levels of the central pretectal nucleus, the nucleus of the medial longitudinal fascicle, the ventral nucleus of the semicircular torus, the secondary gustatory nucleus, the trigeminal motor nucleus, the eurydendroid cells, the medial auditory nucleus of the medulla and the octaval nucleus. For the first time, we are reporting on calretinin-positive cells in the rostral and proximal pars distalis of the adenohypophysis. Although, it seems speculatory, calretinin-expressing cells in the pituitary gland may be involved in hormonal regulation and hence, calretinin might play a significant role in governing hypophysial functions in fishes. Our results suggest that calretinin shows species-specific variations also among the teleost fish, similar to mammals.

Calretinin immunoreactivity in the brain of the zebrafish,Danio rerio: Distribution and comparison with some neuropeptides and neurotransmitter-synthesizing enzymes. II. Midbrain, hindbrain, and rostral spinal cord

The distribution of calretinin (CR) in the brainstem and rostral spinal cord of the adult zebrafish was studied by using immunocytochemical techniques. For analysis of some brainstem nuclei and regions, CR distribution was compared with that of complementary markers (choline acetyltransferase, glutamic acid decarboxylase, tyrosine hydroxylase, neuropeptide Y). The results reveal that CR is a marker of various neuronal populations distributed throughout the brainstem, including numerous cells in the optic tectum, torus semicircularis, secondary gustatory nucleus, reticular formation, somatomotor column, gustatory lobes, octavolateral area, and inferior olive, as well as of characteristic tracts of fibers and neuropil. These results indicate that CR may prove useful for characterizing a number of neuronal subpopulations in zebrafish. Comparison of the distribution of CR observed in the brainstem of zebrafish with that reported in an advanced teleost (the gray mullet) revealed a number of similarities, and also some interesting differences. Our results indicate that many brainstem neuronal populations have maintained the CR phenotype in widely divergent teleost lines, so CR studies may prove very useful for comparative analysis.

Development of NADPH-diaphorase/nitric oxide synthase in the brain of the urodele amphibian Pleurodeles waltl

In the present study, the ontogenesis of nitrergic neurons has been studied in the urodele amphibian Pleurodeles waltl by means of NADPH-diaphorase (NADPHd) histochemistry and neuronal nitric oxide synthase (NOS) immunohistochemistry. Embryonic and larval stages were studied. Except for the olfactory fibers and glomeruli, both methods were equally suitable to reveal nitrergic structures in the brain. The earliest positive neurons were observed in the inferior reticular nucleus (Ri) in the caudal rhombencephalon at embryonic stage 30. At stage 33b, weakly reactive cells appeared in the tegmentum of the mesencephalon and isthmus, in the ventral hypothalamus (VH), and in the proximity of the solitary tract (sol). At initial larval stages (stages 34-38), two new groups appeared in the caudal telencephalon (future amygdaloid complex (Am)) and in the middle reticular nucleus (Rm) of the rhombencephalon. During the active larval life (stages 39-55c) the nitrergic system developed progressively both in number of cells and fiber tracts. At stages 39-42 reactive cells were found in the inner granular layer (igl) of the olfactory bulb, the telencephalic pallium, the pretectal region, the optic tectum (OT) and retina. New populations of nitrergic cells appear during the second half of the larval period (stages 52-55). Rostrally, reactive cells were found in the telencephalic diagonal band (DB) nucleus, medial septum and in the thalamic eminence (TE), whereas caudally cells appeared in the raphe (Ra) and the descending trigeminal nucleus (Vd). The last changes occurred during the juvenile period (metamorphic climax), when cells of the spinal cord (sc) and the preoptic area became positive. The sequence of appearance of nitrergic cells revealed a first involvement of this system in reticulospinal control, likely influencing locomotor behavior. As development proceeds, cells in different sensory systems expressed progressively nitric oxide synthase in a pattern that shows many similarities with amniotes.

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.