A genome-wide association study for myopia and refractive error identifies a susceptibility locus at 15q25

Myopia and hyperopia are at opposite ends of the continuum of refraction, the measure of the eye's ability to focus light, which is an important cause of visual impairment (when aberrant) and is a highly heritable trait. We conducted a genome-wide association study for refractive error in 4,270 individuals from the TwinsUK cohort. We identified SNPs on 15q25 associated with refractive error (rs8027411, P = 7.91 × 10⁻⁸). We replicated this association in six adult cohorts of European ancestry with a combined 13,414 individuals (combined P = 2.07 × 10⁻⁹). This locus overlaps the transcription initiation site of RASGRF1, which is highly expressed in neurons and retina and has previously been implicated in retinal function and memory consolidation. Rasgrf1(-/-) mice show a heavier average crystalline lens (P = 0.001). The identification of a susceptibility locus for refractive error on 15q25 will be important in characterizing the molecular mechanism responsible for the most common cause of visual impairment.

RasGRF1 disruption causes retinal photoreception defects and associated transcriptomic alterations

RasGRF1 null mutant mice display impaired memory/learning and their hippocampus transcriptomic pattern includes a number of differentially expressed genes playing significant roles in sensory development and function. Odour avoidance and auditory brainstem response tests yielded normal results but electroretinographic analysis showed severe light perception impairment in the RasGRF1 knockouts. Whereas no structural alterations distinguished the retinas of wild-type and knockout mice, microarray transcriptional analysis identified at least 44 differentially expressed genes in the retinas of these Knockout animals. Among these, Crb1, Pttg1, Folh1 and Myo7a have been previously related to syndromes involving retina degeneration. Interestingly, over-expression of Folh1 would be expected to result in accumulation of its enzymatic product N-acetyl-aspartate, an event known to be linked to Canavan disease, a human cerebral degenerative syndrome often involving blindness and hearing loss. Consistently, in vivo brain nuclear magnetic resonance spectroscopy identified higher levels of N-acetyl-aspartate in our RasGRF1-/- mice and immunohistochemical analysis detected reduced levels of aspartoacylase, the enzyme which degrades N-acetyl-aspartate. These studies demonstrate for the first time the functional relevance of Ras signalling in mammalian photoreception and warrant further analysis of RasGRF1 Knockout mice as potential models to analyse molecular mechanisms underlying defective photoreception human diseases.

Characterization of NADPH-diaphorase-positive glial cells of the tench optic nerve after axotomy

NADPH-diaphorase (ND) positive cell types were characterized throughout the optic nerve of the tench in normal conditions and after optic nerve transection with survival periods of 1, 3, 7, 14, 30, 60, 120 and 180 days. Astrocytic markers (S100 and glutamine synthetase) and the microglial marker tomato lectin were employed. In the control prechiasmatic optic nerve two types (types I and II) of ND-positive glial cells appeared. All type I cells showed S100 immunoreactivity, whereas only a subpopulation of them were positive to glutamine synthetase. Type II cells only presented S100 immunoreactivity. In the control anterior optic tract, all ND-positive glial cells (type III) presented immunolabeling to S100 and glutamine synthetase. After transection, types I and II did not show any changes in the staining patterns for the glial markers when observed. Two new types of ND-positive glial cells (types IV and V) were observed after axotomy. All type IV cells were S100-immunopositive, and a subpopulation presented glutamine synthetase immunolabeling. Only a subpopulation of type V cells showed glutamine synthetase immunostaining. The presence of type IV or V cells in the lesioned optic nerve occurred simultaneously with significant decreases or absence of type I cells. These data suggest that type I and III cells are astrocytes and type II cells are oligodendrocytes. Types IV and V cells are the result of the activation of type I cells after optic nerve section. The polymorphism observed in ND-positive cells may reflect different cell functions during degenerative and regenerative processes.

Laser microdissection and microarray analysis of the hippocampus of Ras-GRF1 knockout mice reveals gene expression changes affecting signal transduction pathways related to memory and learning

We used manual macrodissection or laser capture microdissection (LCM) to isolate tissue sections of the hippocampus area of Ras-GRF1 wild type and knockout mice brains, and analyzed their transcriptional patterns using commercial oligonucleotide microarrays. Comparison between the transcriptomes of macrodissected and microdissected samples showed that the LCM samples allowed detection of significantly higher numbers of differentially expressed genes, with higher statistical rates of significance. These results validate LCM as a reliable technique for in vivo genomic studies in the brain hippocampus, where contamination by surrounding areas (not expressing Ras-GRF1) increases background noise and impairs identification of differentially expressed genes. Comparison between wild type and knockout LCM hippocampus samples revealed that Ras-GRF1 elimination caused significant gene expression changes, mostly affecting signal transduction and related neural processes. The list of 36 most differentially expressed genes included loci concerned mainly with Ras/G protein signaling and cytoskeletal organization (i.e. 14-3-3gamma/zeta, Kcnj6, Clasp2) or related, cross-talking pathways (i.e. jag2, decorin, strap). Consistent with the phenotypes shown by Ras-GRF1 knockout mice, many of these differentially expressed genes play functional roles in processes such as sensory development and function (i.e. Sptlc1, antiquitin, jag2) and/or neurological development/neurodegeneration processes affecting memory and learning. Indeed, potential links to neurodegenerative diseases such as Alzheimer disease (AD) or Creutzfeldt-Jacobs disease (CJD), have been reported for a number of differentially expressed genes identified in this study (Ptma, Aebp2, Clasp2, Hebp1, 14-3-3gamma/zeta, Csnk1delta, etc.). These data, together with the previously described role of IRS and insulin (known Ras-GRF1 activators) in AD, warrant further investigation of a potential functional link of Ras-GRF1 to neurodegenerative processes.

Chemical organization of the macaque monkey olfactory bulb: III. Distribution of cholinergic markers

The distribution patterns of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were studied in the olfactory bulb (OB) of three species of macaque. AChE was detected by a histochemical method and ChAT immunoreactivity by immunocytochemistry. Similar results were observed in all species analyzed. With the exception of the olfactory nerve layer, all layers of the macaque monkey OB demonstrated a dense innervation of AChE- and ChAT-positive fibers. The distribution patterns of AChE- and ChAT-labeled fibers were similar for both cholinergic markers, although the number of AChE-labeled fibers was clearly higher than the number of ChAT-immunoreactive fibers. The highest density of AChE and ChAT-stained fibers was observed in the interface between the glomerular layer and the external plexiform layer and in the internal plexiform layer. Dense bundles of labeled fibers were observed in the caudal OB, coursing from the olfactory peduncle. All ChAT-immunopositive elements were identified as centrifugal fibers, derived from neurons caudal to the OB. Neither olfactory fibers nor intrinsic neurons were observed after ChAT immunocytochemistry. However, a few AChE-positive cells were observed in the glomerular layer and in both external and internal plexiform layers. These neurons were presumably identified as periglomerular cells, superficial short-axon cells, and/or external tufted cells and deep short-axon cells. Contrary to other neurotransmitters and neuroactive substances, the distribution patterns of ChAT and AChE activities in the macaque monkey OB closely resembled the patterns described in macrosmatic mammals and showed laminar differences with the distribution pattern observed in humans.

Teratogenic effects of ethanol exposure on zebrafish visual system development

Ethanol intake during pregnancy can produce a wide range of adverse effects on nervous system development including fetal alcohol syndrome (FAS). The most severe congenital malformation observed in newborns with FAS is cyclopia. In this study, we have exposed zebrafish embryos to different ethanol concentrations (2.4%, 1.5% or 1.0%) during eye morphogenesis in four zebrafish strains (AB, EK, GL and TL). In addition, we have studied the survival rate of the cyclopic animals to the end of larval development. The zebrafish strains GL and AB generated the higher percentage of cyclopic animals after exposure to 2.4% ethanol, while EK showed the higher percent cyclopic animals using 1.5% and 1.0% ethanol. The EK strain showed the higher percent survival during the larval period at all ethanol concentrations (2.4%, 1.5% and 1.0%). Moreover, we have investigated cytoarchitectural alterations in the main components of the visual pathway-retina and optic tectum-and ethanol treatment affects both the retina and the optic tectum. The lamination of neural retina is clearly delayed in treated larvae 3 days postfertilization and the thickness of the pigmented epithelium is considerably reduced. With regard to the optic tectum, treatment with ethanol alters the normal pattern of tectal lamination. The use of zebrafish EK strain is a suitable in vivo vertebrate model system for analyzing the teratogenic effect of ethanol during vertebrate visual system morphogenesis as it relates to both cyclopia and FAS.

Tyrosine hydroxylase immunoreactivity in the developing visual pathway of the zebrafish

We analyzed the distribution of tyrosine hydroxylase immunoreactivity in the central nervous zones involved in the processing of visual information during zebrafish ontogeny, employing a segmental approach. In the retina, we observed immunolabeled cells in the inner nuclear layer after hatching. From the juvenile stages onwards, some of these cells presented two immunolabeled processes towards the inner and outer plexiform layers of the retina, which are identified as interplexiform cells. In the adult zebrafish retina, we have identified two cellular types displaying immunoreactivity for tyrosine hydroxylase: interplexiform and amacrine cells. In the optic tectum, derived from the mesencephalon, no immunolabeled neurons were observed in any of the stages analyzed. The periventricular gray zone and the superficial white zone display immunostained neuropile from the end of fry life onwards. At the 30-day postfertilization, the tyrosine hydroxylase immunoreactive neuropile in the optic tectum presents two bands located within the retinorecipient strata and deeper strata, respectively. All diencephalic regions, which receive direct retinal inputs, show immunolabeled cells in the preoptic area, in the pretectum, and in the ventral thalamus from embryonic stages onwards. During the fry development, the immunolabeled neurons can be observed in the periventricular pretectum from 15-days postfertilization and in both the ventrolateral thalamic nucleus and suprachiasmatic nucleus from 30-days postfertilization. The transient expression of tyrosine hydroxylase is observed in fibers of the optic tract during fry and juvenile development. The existence of immunolabeled neuropile in the zebrafish retinorecipient strata could be related to the turnover of retinotectal projections.

Comparative analysis of the distribution of choline acetyltransferase in the central nervous system of cyprinids

The general organization of the cholinergic system in the central nervous system is similar among vertebrates, though fish show higher variability. Thus, in zebrafish, cholinergic cells are absent from the habenula and the rhombencephalic reticular formation, where such neurons are present in most vertebrate species analyzed. In this work, we compared the distribution of choline acetyltransferase in the central nervous system of both zebrafish and tench, in order to investigate whether these divergences in the distribution of cholinergic cells in zebrafish are species-specific, or a feature shared by members of the cyprinid family. Our data show that these two cyprinid possess in common some peculiarities in their cholinergic system that are not present in the rest of fish analyzed (e.g. absence of cholinergic cells in the habenula and their presence in the descendent octaval nucleus). Nonetheless, some cholinergic cells were observed in the dorsal thalamus and rhombencephalic reticular nuclei of the tench, which were absent in the same regions in zebrafish. The comparative analysis suggests a divergent evolution of the cholinergic system among close-related cyprinid species.

Development of the cholinergic system in the brain and retina of the zebrafish

We have analyzed the distribution pattern of choline acetyltransferase (ChAT) in the zebrafish brain and retina during ontogeny. ChAT-immunoreactive (ChAT-ir) neurons are observed in the prosencephalon from 60 h postfertilization (hpf) onwards, exclusively in the preoptic area (basal plate of p6) derived from the secondary prosencephalon. In the mesencephalon, ChAT-ir cells are observed in both the optic tectum and the tegmentum. Stained cells in the tegmentum are observed from 60 hpf onwards, while in the optic tectum they appear after hatching. In the rhombencephalon, ChAT-ir cells are first observed in the isthmic region (rh1) and in the medulla oblongata (rh5-rh7) at the end of embryonic life. The rhombencephalic cholinergic cell groups develop in a gradual caudorostral sequence. Motoneurons of the spinal cord are ChAT-ir from 48 hpf onwards. The retina displays ChAT-ir neuropil in both the inner and outer plexiform layers from embryonic life, whereas stained amacrine cells are only observed after hatching. The staining in the outer plexiform layer gradually decreases during juvenile development. The optic nerve axons show a transient expression of ChAT at the end of embryonic development. The early presence of ChAT immunolabeling suggests an important neuromodulator role for acetylcholine in the first developmental stages.

Cholinergic elements in the zebrafish central nervous system: Histochemical and immunohistochemical analysis

Recently, the zebrafish has been extensively used for studying the development of the central nervous system (CNS). However, the zebrafish CNS has been poorly analyzed in the adult. The cholinergic/cholinoceptive system of the zebrafish CNS was analyzed by using choline acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) histochemistry in the brain, retina, and spinal cord. AChE labeling was more abundant and more widely distributed than ChAT immunoreactivity. In the telencephalon, ChAT-immunoreactive (ChAT-ir) cells were absent, whereas AChE-positive neurons were observed in both the olfactory bulb and the telencephalic hemispheres. The diencephalon was the region with the lowest density of AChE-positive cells, mainly located in the pretectum, whereas ChAT-ir cells were exclusively located in the preoptic region. ChAT-ir cells were restricted to the periventricular stratum of the optic tectum, but AChE-positive neurons were observed throughout the whole extension of the lamination except in the marginal stratum. Although ChAT immunoreactivity was restricted to the rostral tegmental, oculomotor, and trochlear nuclei within the mesencephalic tegmentum, a widespread distribution of AChE reactivity was observed in this region. The isthmic region showed abundant AChE-positive and ChAT-ir cells in the isthmic, secondary gustatory and superior reticular nucleus and in the nucleus lateralis valvulae. ChAT immunoreactivity was absent in the cerebellum, although AChE staining was observed in Purkinje and granule cells. The medulla oblongata showed a widespread distribution of AChE-positive cells in all main subdivisions, including the octavolateral area, reticular formation, and motor nuclei of the cranial nerves. ChAT-ir elements in this area were restricted to the descending octaval nucleus, the octaval efferent nucleus and the motor nuclei of the cranial nerves. Additionally, spinal cord motoneurons appeared positive to both markers. Substantial differences in the ChAT and AChE distribution between zebrafish and other fish species were observed, which could be important because zebrafish is widely used as a genetic or developmental animal model.

Distribution of calbindin D-28k in the entorhinal, perirhinal, and parahippocampal cortices of the macaque monkey

We examined the distribution of calbindin D-28k-immunoreactive (CB-IR) neurons, fibers, and neuropil in the entorhinal (area 28), perirhinal (areas 35 and 36), and parahippocampal (areas TH and TF) cortices in the macaque monkey. Two main findings are reported. First, except for CB-IR neurogliaform cells that are only observed in the parahippocampal cortex, the morphology of CB-stained pyramidal and nonpyramidal cells were similar across the three cortical areas examined. Second, we find that the topography of CB staining differed between the three areas. The entorhinal cortex exhibits the most striking gradient of CB staining such that the most anterior and medial portions are most strongly labeled, whereas posterior and lateral areas exhibit only weak labeling. The labeling throughout the perirhinal and parahippocampal cortices is more homogeneous. Area 35 contains only lightly stained neuropil and few CB-IR cells. Area 36 and areas TH and TF of the parahippocampal cortex contain a moderate to high density of CB-IR cells and fibers throughout their full rostrocaudal extents, although each area exhibits unique laminar patterns of staining. In all areas examined, the highest density of CB-positive cells and fibers is observed in superficial layers with lower densities of CB-positive cells and fibers present in deep layers. These findings, taken together with our current understanding of the connections of these areas may have implications for understanding the circuit properties of the entorhinal, perirhinal, and parahippocampal cortices areas in both normal and disease states.

Changes in immunoreactivity to calcium-binding proteins in the anterior olfactory nucleus of the rat after neonatal olfactory deprivation

The effects of olfactory deprivation on the density of neuronal populations expressing the calcium-binding proteins calbindin D-28k, calretinin, and parvalbumin in the anterior olfactory nucleus of the rat were studied immunohistochemically in 60-day-old rats subjected to unilateral naris closure on the day of birth. The neuronal populations were characterized morphologically and topologically, and the density of each cell type was calculated in each subdivision of the anterior olfactory nucleus at seven rostrocaudal levels. Data were gathered into three groups: data from either the ipsilateral or contralateral anterior olfactory nucleus of experimental animals and data from control animals. Statistical analysis indicated that disruption of the normal afferent activity to one olfactory bulb affects the expression of the calcium-binding proteins investigated in the anterior olfactory nucleus, as revealed by variations in the density of certain neuronal populations. The observed effects were very heterogeneous and could not be related to any specific neuronal type, location, or to the expression of a given calcium-binding protein. Nevertheless, as a general rule the most affected neuronal populations were those expressing calbindin D-28k located in the rostral subdivisions. These subdivisions are the latest to develop in mammals and are those that receive the largest amount of inputs from the olfactory bulb.

Targeted disruption of Ras-Grf2 shows its dispensability for mouse growth and development

The mammalian Grf1 and Grf2 proteins are Ras guanine nucleotide exchange factors (GEFs) sharing a high degree of structural homology, as well as an elevated expression level in central nervous system tissues. Such similarities raise questions concerning the specificity and/or redundancy at the functional level between the two Grf proteins. grf1-null mutant mice have been recently described which showed phenotypic growth reduction and long-term memory loss. To gain insight into the in vivo function of Grf2, we disrupted its catalytic CDC25-H domain by means of gene targeting. Breeding among grf2(+/-) animals gave rise to viable grf2(-/-) adult animals with a normal Mendelian pattern, suggesting that Grf2 is not essential for embryonic and adult mouse development. In contrast to Grf1-null mice, analysis of grf2(-/-) litters showed similar size and weight as their heterozygous or wild-type grf2 counterparts. Furthermore, adult grf2(-/-) animals reached sexual maturity at the same age as their wild-type littermates and showed similar fertility levels. No specific pathology was observed in adult Grf2-null animals, and histopathological studies showed no observable differences between null mutant and wild-type Grf2 mice. These results indicate that grf2 is dispensable for mouse growth, development, and fertility. Furthermore, analysis of double grf1/grf2 null animals did not show any observable phenotypic difference with single grf1(-/-) animals, further indicating a lack of functional overlapping between the two otherwise highly homologous Grf1 and Grf2 proteins.

Effects of axotomy on the expression of NADPH-diaphorase in the visual pathway of the tench

The distribution of NADPH-diaphorase (ND) positive elements was analyzed throughout the visual pathway of the tench in normal conditions and after optic nerve transection. In the control retina, ND-labeled elements were observed in the photoreceptor, inner nuclear, outer nuclear and ganglion cell layers. In the optic nerve of control animals, small and numerous ND-positive glial cells that were identified as presumably astrocyte-like cells were observed. In the optic tracts and optic tectum, a different type of ND-positive glial cell was detected. Axotomy induced severe changes in the ND staining pattern in the visual pathway. A decrease in the number of ND-stained cells was detected in the retina. In the optic nerve of lesioned animals, the number of small cells gradually decreased, whereas the number of large cells did not change. Two new ND-positive cell populations were observed after the lesion: microglial-like cells appeared close to the lesioned area from 24 h to 7 days after transection, and astrocyte-like cells were found throughout the optic nerve from 14 days up to at least 120 days. The total number of ND-stained glial cells increased at 30 and 60 days and returned to control parameters at 120 days. In addition, the number of ND-positive cells increased at the same survival times in the optic tracts and in the retinorecipient strata of the optic tectum with respect to control animals. Thus, degenerative/regenerative processes in the fish visual pathway are accompanied by an increase in the number of ND-positive cells. Synthesis of nitric oxide is elicited in microglial-like cells as a response to axon injury, whereas the expression in astrocyte-like cells seems to be associated with both normal processes under physiological conditions and with the regenerative phase after the lesion.

Volumetric changes in the anterior olfactory nucleus of the rat after neonatal olfactory deprivation

The effect of olfactory deprivation in the postnatal development of the anterior olfactory nucleus (AON) was studied in 60-day-old rats which underwent unilateral naris closure after birth (postnatal day 1). Volumetric and morphometric analyses of the AON ipsilateral and contralateral to the closed naris were performed and data were statistically compared among them and with those of control animals. The volumes of the AONs and those of their subdivisions were calculated by the Cavalieri method and the area of the subdivisions was measured at seven established rostrocaudal levels. Whereas no statistically significant differences were detected between the ipsilateral and the contralateral AONs, comparison of these with controls revealed significant reductions in the volumes and dimensions of most AON subdivisions. The reduction was larger in the ipsilateral than in the contralateral AON and more pronounced in the rostralmost subdivisions (external and lateral) than in the caudal ones, the dorsal subdivision not being affected. These data demonstrate that the disruption of the normal afferent activity to one olfactory bulb has effects on the postnatal development of both the ipsilateral and the contralateral AONs. In addition, the most affected subdivisions were those that develop later and that receive the bulk of projections from the olfactory bulb, suggesting that the degree of maturity is an important factor in susceptibility to changes induced by reduced afferent activity. Finally, the results indicate that, contrary to the olfactory bulb, the contralateral AON cannot be used as a control structure in deprivation studies.

Calretinin-, neurocalcin-, and parvalbumin-immunoreactive elements in the olfactory bulb of the hedgehog (Erinaceus europaeus)

The distribution pattern and morphology of calretinin-, neurocalcin-, and parvalbumin-immunoreactive neurons were studied in the main and accessory olfactory bulbs of the hedgehog. The detection of these markers was carried out by using monoclonal or polyclonal antibodies and the avidin-biotin-immunoperoxidase method. Specific neuronal populations were positive for these calcium-binding proteins in the hedgehog olfactory bulb, revealing both similarities to and differences from the data reported in the olfactory bulb of rodent species. The distribution pattern of each calcium-binding protein studied in the accessory olfactory bulb was highly similar to that described in other macrosmatic species. However, in the main olfactory bulb, the markers analyzed were expressed in similar interneuronal populations as they are in the rodent olfactory bulb, whereas cell groups categorized as projecting neurons demonstrated striking differences in the expression of these calcium-binding proteins. These results suggest that the expression of calcium-binding proteins in a given brain region is not a constant feature among species despite a similar organization but that different factors could influence their expression. Thus, the accessory olfactory system involved in the processing of specific and similar olfactory cues among species demonstrates a more constant organization among species. By contrast, the functionally important role of the main olfactory system in the hedgehog is accompanied by a more complex organization, which is reflected in an increased diversity of calcium-buffering systems.

A sexually dimorphic group of atypical glomeruli in the mouse olfactory bulb

Atypical glomeruli (AtG) are clearly distinguishable from typical ones because of their strong cholinergic innervation. AtG are located in defined positions in the caudal half of the main olfactory bulb of rodents. The AtG partially overlap with other specialized olfactory subsystems, such as the modified glomerular complex, which is close to the accessory olfactory bulb. So far, possible sex differences in these specialised olfactory systems have not been investigated. In this work we have identified AtG in the mouse by means of acetylcholinesterase histochemistry and compared the number and size of these glomeruli between the sexes and also between the two strains that demonstrate intraglomerular synaptic differences, i.e. BALB/c and CD-1 mice. First, we divided the AtG into three types according to their position (I, rostral-most; II, around the accessory olfactory bulb; III, caudal-most) or their reactivity to acetylcholinesterase histochemistry (AtG type II being the least reactive glomeruli). ANOVA analyses revealed differences in the maximum diameter of glomeruli among the three types, but not in their sectional areas, indicating that all three types have different shapes. Moreover, both morphoplanimetric parameters were seen to be different between the two strains studied and also between the sexes: male mice and BALB/c animals had the largest glomeruli. The number of AtG was also significantly different between the sexes and strains, although these factors presented a strong interaction. Thus, the males had higher numbers of AtG in the CD-1 strain whereas in the BALB/c mice males demonstrated fewer AtG than females. These differences in number were largely due to AtG type II. The present work is evidence that AtG type II is a sexually dimorphic group of specialized glomeruli located in the main olfactory bulb.

Expression of neuronal nitric oxide synthase/NADPH-diaphorase during olfactory deafferentation and regeneration

Neuronal nitric oxide synthase (nNOS) expression can be regulated under natural or experimental conditions. This work aims at elucidating whether the expression of nNOS or its related NADPH-diaphorase (ND) activity are modified by manipulation of the normal inputs to neurons. We used the olfactory bulbs from two mouse strains, BALB and CD1, because they show divergences in their synapse patterns, and these differences affect periglomerular cells, interneurons expressing tyrosine hydroxylase or nNOS/ND. The olfactory inputs to these neurons can be disrupted by inhalation of methyl bromide. The effect of this gas on olfactory axons, as well as the synaptic features in both mouse strains, were studied using electron microscopy. The changes in expression were analysed qualitatively and quantitatively at different times after lesion to nine topographical regions of the olfactory bulb. Methyl bromide inhalation induced a degeneration of olfactory axons in both strains, but had different effects on the expression of nNOS/ND and tyrosine hydroxylase. In BALB mice, where periglomerular cells do not receive direct inputs from olfactory axons, no changes were detected in tyrosine hydroxylase or in ND expression. In CD1 periglomerular cells, where olfactory axons establish direct synapses, a significant down-regulation of both markers was observed. These changes were observed differentially across the olfactory bulb, being more pronounced in rostral regions and more acute for ND than for tyrosine hydroxylase. Our results indicate that the synaptic inputs influence the expression of ND activity related to nNOS and that the activation of the enzyme is more severely affected than its protein expression.

Distribution of parvalbumin immunoreactivity in the brain of the tench (Tinca tinca L., 1758)

The distribution of parvalbumin (PV) immunoreactivity in the tench brain was examined by using the avidin-biotin-peroxidase immunocytochemical method. This protein was detected in neuronal populations throughout all main divisions of the tench brain. In the telencephalic hemispheres, PV-immunopositive neurons were distributed in both the dorsal and ventral areas, being more abundant in the area ventralis telencephali, nucleus ventralis. In the diencephalon, the scarce distribution of PV-containing cells followed a rostrocaudal gradient, and the most evident staining was observed in the nucleus periventricularis tuberculi posterioris and in a few nuclei of the area praetectalis. In the mesencephalon, abundant PV-immunoreactive elements were found in the tectum opticum, torus semicircularis, and tegmentum. In the tectum opticum, PV-immunoreactivity presented a laminar distribution. Three PV-containing neuronal populations were described in the torus semicircularis, whereas in the tegmentum, the PV staining was mainly located in the nucleus tegmentalis rostralis and in the nucleus nervi oculomotorii. In the metencephalon, Purkinje cells were PV-immunopositive in the valvula cerebelli, lobus caudalis cerebelli, and in the corpus cerebelli. In the myelencephalon, PV immunoreactivity was abundant in the nucleus lateralis valvulae, in the nucleus nervi trochlearis, nucleus nervi trigemini, nucleus nervi abducentis, nucleus nervi glossopharyngei, and in the formatio reticularis. Mauthner cells were also PV immunostained. By contrast to other vertebrate groups, only a restricted population of PV-containing neurons was GABA-immunoreactive in the tench, demonstrating that this calcium-binding protein cannot be considered a marker for GABAergic elements in the teleost brain. This study demonstrates a low phylogenetic conservation of the distribution of PV comparing teleosts and tetrapods.

Expression of ZFOR1, a delta-opioid receptor, in the central nervous system of the zebrafish (Danio rerio)

Opioid receptors, besides mediating the effects of analgesic compounds, are involved in drug addiction. Although a large amount of work has been done studying these receptors in mammals, little information has been obtained from nonmammalian vertebrates. We have studied the regional distribution in the central nervous system (CNS) of the zebrafish of the recently cloned delta-opioid receptor homologue ZFOR1 using nonradioactive in situ hybridization. Our findings show that different nuclei within the main subdivisions of the brain displayed specific mRNA signal. The expression is widespread throughout the brain, but only specific cells within each nucleus displayed ZFOR1. Stained cells were abundant in the telencephalon, both in the olfactory bulb and telencephalic hemispheres, and in the diencephalon, where expression was observed in all the different subdivisions. In the mesencephalon, expression of ZFOR1 was abundant in the periventricular layer of the optic tectum. In the cerebellum, expression of ZFOR1 was detected in valvula cerebelli, corpus cerebelli, and lobus vestibulolateralis in both granule and Purkinje cells. In the myelencephalon, cells expressing ZFOR1 were also distributed in the octavolateralis area, the reticular formation, and the raphe nuclei, among others. Also, ZFOR1 was detected in cells of the dorsal and ventral horn of the spinal cord. This work presents the first detailed distribution of a delta-opioid receptor in the CNS of zebrafish. Distribution of ZFOR1 expression is compared with that of the delta-opioid receptor described in mammals.

Distribution of acetylcholinesterase and choline acetyltransferase in the main and accessory olfactory bulbs of the hedgehog (Erinaceus europaeus)

The distribution of cholinergic markers was studied in the main olfactory bulb (MOB) and accessory olfactory bulb (AOB) of the western European hedgehog (Erinaceus europaeus) by using choline acetyltransferase (ChAT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry. A dense network of AChE-containing and ChAT-immunoreactive fibers was observed innervating all layers of the MOB except the olfactory nerve layer, where neither AChE- nor ChAT-labeled elements were found. The highest density of AChE- and ChAT-positive axons was found in the glomerular layer (GL)/external plexiform layer (EPL) boundary, and in the internal plexiform layer. This general distribution pattern of ChAT- and AChE-stained axons resembled the distribution pattern found in rodents. Nevertheless, some interspecies differences, such as the lack of atypical glomeruli in the hedgehog, were also found. In addition to fibers, a population of noncholinergic and presumably cholinoceptive AChE-active neurons was observed in the hedgehog. All mitral and tufted cells of the hedgehog MOB showed a dark AChE staining unlike previous observations in the mitral and tufted cells of rodents. As in other species previously reported, subpopulations of external tufted cells and short-axon cells were also AChE-active. Finally, a population of small AChE-containing cells was observed in the EPL of the hedgehog MOB. The size, shape, and location of these cells coincided with those of satellite and perinidal cells, two neuronal types described previously in the EPL of the hedgehog and not present in the rodent MOB. The AOB of the hedgehog showed a distribution of AChE- and ChAT-positive fibers similar to the rodent AOB. Nevertheless, a heterogeneous innervation of vomeronasal glomeruli by bundles of AChE- and ChAT-labeled axons found in the hedgehog has not been previously found in any other species. As in the MOB, all mitral cells in the AOB showed a strong AChE activity. These results demonstrate some similarities but also important differences between the distribution of ChAT and AChE in the MOB and AOB of rodents and this primitive mammalian. These variations may indicate a different organization of the cholinergic modulation of the olfactory information in the insectivores.

Differential brain expression of a new beta-actin gene from zebrafish (Danio rerio)

It has been shown that actin genes exhibit distinct tissue and stage-specific patterns of expression. We have cloned a new beta-actin gene from the teleost zebrafish (Danio rerio), a well-established model for developmental studies, and analysed its expression by Northern blot and in situ hybridization studies. Our results suggest that in adult brain zebrafish, this new gene is expressed during neuronal cell proliferation.

Chemical anatomy of the macaque monkey olfactory bulb: NADPH-diaphorase/nitric oxide synthase activity

The distribution and the morphology of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (ND)-active and neuronal nitric oxide synthase (NOS)-immunoreactive neurons and fibers were studied in the olfactory bulb of three species of primates, i.e., the cynomolgus macaque monkey (Macaca fascicularis), the Japanese macaque monkey (Macaca fuscata), and the pig-tail macaque monkey (Macaca nemestrina). The ND staining was carried out by means of a direct histochemical method with beta-NADPH as cosubstrate and nitro blue tetrazolium as chromogen. The NOS immunostaining was carried out by using a polyclonal antibody and the avidin-biotin peroxidase method. Similar results were found in the three species, where a distinct distribution pattern of ND/NOS-stained neurons and fibers was observed. All olfactory fibers demonstrated ND-positive labeling but they were NOS-immunonegative. In the superficial modulatory area of the olfactory bulb, a few weakly ND- and NOS-positive periglomerular cells, stellate cells, and darkly stained superficial short-axon cells were observed. In the inframitral layers, granule cells, deep stellate cells, and deep short-axon cells were distinguished. Short-axon cells had oriented morphologies and spiny dendrites. Many thick, varicose ND/NOS-stained fibers identified as centrifugal fibers were observed in the white matter, granule cell layer, internal plexiform layer, mitral cell layer, and external plexiform layer. This distribution of ND activity and NOS immunoreactivity showed similarities to and differences from what has been reported in the olfactory bulb of macrosmatic mammals including rodents (rat, mouse, and hamster) and insectivores (hedgehog). These data confirm that the complexity of the ND/NOS staining in the olfactory bulb of one species correlates with the importance of olfaction in the biology of such species.

Transient expression of calretinin in the trout habenulo-interpeduncular system during development

Calcium-binding proteins control calcium homeostasis during neural development. The expression of one of these proteins, calretinin (CR), was monitored by immunohistochemistry in the developing habenulo-interpeduncular system of the rainbow trout, a conserved region of the brain along vertebrate phylogeny that undergoes a neurochemical reorganization in late development. No CR-immunoreactivity was observed in the habenulo-interpeduncular system during the embryonic development. CR-immunolabeling appeared in newly hatched fry and during the fry development the number of CR-immunostained elements increased progressively. During the juvenile stages (from 30 days post-hatching onwards) a gradual decrease in the number of CR-immunostained cells occurred, until its complete disappearance in adults. These variations in CR expression may represent the variable calcium-buffering needs during different developmental stages.

Parvalbumin immunoreactivity during the development of the cerebellum of the rainbow trout

The distribution of parvalbumin immunoreactivity in the developing cerebellum of the rainbow trout was studied by using a specific monoclonal antibody and the avidin-biotin peroxidase method. Parvalbumin immunoreactivity was absent during the embryonic development of the cerebellum. The first immunoreactive elements, identified by their localization and posterior morphological evolution as immature Purkinje cells, appeared at 6 days posthatching in the presumptive corpus cerebelli and lobus vestibulolateralis. The labeling extended throughout the cerebellum following a caudorostral gradient, and in 21 days alevins, parvalbumin immunoreactive Purkinje cells were also observed in the valvula cerebelli. The appearance of parvalbumin-immunostaining in the Purkinje cells was not simultaneous; the labeling was observed initially in the cell body, extending gradually to the dendritic branches and finally to the axon. From 1 year onwards, parvalbumin immunoreactive terminal puncta from the Purkinje cell axons were observed surrounding the cell bodies of eurydendroid cells, that were parvalbumin immunonegative in all developmental stages studied. The spatio-temporal pattern of parvalbumin immunoreactivity in the rainbow trout cerebellum is different to previous observations in the cerebellum of amniotes.

NADPH-diaphorase histochemistry reveals heterogeneity in the distribution of nitric oxide synthase-expressing interneurons between olfactory glomeruli in two mouse strains

The expression of nitric oxide synthase (NOS) in the olfactory bulb was compared between two mouse strains, CD-1 and BALB/c, that differ in the connectivity within their olfactory glomeruli, their content of tyrosine hydroxylase, and their response to olfactory deafferentation. Labelled cells were qualitatively and quantitatively analyzed by both immunohistochemistry for NOS and histochemistry for nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (ND). Both periglomerular cells and short-axon cells were observed with both techniques employed, and their colocalization in the same neurons demonstrated that ND is a reliable marker for NOS-expressing cells in the mouse olfactory bulb (OB). The histochemical technique differentiates two types of glomeruli: ND-positive and ND-negative. Olfactory glomeruli in the CD-1 strain were about 7% larger than those in the BALB/c animals. While the density of NOS/ND-containing periglomerular cells was similar between both strains studied, more NOS/ND-labelled cells were observed in the ND-positive glomeruli (P = 0.002). Since periglomerular cells in the BALB/c strain do not receive direct olfactory receptors synapses, the present results indicate that such inputs do not regulate the expression of NOS and ND activity in the periglomerular cells. The different densities of NOS/ND-expressing periglomerular cells may indicate that nitric oxide is implicated in a differential modulation of the odor response within both types of chemically distinct glomeruli in the mouse olfactory bulb.

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

The co-localization of calretinin (CR) and parvalbumin (PV) immunoreactivity with nicotinamide adenine dinucleotide phosphate-diaphorase (ND) activity was analyzed in the Mauthner cells of the tench. Mauthner cells were ND active, and ND staining was observed in the soma, axon cap region, and axon of these neurons. CR co-localized with ND in the axon of the Mauthner cells but not in the cell body or in the dendrites, whereas PV immunoreactivity co-localized with ND in the soma, axon and dendrites. The presence of two different calcium-binding proteins in the Mauthner cells indicates that these neurons need complex calcium-buffering systems. The co-localization of these calcium-binding proteins with ND might suggests their involvement in nitric oxide-related events.

Cloning, molecular characterization, and distribution of a gene homologous to delta opioid receptor from zebrafish (Danio rerio)

A full-length cDNA, ZFOR1, has been isolated from the teleost zebrafish (Danio rerio) using a probe from rat mu opioid receptor. ZFOR1 encodes a 373 amino acid protein with seven potential transmembrane domains that shows a high degree of homology to mammalian delta opioid receptor. We have also isolated a genomic clone which contains two exons of ZFOR1, homologous to exons 2 and 3 in mouse and human delta opioid receptor. Expression of ZFOR1 appears to be restricted to nervous tissue as assessed by Northern blot. In situ hybridization in zebrafish brain with specific probes revealed several discrete areas of ZFOR1 expression; higher levels are detected in dorsal telencephalic areas, the periventricular layer of the optic tectum, and the granular layer of the cerebellum. This is the first molecular evidence of the presence of the delta opioid receptor in a non-mammalian species and suggests that it has been highly conserved throughout vertebrate evolution.

Nonspecific labeling of myelin with secondary antisera and high concentrations of Triton X-100

Triton X-100 is used in immunohistochemistry to make tissue permeable, to present certain antigens to antisera, and to prevent certain nonspecific interactions. This detergent is routinely dissolved in buffers at concentrations of 0.01-0.2%. Using high concentrations of Triton X-100 (0.2-2%) and anti-immunoglobulins G (anti-IgGs), labeling of myelin and microglia was detected in fixed brain tissue by indirect fluorescence and avidin-biotin-immunoperoxidase techniques. Differences were found between the species studied (mouse and rat), the type of anti-IgG (anti-mouse, anti-rabbit, anti-sheep, anti-rat, or anti-guinea pig), the detergent concentration, and whether Triton X-100 was included in the incubation media or applied as a pretreatment. Mouse brain displayed strong myelin labeling with all anti-IgGs but rat brain only with anti-rabbit or anti-sheep IgGs. Staining of ramified microglia occurred only in mouse tissue when anti-mouse IgG was used. Nonspecific staining of myelin was also intense in paraffin-embedded tissue and in human brain frozen sections. These results are significant for the prevention of undesirable staining in routine immunolabeling and they also provide a comparatively inexpensive, easy to perform strong labeling of myelin. In addition, the double marker signal (peroxidase and fluorescence) is useful for double labeling studies. (J Histochem Cytochem 46:109-117, 1998)

Calretinin immunoreactivity in the developing olfactory system of the rainbow trout

The distribution of calretinin immunoreactivity in the developing olfactory system of the rainbow trout was studied by using an indirect immunocytochemical method. Calretinin immunoreactivity was firstly detected at 150 day-degrees in the olfactory placode, where labeled primordial cells were observed. At 250 day-degrees, precursor cells of the olfactory receptor neurons located in the olfactory pit were calretinin-immunoreactive. At 300 day-degrees, recognizable olfactory receptor neurons displayed calretinin immunoreactivity in the olfactory epithelium, and calretinin-immunopositive olfactory axons reached the presumptive olfactory bulb. After hatching (400 day-degrees) and during the subsequent development and maturation of the olfactory system, the number of calretinin-immunopositive olfactory receptor cells increased and distributed homogeneously throughout the olfactory epithelium. Accordingly, new positive olfactory fibers arrived to the olfactory bulb arborizing in olfactory glomeruli distributed in nine different terminal fields. Six days after hatching, calretinin-immunopositive interneurons within the olfactory bulb were also observed. The size and number of calretinin-immunoreactive interneurons increased from this stage to adulthood. The adult pattern demonstrated both similarities and differences with the distribution of calretinin immunoreactivity previously described in the olfactory system of mammals.

Calcium-binding proteins in the periglomerular region of typical and typical olfactory glomeruli

The distribution of chemically identified neuronal populations was studied in the glomerular layer of the rat olfactory bulb using calcium-binding protein immunocytochemistry combined with acetylcholinesterase histochemistry. Four calcium-binding proteins (calbindin D-28k, parvalbumin, calretinin, and neurocalcin) were analyzed in the periglomerular region of two different glomerular subsets; typical and atypical glomeruli. Atypical glomeruli were clearly distinguishable from typical ones by their dense network of acetylcholinesterase-positive centrifugal fibers. Each calcium-binding protein studied showed a specific distribution pattern in the rat olfactory bulb. Calbindin D-28k-, calretinin-, and neurocalcin-immunoreactive neurons were specially abundant in the glomerular layer. These three calcium-binding proteins had their main expressions in neuronal subpopulations directly involved in the glomerular circuitries of the rat olfactory bulb. Specific populations of periglomerular cells were stained for calbindin D-28k, parvalbumin, calretinin, or neurocalcin, whereas external tufted cells were only immunoreactive to neurocalcin. Both neuronal types, periglomerular cells and external tufted cells, were found in the periglomerular region of both glomerular subsets. Nevertheless, a homogeneous distribution of calbindin D-28k- or calretinin-immunopositive periglomerular cells were found between typical and atypical glomeruli, whereas the neurocalcin-immunostained external tufted cells were statistically more abundant in typical glomeruli than atypical ones (P < 0.001). These data suggest that some neuronal subpopulations are related with general properties of the glomerular physiology, and they have a homogeneous distribution in different subsets of glomeruli, whereas other chemically identified populations are related with a finer tuning of the olfactory processing, and they are segregately distributed in relation to particular glomerular subsets. In addition, this work adds new differences in the cellular composition of typical and atypical glomeruli.

Neurocalcin immunoreactivity in the rat accessory olfactory bulb

The distribution and morphology of neurocalcin-immunopositive neurons have been studied in the rat accessory olfactory bulb. Different subsets of neurons displaying neurocalcin immunoreactivity were found in the glomerular layer, the external plexiform layer and the internal plexiform layer. The most abundant staining was detected in the glomerular layer where neurocalcin-immunoreactive periglomerular cells and external tufted cells were observed in the lateral glomeruli, whereas the central region of this layer was practically devoid of immunopositive neurons. In the external plexiform layer, medial tufted cells and Van Gehuchten cells displayed neurocalcin immunoreactivity. In the internal plexiform layer, interneurons classified as horizontal cells and vertical cells of Cajal were neurocalcin-immunoreactivity. In the internal plexiform layer, interneurons classified as horizontal cells and vertical cells of Cajal were neurocalcin-immunostained. The staining pattern for neurocalcin in the accessory olfactory bulb showed similarities with the immunostaining described in this brain region for another EF-hand calcium binding protein, calbindin D-28k. However, after double immunohistochemical labeling, colocalization of both proteins in the same neuron was not observed, reflecting a biochemical heterogeneity within morphologically homogeneous neuronal groups.

Nitric oxide synthase in the brain of a urodele amphibian (Pleurodeles waltl) and its relation to catecholaminergic neuronal structures

The neuronal structures with NADPH-diaphorase activity and nitric oxide synthase (NOS) immunoreactivity have been studied in the brain of the urodele amphibian Pleurodeles waltl by means of histochemical and immunocytochemical techniques. Both approaches resulted in the selective labeling of the same neurons and fiber tracts in the brain, except for the primary olfactory fibers that did not stain for NOS but were positive for NADPH-diaphorase. NOS-containing neurons were found in the olfactory bulbs, pallial regions, septum, caudal striatum, amygdala and preoptic area. Only a few diencephalic cells were labeled in the posterior tubercle and ventral hypothalamus. In the brainstem, abundant cells were labeled in the tectum, mesencephalic tegmentum and isthmic region. The most conspicuous cell population was found in the isthmic-pretrigeminal region. Particularly well stained cells were distributed throughout the rhombencephalon in areas related to the descending trigeminal tract, solitary tract, raphe nucleus and the mid-caudal reticular formation. In the cervical spinal cord, NOS-containing cells were present in the dorsal, intermediate and ventral grey fields. Cells in the preoptic, postotic and dorsal root ganglia were also labeled. Double labeling techniques revealed an extensive codistribution of neurons with NOS and catecholamines in the urodele brain but actual colocalization in the same cells was never observed. The organization of the central systems in urodeles with NOS appears to share many features not only with other anamniotes but also with amniotes.

Nitric oxide synthase activity in the olfactory bulb of anuran and urodele amphibians

Nitric oxide synthase activity was studied by means of NADPH-diaphorase activity and nitric oxide synthase immunoreactivity in the main and accessory olfactory bulbs of the frog Rana perezi and the newt Triturus marmoratus. In both species, NADPH-diaphorase staining was observed in all olfactory fibers. Vomeronasal fibers were NADPH-diaphorase-positive in Triturus but they were NADPH-diaphorase-negative in Rana. Nitric oxide synthase immunoreactivity was not observed in the primary afferents in any case. Granule cells were NADPH-diaphorase-positive and nitric oxide synthase-immunopositive in the main and accessory olfactory bulb of Rana, and in the main olfactory bulb of Triturus. The homogeneous NADPH-diaphorase staining of olfactory fibers is similar to what has been reported in teleosts, and it contrasts with the spatial segregation of NADPH-diaphorase-positive and -negative olfactory projections in rodents. These results confirm the interspecies variability of the NADPH-diaphorase/nitric oxide synthase distribution in the olfactory system of vertebrates.

Topographical distribution of NADPH-diaphorase activity in the central nervous system of the frog, Rana perezi

The distribution of NADPH-diaphorase (ND) activity was histochemically investigated in the brain of the frog Rana perezi. This technique provides a highly selective labeling of neurons and tracts. In the telencephalon, labeled cells are present in the olfactory bulb, pallial regions, septal area, nucleus of the diagonal band, striatum, and amygdala. Positive neurons surround the preoptic and infundibular recesses of the third ventricle. The magnocellular and suprachiasmatic hypothalamic nuclei contain stained cells. Numerous neurons are present in the anterior, lateral anterior, central, and lateral posteroventral thalamic nuclei. Positive terminal fields are organized in the same thalamic areas but most conspicuously in the visual recipient plexus of Bellonci, corpus geniculatum of the thalamus, and the superficial ventral thalamic nucleus. Labeled fibers and cell groups are observed in the pretectal area, the mesencephalic optic tectum, and the torus semicircularis. The nuclei of the mesencephalic tegmentum contain abundant labeled cells and a conspicuous cell population is localized medial and caudal to the isthmic nucleus. Numerous cells in the rhombencephalon are distributed in the octaval area, raphe nucleus, reticular nuclei, sensory trigeminal nuclei, nucleus of the solitary tract, and, at the obex levels, the dorsal column nucleus. Positive fibers are abundant in the superior olivary nucleus, the descending trigeminal, and the solitary tracts. In the spinal cord, a large population of intensely labeled neurons is present in all fields of the gray matter throughout its rostrocaudal extent. Several sensory pathways were heavily stained including part of the olfactory, visual, auditory, and somatosensory pathways. The distribution of ND-positive cells did not correspond to any single known neurotransmitter or neuroactive molecule system. In particular, abundant codistribution of ND and catecholamines is found in the anuran brain. Double labeling techniques have revealed restricted colocalization in the same neurons and only in the posterior tubercle and locus coeruleus. If ND is in amphibians a selective marker for neurons containing nitric oxide synthase, as generally proposed, with this method the neurons that may synthesize nitric oxide would be identified. This study provides evidence that nitric oxide may be involved in novel tasks, primarily related to forebrain functions, that are already present in amphibians.

Segregated distribution of nitric oxide synthase-positive cells in the periglomerular region of typical and atypical olfactory glomeruli

Using double-staining techniques, the distribution of NADPH-diaphorase (ND)- and nitric oxide synthase (NOS)-positive cells was compared in the periglomerular region of typical and atypical rat olfactory glomeruli. Dorsomedial and ventrolateral atypical glomeruli contained similar number of ND/NOS-positive periglomerular cells. The number of ND/NOS-stained periglomerular cells was much higher (P < 0.001) in typical than in atypical glomeruli. The present results indicate that, in addition to described neurochemical and ultrastructural differences between the neuropile of typical and atypical glomeruli, there are also marked differences in the phenotype of periglomerular interneurons of both glomerular subsets.

Colocalization of NADPH-diaphorase and acetylcholinesterase in the rat olfactory bulb

The colocalization of NADPH-diaphorase and acetylcholinesterase activities in the rat main and accessory olfactory bulbs has been studied by successive double histochemical staining of the same sections. In the main olfactory bulb, three patterns of glomerular labeling were found: typical/NADPH-diaphorase-positive, typical/NADPH-diaphorase-negative, and atypical/NADPH-diaphorase-negative glomeruli. Although both enzymatic activities were present in periglomerular cells and superficial short-axon cells, colocalization of NADPH-diaphorase and acetylcholinesterase was not observed in these neuronal types. By contrast, both enzymes were colocalized in a small subpopulation (less than 3% of NADPH-diaphorase- or acetylcholinesterase-positive cells) of short-axon cells located in the external plexiform layer, internal plexiform layer, granule cell layer, and white matter. In the accessory olfactory bulb, deep short-axon cells were the only neurons where both enzymes were present, and colocalization of both markers was observed in some of these cells located in the granule cell layer.

Calbindin D-28k immunoreactivity in the rat accessory olfactory bulb

The distribution pattern and the morphology of calbindin D-28k-immunoreactive neurons were studied in the accessory olfactory bulb of the rat using a monoclonal antibody and the avidin-biotin-immunoperoxidase method. Positive neurons were observed in all layers but the vomeronasal nerve layer. Scarce mono-dendritic periglomerular neurons were calbindin D-28k-immunoreactive. Different morphological types of short-axon cells were calbindin D-28k-immunostained, with different degrees of intensity, in the boundary between the internal and external plexiform layer. In addition, deep short-axon cells located in the granule cell layer were calbindin D-28k-immunopositive. By contrast, previous studies described all cells in the rat accessory olfactory bulb as calbindin D-28k-immunonegative. The staining pattern in the rat accessory olfactory bulb showed both similarities and differences with the distribution pattern of the same calcium-binding protein in the main olfactory bulb.

Calretinin-like immunoreactivity in the optic tectum of the tench (Tinca tinca L.)

The distribution of calretinin-like immunopositive cells and fibers in the optic tectum of the tench (Tinca tinca) was studied by using a polyclonal antibody and the avidin-biotin-peroxidase technique. A clear laminated pattern of calretinin-like immunoreactivity was observed. The stratum periventriculare demonstrated a large number of strongly labeled cells whereas in the strata album centrale and griseum centrale, and at the boundary between the strata griseum centrale and fibrosum et griseum superficiale, some scarce, weakly immunostained cells were observed. No immunoreactive cells were seen in the strata fibrosum et griseum superficiale, opticum and marginale. Cells belonging to neuronal types X and XIV, previously characterized using Golgi impregnation, were found to be calretinin-like immunoreactive. Most calretinin-like immunopositive fibers were found in the strata fibrosum et griseum superficiale and opticum with a distribution pattern similar to retinotectal axons in these layers. In agreement with previous biochemical studies, our data suggest that, by contrast to all other classes of vertebrates, instead of calretinin and calbindin D-28k, only one protein is present in teleosts. Nevertheless, the calretinin-like immunostaining pattern in the teleost optic tectum was more complex than that previously described for calbindin D-28k. When compared to the calretinin-immunostaining in the rat superior colliculus, it is evident the presence in both amniotes and anamniotes of calretinin-immunopositive retinotectal axons. However, the distribution patterns of intrinsic calretinin-immunoreactive cells were different.(ABSTRACT TRUNCATED AT 250 WORDS)

NADPH-diaphorase active and calbindin D-28k-immunoreactive neurons and fibers in the olfactory bulb of the hedgehog (Erinaceus europaeus)

The hedgehog, a macrosomatic insectivore with an extraordinary development of the olfactory structures, has a crucial value for any phylogenetic or comparative study in mammals. The distribution pattern and morphology of NADPH-diaphorase-active and calbindin D-28k-immunoreactive neurons were studied in the main and accessory olfactory bulbs of the hedgehog. NADPH-diaphorase (ND) staining was carried out by a direct histochemical method, and the calbindin D-28k (CaBP) immunoreaction by using a monoclonal antibody and the avidin-biotin-immunoperoxidase method. The possible coexistence of both markers was determined by sequential histochemical-immunohistochemical double labeling of the same sections. Specific neuronal populations were positive for both ND and CaBP markers. No cell colocalized both stains in the hedgehog olfactory bulb. A subpopulation of olfactory fibers, and a subpopulation of olfactory glomeruli, located on the medial side, were positive for ND. Surrounding both the ND-positive and ND-negative glomeruli, there were ND- and CaBP-positive periglomerular cells, the latter group being much more abundant. A subpopulation of superficial short-axon cells was CaBP positive but, contrary to what is observed in rodents, this neuronal type was always ND negative. In addition, three neuronal types were observed in the GL-EPL border after CaBP immunostaining. These neuronal types have not been previously described either in the hedgehog or in the rodent olfactory bulb. Horizontal cells and vertical cells of Cajal were also observed after both ND and CaBP labeling. Distinct groups of ND- and CaBP-positive cells, differing in size, shape, dendritic branching pattern, and staining intensity, were distinguished in the granule cell layer and in the white matter. The large and medium-sized cells were identified as a very heterogeneous population of deep short-axon cells, whereas a subpopulation of granule cells was ND positive. The accessory olfactory bulb showed ND staining in all vomeronasal fibers and glomeruli, and in subpopulations of periglomerular cells, granule cells, and deep short-axon cells. The CaBP immunolabeling was more restricted and located in subpopulations of periglomerular cells and in deep short-axon cells. These results indicate different and more complex ND and CaBP staining patterns in the hedgehog olfactory bulb than those previously described in rodents, including the presence of specific, chemically and morphologically defined new neuronal types.

Histochemical localization of NADPH-diaphorase in the rat accessory olfactory bulb

The distribution of NADPH-diaphroase activity was examined in the accessory olfactory bulb of the rat using a direct histochemical technique. Labeled fibers and somata were found in all layers of the accessory olfactory bulb. The entire vomeronasal nerve and all vomeronasal glomeruli were strongly labeled, contrary to the main olfactory bulb, where only dorsomedial olfactory glomeruli displayed NADPH-diaphorase activity. NADPH-diaphorase positive neurons were identified as periglomerular cells in the glomerular layer and external plexiform layer, horizontal cells in the internal plexiform layer, and granule cells and deep short-axon cells in the granule cell layer. The labeled dendrites of the granule cells formed a dense neuropile in the granule cell layer, internal plexiform layer and external plexiform layer. The staining pattern in the accessory olfactory bulb was more complex than what has been previously reported, and demonstrated both similarities and differences with the distribution of NADPH-diaphorase in the main olfactory bulb.

Parvalbumin immunoreactivity in the telencephalic hemispheres of the tench, Tinca tinca

The distribution of parvalbumin immunoreactivity in the telencephalic hemispheres of the tench (Tinca tinca L.) was studied using a monoclonal antibody and the avidin-biotin immunoperoxidase method. A wide distribution of immunoreactive structures was found in both dorsal and ventral areas of the telencephalic hemispheres. Normally, the parvalbumin-immunostained neurons in the dorsal area were smaller, more weakly stained, and more scattered than those in the ventral one. In the dorsal area, parvalbumin-immunoreactivity was observed in practically all divisions. The highest density of positive somata was found in the lateral nucleus. Density of stained fibres was generally low. Labelling in the ventral area appeared in the ventral and dorsal nuclei, with a high density of both immunoreactive fibres and cell bodies. Neurons were seen close to the ventricle, arranged in two groups of neurons with different sizes and morphologies. The distribution and morphological characteristics of the parvalbuminergic cells were similar to those of previously described GABAergic elements, suggesting a possible colocalization of both substances in the teleost telencephalon, as it has been observed in different telencephalic areas of land vertebrates. On the other hand, significant differences were seen between the distribution of parvalbumin in the telencephalic hemispheres of the tench in comparison with its distribution pattern in supposed homologous structures of the forebrain of amniotes.

Calbindin D-28K and NADPH-diaphorase activity are localized in different populations of periglomerular cells in the rat olfactory bulb

Calbindin D-28k (CaBP) immunocytochemistry and NADPH-diaphorase (ND) histochemistry have been combined in the rat olfactory bulb by successive incubations of the same sections. The outer strata showed a similar neuronal staining pattern for both markers with positive periglomerular neurons (although the CaBP-stained periglomerular cells were six-fold more abundant than the ND-active ones) and larger neurons scattered in the glomerular and external plexiform layers. Both populations of periglomerular cells were distinct but they did not show specific morphological characteristics nor a predominant distribution around ND-positive and negative glomeruli. The colocalization study demonstrates that the larger ND and CaBP-stained juxtaglomerular cells, identified according to their size, location and processes branching patterns as two types of short axon cells (superficial short-axon and Van Gehuchten Cells) were also independent populations.