Secretagogin expression in the mouse olfactory bulb under sensory impairments

The interneurons of the olfactory bulb (OB) are characterized by the expression of different calcium-binding proteins, whose specific functions are not fully understood. This is the case of one of the most recently discovered, the secretagogin (SCGN), which is expressed in interneurons of the glomerular and the granule cell layers, but whose function in the olfactory pathway is still unknown. To address this question, we examined the distribution, generation and activity of SCGN-positive interneurons in the OB of two complementary models of olfactory impairments: Purkinje Cell Degeneration (PCD) and olfactory-deprived mice. Our results showed a significant increase in the density of SCGN-positive cells in the inframitral layers of olfactory-deprived mice as compared to control animals. Moreover, BrdU analyses revealed that these additional SCGN-positive cells are not newly formed. Finally, the neuronal activity, estimated by c-Fos expression, increased in preexisting SCGN-positive interneurons of both deprived and PCD mice -being higher in the later- in comparison with control animals. Altogether, our results suggest that the OB possesses different compensatory mechanisms depending on the type of alteration. Particularly, the SCGN expression is dependent of olfactory stimuli and its function may be related to a compensation against a reduction in sensory inputs.

Changes in the serotonergic system and in brain-derived neurotrophic factor distribution in the main olfactory bulb of pcd mice before and after mitral cell loss

The serotonergic centrifugal system innervating the main olfactory bulb (MOB) plays a key role in the modulation of olfactory processing. We have previously demonstrated that this system suffers adaptive changes under conditions of a lack of olfactory input. The present work examines the response of this centrifugal system after mitral cell loss in the Purkinje cell degeneration (pcd) mutant mice. The distribution and density of serotonergic centrifugal axons were studied in the MOB of control and pcd mice, both before and after the loss of mitral cells, using serotonin (5-HT) and 5-HT transporter immunohistochemistry. Studies of the amount of 5-HT and its metabolite, 5-hydroxyindole acetic acid (5-HIAA), were performed by means of high-performance liquid chromatography (HPLC), and the relative amounts of brain-derived neurotrophin factor, BDNF, and its major receptor, tropomyosin-related kinase B (TrkB), were measured by Western blot. Our study revealed that the serotonergic system develops adaptive changes after, but not before, mitral cell loss. The lack of the main bulbar projection cells causes a decrease in the serotonergic input received by the MOB, whereas the number of serotonergic cells in the raphe nuclei remains constant. In addition, one of the molecules directly involved in serotonergic sprouting, the neurotrophin BDNF and its main receptor TrkB, underwent alterations in the MOBs of the pcd animals even before the loss of mitral cells. These data indicate that serotonergic function in the MOB is closely related to olfactory activity and that mitral cell loss induces serotonergic plastic responses.

Long-lasting changes in the anatomy of the olfactory bulb after ionizing irradiation and bone marrow transplantation

The adult brain is considered to be a radioresistant organ since it is mainly composed of non-dividing cells. However, in adult animals there are a few neurogenic brain areas that are affected by ionizing radiation whose plasticity and capacity for recovery are still unclear. Here, mice were irradiated with a minimal lethal dose of radiation in order to determine its effects on the subventricular zone (SVZ), the rostral migratory stream (RMS), and the olfactory bulb (OB). These regions underwent a dramatic reduction in cell proliferation and ensuing morphological alterations, accompanied by a patent reactive gliosis. Bone marrow stem cell (BMSC) transplants were also performed after the radiation treatment to allow the mouse survival with a view to analyzing long-term effects. Normal proliferation rates were not recovered over time and although bone marrow-derived cells reached the brain, they were not incorporated into the SVZ-RMS-OB pathway in an attempt to rescue the damaged regions. Since neurogenesis produces new interneurones in the OB, thus feeding cell turnover, the volume and lamination of the OB were analyzed. The volume of the OB proved to be dramatically reduced at postnatal day 300 (P300), and this shrinkage affected the periependymal white matter, the granule cell layer, the external plexiform layer, and the glomerular layer. These results should be taken into account in cell therapies employing BMSC, since such cells reach the encephalon, although they cannot restore the damage produced in neurogenic areas. This study thus provides new insight into the long-term effects of ionizing radiation, widely employed in animal experimentation and even in clinical therapies for human beings.

Sexual dimorphic stages affect both proliferation and serotonergic innervation in the adult rostral migratory stream

One of the sexual dimorphic differences in adult rodents is neural proliferation. Here we demonstrate that physiological hormone stages can modulate this proliferation in the adult forebrain. Female mice, both pregnant and synchronized in oestrus, exhibited higher proliferating cell percentages than males in both the rostral migratory stream (RMS) and the olfactory bulb (OB). Moreover, although the hormonal component also influenced the subventricular zone (SVZ), no differences in proliferation were observed in this region. In addition, both groups of females had higher numbers of serotonergic fibres in these regions. Serotonin may therefore be related to the mechanism of action by which hormones can affect cell proliferation of this brain region. We also evaluated cell death in the SVZ in males and females, finding that this was higher in the former. Taken together, our results support the idea that in female rodents more neuroblasts are able to reach the RMS and then proliferate, apoptosis being an additional mechanism affecting the low proliferation of cells in the RMS and OB in males. Thus, proliferation in the RMS is influenced by sexual dimorphism.

Changes in cell migration and survival in the olfactory bulb of the pcd/pcd mouse

Postnatally, the Purkinje cell degeneration mutant mice lose the main projecting neurons of the main olfactory bulb (OB): mitral cells (MC). In adult animals, progenitor cells from the rostral migratory stream (RMS) differentiate into bulbar interneurons that modulate MC activity. In the present work, we studied changes in proliferation, tangential migration, radial migration patterns, and the survival of these newly generated neurons in this neurodegeneration animal model. The animals were injected with bromodeoxyuridine 2 weeks or 2 months before killing in order to label neuroblast incorporation into the OB and to analyze the survival of these cells after differentiation, respectively. Both the organization and cellular composition of the RMS and the differentiation of the newly generated neurons in the OB were studied using specific markers of glial cells, neuroblasts, and mature neurons. No changes were observed in the cell proliferation rate nor in their tangential migration through the RMS, indicating that migrating neuroblasts are only weakly responsive to the alteration in their target region, the OB. However, the absence of MC does elicit differences in the final destination of the newly generated interneurons. Moreover, the loss of MC also produces changes in the survival of the newly generated interneurons, in accordance with the dramatic decrease in the number of synaptic targets available.

Distribution of Neurocalcin-Containing Neurons Reveals Sexual Dimorphism in the Mouse Olfactory Bulb

Olfactory sexual dimorphism has mainly been described in the vomeronasal system, in relation to reproductive behavior, while evidence of sexual dimorphism in the main olfactory bulb (OB) remains scarce. There are no data indicating sex-related differences in the neurochemistry of intrinsic olfactory elements. Neurocalcin (NC) is a calcium-binding protein that is expressed in specific neuronal populations of the central nervous system. Here we analyzed by immunohistochemistry the NC-containing neurons in the mouse main OB, comparing both their quantities and their locations between male and female animals. NC cell density was higher in males than in females in specific locations of the glomerular layer, the external plexiform layer, the mitral cell layer, and the internal plexiform layer. This divergence in the numbers of NC cells was especially patent in central rostrocaudal levels. The NC-containing neurons exhibiting sexual divergence were identified as both juxtaglomerular and short-axon cells. This is the first description of sexual dimorphism regarding neurons belonging to the mouse main OB. According to their distribution in the OB, neurocalcin-immunoreactive interneurons could reflect a sexually dimorphic regulation of specific odorants.

Heterogeneous targeting of centrifugal inputs to the glomerular layer of the main olfactory bulb

The centrifugal systems innervating the olfactory bulb are important elements in the functional regulation of the olfactory pathway. In this study, the selective innervation of specific glomeruli by serotonergic, noradrenergic and cholinergic centrifugal axons was analyzed. Thus, the morphology, distribution and density of positive axons were studied in the glomerular layer of the main olfactory bulb of the rat, using serotonin-, serotonin transporter- and dopamine-beta-hydroxylase-immunohistochemistry and acetylcholinesterase histochemistry in serial sections. Serotonin-, serotonin transporter-immunostaining and acetylcholinesterase-staining revealed a higher heterogeneity in the glomerular layer of the main olfactory bulb than previously reported. In this sense, four types of glomeruli could be identified according to their serotonergic innervation. The main distinctive feature of these four types of glomeruli was their serotonergic fibre density, although they also differed in their size, morphology and relative position throughout the rostro-caudal main olfactory bulb. In this sense, some specific regions of the glomerular layer were occupied by glomeruli with a particular morphology and a characteristic serotonergic innervation pattern that was consistent from animal to animal. Regarding the cholinergic system, we offer a new subclassification of glomeruli based on the distribution of cholinergic fibres in the glomerular structure. Finally, the serotonergic and cholinergic innervation patterns were compared in the glomerular layer. Sexual differences concerning the density of serotonergic fibres were observed in the atypical glomeruli (characterized by their strong cholinergic innervation). The present report provides new data on the heterogeneity of the centrifugal innervation of the glomerular layer that constitutes the morphological substrate supporting the existence of differential modulatory levels among the entire glomerular population.

Dopaminergic modulation of nNOS expression in the pituitary gland of male rat

Nitric oxide is an unconventional transmitter since it is not transported and released by exocytosis. In the pituitary gland, nitric oxide is locally synthesised by gonadotroph and folliculo-stellate cells. Dopamine, the principal central inhibitory signal in prolactin release, may exert its inhibitory effects by stimulation of nitric oxide production. However, the effects of dopaminergic modulation on nitric oxide-producing pituitary cells have not been analysed. Therefore, we examined the effects of intraventricular administration of the dopamine antagonist haloperidol (40 microg) on the pituitary expression of neuronal nitric oxide synthase (nNOS) in male adult rats. In untreated and control animals, nNOS-positive cells were very similar. Two types of nNOS-positive cells appeared in the pars distalis: round or polygonal cells and stellate cells. Although some isolated cells were found, the nNOS-positive cells commonly appeared grouped in clusters close to blood vessels. nNOS immunoreactivity appeared as a uniform staining throughout the cytoplasm, including cell prolongations. The number and size of nNOS-expressing cells in the pituitary gland decreased significantly after treatment with haloperidol (p<0.01). To evaluate the potential direct effect of dopamine on pituitary cells, pituitary monolayer cultures were treated with dopamine during a time-course of 12 h. Our in vitro studies revealed that dopamine increases the percentage of nNOS-positive cells and augments cellular area (p<0.05). These results demonstrate that: (1) treatment of rats in vivo with a dopamine antagonist significantly decreases expression of nNOS in the pituitary and (2) in vitro dopamine exerts a direct effect on pituitary cultures by increasing nNOS-positive cells. Thus, these findings suggest that dopamine may function as a physiological stimulator of nNOS expression in the rat pituitary gland.

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.

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.

Bilateral olfactory deprivation reveals a selective noradrenergic regulatory input to the olfactory bulb

Unilateral olfactory deprivation in the rat induces changes in the catecholaminergic system of the olfactory bulb. Nevertheless, evidence suggests that unilateral deprivation does not fully prevent stimulation of the deprived bulb. The present report analyses the response of the catecholaminergic system of the olfactory bulb in fully deprived rats obtained by bilateral naris occlusion. The complete deprivation produces more rapid and dramatic changes in both the intrinsic and extrinsic catecholaminergic systems of the olfactory bulb. Intrinsic responses involve a rapid decrease in dopamine-containing cells to about 25% of controls, correlated with a decreased Fos expression in juxtaglomerular cells of all olfactory glomeruli, with the only exception of those of the atypical glomeruli which maintain unaltered expression of both markers. In parallel with these events, there is a progressive increase in the density of extrinsic noradrenergic axons arising from neurons in the locus coeruleus, which shows, in parallel, a progressive increase in Fos expression. This model demonstrates plastic changes in the catecholaminergic system of the olfactory bulb forming a valid morphological substrate for lowering thresholds in the processing of olfactory information. In addition to this generalized response, there is another one, directed to a specific subset of olfactory glomeruli (atypical glomeruli) involved in the processing of odor pheromone-like cues related to behavioral responses, that could be responsible for keeping active this reduced and selected group of glomeruli carrying crucial olfactory information. These results indicate the existence of adaptive changes in the catecholaminergic system of the olfactory bulb as a response to the lack of afferent peripheral stimulation. These changes involve dopamine- and noradrenaline-immunoreactive elements, in a strategy presumably directed at maintaining to the highest possible level the ability to detect olfactory signals.

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.

Co-localization of cart peptide immunoreactivity and nitric oxide synthase activity in rat hypothalamus

Because of the reported presence of both CART peptide and NOS activity in the same hypothalamic nuclei, their colocalization was examined. Eighteen percent of the neurons in the supraoptic nuclei, and 16% of the neurons in the paraventricular nucleus contained both CART immunoreactivity and NOS activity. Many other neurons in these regions stained for only one marker although they were often close by. Thus, CART peptides and NO may interact in these regions.

Distribution of the calcium-binding proteins parvalbumin, calbindin D-28k and calretinin in the retina of two teleosts

Using monoclonal antibodies against parvalbumin (PV) and calbindin (CB), and a polyclonal antiserum against calretinin (CR), the expression patterns of these proteins in the retina of the tench and rainbow trout were studied at light microscopic level in in toto preparations and radial sections. Parvalbumin was present in subpopulations of small amacrine cells in both species, but these cells were more abundant and had a clear centre-periphery gradient distribution in the tench. Using the McAB 300 monoclonal antibody against CB, glial cells such as Müller cells, astrocytes in the nerve fibre layer, and sparse large cells close to the entrance of the optic nerve were observed in both species. Moreover, this antibody strongly labelled H1 horizontal cells and their thick axon terminals in the tench retina, whereas only a small population of amacrine cells was stained in the trout. Calretinin was expressed in different types of ganglion cells and numerous neurones located in the inner plexiform layer in both species, but was more abundant and more strongly stained in the trout retina, where some bipolar cells were easily distinguishable. A comparison to current results in other vertebrate species is offered.

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.

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.

NADPH-diaphorase/nitric oxide synthase-positive elements in the human olfactory bulb

The distribution and morphology of nitric oxide-synthesizing elements in the human olfactory bulb were studied using NADPH-diaphorase histochemistry and nitric oxide synthase immunohistochemistry. NADPH-diaphorase was detected in all olfactory fibers and groups of superficial short-axon cells, deep short-axon cells, stellate cells and abundant centrifugal fibers. Similar cell types were nitric oxide synthase immunoreactive but olfactory fibers were immunonegative. The distribution patterns of nitric oxide-synthesizing elements showed significant differences from what has been reported in the olfactory bulb of macrosmatic mammals including rodents and insectivores. These differences are likely to correlate with interspecies differences in the processing of olfactory information.

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.

Calretinin immunoreactivity in the anterior olfactory nucleus of the rat

Calretinin-immunoreactive structures in the anterior olfactory nucleus of the rat were studied using a polyclonal antibody, which does not cross-react with the highly homologous calcium-binding protein calbindin-D28k, and the avidin-biotin-peroxidase technique. Calretinin-immunopositive neurons were found in all regions of the anterior olfactory nucleus, with the highest number in the medial subdivision and dorsal transition area. The immunostained neurons, although morphologically heterogeneous, demonstrated typically small size. In addition to neuronal somata, calretinin-immunopositive fibres and terminals, some of them forming basket-like arrangements surrounding immunonegative neurons, were observed. Although calretinin and calbindin-D28k colocalize in several brain regions, and both proteins showed an extensive overlap in the anterior olfactory nucleus, immunostained semithin sections demonstrated that calretinin does not co-localize with calbindin-D28k in this nucleus.

McAB 300 antibody against calbindin D-28K is a glial marker in the teleost brain

The monoclonal antibody McAB 300 against calbindin D-28 k demonstrated an immunostaining pattern in the teleost brain completely different to those obtained in other classes of vertebrates, or after using in the teleost brain other monoclonal and polyclonal antibodies raised against the same protein. Although calbindin D-28k is considered a neuronal marker, McAB 300 specifically stained glial cells throughout the brains of teleosts, with the only exception of some retinal amacrine and horizontal cells.

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)

Tyrosine hydroxylase-like immunoreactivity in the brain of the teleost fish Tinca tinca

The distribution of tyrosine hydroxylase-like immunoreactivity has been studied in the central nervous system of the tench (Tinca tinca) using a monoclonal antibody and the avidin-biotin-immunoperoxidase technique. Immunoreactive elements were found in all brain subdivisions. Thus, catecholaminergic neurons and fibers were detected in most nuclei of the ventral telencephalon and in the pars centralis and lateralis of the dorsal telencephalon. The diencephalon was the brain subdivision where largest density of immunoreactive elements were found, mainly located in the periventricular region. The mesencephalon and metencephalon only demonstrated immunoreactive fibers, and no immunoreactive cell bodies were observed in these regions. The myelencephalon showed three groups of immunoreactive neurons located at isthmal level, in the central medullary area, and at the medullary-spinal cord transition area. The distribution of catecholaminergic elements in the tench brain revealed a general pattern shared by most teleosts. The number and distribution of catecholaminergic elements was similar to those described in other teleostean species in the caudal region of the brain. However, noticeable differences were found in areas related to the integration of different sensory information, specially in the telencephalon and diencephalon, suggesting a relationship among the functional level of each sensorial system and the complexity of the catecholaminergic innervation of their integration regions. Additionally, this study revealed the presence of an important number of cerebrospinal fluid-contacting cells in the organum paraventricularis expressing tyrosine hydroxylase that in most investigated teleostean species were tyrosine hydroxylase-immunonegative despite they contained catecholamines. This data argues for distinct evolutionary patterns in the hypothalamic catecholaminergic system among different teleostean species.

A BCR-ABL(p190) fusion gene made by homologous recombination causes B-cell acute lymphoblastic leukemias in chimeric mice with independence of the endogenous bcr product

BCR-ABL(p190) oncogene is the result of a reciprocal translocation between chromosomes 9 and 22 and is associated with B-cell acute lymphoblastic leukemia (B-ALL) in humans. Current models expressing the BCR-ABL(p190) chimeric gene fail to consistently reproduce the phenotype with which the fusion gene is associated in human pathology, mainly due to the difficulty of being expressed in the appropriate cell type in vivo. We have used here homologous recombination in ES cells to create an in-frame fusion of BCR-ABL(p190) that mimics the consequences of the human chromosomal translocation by fusion of BCR-ABL coding sequences into the bcr endogenous gene. The chimeric mice generated with the mutant embryonic stem cells systematically develop B-ALL. Using these chimeric mice, we further show that BCR-ABL oncogene does not require the endogenous bcr product in leukemogenesis. Our results show that BCR-ABL(p190) chimeric mice are a new model to study the biology of the BCR-ABL oncogene and indicate the efficacy of this strategy for studying the role of specific chromosome abnormalities in tumor development.

Transient expression of NADPH-diaphorase/nitric oxide synthase in the paratenial nucleus of the rat thalamus

The distribution pattern of nitric oxide synthesizing neurons was studied in the paratenial nucleus throughout the rat development using the NADPH-diaphorase (ND) histochemical method and nitric oxide synthase (NOS) immunocytochemistry. The onset of ND/NOS activity in the paratenial nucleus was detected in the postnatal life day 1. Until the postnatal stage 4, a quick increase in the number and staining intensity of the ND/NOS positive neurons was observed. From postnatal day 4 to postnatal day 6, these variations continued slowly, whereas an increase in the neuronal size was evident. In these stages, densely packed ND/NOS-labeled neurons were observed. From stages 6 to 10, the ND/NOS-positive elements demonstrated similar number, size, and staining intensity. These cells had medium size, variable morphology and showed reaction product in the cell bodies and, at most, their proximal dendrites. After postnatal day 10, a quick decrease in the staining intensity and in the number of ND/NOS-labeled elements was detected, although no changes were observed in their morphological characteristics. Postnatal day 15 was the last developmental stage studied in which ND/NOS-positive elements were observed. Finally, the paratenial nucleus did not present ND/NOS-positive elements in adult animals. This transient expression of the ND/NOS-activity suggests a role of nitric oxide in the reorganization of the paratenial nucleus during the first postnatal fortnight.

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.

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.

Nicotinamide-adenine-dinucleotide-phosphate diaphorase-positive neurons and fibers in the nucleus olfactorius anterior of the rat

The distribution patterns of NADPH-diaphorase activity in the nucleus olfactorius anterior (NOA) and anterior commissure (AC) of the rat were described using an histochemical technique. In the lateral, dorsal, ventral, medial and posterior subdivisions of the NOA we have demonstrated heavily stained elements (neurons and processes), and slightly labelled cell bodies. The neurons were mainly located in the inner zone of these subdivisions. However, in the external subdivision (NOAe) strongly stained fibers and weakly labelled cell bodies were present. The NOA transitions areas showed the same NADPH-diaphorase activity distribution patterns as those of the corresponding NOA subdivisions. In the AC we described scarce NADPH-diaphorase positive fibers parallelly oriented to the unstained commissural fibers, and scattered stained neurons.

Discrete reduction patterns of parvalbumin and calbindin D-28k immunoreactivity in the dorsal lateral geniculate nucleus and the striate cortex of adult macaque monkeys after monocular enucleation

We analyzed the immunohistochemical distribution of the two calcium-binding proteins, parvalbumin (PV) and calbindin D-28k (CB), in the primary visual cortex and lateral dorsal geniculate nucleus (dLGN) of monocularly enucleated macaque monkeys (Macaca fascicularis and Macaca nemestrina) in order to determine how the expression of PV and CB is affected by functional inactivity. The monkeys survived 1-17 weeks after monocular enucleation. The distribution pattern of each of the proteins was examined immunocytochemically using monoclonal antibodies and compared with that of the metabolic marker cytochrome oxidase (CO). We recorded manually the number of immunostained neurons and estimated the concentration of immunoreactive staining product using a computerized image-acquisition system. Our results indicate a decrease of approximately 30% in the labeling of PV-immunoreactive (ir) neuropil particularly in those layers of denervated ocular-dominance columns receiving the geniculocortical input. There was no change in the number of PV-ir neurons in any compartment irrespective of the enucleation interval. For CB-ir, we found a 20% decrease in the neuropil labeling in layer 2/3 of the denervated ocular-dominance columns. In addition, a subset of pyramidal CB-ir neurons in layers 2 and 4B, which are weakly stained in control animals, showed decreased labeling. In the dLGN of enucleated animals, PV-ir and CB-ir were decreased only in the neuropil of the denervated layers. From these results, we conclude that cortical interneurons and geniculate projection neurons still express PV and CB in their cell bodies after disruption of the direct functional input from one eye. The only distinct decrease of PV and CB expression is seen in axon terminals from retinal ganglion cells in the dLGN, and in the axons and terminals of both geniculocortical projection cells and cortical interneurons in the cerebral cortex.

Parvalbumin immunoreactive neurons and fibres in the teleost cerebellum

The distribution of parvalbumin- (PV) immunopositive cell bodies and fibres in the cerebellum of two species of freshwater teleosts (Salmo gairdneri and Barbus meridonalis) was studied using a monoclonal antibody and the avidin-biotin immunoperoxidase technique. A clear laminated pattern of PV immunoreactivity was observed. After PV-immunostaining, Purkinje cells were strongly labelled in their cell bodies, the initial segments of the axons and the dendritic trees. In the molecular layer, only the dendritic branches of the Purkinje cells were PV-positive. In the granule cell layer, extensive axonal plexuses and scattered cell bodies were observed. Most of the immunopositive perikarya were unequivocally identified as displaced Purkinje cells, whereas a reduced number of smaller neurons with unstained dendrites was also found. Eurydendroid cells, the efferent neurons of the teleost cerebellum, were negative; however, they were impinged upon by numerous PV-positive boutons, corresponding to terminals of Purkinje cell axons. Parallel fibres and climbing fibres, as well as stellate cells and granule cells were negative. Basket cells (or deep stellate cells) whose existence in the teleost cerebellum is discussed, were also not observed. The immunoreactivity distribution pattern for PV in the teleost cerebellum differs from previous observations on the localization of this protein in the cerebellum of amniotes.