A new quantitative film autoradiographic method of quantifying mRNA transcripts for in situ hybridization

Improving Performance of Breast Cancer Risk Prediction by Incorporating Optical Density Image Feature Analysis: An Assessment

RATIONALE AND OBJECTIVES

The purpose of this study is to improve accuracy of near-term breast cancer risk prediction by applying a new mammographic image conversion method combined with a two-stage artificial neural network (ANN)-based classification scheme.

MATERIALS AND METHODS

The dataset included 168 negative mammography screening cases. In developing and testing our new risk model, we first converted the original grayscale value (GV)-based mammographic images into optical density (OD)-based images. For each case, our computer-aided scheme then computed two types of image features representing bilateral asymmetry and the maximum of the image features computed from GV and OD images, respectively. A two-stage classification scheme consisting of three ANNs was developed. The first stage included two ANNs trained using features computed separately from GV and OD images of 138 cases. The second stage included another ANN to fuse the prediction scores produced by two ANNs in the first stage. The risk prediction performance was tested using the rest 30 cases.

RESULTS

With the two-stage classification scheme, the computed area under the receiver operating characteristic curve (AUC) was  0.816 ± 0.071, which was significantly higher than the AUC values of 0.669 ± 0.099 and 0.646 ± 0.099 achieved using two ANNs trained using GV features and OD features, respectively (P < .05).

CONCLUSION

This study demonstrated that applying an OD image conversion method can acquire new complimentary information to those acquired from the original images. As a result, fusion image features computed from these two types of images yielded significantly higher performance in near-term breast cancer risk prediction.

Tissue quantification of radioiodine thyroid uptake in humans by an isotopic imaging technique on slides

BACKGROUND

Thyroid metabolism involves iodine, which allows us to use radioactive iodine for diagnostic and therapy purposes. The efficiency of radioiodine therapy depends on several parameters; the ability of thyroid tissue to uptake radioactive iodine is one of them.

OBJECTIVE

The objective of this work is to quantify the radioactive iodine uptake on thyroid tissue.

METHODS

In this work, we developed a method to quantify the in vivo uptake of iodine-131 on sections of thyroid glands removed by thyroidectomies. We performed an analysis of histological sections of the thyroid tissue by beta imaging. We had the opportunity to quantify the fixed radioactivity and to analyze its distribution in the thyroid gland, thanks to the good spatial resolution available with the type of detector used.

RESULTS

The results gave a high image resolution showing the heterogeneity of iodine-131 fixation by the thyroid tissue. We were able to quantify the tissue radioactivity in mega Becquerel (MBq) per volume unit.

CONCLUSION

This work has shown that the direct quantification of the thyroid tissue uptake is possible using the beta imaging system.

A High-Throughput Radiometric Kinase Assay

Aberrant kinase signaling has been implicated in a number of diseases. While kinases have become attractive drug targets, only a small fraction of human protein kinases have validated inhibitors. Screening of libraries of compounds against a kinase or kinases of interest is routinely performed during kinase inhibitor development to identify promising scaffolds for a particular target and to identify kinase targets for compounds of interest. Screening of more focused compound libraries may also be conducted in the later stages of inhibitor development to improve potency and optimize selectivity. The dot blot kinase assay is a robust, high-throughput kinase assay that can be used to screen a number of small-molecule compounds against one kinase of interest or several kinases. Here, a protocol for a dot blot kinase assay used for measuring insulin receptor kinase activity is presented. This protocol can be readily adapted for use with other protein kinases.

Reduced serotonin receptor subtypes in a limbic and a neocortical region in autism

Autism is a behaviorally defined, neurological disorder with symptom onset before the age of 3. Abnormalities in social-emotional behaviors are a core deficit in autism, and are characterized by impaired reciprocal-social interaction, lack of facial expressions, and the inability to recognize familiar faces. The posterior cingulate cortex (PCC) and fusiform gyrus (FG) are two regions within an extensive limbic-cortical network that contribute to social-emotional behaviors. Evidence indicates that changes in brains of individuals with autism begin prenatally. Serotonin (5-HT) is one of the earliest expressed neurotransmitters, and plays an important role in synaptogenesis, neurite outgrowth, and neuronal migration. Abnormalities in 5-HT systems have been implicated in several psychiatric disorders, including autism, as evidenced by immunology, imaging, genetics, pharmacotherapy, and neuropathology. Although information is known regarding peripheral 5-HT in autism, there is emerging evidence that 5-HT systems in the central nervous system, including various 5-HT receptor subtypes and transporters, are affected in autism. The present study demonstrated significant reductions in 5-HT1A receptor-binding density in superficial and deep layers of the PCC and FG, and in the density of 5-HT(2A) receptors in superficial layers of the PCC and FG. A significant reduction in the density of serotonin transporters (5-HTT) was also found in the deep layers of the FG, but normal levels were demonstrated in both layers of the PCC and superficial layers of the FG. This study provides potential substrates for decreased 5-HT modulation/innervation in the autism brain, and implicate two 5-HT receptor subtypes as potential neuromarkers for novel or existing pharmacotherapies.

Training-induced changes in the expression of GABAA-associated genes in the amygdala after the acquisition and extinction of Pavlovian fear

Previous work suggests the gamma-aminobutyric acid (GABA)ergic system may be dynamically regulated during emotional learning. In the current study we examined training-induced changes in the expression of GABA(A)-related genes and the binding of GABA receptor radioligands in the amygdala after the acquisition and extinction of Pavlovian fear. Using in situ hybridization, we examined the expression pattern changes of mRNAs for GABAergic markers in the lateral, basolateral and central subdivisions of the amygdala in C57Bl/6J mice. These markers included GABA-synthesizing enzymes (GAD67 and GAD65), major GABA(A) receptor subunits (alpha1, alpha2, alpha3, alpha5, beta2 and gamma2) and the expression of mRNAs that are involved in a variety of GABA-related intracellular processes, including GABA transporter-1 (GAT1), GABA(A) receptor-associated protein and the GABA(A) clustering protein, gephyrin. With fear conditioning, we found decreased mRNA levels of alpha1, alpha5 and GAD67, as well as deceased benzodiazepine binding in the amygdala. Fear extinction induced an increase in mRNA levels of alpha2, beta2, GAD67 and gephyrin, as well as a decrease in GAT1. Together, these findings indicate that the acquisition of fear induced a downregulation of mRNA markers related to a decrease in amygdala GABAergic function, whereas the acquisition of fear extinction produced an upregulation of GABAergic markers related to enhanced GABAergic transmission.

Quantitative methods for genome-scale analysis of in situ hybridization and correlation with microarray data

This study introduces a novel method for standardized relative quantification of colorimetric in situ hybridization signal that enables a large-scale cross-platform expression level comparison of in situ hybridization with two publicly available microarray brain data sources.

With the emergence of genome-wide colorimetric in situ hybridization (ISH) data sets such as the Allen Brain Atlas, it is important to understand the relationship between this gene expression modality and those derived from more quantitative based technologies. This study introduces a novel method for standardized relative quantification of colorimetric ISH signal that enables a large-scale cross-platform expression level comparison of ISH with two publicly available microarray brain data sources.

Trans-synaptic regulation of calmodulin gene expression after experimentally induced orofacial inflammation and subsequent corticosteroid treatment in the principal sensory and motor trigeminal nuclei of the rat

The cutaneous and mucosal surfaces in the infraorbital region around the whisker pad are innervated by the maxillary division of the afferent fibers of the trigeminal nerve, while certain ganglion cells project to the principal sensory trigeminal nucleus (Pr5). In turn, some of the neurons in the Pr5 project to the motor trigeminal nucleus (Mo5), whose neurons do not innervate the infraorbital skin. We analyzed the calmodulin (CaM) gene expression in these nuclei after dithranol-induced inflammation and subsequent treatment with corticosteroid in the infraorbital skin. CaM gene-specific mRNA populations were detected through quantitative image analysis of the distribution of CaM gene-specific riboprobes in brain stem cryostat sections of control rats and rats chronically treated with dithranol, corticosteroid or both. These nuclei displayed a differentially altered CaM gene expression in response to the treatments. While the CaM I and II mRNA contents were increased, the CaM III transcripts remained unaltered after chronic dithranol treatment in the Mo5. In the Pr5, however, the CaM mRNA contents were either unchanged (CaM I and III) or increased (CaM II). Subsequent corticosteroid treatment reversed the stimulatory effects of dithranol on the expression of all the CaM genes in the Mo5, but was without significant effects on the CaM I and II genes, or even increased the CaM III mRNA contents in the Pr5. Corticosteroid treatment alone was either ineffective or decreased the levels of CaM mRNAs in these nuclei. These data suggest that peripheral noxae of dermal origin may result in a trans-synaptically acting differential regulation of the multiple CaM genes in the brain.

Differential calmodulin gene expression in the nuclei of the rat midbrain-brain stem region

We investigated the expression patterns of the three calmodulin (CaM) genes, using in situ hybridization techniques, to detect gene-specific [(35)S]- and digoxigenin-labeled cRNA probes complementary to the multiple CaM mRNAs in the nuclei of the midbrain-brain stem region of the adult rat. The distinct CaM genes were widely expressed throughout this region with moderate intensities. In spite of the similar general pattern, significant differences in the distributions of the multiple CaM mRNA species were found in certain areas. In general, the CaM III mRNAs were most abundant, followed by the CaM I and CaM II mRNA populations. Most of the transcripts were found in the neuronal somata comprising the medullar nuclei, while much less label was detected in the neuropil. The CaM III mRNAs were more than 2.5 times more abundant than the CaM II mRNAs in the nucleus of the trapezoid body, and more than two times more abundant in the motor trigeminal nucleus, the principal sensory trigeminal nucleus and the olivary nucleus. The CaM III mRNAs were less dominant in the medial lemniscus, the inferior colliculus and the pontine reticular nucleus than those of the other CaM gene-specific transcripts. The CaM mRNA levels were low to moderate, without significant differences, in the mesencephalic trigeminal nucleus. The differential control of the expression of the CaM genes may contribute to the regulation of the multiple neuronal functions linked to this complex brain region and regulated by different CaM-dependent mechanisms via its target proteins.

Multiple calmodulin mRNAs are selectively transported to functionally different neuronal and glial compartments in the rat hippocampus. An electron microscopic in situ hybridization study

The ultrastructural distribution of the calmodulin (CaM) mRNAs transcribed from the three CaM genes was studied in the CA1 region of the adult rat hippocampus by means of electron microscopic in situ hybridization. Digoxigenin-labeled CaM gene-specific riboprobes were detected with nanogold-anti-digoxigenin antibody conjugate. The CaM mRNAs were differentially distributed in both the neuronal and glial cell compartments. The greatest difference in neuronal distribution of the CaM mRNAs was found in the dendrites, where the mRNAs transcribed from the CaM I and III genes were much more abundant than the CaM II mRNA. The neuronal perikarya were heavy labeled for all the CaM mRNAs. Interestingly, the myelinated axons and axon terminals also contained small amounts of nanogold particles for all the CaM mRNAs, which diminished with increasing distance from the soma. Most of the synaptic profiles, however, contained labeling only in the postsynaptic region. The CaM mRNAs were differentially distributed in the glial cells. While the glial cell somata were only lightly labeled, surprisingly concentrated labeling was present in the perisynaptic and perivascular astrocytic processes. In general, the CaM II mRNA was the least represented in the glial processes. Only a very low CaM gene expression was observed in the endothelial and resting microglial cells. These results provide ultrastructural evidence for differential targeting of the multiple CaM mRNA transcripts to the intracellular compartments and suggest their microdomain-specific regulation.

Repeated 4-aminopyridine seizures reduce parvalbumin content in the medial mammillary nucleus of the rat brain

Parvalbumin (Pv) containing fast spiking neurons play a crucial role in synchronizing the activity of excitatory neuronal circuits in the brain. Alterations of parvalbumin content in these neurons can affect their spike characteristics and, ultimately, may increase the susceptibility of neuronal circuits to epileptic seizures. In the present study, we examined whether repeated 4-aminopyridine (4-AP)-induced seizures modify the regional parvalbumin contents in the rat brain. 4-Aminopyridine was injected intraperitoneally in adult rats, controls received the solvent. Animals were sacrificed at 3 h after a single acute treatment, or following repeated, daily treatments of 12 days. In situ hybridization (ISH) indicated significantly decreased parvalbumin mRNA level in the medial mammillary nucleus (MM) at 12 days. Western blotting revealed 20.1% significant decrease of parvalbumin content in the medial mammillary area, while parvalbumin immunohistochemistry indicated no change of the number of immunoreactive cells in the medial mammillary nucleus. The results reveal the downregulation of the transcription of the parvalbumin gene and the decrease of parvalbumin synthesis in medial mammillary nucleus neurons in response to experimental seizures.

Regional and progressive changes in brain expression of complexin II in a mouse transgenic for the Huntington's disease mutation

Changes in mRNA expression of soluble NSF-attachment protein receptors (SNAREs) and SNARE-associated proteins have been shown to occur in a number of disorders such as schizophrenia, Alzheimer's disease and Parkinson's disease. We have shown previously that there is a decrease in protein levels of the SNARE-associated protein, complexin II (CPLXII) in Huntington's disease brain and in the R6/2 mouse model of Huntington's disease. In the current study, we used quantitative in situ hybridisation to examine mRNA expression of SNAREs (25 kDa synaptosome-associated protein (SNAP-25), syntaxin-1A and synaptobrevin-2) and SNARE-associated proteins (alpha-SNAP, CPLXI and CPLXII) in brain of R6/2 mice and their wild type littermates between 3 and 15 weeks of age. We found an early and progressive decrease of CPLXII expression in R6/2 mice brains. In contrast, no changes in SNARE expression were seen in R6/2 brains compared with wild type brain. Further, while decreased expression of alpha-SNAP and CPLXI was seen, this was not until 15 weeks of age and even then the changes were small. We suggest that downregulation of expression of mRNA encoding SNARE-associated proteins, first CPLXII and later CPLXI and alpha-SNAP, contributes to the progressive neuropathology of the R6/2 mouse model of Huntington's disease.

Calmodulin gene expression in the neural retina of the adult rat

Calmodulin (CaM) mRNAs are expressed with low abundancy in the adult rat neural retina. However, when digoxigenin (DIG)-labeled cRNA probes specific for each CaM mRNA population were hybridized at slightly alkaline pH (pH 8.0), the widespread distribution of CaM mRNA-expressing cells was revealed, with similar abundance for all three CaM genes. The CaM genes displayed a uniquely similar, layer-specific expression throughout the retina, and no significant differences were found in the distribution patterns of the CaM mRNA populations or the labeled cell types. The strongest signal for all CaM mRNAs was demonstrated in the ganglion cell layer and the inner nuclear layer, where the highest signal intensity was found within the inner sublamina. Similarly intermediate signal intensities for all CaM genes were detected in the inner and outer plexiform layers, within the vicinity of the outer limiting membrane and in the retinal pigment epithelium. A very low specific signal was characteristic in the outer nuclear layer and the photoreceptor inner segment layer, while no specific hybridization signal was observed in the photoreceptor outer segment layer. In summary, all CaM genes exhibited a similar and a characteristically layer-specific expression pattern in the adult rat retina.

Ontogeny of calmodulin gene expression in rat brain

Calmodulin (CaM), a multifunctional intracellular calcium receptor, is a key element in signaling mechanisms. It is encoded in vertebrates by multiple apparently redundant genes (CaM I, II, III). To investigate whether differential expression takes place in the developing rat brain, a quantitative in situ hybridization analysis was carried out involving 15 brain areas at six ages between embryonic day 19 and postnatal day 20 (PD20) with gene-specific [(35)S]cRNA probes. A widespread, developmental stage-specific and differential expression of the three CaM genes was observed. The characteristic changes in the CaM mRNA levels in the examined time frame allowed the brain regions to be classified into three categories. For the majority of the areas (e.g. the piriform cortex for CaM III), the signal intensities peaked at around PD10 and the expression profile was symmetric (type 1). Other regions (e.g. the cerebral cortex, layer 1 for CaM II) displayed their highest signal intensities at the earliest age measured, followed by a gradual decrease (type 2). The signal intensities in the regions in the third group (e.g. the hypothalamus for CaM III) fluctuated from age to age (type 3). Marked CaM mRNA levels were measured for each transcript corresponding to the three CaM genes in the molecular layers of the cerebral and cerebellar cortici and hippocampus, suggesting their dendritic translocation. The highest signal intensity was measured for CaM II mRNA, followed by those for CaM III and CaM I mRNAs on PD1. However, the CaM II and CaM III mRNAs subsequently decreased steeply, while the CaM I mRNAs were readily detected even on PD20. Our results suggest that during development (1) the transcription of the CaM genes is under differential, area-specific control, and (2) a large population of CaM mRNAs is targeted to the dendritic compartment in a gene-specific manner.

Increased concentrations of radioisotopically-labeled complementary ribonucleic acid probe, dextran sulfate, and dithiothreitol in the hybridization buffer can improve results of in situ hybridization histochemistry

The goal of the present studies was to optimize mRNA detection with radioisotopic in situ hybridization histochemistry (ISHH). Test experiments performed on sections of rat brain tissue used computer-assisted image analysis to compare autoradiographic signals resulting when varying concentrations of (35)S-labeled cRNA probes, dextran sulfate (DS), and dithiothreitol (DTT) were used for ISHH. We found that greatly enhanced corrected signal density (total density of signal area minus background density) was obtained using concentrations of probe and/or DS that were several-fold higher than those widely recommended in published ISHH procedures (probe concentration >4 x 10(4) cpm/microl; DS concentration >10%). Extended hybridization reaction (>16 hr) also significantly augmented the corrected signal density. Finally, nonspecific probe binding was greatly reduced and corrected signal density enhanced by including 750-1000 mM, rather than the widely used 10-200 mM DTT, in the hybridization buffer. These observations indicate that the low efficiency of hybridization and the formation of high background may largely compromise the sensitivity of routine ISHH procedures. We suggest that the new method using increased concentrations of (35)S-labeled cRNA probe, DS, and DTT will be especially important for the cellular localization of rare mRNA species.

Differential expression of multiple calmodulin genes in cells of the white matter of the rat spinal cord

Calmodulin (CaM) displays complex cytoplasmic and synaptic functions in the nervous system. However, the very little information that is available on the gene expression of the multiple CaM genes in different glial cell types are from brain tissues of rodents, and no data have been published on their CaM gene expression in the spinal cord. Therefore, we have modified and tested a color in situ hybridization method sensitive enough to detect mRNA populations in cells with low CaM mRNA abundances in the white matter of the rat lumbar spinal cord. Morphologically, two distinct cell types expressing CaM mRNAs were detected. Differential CaM gene expression was demonstrated in medium-sized astrocyte-like cells that reside predominantly in the dorsal column of the spinal cord, where CaM I mRNA was most abundant, followed by the CaM III and CaM II mRNA populations. The oligodendrocytes displayed a less differential CaM gene expression in both the dorsal and the lateral columns, but the CaM I gene had a slightly higher expression level than those of the other CaM genes. The results indicate that the CaM gene expression profile of the spinal cord is richer and more complex than previously thought on the basis of conventional radioactive in situ hybridization techniques. Thus, when a method that is sufficiently sensitive was used, more cell types could be demonstrated to express CaM mRNAs; hence, in spite of their lower CaM expression, glial cells could also be visualized.

Differential calmodulin gene expression in the rodent brain

Apparently redundant members of the calmodulin (CaM) gene family encode for the same amino acid sequence. CaM, a ubiquitous cytoplasmic calcium ion receptor, regulates the function of a variety of target molecules even in a single cell. Maintenance of the fidelity of the active CaM-target interactions in different compartments of the cell requires a rather complex control of the total cellular CaM pool comprising multiple levels of regulatory circuits. Among these mechanisms, it has long been proposed that a multigene family maximizes the regulatory potentials at the level of the gene expression. CaM genes are expressed at a particularly profound level in the mammalian central nervous system (CNS), especially in the highly polarized neurons. Thus, in the search for clear evidence of the suggested differential expression of the CaM genes, much of the research has been focused on the elements of the CNS. This review aims to give a comprehensive survey on the current understanding of this field at the level of the regulation of CaM mRNA transcription and distribution in the rodent brain. The results indicate that the CaM genes are indeed expressed in a gene-specific manner in the developing and adult brain under physiological conditions. To establish local CaM pools in distant intracellular compartments (dendrites and glial processes), local protein synthesis from differentially targeted mRNAs is also employed. Moreover, the CaM genes are controlled in a unique, gene-specific fashion when responding to certain external stimuli. Additionally, putative regulatory elements have been identified on the CaM genes and mRNAs.

Methods for quantification of in situ hybridization signals obtained by film autoradiography and phosphorimaging applied for estimation of regional levels of calmodulin mRNA classes in the rat brain

Comparative analysis of the regional abundances of the various mRNAs in neural tissues requires the quantitation of target nucleic acid sequences while their tissue distribution is preserved. A quantitative in situ hybridization protocol is presented for the assessment of regional levels of calmodulin (CaM) I, II and III mRNAs in the rat brain. Coronal brain cryostat sections were hybridized with multiple CaM [35S]cRNA probes and co-exposed to an autoradiographic film or storage phosphor screen, together with a membrane-based radioactive standard scale. The membrane scale was calibrated against a brain paste standard scale. Regression analyses of the sensitometric graphs of standard scales corresponding to the autoradiographic film and to the storage phosphor screen were performed by means of exponential (ROD=p(1)(1-exp[-p(2)x])) and linear (LI=ax) functions, respectively (ROD is relative optical density, LI is labeling intensity, and x is radioactivity). The ROD/LI values for the hybridized brain regions were converted into cRNA probe copy numbers (estimations of mRNA copy numbers) through use of the above standard scales. This method was applied to compare the regional abundances of multiple CaM mRNAs in the brains of control, dehydrated, chronic ethanol-treated and ethanol withdrawal-treated animals.

Multiple calmodulin genes exhibit systematically differential responses to chronic ethanol treatment and withdrawal in several regions of the rat brain

Ethanol induces profound alterations in the neuronal signaling systems, including the calcium (Ca(2+)) signaling. Prolonged exposure to ethanol evokes adaptive changes in the affected systems as they strive to restore the normal neuronal function. We investigated the involvement of calmodulin (CaM) genes, coding for the major mediator protein of intracellular Ca(2+) signals, in these adaptive processes at the mRNA level. The changes induced in the regional abundances of the CaM I, II, and III mRNA classes by chronic ethanol treatment and withdrawal were examined by means of quantitative in situ hybridization, employing gene-specific [35S]cRNA probes on rat brain cryostat sections. Regional analysis of the resulting changes in mRNA levels highlighted brain areas that belong in neuronal systems known to be especially sensitive to the action of ethanol. The results revealed systematically differential regulation for the three mRNA classes: the CaM I and CaM III mRNA levels displayed increases, and CaM II levels decreases in the affected brain regions, in both chronic ethanol- and withdrawal-treated animals. As regards the numbers of brain regions undergoing significant alterations in mRNA content, the CaM I mRNA levels exhibited changes in most brain areas, the CaM II levels did so in a lower number of brain regions, and the CaM III levels changed in only a few brain areas. These results suggest a differential regulation for the CaM genes in the rat brain and may help towards elucidation of the functional significance of the multiple CaM genes in the mammalian genome.

Calculation of maximal hybridization capacity (Hmax) for quantitative in situ hybridization: a case study for multiple calmodulin mRNAs

In estimations of mRNA copy numbers, quantitative in situ hybridization (ISH) is expected to be performed at saturating probe concentration. In practice, however, this condition can rarely be fulfilled when medium to high amounts of transcripts exist and/or in large-scale experiments. To resolve this problem, we developed and tested a double-step procedure involving the use of calmodulin (CaM) I, II, and III [(35)S]-cRNA probes on adult rat brain sections; the hybridization signals were detected with a phosphorimager. By means of hybridization at increasing probe concentrations for a time sufficient for saturation, saturation curves were created for and maximal hybridization capacity (Hmax) values were assigned to selected brain areas. The Kd values of these various brain areas did not differ significantly, which allowed the creation and use of one calibration graph of Hmax vs hybridized [(35)S]-cRNA values for all brain areas for a given probe concentration. Large-scale ISH experiments involving a subsaturating probe concentration were performed to estimate Hmax values for multiple CaM mRNAs. A calibration graph corresponding to this probe concentration was created and Hmax values (expressed in ISH copy no/mm(2) units) were calculated for several brain regions via the calibration. The value of the method was demonstrated by simultaneous quantification of the total accessible multiple CaM mRNA contents of several brain areas in a precise and economical way.

Water deprivation upregulates the three calmodulin genes in exclusively the supraoptic nucleus of the rat brain

Calmodulin (CaM), the ubiquitous intracellular calcium-binding protein, is coded by three bona fide CaM genes (CaM I, CaM II and CaM III) in mammals. They code for the same protein and are transcribed at particularly high levels in the brain, where CaM plays an essential role in basic neuronal functions. In this study, the expression of the three CaM genes in response to osmotic stimuli by water deprivation was investigated in the rat brain, with particular interest as concerns the hypothalamic magnocellular nuclei. CaM mRNA levels were determined by quantitative in situ hybridization autoradiography with gene-specific [35S]cRNA probes. In response to osmotic challenge, it was found that upregulation of the three CaM genes participates in the activation of the hypothalamo-hypophyseal system in the supraoptic nucleus (SON) (126% to 169%), but not in the magnocellular part of the paraventricular hypothalamic nucleus (PVN) (-10%). CaM mRNA levels decreased by 10%-15% in the suprachiasmatic nucleus (SCh) and many other extrahypothalamic brain areas. The opposite responses of the CaM gene expression in the SON and the magnocellular part of the PVN suggest a functional difference between them. Moreover, the significantly different magnitudes of the changes in the CaM mRNA levels in the SON nucleus (138%, 126% and 169% for CaM I, CaM II and CaM III, respectively) exemplify the precise differential control of the CaM gene expression in the brain.

Differential distribution and intracellular targeting of mRNAs corresponding to the three calmodulin genes in rat brain. A quantitative in situ hybridization study

To investigate the pattern of expression of the three calmodulin (CaM) genes by in situ hybridization, gene-specific [35S]-cRNA probes complementary to the multiple CaM mRNAs were hybridized in rat brain sections and subsequently detected by quantitative film or high-resolution nuclear emulsion autoradiography. A widespread and differential area-specific distribution of the CaM mRNAs was detected. The expression patterns corresponding to the three CaM genes differed most considerably in the olfactory bulb, the cerebral and cerebellar cortices, the diagonal band, the suprachiasmatic and medial habenular nuclei, and the hippocampus. Moreover, the significantly higher CaM I and CaM III mRNA copy numbers than that of CaM II in the molecular layers of certain brain areas revealed a differential dendritic targeting of these mRNAs. The results indicate a differential pattern of distribution of the multiple CaM mRNAs at two levels of cellular organization in the brain: (a) region-specific expression and (b) specific intracellular targeting. A precise and gene-specific regulation of synthesis and distribution of CaM mRNAs therefore exists under physiological conditions in the rat brain.