Postnatal Development Of Rat Brain Research Articles

Expression of Dystrophin Dp71 Splice Variants Is Temporally Regulated During Rodent Brain Development.

Dystrophin Dp71 is the major product of the Duchenne muscular dystrophy (DMD) gene in the brain, and its loss in DMD patients and mouse models leads to cognitive impairments. Dp71 is expressed as a range of proteins generated by alternative splicing of exons 71 to 74 and 78, classified in the main Dp71d and Dp71f groups that contain specific C-terminal ends. However, it is unknown whether each isoform has a specific role in distinct cell types, brain regions, and/or stages of brain development. In the present study, we characterized the expression of Dp71 isoforms during fetal (E10.5, E15.5) and postnatal (P1, P7, P14, P21 and P60) mouse and rat brain development. We finely quantified the expression of several Dp71 transcripts by RT-PCR and cloning assays in samples from whole-brain and distinct brain structures. The following Dp71 transcripts were detected: Dp71d, Dp71d∆71, Dp71d∆74, Dp71d∆71,74, Dp71d∆71-74, Dp71f, Dp71f∆71, Dp71f∆74, Dp71f∆71,74, and Dp71fΔ71-74. We found that the Dp71f isoform is the main transcript expressed at E10.5 (> 80%), while its expression is then progressively reduced and replaced by the expression of isoforms of the Dp71d group from E15.5 to postnatal and adult ages. This major finding was confirmed by third-generation nanopore sequencing. In addition, we found that the level of expression of specific Dp71 isoforms varies as a function of postnatal stages and brain structure. Our results suggest that Dp71 isoforms have different and complementary roles during embryonic and postnatal brain development, likely taking part in a variety of maturation processes in distinct cell types.

Developmental Changes of Glutamate and GABA Receptor Densities in Wistar Rats.

Neurotransmitters and their receptors are key molecules of signal transduction and subject to various changes during pre- and postnatal development. Previous studies addressed ontogeny at the level of neurotransmitters and expression of neurotransmitter receptor subunits. However, developmental changes in receptor densities to this day are not well understood. Here, we analyzed developmental changes in excitatory glutamate and inhibitory γ-aminobutyric acid (GABA) receptors in adjacent sections of the rat brain by means of quantitative in vitro receptor autoradiography. Receptor densities of the ionotropic glutamatergic receptors α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainate and N-methyl-D-aspartate (NMDA) as well as of the ionotropic GABAA and metabotropic GABAB receptors were investigated using specific high-affinity ligands. For each receptor binding site, significant density differences were demonstrated in the investigated regions of interest [olfactory bulb, striatum, hippocampus, and cerebellum] and developmental stages [postnatal day (P) 0, 10, 20, 30 and 90]. In particular, we showed that the glutamatergic and GABAergic receptor densities were already present between P0 and P10 in all regions of interest, which may indicate the early relevance of these receptors for brain development. A transient increase of glutamatergic receptor densities in the hippocampus was found, indicating their possible involvement in synaptic plasticity. We demonstrated a decline of NMDA receptor densities in the striatum and hippocampus from P30 to P90, which could be due to synapse elimination, a process that redefines neuronal networks in postnatal brains. Furthermore, the highest increase in GABAA receptor densities from P10 to P20 coincides with the developmental shift from excitatory to inhibitory GABA transmission. Moreover, the increase from P10 to P20 in GABAA receptor densities in the cerebellum corresponds to a point in time when functional GABAergic synapses are formed. Taken together, the present data reveal differential changes in glutamate and GABA receptor densities during postnatal rat brain development, which may contribute to their specific functions during ontogenesis, thus providing a deeper understanding of brain ontogenesis and receptor function.

A Multidisciplinary Approach Reveals an Age-Dependent Expression of a Novel Bioactive Peptide, Already Involved in Neurodegeneration, in the Postnatal Rat Forebrain.

The basal forebrain has received much attention due to its involvement in multiple cognitive functions, but little is known about the basic neuronal mechanisms underlying its development, nor those mediating its primary role in Alzheimer’s disease. We have previously suggested that a novel 14-mer peptide, ‘T14’, could play a pivotal role in Alzheimer’s disease, via reactivation of a developmental signaling pathway. In this study, we have characterized T14 in the context of post-natal rat brain development, using a combination of different techniques. Ex-vivo rat brain slices containing the basal forebrain, at different stages of development, were used to investigate large-scale neuronal network activity in real time with voltage-sensitive dye imaging. Subsequent Western blot analysis revealed the expression profile of endogenous T14, its target alpha7 nicotinic receptor and the familiar markers of Alzheimer’s: amyloid beta and phosphorylated Tau. Results indicated maximal neuronal activity at the earliest ages during development, reflected in a concomitant profile of T14 peptide levels and related proteins. In conclusion, these findings show that the peptide, already implicated in neurodegenerative events, has an age-dependent expression, suggesting a possible contribution to the physiological mechanisms underlying brain maturation.

Spatiotemporal expression patterns of chondroitin sulfate proteoglycan mRNAs in the developing rat brain.

Chondroitin sulfate proteoglycans (CSPGs) are pluripotent components of the extracellular matrix in the brain. Although previous studies have examined the developmental change in certain CSPGs in the whole brain, no known systematic studies have been carried out on the temporal or spatial expression of CSPGs. Here, we used quantitative real-time PCR to examine the CSPG mRNAs expression in the postnatal developing rat brain starting from postnatal day 5-42, mainly focusing on the parietal cortex, hippocampus, and corpus callosum. Results were further verified by immunohistochemistry. Our results showed that aggrecan, brevican, phosphacan, and NG2 generally showed upregulation across developmental stages in all three regions. Neurocan showed a rapid increase until postnatal day 10 in all three regions. Versican, however, showed a sharp decrease until postnatal day 10. Cross-region analysis showed higher expression of most CSPG members in the corpus callosum during later stages of development. Further immunohistochemistry staining confirmed our results by showing prominent CSPGs protein expression in the corpus callosum. In summary, our study reported specific temporal-expression and spatial-expression patterns of the CSPGs species. These results are consistent with the known roles of these members in neurodevelopment. The current study provided clues for the development of CSPGs as potential treatment targets in neurodevelopmental disorders.

Atlas of the Postnatal Rat Brain in Stereotaxic Coordinates.

The series of atlases of the developing rat brain in stereotaxic coordinates that we propose here1,2 has been conceived as a tool for the exploration of the rat brain in vivo during the postnatal period, offering a choice of bregma and lambda as the reference points. We suggest to use this atlas, which provides stereotaxic coordinates, in combination with other histological atlases, where brain structures and boundaries between them were assessed using histochemistry or quantative magnetic resonance techniques, but where stereotaxic coordinates are not available (Ramachandra and Subramanian, 2011; Calabrese et al., 2013; Ashwell and Paxinos, 2015) or provided (at P10, P21, and P39) but not within the bregma-lambda metrics (Sherwood and Timiras, 1970). The neonatal rat is a powerful model for the study of the early stages of central nervous system development. Comparative developmental studies suggest that the first two postnatal weeks in the rat roughly correspond to the second half of gestation and the early postnatal period in humans, with the electrical brain activity patterns expressed during this period and their developmental trajectories matching the patterns observed in premature human neonates (Clancy et al., 2001, 2007; Khazipov and Luhmann, 2006; Colonnese et al., 2010; Workman et al., 2013) (see also http://www.translatingtime.net/). Recent advances in the understanding of the developing brain functions largely came from the use of techniques to record brain activity from neonatal and adolescent rats in vivo, notably in head restrained animals (Leinekugel et al., 2002; Khazipov et al., 2004; Minlebaev et al., 2011; Tiriac et al., 2012; Yang et al., 2013). However, the rat brain grows rapidly and non-proportionally during the postnatal period and brain structures change their position in relation to the conventional skull marks such as bregma and lambda, making difficult to perform targeted recordings, stimulations, lesions, or local drug injections in precise anatomical locations. Hence the importance of a developmental atlas of the rat brain in stereotaxic coordinates. Several examples of histology atlases series of the developing rat brain have been published (Table ​(Table1).1). The Atlas by Sherwood and Timiras “A Stereotaxic Atlas of the Developing Rat Brain” atlas includes three postnatal time points: postnatal days P10, P21, and P39 (Sherwood and Timiras, 1970). Ashwell and Paxinos' “Atlas of the Developing Rat Nervous System” provides photographs and accompanying diagrams of coronal and sagittal sections of rats aged E12, E13, E14, E16, E17, E19, and P0 (Ashwell and Paxinos, 2015). “Atlas of the Neonatal Rat Brain” by Ramachandra and Subramanian describes rat brains at P1, P7, and P14 (Ramachandra and Subramanian, 2011). More recently, Calabrese, Badea, Watson, and Johnson published their “Quantitative magnetic resonance histology atlas of postnatal rat brain development with regional estimates of growth and variability” based on the study of P0, P2, P4, P8, P12, P18, P24, P40, and P80 rats (Calabrese et al., 2013). Among these atlases, only the atlas by Sherwood and Timiras (1970) provides stereotaxic coordinates and yet for only three postnatal days P10, 21, and P39. Stereotaxic atlases for the early postnatal period are not available, however. Table 1 Atlases of the developing rat brain. The series of atlases of the developing rat brain in stereotaxic coordinates that we propose here has been conceived as a tool for the exploration of the rat brain in vivo during the postnatal period, offering a choice of bregma and lambda as the reference points. Each atlas contains a series of microphotographs of wet, non-stained 200 micron coronal brain sections in oblique light, obtained from postnatal days P0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 14, and 21 rats, with an indication of the main brain structures. Wet non-stained sections were used to avoid deformation, shrinkage and lessening associated with staining and mounting procedures, particularly when manipulating immature tissue. Because we did not stain sections, the images do not provide cellular resolution and not all brain structures and boundaries between them can be easily identified. Therefore, only certain brain structures are labeled without boundaries. Used in combination with the existing high image resolution atlases of the developing rat brain (Sherwood and Timiras, 1970; Ramachandra and Subramanian, 2011; Calabrese et al., 2013; Ashwell and Paxinos, 2015), this atlas may be useful for targeted recordings, stimulations, and drug injections in different brain structures at various postnatal ages. This atlas has been successfully used in several previous studies (Minlebaev et al., 2011; Petit et al., 2014; Tyzio et al., 2014).

Chronic Fluoxetine Treatment Changes S100B Expression During Postnatal Rat Brain Development

Fluoxetine, a selective serotonin reuptake inhibitor, is approved for treatment of childhood depression. In rats, fluoxetine influences neuronal development, but it is unclear whether it also influences glia development. S100B is a glia-derived calcium-binding protein, which may influence the development of serotonergic fibers and, vice versa, serotonin may influence the expression of S100B. The purpose of this study was to investigate whether fluoxetine treatment influences the expression of S100B during postnatal development, and whether potential changes are regionally dependent upon the time frame of drug administration. S100B gene expression and S100B protein expression in three different brain regions (frontal cortex, hippocampus, and striatum) were studied by real-time polymerase chain reaction (PCR) and immunohistochemistry, respectively. First, a short-term effect, 24 hours after a 14 day fluoxetine treatment (5 mg/kg/bw s.c.) of rats either from postnatal day (PD) 1 to 15, 21 to 35, or 50 to 64, was investigated. Then, the same treatment was used to analyze S100B gene and protein levels at PD 90 (long-term effect). At PD 90, a significant increase of gene and protein expression was observed in all regions if rats were treated during PDs 21-35, whereas treatment during other periods had no long-term effects. A short-term effect 24 hours after fluoxetine treatment was found for almost all development stages and regions, demonstrated by a significant increase of S100B. These results support recent research indicating a highly drug-sensitive period (i.e., periadolescence) of rat brain development. Therefore, further clinical studies should be performed to clarify whether such a sensitive period also exists in children.

DNA methylation markers in the postnatal developing rat brain

In spite of intense interest in how altered epigenetic processes including DNA methylation may contribute to psychiatric and neurodevelopmental disorders, there is a limited understanding of how methylation processes change during early postnatal brain development. The present study used in situ hybridization to assess mRNA expression for the three major DNA methyltranserases (DNMTs) – DNMT1, DNMT3a and DNMT3b – in the developing rat brain at seven developmental timepoints: postnatal days (P) 1, 4, 7, 10, 14, 21, and 75. We also assessed 5-methylcytosine levels (an indicator of global DNA methylation) in selected brain regions during the first three postnatal weeks. DNMT1, DNMT3a and DNMT3b mRNAs are widely expressed throughout the adult and postnatal developing rat brain. Overall, DNMT mRNA levels reached their highest point in the first week of life and gradually decreased over the first three postnatal weeks within the hippocampus, amygdala, striatum, cingulate and lateral septum. Global DNA methylation levels did not follow this developmental pattern; methylation levels gradually increased over the first three postnatal weeks in the hippocampus, and remained stable in the developing amygdala and prefrontal cortex. Our results contribute to a growing understanding of how DNA methylation markers unfold in the developing brain, and highlight how these developmental processes may differ within distinct brain regions.

A quantitative magnetic resonance histology atlas of postnatal rat brain development with regional estimates of growth and variability

There has been growing interest in the role of postnatal brain development in the etiology of several neurologic diseases. The rat has long been recognized as a powerful model system for studying neuropathology and the safety of pharmacologic treatments. However, the complex spatiotemporal changes that occur during rat neurodevelopment remain to be elucidated. This work establishes the first magnetic resonance histology (MRH) atlas of the developing rat brain, with an emphasis on quantitation. The atlas comprises five specimens at each of nine time points, imaged with eight distinct MR contrasts and segmented into 26 developmentally defined brain regions. The atlas was used to establish a timeline of morphometric changes and variability throughout neurodevelopment and represents a quantitative database of rat neurodevelopment for characterizing rat models of human neurologic disease.

Existence of Tenascin-C Isoforms in Rat that Contain the Alternatively Spliced AD1 Domain are Developmentally Regulated During Hippocampal Development

Tenascin-C (TN-C) is a multimodular glycoprotein of the extracellular matrix which is important for the development of the nervous system and has a range of different functions which are mediated by the different protein domains present. TN-C contains eight constitutive fibronectin type III (FNIII) domains and a region of alternatively spliced FNIII domains. In the mouse and chick, six of these domains have been described and characterized, whereas in human there are nine of them. In this report, we show that seven alternatively spliced FNIII domains exist in rat and describe the differential expression pattern of the additional domain AD1 during embryonic and postnatal rat brain development. The AD1 domain of rat is homologous to the ones described in human and chick proteins but does not exist in mouse. Its expression can be located to the developing rat hippocampus and the lining of the lateral ventricle, regions where the TN-C protein may affect the behavior of stem and progenitor cells. During hippocampal development AD1 and the other alternatively spliced domains are differentially expressed as shown by RT-PCRs, immunocytochemistry and in situ hybridizations.

DGKι regulates presynaptic release during mGluR-dependent LTD

Diacylglycerol (DAG) is an important lipid second messenger. DAG signalling is terminated by conversion of DAG to phosphatidic acid (PA) by diacylglycerol kinases (DGKs). The neuronal synapse is a major site of DAG production and action; however, how DGKs are targeted to subcellular sites of DAG generation is largely unknown. We report here that postsynaptic density (PSD)-95 family proteins interact with and promote synaptic localization of DGKι. In addition, we establish that DGKι acts presynaptically, a function that contrasts with the known postsynaptic function of DGKζ, a close relative of DGKι. Deficiency of DGKι in mice does not affect dendritic spines, but leads to a small increase in presynaptic release probability. In addition, DGKι-/- synapses show a reduction in metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD) at neonatal (∼2 weeks) stages that involve suppression of a decrease in presynaptic release probability. Inhibition of protein kinase C normalizes presynaptic release probability and mGluR-LTD at DGKι-/- synapses. These results suggest that DGKι requires PSD-95 family proteins for synaptic localization and regulates presynaptic DAG signalling and neurotransmitter release during mGluR-LTD.

Early postnatal development of rat brain is accompanied by generation of lipofuscin-like pigments

The increased generation of free radicals results in the formation of fluorescent end-products of lipid peroxidation, lipofuscin-like pigments (LFPs). The authors observed that LFPs are generated in rat brain after a normal birth during 5 postnatal days. The experimental design of the study comprised 10 groups of animals. The authors measured prenatal values 1 day and 7 days before birth, and then the animals were sampled on postnatal day 1, 2, 5, 10, 15, 25, 35, and 90. Maximum LFP concentration is achieved on the postnatal day 2. Starting from postnatal day 10, LFP concentration returns to prenatal values. A new rise in LFP concentration is observed at 3 months of age. This is associated with the beginning of the aging process. LFPs were characterized by fluorescence spectroscopy using tridimensional excitation spectra, synchronous spectra and their derivatives, and HPLC with fluorescence detection. It was possible to discern several tens of fluorescent compounds of unknown structure that are generated and metabolized during early development. The authors suggest that LFPs are formed after respiratory burst of microglia phagocytosing apoptotic cells.

Changing numbers of neuronal and non-neuronal cells underlie postnatal brain growth in the rat

The rat brain increases >6x in mass from birth to adulthood, presumably through the addition of glial cells and increasing neuronal size, without the addition of neurons. To test this hypothesis, here we investigate quantitatively the postnatal changes in the total number of neuronal and non-neuronal cells in the developing rat brain, and examine how these changes correlate with brain growth. Total numbers of cells were determined with the isotropic fractionator in the brains of 53 Wistar rats, from birth to young adulthood. We find that at birth, >90% of the cells in the rat brain are neurons. Following a dormant period of approximately 3 days after birth, the net number of neurons in the cerebral cortex, hippocampus, and remaining tissue (excluding cerebellum and olfactory bulb) doubles during the first week, then is reduced by 70% during the second postnatal week, concurrently with net gliogenesis. A second round of net addition of 6 million neurons is observed in the cerebral cortex over the following 2 weeks. During the first postnatal week, brain growth relates mainly to increased numbers of neurons of larger average size. In the second and third weeks, it correlates with increased numbers of non-neuronal cells that are smaller in size than the preexisting neurons. Postnatal rat brain development is thus characterized by dramatic changes in the cellular composition of the brain, whose growth is governed by different combinations of cell addition and loss, and changes in average cell size during the first months after birth.

Synaptic removal of diacylglycerol by DGKζ and PSD-95 regulates dendritic spine maintenance

Diacylglycerol (DAG) is an important lipid signalling molecule that exerts an effect on various effector proteins including protein kinase C. A main mechanism for DAG removal is to convert it to phosphatidic acid (PA) by DAG kinases (DGKs). However, it is not well understood how DGKs are targeted to specific subcellular sites and tightly regulates DAG levels. The neuronal synapse is a prominent site of DAG production. Here, we show that DGKzeta is targeted to excitatory synapses through its direct interaction with the postsynaptic PDZ scaffold PSD-95. Overexpression of DGKzeta in cultured neurons increases the number of dendritic spines, which receive the majority of excitatory synaptic inputs, in a manner requiring its catalytic activity and PSD-95 binding. Conversely, DGKzeta knockdown reduces spine density. Mice deficient in DGKzeta expression show reduced spine density and excitatory synaptic transmission. Time-lapse imaging indicates that DGKzeta is required for spine maintenance but not formation. We propose that PSD-95 targets DGKzeta to synaptic DAG-producing receptors to tightly couple synaptic DAG production to its conversion to PA for the maintenance of spine density.

Expression pattern of Anosmin‐1 during pre‐ and postnatal rat brain development

Anosmin-1 participates in the development of the olfactory and GnRH systems. Defects in this protein are responsible for both the anosmia and the hypogonadotrophic hypogonadism found in Kallmann's syndrome patients. Sporadically, these patients also manifest some neurological symptoms that are not explained in terms of the developmental defects in the olfactory system. We describe the pattern of Anosmin-1 expression in the central nervous system during rat development using a novel antibody raised against Anosmin-1 (Anos1). The areas with Anos1-stained neurons and glial cells were classified into three groups: (1) areas with immunoreactivity from embryonic day 16 to postnatal day (P) 15; (2) areas with Anosmin-1 expression only at postnatal development; (3) nuclei with immunoreactivity only at P15. Our data show that Anos1 immunoreactivity is detected in projecting neurons and interneurons within areas of the brain that may be affected in patients with Kallmann's syndrome that develop both the principal as well as sporadic symptoms.

A dynamic expression pattern of sGαi2 protein during early period of postnatal rat brain development

The function of sGαi2 protein in central nervous system is not well understood. Therefore to explore the possible role of this protein in postnatal brain development, we have analyzed the protein expression pattern of brain obtained from rats of postnatal day 0 (P0) to P90 by dot-blots and immunocytochemistry techniques. In dot-blots, both nuclear and membrane fractions showed a gradual decrease from P0 to P60. Highest protein level was observed at the age of P0. There was also a trend of decline in the sGαi2 protein from P0 to P90 in brain sections stained by immunocytochemistry method. At P0, the protein labeling was highest in cerebral cortex, hippocampus, cerebellum and mitral cell layer. In cerebral cortex, a drop in the immunolabeling of sGαi2 protein was observed at P3, which was significantly increased at the age of P5. However, in striatum and olfactory tubercle, it was maintained through P0–P10 and P0–P5, respectively. Thalamus was one of the areas where labeling was not as strong as cortex, hippocampus or striatum. In contrary to other areas, immunostaining of sGαi2 in corpus-callosum and lacunosum-moleculare was not seen at P0 and appeared in advanced postnatal ages. A detectable level of sGαi2 protein was observed at P5 in carpus-callosum and at P20 in lacunosum-moleculare. A high level of sGαi2 protein in the period when cellular layer organization and synaptic innervations, synaptic connections and maturation take place, suggests for a potential role of this protein in the early postnatal brain development.

Early postnatal development of rat brain: In vivo diffusion tensor imaging

Perinatal hypoxia is a major cause of neurodevelopmental deficits. Neuronal migration patterns are particularly sensitive to perinatal hypoxia/ischemia and are associated with the clinical deficits. The rat model of hypoxia/ischemia at P7 mimics that of perinatal injury in humans. Before assessing the effects of postnatal injury on brain development, it is essential to determine the normal developmental trajectories of various brain structures in individual animals. In vivo longitudinal diffusion tensor imaging (DTI) was performed from postnatal day 0 (P0) to P56 on Wistar rats. The DTI metrics, mean diffusivity (MD), fractional anisotropy (FA), axial (lambdal) and radial (lambdat) diffusivities, were determined for four gray matter and eight white matter structures. The FA of the cortical plate and the body of corpus callosum decreased significantly during the first 3 weeks after birth. The decrease in the cortical plate's FA value was associated mainly with an increase in lambdat. The initial decrease in FA of corpus callosum was associated with a significant decrease in lambdal. The FA of corpus callosum increased during the rest of the observational period, which was mainly associated with a decrease in lambdat. The FA of gray matter structures, hippocampus, caudate putamen, and cortical mantle did not show significant changes between P0 and P56. In contrast, the majority of white matter structures showed significant changes between P0 and P56. These temporal changes in the DTI metrics were related to the neuronal and axonal pruning and myelination that are known to occur in the developing brain.

Allometry of Postnatal Rat Brain Development Prenatally Exposed to Aspirin

Allometry of Postnatal Rat Brain Development Prenatally Exposed to Aspirin

μ Opioid Receptor Coupling to Gi/oProteins Increases during Postnatal Development in Rat Brain

Mu opioid receptors are densely expressed within rat striatum and are concentrated in anatomically discrete patches called striosomes. The density of striosomal mu receptors remains relatively constant during postnatal development, but little is known about their functional maturation. We examined the extent of G protein coupling by mu opioid receptors in rat brain during development, focusing on striosomes within the striatum because of receptor density. The mu receptors were quantified using [(3)H][d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) autoradiography. Adjacent sections were analyzed for DAMGO-stimulated guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding to assess mu receptor activation of G(i/o) proteins. Striosomal mu receptor expression increased only slightly between postnatal day 5 and adult. In contrast, mu receptor-stimulated [(35)S]GTPgammaS binding increased from 0.13 to 2.6 fmol/mg tissue over the same period, a 20-fold difference. The ratio of specific DAMGO-stimulated [(35)S]GTPgammaS binding to [(3)H]DAMGO binding, representing the relative number of G proteins activated per receptor, increased 19-fold between postnatal day 5 and adult. Similar patterns were observed throughout the striatum and other brain regions such as the nucleus accumbens, although the extent of change varied from region to region. These data indicate that mu opioid receptors exhibit enhanced function in the adult rat brain compared with the neonate. These data also suggest that this increase in G protein coupling is developmentally regulated and that in the developing rat brain the density of mu opioid receptor expression may not necessarily correlate with receptor activation of G proteins.

Effect of perinatal asphyxia on tyrosine hydroxylase and D2 and D1 dopamine receptor mRNA levels expressed during early postnatal development in rat brain

This study was designed to investigate the postnatal developmental plasticity of the mesostriatal and mesolimbic dopamine systems that occurs following perinatal asphyxia. The time course and patterning of the changes in levels of tyrosine hydroxylase (TH), and D1 and D2 dopamine receptor (R) mRNA in the cell body region, substantia nigra and ventral tegmental area (SN/VTA), and projection fields, striatum and limbic regions at the age of 6 and 24 h, and 1 week after asphyxia were studied with a quantitative reverse transcription polymerase chain reaction method with appropriate internal cRNA standard. In Caesarean-delivered control rats (Sprague–Dawley), TH, D2R and D1R mRNA levels showed regional and temporal specificity in both absolute levels and developmental kinetics during the first week of life. TH mRNA levels were >10-fold higher in SN/VTA than in striatum and limbic regions. Compared to Caesarean delivered controls, severe asphyxia (15–20 min) induced an increase of TH and D2R mRNA in SN/VTA 6 h and 1 week after birth. In addition, asphyxia induced an increase of TH mRNA in the projection fields, striatum and limbic regions, at 1 week. Perinatal asphyxia did not appear to exert any effect on D1R mRNA levels. No differences in any of the parameters were observed between spontaneous- and Caesarean-delivered animals. The present results indicate that perinatal asphyxia triggers coordinated changes in the expression of TH, and dopamine receptor mRNA in SN/VTA, striatum and limbic regions. These changes may affect differently dopamine D2R and D1R expression along development, contributing to long-term neurocircuitry imbalances.

Changes of steroidogenic acute regulatory protein mRNA expression in postnatal rat development

The present study investigated the expression pattern of steroidogenic acute regulatory protein (StAR) mRNA in several brain regions and peripheral endocrine organs using Northern blot, RT-PCR and in situ hybridization. StAR mRNA in the adrenal gland was detected at birth and decreased for 2 weeks postnatally. In gonads, it was also detected at birth though at a lower level than adrenal, and was maintained until week 3. Thereafter StAR mRNA expression in both endocrine organs was increased. Though the amount of StAR mRNA in the brain was much less than that of peripheral endocrine organs, it was expressed from birth and, in general, appeared to gradually increase during postnatal development. A gradual increase was found in the hypothalamus, while a sigmoidal expression was shown in the olfactory bulb. The increased expression of StAR mRNA in the postnatal period suggests that it might have a role in the regulation of neurosteroidogenesis needed in neuronal cell growth and differentiation in postnatal rat brain development.