Regions Of Neonatal Rat Brain Research Articles

Assessment of myelination development in neonatal rats using chemical exchange saturation transfer (CEST) 7-T MRI.

Myelination is a crucial process in the nervous system. This study aimed to evaluate the progression of myelin sheath development in different brain regions of neonatal rats at distinct developmental stages using Chemical Exchange Saturation Transfer (CEST) 7-T MRI. Male SD rats of different ages (3days, 1week, 2weeks, 3weeks, 1month, 2months) were selected for the study. Advanced in vivo MRI experiments were conducted using a 7-T MRI scanner. Custom MatLab scripts were employed to generate MR images and process the data. Myelin staining was used to assess myelin distribution in various brain regions. Statistical analysis was performed using repeated measures multivariate analysis of variance (MANOVA) and Spearman's rank correlation. The progression of myelination was significantly different in different brain regions (F(5, 30) = 3.34, P < 0.05), with the corpus callosum showing an accelerated rate of myelination. Within the first month alone, there was an increase of 46.1% in myelination (t(35) = 2.29, P < 0.05). The hypothalamus and internal capsule exhibited a more gradual yet consistent increase in myelination over the two-month period, with increases of 47.1% (t(35) = 2.27, P < 0.05) and 39.8% (t(35) = 2.59, P < 0.05), respectively. A substantial positive correlation was found between the MRI-based and histological measurements of myelination (r = 0.31, P < 0.05). This study demonstrates the potential of CEST 7-T MRI as a non-invasive tool for assessing myelination progression and provides insights into the differential myelination rates across various brain regions during early development.

Maternal diets affected ceramides and fatty acids in brain regions of neonatal rats with prenatal ethanol exposure

ABSTRACT Objectives: Ceramide (Cer), known as apoptotic markers, increases with prenatal ethanol (EtOH) exposure, resulting in neuroapoptosis. Whether maternal nutrition can impact Cer concentrations in brain, via altering plasma and brain fatty acid compositions have not been examined. This study compared a standard chow with a formulated semi-purified energy dense (E-dense) diet on fatty acid composition, Cer concentrations, and apoptosis in plasma and brain regions (cortex, cerebellum, and hippocampus) of pups exposed to EtOH during gestation. Methods: Pregnant Sprague–Dawley rats were randomized into four groups: chow (n = 6), chow + EtOH (20% v/v) (n = 7), E-dense (n = 6), and E-dense + EtOH (n = 8). At postnatal day 7, representing the peak brain growth spurt in rats, lipids, and apoptosis were analyzed by gas chromatography and a fluorometric caspase-3 assay kit, respectively. Results: Maternal E-dense diet increased total fatty acid concentrations (p < 0.0001), including docosahexaenoic acid (DHA) (p < 0.0001) in plasma, whereas DHA concentrations were decreased in the cerebellum (p < 0.03) of pups than those from chow-fed dams. EtOH-induced Cer elevations in the hippocampus of pups born to dams fed chow were reduced by an E-dense diet (p < 0.02). No significant effects of maternal diet quality and EtOH were observed on caspase-3 activity. No significant correlations existed between plasma/brain fatty acids and Cer concentrations. Discussions: Maternal diet quality affected fatty acid compositions and Cer concentrations of pups with prenatal EtOH exposure, differently. Maternal nutrition has the potential to prevent or alleviate some of the adverse effects of prenatal EtOH exposure.

Abstract 60: Inter-alpha Inhibitor Proteins Reduce the Quantity of Microglia in the Hippocampus After Hypoxic-ischemic Brain Injury in the Neonate

Background: Inter-alpha inhibitor proteins (IAIPs) are immunomodulatory proteins that act as anti-inflammatory agents in hypoxic-ischemic (HI) injury. We have recently shown that administering IAIP after HI improves histopathological brain injury, and behavioral outcomes in neonatal rats. Microglia are glial cells that act as macrophages in the brain and are important constituents in the neuroinflammatory response. Objective: To determine the effect of IAIP treatment on microglial expression in specific brain regions of neonatal rats after HI brain related injury. Methods: The Vannucci model was used to induce neonatal HI brain injury. Postnatal day 7 rats were assigned to a non-ischemic sham-control group (Sham, n=11), a right carotid ligation and hypoxia exposed (8% oxygen for 90 min) placebo-treated group (IschPL, n=12), or a right carotid ligation and hypoxia IAIP-treated group (Isch-IAIP, n=12). The sex of the rats was recorded. IAIP (30 mg/kg) or PL was given intraperitoneally at 0, 24 and 48 h after HI. 72 h after HI, brains were collected, sectioned, and prepared for slides. We performed immunohistochemistry by staining with Iba-1 (selective for microglia) and DAPI. Stereological analyses were then performed with the StereoInvestigator 10.0 Fractionator probe without knowledge of group assignment to quantify microglia present in the whole hemisphere, cortex, corpus callosum, and hippocampus. Results: The number of Iba-1 positive microglial cells per area of tissue was lower in Sham than in the Isch-PL animals in the cortex, hippocampus, and hemisphere of female and in the hippocampus and corpus callosum of male rats (P &lt;0.05). IAIP treatment appears to reduce the number of Iba-1 positive cells across all brain regions compared with the PL treated HI in the male but not female neonatal rats. Post hoc analysis showed that IAIP treatment significantly reduced the number of positive Iba-1 cells in the hippocampus of the male rats (P&lt;0.01).

Effects of different endocrine disruptor (EDC) mixtures on gene expression in neonatal rat brain regions: Focus on developing excitatory synapses

Effects of different endocrine disruptor (EDC) mixtures on gene expression in neonatal rat brain regions: Focus on developing excitatory synapses

Morphine-enhanced apoptosis in selective brain regions of neonatal rats

Prolonged neonatal opioid exposure has been associated with: antinociceptive tolerance, long-term neurodevelopmental delay, cognitive, and motor impairment. Morphine has also been shown to induce apoptotic cell death in vitro studies, but its in vivo effect in developing rat brain is unknown. Thus, we hypothesized that prolongued morphine administration in neonatal rats in a model of antinociceptive tolerance and dependence is associated with increased neuroapoptosis. We analyzed neonatal rats from the following groups (1) naïve group (n=6); (2) control group (normal saline (NS), n=5), and (3) morphine group (n=8). Morphine sulfate or equal volume of NS was injected subcutaneously twice daily for 6½ days starting on postnatal day (PD) 1. Development of antinociceptive tolerance was previously confirmed by Hot Plate test on the 7th day. Evidence of neuronal and glial apoptosis was determined by cleaved caspase-3 immunofluorescence combined with specific markers. At PD7, morphine administration after 6½ days significantly increased the density of apoptotic cells in the cortex and amygdala, but not in the hippocampus, hypothalamus, or periaqueductal gray. Apoptotic cells exhibited morphology analogous to neurons. Irrespective of the treatment, only a very few individual microglia but not astrocytes were caspase-3 positive. In summary, repeated morphine administration in neonatal rats (PD1–7) is associated with increased supraspinal apoptosis in distinct anatomical regions known to be important for sensory (cortex) and emotional memory processing (amygdala). Brain regions important for learning (hippocampus), and autonomic and nociceptive processing (hypothalamus and periaqueductal gray) were not affected. Lack of widespread glial apoptosis or robust glial activation following repeated morphine administration suggests that glia might not be affected by chronic morphine at this early age. Future studies should investigate long-term behavioral sequelae of demonstrated enhanced apoptosis associated with prolonged morphine administration in a neonatal rat model.

The interrelationship between BDNF and its precursor and the level of active caspase-3 in the brain regions of neonatal rats

Brain-derived neurotrophic factor (mat-BDNF) promotes neuronal survival, whereas its precursor protein (pro-BDNF) induces cell death, which indicates the opposite but potentially important roles of both forms of this neurotrophin in brain development. We studied the contents of mat- and pro-BDNF and active caspase-3 in the brain regions of 8-day-old rat pups. Taking the level of caspase-3 in the cerebral cortex into account we may conclude that intense apoptosis occurs in this structure; however, the ratio of mat-BDNF to pro-BDNF in this region was the lowest among all structures studied. In contrast, in the brainstem of neonatal rats, where processes of cell proliferation and elimination are completed, the mat-BDNF/pro-BDNF ratio was substantially higher compared to the cortex. The mat-BDNF/pro-BDNF ratio in the cerebellum and hippocampus also supports the inverse relationship between this index and the level of active caspase-3 in different brain regions. Our data suggest that both forms of BDNF are involved in the determination of cell fate in the developing brain.

Developmental exposure to organophosphates triggers transcriptional changes in genes associated with Parkinson's disease in vitro and in vivo

Epidemiologic studies support a connection between organophosphate pesticide exposures and subsequent risk of Parkinson's disease (PD). We used differentiating, neuronotypic PC12 cells to compare organophosphates (chlorpyrifos, diazinon), an organochlorine (dieldrin) and a metal (Ni(2+)) for their effects on the transcription of PD-related genes. Both of the organophosphates elicited significant changes in gene expression but with differing patterns: chlorpyrifos evoked both up- and downregulation whereas diazinon elicited overall reductions in expression. Dieldrin was without effect but Ni(2+) produced a pattern resembling that of diazinon. We then exposed neonatal rats to chlorpyrifos or diazinon for the first 4 days after birth and examined the expression of PD-related genes in the brainstem and forebrain. Chlorpyrifos had no significant effect whereas diazinon produced significant increases and decreases in expression of the same PD genes that were targeted in vitro. Our results provide some of the first evidence for a mechanistic relationship between developmental organophosphate exposure and the genes known to confer PD risk in humans; but they also point to disparities between different organophosphates that reinforce the concept that their neurotoxic actions do not rest solely on their shared property as cholinesterase inhibitors. The parallel effects of diazinon and Ni(2+) also show how otherwise unrelated developmental neurotoxicants can nevertheless produce similar outcomes by converging on common molecular pathways, further suggesting a need to examine metals such as Ni(2+) as potential contributors to PD risk.

Exposure to Organophosphates Reduces the Expression of Neurotrophic Factors in Neonatal Rat Brain Regions: Similarities and Differences in the Effects of Chlorpyrifos and Diazinon on the Fibroblast Growth Factor Superfamily

BackgroundThe fibroblast growth factor (FGF) superfamily of neurotrophic factors plays critical roles in neural cell development, brain assembly, and recovery from neuronal injury.ObjectivesWe administered two organophosphate pesticides, chlorpyrifos and diazinon, to neonatal rats on postnatal days 1–4, using doses below the threshold for systemic toxicity or growth impairment, and spanning the threshold for barely detectable cholinesterase inhibition: 1 mg/kg/day chlorpyrifos and 1 or 2 mg/kg/day diazinon.MethodsUsing microarrays, we then examined the regional expression of mRNAs encoding the FGFs and their receptors (FGFRs) in the forebrain and brain stem.ResultsChlorpyrifos and diazinon both markedly suppressed fgf20 expression in the forebrain and fgf2 in the brain stem, while elevating brain stem fgfr4 and evoking a small deficit in brain stem fgf22. However, they differed in that the effects on fgf2 and fgfr4 were significantly larger for diazinon, and the two agents also showed dissimilar, smaller effects on fgf11, fgf14, and fgfr1.ConclusionsThe fact that there are similarities but also notable disparities in the responses to chlorpyrifos and diazinon, and that robust effects were seen even at doses that do not inhibit cholinesterase, supports the idea that organophosphates differ in their propensity to elicit developmental neurotoxicity, unrelated to their anticholinesterase activity. Effects on neurotrophic factors provide a mechanistic link between organophosphate injury to developing neurons and the eventual, adverse neurodevelopmental outcomes.

Developmental exposure to terbutaline and chlorpyrifos: pharmacotherapy of preterm labor and an environmental neurotoxicant converge on serotonergic systems in neonatal rat brain regions

Developmental exposure to unrelated neurotoxicants can nevertheless produce similar neurobehavioral outcomes. We examined the effects of developmental exposure to terbutaline, a tocolytic β 2-adrenoceptor agonist used to arrest preterm labor, and chlorpyrifos (CPF), a widely used organophosphate pesticide, on serotonin (5HT) systems. Treatments were chosen to parallel periods typical of human developmental exposures, terbutaline (10 mg/kg) on postnatal days (PN) 2–5 and CPF (5 mg/kg) on PN11-14, with assessments conducted on PN45, comparing each agent alone as well as sequential administration of both. Although neither treatment affected growth or viability, each elicited similar alterations in factors that are critical to the function of the 5HT synapse: 5HT 1A receptors, 5HT 2 receptors, and the presynaptic 5HT transporter (5HTT). Either agent elicited global increases in 5HT receptors and the 5HTT in brain regions possessing 5HT cell bodies (midbrain, brainstem) as well as in the hippocampus, which contains 5HT projections. For both terbutaline and CPF, males were affected more than females, although there were some regional disparities in the sex selectivity between the two agents. Both altered 5HT receptor-mediated cell signaling, suppressing stimulatory effects on adenylyl cyclase and enhancing inhibitory effects. When animals were exposed sequentially to both agents, the outcomes were no more than additive and, for many effects, less than additive, suggesting convergence of the two agents on a common set of developmental mechanisms. Our results indicate that 5HT systems represent a target for otherwise unrelated neuroteratogens.

Variations of elemental distribution in brain regions of neonatal rats at different iodine intakes.

Iodine deficiency (ID) can result in irreversible damage to the brain during the fetal and neonatal stages. As the active center of many enzymes, trace elements play essential roles in brain function. In this work, the relative contents and distributions of elements (Cl, Br, Fe, Cu, and Zn) in two important brain regions, the cerebral cortex and hippocampus, of the iodine-deficient model rats were determined by the synchrotron radiation X-ray fluorescence (SRXRF) method. Meanwhile, the ID rats were supplemented with adequate and excessive iodine, respectively. The results indicated that the distributions of trace elements could be influenced by the different iodine intakes in the stage of brain development. In contrast to the control group, the contents of Cl, Br, and Zn in two brain regions showed a significant increase in the ID group; however, both Fe and Cu decreased in the cerebral cortex and increased in the hippocampus in the ID group. In addition, only slight changes of elemental contents in brain were found between the adequate and excessive iodine-supplemented rats.

Perinatal Iron Deficiency Decreases Cytochrome c Oxidase (CytOx) Activity in Selected Regions of Neonatal Rat Brain

deUngria, Marissa; Rao, Raghavendra; Wobken, Jane D.; Luciana, Monica; Nelson, Charles A.; Georgieff, Michael K.

Perinatal iron deficiency decreases cytochrome c oxidase (CytOx) activity in selected regions of neonatal rat brain.

Intrauterine growth retardation and diabetes mellitus during human gestation result in significant losses of fetal and neonatal brain iron. Brain iron deficiency is associated with impaired cognitive processes including memory and attention. The regional distribution of iron staining and cytochrome c oxidase (CytOx) activity have not been mapped in the iron-sufficient or -deficient neonatal rat. CytOx is the iron-containing terminal enzyme in oxidative phosphorylation; its activity reflects neuronal metabolism. We hypothesized that neonatal brain iron deficiency differentially decreases iron and CytOx activity in brain regions, with more pronounced losses in structures involved in recognition memory. Pregnant Sprague Dawley rats were fed either an iron-deficient or -fortified diet from gestational d 1 until postnatal d 10. Iron staining and CytOx activity of 20 brain structures were mapped histochemically in 25 rats from each group. Brain iron staining was reduced from 75% to 100% and CytOx staining was decreased from 0% to 42% in the iron deficient group (p < 0.001). Areas with significantly reduced CytOx activity (p < 0.001) included all measured subareas of the hippocampus (CA1: 42%, CA3ab: 34%, CA3c: 33%, and dentate gyrus: 32%), the piriform cortex (17%), the medial dorsal thalamic nucleus (28%), and the cingulate cortex (41%). In contrast, the anterior thalamic nucleus, the lateral amygdaloid nucleus, and the medial habenula, areas not involved in higher cognitive functions, did not have significantly reduced CytOx activity (0%, 10%, and 16%, respectively). We conclude that perinatal iron deficiency differentially reduces neuronal metabolic activity, specifically targeting areas of the brain involved in memory processing.

Angiotensin II activates distinct signal transduction pathways in astrocytes isolated from neonatal rat brain

In previous studies, we showed that angiotensin II (Ang II) and its congener peptides-angiotensin-(2-8) [Ang-(2-8)] and angiotensin-(1-7) [Ang-(1-7)]-activate 2 distinct signal transduction pathways in a mixed population of human cortical astrocytoma cells. This suggested that different populations of astrocytes could be heterogeneous with respect to their expression of Ang II receptors or the responses to which these receptors are coupled. To compare the responses which are activated by Ang II and its congener peptides in astrocytes from different brain regions, we measured phospholipase C (PLC) activity and prostaglandin release in isolated astrocytes from 4 different areas of neonatal rat brain. In medullary and cerebellar astrocytes, Ang II activated a phosphoinositide-specific PLC in a dose-dependent manner with EC50s of 1.74 and 1.86 nM, respectively. Ang-(2-8) also caused an increase in inositol phosphate release. PLC activity was coupled to an AT1 receptor in both medullary and cerebellar astrocytes, as demonstrated by the inhibition of Ang II-activation of inositol phosphate release by the AT1 antagonist losartan. The AT2 antagonist PD 123319 was ineffective. Ang II and Ang-(2-8) also released prostacyclin from medullary and cerebellar astrocytes, measured as the release of its stable metabolite 6-keto-PGF1 alpha. In contrast, Ang II did not activate PLC or release prostaglandins in astrocytes isolated from the cortex or hypothalamus. In addition, Ang-(1-7) did not stimulate the release of inositol phosphates or prostacyclin in astrocytes from any of the neonatal rat brain regions examined. However, bradykinin (1 microM) activated PLC or released prostacyclin in astrocytes isolated from all 4 brain regions. These results suggest that Ang II receptors on region-specific astrocytes activate distinct signal transduction mechanisms in response to different angiotensin peptides.

Expression of mRNAs coding for the transforming growth factor- β receptors in brain regions of euthyroid and hypothyroid neonatal rats and in adult brain

The TGF- β family of peptides has been postulated to play a role in control of the cell cycle but also may act in the developing brain to influence neuronal differentiation and survival. Because reception of TGF- β signals requires the simultaneous expression of all three known receptor subtypes, we examined two neonatal rat brain regions in which neurogenesis has been largely completed. mRNA coding for all three receptors was detectable in both the forebrain and brainstem but only the type II receptor in brainstem showed a difference from adult levels of expression. Animals given perinatal PTU treatment to achieve congenital cretinism did not show significant differences in expression of any of the receptor subtypes in either of the regions, despite the fact that the treatment is known to cause anomalies of neuronal differentiation. These results indicate that regions in which neurons are undergoing axonogenesis and synaptogenesis rather than neurogenesis, nevertheless express the mRNAs coding for TGF- β receptors and are thus likely to be receptive to trophic signals mediated through TGF- β. However, synthesis and release of TGF- β, rather than receptor expression per se, is more likely to be the major point for regulation of signaling. The potential roles of TGF- β in developmental events outside of the cell cycle, such as synaptogenesis and apoptosis, need to be examined.

Acute stimulation of ornithine decarboxylase in neonatal rat brain regions by nicotine: a central receptor-mediated process?

Nicotine exposure during development alters central nervous system structure and function. In the current study, we examined the acute effects of nicotine (3 mg/kg) on developing rat brain by monitoring ornithine decarboxylase (ODC), a marker for perturbed cell development; ODC controls polyamine biosynthesis and thus regulates cell differentiation. Three brain regions were selected that differ both in their timetables for maturation and in nicotinic receptor concentrations: midbrain + brainstem (earliest development, highest receptor concentration), forebrain (intermediate profiles) and cerebellum (latest development and lowest receptor concentration). Nicotine caused stimulation of ODC within 1 h after drug administration, an effect that displayed both age- and region-dependence corresponding to the development of central nicotinic receptors: effects appeared earliest and were largest in magnitude in midbrain + brainstem and forebrain, and appeared last and with smaller magnitude in the cerebellum. Central receptor involvement was confirmed at 8 days postpartum by demonstrating desensitization of the response after repeated nicotine administration, and by evoking equivalent effects with direct introduction of a small dose of nicotine into the central nervous system. Later in development, acute stimulation of ODC by nicotine became less selective, reflecting secondary actions mediated through systemic hypoxia caused by the drug; this conclusion was confirmed by the absence of desensitization after repeated nicotine administration, and by the failure of centrally administered nicotine to evoke a full stimulatory response. Nicotine-induced ischemia did not contribute to stimulation of ODC seen at the 1 h time point: pretreatment with chlorisondamine, a ganglionic nicotinic antagonist, failed to alter the central stimulatory response. In light of the role of ODC and the polyamines in cell differentiation, axonogenesis and synaptogenesis, receptor-mediated and hypoxia-mediated effects of nicotine on this enzyme are likely to contribute to nervous system alterations associated with developmental exposure.

Immunocytochemical localization of mitochondrial malate dehydrogenase in primary cultures of rat astrocytes and oligodendrocytes.

To assess the oxidative metabolism of glial cells, we visualized mitochondrial malate dehydrogenase (mMDH) in purified cultures of neonatal rat polygonal and process-bearing astrocytes as well as in oligodendrocytes, using indirect immunofluorescence. Double immunofluorescent localization of rabbit anti-mMDH and either mouse monoclonal antiglial fibrillary acidic protein or anti-myelin basic protein demonstrated that both process-bearing astrocytes and oligodendrocytes showed uniformly intense anti-mMDH immunoreactivity in their cell bodies. However, immunoreactivity to mMDH among polygonal astrocytes varied from very weakly positive to intensely positive. Experiments with rhodamine 123, a mitochondrion-specific fluorochrome, indicated that polygonal astrocytes contain relatively similar numbers of mitochondria; this suggested that the variable intensities of anti-mMDH immunoreactivity observed did not result from differences in mitochondrial numbers. In cultures of polygonal astrocytes maintained in a chemically defined medium containing growth factors and hormones, or in complete culture medium containing 1mM N6, O2-dibutyryl adenosine 3',5'-cyclic phosphate, the resultant stellate astrocytes still showed their original variable levels of anti-mMDH immunoreactivity. This suggested that the mMDH distribution pattern did not depend on the degree of morphological differentiation. Furthermore, cultures of polygonal astrocytes isolated from four specific regions of neonatal rat brain showed variable but reproducible profiles of anti-mMDH immunoreactivity. Our results suggest that there may be an appreciable range in the level of oxidative metabolism among individual polygonal astrocytes in culture.

Inhibition of DNA synthesis in neonatal rat brain regions caused by acute nicotine administration

Perinatal exposure to nicotine has been shown to cause morphological and neurobehavioral abnormalities in developing brain. In the current study, neonatal rats were given an acute injection of nicotine (3 mg/kg) at 1, 3, 8, 10 or 15 days of age, and [ 3 H] thymidine incorporation into DNA examined over the 30-min period after drug administration. Three brain regions were used that differ in their timetables of cell maturation and in their concentrations of nicotinic receptors. Nicotine inhibited DNA synthesis in all brain regions but with a rank order of effect corresponding to the concentration of nicotinic receptors, namely midbrain + brainstem ⩾ cerebral cortex > cerebellum. Superimposed on this hierarchy, periods of rapid cell replication were more sensitive to nicotine, so that drug effects in the cerebellum, which develops last, became significant past the point at which nicotine no longer affected DNA synthesis in the other regions. The inhibitory effect of nicotine was also found in fetal brain on gestational day 20 after injection of nicotine to pregnant rats. Studies with adrenergic and ganglionic blocking agents and with 100% O 2 indicated that autonomic and respiratory actions of nicotine, including ischemia, cardiac arrhythmias and hypoxia, could not solely account for the inhibition of DNA synthesis in neonatal brain. In contrast, injection of a small amount (2 μg) of nicotine directly into the central nervous system readily caused inhibition; the same small dose given systemically had no effect. These data suggest that nicotine damages the developing brain, in part, through direct actions on cell replication.

Effects of MK-801 on DNA synthesis in neonatal rat brain regions under normoxic and hypoxic conditions

Global metabolic insults such as ischemia/hypoxia, damage neural cells through release of excitatory amino acids and their subsequent actions at the N- methyl- d- aspartate (NMDA) receptor. NMDA receptors are highly expressed in neonatal rat brain, and the current study examines the effects of receptor blockade with MK-801 on DNA synthesis under normoxic and hypoxic conditions. At one day of age, hypoxia alone caused a decrease in [ 3H]thymidine incorporation into DNA throughout the brain, whereas MK-801 alone decreased incorporation selectively in regions known to be enriched in NMDA receptors. MK-801 afforded no protection from hypoxia and instead exacerbated the effects of hypoxia in the cerebellum. At 8 days of age, hypoxia alone or MK-801 alone still produced the same patterns of inhibition of DNA synthesis, but MK-801 neither prevented nor exacerbated the effects of hypoxia; animals receiving MK-801 showed a significant incidence of hypoxia-induced mortality. These data suggest that excitatory actions exerted at the NMDA receptor serve to maintain cell replication in neonatal brain and, as distinct from the situation for excitatory amino acid-induced cell death, these receptors do not participate in adverse effects of hypoxia on DNA synthesis.

Astrocytes cultured from specific brain regions differ in their expression of adrenergic binding sites

We sought to characterize regional heterogeneity of astrocytes using adrenergic receptor sites as cellular markers. Primary cultures made from 6 regions of neonatal rat brain consisted almost exclusively of astrocytes. Membranes from astrocytes cultured 1–3 weeks were prepared for radioligand binding assays of β- and α 2-adrenergic sites using the ligands [ 3H]dihydraalprenolol and [ 3H] p-aminoclonidine, respectively. Receptor expression was not affected by time in culture. Astrocytes from different brain regions varied up to 3-fold with respect to number but not affinity for both classes of adrenergic binding site with a rank order of cerebral cortex = superior colliculus > hippocampus = ventral midbrain⩾caudate nucleus⩾hypothalamus. Binding to β- and α 2-adrenergic receptors was positively correlated across brain regions. Astrocytic receptor binding in each region did not correspond to total receptor levels assessed by quantitative autoradiography. We conclude that: (a) astrocytes are markedly heterogeneous between major brain regions with respect to expression of adrenergic binding sites; (b) regional variations in the density of adrenergic binding sites in brain reflect, in part, local specialization of astrocytes; and (c) a substantial proportion of the adrenergic binding sites in some brain regions may be on astrocytes.

Trophic control of the ornithine decarboxylase/polyamine system in neonatal rat brain regions: lesions caused by 6-hydroxydopamine produce effects selective for cerebellum

Norepinephrine has been hypothesized as a trophic factor influencing postnatal development of the cerebellum. In the current study, neonatal rats were given 6-hydroxydopamine (6-OHDA) to destroy noradrenergic projections and the effects on the ornithine dexarboxylase (ODC)/polyamine system were evaluated; ODC initiates the synthesis of polyamines, which are known to control cellular development in the cerebellum, and neonatal ODC activity is regulated in part by β-adrenergic receptors. Intracisternal administration of 6-OHDA resulted in complete and permanent depletion of cerebellar norepinephrine and a deficit in ODC, polyamine levels and cerebellar growth. Subcutaneous administration of 6-OHDA, which caused only a small initial reduction in cerebellar norepinephrine, did not affect ODC and had only minor effects on tissue growth. Indeed, levels of the polyamines tended to be elevated after subcutaneous 6-OHDA, associated with postweaning elevations in norepinephrine, results which are probably indicative of axonal regeneration. In contrast to the effects of 6-OHDA on cerebellar development, neither the intracisternal nor subcutaneous drug treatment had any effect on cerebral cortical polyamines or growth, although the intracisternal treatment did impair ODC activity early in development. These data suggest that postnatal noradrenergic input, acting through the ODC/polyamine pathway, plays a selective role in cerebellar development.