Biomedical subjects

J L Nuñez

Publications and source records attributed to J L Nuñez.

13 recordsLinked to original sources

PubMed2005

Glutamate enhances survival and proliferation of neural progenitors derived from the subventricular zone.

Extracellular glutamate levels increase as a consequence of perinatal hypoxia/ischemia, causing the death of neurons and oligodendrocytes. Precursors in the subventricular zone (SVZ) also die following perinatal hypoxia/ischemia; therefore we hypothesized that glutamate would stimulate the death of neural precursors. Here we demonstrate using calcium imaging that SVZ derived neural stem/progenitor cells respond to both ionotropic and metabotropic excitatory amino acids. Therefore, we tested the effects of high levels of glutamate receptor agonists on the proliferation, survival, and differentiation of SVZ derived neural stem/progenitor cells in vitro. We show that high levels of glutamate, up to 1 mM, are not toxic to neural precursor cultures. In fact, stimulation of either the kainate receptor or group 2 metabotropic glutamate receptors (group 2 mGluR) reduces basal levels of apoptosis and increases neural precursor proliferation. Furthermore, group 2 mGluR activation expands the number of multipotent progenitor cells present in these cultures while maintaining equivalent mature cell production. We conclude that the glutamate released following perinatal hypoxia/ischemia may act to acutely promote the proliferation of multipotent precursors in the subventricular zone.

Animals↗

PubMed2004

Cell death in the rat hippocampus in a model of prenatal brain injury: time course and expression of death-related proteins.

Survival rates have increased dramatically for very premature (gestational week 24-28) infants. However, many of these infants grow up to have profound cognitive, motor and behavioral impairments due to brain damage. We have developed a novel model of prenatal infant gray matter injury. During the neonatal period, GABA is an excitatory neurotransmitter. GABA(A) receptor activation results in chloride efflux and membrane depolarization sufficient to open L-type voltage sensitive calcium channels. Our model involves excessive GABA(A) receptor activation in the newborn rat, with damage due to the resultant excessive calcium influx, not GABA(A) receptor activation itself. A common feature among numerous insult pathologies in the neonatal brain is an elevation in the intracellular levels of calcium. The goals of the present study were: 1) to document the time course and amount of cell death (both apoptotic and necrotic), and 2) to investigate the effect of GABA(A) receptor activation on the time course and expression of three cell death-related proteins (caspase-9, bax and bcl-2) in our model of prenatal brain injury. The magnitude of cell death, using TdT-mediated dUTP nick end labeling and Cresyl Violet to quantify the incidence of apoptotic and necrotic cells, was region dependent (CA1>CA2/3>dentate gyrus) and persisted for at least 5 days following insult. There was a relative increase in the amount of bax to bcl-2 protein, and increased protein levels of caspase-9, indicative of cell death. These findings are consistent with mechanisms of cell death seen in other types of early brain insult, and highlight a conserved cascade of events leading to cell death in the developing brain.

Animals↗

PubMed2003

Androgen receptor expression in the developing male and female rat visual and prefrontal cortex.

Gonadal steroid hormones are known to influence the development of the cerebral cortex of mammals. Steroid hormone action involves hormone binding to cytoplasmic or nuclear receptors, followed by DNA binding and gene transcription. The goals of the present study were twofold: to determine whether androgen receptors are present during development in two known androgen sensitive regions of the rat cerebral cortex, the primary visual cortex (Oc1) and the anterior cingulate/frontal cortex (Cg1/Fr2); and to determine whether androgen receptor (AR) expression in these regions differs between developing males and females. We used immunocytochemistry to detect AR protein on postnatal days 0, 4, and 10, and in situ hybridization to detect AR mRNA on postnatal day 10 in male and female rats. The level of AR expression was specific to the cortical region, with higher AR immunoreactive cell density and more AR mRNA in Oc1 than in Cg1/Fr2. AR immunoreactive cell density increased with age in both regions. Finally, on postnatal day 10, males had a higher AR immunoreactive cell density and more AR mRNA in Oc1 than did females. Thus, the presence of ARs may allow androgens to directly influence the development the cerebral cortex.

Animals↗

PubMed2003

Sex differences in response to kainic acid and estradiol in the hippocampus of newborn rats.

Premature and full-term human infants are at considerable risk of excitotoxic-mediated brain damage due to hypoxia-ischemia, infection or other trauma. Glutamate receptor activation is a major source of excitoxicity in the adult and developing brain, and the hippocampus is particularly vulnerable to damage. The seven-day-old rat is a widely used model of pediatric brain damage, in large part due to the relative insensitivity of the brain to exogenous glutamate treatment prior to this age. We have reexamined the possible role of glutamate in pediatric brain damage in the newborn rat using kainic acid treatment and attending to the sex of the animal as well as the effects of pretreatment with the gonadal steroid estradiol. Consistent with previous studies, we found no evidence of damage 7 days posttreatment in the CA1 region of the hippocampus in males or females. There was also little to no damage in the CA2/3 or dentate gyrus of males. In females, however, kainic-acid treatment induced substantial damage in the dentate gyrus and moderate damage in CA2/3, as assessed by neuron number and regional volume. Pretreatment with estradiol was protective against kainic acid-induced damage in females but was permissive for damage in the dentate gyrus of males. Estradiol treatment in the absence of kainic acid treatment was also neuroprotective in females in that it increased neuron number and volume throughout the hippocampal formation, suggesting that the basis of the sex difference observed in hippocampal volume was hormonally mediated. There was no effect of exogenous estradiol given to males in the absence of kainic acid. We conclude that the newborn female rat brain, but not the male, is sensitive to glutamate-mediated toxicity and that gonadal steroids play a complex role in both naturally occurring sex differences in hippocampal volume and response to injury.

Animals↗

PubMed2002

GABA mediates steroid-induced astrocyte differentiation in the neonatal rat hypothalamus.

Our previous work has demonstrated that astrocytes in the developing arcuate nucleus of the rat hypothalamus are sexually dimorphic as a result of differential exposure to oestradiol. Moreover, our experiments in neonatal rats suggest an absence of oestrogen receptors (ER) in arcuate nucleus astrocytes in vivo. This, along with the conspicuous lack of evidence in the literature confirming the presence of ER in arcuate nucleus astrocytes of the neonatal rat brain, led us to question the mechanism by which oestrogen induces changes in arcuate nucleus astrocyte morphology. Based on our previous findings that oestradiol increases gamma-aminobutyric acid (GABA) levels in the neonatal rat arcuate, we hypothesize that GABA is released from neighbouring oestrogen-sensitive neurones and alters arcuate nucleus astrocyte morphology. Here, we report that in vivo reduction of GABA synthesis in the neonatal rat brain by antisense oligodeoxynucleotides to glutamic acid decarboxylase prevented gonadal steroid-induced astrocyte differentiation in males and testosterone-treated females. Conversely, activation of GABAA receptors with the agonist muscimol increased astrocyte differentiation in females in the absence of gonadal steroids. Given that GABA is made only in neurones and that its synthesis is increased by oestradiol, we conclude that it acts as a diffusible factor inducing the differentiation of neighbouring astrocytes.

Animals↗

PubMed2001

Cell death in the development of the posterior cortex in male and female rats.

Work from our laboratory has shown that adult male rats have 19% more neurons than female rats in the binocular region and 18% more in the monocular region of the primary visual cortex (Reid and Juraska [1992] J Comp Neurol 321:448-455; Nuñez et al., [1999] Soc Neurosci Abstr 25:229). In the current experiment, we investigated whether cell death in male and female rats (postnatal days 2-35) contributes to the formation of these differences. Using stereological techniques, we investigated neuron density along with pyknotic and apoptotic (TdT-mediated deoxyuridine triphosphate nick end-labeled) cell density in the developing posterior cortex (future primary visual cortex). Although no sex differences in neuronal density were found in early development, we observed a differential time course of cell death between the sexes. Consistent with earlier reports, males displayed a rapid rise in cell death, with a peak on day 7 followed by a sharp decline to negligible levels by day 15. Females, however, displayed moderate peaks of cell death on days 7 and 11, with the persistence of low-to-modest levels until day 25. Similar patterns were obtained from both pyknotic and apoptotic cell quantification. Also, a formula was developed to estimate the percentage of cells that die during development and the amount of time a dying cell is visible. This study demonstrates that there is a prolonged period of cell death in the posterior cortex of developing female rats that appears to result in more cell death in females than males. This may be an important mechanism by which the sex difference in adult neuron number is created.

Aging↗

PubMed2000

Androgens reduce cell death in the developing rat visual cortex.

We have previously shown that males have more neurons than females in the primary visual cortex, and neonatal androgens play an important role in this difference. Also, we have found that females experience more cell death during development in this region than in males. Therefore, we hypothesized that the neonatal hormone environment directly influences the amount of cell death. In the present experiment, female rats were implanted with dihydrotestosterone (DHT) or estradiol at postnatal day 1. These animals, along with control males and females, were sacrificed on postnatal days 6, 11 and 25. Using unbiased stereology to quantify neuronal and pyknotic cell density, we observed that females implanted with DHT had a similar pattern and proportion of cells dying as control males. Additionally, developmental cell death in females implanted with estradiol was not significantly different than control females. Thus, neonatal androgens have an inhibitory effect on developmental cell death in the rat primary visual cortex.

Animals↗

PubMed2000

Neonatal halothane anesthesia affects cortical morphology.

Neonatal cryoanesthesia has recently been documented to affect morphology and behavior after a single exposure [Dev. Brain Res. 111 (1998) 89; Horm. Behav. 37 (2000) 169]. In the current experiment, we investigated the effect of one-time exposure to halothane inhalant anesthesia on neonatal rats of both sexes. Fifteen minutes of exposure on postnatal day one resulted in detectable changes in the volume of the visual cortex at 3 months. Thus, neonatal halothane alters neural development and its effects are observable in the adult rat.

Anesthesia↗

PubMed2000

Myelination in the splenium of the corpus callosum in adult male and female rats.

Previous work reported increases in the number of myelinated axons in the splenium of the rat corpus callosum between 25 and 60 days of age. In the present study, we quantified the area occupied by myelinated axons using a light microscopic point counting technique at 60, 120 and 180 days. Myelinated axons increased across these ages (p=0.001). Thus, myelination of the rat corpus callosum persists well into adulthood.

Age Factors↗

PubMed2000

Hippocampal anatomy and water maze performance are affected by neonatal cryoanesthesia in rats of both sexes.

There is recent evidence that cryoanesthesia, commonly used during neonatal hormone manipulations (e.g., gonadectomy), has deleterious effects on the morphology of the splenium of the corpus callosum and primary visual cortex in adult rats of both sexes. (Nuñez and Juraska, 1998; Nuñez, Kim, and Juraska, 1998). In the present study, the effect of neonatal cryoanesthesia on the morphology of the hippocampus and dentate gyrus and on performance in the Morris water maze was investigated. Cold exposure for as brief as 30 min (5 degrees C) on Postnatal Day 1 resulted in a significant decrease in the volume of the hippocampus and in brain weight of adults. Performance on the water maze was also impaired in cold-exposed animals. This study indicates that not only morphology but also behavioral performance in adulthood are affected by neonatal cryoanesthesia.

Adjuvants, Anesthesia↗

PubMed2000

Interaction of poly methyl vinyl ether/maleic anhydride-dimiristoyl phosphatidylcholine: a model bioadhesion study.

The objective of this work is to study the interaction of a copolymer, poly methyl vinyl ether/maleic anhydride (PMV/MA) used in pharmaceutical dosage form and a phospholipid L-alpha-dimiristoyl phosphatidylcholine (DMPC) with the aim of developing a bioadhesive system. Glycerine is the plastifiant used to make PMV/MA insoluble. We have studied copolymer-plastifiant compatibility with differential scanning calorimetry and we have studied the influence that the solvents produce on the copolymer by infrared spectroscopy. Monolayer experiments were carried out with a Wilhelmy-type surface balance. The purpose of these experiments is to obtain molecular information about interaction PMV/MA-glycerine system with DMPC. The results show that there are attractive forces and it is a spontaneous process.

Acetone↗

PubMed1998

Neonatal cryoanesthesia affects the morphology of the visual cortex in the adult rat.

Hypothermia is often employed as an anesthetic for manipulations of neonatal animals. We previously reported [J. Nuñez, J.M. Juraska, The effect of neonatal cryoanesthesia on the gross size of the splenium of the corpus callosum, Dev. Psychobiol. 30 (1997) 259; J. Nuñez, J.M. Juraska, The size of the splenium of the rat corpus callosum: influence of hormones, sex ratio and neonatal cryoanesthesia, Dev. Psychobiol., in press.] that the area of the splenium of the adult rat corpus callosum negatively correlated with the time neonatal pups spent in the cold. In the present study, we examined the effect of exposure to neonatal hypothermia (0, 15, 30 and 60 min at 4 degreesC, within 2 h of birth) on the thickness and volume of the binocular (Oc1B) and monocular (Oc1M) fields of the adult rat visual cortex. The number of neurons and glia in layer 2/3 in these areas was also assessed in the 0 and 60 min cold-exposed groups. Cryoanesthesia significantly decreased the length, thickness, volume and number of neurons and glia in both Oc1M and Oc1B. We also observed significant effects of cold exposure on the thickness of individual cortical layers, with some layers affected more than others after differential exposure times. Sex differences (males greater than females) were observed in a number of measures after varying amounts of time in cold and in the absence of cold exposure, in confirmation of previous work from our lab [S.N.M. Reid, J.M. Juraska, Sex differences in the gross size of the rat neocortex, J. Comp. Neurol. 321 (1992) 442-447; S.N.M. Reid, J.M. Juraska, Sex differences in neuron number in the binocular area of the rat visual cortex, J. Comp. Neurol. 321 (1992) 448-455.]. The present study points to the potential confound of using cryoanesthesia on neonatal animals to study cortical structure or function.

Aging↗

PubMed1998

The size of the splenium of the rat corpus callosum: influence of hormones, sex ratio, and neonatal cryoanesthesia.

The splenium (posterior 1/5) of the corpus callosum is sexually dimorphic in the adult rat brain. In the present study we examined the role of developmental hormones and cryoanesthesia (which is normally used during the performance of neonatal hormone manipulations) on the gross size of the splenium in male and female rats. There was a sex difference in splenial size (male > female) among nonhormonally manipulated animals, p = .0007. While neonatal castration was ineffective in altering the size of the male splenium, testosterone injections in females were found to increase the size of the splenium relative to oil-injected females, p = .05. The effect of developmental testosterone was further observed: Sex ratio (males to females) of the litter correlated with splenial area in females, r = .55, p = .03. Duration of cryoanesthesia negatively correlated with splenial area in males, r = -.81, p = .03, with a similar trend in females.

Animals↗