Ontogeny of nitric oxide synthase I and III protein expression and enzymatic activity in the guinea pig hippocampus

The early ontogeny of neuronal nitric oxide synthase systems in the zebrafish

To examine a putative role for neuronal nitric oxide synthase (nNOS) in early vertebrate development we investigated nNOS mRNA expression and cGMP production during development of the zebrafish Danio rerio. The nNOS mRNA expression in the central nervous system (CNS) and periphery showed a distinct spatio-temporal pattern in developing zebrafish embryo and young larvae. nNOS mRNA expression was first detected at 19 h postfertilisation (h.p.f.), in a bilateral subpopulation of the embryonic ventrorostral cell cluster in the forebrain. The number of nNOS mRNA-expressing cells in the brain slowly increased, also appearing in the ventrocaudal cell cluster from about 26 h.p.f., and in the dorsorostral and hindbrain cell cluster and in the medulla at 30 h.p.f. A major increase in nNOS mRNA expression started at about 40 h.p.f., and by 55 h.p.f. the expression constituted cell populations in differentiated central nuclei and in association with the proliferation zones of the brain, and in the medulla and retina. In parts of the skin, nNOS mRNA expression started at 20 h.p.f. and ended at 55 h.p.f. Between 40 and 55 h.p.f., nNOS mRNA expression started in peripheral organs, forming distinct populations after hatching within or in the vicinity of the presumptive swim bladder, enteric ganglia, and along the alimentary tract and nephritic ducts. Expression of nNOS mRNA correlated with the neuronal differentiation pattern and with the timing and degree of cGMP production. These studies indicate spatio-temporal actions by NO during embryogenesis in the formation of the central and peripheral nervous system, with possible involvement in processes such as neurogenesis, organogenesis and early physiology.

Brain growth spurt-prenatal ethanol exposure and the guinea pig hippocampal glutamate signaling system

This study tested the hypothesis that prenatal ethanol exposure (PEE) during the brain growth spurt (BGS) in the guinea pig suppresses the glutamate-NMDA receptor-nitric oxide synthase (NOS) signaling system in the developing hippocampus. Pregnant guinea pigs [term, about gestational day (GD) 68] received daily oral administration of 2 g ethanol/kg maternal body weight/day on GD 43 and/or GD 44 and then 4 g ethanol/kg maternal body weight/day from GD 45 to GD 62, isocaloric-sucrose/pair-feeding or water. Offspring were studied at GD 63 (near-term fetus) and postnatal day (PD) 10 (young postnatal life). Maternal blood ethanol concentration during ethanol treatment, pregnancy outcome variables, no change in spontaneous locomotor activity, and decreased brain and cerebral cortical weight data were reported previously [Neurotoxicol. Teratol. 23 (2001) 355]. This BGS-PEE regimen did not affect hippocampal stimulated glutamate release in young postnatal offspring, NMDA receptors as assessed by [3H]MK-801 binding, or NOS activity in near-term fetal offspring. Furthermore, BGS-PEE did not affect the number of hippocampal CA1 and CA3 pyramidal cells and dentate gyrus granule cells in defined locations of these three regions in the hippocampal formation. These findings are in contrast to the effects of chronic prenatal exposure to this ethanol regimen throughout gestation, including suppression of the hippocampal glutamate-NMDA receptor-NOS signaling system, decreased number of hippocampal CA1 pyramidal cells, increased spontaneous locomotor activity, and impaired performance in the Morris water maze.

Effects of chronic prenatal ethanol exposure on cGMP content and glutamate release in the hippocampus of the neonatal guinea pig

The glutamate-N-methyl-D-aspartate (NMDA) receptor-nitric oxide synthase (NOS)-cGMP signal transduction system plays key neurotrophic and intercellular communication roles in the hippocampus. In the guinea pig, chronic prenatal ethanol exposure (CPEE), via maternal ethanol administration, suppresses the hippocampal glutamate-NMDA receptor-NOS pathway in the near-term fetus and decreases stimulated glutamate release in the hippocampus of young postnatal offspring, with no effect on NMDA receptor number or NOS activity. At present, the effect of CPEE on cGMP, a key second messenger of the glutamate signal transduction system, in the hippocampus is not known. The objective of this study was to test the hypothesis that CPEE suppresses the hippocampal glutamate signal transduction system in the neonatal guinea pig at the levels of cGMP content and glutamate release. Timed pregnant guinea pigs received chronic oral administration of 4 g ethanol/kg maternal body weight/day, isocaloric-sucrose/pair-feeding, or water treatment throughout gestation. CPEE decreased brain and hippocampal weights at postnatal day (PD) 1 and PD 5 (P<.05). CPEE did not affect basal, NMDA (1, 10, or 100 microM)-stimulated, or K(+) (15 or 30 mM)-stimulated cGMP content in transverse hippocampal slices at PD 1 or 5. At 60 mM K(+), however, CPEE decreased stimulated hippocampal cGMP content at PD 1 (P<.05) and increased stimulated cGMP content at PD 5 (P<.05). In transverse hippocampal slices, CPEE did not affect basal or K(+) (40 or 45 mM)-stimulated glutamate release at PD 1 or 5, or NMDA (50 microM)-stimulated glutamate release at PD 1, but did decrease NMDA (50 microM)-stimulated glutamate release at PD 5 (P<.05). The data demonstrate that the effects of CPEE on stimulated cGMP content and glutamate release in the hippocampus of the neonatal guinea pig are stimulating agent- and age-dependent.

Ethanol neurobehavioral teratogenesis and the role of the hippocampal glutamate-N-methyl-D-aspartate receptor-nitric oxide synthase system

The purpose of this review is to evaluate a proposed mechanism for ethanol neurobehavioral teratogenesis in the hippocampus, involving suppression of the glutamate-N-methyl-D-aspartate (NMDA) receptor-nitric oxide synthase (NOS) system. It is postulated that suppression of this signal transduction system in the fetus by chronic maternal consumption of ethanol plays a key role in hippocampal dysmorphology and dysfunction in postnatal life. This mechanism is evaluated critically based on the current literature and our research findings. In view of the apparent time course for loss of CA1 pyramidal cells in the hippocampus produced by chronic prenatal ethanol exposure that manifests in early postnatal life, it is proposed that therapeutic intervention, which targets the glutamate-NMDA receptor-NOS system, may prevent or lessen the magnitude of postnatal hippocampal dysfunction.

Effects of chronic prenatal ethanol exposure on locomotor activity, and hippocampal weight, neurons, and nitric oxide synthase activity of the young postnatal guinea pig

Decreased nitric oxide synthase (NOS)-catalyzed formation of NO from L-arginine may be involved in ethanol teratogenesis involving the hippocampus. This hypothesis was tested by determining the effects of chronic prenatal ethanol exposure on locomotor activity and on hippocampal weight, number of CA1 and CA3 pyramidal cells and dentate gyrus granule cells, and NOS activity of the postnatal guinea pig. Timed, pregnant guinea pigs received one of the following chronic oral regimens throughout gestation: 4 g ethanol/kg maternal body weight/day, isocaloric-sucrose/pair-feeding, or water. At postnatal day (PD) 10, spontaneous locomotor activity was measured. At PD 12, histological analysis was performed on the hippocampal formation, in which hippocampal CA1 and CA3 pyramidal cells and dentate gyrus granule cells were counted; body, brain, and hippocampal weights were measured; and hippocampal NOS enzymatic activity was determined using a radiometric assay. Chronic prenatal ethanol exposure produced hyperactivity, decreased the brain and hippocampal weights with no change in body weight, decreased the number of hippocampal CA1 pyramidal cells by 25-30%, and had no effect on hippocampal NOS activity compared with the two control groups. These data, together with our previous findings in the fetal guinea pig, demonstrate that chronic prenatal ethanol exposure decreases hippocampal NOS activity in near-term fetal life that temporally precedes the selective loss of hippocampal CA1 pyramidal cells in postnatal life.