Developmental and Regional Differences in Nitric Oxide Synthase Activity and Blood Flow in the Sheep Brain

Abstract

Nitric oxide synthase (NOS) participates in the regulation of cerebral blood flow and neurotransmitter release and as a second messenger of glutamatergic and cholinergic systems. Developmental differences in NOS activity have been described in the rat, but not in a species with longer gestation and a larger, lobulated brain at birth. We assayed NOS activity by conversion of [14C]L-arginine to [14C]L-citrulline in 50-mg tissue samples from eight brain regions in sheep at 70, 92, 110, and 135 days gestation (term = 145 days); newborns (< 7 days); and adults to test the hypothesis that NOS activity in the brain is developmentally regulated from midgestation through adulthood and matures along the neuroaxis in parallel with the known development of cerebral blood flow and neuronal activity. Three patterns of maturation of NOS activity were evident: increasing to or exceeding adult levels before 70 days gestation in the thalamus, cerebellum, and medulla; increasing to adult levels between 70 and 92 days in the hippocampus; and increasing to adult levels after 92 days in the cortex and caudate. Additionally, there were regional differences in cortical NOS activity: at 70 and 92 days of gestation, frontal cortex NOS activity was greater than parietal or occipital activity, and at 135 days gestation and in the newborn and adult, cortical and caudate activity exceeded that in most of the more caudal regions. The up to fourfold increase in regional cortical NOS activity between 92 and 135 days gestation was associated with twofold increases in cerebral blood flow and oxygen consumption during this period. Inhibition of NOS activity with administration of 60 mg/kg of NG-nitro-L-arginine methylester (L-NAME) resulted in 27% and 25% reductions in cerebral blood flow at 93 and 133 days gestation. While the associated increases in NOS activity with increases in CBF and CMRO2 do not appear causative, at various points in gestation the development of NOS activity may participate in the development of mature patterns of cerebral blood flow regulation in parallel with development of synaptic and electrical activity.

Regulation of eNOS Expression in Brain Endothelial Cells by Perinuclear EP 3 Receptors

“…We recently reported that some of the biological effects of prostaglandins, specifically prostaglandin E 2 (PGE 2 ), involve the induction of eNOS in cerebral microvascular endothelium and are mediated distinctly via EP 3 receptors; 2 this effect of PGE 2 operates in the mature and the developing subject where it may be instrumental in controlling oxygenation of neuronal tissues. 3 The biological actions of prostaglandins have been attributed to their interaction with cell surface G protein-coupled receptors. However, circumstantial evidence supports the idea that prostaglandins, either formed within the cell or captured from extracellular space, may also act intracellularly.…”

“…4,5 A specific prostaglandin transporter that facilitates the influx of prostaglandins has also been identified. 6,7 More importantly, in addition to plasma membrane EP 3 receptors, presence of functional perinuclear EP 3 receptors for PGE 2 has been demonstrated in a variety of cells such as cerebral microvascular ECs, Swiss 3T3 cells, and host cells HEK293. 8,9 Genomic effects of PGE 2 through its perinuclear receptor, notably on highly inducible genes such as mitogenic transcription factor c-fos and iNOS, have been recently reported.…”

“…Because COX-2 localizes principally to the nuclear envelope 4 and this enzyme plays a dominant role in prostaglandin production in brain microvasculature in early postnatal development, 10 one could speculate that in the presence of functional intracellular prostaglandin receptors, PGE 2 -induced upregulation of eNOS gene might involve EP 3 receptors localized intracellularly, specifically at the cell nucleus. 2 The present study was undertaken to test the hypothesis that PGE 2 receptor EP 3 on nuclear envelope exhibits different functions from those on plasma membrane, such that PGE 2 -induced eNOS expression is largely mediated by activation of nuclear EP 3 receptors in brain microvascular ECs.…”

Constitutive Nitric Oxide Synthase Activity in the Prefrontal Cortex of Rats as an Index of Emotional State Before Death

“…From this pool, only the eNOS activity values obtained from the eight animals that slept during the termination procedure were included in the results for this pool (Table 1). (Giulivi et al, 1998;Northington et al, 1997). Although the present study did not use high-speed or differential centrifugation to separate the supematant and particulate fractions, the percentage of endothelium versus brain tissue in the sample would argue in favor of nNOS activity.…”

Role of Nitric Oxide Synthase in the Function of the Central Nervous System under Normal and Infectious Conditions

“…In the brain, NOS regulates cerebral blood flow and neurotransmitter release, and the proper operative eNOS/NO system accounts for the microenvironment homeostasis that is essential for the normal functioning of neurons and glial cells [38]. Therefore, the NO produced by NOS results in vasodilation and controls vascular resistance, platelet adhesion and aggregation, leukocyte-to-endothelium interaction, and the maintenance of BBB integrity [36].…”