Nuclear Magnetic Resonance Spectroscopy Study on Energy Metabolism, Intracellular pH, and Free Mg²⁺ Concentration in the Brain of Transgenic Mice Overexpressing Human Ornithine Decarboxylase Gene

Abstract

We have generated a transgenic mouse line strikingly overexpressing the human ornithine decarboxylase (ODC) gene in their brain. Brain ODC activity was increased in the transgenic animals by a factor of 70 in comparison with their nontransgenic littermates. The content of brain putrescine, the product of ODC, was greater than 60 mumol/g of tissue in the transgenic mice, whereas in the normal animals it was below the level that could be detected by an HPLC method. The concentrations of the higher polyamines (spermidine and spermine) were not significantly different from control values. 31P nuclear magnetic resonance (31P NMR) spectroscopy analyses revealed a significantly reduced (40%) free Mg2+ concentration as calculated from the chemical shift differences of the nucleoside triphosphate alpha and beta peaks in the brains of the transgenic animals. The lower free Mg2+ concentration in the brains of ODC transgenic mice was not a consequence of altered intracellular pH or changes in cellular high-energy metabolites. 1H NMR showed no differences in brain choline/N-acetylaspartate and total creatine/N-acetylaspartate ratios between the two animal groups. These ODC transgenic animals may serve as models in vivo for studies on cerebral postischemic events and on epilepsy, as polyamines are supposed to be involved in these processes.

Genetic approaches to the cellular functions of polyamines in mammals

“…Mg 2+ is a well known voltage‐dependent, physiological blocker of the glutamate‐mediated excitatory currents inhibiting ionic conductance through the NMDA channel [61]. Thus, elevated free Mg 2+ could potentially block the NMDA receptor, yet our studies revealed that free Mg 2+ was significantly lowered (40%) in the brain of transgenic animals [62]. Taken together, these results suggest that endogenous putrescine may play a physiologically relevant role at the NMDA receptor as these receptors have a well documented role in the induction of seizure activity [63] and mediating spatial encoding [64].…”

Neuroprotective role of ornithine decarboxylase activation in transient focal cerebral ischaemia: a study using ornithine decarboxylase-overexpressing transgenic rats

“…In neurobiological studies, we have used ODC‐overexpressing transgenic mice (Halmekytö et al . 1991; Kauppinen et al . 1992) and rats (Lukkarinen et al .…”

“…Putative mechanisms of actions involve N-methyl-D-aspartate (NMDA) receptors (Paschen, 1992) or intracellular calcium homeostasis (Komulainen & Bondy, 1987). In neurobiological studies, we have used ODC-overexpressing transgenic mice (Halmekytö et al, 1991;Kauppinen et al, 1992) and rats (Lukkarinen et al, 1997) that have constitutively high cerebral putrescine (70-100 µmol/kg) without alterations in higher polyamines. The transgene is expressed uniformly in the brain tissue (Halonen et al, 1993;Lukkarinen et al, 1997).…”

Preserved induction of long-term potentiation in the stratum radiatum in the CA1 field of hippocampal slices from transgenic mice overexpressing ornithine decarboxylase and overproducing putrescine

“…An additional confounding factor related to in vitro measurements is the fact that the same concentration of extracellular Mg 2ϩ was used for control and transgenic mice in in vitro experiments, but endogenous Mg 2ϩ levels have been found to be slightly lowered in transgenic mice (Kauppinen et al, 1992). Therefore, in vivo studies are needed to assess the relationship between impaired learning and long-term potentiation in ODC mice.…”

“…Recently, transgenic mouse lines which overexpress the human ODC gene have been developed (Halmekytö et al, 1991). It has been shown that higher ODC activity in these animals relative to nontransgenic littermates leads to elevated levels of polyamines, especially putrescine, in the brain (Halmekytö et al, 1991;Kauppinen et al, 1992;Halonen et al, 1993). Since ODC transgenic mice serve as excellent animal models to study the role of increased putrescine levels on brain function (Kauppinen and Alhonen, 1995), we examined short-and long-term synaptic enhancements in the CA1 area of the hippocampus in those mice by recording extracellular field potentials using standard techniques in vitro.…”